Experimental Study on the Limit States of Butterfly-Shaped Structural Fuses

Structural fuses are replaceable elements of a structure that are designed to yield and protect the surrounding members from damage and then be replaceable after a major seismic event. One type of structural fuse consists of a steel plate with cutouts leaving butterfly-shaped links (i.e., butterfly-shaped structural fuse) that has been shown to produce advantageous behavior such as (1) promoting yielding along the link length, thus maximizing the amount of dissipated seismic energy, and (2) maintaining full and stable hysteretic behavior through large shear angles. Prior research has identified three main limit states for butterfly-shaped links: flexural yielding, shear yielding, and lateral torsional buckling. Although most studies focus on flexural yielding because it promotes the largest ductility, it is necessary to understand all three limit states for proper structural fuse design. An experimental study was conducted to systematically examine the three limit states of butterfly-shaped structural fuses. First, each limit state is described, and generalized equations are presented to predict stiffness, which limit state will control, and the associated shear strength. Then, the experimental program is presented including eight 762 mm×762 mm specimens to investigate the behavior of butterfly-shaped structural fuses undergoing these limit states. The equations are shown to be capable of predicting which limit state would occur and produce a ratio of measured to predicted shear strength of 1.07 on average. The equation for stiffness showed more variability in its accuracy but resulted in an average ratio of measured to predicted stiffness equal to 0.88. The presentation and validation of design equations are intended to facilitate the design of butterfly-shaped structural fuses for use in engineering practice.