Continuous Timber Diaphragms

Abstract

Current design assumptions for diaphragms assume support conditions which are either simple span or fully continuous. The building codes require a design based on the highest values for moment and shear obtained under either of these two support conditions. More practical criteria for assessing continuity conditions at supports for wood diaphragms are needed. This investigation is to determine experimentally the effects of continuity conditions on timber floor diaphragms with plywood sheathing subject to inplane loads. Previous testing programs have evaluated simply‐supported diaphragms subject to uniform loading; this study evaluates the effects of other support conditions and non‐uniform loads. Static loading conditions were used to evaluate the response of the diaphragm for both deflection and ultimate strength. Six 8 ft×16 ft (2.44 m×4.88 m) floor diaphragms typical of certain residential construction techniques with three different sets of boundary and loading conditions were tested in accordance with ASTM E72. The tests demonstrated that: (1) Continuity over a rigid support apparently does not increase the unit shear resistance values of the diaphragm; (2) concentrated loads on the diaphragm produce lower load factors than moment‐equivalent uniform loads at a given load level; (3) there is not an apparent direct relationship between relative panel displacement and overall diaphragm deflection for the size diaphragms tested; and (4) local panel buckling has a minimal effect on overall diaphragm failure patterns.