Developing Model

How does SAP2000 internally distributes moving loads from lanes to frames?

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There are several links created at each bearing location. What do these links represent?

See bridge Bridge bearings page

How can I model a concrete box bridge using BrIM for which its deck is rigidly (without bearings) connected to its bents and abutments?

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1. Define fixed bridge bearing via "BrIM > Bearings > Add New Bridge Bearing" and set fixed release type for all DOFs.
2. Define abutment with integral girder support condition (via "BrIM > Abutments > Add New Bridge Abutment").
3. Define bridge bent with integral girder support condition (via "BrIM > Bents > Add New Bridge Bent").
4. Use "BrIM > Bridge Objects > Modify/Show Bridge Object" menu command to assign the previously defined fixed bearing to the abutments and bents with rigid connection to the superstructure. The menu command will open Bridge Object Data form that can be used the complete the following actions:
   1. Under "Modify/Show Assignments" heading, choose Abutments and click the "Modify/Show" button. Then assign the previously defined fixed bearing to the abutments.
   2. Under "Modify/Show Assignments" heading, choose Bents and click the "Modify/Show" button. Then assign the previously defined fixed bearing to the bents.
5. Review the entities created by the bridge modeler at each superstructure to substructure connection to make sure that they correctly represent the modeling intention.

See also girder Girder support condition page for additional information on integral bent and abutments.

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Extended Question: For my particular model, the Bridge Modeler generates hundreds frame sections since the superstructure is highly curved and the cross-section varies. If I want to reduce the moment of inertia of the superstructure (cracked concrete, Icr = 0.5 Ig, Jcr = 0.05 J), do I need to go to Section "Property > Frame Properties" and set modifiers one by one? This is lots of work and very inefficient, I was wondering if there’s any easier way to model the cracked concrete for the superstructure.

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• Define a group that will contain all superstructure frame elements. Such group can be defined directly on the "Bridge Object Data" form via the "Staged Construction Groups" assignment.
• Define frame property modifier to be used via "Define > Name Property Sets > Frame Modifiers" menu command.
• Define staged construction load case, and add all elements and apply the modifiers in the first stage. Then apply other loads in the subsequent stages.

Using the above approach is the most flexible, since the structures with full and reduced stiffnesses coexist in a single model. Please note that as of V14.0.0, we allow to run staged construction analysis with a single stage, even for users that do not have the staged construction license. This allows to evaluate multiple configurations of the structure which is exactly your case. You could then run subsequent analyses by using stiffness at the end of this single-stage staged construction load case.

You could also use interactive Interactive database editing ("Edit > Interactive Database Editing") to assign modifier to multiple members from a single location.

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Any manually added objects are not added to the section cuts. The force/moment diagrams will be correct for the final structure at all sections that have not been modified. Manually added members, such as diaphragms, may carry load and take it away from objects that are part of a section cut, thus reducing the section cut force. They can only affect section cuts to which they are connected.

See bridge Bridge forces and stresses diagrams for additional details.

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Answer: The spine BrIM model uses a single body Body constraint to connect a joint of the superstructure frame element with all the joints representing the top of bearing links at a given substructure unit. While this modeling approach is adequate to obtain global response of the structure, it does not fully capture the distribution of the superstructure load to the individual bearings. You would need to update the Linked Bridge Model as Area Model to get more meaningful bearing forces for the design of bearings and the pier caps.

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The design is for prestressed concrete box girder sections only and as of SAP2000 V12 there are no provisions for mild reinforcement. You could possibly model mild steel reinforcement as a tendon with zero force, but the design would not really be correct. For example, the mild reinforcement would be treated as tendon for flexural check, but the code distinguishes between the two. Only the stress check would provide adequate results. (Refs: Email | date = 081120 | from = ok | to = syx | subject = RE: add mild steel in BrIM)

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