PowerPack for Advance Steel Stair Macros – Understanding the Philosophy


The Stair macros available with PowerPack for Advance Steel are powerful tools for anyone who wants to create stairs, but they are not magic.

To get the best from these macros it’s important to understand the philosophy of how it’s working. This philosophy is based on 4 aspects that you must have in mind before using the macro.

Let’s start with the first one.

A. The 2D setting out points defined

To ensure the macro works as expected, you need to have the 2D setting out points defined.

This is an important step to be done before starting the modeling.

The PowerPack Premium Stair tools use different setting out points. You need the bottom point of the first tread & top point of the last tread, exactly how is showed in the image below.

B. Don’t forget about the overlap

If your stair has a constant overlap, then move your last point horizontally to include the overlap.

In the example below the overlap is 50mm, therefore the blue point was moved with 50mm.

C. Know the length of the landing extension

For the staircases with 2 or 3 flights you need to know the length of the landing extension before using the macro.

In the example below, you can see 2 landing extensions for a stair with 2 flights: one of 230 mm in blue and the second of 460 mm in red.

D. Turning points for multiflight stairs

For the multiflight stairs created with the PowerPack macros, you need to define the turning points at the ground level, as you can see in examples below.

Going through these 4 steps before starting to use the Stair macro, will ensure that the macro is working as you expected and you will get the full benefits of its features.

How to activate “Advance stability” analysis on steel elements in Advance Design


In order to perform second order analysis on steel elements in Advance Design, Steelwork Design “To calculate” option must be activated from the element’s property list.

Figure 1 – Steelwork Design Activation

This feature is available either for each individual steel profile or for a multiple selection, by checking 2nd order with warping and imperfections checkbox, setting the Number of iterations and Stability 2nd order parameters.

Figure 2 – Advance Stability Activation

The “Advanced stability (2nd order)” parameters can be found in the Steelwork Design section of the property sheet for steel members. 

Figure 3 – Advance Stability Options

(1)    Checking the “2nd order with warping and imperfections” box will perform the analysis of the selected members during the steel calculation sequence. 
(2)    The 2nd order analysis being an iterative process , the user can set the maximum number of iterations. 


The 2nd order analysis uses the user-defined imperfections in order to determine the final 2nd efforts. The imperfections are applied step by step, incrementally, until the final imperfection defined by the user is achieved. At every iteration, the 2nd order efforts are recalculated starting with the previously calculated efforts. Calculations are made until convergeance – defined as the difference between 2 succesive iterations (automatically managed internally by the solver) – is achieved,  or until the maximum number of iterations is achieved. 


(3)    The “Stability – 2nd order parameters” will give access to a dialog where the user can define the various parameters to be considered during the analysis of the selected members. 
The definition dialog will show 4 tabs: 
•    Nodal springs
•    Bedding
•    Imperfections EC3
•    Loads offset

Figure 4 – Advance Stability Assumptions

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How to define nodal springs in “advance stability (second order analysis) solver


Although the “Advanced stability” from Advance Design feature considers the individual member, the intersections with the other elements are of course taken into account. In fact, the intersections are turned into nodal springs

Figure 1 – Auto Detect Spans Option

The selected member has intersections with other elements at x = 0.00m and x = 4.00m.

The “Auto-detect spans” button enables the users to see the intersections and alter the behavior of the corresponding springs.

The users can also add or delete nodal springs (only user-added nodal springs can be deleted) from the grid using the “Add” and “Delete” buttons. Moreover, they can reset the grid with the help of the “Reset” button.

Note: Even if the user does not open the Advance stability definition parameters, Advance Design will automatically take into consideration the intersections with the other elements during the analysis.

Note: If geometrical parameters are modified after the “Advance Stability” option is checked for steel members, “Reset” and “Auto-Detect Spans” options must be selected in order to reinitialize the position of the nodal springs. Any modifications made in the Advance stability window will be reset to default. Otherwise, the calculation will not be successful.

For each nodal spring, the user can set the status for each of the seven DOF.

    TxTy and Tz stand for the displacement along the x, y and z axes respectively 

    RxRy and Rz stand for the rotation about the x, y and z axes respectively

    Rw is the warping

Figure 2 – The seven Degrees of Freedom

Available statuses are:

  • Free: enables the release for the considered degree-of-freedom ;
  • Fixed: disables the release for the considered degree-of-freedom (this translates into a very high stiffness);
  • Auto: lets Advance Design automatically determine whether the degree-of-freedom is free or treated as an elastic release (the stiffness of which is automatically computed by Advance Design for each combination);
  • Elastic: defines an elastic release for the considered degree-of-freedom (stiffness imposed by user).

When set on “Auto“, Advance Design is able to compute the appropriate stiffness of the release as Force/Displacement, resulting in a stiffness value for each combination.

 Figure 3 – Stiffness definition

Warning: the “Auto” status means that the “Advanced stability” feature will attempt to re-create the boundary conditions based on the Forces and Displacements diagrams from the global model.

This can be challenging in some cases as the automatic determination has its own limitations.

For example, zero forces on a given node can either mean:

  • The degree-of-freedom (DOF) is free;
  • The DOF is fixed but no force was acting in the given direction.

Therefore, we would advise the users to manually set the free DOF”s on “Free” whenever possible as the “Advanced stability” feature is not able to import the boundary conditions defined on the member in the global model. The “Advanced stability” feature can only deduce the boundary conditions from the Forces and Displacements diagrams it imports from the global model.

We would also advise the users to make sure the member does not feature a free “Rx” DOF on both ends as this could lead to a numerical instability if no other intermediate nodal spring exists.

Setting the “Rx” DOF on “Fixed” can be a solution when the “Auto” detection method fail.

Figure 4 – Degrees of Freedom Status

The “Position” property enables the user to define an eccentric spring.

Eccentricity is meant in the z direction (Upper fiber, Neutral, Bottom fiber or User value).

Figure 5 – Nodal Springs Position Eccentricity

Stiffness auto correction 
There are cases when, by activating the “Auto-detect spans” option, the automatically calculated stiffness does not meet the minimum criteria in order to successfully perform the 2nd order analysis (for example, when displacements are automatically imposed at an element”s ends for which the automatically calculated stiffness is insufficient). By activating the “Stiffness auto correction” option, the program automatically imposes a minimum stiffness in order to successfully perform the analysis, but only when the values are very small.

Figure 6 – Stiffness Auto Correction Activation

Generally, the warping DOF (degree-of-freedom) is free and fixing it requires special rules for detailing, like the end plates, beam extensions, flat stiffeners.

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How to analyze irregular reinforced concrete cross-sections?


The reinforced concrete linear elements are usually characterized by square, rectangular or circular cross-sections. Advance Design computes the reinforcement for such elements with the Reinforced Concrete (RC) Design expert. For irregular, user defined cross sections, the RC design falls outside the standard procedure. Therefore, the real reinforcement may be determined following an iterative process, as described in the next steps:

1. Add a new user defined cross-section – follow the steps from Figure 1

Figure 1 – Steps to define a new user section

2. Define the cross-section geometry (shape and reinforcement position) and material in the Cross Sections module: draw the shape by point coordinates, define the reinforcement (automatic or manually) and concrete cover, define the material and calculation settings.

Note: It is recommended to define the initial reinforcement from the minimum reinforcement area.

Figure 2 – Define the cross-section shape and place the reinforcement

3. Set parameters and calculate the cross-section properties

Figure 3 – Calculation settings

4. Export the cross-section to the Advance Design library

Figure 4 – Close and export the cross-section to Advance Design library

5. The user defined section is attributed to the desired linear elements (columns). Run FEM and RC Design analysis.

6. On the selected element, check the RC design – element reinforcement results. The real reinforcement (imposed) can be compared to the theoretical reinforcement (computed). The verification can be observed on the interaction curves also. The section solicitation point should fall inside and close to the capacity curve (My/Mz, Fx/My, Fx/Mz), for a safe and economic design. If the imposed reinforcement does not satisfy these conditions, the initial reinforcement is increased: restart from Step 2.

Figure 5 – Check the proposed reinforcement

Graphical model validation by displaying it in colors in Advance Design


In this short article, we will look at one of the model validation methods available in Advance Design – displaying modelled elements in color according to selected criteria. Although this functionality is more general and can be used simply to improve the way a model is presented in a view or for documentation, today we will focus on its advantages for model verification.

