Question
How can stirrups with varying spacing be modeled in a girder?
Answer
This is a common scenario encountered by many modelers during rebar detailing. In most girders, stirrups are closely spaced near the supports and widely spaced at the midspan to accommodate the varying shear demands. To model such stirrups with varying spacing in CIM, a user-defined arrangement can be applied.
Let us consider an example where the main longitudinal rebars of the girder have already been modeled, and now we aim to place outer stirrups at a spacing of 150 mm near the supports and 250 mm at the midspan.
Follow the steps below to model stirrups with varying spacing:
Step-by-Step Procedure:
Step 1: In the Girder Curve Library, enter the Rebar Mode at the starting face of the girder.
Note: For those unfamiliar with basic rebar modeling, please refer this link.
Step 2: Let the default rebar properties remain unchanged. Since we are modeling stirrups, select the ‘Shear Reinforcement’ radio button.
Step 3: Enable the ‘Closed Rebar’ option, as stirrups to be modelled are closed.
Step 4: Enable the ‘Align Bending Center’ option.
Step 5: Click the ‘Select’ tab. It will turn blue, indicating that rebar elements can now be selected.
Step 6: Select the rebar in the following order using the left mouse button:
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Top left corner
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While holding the Ctrl key, click on:
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Bottom left corner
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Bottom right corner
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Top right corner
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Step 7: Click the Green Tick icon at the bottom of the panel to apply the selection.
Now you may observe that the outer stirrup is now modeled.
Step 8: Click on the ‘Array’ tab to extend stirrups throughout the girder.
Step 9: Click on the ‘Property’ tab at the top of the panel.
Step 10: Under the ‘Arrangement’ section, select ‘User Defined’ from the dropdown menu.
Step 11: In the input cell, enter the following values:
20@0.15,75@0.25,20@0.15
Explanation:
- 20@0.15 → 20 stirrups at 150 mm spacing
- 75@0.25 → 75 stirrups at 250 mm spacing
- The unit system is in meters, hence 0.15 m = 150 mm.
If you observe the units cell located at the bottom right corner of the screen, you will notice that the current unit system is set to meters. This is why the spacing values have been specified in meters.
Step 12: Click on the ‘Array’ tab.
Step 13: Ensure that ‘Tapered Array’ is selected (this is the default option).
Step 14: Select the stirrup using the left mouse button.
Step 15: Click on the ‘Select Plane’ tab under the ‘Define End Plane’ section. The button will turn blue, indicating that plane can now be selected.
Step 16: Using the left mouse button, select the plane at the end of the girder.
Step 17: Click on the Green Tick icon at the bottom to apply the array.
After completing these steps, you will see that the stirrups have been successfully modeled with varying spacing, closely spaced at the girder supports and more widely spaced at the midspan.
This is the process of modelling stirrups with varying spacing along the length of the girder.