Experimental and numerical study of square HSS BIEs under cyclic loading

Abstract

Braces with Intentional Eccentricity (BIEs) have recently been introduced as an alternative to traditional Concentrically Loaded Braces (CLBs) whose performance may overcome some of the shortcomings of the latter. It is postulated that the onset of local buckling in BIEs is delayed owing to a more even distribution of the strain demands under compression loading. Further, the significant post-yielding stiffness of the system can provide control over the predicted displacement levels under the action of the design earthquake. In this article, the results of the testing of four full-scale square ASTM A1085 HSS BIE specimens subjected to reversed cyclic loading are presented. The HSS members and eccentricities were selected with the intention of comparing the response of braces complying with and exceeding the CSA S16-14 global and local slenderness limits. The introduction of the eccentricity was achieved by means of side plates linking the HSS to bolted knife and gusset plate assembly connections. The experimental program is expanded and complemented with finite element analyses of additional BIE and CLB models. The experimental and numerical results show that the BIEs’ response displays the purported benefits of the introduction of the eccentricity. However, it was also found that fracture due to the rotational demand under tensile load at the bracing member’s ends can govern the failure mode of BIEs that are more resistant to developing local buckling at mid-length. The implications of the results to the design of Frames with Intentionally Eccentric Braces (FIEBs) are discussed.