Suspension Bridge Analysis Control

The suspension bridge model created from Suspension Bridge Wizard is modified to suit the user intention and analyzed once again to determine an accurate initial configuration.

Suspension Bridge Wizard performs an initial configuration analysis only considering the cable system. In order to perform an initial configuration analysis considering the global system of a bridge, re-analysis using this function is needed.

This process is required for a self-anchored suspension bridge, as the coordinates of the entire cable system are changed by the axial displacement occurring in the girder.

From the Main Menu select Analysis >  Analysis Control > Suspension Bridge.

Control Parameters

Number of Iteration: Enter the number of iterations for nonlinear analysis.

Convergence Tolerance: Enter the convergence tolerance, which will be used for acceptance of errors.

Analysis Method

Initial Force : Determine an initial configuration of a suspension bridge model by updating initial forces

Optimal Approach : Determine an initial configuration of a suspension bridge model by updating design parameters satisfying the specified constraint condition.

When Initial Force is selected

Node Group to be Updated

Select the node group whose coordinates will be updated.  The nodes for the cable elements of a suspension bridge are continuously updated in the process of optimizing the equilibrium state.  Accordingly, it is recommended to group all the cable nodes.  Nodes at each end of a cable, which are affixed to supports, are excluded. However, the node at the sag point is included in the group although it is not updated.

Sag Point Group

Since the sag value of the main cables at the center of the center span is defined by the user, these nodes must be excluded from being updated. Therefore, one Sag Point node (2 nodes for a 3-D bridge) must be assigned to a group.

Constant Horizontal Force of Cable

Using an initial configuration analysis, determine the equilibrium state which exhibits the horizontal cable forces inputted by the user.

Main Cable Group: Select the Element Group to which the main cables of a suspension bridge are assigned.

Horizontal Force: Enter the horizontal cable force.

Define Girder Z-Displacement Condition

When the rigorous method is used in the initial configuration analysis for the global system of a suspension bridge, some moments may occur in the girder.

By defining a Hanger Cable Group using this option, we can control the vertical displacement at nodes where girder and hanger cross and accordingly, we can minimize the moment resisted by the girder.

When Optimal Approach is selected

Cable Group to be Updated

Select the cable element group whose design parameters will be updated by optimal approach.

Sag Point Group

Since the sag value of the main cables at the center of the center span is defined by the user, these nodes must be excluded from being updated. Therefore, one Sag Point node (2 nodes for a 3-D bridge) must be assigned to a group.

Define Constraints

Define the constraint condition for Truss Force, Displacement and Beam Force. In order to obtain the desired initial configuration from optimal approach, we can control the girder moments by defining the constraint condition of beam forces. By clicking [Table] button, we can use Copy & Paste command from MS Excel.

Load Cases to be Considered

Load Case

Select load cases with which cable tensions become equilibrium. Generally, self weight and dead load are selected.

To enter a new or additional load case

Enter the Load Case and Scale Factor; and click .

To modify the scale factor for a previously entered load case

After selecting the relevant load case, modify the scale factor, and click  .

To delete a previously entered load case

Select the relevant load case, and click  .

Note
Upon completing the data input, click     and . The process of analysis updates the nodal coordinates and tensions of the main cables. In addition, the equilibrium forces in the structure due to the cable forces and the girder뭩 self weight are calculated. The equilibrium forces can be check in a table format from Load>Initial Forces> Equilibrium Element Nodal & Member Forces. After the analysis is performed, if   is clicked again, the program will establish the previous data for the cable force as the initial force and perform the analysis again.

In this detail analysis, it continuously updates the member internal forces by repetitive analyses in order to find the optimum equilibrium configuration. Spring supports can not be used in this process. If spring supports are required, Elastic Link support should be used to substitute the properties.

To consider the self-weight of the cables, the load which defining the self weight should be included to the selected Load Case.

 To perform another analysis or to delete the entire inputted data, click on.