Join Advance Design Award


Graitec, as a global software editor in the Design, Structural, Fabrication, and Data Management arena organizes an international contest dedicated to structural engineers and design offices.

The award is for the best practical use of Advance Design in Steel / Timber / Concrete design projects. This contest is open to customers and students who want to showcase their experience and technical knowledge through a project executed in Advance Design software. The projects will be judged by a professional jury. The final nominees and the winning projects will be made public to a wide audience through extensive marketing including social media.

Award Calendar:

•             10.3.2021 Contest launch – Project submission opens

•             30.7.2021 Entries close – Deadline for project submission

•             10.9.2021 Project Confirmation – Confirmation and announcement of projects accepted

•             11.10.2021 Jury Deliberation – Selection of winners

•             19.10.2021 Announcement of Results – Announcement of winners at the Advance Design User Summit 2021

Contest criteria:

The independent contest jury will gather in October 2021 to evaluate the projects. The judging will be done under the guidance of a dedicated Graitec Group representative. The representative is in charge of the contest. The jury will evaluate the projects taking the following criteria into consideration:

  • Technical level of the design, detailing and/or calculations.
  • Originality and prestige of the project.
  • Attractiveness, detail and presentation of the project.
  • Optimal use of software’s functionality.
  • The “story” behind the project – difficulties overcome, innovative approaches, benefits gained, etc.

Jury:

An independent and international jury composed of academics and professionals in the field will judge the submitted entries. Meet the members of our jury:

  • Francis Guillemard – Jury Chairman /  GRAITEC President of the Group and Chairman of the board / France
  • Rawad Assaf / ISSAE – CNAM Liban/ Lebanon
  • Olivier Chappat / Bouygues Bâtiment Ile-de-France / France
  • Piotr Nazarko / Rzeszow University of Technology / Poland
  • Rodrigue Coyere / EIFFAGE CONSTRUCTION Structural design office / France
  • Daniel Bitca / Technical University of Civil Engineering Bucharest / Romania
  • Mike Vance / Steelway Building Systems / Canada
  • Joseph Pais / GRAITEC INNOVATION / France

For more information, please visit Advance Design Award website – https://www.advancedesignaward.com/

Jiri Bendl, GRAITEC, Vice President SIMULATE comments: “Through the Advance Design Award organizations we want to reward our customers for being members of the ever-growing SIMULATE community and we want to encourage students to use the best possible tools for structural analysis. It is a great pleasure for me to be part of this project!”

About GRAITEC

Founded in 1986, GRAITEC is an international group (13 countries worldwide – 48 offices) helping construction and manufacturing professionals to successfully achieve their digital transformation by providing BIM and Industry 4.0 software and consultancy. GRAITEC is a developer of high-performance BIM applications as well as an Autodesk Platinum Partner in Europe and Gold Autodesk Partner in North America and Russia. With more than 550 employees including 200 BIM consultants, GRAITEC is an innovation-focused company whose products are used by more than 100,000 construction professionals worldwide.

For more information, please visit GRAITEC website – https://www.graitec.com/

For further information about Advance Design Award, please contact:

Lukasz Jedrzejewski, GRAITEC

Phone: +48 792 23 86 93

Email: lukasz.jedrzejewski@graitec.com

How to determine the shear stiffness of trapezoidal sheeting according to EN1993-1-3 ?


According to EN1993-1-3, formula (10.1b), the shear stiffness of trapezoidal sheeting connected to a purlin may be calculated as :

With:

  • t : thickness of sheeting (in mm)
  • broof: width of the roof (in mm) (roof dimension parallel to the direction of the panel ribs)
  • s: spacing between purlins
  • hw: profile depth of sheeting

Assume a purlin connected to the following trapezoidal sheeting, at each rib:

Roof width : 6,00m

Distance between purlins : 2,50m

This result sin a shear stiffness of 8361 kN.

Formula (10.1b) assumes the purlin is connected at each rib to the trapezoidal sheeting :

Purlin connected at each rib

In case the purlin is not connected at each rib but at every other rib, only a small portion (20%) of this S stiffness can be considered :

Purlin connected every other rib

If this value exceeds a certain value (Smin), the purlin may be regarded as laterrally restrained in the plane of the sheeting.

Assume an IPE140 purlin:

Iw = 1980 cm6 (warping constant of the purlin)

It = 2,45 cm4 (torsion constant of the purlin)

Iz = 44,92 cm4 (minor axis inertia of the purlin)

h = 140 mm (height of the purlin)

L = 6,00m (span of the purlin)

In our case, S > Smin.
The condition is met and the purlin may be regarded as laterally restrained.