Let us start with the topic of verification of local system of axes of surface elements. Checking and eventual change of local systems is an important step in the verification of the model, because by proper arrangement of local systems we have control over the uniformity of the FEM results and the reinforcement directions. Each modelled planar element has its own local system of axes, which is set automatically. Knowing the basic rules of automatic local axis system setting (as for example that the x-axis of the local system is usually defined along the first edge of the drawn contour) we can often control it ourselves. However, this is not always convenient or possible, especially when the model has been imported. Checking the local layout of axes for one or more elements is not a problem – we can simply select a surface element and we see its local axis symbol by default. The colors of the axes correspond to the colors of axes of the global coordinate system, i.e., the red axis is local x, the green one is local y and the blue one is local z.

However, it is much more interesting how we can quickly check the local axis settings for a larger number of elements / for the whole model.  To do this in Advance Design, we can use a very versatile tool to display objects in color according to selected criteria, available in the Display Settings window. In the ‘Color’ command group, there is a list for selecting coloring criteria, as well as additional options including displaying a legend and displaying the element’s local system axis during element selection.

For our purposes, of the many criteria available here, three will be useful to us: Local x orientation, Local y orientation and Local x orientation. All these modes are used to indicate in which direction the axes of the local system are oriented relative to the global system.

Take a look at the image below showing an example of the effect of using the ‘Local x orientation’ option.

The surface elements are colored and thanks to the legend we can immediately see how the local x-axis is oriented. For example, dark blue means that the local x-axis is pointing in the Y- direction of axis of the global system, light blue means that it is pointing in the Z- direction (down), while red means that it is pointing in the Z+ direction (up). We can easily confirm this just by selecting elements, as then we can see symbols of local systems.

If we now want to unify the orientation of the local axes, all we need to do is select the relevant elements, which is very easy thanks to the colors, and then choose one of the dedicated commands: Local Axis or Local Axis on direction.

On a similar basis, we can verify the orientation of the other axes of the local system of planar elements, but in the same way we can verify the local systems of linear elements. Of course, for this purpose, it is best if we filter out only the linear elements for presentation. But the same types of coloring styles as for surface elements can be used for this purpose.

The layout of local axes is not all that we can verify with coloring. The same tool can be used to verify the correctness of the modeling according to other criteria – for example thicknesses.

On the same principle, we will also check the cross-section of linear elements or the material that has been assigned to different elements of the model. But that’s not all. In a similar way, we can color elements according to their type, system assignment, or super element affiliation. And, other objects, such as loads by category or steel connections by type.  I recommend that all Advance Design users become familiar with all the available coloring criteria because using them increases the control over the model.

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How to simulate membrane behavior in Advance Design using DOF constraints?


In order to simulate the membrane effect in a structure in Advance Design, “DOF (Degree of freedom) constraint” object can be used with the Tx and Ty translations restrained.  DOF constraint object is also named as Master-Slave connection. The command can be found in “Objects” ribbon tab:

Figure 1 – DOF constraint localization

The following properties regarding restraints definition are defined for the “DOF constraint” (Master-Slave connection):

Figure 2 – DOF constraint properties

For example, the response of the DOF constraint is compared with the response of a membrane in a simple 3D structure subjected to lateral loads. In this model, the elements’ self-weight is not considered.

Figure 3 – DOF constraint model view
Figure 4 – Membrane model view

Since the master-slave connection imposes to all component nodes the same DOF restraints (translations/rotations), the master node can be placed anywhere on the perimeter. In order to simulate the same response, the nodes must be placed on the same position as the mesh nodes of the membrane:

Figure 5 – DOF constraint mesh view
Figure 6 – Membrane mesh view

The similar response of the two objects (master slave connection with Tx and Ty translations restrained and membrane) can be verified by comparing the results of the FEM analysis:

Figure 7 – Displacements comparison between the two models
Figure 8 – Axial force comparison between the two models
Figure 9 – Bending moments on columns comparison between the two models
Figure 10 – Bending moments on beams comparison between the two models

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Join BIM WORKFLOW WEEK!


BIM WORKFLOW WEEK is an online event organized by GRAITEC for structural engineers and detailers. Nowadays, you can streamline your BIM workflows using Graitec and Autodesk technologies together. Bridge the gap between all stakeholders and discover how you can develop and improve your construction projects in a digital thread!

Each day we will run a webinar to show how easy it is to streamline your daily work! We show how to apply a complete BIM workflow from design to detailing on all your projects during the webinars! Don’t wait and register today!

BIM WORKFLOW WEEK AGENDA:

Monday – 15/03/2021 – CREATE YOUR BIM MODELS WITH REVIT AND SIMULATE THEM WITH ADVANCE DESIGN

Are you a structural engineering company doing construction projects with Revit® from Autodesk in a BIM environment? In this webinar, we will propose you a way to streamline your projects, starting to CREATE BIM data in Revit, exporting it to Advance Design to SIMULATE your building and synchronize back in Revit all changes. Discover how easy it is to link Autodesk Revit and Graitec Advance design to simulate and optimize your steel an concrete projects.

Tuesday – 16/03/2021 – ENRICH YOUR 3D BIM REVIT MODEL WITH ANALYTICAL DATA AND RESULTS USING ADVANCE DESIGN

In this webinar, we will go deeper in the integration between Autodesk Revit and Advance Design: exchanging and synchronizing geometrical data is a good point but is not enough to enable a real BIM structural workflow. During this session, you will discover how to enrich your Revit model with finite element results and theoretical reinforcement values using Advance Design with an effective synchronisation mechanism controlled by the user!

Wednesday – 17/03/2021 – APPLY AN EFFECTIVE BIM WORKFLOW FOR ALL YOUR REBAR PROJECTS IN REVIT!

In this BIM era, it’s time for you to manage your rebar projects with 3D models using Autodesk Revit®! Join us to this webinar and discover how you can use the Autodesk platform and Advance Design together to produce 3D Design-driven rebar cages for Beams-Columns-Footings-Slabs-Walls & Shear Walls, automate the drawing views creation with all tags and annotations, produce final drawings and manage in real time all your rebar projects!

Thursday – 18/03/2021 – STEEL CONNECTIONS DESIGN REINVENTED FOR ADVANCE STEEL USERS!

If you’re a structural engineer or a steel detailer using Advance Steel and want to save time, cost and reduce your carbon footprint, Graitec now offers a solution to complement and optimise your current workflow. To facilitate analysing these complex 3D steel connections, Advance Steel joints can now be exported to Graitec Advance Design Connection!

Friday – 19/03/2021 – APPLY A COMPLETE BIM WORKFLOWS FROM DESIGN TO DETAILING ON ALL YOUR STEEL PROJECTS!

In this webinar, we will go through a complete BIM workflow from design to detailing using Autodesk Advance Steel and Graitec Advance Design together. You will discover how easy it is to design and optimise a steel structure with Graitec Advance Design, including steel joints. Then, we will end by exporting the model to Advance steel to create drawings, BOM lists and CNC files fir the fabrication.

How to optimize steel elements in accordance with the deflection criterion?


The shape optimization calculation for steel elements can be performed in Advance Design  considering the condition of maximum deflection. Then, new cross-sections are searched if the deflection ratio is greater than the set limit (default 100%).


Thanks to this option from Advance Design, it is possible to optimize steel elements while using more criteria at the same time, like searching and selecting for profiles that must meet the conditions for maximum load capacity (strength/stability) and maximum deflection, independently or at the same time. This is especially useful for design of steel structural elements that exceed the maximum deflection while meeting the load capacity condition.

The optimization assumptions can be found in the Optimisation tab from Steel Design Calculation Assumptions dialog. Under the “Find new sections” paragraph, a new option is available to activate the deflection criterion and to set the maximum allowable deflection ratio considered for the cross section optimization. These assumptions apply to all steel members from the model which have Steelwork DeDefault optimization assumptionssign option from the element’s properties activated. The limits imposed in this tab apply to all cross sections as a group and cannot be applied differentially for singular element.

By default, the deflection ratio optimization is unchecked:

Figure 1 – Default optimization assumptions

By checking the “if the max/all deflection ratio is greater than:” option, the user can impose the maximum ratio.

Figure 2 – Activation of the deflection optimization criterion

Once the steel calculation is completed, the strength/stability and deflection work ratios of steel elements are compared with the specific criterion, and other cross sections that meet the imposed conditions are suggested.
The results of steel elements optimization are displayed in the Suggested shapes dialog, displaying the current strength/stability and deflection ratios. If the ratios are greater than the imposed limits (100% by default), the current ratio is displayed in red. For such cases, if the deflection criterion is activated, the next cross section from the catalog that will meet the required criterion will be suggested, displaying also the ratio for that section.

