UFC 4-023-03
25 January 2005
3-2.10
Nonlinear Dynamic Analysis Procedure.
Perform the following steps in a Nonlinear Dynamic Analysis.
1. Distribute the mass of the structure throughout the model in a realistic
manner; lumped masses are not allowed, unless to represent mechanical
equipment, pumps, architectural features, and similar items. Distribute mass
along beams and column as mass per unit length; for slabs and floors,
represent the mass as mass per unit area. If any portion of the structure is
represented by solid elements, distribute the mass as mass per unit volume.
2. Prior to the removal of the load-bearing element, bring the model to static
equilibrium under the loads from Section 3-2.4.1; the process for reaching
equilibrium under gravity loads will vary with analysis technique.
3. With the model stabilized, remove the appropriate load-bearing element
instantaneously. For AP analyses for load-bearing elements that do not have
adequate vertical tie force capacity, remove the element in accordance with
the material-specific requirements given in Chapters 4 to 8 (see Section 3-
2.3.1). For AP analyses of MLOP and HLOP structures, remove the column
or load-bearing wall per Sections 3-2.3.2 and 3-2.3.3.
4. Continue the dynamic analysis until the structure reaches a steady and stable
condition (i.e., the displacement history of the model reaches a near constant
value, with very small oscillations and all material and geometric nonlinear
processes have halted).
5. During or after the analysis, compare the predicted element and connection
forces and deformations against the acceptability criteria that are shown
generically in Table 3-1. To demonstrate compliance with the acceptability
criteria, a software package with modules that perform building code checks
may be used, providing the modules can be tailored to check the criteria in
Table 3-1. Confirm that all material-specific code provisions for bracing,
compactness, flexural-axial interaction, etc, are met.
6. If none of the structural elements or connections violates the acceptability
criteria during the dynamic motion of the structure, the analysis is complete
and satisfactory resistance to progressive collapse has been demonstrated.
If any of the structural elements or connections violate the acceptability
criteria, perform the following procedure:
A. At the point in the load history when the element or connection fails the
acceptability criteria, instantaneously remove the element or connection
from the model, per Table 3-1.
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