FEMA P55 Coastal Construction Manual, Fourth Edition - Mad Cad

Volume II DESIGNING THE BUILDING 9
EXAMPLE 9.7. UPLIFT AND COMPRESSION DUE TO SHEAR WALL OVERTURNING
(concluded)
• The total shear load for south wall assuming flexible diaphragm distribution of roof diaphragm
load is calculated as follows:
Shear load in south shear walls = (17.5 ft)(410 plf) = 7,175 lb
Shear wall segment aspect ratio (see Illustration B):
• Each shear wall segment must meet the requirements for shear wall aspect ratio in order to be
considered as a shear resisting element. For wood structural panel shear walls, the maximum
ratio of height to length (e.g., aspect ratio, h/L) is 3.5:1.
• The aspect ratio for shear wall segments in Illustration A can be calculated as follows:
Aspect ratio of 6-ft long shear wall segment: 1.67 < 3.5
Aspect ratio of 3-ft long shear wall segment: 3.33 < 3.5
Unit shear, v = total shear load/shear wall length =
Uplift (T) and compressive force (C) at shear wall ends due to overturning
= (598 plf)(10-ft wall height) = 5,980 lb
COASTAL CONSTRUCTION MANUAL
598 plf
Note: As seen in this example, tension and compression forces due to shear wall overturning can be large.
Alignment of shear wall end posts with piles below facilitates use of standard connectors and manufacturers’
allowable design values. A check of the pile uplift and compressive capacity in soil is needed to ensure an
adequate load path for overturning forces.
Because of the magnitude of overturning induced uplift and compression forces, it is desirable to align shear
wall ends with piles to provide direct vertical support and to minimize offset of the tension or compression
load path from the axis of the pile. Where shear wall end posts are aligned with piles below, detailing that
allows connection of the shear wall end post holddown directly to the pile is desirable to minimize forces
transferred through other members such as the support beams. Where direct transfer of overturning induced
uplift and compression forces into the pile is not possible, minimizing the offset distance reduces bending
stresses in the primary support beam (see Figure 9-20). For the holddown connection shown in Figure 9-20,
the manufacturers’ listed allowable load will be reduced because the bolted connection to the wood beam is
loaded perpendicular to grain rather than parallel to grain.
9-23