Figure 3 – Suggested shapes according to selected criterion

By opening the Accepted solutions flyout, we can select the suggested shape or other section from the same catalog.

Figure 4 – Selection of accepted solutions

After accepting the suggested (or imposed) sections, from the Accept all option, a new steel calculation is required, in order to recalculate the new sections and have correct results in the shape-sheet of the elements and reports.
This optimization sequence is directly dependent with the sorting mode selected in the Sort profiles tab from steel Calculation assumptions. By default, the “Envelope criterion” option is selected, which means that the suggested profiles will meet both deflection criterion and strength/stability criterion.

Figure 5 – Default sort mode for section optimization

If the Envelope criterion is selected, the new profiles are suggested from both cases, if the deflection or strength/stability criterion are exceeded:

Figure 6 – Suggested shapes according to envelope criterion

If the Deflection criterion is selected, then the new profiles are suggested only if the deflection ratio is exceeded:

Figure 7 – Suggested shapes according to deflection criterion

If the Strength/stability criterion is selected, then the new profiles are suggested only if the deflection ratio is exceeded:

Figure 8 – Suggested shapes according to strength/stability criterion

In order for the deflection criterion based optimization to be computed, both Steelwork Design and Deflections options from element’s property list must be checked. The optimization based on deflection will be made according to the parameters introduced in the property list:

Figure 9 – Element property check


If the deflection verification is unchecked for an element, then “N/A” (Not available) message will be displayed for the Deflection work ratio in the Suggested shapes dialog.

This new feature makes result checking easier, thanks to the possibility of presenting a ratio for deflection during shape optimization. It also gives you the possibility to select optimal steel profiles considering the deflection. Various options from the Assumptions dialog help you get specific results for the steel elements used in design and enhance the workflow.

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Advance Steel SDNF export – how and where to create new entries?


Recently this question came up from a colleague on how and where you find the Database entries behind the SDNF Export from Advance Steel.   So, this is what is behind todays idea for the blog.  

Within Advance Steel there are many different types of Export/import options, the core one of these is the SMLX options for transfer from Advance steel to Revit to Advance Steel, but sometimes over more traditional export formats are needed, in this case the SDNF format (Steel detailing neutral format) was being used to link to a Steel and piping software, the user was using Advance steel to complete their steel process but wishes to update within their piping platform. The simple answer is that the SDNF export uses the Databases called the GTC mapping, but which one, as there are two locations and then which tables, as there are several within the database. So, with this goal in mind, we looked into the actual database and more importantly which table and how the entries in the table are completed.   The conclusions of this and approach is explained in the attached document link, but the summary is that for the export process the GTC mapping database, that is located under the Advance folder of Autodesk within your program files, is where you need to look and it is using the table called the ‘Profile Export conversions’, under the Advance Steel type. Also, the entries for the table can be created using the ‘Autodesk one to one mapping’ or can use the ‘expression format’ that is common within the database entries.

Advance Steel SDNF Export Mapping

Using Advance Steel 2021 version and the for the Export to SDNF option via the ribbon, we look at how to make a section group into the Export systems.

Which Database

For the SDNF mapping the database is the GTC mapping.MDB database, this is found under the Advance\data folder of Autodesk within your program files.

C:\ProgramData\Autodesk\Advance\Data

Note: to see this you may have to enable hidden files and folders under the windows explorer options.

The data base is an Microsoft access database, the best way to edit this is with ‘Access’.

Which Table/s

So the heading says which tables, for good reason, the system actually uses the Profile Export conversion table:

Although if you are creating entries via the mapping dialog that appears in the software, if it finds a beam type not mapped previously, in that case it creates two entries, with the other being in the GTC profile conversion.  If you do create entries manually, you can go in and remove these, as they are not used.

How to find an entry in the table.

For the Access field , you can filter this down by checking the box under the column filter to show only those elements:

In this case just uncheck select all, then scroll the list and check for example HEB

You will see several listings for HEB, some with different GTC standard and export applications listed.

But actuall none of these may be any good to export exactly what you need.  For example the line 1011 would look good for this export to SDNF,  but trying this it is not doing what you would expect.

The issue is coming from the  GTC standard, this does not have the correct reference that is aligned to the entry in the profile master table. That is the tynename text used in the profile master table, under the astorprofiles database.

The HEB reference is using the other table, and obsolete one.

The solution

The easiest way round this is to create a new table reference, to reflect the correct string and references,  so you can either manually do this, or maybe just take a few sections and map them, and look for the entries in the DB table,  they should start with prefix of 20000.

By mapping these manually, the GTC standard is created , so you can use this to form the string required.

If you have Excel this is an ideal platform in which to do this and create them and copy and paste back into Excel.

So, this is the simple way to create a line entry, then copy it out, then use the functions of Excel and expand the entries to cover all the sections from the profile table.  This can take some time to create, but more importantly they add lots of entries to the main DB.

But there is another way to reduce this input.

Single line entry using Expressions

Within the GTC database, the user will notice there are entries, which appear to use a code abbreviation, a formula so to speak.

 These expressions come from a format called regular expressions and there is some good information on this via this website link:  ‘learn RegEx Experssion  this website very useful, very good step by step tutorial.  Take note there are many websites that explain this concept so feel free to google it and suggest others.’

This example the HEB beam mapping.

So from the previous entry in the profile export conversion table we can see the expression elements used in the line, so whilst in Access you can copy the line and paste it into Excel changing the key value to a more suitable entry, then comparing this to the manual lines, we can create a combined entry and paste it back into the Access table.

So with this line pasted back into the Access database, then close any open session of AS, close the access Database, Open the Profile export conversation table, then paste in the new entry, copied from excel.

Using this/ testing.

Create a simple model of the sections in question, then with new session of Advance steel open,  run the process for using these new entries. Select the SDNF button and process the HEB thorough the new table entries. If this is understood correctly and we run the export and the Advance steel mapping is present the process should complete within out the need for one-by-one map process.

The output

Checking the SDNF file format and naming etc, your notepad of notepad ++, you can view the file and see the names created in the listing.

All this from one line in a table, this is the process used, beyond the manual mapping of sections, it is also used for the Revit transfer of objects via the SMLX format, again using these expressions to map multiple entries.  Please see the Autodesk University class that I had the privilege to present, over the Revit AS workflow, you see the same in this class for Revit and AS.

https://www.autodesk.com/autodesk-university/class/Steel-Fabrication-Transfer-Revit-Advance-Steel-Under-Hood-2019

Graitec PowerPack – Reinforce and Design Multispan Beams in Revit


As a very common assumption for numeric models made In Revit, multispan beams are modelized as a series of colinear individual beams.

Thus, it’s make it easier for users to produce the formwork drawings, especially when placing beam tags which could include a mark number. This mark number (visible on the identity data in Revit Properties windows) could be set as unique per element, depending the codification rules of the project. It is possible to place the same value for several objects but in this case, the number indicated in the tag will be the same for all objects containing the same mark number.

Figure 1 – Mark Number filled in Revit

In addition, for quantity take off, bill of materials trough Revit schedules, it is more practical and accurate to create several single beams for each span in Revit, rather than one single very long beam.

Figure 2 – Example of multispan beams, with two different mark numbers.

Graitec PowerPack propose through the Main bars command, a powerful wizard dedicated to reinforce structural elements such as columns, footing, walls or beams. This wizard proposes advance settings to define directly a full and complete 3D rebar cage instead of placing the bars one per one.

Figure 3 – Main bars command interface applied to beam.
Figure 4 – Example of reinforced beams generated with Main bars command

Nevertheless, to be reinforced as multispan beams, colinear beams should be consider as one, especially for the connection between to beams if we want to generate the appropriate reinforcement including a good management of the area connecting the two beams.

So, at this stage, users are often dealing with a dilemma between having on one hand a right formwork model composed of individual beams (enabling a good numbering identification for tags and good formwork quantities) and the other hand, having a long single beam for all the spans (which will be closer better to prepare the reinforcement part and not practical for the formwork model management).

To satisfy all requirements for having a good formwork model and a good model, compliancy with our tools to generate the appropriate rebar cage, Graitec PowerPack propose a specific command named MultiSpan Beam.

