Designing for Earthquakes

Wood is a proven choice for seismic-resistive construction
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SDPWS 4.3: Wood-frame shear walls sheathed with other materials (applicable for bearing wall systems A17 and building frame system B24 per ASCE 7-10)

▶  This system includes shear panels of particleboard, structural fiberboard, gypsum wallboard, gypsum base for veneer plaster, water-resistant gypsum backing board, gypsum sheathing board, gypsum lath and plaster, and Portland cement plaster, or lumber sheathing with fastening and shear wall aspect ratio varying by shear panel type.
▶  All framing members and blocking used for shear wall construction are 2-in. nominal or greater.

▶  Foundation anchor bolts have a steel plate washer under each nut not less than 0.229 in. x 3 in. x 3 in. in size except in some cases where standard cut washers are explicitly permitted.

▶  Design for shear and overturning provides for properly sized tension and compression chords and shear and overturning anchorage.

▶  Allowable unit shear strengths span a wide range across different sheathing materials. For 1/2-in. gypsum wallboard, allowable unit shear strengths range from 75 plf (sheathed on one side, unblocked panel edges, and 7-in. fastener spacing at panel edges) to 360 plf (sheathed on two sides, blocked panel edges, and 4-in. fastener spacing at panel edges). Particleboard, structural fiberboard, horizontal lumber and vertical board shear walls are permitted in seismic design categories A, B and C.

▶  Gypsum wallboard, gypsum base for veneer plaster, water-resistant gypsum backing board, gypsum sheathing board, gypsum lath and plaster, or Portland cement plaster, and diagonal lumber shear walls are permitted in seismic design categories A, B, C and D.

Example Calculation of Seismic Base Shear for Different R-Factor Systems

 

[ Page 7 of 13 ]                
Originally published in Engineering News-Record

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