Seismic behavior of hybrid coupled shear wall with replaceable U-shape steel coupling beam using terrestrial laser scanning

The hybrid coupled shear wall (HCW) with replaceable coupling beam (CB) is an optimal component to recover buildings promptly after a severe earthquake. However, the reinstallation may be difficult or impossible with an identical CB because of the inelastic relative dislocation between two wall piers. This study proposes a novel HCW with different reinforcement ratios in the connection, which was tested under cyclic loading. After the test, the bolt holes can be located through terrestrial scanning, which is then utilized to fabricate a new CB that can accommodate the deformation between two wall piers. The newly replaced HCW system was also tested. As a result, all virgin test specimens fail in web fracture and show a significant inelastic chord rotation of 0.2 rad, exhibiting an excellent energy dissipation capacity. Meanwhile, the new method to locate the bolt holes after the test is feasible. The replaced HCW fails in the pull-off of anchor bars and shows poor seismic behavior due to the unpatched concrete cover in the connection. To improve the energy dissipation for the replaced HCW, high-strength grouting in the connection can be used and high-strength material can be used to replace the usual anchor bolts.

Progressive Collapse Resisting Capacity of RC Flat Slab Buildings with Varying Spans and Storey Heights

With no beams, reinforced concrete flat slab buildings are typically built to advance urban growth and to meet the architectural needs of large spans and low storey heights. Its behaviour to avoid a progressive collapse must therefore be investigated. In this research, the progressive collapse resistance of six-storey RC flat slab buildings with varying span lengths and floor heights is assessed by subjecting the building to three different instances of instantaneous removal of columns in the first storey, performing dynamic progressive collapse analysis as per GSA guidelines, and comparing the evaluated joint displacements and chord rotations at column removal locations with the permissible chord rotation for flat slab buildings as per DoD guidelines. The results have shown that the studied flat slab building with all different span lengths and floor heights is prone to progressive collapse. It is also observed that the vertical displacements and chord rotations at column removal positions increase as the span lengths and storey heights are increased alternately.

Research on the resistance of modified bolted connection under progressive collapse scenario

Beam-to-column connection configurations, such as welded, bolted, and mixed welded-bolted connections, play an important role in structural resistance and ductility under middle column-removal scenarios. This paper illustrates full-scale laboratory tests of two steel frame assemblies with different connection details under the progressive collapse scenario. One specimen adopts the modified conventional technique which has reinforced welded flange-bolted web connection (SC-WR), and the other specimen uses a slotted-hole connection based on the former (SC-WB). The failure modes, load transfer mechanism, and vertical resistance are analyzed in the test. Both connection configurations exhibit satisfactory load resistance and ductility supply. Specimen SC-WB shows the higher ultimate vertical capacity and greater chord rotation at later catenary stage due to a sufficient redistribution of the stress with the modified bolted shear tab. Moreover, finite element models (FEM) are developed and validated against the test data. FEM can accurately simulate the mechanical behaviors and the failure of specimens, which can provide an effective reference for the beam-to-column connection configurations in similar working conditions. Finally, a simplified mechanical model is exhibited in accordance with the experimental and numerical results to reveal the effect of the catenary mechanism. This result suggests that the duration of the catenary mechanism, rather than the magnitude of the axial force, plays an essential role in the resistance of vertical load.

Damage Deformation of Flexure-Yielding Steel-Reinforced Concrete Coupling Beams: Experimental and Numerical Investigation

SRC coupling beams offer many significant advantages, including the reduction in section depth, reduced congestion at the wall boundary region, improved degree of coupling for a given beam depth, and improved deformation capacity. In this paper, 7 half-scale flexure-yielding SRC coupling beams designed according to Chinese approach have been tested under cyclic loads. Detailed parameters such as aspect ratios, steel reinforcement ratios, and steel flange-web ratios were systematically studied, and the damage behavior of SRC coupling beams were presented in this paper. The test results show that the aspect ratio, steel ratio, and steel flange-web ratio have great influence on the damage behavior of SRC coupling beams. Three-dimensional nonlinear finite element models were constructed and benchmarked through comparison with test results for both global and local damage deformation behavior. Based on the material damage and strength degradation, four performance levels were defined and corresponding chord rotation limits were obtained through the verified numerical analysis.

Evaluation of Progressive Collapse Resistance of Steel Moment Frames Designed with Different Connection Details Using Energy-Based Approximate Analysis

This study evaluates the progressive collapse resistance performance of steel moment frames, individually designed with different connection details. Welded unreinforced flange-bolted web (WUF-B) and reduced beam section (RBS) connections are selected and applied to ordinary moment frames designed as per the Korean Building Code (KBC) 2016. The 3-D steel frame systems are modeled using reduced models of 1-D and 2-D elements for beams, columns, connections, and composite slabs. Comparisons between the analyzed results of the reduced models and the experimental results are presented to verify the applicability of the models. Nonlinear static analyses of two prototype buildings with different connection details are conducted using the reduced models, and an energy-based approximate analysis is used to account for the dynamic effects associated with sudden column loss. The assessment on the structures was based on structural robustness and sensitivity methods using the alternative path method suggested in General Services Administration (GSA) 2003, in which column removal scenarios were performed and the bearing capacity of the initial structure with an undamaged column was calculated under gravity loads. According to the analytical results, the two prototype buildings satisfied the chord rotation criterion of GSA 2003. These results were expected since the composite slabs designed to withstand more than 3.3 times the required capacity had a significant effect on the stiffness of the entire structure. The RBS connections were found to be 14% less sensitive to progressive collapse compared to the WUF-B ones.