Figure 5 – MultiSpan Beam command

This command will create a specific shared parameter (named “G.Beam Continuity Group”) to all individual beams supposed to be part of the same multispan serie.

It will assign the same value for this shared parameter so that the Main bar command (dedicated to create the rebar cage) will understand that this group of beams as to be consider as one multispan beam. Users just have to launch the command and select the beam belonging to the same multispan serie.

Figure 6 – MultiSpan Beam name in Revit properties

Once the selection of beam is done and validated, we can see in the dialog box all the beams which are going to be group in a reinforcement point of view. The Mark Number is indicated as well, and it is still possible to adjust the selection by removing elements or adding new ones.

Figure 7 – Multispan Beam definition

With this command, users could keep continue to model beams as individual beams and then, will be able to use our Main Bar command as a 3D rebar cage generator. The reinforcement of a selection of beams will be then consider as multispan. Main Bar will automatically detect the spans and users could switch to one span to another one, to define the reinforcement for each span individually.

Figure 8 – Main bar command launch on a multispan beam

With this command, the right reinforcement will be then generated for the extremities of the span and for each connections of the intermediate beams composing the span.

Figure 9 –Multispan beam reinforced with Main bars command

This notion could be also use for Graitec structural Design engine embedded in Revit, centralized in the ribbon PowerPack Design. The purpose of those tools is to launch design directly in Revit.

Figure 10 – Geometry command from PowerPack Design tab

The command Geometryopen a dialog bow where each span corresponding to each individual beam are visible and recognized correctly by the software. Here, users could change section and control the geometry of each span without affecting and modifying the whole span. Thanks to this, after selecting just one beam and using the Calculate command from the PowerPack Design tab, the software will calculate the complete multispan beam with the adapted reinforcement assumptions and generate the full rebar cage.

Figure 7 – Reinforcement for multispan beam, generated by design input and calculate command from PowerPack Design tab

Multispan Beam is a very practical command, easy to implement in your current workflow and which will really speed up the 3D rebar cage reinforcement generation based on your custom formwork model.

Wind action evaluation on vaulted roofs


The present article explains how to determine wind loads on vaulted roofs at the Eurocode 1. Specifically, we will show how to use Figure 7.11 from EN1991-1-4, which provides the external pressure coefficients on vaulted roofs with rectangular base:

We will consider a structure with following dimensions:

f = 2,51m

h = 3,20m

d = 9,60m

The developed length of the vaulted roof will be split into 4 equal parts, for zone A, zone B (repeated twice) and zone C:

For each of these zones, the external pressure coefficient (Cpe10) is read on a graph, depending on the f/d and h/d ratios.

In our case:

f/d = 2,51 / 9,60 = 0,26

h/d = 3,20 / 9,60 = 0,33

  • For zone A

We start on the f/d axis until we reach the two diagrams related to zone A:

  • For h/d = 0, we read Cpe10,A = +0,42
  • For h/d ≥ 0,5, we read Cpe10,A = +0,16

We then perform a linear interpolation because in our case, 0 ≤ h/d ≤ 0,5:

For h/d = 0,33, we get: Cpe10,A = +0,25

  • For zone B

We start on the same position on f/d axis, but this time, we reach the zone B diagram.

We read: Cpe10,B = -0,96

  • For zone C

We read: Cpe10,C = -0,40

In the end:

For zone A => Cpe10,A = +0,25

For zone B => Cpe10,B = -0,96

For zone C => Cpe10,C = -0,40

Starting from version 2021, vaulted roofs at the Eurocode 1 are covered by the climatic generator of Advance Design.

Wind actions, whether 2D or 3D, are instantly generated:

As prescribed in the Eurocde 1, roof is divided into 4 equal zones.

The name of each zone as well as their Cpe value can even be displayed with a dedicated annotation:

Conclusion

The evaluation of wind action on vaulted roofs by reading the graph from the Eurocode 1 can be tedious, with a high risk of error.

Fortunately, in Advance Design, this process is fully automated. Wind forces are created instantly, and they can be updated in a single click whenever a modification is made on the building.

Synchronization of Advance Design model with Revit via Graitec BIM Connect


The calculated structure can be synchronised with the Revit input model; to do this you export the model from Graitrec’s structural analysis software, Advance Design, using BIM Connect. Then select the synchronisation option in Revit and indicate the location of the exported file. The software generates a list of all elements, creating a breakdown of added, changed and deleted elements.

After reviewing the changes that have occurred in relation to the calculation, you can accept, ignore or remove the changes from the sync list. Once the changes are accepted, the model in Autodesk Revit will update.

In Revit, using the PowerPack Design module, it is also possible to design foundations together with the calculation of the reinforcement, based on given conditions. After the calculations, reinforcement drawings can be generated automatically. Most of the drawing’s components such as sections, their location, used labels, dimension lines or lists/bar schedules can be saved by the user in a template which is a native Revit file. From this, PowerPack will generate the drawings.

It remains to define the steel connections. This can be done directly in Revit or using Dynamo, but for the sake of shop drawings, it is suggested to export the model to Advance Steel. The connection calculations themselves can be carried out in Advance Design structural analysis software, using the Steel Connection Designer module.

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FEA results for surface elements


Monolithic floor slabs are currently one of the most popular solutions. Depending on the structural system used, they can cover relatively large spans.

In most cases, the slabs are reinforced with a two-way orthogonal grid up and down. A common misconception among designers is that the determination of the cross-sectional area of this reinforcement for the ultimate limit state is based solely on the bending moments which are the same for the directions of the reinforcement. Thus the dimensioning of the reinforcement in direction “x” would be based on the bending moment Myy and the reinforcement “y” on the moment Mxx.

The example of a simple two-span slab, in which one span operates in a decidedly unidirectional manner and the other in a bidirectional manner, shows how to determine the authoritative, dimensioning moments. The loads and geometry are not particularly relevant. We will mainly discuss the nature of the plate work without attaching importance to values. The model and calculations were made with Graitec Advance Design.

It must be remembered that the orthogonal reinforcement grid results from a certain compromise between its optimality from the load-bearing point of view and the ease of subsequent execution on site. In reality the directions of the principal moments can be and in many places are deviated from the direction of the moment Mxx or Myy. Therefore, the most optimal reinforcement would be one designed according to the trajectory and based on the values of the principal moments M1 and M2.

Remember that the values of the principal moments must be interpreted with their directions, since they are not local or global values of the structure. Where the principal directions coincide with the directions of our reinforcement, i.e. x and y, this means that the dimensioning value of the bending moment will be the moments Mxx and Myy and the trajectory of this reinforcement is the best possible.

It is easy to see that the directions of the principal moments coincide with the x/y direction in the central bands, but deviate at the corners. Most designers who have ever dimensioned slab reinforcement in more sophisticated FEA-based software have probably noticed that the reinforcement map does not correlate directly with the maps of orthogonal bending moments in the local floor system.

The “butterfly” shape of the two-way free-supporting slab and the top reinforcement of the corners in both the X and Y directions are very characteristic. This is usually the most questionable aspect for designers – after all, the bending moment maps in no way correspond to this distribution of reinforcement – but it is perfectly normal behaviour.

The devil is in the torsional moment Mxy/Myx. Its presence is responsible for the deviation of the moments from the x/y direction. In the main directions we are only talking about the moment M1 and M2, there is of course no torsional moment there. If you decide to deviate from the main trajectory and reinforce the slab with orthogonal mesh, you must take this moment into account in the dimensioning of the reinforcement. The program Advance Design does this automatically of course by determining the relevant dimensioning moment at each grid point. In short, this means the projection of the principal moments onto the reinforcement directions.

Influence of dimensioning forces on the dimensioning of reinforced concrete

When dimensioning reinforced concrete members, the program determines the dimensioning forces which the user can display on the structure at any time.

Literature on the principles of reinforcement design for reinforced concrete slabs recommended the use of bottom diagonal reinforcement in the corners of free-supported slabs with a certain cross-sectional area (most often referred to as maximum span reinforcement in this literature). Designers usually use such reinforcement, but often without being aware of the design necessity. It is important to realize that the above-designed orthogonal X/Y reinforcement taking into account the torsional moment closes the topic and we are not required to use any additional reinforcement with a trajectory separate from the orthogonal reinforcement. The fact remains, however, that orthogonal reinforcement is not fully optimal. 

To illustrate this phenomenon, it has been decided to model in the corner a slab whose local directions (and thus also the directions of the reinforcement in the adopted settings) are in accordance with the directions of the principal moments.

