International Concrete Abstracts Portal

Ultra-high performance concrete (UHPC) is a forward-looking material ideal for use in large-scale civil infrastructure systems. However, due to its unique mix, when UHPC is used in actual structures in conjunction with materials like steel reinforcement, it may lead to unexpected behavior. Therefore, this study analyzed the behavior of reinforced UHPC (R-UHPC) for use in actual structures, focusing specifically on beams among various structural components, with a particular emphasis on their flexural behavior. For this purpose, the study collected and comprehensively analyzed experimental data from flexural tests of R-UHPC beams conducted to date, identifying basic mechanics, peculiarities, and considerations in structural design. This study highlights that, besides the commonly known longitudinal reinforcement ratio, numerous factors such as beam length, height, number of tension reinforcement layers, strength, etc., can influence the flexural behavior of R-UHPC beams and demonstrate how these elements impact the performance.

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.

This study examines the lateral cyclic response of a repaired damaged bridge pier originally reinforced with fiber-reinforced polymer (FRP) bars, particularly glass FRP (GFRP), as a corrosion-resistant and durable alternative to traditional steel. An as-built large-scale hybrid (GFRP-steel) reinforced concrete (RC) column had an outer cage reinforced with GFRP bars and an inner cage reinforced with steel reinforcing bars. The columns were first tested under cyclic lateral loading, where the hybrid specimen demonstrated ductility and energy dissipation capacity comparable to the conventional single-layer steel RC column. Following these initial tests, both specimens were repaired using FRP wraps and retested under the same loading protocol, resulting in a total of four tests. Enhanced structural integrity and energy dissipation demonstrate the effectiveness of innovative repair techniques in seismic engineering. These findings provide a blueprint for resilient infrastructure in earthquake-prone areas and contribute to advancements in bridge design and repair strategies.

This paper presents the interface shear between ordinary concrete and ultra-high-performance concrete (UHPC) connected with glass fiber-reinforced polymer (GFRP) reinforcing bars. Following ancillary tests on reinforcing bar fracture under in-plane shear loading, concrete-reinforcing bar assemblies are loaded to examine capacities and failure modes as influenced by the size, spacing, and number of the reinforcing bars. While the shear behavior of bare reinforcing bars is primarily governed by the orientation of the load-resisting axes in the glass fibers and their volume, the size and spacing of the reinforcement largely control the interface capacity by affecting the load-transfer mechanism from the reinforcing bar to the concrete. The degree of stress distribution affects the load-displacement response of the interface, which is characterized in terms of quasi-steady, kinetic, and failure regions. The primary failure modes of the interface comprise rebar rupture and concrete splitting. The formation of cracks between the ordinary concrete and UHPC results from interfacial deformations, leading to spalling damage when applied loads exceed service levels. An analytical model is formulated alongside an optimization technique. The capacities of the interface in relation to the reinforcing bar rupture and concrete splitting failure modes are predicted. Furthermore, a machine learning algorithm is used to define a failure envelope and propose practice guidelines through parametric investigations.

The ACI CODE-318-19 provisions for one-way shear strength (V_c) in reinforced concrete (RC) members were majorly modified for the first time since 1963. ACI CODE-318-19 equation addresses certain previously identified limitations of the well-known V_c= 0.17λ√f_c′b_wd equation for members without shear steel reinforcement, incorporating factors such as size effect and the influence of longitudinal reinforcement ratio. This study takes a multi-metric approach to evaluate the accuracy and safety of ACI CODE-318-19’s one-way shear relationship for RC members without stirrups. ACI CODE-318-19 predictions are compared against those of its predecessor and other state-of-the-art models, using a database of experimental results gathered by joint ACI-ASCE Committee 445 and DAfStb. This study shows that the ACI CODE-318-19 equation significantly improved accuracy and safety over the ACI CODE-318-14 provisions. One-way shear predictions of ACI CODE-318-19 for RC members without shear reinforcement are generally comparable to existing models, though certain aspects may benefit from continued development and refinement.