Segmented Shear Wall Design

Allowable Shear Table
          It is important for designers to understand how to use IBC Table 2306.4.1 and UBC Table 23-II-I-1, "Allowable Shear for Wood Structural Panel Shear Walls."   This table can also be found in the Allowable Stress Design (ASD) Manual for Engineered Wood Construction and in the back of the Design of Wood Structures textbook (Breyer, Fridley and Cobeen, 1999). 
          The table relates sheathing thickness, nail size and spacing, sheathing grade and allowable unit shear to enable determination of an appropriate construction configuration.  Depending on the given information, the table may be used in different ways to find the unknown parameters.  The tabulated values of allowable unit shear are for shear walls sheathed on one side only.  Unit shear values are additive for walls with structural sheathing on both sides.  

           It is important to note that the footnotes of the table play a key role in the design process.  The footnotes relate information on intermediate nail spacing (the spacing of the nails on the studs that are not located at the edges of the sheathing panels), sill plate thickness, and alternate allowable unit shear values.  Often times the footnotes may dictate the design of the shear wall.

          The following example demonstrates how the table may be used to find the necessary information for design.  Keep in mind this is only one approach for using IBC Table 2306.4.1 and UBC Table 23-II-I-1.  

          A shear wall will be built in IBC Seismic Design Category C (UBC Seismic Zone 2B) using sheathing grade plywood panels (e.g., C-D sheathing) applied over 2x6 Douglas Fir-Larch studs that are 16 inches on center (o.c.).  The sheathing will be attached using 8d common nails.  The shear wall must resist a unit shear due to seismic loading of 375 plf.  Determine the minimum sheathing thickness and the nail spacing to meet these requirements.

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Footnote: The values for 3/8 in and 7/16 inch panels applied directly to framing may be increased to values shown for 15/32 panels provided studs are spaced at a maximum of 16 inches on center or panels are applied with long dimension across studs.
        The following pages provide an opportunity to practice using the IBC or UBC Allowable Shear Table.  You will need a copy of the IBC or UBC table in front of you to answer the questions.  Read the questions carefully and select the appropriate values from the IBC or UBC table.  Be sure to consult the footnotes to the table as they may have bearing on the final answer.

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Topics of this module include:

Introduction, Load Path, Segmented Design Method, Wall Shear, Dimension Ratios, Chord Design
 Anchorage, Deflection, Perforated Design Method, Method Comparison, Shearwall Failures