STITCH SPACING AND LOCAL BUCKLING IN SEISMIC-RESISTANT DOUBLE-ANGLE BRACES

The behavior of back-to-back double-angle bracing members subjected to out-of-plane buckling under severe cyclic load reversals is investigated. Eight full-size bracing members made of double angles of A36 steel with welded stitches and end gusset plates were tested under large cyclic deformations representative of severe earthquakes. Two types of section configuration were investigated, which included conventional and strengthened back-to-back sections. The first specimen was designed according to the current design practice, and the effects of stitch spacing and width-thickness ratio were studied by changing those parameters in subsequent specimens. The tests showed that early fracture due to severe local buckling of the outstanding legs was the common mode of failure of conventional back-to-back angles. Local buckling was so dominant that stitch spacing did not play a major role. Smaller width-thickness ratio reduced the severity of local buckling, leading to an increase in ductility and energy dissipation capacity. Strengthening of conventional back-to-back angles by welding two inclined plates did not improve member response because of asymmetrical buckling.