TR.31.7 Definition of Direct Analysis Members
This set of commands may be used to define the members whose flexural stiffness or axial stiffness is considered to contribute to the lateral stability of the structure. These parameters are then used by the program to generate a set of lateral loads as defined in Appendix 7 of ANSI/AISC 360-05 when a PERFORM DIRECT ANALYSIS command is used.
General Format
DEFINE DIRECT
FLEX (f1) list-spec
AXIAL list-spec
FYLD (f2) list-spec
Where:
list-spec = * { XR f4 f5 | YR f4 f5 | ZR f4 f5 | MEMBERS mem-list | LIST memb-list | ALL }
| Parameter | Default Value | Description |
|---|---|---|
| FLEX f1 | 1.0 | The initial τb value (See Appendix 7 ANSI/AISC 360-05). Members listed with FLEX will have their EI factored by 0.80 times τb while performing the global solution. |
| AXIAL | - | Members listed with AXIAL will have their EA factored by 0.80 while performing the global solution. Although reduced stiffness is considered for analysis, the program considers the full value of E for both flexural and axial design. |
| FYLD f2 | 36.0 ksi | Yield Strength in current units. |
| XR | YR | ZR f4, f5 | - | Upper and lower range values, respectively, used when specifying a range for FLEX or FYLD. |
For specifying NOTIONAL LOADs, please see TR.32.13 Notional Loads. The notional loads and the factor used is specified entirely in the loading data.