Slide 19 of 67
Notes:
- Stiffness and Aspect Ratios
- The most important factor in stiffness is the height to width ratio
- Long short walls are stiffer than tall narrow ones.
- For a wall of constant height, the stiffness will grow exponentially as the wall length increases.
- To help control stiffness, the UBC requires a minimum wall length for any given wall height.
- This allowable dimension ratio changes for each type of sheathing material and its construction.
- Wood structural panels can have smaller shear wall lengths than cement plaster or gypsum wallboard.
- When this sheathing is fastened at all of its edges, the UBC also permits smaller shear wall lengths.
- Allowable Aspect Ratios – Table 1
- These codes apply to new construction or retrofit
- Shows minimum width of wall for 8-foot high wall, depending on what material is used.
- Go over different materials Allowable shear values for gypsum lath and wallboard must be reduced 50% in Seismic Zones 3 and 4.
- The 1997 Uniform Building Code reduces the maximum allowable height-to-width ratios.
- 1:1 for conventional diagonal sheathing and
- 2:1 for special diagonal sheathing, wood structural panels and particleboard in Seismic Zones 3 and 4.