When using orthogonal reinforcement, both top and bottom reinforcement in both X/Y directions were required. For trajectory reinforcement, a bottom reinforcement perpendicular to the bisector and an upper reinforcement parallel to the bisector is sufficient. This means that the principal moments are at this point deviated by 45º from the X/Y direction.

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An easy way to design repetitive reinforced concrete elements faster


Use your current project as a template!

One of the most time-consuming stages during the design of reinforced concrete structures is the calculation and generation of documentation for elements such as beams or reinforced concrete columns. And usually, it is not about the complexity of calculations or difficulties in generating drawings, but rather a large number of such elements in each project. And as in practice, we use dedicated software for designing, and it is mainly on the capabilities of this software and the ability to use it that the efficiency of work depends.

 In this short article, we will address one of the key issues to reduce work time, namely creating and using design templates in design modules of Advance Design. The mechanisms described below are available in all design modules, including RC Beam, RC Column, RC Wall, RC Footing and Steel Connection module.

Creating project templates with Advance Design modules is very simple and consists in saving the current settings from the current project to a file. To start with, we perform a full design process of an element (for example the first beam in the project), and as a result, all the required settings are already defined and tested. Then we call the command to save the template and enter a name for the template file. From now on, the same settings as in the current project can be applied to other similar elements.

Saving the new template is possible when we run the module for dimensioning in the standalone version (image above) as well as from the menu in Advance Design (image below). In both cases, the template is saved to the selected location on disk as a file.

Thanks to the fact that template creation is based on saving settings of the current task we can easily add new templates in every stage of work.

Generally, it is a good idea to prepare one or more general templates. We set parameters that we always want to use in all projects, like settings related to design codes, general reinforcement settings, range of reinforcing bar diameters used, etc. These will be starter templates, primarily used for the first element in a given project.

Then, while working with a given new project, it is usually useful to prepare several current templates, specific for that project. These may be templates with different settings related to the location of the element in the building (then they differ in settings like concrete cover, fire conditions, etc.), or templates related to geometry (for example separate for edge beams, T-beams, etc.), or with different settings related to reinforcement design (for example with other methods of constructing transverse reinforcement). It all depends on us.

It is important that when saving the template, all information is stored, including project settings, geometry, design parameters, reinforcement parameters or list of load cases and combinations.

But even more interesting is the fact that in Advance Design modules, when applying templates, we can decide on the scope of data that is loaded from the template. That means that when creating a new task based on a template, we can easily choose what to load from the template. Let’s see a simple example. We have saved a template for a multi-span T-beam with specific reinforcement settings, with defined specific list of load combinations, etc.

Next, we want to use this template to design another beam, but this time it will be a single-span beam with a different list of load cases while keeping all the other settings. To do this, when creating a new job, we can deselect the geometry and load settings when selecting a template:

The above method is useful, especially when creating new elements / subsequent beams in the standalone version of the program, when we enter all the data ourselves, including loads.

The approach is slightly different if we base on the FE model prepared in Advance Design and perform calculations in the design modules directly in Advance Design, or if we perform design calculations in stand-alone modules after exporting the element data to files. In this case, we are not defining the element from scratch because we already have the element with a defined geometry and internal forces, but we want to use our own templates to set all other parameters of the element. To do so, the template must be assigned to the element in Advance Design before sending it to the dimensioning module. This selection is made from the element properties in Advance Design.

Remember that the list of available templates then shows the names of template files located in the corresponding subdirectory on disk, which is different for each element category (beams, columns, walls, foundations or steel connections). All of these subdirectories are grouped into one master template directory in the User Folders of Advance Design’s design modules. The location of these directories is visible, for example, when saving templates.

So if you want to use different ranges of templates for different projects, it’s most convenient to simply archive/copy individual subdirectories or the entire main element template directory.

Of course, the use of project templates is basic but not the only way to increase the efficiency of the design process. Another way is to use your own drawing templates used by the Advance Design modules so that the time spent preparing and adjusting the reinforcement drawings is greatly reduced.

Another way is to optimize the workflow – for example, we can easily export the data for the design of reinforced concrete elements from Advance Design to files, separately for each element, and then distribute them to the individual team members. Then they can carry out the design and documentation process in parallel on separate computers using the stand-alone versions of the modules. In addition, the reinforcement files can be copied back into the project structure in Advance Design.

But this is a topic for a separate story…

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Linear buckling analysis in Advance Design


Loss of element stability

As well as calculating linear and non-linear statics, Advance Design can also perform what is commonly known as a buckling analysis. Buckling is the loss of stability of an element under axial compression force. As long as this force does not reach a certain critical value, the element will only shorten. Beyond this critical value, the element is thrown out of equilibrium, which is also called buckling. A structure can only be said to be stable if it can return to its original form after being tilted out of equilibrium.

The phenomenon of loss of stability in general is a rather complex issue. The linear buckling analysis itself, however, is quite easy to set up and carry out. It involves solving an eigenproblem that results in eigenvalues and eigenmodes. We will call the eigenvalue the critical multiplier and the eigenmodes simply the stability loss form. The force in an element multiplied by the critical multiplier is the critical force at which the element loses stability.

In simple cases (e.g. isolated elements), the critical force may be determined from Euler’s formula:

The designer must instead estimate the buckling length of the member, which is sometimes relatively easy. The forms of loss of stability and the buckling length for simple static schemes are generally known and are presented, for example, in EN 1992-1-1.

The problem starts to arise with unusually braced structures, where it is not so easy to estimate the rotational stiffness of the nodes. By solving a linear buckling analysis, it is possible to know the critical force and thus the buckling length.

Linear buckling analysis

The buckling analysis gives an answer to how close an element/structure is to losing its equilibrium state. If the critical factor is less than 1 (i.e. the load would have to be less than that currently occurring) the structure can practically be excluded from further calculations. The value of this multiplier if it is greater than 1 will give us information how sensitive the structure may be to second order effects and imperfections. This is mentioned in clause 5.2.1(3) of EN 1993-1-1, where it allows the use of 1st order analysis in calculations, provided that αcr > 10.

For a simple example of a cantilevered steel column (IPE400) 8.00m high loaded with a unit axial force, the results of the buckling analysis are presented below.

The first two forms of buckling are in the direction of the weaker axis of the section, the third in the stronger axis. The smallest critical factor is 106.68, assuming that the force was unit. That is, if the axial force was 106.68kN the column would buckle. Looking at the form of the loss of stability in each plane it is easy to see that the buckling length is 2*L – you can also ask the software for this figure – for evidence it will be determined using Euler’s formula.

An analogous check can be made in the second plane, the lowest coefficient of which corresponds to the third form of loss of stability. For a classic cantilever in both planes, 16.0m is expected in this case.

As you can see, buckling analysis is easy to carry out and accurate in simple cases. The case shown is as simple as possible, where the bar is subjected to axial, ideal compression.

The important thing to remember is that simple buckling analysis is fully linear – that is, both geometrically and material-wise. It is a very fast tool giving an answer in a short time about the potential behaviour of the structure, but it does not take into account 2nd order effects, and the material works elastically throughout.

In a situation where the whole structural system is analysed, and not just a separate element, the matter is somewhat more complicated – the critical factor, closely related to the form of loss of stability, should be identified with the elements that lose stability in this form. For a simple frame, analysed only in the plane of the system, 20 successive forms of loss of stability were obtained. The axial forces are shown below (only in members that are in compression, assuming that they do not lose stability in tension).

As shown in the image below, the 1st form of loss of stability is a global, canted form. The frame columns clearly lose stability in this form – the critical multiplier is 356.19, so with an axial force of 10.16kN, the critical force is 3618.89kN. Each subsequent form is responsible for the loss of stability of the compressed upper chord and the compressed posts and diagonals of the truss. The multiplication factors of these forms cannot, of course, be taken into account for the determination of the critical force and buckling length of the columns for example. Members that were not in compression in the buckling case do not lose stability.

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FEM modelling versus reality


With the advent of all kinds of computer methods supporting the work of the constructor, we began to design increasingly complex systems, whose work we could previously only estimate using various simplified, tabular methods, supported by analysis and research, but giving little room for manoeuvre in terms of geometry, load patterns, etc. The most popular method for the analysis of building structures is nowadays, and has been for many years, FEM, or Finite Element Method. When designing with such a system we can, to a large extent, model practically any object. This is easy for certain structures, but it should be remembered that the model is only a certain approximation of reality and will behave exactly as we have imposed it.

