2nd Croatian Conference on Earthquake Engineering 2CroCEE

The aim of this study is to evaluate the feasibility of seismically strengthening existing steel frames. Through computational analysis of the existing bare frame, two methods of seismic strengthening are proposed. The expected behaviour of each of the three tested steel frames was determined through an initial iterative calculation using numerical models. The dimensions for the two types of strengthening were established based on numerical analysis of the bare frame: one utilizing a specialized inverted V-bracing (Chevron) system, and the other utilizing a dissipative TADAS connection. Following the design of the strengthening, three frames were subjected to static reversed cyclic displacement control tests up to failure, according to FEMA 461. The experimental testing of the bare frame (BF) and TADAS frame (TF) was halted due to the emergence of significant global out-of-plane instability, and testing of the Chevron frame (CF) was discontinued following a brace tensile failure. The ductility of the Chevron frame (CF) is found to be 0.6 times lower, while that of the TADAS frame (TF) is 1.4 times higher in comparison to the bare frame (BF). The initial stiffness of the system is 5 times higher in the CF and 2 times higher in the TF than that of the BF. The cyclic responses of the specimens exhibit a symmetrical behaviour. The TADAS frame dissipates 4 times more energy at the point of failure (brace fracture vs out-of-plane instability) than the CF. Careful design of the braces and plates of the TADAS element is necessary to maintain the plasticization hierarchy.