Bridge object force and stress diagrams FAQ

Obtaining bridge force and stress diagrams

Question: How does the software obtain bridge force and stress diagrams?

Answer: The program uses section cuts defined by groups to obtain bridge forces and stresses diagrams. These section cuts are automatically formed as part of the bridge model using the parametric definition and can be reviewed via "Display > Show Tables > MODEL DEFINITION > Bridge Data > Bridge Object Data > Table: Bridge Section Cuts 01 - General and Table: Bridge Section Cuts 02 Groups".

The coordinate system for each bridge section cut can be found in the table "Bridge Section Cuts 01 – General", fields "DirCos??":

• The local 1 axis of the bridge section cut is tangential to the layout line used for the bridge object where the layout line intersects the section cut, and points in the up-station direction.
• The local 2 axis of the bridge section cut is normal to the layout line used for the bridge object where the layout line intersects the section cut. It is also normal to the bridge deck (with super-elevation) at the layout line, and points in the upward direction.
• The local 3 axis of the bridge section cut is normal to the local 1 and 2 axes, following the right-hand rule. It lies in the plane of the deck (with super-elevation), and points toward the right edge of deck.

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.

Bridge response after manual modification

Question: If the bridge object is manually modified, are the the bridge object forces and stresses still correct? If I delete certain elements of a bridge deck section, are the results of bridge object response display still valid? If I divide certain elements, does the results of bridge object response display still valid?

Answer: The bridge forces and stresses diagrams accessible on the "Bridge Object Response Display" form are based on section cuts that utilize only the objects created by the bridge modeler. Any manually added/removed/modified entities would not be correctly accounted for in the section cuts. Therefore, manually deleting or dividing bridge superstructure frame, shell or solid objects will, in general, result in incorrect forces and stresses being reported on the "Bridge Object Response Display" form.