Large-Scale Experimental Results for Self-Centering Beams with Resilient Seismic Performance

Abstract

Although several self-centering seismic systems have been developed in the past, their implementation in practice has been relatively limited. Unusual field construction practices, perceived initial cost premiums and deformation incompatibility with the gravity framing are some of the issues that may be factors. A self centering beam moment frame (SCB-MF) has been developed that mitigates several of these issues. The self-centering beam (SCB) can be shop fabricated with a restoring force mechanism which eliminates deformation incompatibility and allows conventional field construction methods. The strength and stiffness of the beam are decoupled resulting in a cost-effective system that may be competitive with conventional moment frames. This paper describes an experimental program on two-thirds scale one-bay SCB specimens. Parameters that were varied in these tests include SCB depth, initial post-tensioning stress, ratio of initial post-tensioning force to fuse yield capacity, and nominal moment strength of the system. A detailed description of the test setup, post-tensioning procedure, and implementation of the energy dissipation fuse will be presented. Finally, the testing results including the behavior of the individual components (energy dissipation fuse, PT strands and beam) and global system behavior will be summarized.

Experimental investigation of miniature buckling restrained braces for use as structural fuses

“…During earthquake loading, the concentric tubes move relative to each other, thereby forming a gap between the tubes and free-floating anchorage plates that slide over the connection region. The posttensioning strands act to close this gap, bring the concentric tubes back into alignment, and thus force the SCB back to its original configuration after the earthquake ground motion ceases [23].…”

“…The MBRBs developed in this paper were subsequently used in large-scale testing of the selfcentering beam [23]. Thus, several geometric and design requirements associated with the largescale self-centering beam specimens were used as a guideline for the design of the miniature BRB test specimens described herein.…”

“…The moment capacity of the SCB stems from a combination of the yield capacity of the MBRBs and the initial force in the post-tensioning strands. In the typical SCB configuration [23], four MBRBs are located on the sides of the SCB to keep their center of force concentric with the centerline of the tubes and post-tensioning force. The required yield force for a single MBRB was between 30 to 95 kN which is the range of capacity tested in the current study.…”

“…The yield capacity of the element, P y , as given in Table 1 is based on the measured yield stress of the core plate material equal to 450 MPa and 437 MPa for MBRB-610 and MBRB 914 specimens respectively (coupon tests described in the following paragraph). As described in the previous section, the core plate reduced section area was selected to produce the required yield capacities associated with energy dissipation elements in related self-centering beam specimens [23]. The range of the MBRB yield capacities tested was 30 kN-95 kN.…”

“…(1), it is clear that a deeper SCB will result in larger levels of MBRB deformation. Therefore, to test the MBRBs under more severe loading conditions, the displacement protocol was based on the deeper of the two SCBs tested, = 622 mm [23]. The elongation associated with 4% target story drift from the AISC 341-10 loading sequence was 24.88 mm, and the rest of the cyclic displacement protocol was scaled accordingly as shown in Figure 8.…”