PUSHOVER TESTS OF STEEL CONCENTRICALLY BRACED FRAMES WITH GUSSET PLATE CONNECTIONS

To explore the loading capacity, ductility performance, response modification coefficient, stress mode of gusset connection, and failure mechanism of steel concentrically braced frame, and to obtain the secondary moments on the columns and the beams, pushover tests were carried out on two 3-story braced frame models with 1:2.6 scale. The results indicate the lateral rigidity will decrease markedly after the out-of-plate buckling of the compressive braces, but the horizontal loading capacity will be maintained and strengthened by the tensile member in cheveron bracings. The inter-story drift ratio of each braced frame is much higher than the limitation of seismic code, and the studied frames show a greater ductility ratio and response modification coefficient. The secondary moment in the beams and columns near the location of gusset plate is notable. Based on the elastic limit state of the test frames, the secondary moment ratio is proposed. Although the brace-end extends a longer distance into the gusset plate, the gusset plate can also be out-of-plane rotated along a plastic arc-like curve, and shown greater loading capacity and plastic deformation capacity than that of the connected brace. The brace buckling or yielding is prior than the fracture of its guest plate connections, and this rational failure mode can ensure good seismic performance for the steel concentrically braced frames.