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# [Civil]How is the Required Performance Calculated for the Bridge Support Evaluation?

## Question

How is the required performance calculated for the bridge support evaluation?

The required performance used for support evaluation is the smaller of the sectional strength of the pier column and the combined elastic seismic force. However, since piers are often not modeled, and it is common to view them as rigid structures, they do not have a sectional strength. Therefore, the combined elastic seismic force becomes the required performance.

In the Seismic Performance Evaluation option, the process of calculating the combined elastic seismic force of a bridge is different from that of a pier. In the case of piers, the sum of shear forces generated at the top of the columns is used as the combined elastic seismic force, but as mentioned earlier, since the piers are not modeled, the shear force generated by the support link is used as the required performance.

We don't output the history that happens to the bridge support Link separately in the report, so if you need a basis for the calculation, you'll need to look at the bridge support Link history results calculated in Civil.

The required performance (combination elastic seismic force) used for the evaluation of the alternating support uses the result of the load combination with the largest link resistance among all load combinations assigned to the Seismic Load Combination Type.

Therefore, you need to look at the individual evaluated load combination results, not the enveloped evaluated load combination results.

Please note that all signs are considered when summing the link resistance results of individual load combinations.

Let's take an example using the follow-along model (PSC Beam Multi-column Seismic Performance Evaluation) posted on the technical website.

In the example model, there are a total of 8 braces placed at the point of view shift, and all braces are stiffened in both axial and diagonal directions with elastic braces. The brace links are numbered 1 to 8.

If you transfer the results of each load combination from Link 1 to Link 8 to Excel, you can see that the required performance for the axial direction is determined by the eLCB5(max) load combination as shown below.

Note that the Result Table data for Elastic Link in Civil is output on a node basis, so you'll need to compare Link histories by summing and halving.

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