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Hold-down eccentricity

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I recently attended a techinical seminar by USP Lumber Connectors on shear 
wall cyclic testing on various " site-built " shear walls with numerous types 
of commonly used hold- down connectors.

The tests were done at UC Irvine under the direction EQE International.  Los 
Angeles City shear wall testing was also done there.  The wall panel, 
hold-downs and post configurations were selected to accentuate performance of 
the hold-hardware.

The  results were interesting in that out of 27 tests to plywood fastening 
failure, only one 4 x 4 post broke and that was due to a natural defect in 
the wood ( a knot ).  The posts were D.F. Larch #1.  Calculated bending and 
tension interaction indicated gross inadequacy in all samples.  Anchor bolts 
were also over stressed but there was no sill plate failure

The maximum deflection of one 2:1 aspect ratio shear wall was 3/4" due 
primarily to the crushing of the sill plate (3/8").  All groups of wall 
panels achieved UBC allowable shear values for the plywood and fasteners 
prior to reaching yield limit state or the code allowed drift.

Perhaps one way to reduce deflection in a shear panel that has large axial 
post loads due to seismic is to put a galvanized light gauge, post sized 
plate on the bottom and set the post down on the concrete.  Install the sill 
plate  between the end posts instead of under them.

Ray Shreenan