25 January 2005
Damage Limits for the Structure.
In AP analysis with any of the three methods (Linear Static, Nonlinear Static,
and Nonlinear Dynamic), the designer must quantify the extent of damage during the
analysis and at the end of the analysis.
Damage Limits for Removal of External Column or Load-Bearing Wall
For the removal of a wall or column on the external envelope of a building t,
the Damage Limits require that the collapsed area of the floor directly above the
removed element must be less than the smaller of 70 m2 (750 ft2) or 15% of the total
area of that floor and the floor directly beneath the removed element should not fail. In
addition, any collapse must not extend beyond the structure tributary to the removed
Damage Limits for Removal of Internal Column or Load-Bearing Wall
For the removal of an internal wall or column of a building, the Damage Limits
require that the collapsed area of the floor directly above the removed element must be
less than the smaller of 140 m2 (1500 ft2) or 30% of the total area of that floor, and the
floor directly beneath the removed element should not fail. In addition, any collapse
must not extend beyond the bays immediately adjacent to the removed element.
Acceptability Criteria for Structural Elements and Connections.
The Acceptability Criteria for the AP method consist of strength requirements
and deformation limits. The moments, axial forces, and shears that are calculated for
the elements and connections in each AP analysis are the Required Strengths, as
defined in Equation 3-2. These Required Strengths must be compared to the Design
Strengths of each element and connection, as shown generically in Table 3-1. In
addition, the deflection and rotations that are calculated in the AP model must be
compared against the deformation limits that are specific to each material type. If any
structural element or connection violates an acceptability criteria (strength or
deformation), modifications must be made to the model before it is re-analyzed, as
indicated in Table 3-1 and discussed in more detail in the following sub-sections.
The acceptability criteria for flexural loads is based on the flexural design
strength of the structural element, including the strength reduction factor Φ, and the
over-strength factor Ω applied to the material properties as appropriate. In calculating
the flexural design strength, account for the material-specific factors that can reduce the
flexural design strength, such as compactness and lateral bracing for structural steel,
amount of rebar in reinforced concrete, etc.
When the internal moment (flexural required strength) determined by the AP
model exceeds the flexural design strength of an element, the element is either