Load Duration and Seasoning Effects on Mortise & Tennon Joinery

Figure 1-2 Typical Bent Types from Schmidt <strong>and</strong> Daniels (1999)
Often a timber frame designer has to over design a compression knee brace because
of the uncertainty in strength <strong>and</strong> stiffness of a knee brace in tension. The compression
joint is over designed because the knee brace in tension is assumed have zero tensile
capacity. The majority of timber frame knee brace connections are mortise <strong>and</strong> tenon
joints. A set of design st<strong>and</strong>ards would allow a timber frame designer to let the tension
brace carry a portion of the lateral load.
<strong>Load</strong> duration <strong>and</strong> seasoning effects are also of concern when designing a timber
frame joint. Timber frames are frequently cut <strong>and</strong> assembled while timbers are still
green. In most cases cost <strong>and</strong> schedule constraints limit the amount of time that timbers
can be seasoned prior to cutting for a frame. This results in frames with high initial
moisture content. Long term effects on joint strength <strong>and</strong> stiffness are of concern
particularly when analyzing or designing for serviceability. These long-term effects on
traditional timber frame joinery are also beyond the scope of current design
specifications. This research addresses <strong>and</strong> considers the effects of load duration on
strength, stiffness <strong>and</strong> detailing requirements of mortise <strong>and</strong> tenon joints
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