In Advanced Design, such a purlin may have its ‘Continuous restraint along flange’ property enabled on the upper flange :

For more complex cases, when the member is prone to torsional effects (Channel or Z section for example), a more sophisticated calculation may be required (2nd order calculation with warping).

In this case, the shear stiffness (S) may be taken into account as the ‘Shear field’ parameter from the ‘Advanced stability’ dialog :

ArchiWIZARD integration in Revit


ArchiWIZARD allows a link with all the BIM solutions on the market thanks to a direct import in IFC format, SketchUp format and in REVIT format. ArchiWIZARD is responsible for the automatic creation of the energy model (rooms, walls, bays, thermal bridges, environmental elements) from the 3D digital architectural model. This common energy model is used for all ArchiWIZARD’s simulation engines.

Figure 1 – Environment ArchiWIZARD

A. REVIT model import
ArchiWIZARD has a standalone version and a direct ArchiWIZARD plug-in in REVIT.
The 3D model is exported by the geometric analysis in the ArchiWIZARD standalone version, and with the REVIT energy model in the ArchiWIZARD plugin of REVIT (process called BIM import).

Figure 2 – Two types of import

• Geometric analysis Import:
This is a simple geometry analysis of the 3D model. ArchiWIZARD will detect these closed volumes and it creates the project walls accordingly.
This geometric analysis will be used to generate an energy model adapted to the module used in ArchiWIZARD (Real-time module, STD module, Regulatory modules, etc.).

Figure 3 – Import by geometric analysis

• REVIT BIM import:
This feature can only be used in the ArchiWIZARD version integrated with the plug-in REVIT software and allows to generate an energy model based on parameters (location, wall compositions, materials and their thermal properties, name and room dimensions, among others ) from REVIT energy model and, of course, to get access to all ArchiWIZARD features.

Figure 4 – REVIT energy model preview in gbXML

B. Real time data synchronization
ArchiWIZARD and REVIT models are linked and some properties like thermal properties are synchronized in real time without having to synchronize.

Figure 5 – Parameter synchronization in real time
  • Display results in REVIT

Some ArchiWIZARD results may be displayed in the current Revit view such as light range, light comfort or thermal loads EN12831.

Figure 6 – ArchiWIZARD solar imagery generated in REVIT view

D. Access to all ArchiWIZARD features and interface

All ArchiWIZARD functionalities are accessible and operational in the Revit environment via the control ribbon.

Figure 7 – ArchiWIZARD control ribbon in REVIT view

Working with the ArchiWIZARD plugin gives access to both software simultaneously. The constant exchange of information in this BIM environment allows to optimally enrich REVIT’s 3D model as well as the ArchiWIZARD’s thermal model.

Extend Profile Controls content for Railing macros from PowerPack for Autodesk Advance Steel


One of the benefits of the Railing macros, available in PowerPack for Advance Steel, is that the library of profiles used to create the railing can be extended.

In other words, the user can add any section to the Railing macros from the Stairs and Railing Vault.

This feature is available starting with version 2021.1 of PowerPack for Autodesk Advance Steel.

Stairs and Railings Vault

All the Graitec railing macros can be configured to use records from the Autodesk Advance Steel AstorRules database – JointsGUIAllowedSections table. This behavior is like some Advance Steel standard joints.

This flexibility of the macros offers the users to go beyond existing restrictions and extend the list of available sections in the profile selection controls, for each type of main railing element such as:

  • post
  • top rail
  • middle rail
  • kick rail
Profile selection control inside the dialog 

To make this work, the following strings (names) for the JointName and JointControl columns in the table, for each railing macro and each main element type inside the macros, must be used:

How it works?

  1. Open the Table Editor from MANAGEMENT TOOLS – AstorRules database – JointsGUIAllowedSections table.
  2. Create a new table entry for the desired user section.

Add a new entry inside JointsGUIAllowedSections table:

Example: add half round solid sections to be used for the top handrail inside the Standard railing macro

New entry in JointsGUIAllowedSections table

Update the database and reload it in Advance Steel using the Reopen database option. Next time the Standard Railing macro is opened, the new type of profile section can be used inside the railing:

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.

Learn more about Advance Design!

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.

Learn more about Advance Design!

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.

Learn more about Advance Design!

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.

Learn more about Advance Design!

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…

Learn more about Advance Design!

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.

Learn more about Advance Design!

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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