The FEM method relies on discretisation and takes into account any boundary conditions we ask for. Is the footing really a full restraint as we are used to modelling? Is a reinforced concrete beam really able to transmit the full moment according to the stiffness of the elements to a reinforced concrete wall? After all, it depends to a large extent on the solution of the reinforcement, on the solution of the steel connections, on the nature of the work… What we model for calculations we must try to reproduce as faithfully as possible in the detailed design – or vice versa.

Today, I would like to focus on the issue of stiffness of support elements, above all beams, and why this phenomenon must not be underestimated or whether we can somehow compensate for its lack of consideration. Using this example, I will also introduce the possibilities of Graitec Advance Design, which allows these problems to be dealt with automatically – it has tools for taking into account the actual stiffness in several ways.

Although slab-and-beam systems have somewhat given way to other systems, they are still used – if not fully, at least as a mixed system with another. In plate and column systems, it is sometimes necessary to use edge beams (for stiffening or to deal with shear punching in edge and corner columns) or transfer beams, in slab faults etc.

For the purposes of this article, a simple model of a residential building with services on the ground floor, with 6 overground storeys, founded on a foundation slab was prepared. 15cm thick slab in a slab-and-beam system on 25x50cm beams,. The whole structure is stiffened with a reinforced concrete communication shaft. We will consider the first residential storey, i.e., the floor above the ground floor. Loading by own weight, finishing and service category A.

The difficulty in this type of building in terms of modelling is to correctly account for the stiffness of the support members and their interaction with the floor slab. And this has to be taken into account in two ways. On the one hand, it is a modelling issue – the beams are modelled in the axis of the slab, but in reality they are subgrades/tensioners and their stiffness is actually much higher, often 2-3 times. On the other hand, in the case of reinforced concrete structures, for the purposes of statics, we analyse the structure in the elastic state taking into account only the stiffness of the uncracked concrete section. In fact, we should recognise what the stiffness will be with the actual reinforcement and scratching under this reinforcement. And here, exactly, there will be places where the stiffness decreases, but also places where it increases. It may not seem obvious that the beam in the second phase may be stiffer in some places, but there are places where the cross-sectional forces are close to 0, and yet we use there at least structural reinforcement.

I will try to discuss all these issues and how they are solved in Advance Design using the example of the building shown.

Displacements in the first phase of work are shown. It should be remembered that the building is elastically supported, so we cannot interpret these displacements directly as deflections. The whole building settles on the ground, additionally columns experience some deformations. The results are presented for a quasi-steady combination, as for this combination we will consider later the long-term effects in the outlined phase.

For the current model, no action has yet been taken to account in any way for the actual stiffness of the beams, either due to their position (slab uplift) or to the cracking (phase II).

Methods to consider stiffness of beams in FEM

Various methods, more or less faithful but also more or less labour-intensive, are commonly used to consider the stiffness of beams. For some time, designers used a tool built into most FEA programs, the offset – the physical offset of an element from its original position. But it is important to remember how this operation works. The beam is connected to the original nodes by rigid ties, which leads to the element working in a kind of “truss” fashion – the plate is the top chord, the beam offset under the plate is the bottom chord, and the rigid ties are the posts of our mental truss. This results in a reduction of the original moment and the introduction of longitudinal forces according to the principles of work, i.e. the slab begins to be in compression and the beam in tension. It is necessary to include all these forces in the model in some way, but we cannot directly size the beam in bending with tension. Tension would lead to a situation where the reinforcement in the span works both bottom and top, and we know very well from the nature of the beam work that the bottom reinforcement will be important for us in the span zone.

We would need to bring the condition into pure bending, and by using only an offset we are actually reducing the bending moment. We should reduce the forces in our “truss” by considering the action of the integral of the compressive force on the offset arm and include the moment from the effective part of the slab to size the beam. If we were to do this every time, in every beam and every section manually, and then manually size the beam, i.e. use simple calculators with our forces instead of using the forces from our model, we would conclude that using an offset is, in short, silly.

To illustrate this, we will also model the offset in Advance Design. The program has an automatic tool which will perform the whole process of force reduction to pure bending for offset beams for us – this option is called “Rib design” and I will talk about it later. Now, let’s focus on a simple offset and the nature of work of elements using it…something like this can be modelled in any FEA program.

Please note that the moments in the span have decreased from 170kNm to 115kNm. There is also a drastic tensile force of >700kN at these locations. An untrained designer could size the beam for the bending moment alone, which is significantly underestimated, or possibly incorrectly account for the tensile force.

Importantly, this method accurately represents the stiffness of the beams – the floor deflections in this situation are real. The problem is mainly due to the internal forces in the beam as proven.

Note – an offset can be modelled in Advance Design and not included in the FE at the same time. This is important in the age of BIM and exchange of models between different programs. In software for modeling building structures for design documentation purposes such as Revit we model beams in their real geometry. Advance Design will allow us to take into account the position of beams with offset, and it is the designer who decides if, and how, he will take it into account in FEM. This gives a great deal of freedom and goes a step further for designers working with BIM.

Another popular method, also fully operated by Advance Design, is to artificially increase the section inertia resulting from its actual displacement. The moment of inertia is best determined using Steiner’s Theorem, which in brief makes the moment of inertia dependent on the position of the centre of gravity relative to the axis for which it is calculated. What we want to achieve is easily described by the image below:

For the beam in the example it is 0.175m – this is also the offset value used above. The moment of inertia of the beam in the axis of the floor is 260416.66cm4, while that of the offset beam is 643429.16cm4. It follows that I need to increase the inertia of the modelled beam by 2.47 times.

In the 2020 version of Advance Design, the designer can define a factor to increase or decrease stiffness for both bending, compression/extension and torsion.

This method is simple, fast and produces correct results. The only thing that is not taken into account is the interaction of the beam with the slab over a certain distance, which the standard defines as the ‘effective width’.

Advance Design Advanced Tools

For one of the beams, I have defined the Rib Design option and specified the collaborative width of the slab. Please note its presentation- the beam is defined at the offset, but the slab is drawn into the collaboration. Note that this is an option to dimension a reinforced concrete element, not the FE model itself – the forces to be dimensioned will be determined as I said earlier (reducing longitudinal forces to bending).

The diagram on the right shows bending moments for a beam with a defined offset – this is very characteristic, the diagram is serrated due to the use of rigid connections in FEM nodes. As you can see, the dimensioning forces for reinforced concrete after the action of the rib design module have a classical shape – the values are correct. You can read more about how this tool works in the document “Advance Design 2016 – What’s new”, as this option has appeared in this version.

NOTE: Advance Design has also determined the stiffness in 2nd phase and the forces for the dimensioning take into account the section cracking. I show the stiffness distribution in the cracked member at the summary of the article below.

Please note that in the area of the highest moments (i.e. highest cracking) the section loses stiffness by almost 50%. At force levels close to zero, the stiffness increases – because the cross-section is not subjected to cracking and there is nevertheless continuous actual reinforcement.

I will try to talk more about the consideration of stiffness of reinforced concrete elements due to cracking on another occasion – today I tried to focus mainly on aspects of correct FEM modelling.

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Flipping a section without altering its local axes in Advance Design


In this article, we will show you how to flip or rotate a section while keeping its local axes unchanged.

Why Would I Need That?

Flipping a section is often required when modelling.

For example, on the truss beam below, the Channel section defined on top member will not be left with its default orientation:

Channel section with its default orientation

It will most certainly be flipped, using the ‘Angle’ property:

Channel section is flipped

This will not only rotate the section but also its local axes:

Flipping a section also alters its local axes

The Challenge

This modification of member local axes can be a problem when working in a plane workspace, where several degrees of freedom are automatically disabled due to 2D simplifications:

In a 2D workplane, the Ty, Rx and Rz degrees of freedom (out-of-plane direction) are disabled

Now, how can we define an in-plane rotational release when the corresponding degree-of-freedom (Rz) is not available?

In-plane rotation (Rz) can no longer be controlled due to 2D simplifications

The Solution

Fortunately, there is no need to switch to a 3D workplane.

All you need is to flip the section without altering its local axes.

This can be achieved by adding the ‘S’ character at the end of section name.

This will rotate the section while keeping the in-plane bending about the y-y direction:

Section is flipped but the in-plane rotation remains about y-y

And because the Ry degree-of-freedom is still available, one can simply release it:

The Ry degree-of-freedom is available and can be released

Conclusion

This article showed you how to orientate a member and define the required releases without necessarily switching to a complex 3D workplane.

