Change sections
Section properties may be changed for various structural objects throughout the course of staged construction to simulate the changes which occur from stage to stage, and to model multiple configurations within the same structure. When section properties are changed for a stressed object, the software automatically removes the object, replaces its response with equivalent forces, adds the new section, then reverses the equivalent forces. Forces then redistribute within the new object and throughout the structure.
Additional details are available in the
CSI
Analysis Reference Manual (Nonlinear Static Analysis > Staged Construction > Changing Section Properties, page 399).
Change modifiers
To apply staged construction to composite sections, property modifiers may be changed through either of two procedures. This may be suitable, for example, when a girder initially supports its own weight and the weight of wet concrete which will then cure to become a composite slab system.
These procedures are described as follows:
(1) If the composite section is modeled is a single frame element, model initially only the supporting girder and then use the "Change Modifiers" staged construction operation to account for the increased stiffness and weight of the composite section:
Figure 1 - Change modifiers
Please note that you would need to first create frame property modifiers via "Define > Named Property Sets > Frame Modifiers" menu command.
(2) Explicitly model the individual components (such as the girder by frame elements and the slab by shell elements) of the composite section. To model hardening of the deck concrete, the deck could be initially added with negligible stiffness and full weight and then the stiffness can be increased to full stiffness via property modifiers.
Change supports
While it is not possible to directly change the support or restraint type in the staged construction in SAP2000 V15.0.1 and CSiBridge V15.1.1 (these are the current versions as of 9/2011), this can be accomplished by using frame releases and a dummy frame element:
- Define short and stiff frame element to represent the bearing.
- Use "Define > Named Property Sets > Frame Releases" menu command to define frame releases representing the final bearing condition for the frame element defined in step 1.
- Define "Change Releases" operation in the staged construction load case to change the frame releases.
Figure 2 - Change supports
Please note that the following applies (please see the
CSI
Analysis Reference Manual (Frame Element > End Releases > Named Property Sets, page 116) for details):
"When property modifiers are changed in a staged construction Load Case, they do not change the response of the structure up to that stage, but only affect subsequent response. In other words, the effect is incremental."
This means that the approach described above will work well when supports are being changed by adding restraints, as it is adequate to use the incremental approach in this case. However, the above approach will not capture redistribution of internal forces when supports are being changed by removing restraints. For this case, modeling change of supports by adding and removing link elements would be more appropriate.
When using links, the procedure to change supports would be to remove link element(s) simulating the old support condition and replace it by a link element(s) simulating the new support condition.
Related Incidents:
- Unknown macro: {incident}
Change frame releases
Frame releases may be changed through the process which follows:
- Define frame end releases through Define > Named Property Sets > Frame Releases.
- Apply the end releases by selecting Change Releases within the staged-construction load case.