TR.20.10 Member Property Reduction Factors
In STAAD.Pro, you can specify a set of reduction factors to be applied on the calculated section properties such as area, moments of inertia, and torsional constant. If you want to adopt this approach to account for cracking of concrete sections, refer to Section 10.11.1 of ACI 318 for a set of values to use for these reduction factors depending upon the nature of forces and moments the member is subjected to.
General Format
The format of the command is:
MEMBER CRACKED (CODE IS1893 2016)
{ member-list | group-list } REDUCTION *{ RAX f1 | RIX f2 | RIY f3 | RIZ f4 }
Parameter | Description |
---|---|
RAX f1 | Reduction factor in the axial area.
RAX is not applicable for reduction factors for the IS1893 2016 code. |
RIX f2 | Reduction factor of the torsion constant (about the local x-axis). |
RIY f3 | Reduction factor in the moment of inertia about the local major axis (y-axis). |
RIZ f4 | Reduction factor in the moment of inertia about the local minor axis (z-axis). |
This is a multiplication factor on the property value. It does not signify the amount by which the property is reduced, but, it is simply a value by which the unreduced property is multiplied. Thus, the calculated (or the user-specified value) of the property will be multiplied by the reduction factor to arrive at the value used in the analysis.
For example, a factor of 0.45 defined for RAX will mean that if the cross sectional area of the gross section is 0.8 ft^{2}, the value used in the analysis will be 0.8 × 0.45 = 0.36 ft^{2}.
Multiple factors can be assigned on the same line.
The reduction factor is considered only for analysis but not for design.
Code-Specific Reduction Factors
IS1893 2016 Clause 6.4.3 calls for a reduction of moment of inertia values by 0.35 for beams and 0.7 for columns of concrete members only while analyzing the structure for static seismic and response spectrum/linear dynamic analysis.
Code-specific reduction factors will not affect non-concrete members. A separate stiffness matrix is generated for the use of IS1893 2016 static seismic and response spectra loads. For all other load cases, the analysis is performed using the unreduced stiffness matrix.
The CHANGE command has no affect or code-specific reduction factors.