This simple trick in section naming will let you benefit from all the advantages of a 2D analysis (short calculation time, easy result post-processing) while still getting the expected structural behaviour.

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Generating wind action on temporary structures with Advance Design


Temporary structures should not be designed with the characteristic values of wind velocity or velocity pressure from the Eurocode 1.

Indeed, these characteristic values are determined considering a return period of 50 years, which does not suit the provisional nature of such temporary constructions. Therefore, temporary structures will often be designed with a smaller return period than the usual 50 years.

Return period

Recommended return periods (n) are given in EN1991-1-6: 

This return period value is then used to compute the probability factor (cprob) as per formula (4.2) from EN1991-1-4:

Where:

  • K is the shape parameter defined in the national appendix. The recommended value is K = 0,2
  • p = 1/n (with n being the return period, in years)
  • n is the exponent defined in the national appendix. The recommended value is n = 0,5

 Be careful, in the cprob formula, n (the exponent) should not be mistaken with n (return period).

Of course, considering a 50-year return period in the above formula leads to cprob = 1,0.

Therefore, do not expect any benefit from the cprob factor for structures in use for more than a year:

Wind velocity for a return period of n years is then given by:2

Example

Assume the case of a temporary structure in use from September to November (3 months) in a region where where characteristic wind velocity (for a return period of 50 years) is 24 m/s.

This temporary structure will be designed for a return period of 5 years:

The corresponding probability factor will be:

Resulting I the following wind velocity:

This results in a 15% reduction on wind velocity.

Advance Design results

Advance Design lets the user set the desired return period as well as the shape parameter and the probability exponent.

The corresponding wind velocity is then automatically computed:

Conclusion

Considering the appropriate return period when designing a temporary structure can lead to a significant reduction of wind velocity, thus scaling down the corresponding wind forces.

Not to mention the other parameters, such as the season factor cseason, that can diminish wind action even more.

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Managing user load combinations on Advance Design


When creating a design model for a structure, one of the steps is to prepare combinations for defined load cases. Most often we use the mechanism of automatic generation of combinations, according to the rules of the standard set in the project configuration. If necessary, we can modify the rules and relations between cases or case families using the available mechanisms in the Concomitance between load cases dialog window (available for Eurocode combinations).

However, while working on many projects there are situations when we want to define a set of our own combinations. Of course, in the case of a small number of load cases and a small number of required combinations, this can be done directly in the combination dialog. Nevertheless, in this article we will take a look at more effective methods, which will work especially well in case of a larger number of cases/combinations and when we want to use our own combination definition in other projects. These will be two solutions: using the mechanism to export and import combination definitions using an Excel spreadsheet and the mechanism to import combination definitions as a CBN text file. 

Using an Excel spreadsheet

Starting with version 2020.1 Advance Design allows for easy and quick exchange of combination definitions between the current project and an Excel spreadsheet. For this purpose, there are two dedicated buttons available in the Combinations window.

The Export button exports definitions of all existing in the project load combinations to a new Microsoft Excel spreadsheet. For this a dedicated xlsx file is created on the path selected by the user. The Import button reads definitions of load combinations from the selected spreadsheet and adds them to existing definitions on the current project.

Let’s look at the data structure in the spreadsheet. The first row contains the column names, while the following rows contain the definitions of the subsequent combinations.

  • ID column

This column contains the identification numbers of the successive load combinations.

  • CODE and TYPE columns

These columns contain the combination type text code (CODE) as well as the name of the combination type (TYPE). The names and type codes depend on the settings of the project location – working language and standard for the load combinations. Below is an example of codes and types for the Eurocode settings:

ECULSSTRULS StrGeo
ECULSEQUULS EQU
ECSLSCSLS characteristic
ECSLSFSLS frequent
ECSLSQSLS quasi-permanent
ECELUAAULS

It is important that when editing or creating a worksheet, the combination types in the TYPE column are consistent with the types available for the current standard. Therefore, in the TYPE column, the cell values are selected from the list.

  • CAS and COEFF columns

These columns are always defined in pairs and specify the load case ID number (CAS) and the corresponding coefficient (COEFF). The number of pairs of these columns’ headers should be equal to the maximum number of load cases in the most extended combination. Of course we can reduce or increase the number of pairs of headers if necessary. The number of pairs of values in a given row with the definition of the combination depends only on the given combination, but at least one value pair should be defined.

When you import load combination definitions from a selected spreadsheet, these combinations are added to the list of existing combinations in the current project. If combinations with the same ID number already exist in the project, then the ID number of the imported combinations is changed to the first free number. If the combination definition in the Excel file is incorrect (e.g. contains case numbers that do not exist in the model), then the combination is omitted during import. In these cases a warning appears.

Using the possibilities of a spreadsheet, including the possibility of using complex formulas, macros or cooperation with other programs, we have almost unlimited possibilities to prepare and automate the creation of our own load combinations.

Using CBN files

CBN files are text documents containing combination definitions. Generation of the predefined load combination with using the CBN file is based on loading the file from the disk using the Loads CBN button, located in the Combinations window. We can also preview the contents of the file without the generation of combination by using the View button.

To define your own file with the definition of a combination, you need to create a text file similar in structure to the predefined .cbn files. Lines starting with # or // are used to enter comments / notes and are optional. The remaining lines are treated as definitions of subsequent combinations and consist of case codes and coefficients separated by spaces. Additionally, at the end of each line there is space for the combination code and for the comment. Let’s look through the contents of the sample file:

In this example there are 3 lines of combinations, so 3 combinations will be generated. CASE1, CASE2, CASE3 are the type codes for 3 different load cases. Next to each code there are coefficients given with a character. Codes such as ECELUSTR are codes for the generated combinations. They can be arbitrary texts, in which case they will be used as an additional description, or they can be created in the naming convention for a given standard, so that they are automatically recognized as suitable combinations for design calculations. The text at the end of each line of a combination is optional and is not used during combination generation. It can be our additional description visible only during file preview. Note that in the last combination, in the second and third case coefficients equal to zero appear, which means that this combination will only contain the first load case. Exactly the same effect you get if there are no codes and coefficients for these two last load cases in this line. In the picture below you can see the effect of combination generation for the above example.

When loading the file, combinations are generated according to custom definitions, and the combination code is assigned to combinations accordingly. The combination name is generated based on the combination definition.

Note that when using an Excel file, to identify load cases their ID number is used. This allows you to precisely determine the relationship, regardless of the type of load case. However, in this solution we need to know the ID numbers of these cases before the combination is generated.

In case of CBN files, load case codes are used. Thanks to the codes it is easier to prepare a universal combination definition, which can then be used for many projects, but at the same time we have to be careful about the compatibility of the codes in the CBN file and in the project.

In every new project the load case codes are the same for all load cases. They can then either be modified manually by us or updated automatically by the program during combination generation (the program asks for this during combination generation).

Manual modification of the codes is useful when we have prepared the combination definitions in the CBN file using our own codes. In such a case, we can mark each case explicitly in a given project, making sure that they match the codes in the CBN file.

If you allow the program to automatically complete the codes during combination definition, remember that the same codes are assigned to all cases of a given type. This means that all fixed load cases will have the same code, similarly all snow load cases etc. This solution is convenient when there is no need to combine cases inside the same type.

Let’s see the effect of one exemplary row defining the combination in the CBM file:

 CASE1  +1.10 CASE2  +1.20 CASE3  +1.30 CombA

Example 1. There are 3 different load cases with names and codes respectively:  A – CASE1, B – CASE2 and C – CASE3.   The result will be one combination with all cases:

A*1.1 + B*1.2 + C*1.3

Example 2. There are 2 different load cases with names and codes respectively:  A – CASE1 and B – CASE2.  The result will be one combination:

A*1.1 + B*1.2

Example 3. There are 3 different load cases with names and codes in the project:  A – CASE1, B – CASE1 and C – CASE3. Note that the first two cases have the same code. The result will be two combinations:

A*1.1 + C*1.3

B*1.1 + C*1.3

As you can see both mechanisms, either using an Excel spreadsheet or using CNB text files, allow you to easily and quickly create your own sets of load case combinations in Advance Design. I encourage you to get closer to these solutions and use them while working with your own projects.

