Design of Tension-Only Concentrically Braced Steel Frames for seismic induced impact loading

Tension-Only Concentrically Braced Frames (TOCBFs) exhibit deteriorating pinched hysteretic behaviour during strong earthquakes. It has long been suspected that the sudden increase in tensile forces in the braces of TOCBFs creates detrimental impact loading on the connections and other structural elements. This paper addresses this issue through shake table tests of half scale, two-storey, TOCBF models. By normalizing the hysteresis loops of braces obtained from shake table tests to the yield strength of steel obtained from static tests, the increase in tensile forces in the braces was obtained. Results of dynamic tensile tests on steel coupons under similar strain rates as observed during the shake table tests showed that this increase in tensile forces is caused by a yield strength increase of the steel under high strain rate. A procedure is proposed to predict this increase in tensile forces in the braces at the design stage. The use of this procedure is illustrated by a design example.