Editorial

Abstract

This issue of Structures and Buildings contains papers discussing the seismic retrofit of beam column joints using prestressing wires, the study of a hybrid structural damper for multi-seismic levels, strength reduction factors for wind and earthquake effects, column under-pinning joints with inclined steel bars and observer application in decentralized control of civil structures. The presented papers continue the tradition of this journal to provide results useful for the professional development of its readers. This issue contains papers that have passed the rigorous peer review procedure adopted by the journal and contribute to the areas of knowledge discussed in this editorial.The first paper presents the seismic retrofit of beam-column joints using pre-stressing wires (Huang et al., 2017). This paper highlights the improvements of the seismic performance and enhancements of the shear strength of beam-column joints with non-seismic design, as well as the shortcomings of traditional seismic retrofitting techniques for the joints. Six largescale interior beam-column joints were tested under reversed cyclic loading, where five were strengthened by the proposed technique and one was un-retrofitted as a control specimen. Particular emphasis was placed on the effects of the ratio of prestressed high-strength steel wires, prestressing level of wires and polymer grout layer. Test results showed that the joint shear capacity was increased significantly and cracks in beamcolumn joints were controlled effectively after retrofitting. All retrofitted joint specimens failed in a ductile mode of beam flexural failure, whereas the control specimen failed in a brittle mode of joint shear failure. In addition, the energy dissipation capacity as well as ductility of the retrofitted joint specimens was enhanced significantly.The second paper presents the hybrid structural damper for multi-seismic levels (Hosseini Hashemi and Moaddab, 2017). In this paper two dual-performance designs are introduced as alternatives to the standard steel-plate yielding and friction damper. The new devices are detailed and designed to absorb and dissipate seismic input energy at different levels of ground motion. Both systems are composed of a main fuse to dissipate energy at high-level drift demands encountered in severe earthquakes but also have an auxiliary fuse to control the responses at lower drift demands that normally occur in moderate earthquakes. Six specimens with different specifications were designed and tested. The experimental results prove the efficiency of the dampers at different levels of ground motion. In moderate-level ground motion intensities, the dual-performance characteristics of the dampers permit energy dissipation in the auxiliary fuse without disturbing the main fuse. In high-intensity ground motions, the main fuses are engaged with significant energy-dissipating capability. Moreover, significant enhancements were observed in the plastic rotation capacity of the dampers and the ductility provided.The third paper is ab...