Experimental Cyclic Response of a Novel Friction Connection for Seismic Retrofitting of RC Buildings with CLT Panels

Abstract

The seismic vulnerability of existing RC framed buildings in seismic-prone areas requires affordable and practice-oriented solutions for their retrofitting. In this paper, the authors present a retrofitting solution for RC buildings based on the combined use of cross-laminated timber (CLT) panels and asymmetric friction connections (AFCs). The AFC connection is activated when the force level reaches the design threshold. The energy dissipation of the AFC increases the structural dissipation capacity and reduces the displacement demand. This research presents the outcomes of an experimental campaign on selected prototypes of these AFC connectors. The authors assess their dissipative capacity from cyclic load tests in four different connector arrangements and examine the contribution of aluminum shim layers. The first results highlight the significant dissipation potential of the AFC, although they also provide evidence of the notable sensitivity on the design and constructive details. The authors present a modeling approach to simulate the experimental results.

Experimental and analytical study of Friction Connection for seismic retrofit with Cross‐Laminated Timber (CLT) panels

“…Specimen HYB-2, HYB-3, and HYB_e all had friction coefficients in line with the expectations for aluminium shims, with an average value for the 13 tests equal to 0.22. This value is similar to the findings of the previous experimental campaign, 40 and other values in literature. 48 The tests on the specimen HYB_s, carried out on the setup without CLT panel, show similar friction coefficient values, with a 0.21 average.…”

“…As discussed in Ref., 40 the e‐CLT system experiences two phases: the stick and the slip phases. During the stick phase, the AFC does not activate, and the total resisting force at the i‐th story ($$f_t$$) is the summation of the resisting forces of the CLT panel ($$f_{\text{clt}}$$) and the RC frame ($$f_{\text{rc}}$$).…”

“…F I G U R E 1 (A) Symmetric and (B) Asymmetric Friction connections F I G U R E 2 e-CLT seismic retrofit system, modified from 40 In 1989 Fitzgerald et al 20 devised a friction connection called Slotted Bolted Connection (SBC), characterized by a more straightforward design than the PFD. The proposed SBC worked by sliding channel bracing plate over a gusset plate interconnected by high strength bolts with washers (Belleville spring) for adjusting the bolt tension.…”

“…The retrofit system also provides technological solutions to cover the AFC devices after the panels' installation, ensuring their inspection and maintenance. 39 Boggian et al 40 focused on the shape optimization of the steel profiles and did not study the interaction with the timber component. The experimental activity was directed at isolating the friction behavior of the AFC, representing the innovative part of the system.…”

“…Initially the authors adopted an exponential function, as they did in Ref. 40 However, the exponential function hardly follows the evolution of the friction coefficient observed in the experimental tests. Accordingly, following the well-known formulation by Ref.…”