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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.

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.

Compression development and lap-splice length provisions in ACI 318-19 §25.4.9 and §25.5.5 are reexamined after an example was used to show that existing provisions can produce unexpected results in some design conditions, such as compression lap splices longer than tension lap splices. A historical review of ACI Building Codes shows that existing compression bond length provisions are largely based on provisions adopted before test data were available. The provisions in ACI 318-19 are compared with a database of 89 test results and shown to poorly fit the data. Several compression and tension bond equations are also examined and found to fit the data better. It is shown that compression development and lap-splice lengths can be based on several expressions available in the literature for tension development length with minor modification, including the ACI 318-19 equation for tension development length. Using this approach would simplify design by eliminating the use of different expressions to calculate tension and compression development lengths, prevent calculated lengths from being longer in compression than in tension, and provide a better fit to available data.

Lap-splicing of longitudinal reinforcing bars in shear walls is often encountered in practice, and the transfer of forces in lap-spliced reinforcing bars to the surrounding concrete depends on the bond strength. Buildings with shear walls during an earthquake develop plastic hinges in the shear walls, particularly where the reinforcing bars are lap-spliced. Brittle failure is commonly observed in lap-spliced reinforced shear walls, which needs to be minimized by choosing the appropriate percentage of lap-spliced reinforcing bars. Therefore, it is essential to address the detailing of the lap-spliced regions of reinforced concrete (RC) shear walls. Several seismic design codes provide guidelines on lap-spliced detailing in shear walls related to its location, length of lap-splice, confinement reinforcement, and percentage of reinforcing bars to be lap-spliced. In this study, the percentage of reinforcing bars to be lap-spliced at a section is examined with staggered lap-splicing of 100, 50, and 33% of longitudinal reinforcing bars, in addition to a control RC shear wall without lap-splicing. This study tested four half-scale RC shear walls with boundary element (BE), designed as per IS 13920 and ACI 318, under quasi-static reversed cyclic loading. From the experimental study, it is observed that the staggered lap splicing of reinforcing bars nominally reduces the performance of shear walls under cyclic load in terms of the reduced flexural strength, deformation capacity, energy dissipation, and ductility of the shear walls compared to the control shear wall without lap splicing. It is also observed that the unspliced reinforcing bars do not sustain the cyclic loading in staggered lap-splice after the postpeak. Current provisions of ACI 318, Eurocode 2, and IS 13920 recommend staggered lap-splice detailing in shear walls. However, from the current study, shear walls with different percentages of staggered lap-splices show that the staggered lap-splice detailing in shear walls does not improve its seismic performance.

This paper investigates the seismic performance of exterior beam column joints in special moment frames (SMFs) with varying axial load ratios. Cyclic testing of four additional specimens with an axial load ratio of 0.45 is compared with four companion specimens at 0.10. Each specimen was designed and constructed with Grades 60, 80, or 100 (No. 420, 550, or 690) reinforcement in accordance with ACI 318-19 provisions for special moment frame joints, except for the provisions of joint shear and confinement. While ACI 318-19 tightens confinement requirements for SMF columns and joints, especially under high axial loads, this study reveals that increasing the axial load ratio benefits joint behavior. The study also demonstrates the feasibility of using high-strength reinforcement in exterior beam-column joints of SMFs, provided that appropriate modifications are made. The findings in this study have influenced modifications from ACI 318-19 to the Building Code Requirements for Concrete Structures in Taiwan.