Model screenshot

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Approach 1, using section modifiers (Model B)

Approach 1 is described as follows:

Key modeling steps

• Use the BrIM template to create a 2-span precast-girder bridge. Designate double bearings at the interior pier.

• Manually define 15 continuity links at the interior pier to connect the girders and deck between span 1 and span 2.

• Create three groups for the construction stage analysis of continuity links, deck, and all other objects.

• Use the Define > Named Property Sets > Area Modifiers command to define property modifiers for the deck shell elements. This will simulate the hardening of concrete.

• Set up construction stage analysis with separate stages to:
  
  
  1. Add and load girders;
     
     
  2. Add deck shell elements;
     
     
  3. Reduce the stiffness of deck shell elements to simulate concrete placement;
     
     
  4. Apply the deck dead load;
     
     
  5. Reset the stiffness of the deck shell elements to simulate the hardening of concrete; and
     
     
  6. Add continuity links to the model.

• Save the results at the end of each stage.

• Define moving-load analysis, starting from the end of staged-construction analysis.

Modeling comments

• The bridge has fixed bearings at the bent which restrain vertical, longitudinal, and transverse translation. Sliding bearings at the abutments restrain vertical and transverse translation. For all other bearing DOF, it is necessary to add small stiffness to stabilize the girder before the deck is erected, otherwise stability problems may occur.

Results

• Check bridge forces and stresses for each step of the staged construction analysis to ensure that moments are as expected for a simply-supported condition.

• Check moments for the results of moving-load analysis to ensure that moments are as expected for a continuous-girder system.

Additional screen shots

The moment diagram upon completion of staged construction, after all loads are applied to simply-supported beams elements, is shown in Figure 2:

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Moment induced by live load, applied to a continuous span, is shown in Figure 3:

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Approach 2, changing section properties (Model C)

Approach 2 is described as follows:

Key modeling steps

• Use the Quick Bridge template to create a 2-span precast-girder bridge with double bearings at the interior pier.

• Manually define 15 continuity links at the interior pier to connect the girders and deck between span 1 and span 2.

• Create three groups for the construction stage analysis of continuity links, deck, and all other objects.

• Set up construction stage analysis with separate stages to:
  
  
  1. Add and load the girders;
     
     
  2. Add deck shell elements;
     
     
  3. Reduce the stiffness of the deck shell elements to simulate concrete placement;
     
     
  4. Apply the deck dead load;
     
     
  5. Reset the stiffness of the deck shell elements to simulate the hardening of concrete; and
     
     
  6. Add continuity links to the model.

Attachments

• [SAP2000 V12.0.2 file |Staged-construction analysis of two-span precast-girder bridge^SAP2000 V12.0.2 model B.zip] of Model B (zipped SDB file)