The ASCE 7 standard provides two design methods:
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Load and Resistance Factor Design (LRFD) compares required strength to actual strengths. LRFD provides the actual response of the system, including deflections and loads on supports and structure, when the actual wind or seismic load is applied.
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Allowable Stress Design (ASD) compares actual and allowable stresses. ASD uses load reduction factors (0.7 for seismic events and 0.6 for wind events) when calculating stresses.
CAESAR II uses ASD to evaluate a piping system under wind and seismic loads. To comply with ASCE 7 requirements, you must include the load reduction factors in your load cases for stress compliance.
The following table provides example load combinations showing the use of ASCE 7 load reduction factors (in bold).
Load |
|
|
Stress |
---|---|---|---|
L1 |
W+T1+P1+0.7U1 |
Operating case with seismic load (using the reduction factor) for computing stresses |
OPE |
L2 |
W+T1+P1+U1 |
Operating case with seismic load for computing loads on supports and deflections |
OPE |
L3 |
W+T1+P1+0.6WIN1 |
Operating case with wind load (using the reduction factor) for computing stresses |
OPE |
L4 |
W+T1+P1+WIN1 |
Operating case with wind load for computing loads on supports and deflections |
OPE |
L5 |
W+T1+P1 |
Operating case |
OPE |
L6 |
W+P1 |
Sustained case |
SUS |
L7 |
L1-L5 |
Preparatory case for stress evaluation due to seismic load |
OCC |
L8 |
L3-L5 |
Preparatory case for stress evaluation due to wind load |
OCC |
L9 |
L6+L7 |
Seismic sustained + occasional |
SUS+OCC |
L10 |
L6+L8 |
Wind sustained + occasional |
SUS+OCC |
In CAESAR II 2019 (version 11) and later, the Seismic Wizard no longer includes the 0.7 reduction factor for consistency with wind loads, which never included the 0.6 reduction factor.