UFC 4-023-03
25 January 2005
3-2.9
Nonlinear Static Analysis Procedure.
Perform the following steps in a Nonlinear Static Analysis.
1. For AP analyses for load-bearing elements that do not have adequate vertical
tie force capacity, remove the element from the structural model 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.
2. Apply the loads using a load history that starts at zero and is increased to the
final values defined in Section 3-2.4.2. Apply at least 10 load steps to reach
the total load. The software must be capable of incrementally increasing the
load and iteratively reaching convergence before proceeding to the next load
increment.
3. As the analysis is performed, 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.
4. If none of the structural elements or connections violates the acceptability
criteria during the loading process, 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, remove the element or connection, per Table 3-1.
B. If an element was shown to fail, redistribute the element's loads per
Section 3-2.4.3.
C. Restart the analysis from the point in the load history at which the element
or connection failed and the model was modified. Increase the load until
the maximum load is reached or until another element or connection
violates the acceptability criteria.
D. At each point at which the analysis is halted, check the predicted damage
state against the damage limits in Section 3-2.6. If the damage limits are
violated, re-design and re-analyze the structure, starting with Step 1.
E. If the damage limits are not violated and the total load has been applied,
the design is adequate. If the damage limits are not violated but one of
the acceptability criteria was violated in the re-started analysis, repeat this
process (Steps A through E), until the total load is applied or the damage
limits are violated.
3-20
Previous Page
