International Concrete Abstracts Portal

Coupled walls are widely used as the lateral force-resisting system in tall buildings in seismic regions. Nonlinear response history analyses of such systems rely on first-generation shear- or moment-spring models for the diagonally reinforced coupling beams; these have significant limitations and are inconsistent with the uncracked stiffness assigned to the framing walls. This paper presents a nonlinear hysteretic truss model for diagonally reinforced concrete coupling beams that resolves this inconsistency and validates it against experimental data reported in the literature. The model explicitly couples flexural, shear, and axial deformations through truss action within a unified nonlinear hysteretic framework, a clear improvement over purely phenomenological shear- or moment-spring models. Unlike these, the proposed model develops axial compression when restrained against lengthening and accounts for its effects, allowing shear redistribution between the framing walls. Its applicability is demonstrated through the nonlinear response history analysis of a 15-story coupled-wall building.

With the recent increase in high-rise buildings with core walls, there has been a significant surge in research focused on advanced wind load assessment. Despite the availability of nonlinear analysis, linear methods remain prevalent in practice and research due to their computational efficiency and ease of implementation. This study investigates the wind-induced responses of tall concrete core wall buildings using two commonly adopted linear analytical approaches: spectral analysis (SA) and time history analysis (THA). The agreement between SA and THA is examined, revealing noticeable discrepancies in roof displacement and acceleration responses, with SA yielding non-conservative estimations in certain cases. A comparative evaluation of these linear analysis methods remains of practical importance and provides useful insights that can serve as foundational information for establishing analytical frameworks for performance-based wind design. Since SA is extensively employed in current design standards, this study further reviews the provisions related to the mode shape assumptions and assesses their conservatism.

The seismic design of building diaphragms is one of the most vexing tasks today. Diaphragms are the structural elements primarily designed to transfer in-plane forces to the lateral force-resisting system. Design challenges increase when modeling diaphragms in nonlinear response-history analyses. The main complexity lies in choosing a computationally efficient model and establishing the demands and force distribution throughout the diaphragm. This paper describes two commonly used methods and compares the results in the design forces. A reinforced concrete core-wall building with a flat-slab transfer diaphragm is presented as a case study. Diaphragms were modeled with linear shell elements and the stringer-panel model. Differences in the magnitude of the forces are not significant, although visible differences are observed in the presentation of the results. The stringer-panel model shows a clear and unambiguous load path for the in-plane forces, making it an attractive alternative for the analysis of diaphragms.

High-strength concrete (HSC) with a low water-cement ratio (w/c) may experience large autogenous shrinkage (AS). When shrinkage of concrete is restrained by the subgrade, foundation, or other part of the structure, HSC is more prone to crack. However, studies devoted to the early-age cracking resistance of reinforced HSC under uniaxial restrained conditions and adiabatic conditions are still lacking. In the current research, the effect of reinforcement percentage and reinforcement configuration on the temperature history, shrinkage, stress, and creep behavior of reinforced HSC at early age was analyzed using the temperature-stress test machine. Test results showed that reinforcement could effectively restrain the development of concrete shrinkage and creep. The cracking resistance of HSC increased with increasing reinforcement percentage, evaluated by the integrated criterion. With the same reinforcement percentage, reinforced HSC with distributed reinforcement along with a proper thickness of concrete cover exhibited higher cracking resistance compared with that of central reinforcement.

This paper documents an experimental study on load-transfer mechanisms of six precast concrete (PC) frames with different emulative connections to resist progressive collapse. Load-transfer mechanisms, such as compressive arch action (CAA) and catenary action (CA), were observed during the loading history, while the CA dominated the ultimate load capacity. The robustness of PC frames assembled by mechanical couplers or U-shaped bars was evaluated experimentally and analytically. To improve the robustness of PC frames assembled by U-shaped bars, two refined strategies were introduced: 1) adding additional straight bars in the trough connection; and 2) replacing U-shaped deformed bars with plain bars. It was found that, with the additional straight bars in the beam troughs, the CAA capacity, CA capacity, and deformation capacity can be increased. Replacing U-shaped deformed bars with plain bars can improve the CA capacity and deformation capacity effectively, while it may decrease the CAA capacity slightly. To further understand the load-transfer mechanisms of PC frames with different connections, an analytical elaboration was conducted. It was demonstrated that, at the CAA stage, shear force (related to flexural action) dominated the load-transfer mechanisms. At the CA stage, shear force still dominated the load-transfer mechanisms of the beam-side column interface, while tensile axial force dominated the load-transfer mechanisms of the beam-middle column interface.