International Concrete Abstracts Portal

Slag-based zero-cement concrete (ZC) of high strength (60 MPa [8.70 ksi]) was developed as an eco-friendly construction material. In the present study, to investigate the structural behavior of precast columns using ZC, cyclic loading tests were performed for five column specimens with reinforcement details of ordinary moment frames. Longitudinal reinforcement was connected by sleeve splices at the precast column–footing joint. The test parameters included the concrete type (Portland cement-based normal concrete [NC] vs. ZC), construction method (monolithic vs. precast), longitudinal reinforcement ratio, and sleeve size. The test results showed that the structural performance (failure mode, strength, stiffness, energy dissipation, and deformation capacity) of the precast ZC columns was comparable to that of the monolithic NC and precast NC columns, and the tested strengths agreed with the nominal strengths calculated by ACI 318-19. These results indicate that current design codes for cementitious materials and sleeve splice of longitudinal reinforcement are applicable to the design of precast ZC columns.

Two large-scale beam-column connections with beam longitudinal headed bars were tested to evaluate their susceptibility to breakout failures. The specimens were designed following the strength and transverse reinforcement detailing provisions in Chapter 15 of ACI 318-19. The variable investigated was the headed bar embedment length, which was determined based on either Chapter 25 of ACI 318-19 or recent research at the University of Kansas, the latter leading to a 22% shorter embedment length. Both specimens exhibited beam flexural yielding, but the specimen with shorter bar embedment length experienced significantly more connection damage followed by a concrete breakout failure. Based on the limited test results, it is recommended that nominal joint shear strength be calculated based on a joint effective depth equal to the headed bar embedment length and a shear stress of 1.0λ√(fc' ) (MPa) [12λ√(fc' ) (psi)]. A method for calculating headed bar group anchorage strength in exterior beam-column connections is proposed, which led to reasonable and conservative strength estimates in the test specimens.

This paper presents a novel framework of analysis to assess the resistance of existing reinforced concrete (RC) members experiencing spatial variability of crack patterns and spatial variability of concrete mechanical properties. The spatial variabilities are considered by using digital image processing (DIP) to map crack patterns onto three-dimensional nonlinear finite element (NFE) models where the concrete mechanical properties (compressive strength, tensile strength, damage, and modulus of elasticity) are spatially varied using random fields to form random NFE models (RNFE). The framework was developed and applied to assess a corroded RC beam (determine the distribution of the resistance) and column (determine the reliability of the column at the ultimate limit state). Research findings indicate improved accuracy in assessing the resistance of the corroded members up to 20%, and the adaptivity of the developed framework for performing reliability analysis of existing RC structures.

An approach to improve the progressive collapse resistance of conventional RC frame structure was put forth by using unbonded post-tensioning strand (UPS). Two UPSs with a straight profile are mounted at the bottom of the beam section. A static loading test was conducted on an unbonded prestressed RC (UPRC) beam-column sub-assemblage under a column removal scenario. The structural behaviors of the test specimen, such as the load-carrying capacity, failure mode, post-tensioning force of the UPSs, and rebar strain, were captured. By analyzing the results of the tested substructure, it was found that the compressive arch action (CAA) and catenary action (CTA) were sequentially mobilized in the UPRC sub-assemblage to avert its progressive collapse. The presence of UPSs could significantly improve the load-carrying capacity of conventional RC structures to defend against progressive collapse. Moreover, a high-fidelity finite element (FE) model of the test specimen was built by using the software ABAQUS. The FE model was validated by the experimental results in terms of the variation of vertical load, horizontal reaction force, and post-tensioning force of the UPSs against middle joint displacement (MJD). Finally, a theoretical model was proposed to evaluate the anti-progressive collapse capacities of UPRC sub-assemblages. It was validated by the test result as well as by the FE Models of the UPRC sub-assemblages which were calibrated using the available experimental data.

This study employs advanced nonlinear finite element modeling to investigate Interface Shear Transfer (IST) behavior in RC connections, a crucial factor for bridge durability and safety. The research examines shear transfer mechanisms at the interface between precast girders and cast-in-place deck segments through three experimental methods: beam, push-off, and Iosipescu four-point bending tests. FE simulations evaluated stress distributions, IST capacity, and failure mechanisms. Validation against experimental data shows that the Iosipescu test provides the most accurate representation of IST behavior, exhibiting a stress distribution error margin of only 1%, closely aligning with observed failure patterns. In contrast, the push-off test showed a 30% deviation from empirical data, indicating reduced accuracy in predicting real-world IST behavior. These findings highlight the importance of incorporating the Iosipescu test into IST evaluation protocols, as its greater precision enhances design methodologies for concrete bridges, reduces structural failure risks, and informs future updates to IST-related codes.