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A509.4.5 General Execution Procedure for the Displacement Coefficient Analysis Procedure

2010 Existing Building Code of NY > A5 Earthquake Hazard Reduction in Existing Concrete Buildings and Concrete With Masonry Infill Buildings > A509 Tier 3 Analysis Procedure > A509.4 Displacement Coefficient Analysis Procedure > A509.4.5 General Execution Procedure for the Displacement Coefficient Analysis Procedure

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The general procedure for the execution of the displacement coefficient analysis procedure shall be as follows:

An elastic structural model shall be created that includes all components (existing and new) contributing significantly to the weight, strength, stiffness or stability of the structure, and whose behavior is important in satisfying the intended seismic performance.
The structural model shall be loaded with gravity loads before application of the lateral loads.
The mathematical model shall be subjected to incremental lateral loads using one of the lateral load patterns described in Section A509.4.3. At least two different load patterns shall be used in each principal direction.
The intensity of the lateral load shall be monotonically increased until the weakest component reaches a deformation at which there is a significant change in its stiffness. The stiffness properties of this "yielded" component shall be modified to reflect the post-yield behavior, and the modified structure shall be subjected to an increase in lateral loads (for load control) or displacements (for displacement control) using the same lateral load pattern.
The previous step shall be repeated as more components reach their yield strengths. At each stage, the internal forces and deformations (both elastic and plastic) of all components shall be computed.
The forces and deformations from all previous loading stages shall be accumulated to obtain the total force and deformations of all components at all stages.
The loading process shall be continued until unacceptable performance is detected or until a roof displacement is obtained that is larger than the maximum displacement expected in the design earthquake at the control node.
A plot of the control node displacement versus base shear at various stages shall be created. This plot is indicative of the nonlinear response of the structure, and changes in the slope of this load-displacement curve are indicative of the yielding of various components.
The load-displacement curve obtained in Item 8 shall be used to compute the effective period of the structure, which would then be used to estimate the target displacement (Section A509.4.2).
Once the target displacement has been determined, the accumulated forces and deformations at this displacement shall be used to evaluate the performance of various components.
If either the force-demands in the nonductile components or deformation-demands in the ductile components exceed the permissible values, then the component shall be deemed to violate the performance criterion, indicating that rehabilitation be performed for such elements.

The relation between base shear force and lateral displacement of the control node shall be established for control node displacements ranging between zero and 150 percent of the target displacement, δ_t.

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