International Concrete Abstracts Portal

Compression development and lap splice length provisions in ACI 318-19 §25.4.9 and §25.5.5 are reexamined after an example is 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 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 are shown to poorly fit the data. Several compression and tension bond equations are also examined that fit the data better. It is shown that compression development and lap splice lengths can be based on a number of 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.

This paper investigates the seismic performance of exterior beamcolumn 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.

The ACI 318-19 Building Code does not allow the use of headed bars larger than No. 11 (No. 36) due to insufficient experimental data. Thirty large-scale simulated beam-column joint specimens containing high-strength No. 11 (No. 36), No. 14 (No. 43), or No. 18 (No. 57) headed bars were tested to investigate the effects on anchorage strength of key factors, including bar stress at failure, bar size, bar spacing, embedment length, transverse reinforcement, concrete compressive strength, and loading condition. Specimens exhibited concrete breakout, side splitting, or a combination, with four exhibiting a shear-like failure. Anchorage of larger bars is noticeably influenced by joint shear demand and loading condition. Descriptive equations developed based on 164 tests accurately characterize anchorage strength for headed bars up to No. 18 (No. 57). They indicate that anchorage strength is proportional to concrete compressive strength to a power close to 0.2 and that the contribution of parallel ties for large headed bars is lower than that observed for smaller headed bars.

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 reinforcing bar lap-spliced 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 post-peak. Current provisions of ACI 318, EC2, and IS 13920 recommend staggered lap-splice detailing in shear walls. However, from the current study, shear walls with different percentages of staggered lap splice show that the staggered lap-splice detailing in shear walls does not improve its seismic performance.

To secure emulative seismic performances of precast concrete (PC) special moment frame buildings, two capacity-based connection design options (that is, strong and ductile precast connections) are provided in the current version of ACI 318. However, the evolving performance-based seismic design and response evaluation requires a reasonable estimation of the energy dissipation and corresponding hysteresis damping characteristics so that their potential performance level can be properly predicted. Therefore, this study focuses on the seismic performances, especially the energy dissipation and damping performances of the Code- compliant PC wide beam-column connections. Three PC wide beam-column connection specimens under the ductile connection design principle with different joint details and a reinforced concrete (RC) control specimen were fabricated and tested under reversed cyclic loadings. In addition, an energy-based macro-modeling method was developed to characterize the cyclic responses, including the damping response of PC wide beam-column connections. The test results revealed that the Code-required overstrength of shear-friction strength between PC beam members and cast-in-place (CIP) concrete is crucial to achieving the ductile performance of precast connections. It also appeared that the energy-based macro-modeling method could capture the hysteresis features through the relationship between the equivalent viscous damping (EVD) ratio and the ductility capacity of PC wide beam-column connections.