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For seismic design, on each level and for both directions, Shearwalls checks the maximum amplified story drift computed as per ASCE 7 12.8.6 and Equation 12.8-15 against the limits in ASCE 7 12.12.1.
Structures in seismic design category C, D, E or F having torsional irregularity (Horizontal Irregularity 1 in Table 12.3-1), must use the largest amplified story drift at the edges of the structure. Otherwise, the storey drift at the center of mass is used. Furthermore ASCE 12.3.1.1 indicates that all shear lines must satisfy story drift limitations for the building to be modeled with flexible diaphragms
Maximum Deflection δxe
The program computes and shows the maximum unamplified deflection δxe i.e. s the largest deflection on any shear line arising from seismic forces calculated in 12.8 factored for strength (LRFD) as per 12.8.6
If deflections on a line have been equalised, it is the common deflection of all walls on the line. If not, it is the largest deflection for any segment on the line.
Constant Deflection δc
This is the deflection due to the contribution to hold-down displacement of oversized boltholes, miscuts, gaps, and shrinkage. This deflection is not amplified by the deflection factor, because it is independent of the shear force, which was generated using ductility, overstrength, and Importance factors. The purpose of deflection amplification is to remove the influence of these factors.
The constant deflection for the shearline corresponding to the maximum deflection is shown.
Amplified Deflection δx
Amplified deflection δx from 12.8-15 the maximum deflection are multiplied by the deflection amplification factor Cd and divided by the importance factor I. Defining the constant deflection as δc , Shearwalls uses the formula
δx = δc + ( δxe - δc ) Cd / I.
The values of Cd are from the Site dialog for each direction, the default values being from ASCE 7 Table 12.2-1. They are shown below the table.
The importance factor IE is calculated from the Occupancy category entered in the site dialog, and is also shown below the table.
Deflection at Center of Mass
The values of δx and δxe are also determined and shown at the center of mass, calculated by straight line interpolation of the deflections at the two shear lines on either side of the center of the mass. This value is used for the comparison with the allowable drift for those structures which do not require the deflection at the extreme edges. .
Warning Messages
Failure messages appear beneath the table for each of the conditions – torsionally irregular rigid, other rigid, and flexible diaphragms. In addition, if centre of mass is used and the centre of mass is within limits, but another shear line is not, a warning appears