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Comment: updated page in analysis reference manual


This pages describes the staged construction operations available in SAP2000. The same staged construction operations are available in CSiBridge, but the screenshots below apply to SAP2000. {on-this-page} h1. Change Section The default "Change Section Properties" operation essentially involves removing a stressed object and replacing it with unstressed object. This is documented in CSI Analysis Reference Manual, chapter "Nonlinear Static Analysis", section "Staged Construction > Changing Section Properties". h1. Change Modifiers To model staged construction for a composite section (for example, a girder initially supporting its own weight and the weight of wet concrete slab will become a composite girder after the concrete slab hardens), you could use one of the following approaches: (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: !Change_modifiers_operation.png! 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|kb:Composite behavior]. 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. h1. 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. !Change_releases.png! {info} Please note that the following applies (see CSI Analysis Reference Manual, chapter "Frame Element", section "End Releases > Named Property sets" 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. {info} {hidden-content} Related Incidents: * {incident:no=38146|comment=Changing supports in staged construction.} {hidden-content} h1. Change Frame Releases * Use "Define > Named Property Sets > Frame Releases" menu command to define the frame end releases. * Define "Change Releases" operation in the staged construction load case to apply the frame releases
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The staged-construction applications described in this article were written in context with SAP2000, while they also apply to CSiBridge.

On this page:

Table of Contents

Change sections

Section properties may be changed for various structural objects throughout the course of staged construction. This enables both the simulation of structural changes which occur from stage to stage, and the modeling of 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 both 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 447).

Change modifiers

To apply staged construction to composite sections, property modifiers may be changed through either of two procedures. This may be a suitable application, for example, when a precast girder initially supports its own weight and the weight of wet concrete before the slab cures and becomes a composite deck system.

The two options for changing property modifiers are described as follows:

  1. If the composite section is modeled as a single frame object, only the supporting girder should be modeled initially. First, frame property modifiers should be created through Define > Named Property Sets > Frame Modifiers. Next, apply the Change Modifiers option within staged construction to account for the increased stiffness and weight of the composite section, as shown in Figure 1:


    Image Added

    Figure 1 - Change modifiers


  2. The second option is to explicitly model the individual components of a composite section. For example, a frame object may model the girder, then a shell object may model the slab. To simulate the hardening of concrete within the deck, the deck slab could be initially modeled with negligible stiffness (1e-4) and its full weight, then in a later construction stage, stiffness could be increased to its full value through property modifiers.

Change supports

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As of SAP2000 V15.0.1 and CSiBridge V15.1.1 (September 2011), it is not possible to directly change the type of support or restraint condition.

Frame releases and a dummy frame object may be assigned to change the support or restraint type within staged construction. This may be accomplished through the following process:

  1. Define short and stiff frame objects to represent bearings.
  2. Assign frame releases which represent the final bearing condition of these frame objects by selecting Define > Named Property Sets > Frame Releases.
  3. Within the staged-construction load case, use the Change Releases operation to change the frame releases, as shown in Figure 2:


    Image Added

    Figure 2 - Change releases



Please note that when property modifiers are changed within a staged-construction load case, they do not change the response of the structure up to that stage, and only affect subsequent response. In other words, the effect is incremental. This means that the approach previously described will work well when adding restraints to change supports, but it will not capture the redistribution of internal forces when supports are changed by removing restraints, in which case it would be more appropriate to add and remove links. This is accomplished by first removing the link objects which simulate the previous support condition, then by replacing with links which simulate the new supports.

Additional details are available in the CSI  Analysis Reference Manual (Frame Element > End Releases > Named Property Sets, page 116).

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Related Incidents:

  • Incident 38146: Changing supports in staged construction.

Change frame releases

Frame releases may be changed through the following process:

  • 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.