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D4.A.3 Slenderness Effects and Analysis Considerations

STAAD.Pro provides the user with two methods of accounting for the slenderness effect in the analysis and design of concrete members. The first method is equivalent to the procedure presented in CSA Standard A23.3-94 Clause 10.13. STAAD.Pro accounts for the secondary moments, due to axial loads and deflections, when the PDELTA ANALYSIS command is used. After solving for the joint displacements of the structure, the program calculates the additional moments induced in the structure due to the P-Delta effect. Therefore, by performing a P-Delta analysis, member forces are calculated which will require no user modification before beginning member design. Refer to TR.37.2 P-Delta Analysis Options for additional details on this analysis facility.

The second method by which STAAD allows the user to account for the slenderness effect is through user supplied moment magnification factors (see the parameter MMAG in D4.A.4 Design Parameters). Here the user approximates the additional moment by supplying a factor by which moments will be multiplied before beginning member design. This second procedure allows slenderness to be considered in accordance with Clause 10.14 of the code.

Note: STAAD.Pro does not factor loads automatically for concrete design. All the proper factored loads must be provided by the user before the ANALYSIS specification.

While performing a P-Delta analysis, all load cases must be defined as primary load cases. If the effects of separate load cases are to be combined, it should be done either by using the REPEAT LOAD command or by specifying the load information of these individual loading cases under one single load case. Usage of the LOAD COMBINATION command will yield incorrect results for P-Delta Analysis in STAAD.Pro.