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The R factor is intended to account for inelastic structural behavior and the ability of a structure to displace/deform
and dissipate energy without failing. Since all R factors specified in UBC Table 16-N are greater than unity
(R > 1.0), the R factor effectively reduces the calculated base shear (V) by varying amounts
depending on the ductility of a structure. In general, ductile structural systems should have higher R factors than brittle
structural systems. Typical values of R for many low-rise wood structures are:
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R = 5.5 for light frame wood buildings with shear walls that support gravity loads and simultaneously resist lateral loads
in structures less than 4 stories high
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R = 4.5 for light frame wood buildings with shear walls that support gravity loads and simultaneously resist lateral loads
in structures more than 3 stories high
The following additional R factors also apply to wood structures, but are associated with less commonly used structural systems:
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R = 6.5 for light frame wood buildings less than 4 stories high in which the frame system supports gravity loads
independently of the shear panels that resist lateral loads
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R = 5.0 for light frame wood buildings more than 3 stories high in which the frame system supports gravity loads
independently of the shear panels that resist lateral loads
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R = 5.6 for heavy timber braced frames in which the frame system supports gravity loads independently of
the bracing that resists lateral loads
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R = 2.8 for heavy timber braced frames in which bracing supports gravity loads and simultaneously
resists lateral loads
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