Pao‐Chun Lin

Summary: The damped‐outrigger system has been proposed to improve the performance of conventional outrigger systems in controlling the structural seismic response by increasing the damping and stiffness. The purpose of this study is to demonstrate the effectiveness of using damped‐outrigger systems in midrise buildings and provide engineers with a comparison between conventional structural systems such as moment resisting frame (MRF) and buckling‐restrained braced frame (BRBF) in proposing the most suitable structural system. In this study, the buckling‐restrained brace and viscous damper are adopted as the energy dissipation devices in the damped‐outrigger system. A total of 48 midrise numerical models with various building heights and structural systems are analyzed using nonlinear response history analysis and incremental dynamic analyses. The analysis results show that the midrise buildings equipped with a damped‐outrigger system with either viscous damper or buckling‐restrained brace (BRB) can reach similar and even better seismic performance when compared with the BRBF; it also reduces the structural responses by around 30% for the maximum roof drift and acceleration responses when compared with MRF. The analysis results could provide a reference for structural engineers when selecting suitable lateral force resisting systems for midrise buildings.

This paper introduces a grid-purlin system, which was composed of secondary rectangular-hollow-section grids welded onto the top flange of I-shaped beams of moment frames. The welded grid-purlin itself may play a role of a lateral bracing member for the welded beam. However, the ultimate strength, plastic rotation capacity, or other structural characteristics of this grid-purlin system remain poorly understood. This paper presents two full-scale cyclic loading tests on specimens with I-shaped beams 700 mm deep, 240 mm wide, and 13 m long. The diagonal length of grids in the square grid-purlin of the specimen was 1.3 m on-center, and two different depths of the sections were selected for the purlin sections. Both specimens successfully achieved fully plastic moments at a plastic rotation exceeding 0.04 rad. This shows that the grid-purlin system provides reliable lateral bracing. Continuum finite-element (CFE) analysis was performed to simulate the hysteretic experimental response of the grid-purlin system. This CFE model was used to examine the plastic rotation capacity for a variety of combinations of I-shaped beams and grid-purlins.

The outrigger system is deemed an effective solution for mitigating the seismic responses of tall core‐tube‐type buildings. By incorporating a buckling‐restrained brace (BRB) in the outrigger system (BRB‐outrigger), the BRB‐outrigger reduces seismic response not only through the outrigger mechanism but also through the seismic energy dissipation from the BRB’s hysteretic response. This study investigates the seismic behavior of structures with a single layer BRB‐outrigger and proposes three types of BRB‐outrigger configurations for practical design purposes that fit different architectural requirements. An analytical model, with heights of 64, 128, 256, and 384 m and different outrigger spans was used to investigate the optimal outrigger elevation and required outrigger stiffness for achieving minimum seismic response using spectral analysis and nonlinear response history analysis. The design indexes and design charts based on the analysis results are proposed for preliminary design. Design examples of structures with different BRB‐outrigger configurations utilizing the proposed design charts are demonstrated.