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American Wood Council

How do I use the beam load tables in WSDD?

Beam load tables in WSDD are tabulated based on spans from 4 to 32 feet and for lumber sizes from 2x4 to 24x24 inches.

Typically a user will know the span and load for a given application. The user can select a species, size, and grade for trial use. Using the Design Values for Wood Construction Supplement, the user determines the modulus of elasticity, bending design value, and shear parallel to grain design value of the species, grade and size of lumber. These design values need to be modified for all applicable adjustment factors including load duration and repetitive member factors from the Design Values Supplement and NDS. With this information the user enters the load table with the given bending design value and determines the allowable load for an estimated size. If the allowable load is greater than that required for the application, the species, grade and size selected should then be verified for stiffness and shear. Below each tabulated load value are the required modulus of elasticity and shear design value for the specific application. If the modulus of elasticity and shear design value selected from the Design Values Supplement is greater than the tabulated required modulus of elasticity and shear value, then the species and grade chosen is adequate. If the modulus of elasticity of elasticity or shear design value is less than the tabulated value then the user can either select a larger member, or select a higher lumber grade. For either option, bending design strength has to be re-evaluated to ensure that strength limits are maintained. For multiple members or built-up members, the allowable load would be determined by dividing the actual load by the number of plies selected for that particular member. Linear interpolation for intermediate design values is permitted.

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