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The following illustration shows earthquake forces pushing on the floor joists causing the floor to slide off the top of the cripple wall, and the placement of shear transfer ties securing the floor
joists to the cripple wall.
It is very important that the proper hardware be used to provide the strongest retrofit possible. All shear transfer ties have been rated in terms of their ability to resist earthquakes by the
International Conference of Building Officials (I.C.B.O.) and some are stronger than others. It is the engineer or contractor's responsibility to know which is the strongest and most
appropriate shear transfer tie for each given situation. We have seen many retrofits where a tremendous amount of work was done installing hardware that was extremely weak. These
ineffective retrofits could have been avoided if the engineer or contractor had read current I.C.B.O reports and selected the appropriate hardware.
Code requirements
The two retrofit bulding codes, i.e. The Uniform Code of Building Conservation and The Los
Angeles Building Code, specify the spacing of shear transfer ties, but not the type of shear transfer ties to be used. This is unfortunate because shear transfer ties vary greatly in their
ability to resist earthquake forces. Because no Bay Area cities have adopted a retrofit building code (see False Security ) there are no retrofit code requirements for shear transfer ties in the
Bay Area.
The authors of the above retrofit building codes, being members of public agencies, cannot legally specify one brand of shear transfer tie over another. Bay Area Retrofit, on the other
hand, is not a public agency and we can tell you the way it is:
The most common type of shear transfer tie is the Simpson H-2.5. It can resist 150 pounds of earthquake force. By spending an additional thirty-five cents the Harlen 256A shear transfer tie
can be used instead. It can resist 580 pounds of force, 4 times more than the Simpson H-2.5 and it takes the same amount of time and labor to install. In the case of our example house
used earlier in the Retrofit Engineering discussion (see Retrofit Engineering,) it would cost $7
more to have a retrofit that is 4 times stronger. We say it again...pick your contractor or engineer with care!
The next article in this series is The U.C.B.C. Retrofit Building Code.
Back to Retrofit Design
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