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.

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.

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

(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

Vistit Advance Design LinkedIn page HERE

Visit Advance Design Virtual Stand HERE

Get Advance Design FREE TRIAL HERE

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. 

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.

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

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

    Rw is the warping

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.

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.

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).

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.

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.

Vistit Advance Design LinkedIn page HERE

Visit Advance Design Virtual Stand HERE

Get Advance Design FREE TRIAL HERE

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

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.

3. Set parameters and calculate the cross-section properties

4. Export the cross-section to the 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.

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!

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:

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

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.

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:

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:

Learn more about Advance Design!

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:

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

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.

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

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.

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

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

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

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:

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!