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The Power of Automation in Advance Design


  All modern design applications require a solid testing mechanism in order to detect any regression regarding the quality of the results but also to cover all areas of the application (GUI, CAD, correct workflows, …).

  Advance Design has a mechanism based on a script that works like a batch session. This mechanism was mainly designed as a system for automatic tests to offer access to almost all areas in the application. In this way we can reproduce various scenarios.

  Since it’s quite extensive and very cryptic, the main idea to use this mechanism is to start from a base script and adjusted or completed with the other commands. A base script can be generated by Advance Design. Usually an automatic test in our QA system consist in a model and a script. Both are passed to Advance Design in command line and the application executes the script.

  In the following points we will go into details for such scenarios.

  1. The base model creation

  The first step consists in creating a model using your preferred localization and norms. The creation of load cases and their configuration is also recommended.

 The analysis hypothesis, options for concrete analysis, steel analysis, etc. can also be configured at this step. Then, after saving the model, a back-up is recommended because it will be needed at a later step.

 Until now we could say we have a complete environment. From this point we can start generating the structure elements (linear elements, planar elements, footings….).

2. The elements creation through scripting

2.1. Commands syntax and script composition

  The syntax of a command that creates an element with geometry is composed by:

the_name_of_the_command+space+(x_coordinate;y_coordinate;z_coordinate)[and repeat the ’+ space+(x_coordinate;y_coordinate;z_coordinate)’ for all the points in geometry]

.’ is the coordinate decimal separator, and ‘enter’ is the separator between different commands, so each command is on a different line in a script.

A script contains multiples commands and the last command has to be ’end_auto_script‘.

You can generate a list of commands as bellow in Excel with macros, Dynamo or with another familiar program or tool.

E.G.:

punctual_rigid_support (5.0000;0.0000;0.0000)

punctual_rigid_support (15.0000;0.0000;0.0000)

punctual_rigid_support (15.0000;10.0000;0.0000)

punctual_rigid_support (5.0000;10.0000;0.0000)

linear_element (5.0000;0.0000;0.0000) (5.0000;0.0000;5.0000)

linear_element (15.0000;0.0000;0.0000) (15.0000;0.0000;5.0000)

linear_element (15.0000;10.0000;0.0000) (15.0000;10.0000;5.0000)

linear_element (5.0000;10.0000;0.0000) (5.0000;10.0000;5.0000)

surface_element (5.0000;0.0000;5.0000) (15.0000;0.0000;5.0000) (15.0000;10.0000;5.0000) (5.0000;10.0000;5.0000)

windwall (5.0000;0.0000;5.0000) (15.0000;0.0000;5.0000) (15.0000;10.0000;5.0000) (5.0000;10.0000;5.0000)

windwall (5.0000;0.0000;0.0000) (5.0000;0.0000;5.0000) (5.0000;10.0000;5.0000) (5.0000;10.0000;0.0000)

windwall (5.0000;0.0000;0.0000) (5.0000;0.0000;5.0000) (15.0000;0.0000;5.0000) (15.0000;0.0000;0.0000)

windwall (15.0000;0.0000;5.0000) (15.0000;0.0000;0.0000) (15.0000;10.0000;0.0000) (15.0000;10.0000;5.0000)

windwall (15.0000;10.0000;0.0000) (15.0000;10.0000;5.0000) (5.0000;10.0000;5.0000) (5.0000;10.0000;0.0000)

end_auto_script

This script will generate the elements in the model like in the picture bellow:

In order to create elements using commands as the ones above, when running one of them or the script the following snap modes have to be disabled: extension, tracking, ortho, relative and length on element.

All the commands executed by the user are recorded in the history of the console which is accessible in the input console line (E.G.: selecting an element, calling a ribbon or menu command like creating an element, etc. …).

For checking any executed command syntax, scrolling through the commands history is possible by clicking the input console and pressing left arrow key for each command (using right arrow will walk you back to the last executed command, opposite to the left arrow key, but only after starting to use left arrow). To copy it the recommended way is by selecting the text with the mouse, right clicking it and selecting copy from the contextual menu.

2.2. Script saving, recording and playing

  If the script is generated with Excel/Dynamo/etc. then make sure the generated file has the extension set as .ads.

  For manual script creation a text file with ads extension is needed. It can be created with Notepad or any other text file editor. After the creation of file copy the script described above at point 2.A. in the empty file and save it as your_script_file_name.ads .

  For script recording in AD, right clicking in the input line of the console and choosing ‘start recording’ from the contextual menu starts the recording. After the user interaction with the program (E.G.: selecting an element, calling a ribbon or menu command like creating an element, modifying options in a dialog, etc…), right clicking in the input line of the console and choosing ‘stop recording’ a dialog is launched for choosing the name and the location of the script. There are some limitations that are listed at the end of the document.

  To play the script for scenario 2.1, right click in the input line of the console and choosing ‘Load script’ from the contextual menu starts a dialog to choose the script file. After choosing it AD start playing the commands from the script one by one with a delay between them. The user should not move the mouse or press any key while playback is in progress. At the end a message will be printed in the console that notifies the end of the operation.

3. Model calculation and reports generation

  At this step start recording a new script as described above. The automatic wind, snow, traffic loads, etc… and combination must be generated if needed. Then the analysis model should be created, maybe also the concrete analysis, steel analysis, etc…. Then in the report generation dialog add the needed reports and optionally change the report type: (Doc, docx, xls, xlsx(for the these first 4 extensions Office suite is required), rtf, txt). In the gif sample, the selected type is xls but in the script rtf type is selected in case Office is not installed. The report is generated in the document folder of the model and it is not automatically opened.

   In the end you need to stop the recording. The resulting script can be used as a template script and should be modified/adapted to include the creating elements commands (from the point 2.1.). They should be added right after the last set_unit command:

4. Running the script in batch mode.

  At this step you should use a copy of the backup model from the 1st point. Running a batch mode can be achieved by running a bat in which the command is having the following syntax:

“X:\Path to AD\Bin\AdvanceDesign.exe” /s “Y:\path to script\script name.ads” /m “Z:\path to model\model name.fto”

E.G.:

“C:\Program Files\Graitec\Advance Design\2021\Bin\AdvanceDesign.exe” /s “d:\AutoTests\models for new tests\newtest\combined script.ads” /m “d:\AutoTests\models for new tests\newtest\FTDoc15.fto”

A bat file can be created in Notepad and saved as ‘file_name.bat’ when selecting all types as the extension in the save as dialog.

5. Scripting recording and playback limitations

  • Double-click in pilot; instead, used right click or other commands
  • Combos in toolbars.
  • The Data Grid dialog (different technology, in work).
  • Buttons that open dialogs in Property list and the recording of the GUI operations in that dialogs.
  • Changing properties in property list commands might have to be updated at each version/subversion of AD because the commands are depending on the identifiers of the properties which are changed almost each version.
  • Changing the sections and materials for elements from property list.
  • Changing height for level in Property list
  • Copy/move dialogs.
  • Double-click on result curves in order to save them as *.jpg
  • Only basic modifications in tables are supported
  • The measurement units must be the same as the ones installed by the kit
  • When creating a circle, the radius will be specified in console, not by clicking on the screen.
  • Modifications of snapping are to be done using the toolbar/ribbon.
  • Creating loads on selection.
  • All needed section cuts will be created before starting to register the script.
  • Mesh preview for planar elements.
  • Selecting the work plane.
  • When creating the analysis model, the script should compute a new analysis. When automatically running, if an analysis was computed for the current model, the check boxes for analysis types are disabled, therefore the test will try to open an existent analysis (which does not exist since we should run on a clean model). Therefore, when registering the script, even if the model is a new one and the option to create a new analysis is already selected, select “Create new analysis” and then the analysis type(s).
  • Do not use right click in reports window. Use instead left click and the existing buttons.
  • In order to change the cases/combinations for the report, do not use the Cases/Combinations window. Instead, use the Report properties window (select report and click Properties button) select advanced options to expand the dialog and check the specific case/combination and use the analysis type combo from the below of the extended window:

When adding more family cases or loads, do not use the keyboard to insert the number. Use instead the arrow buttons.

  • The two slides for size from the display options window (Alt+x): or from the ribbon
  • The window for pressure generation.

6. The power of automation

  This tool is very efficient for our QA system but can be very useful also for anyone who wants to automatize repetitive scenarios but also to feed Advance Design with entire building structures extracted from another application. Just do the scenario inside the application, save the script, adapt it if you need it and run it.

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