Development of New Self-centring Friction-based Damage Avoidant Systems for Earthquake-prone Reinforced Concrete Buildings

Veismoradi, Sajad
Zarnani, Pouyan
Quenneville, Pierre
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Doctor of Philosophy
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Auckland University of Technology

The slip friction devices have been investigated and tested in several research studies. Due to the lack of self-centering feature, such dampers might show residual deformation after moderate to severe earthquake actions. To address this shortcoming, self-centering friction-based dampers were introduced that can preserve the advantages of friction damper while introduce self-centering feature to the system. The Resilient Slip Friction Joint (RSFJ) is among the available self-centering devices that combines translational friction sliding with self-centering feature in one compact device and has proven its capability in various structural applications. Inspired by the RSFJ concept, through this study, initially a new self-centering friction damper is introduced named as the Rotational-Resilient Slip Friction Joint that combines the rotational friction with self-centering capability. The Rotational-RSFJ can provide remarkable flexibility in both the damper component design as well as various structural applications. The force-deformation principles of this new damper were provided, along with its numerical verification using finite element analysis. The performance of the damper was experimentally investigated, and the numerical outcomes were validated by the experimental data. The results highlight the damper capability for a stable and repeatable energy dissipation with no requirement for post-event maintenance, than can be utilized for both new design and retrofit purposes.

As the major focus of this study, the possible applications of RSFJ dampers have been investigated for improving the seismic performance of current earthquake-prone buildings (on both local and global levels). As for the local retrofitting, the RSFJ was utilized as a haunch element for strengthening of deficient RC beam-column joints. The proposed system can preserve the benefits of conventional haunch retrofitting system while offering the benefits of RSFJ damper (reliable energy dissipation and recentering force) to weak RC frames. On this basis, a numerical nonlinear model was developed and a design procedure was provided for proper retrofit design of the haunches for beam-column joints of the RC frames. Two beam-column joints (one interior and one exterior) were then selected as a case study for retrofit design and their improved performance demonstrated their enhanced behaviour in terms of energy dissipation, stiffness and strength improvement, along with minimal residual deformation.

As for the global retrofitting of deficient RC frames, the RSFJ-toggle bracing system is introduced and investigated numerically and experimentally. The RSFJ-toggle bracing system can be activated within small drift values of the structure and preserve the frame from excessive damage. Two scaled deficient RC frames representing typical pre-1970s RC moment resisting frames were constructed and tested to investigate the performance of such retrofitting system, as compared to the bare frame. Material testing of the concrete and steel rebars as well as the damper component testing were conducted to gain accurate data for numerical modelling. Recommendations regarding the proper design of various aspects of this retrofitting system were provided in the thesis, including the brace buckling design, instability consideration for the damper, as well as the overall system, connection detailing and gusset plate design requirements. The experimental observations demonstrate the improved behaviour of the frame in terms of energy dissipation and enhanced stiffness and strength for the upgraded RC frame. The numerical model could also capture the behaviour of the system with an acceptable accuracy. As per the findings of this study, the proposed retrofit solution can strengthen the non-ductile RC frames within a limited drift and replace the pinching behaviour of the deficient RC frames with a repeatable reliable semi-flag shape hysteresis performance.

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