International Concrete Abstracts Portal

In high-rise buildings, lower-story columns must withstand significant seismic shear forces while maintaining sufficient deformation capacity. This capacity is provided through effective confinement using transverse reinforcement. The ACI 318-25 building code specifies that confining reinforcement should be proportional to the applied axial load when the axial load exceeds 0.3A_gf'c and requires all longitudinal bars to be laterally supported with seismic hooks. However, the implementation of seismic hooks at both ends of crossties brings challenges for on-site reinforcement assembly.

This study experimentally investigates full-scale RC column specimens subjected to quasi-static cyclic loading while under a constant high axial load. The objectives are to validate the ACI 318-25 confinement requirements and to evaluate the feasibility of relaxing seismic hook requirements. The results confirm that columns designed in accordance with the ACI 318-25 building code satisfy the required 3% deformation capacity. Furthermore, satisfactory seismic performance can be achieved with crossties incorporating alternating 135-degree and 90-degree hooks, although at the expense of increased confining reinforcement.

For the assessment of existing reinforced concrete slab bridges, the shear capacity under concentrated loads and transition to flexural failure are under discussion. Previous research showed an increased shear capacity for slabs under concentrated loads close to the support, so that for assessment, positions farther from the support became governing. This experimental research studies the flexural and shear capacity of reinforced concrete slabs under concentrated loads. For this purpose, six slabs representing 1:2 scale continuous slab bridges were tested at various positions from the support and along the width. The results show two main failure modes: flexural failure (onset of yielding of the reinforcement), and shear failure. Secondary punching was observed as well. The comparison between the test results and calculations methods shows that all considered methods perform reasonably well when both shear and flexure are considered, and the effective width in shear is included, with average tested-to-predicted capacities between 0.92 (Regan’s method) and 1.39 (Extended Strip Model) and coefficients of variation between 15% (Regan’s method) and 25% (ACI 318-19 and Eurocode 2). These insights can be used for the assessment of existing reinforced concrete slab bridges.

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 article presents a robust mathematical framework for computing centroidal polar moments of inertia in a standardized manner, applicable to both regular- and irregular-shaped sections, for use with the traditional ‘ACI Commentary Jc Method.’ The article also showcases with mathematical rigor why, for over 60 years, the standard (traditional) expressions used to compute polar moments of inertia for planar sections embedded in three-dimensional space have been incorrectly derived, and explores the implications of not adopting the correct expressions in design. The mathematical framework for computing polar moments of inertia is developed using advanced calculus, and primitive sections are integrated into the formulation to derive with ease the necessary expressions for the most common sections used in design, namely: rectangular, circular, C-shaped, L-shaped, and regular polygon-shaped sections. Finally, a numerical example is provided to demonstrate the practical implementation of the proposed mathematical framework.

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.