This example is taken directly from the FHWA Strut-and-Tie Modeling Design Examples (NHI 17-071), which provides practical reference cases for bridge engineers. The cantilever bent cap example represents a full D-region behavior due to load and geometric discontinuities, making it an ideal case for applying strut-and-tie modeling and validating results with CSFM.
1 Starting a new project
Let’s launch the IDEA StatiCa Detail application (download the newest version). In the main window of IDEA StatiCa, open the Detail application to start a new project.
In this tutorial, we’ll create a bent cap from scratch, so choose the option to start without using a template. However, templates can be very helpful for your future designs.
In this step, you also define the design code (choose AASHTO) as well as the concrete grade and cover (use concrete 6000 and cover 2.0 in). The design code can be chosen only in this first step of the project.
2 Geometry
The Detail application will open with the Design tab automatically selected. You can define new items using commands in the top ribbon and then you can edit these items in the tree menu. If you want to get to know the application environment better, check out the following article - General interface in Detail application.
We will start with creating the Members. Use button in top ribbon to add a new model entity - Knee joint. Then, select the correct cross-section and dimensions for the column and beam as shown in the image.
Since the Bent cap is trimmed at the column and ended at the beam, no supports are needed.
In order to transfer the loads to the bent cap, bearing pads must be added to the top of the beam. Use the upper ribbon to select "Model entity" and choose the Bearing plate transfer device option. The following article provides a full list of all transfer devices: Load transmitting components
Add two bearing plates along with the proper position, dimensions and material properties as shown in the image below.
Your final geometry should now look like this:
3 Loads and Combinations
To add a load, click on Load case in the ribbon. A load case LC1 is created which will be used for the strength limit state loads. Use the plus (+) button to insert a load impulse within this load case — choose Point Load. Create one more load case LC2 with only Point load impulses for service limit state loads. Self-Weight is already considered in the loads but can also be added under the load impulse options.
In order to be able to distinguish between short-term and long-term effects, make sure to correctly assign Permanent and Transient load case types and input the point load force values F and positions of the point forces according to the pictures. There will be two load impulses per load case to consider loading to both bearing pads.
Load combinations can be created from the top ribbon command Combination. Add two combinations C1 and C2, then click on the pencil icon to edit the combination factors.
In the tree list, the combinations can be adjusted from strength to serviceability. Adjust C2 for serviceability and activate crack width & deflection checks by activating the corresponding checkboxes in the property window under Serviceability combination.
4 Reinforcement
Now design the reinforcement. Click on the Rebar assembly in the section New. Select reinforcement type Group of bars.
Define the properties of GB1, then repeat for GB2 to GB8. You can also use Copy to copy the current reinforcement.
Stirrup and ties are now needed in the bent cap to finalize the model. When using frame joint geometry, stirrup reinforcement assembly is available. Click on the Rebar assembly in the section New and select reinforcement type Group of stirrups.
Define the properties of ST1 and ST2 as shown in the image below.
For a final check, switch back to the Design tab and choose the Real 3D View to inspect the rebar alignment visually.
5 Calculation and Check
Start the analysis by clicking on the Calculate button in the ribbon.
The analysis model is automatically generated. Navigate to Check. On the left, you can see the overall results such as the material utilization.
To go through the detailed checks of each component, start with Strength. This will show concrete checks such as utilization in stress, the direction of principal stresses and strains, which can be switched on in the ribbon. Also, you can change directions and scale of stress.
For detailed results of reinforcement, you need to switch to the Reinforcement tab. This will change the ribbon icons and also will unroll the table for results. You can display results for strains and stresses in each bar and their utilization.
Reinforcement can also be visualized in a rainbow color to better see the compression and tension zones in every bar. Follow the image below to change to rainbow visualization.
Let's go to the Crack limitation check. Besides the icons to switch between the results, there are settings in the ribbon for the user to specify the limit value, and thus obtain a crack limit check.
6 Printing report
Now it is time to print a report of your calculations. Go to the Report tab. You can choose Brief or Detailed type of report and further adjust the report based on your needs in the tree menu. Select the preferred options and press Generate in the top ribbon.
The report is generated, and we can save it as a PDF or export it to an open Microsoft Word file.
You have designed, optimized, and code-checked the reinforced walking column.