International Concrete Abstracts Portal

Progressive collapse behavior of reinforced concrete frame buildings has been studied extensively, but most of the research has concentrated on frames containing seismic details. This paper presents results from analyses of the progressive collapse behavior of reinforced concrete frame buildings containing details used in regions of low seismicity following ACI CODE-318-19. The analytical simulations presented in this paper include the effect of moment redistribution that occurs after plastic moments are reached at sections of maximum moment. Ten-story 3-D frame models were designed in accordance with ACI CODE-318-19 and analyzed under progressive collapse scenarios involving the non-simultaneous removal of an interior and a corner perimeter column following ASCE 76-23. Nonlinear material behavior in these analytical models was captured using a lumped plasticity approach using hinge properties calibrated using results from laboratory experiments of full-scale sub-assemblages representing a portion of the perimeter frame containing details corresponding to non-seismic zones. The effect of catenary action in beams after column removal was included in the analyses, and the potential for premature shear failure of beams was assessed. Furthermore, models were also constructed to investigate the beneficial effects of increased rotational capacity of perimeter beams that result from using closer stirrup spacing at beam ends. This study demonstrates the importance of incorporating properly detailed continuous longitudinal bars enclosed within closely spaced closed stirrups at ends of beams of reinforced concrete frames in non-seismic zones to provide progressive collapse resistance. The study also highlights the importance of considering three-dimensional effects in models of frames to account for out-of-plane moment redistribution after loss of supporting elements.

Precast concrete (PC) moment-resisting frame systems with wide beam sections have been increasingly adopted in the construction industry due to their advantages in reducing the span length of PC slabs perpendicular to wide beam members and improving the constructability of precast construction. To further facilitate fast-built construction, this study introduces a novel PC wide beam-column connection system, where the solid panel zone is prefabricated and integrated into the PC column, allowing the upper floor to be quickly constructed without delay due to the curing time of cast-in-place concrete. Meanwhile, the current ACI CODE-318-19 code imposes strict allowable limits on the width of wide beams and complex reinforcement details as part of a seismic force-resisting system to effectively transfer forces into the joint, considering the shear lag effect. To address this, two full-scale PC wide beam-column test specimens were carefully designed, fabricated, and tested to explore the impact of large beam width and simplified reinforcement details beyond the code limit. The seismic performance was evaluated in terms of lateral strength, deformation capacity, stiffness degradation, failure mechanism, and energy dissipation. Based on the evaluation, the proposed PC wide beam-column connections demonstrated equivalent, or even better, seismic performance than the reinforced concrete control specimen. Additionally, it was found that the presence of corbels can mitigate the shear lag effect in PC wide beam-column connections, and that the current effective beam width limit imposed by ACI CODE-318-19 is conservative for PC wide beam-column connections with corbels.

Filling reinforced concrete (RC) frame spans with RC shear walls constitutes a strategic intervention to existing sub-standard buildings. The efficiency of this intervention depends, among other things, on the behavior of interfaces between the shear wall and the frame elements. The failure of critical interfaces that may lead to undesirable shear sliding of the wall at its base can only be prevented if the interfaces are adequately designed. To investigate the cyclic behavior of interfaces within the composite frame-to-wall members, four frames filled with RC walls, as well as two reference specimens (i.e., a bare frame and a monolithic frame/wall specimen), were subjected to cyclic horizontal displacements. The crucial effect of the interface reinforcement ratio, the detailing, the dowel distribution along the interface, and the embedment length on the behavior of the specimens, in terms of maximum capacity, drift, and failure mode, was confirmed.

In this study, a shear strengthening method for lightly reinforced concrete columns with partial-height masonry infills was proposed. Perforated steel jackets were attached to one face or both faces of the column without removing the cover concrete and finishing mortar. The steel jackets were designed to provide additional shear resistance to the column through interlocking of the ribs at both ends. To investigate the seismic strengthening effects, six column specimens with partial masonry infills were tested under cyclic loading. The tests showed that the specimens with double-face jacketing exhibited an improved seismic performance, whereas there was little or no strengthening effect for the specimens with single-face jacketing. For further investigation on the short column effects due to partial-height infills, modeling parameters to define the stiffness and force-deformation relation of the column and masonry walls were proposed, and the modeling results were compared with the test results. Based on the investigation results, the detailing requirements of steel jacketing and the nonlinear modeling methods of the columns with partial masonry infills were discussed.

Slender reinforced concrete (RC) shear walls have become an integral part of lateral load-resisting mechanisms of modern high-rise structures, especially in earthquake-prone regions. Because the seismic behavior of the wall is governed by its design and detailing, several past studies are available regarding the same. However, limited studies have been carried out regarding the influence of the confinement effect in the web and the boundary elements on the wall behavior. To address this concern, an experimental study of an isolated slender shear wall with an enlarged boundary element (BE) designed in conformance to IS 13920:2016 was undertaken. The specimen was subjected to lateral slow cyclic displacement- controlled loading. The relation between the global and local responses of the wall by means of strain profiles is documented in the present study. The evolution of the strain profiles obtained clearly depict the participation of the transverse reinforcement, indicating the mobilization of the confinement effect.