|
|
|
|
|
Windward z Value
For windward roofs and walls, the design standards require that you evaluate pressures at a each point z on the vertical profile of the surface. In creating the wind load that is transferred to a diaphragm, Shearwalls integrates the varying pressure values p(z) over the whole surface. The value z reported in the log file is the height that has a corresponding pressure p which if it was applied to the whole surface would give the same total load.
For walls, the surface in question is the upper half of the wall on the storey below the diaphragm combined with the lower half of the wall above. For a roof or a gable end, it is just one of the automatically generated panels. The program takes into account the tapering of a hip or gable in integrating pressures.
Interpolation
In all cases, if the design standard allows or stipulates that the design values in tables are interpolated, then the program interpolates. In many cases, the interpolation is done in two parameter dimensions.
Side Pressures
Side pressures, that is, pressures due to wind parallel to the building surfaces, are not considered in MWFRS generation except for the low-rise method, as they are assumed to cancel each other. This is not strictly true for eccentric ridge but the assumption is that these loads are smaller than those generated by perpendicular-to-surface winds.
Side pressure coefficients for are considered for C&C loads where applicable.
Internal Pressures
The program does not consider internal pressure in the generation of MWFRS loads. The net horizontal components of the internal pressure acting on opposing wall and roof surfaces are equal in magnitude and will cancel each other.
Internal pressures are considered for component and cladding loads Loads.
Uplift Loads
Shearwalls does not generate wind uplift loads. These must be input manually to determine the effect on hold-down forces.
Exposure
It is assumed that the Exposure category applies to all wind directions; i.e. it is not possible to define an exposure for wind from one direction and another for the opposite direction or transverse direction. This is the required procedure for the Envelope method and for Component and Cladding loading, as per 27.6.4.2. but can be conservative for the Directional Procedure (26.7.4.1).
Topographic Effect
The topographic factor Kz is based upon ASCE 7 26.8. The program implements H/L > 2 restriction from 26.8.1(4), the height restrictions based on exposure from 26.8.1(5).
The program integrates Kzt over the building surface separately from other factors, resulting in a different average z for Kzt than for the main exposure factors. It reports Kzt and z for Kzt , in log file output for each building surface.