Joist Deflections Simulated By a Computer

A 1-foot wide plywood beam on elastic supports was used as a model in a computer program for simulation of midspan joist deflections in the floor of a factory-manufactured house. The main axis of the plywood beam was oriented perpendicular to the span of the joists and across their centers. Spring constants for the elastic supports of the beam model were based on the flexibilities of the joists and on the rotational resistances of the fasteners. Except for a few instances at plywood joint locations, the differences between measured and calculated deflections were less than 0.020 inches for deflections ranging up to 0.264 inches. Joists adjacent to the ones directly under the applied loads carried from 30 percent to 40 percent of these loads. The most obvious part of this load sharing was accomplished by the two joists on either side of the loaded ones. However, a wave-like, pattern of deflections was observed in the floor perpendicular to the joist spans so that some joists further away from the loaded ones were deflecting in the opposite direction from their movement. Further application of the computer simulation would be to investigate floor design variables.

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