International Concrete Abstracts Portal

Existing one-way shear code provisions are typically developed based on experimental data from simply supported beam tests, but most beams in practice are slender, continuous, and indeterminate. Recent research has shown that when slender, continuous, and indeterminate beams are subject to asymmetric loading (i.e., different loads on multiple spans), the Canadian design code, CSA A23.3:24, can be unconservative. To further assess shear capacity predictions from both CSA A23.3:24 and ACI 318-25 for beams with this type of loading, six indeterminate, continuous beams were tested and monitored with distributed fiber optic sensing (DFOS). The results confirm that asymmetrically loaded beams have lower-than-predicted shear strength, with test-to-predicted ratios for CSA A23.3:24 and ACI 318-25 ranging from 0.67 to 0.84. The experimental observations indicated that the asymmetric loading caused the inflection points to shift, and the resulting crack patterns crossed fewer stirrups than predicted, resulting in lower shear capacities. However, these crack shapes were not observed in a symmetrically loaded beam or in a smaller-scale asymmetrically loaded beam.

A detailed nonlinear finite element (FE) model of the ribbed profile of reinforcement is used to investigate the effects of bar size, bonded length, confinement, and cover-to-bar ratio on the characteristics of local bond strength-slip laws and the type of anticipated bond failure. The ribbed bar model is verified first against experimental results from direct tension pullout tests, and then it is used to investigate and corroborate the parametric behavior of the model with the evidence provided by the experimental database compiled by ACI Committee 408, Bond and Development of Steel Reinforcement. The objective of the study is to extend the bond-slip laws used in FE simulations of concrete structures by accounting for important design variables that affect bond behavior, with particular emphasis on the effects of large bar diameters and confinement. The detailed ribbed bar model is further used to investigate the upper limit of the confinement index, (K_tr+C)/Db, which is set at 2.5 in ACI CODE-318-25, and marks the transition from bond splitting failure to pullout failure.

This study investigates the seismic performance of precast concrete column-foundation connections incorporating dry mechanical splices, so-called column shoes, designed as strong connections per ACI CODE-318-25 and ACI PCI-319-25. Two precast concrete connection specimens—designated PF (full-dry connections, bolted-column shoe only) and PS (semi-dry connections, bolted column shoe combined with grouted splice sleeves)—were tested alongside a reinforced concrete (RC) control specimen with a monolithic connection detail under quasi-static reversed cyclic loading. The precast specimens were designed to satisfy the strong-connection details of the precast concrete special moment frame system to promote the plastic hinge formation outside the mechanical splices. Their seismic response was compared with that of the RC control specimen to justify the emulative seismic performance. The precast specimens exhibited comparable cyclic responses, including the lateral strength, hysteretic behavior, and deformation capacity to that of the monolithic specimen. Strain responses in longitudinal reinforcements in the precast concrete columns across the joint showed that inelastic deformation was relocated to the intended plastic hinge region rather than the location of the mechanical splices. Although the precast specimens exhibited slightly lower post-peak strength, primarily due to localized grout damage for dry connections, the overall seismic performance fully satisfied the acceptance criteria of ACI 374.1. The results indicate that bolted-type dry mechanical splices, when designed using the strong-connection concept, can provide code-compliant seismic performance under severe cyclic inelastic demands while preventing premature damage concentration in the splice region.

Extensive research has explored the size effect on the shear capacity of reinforced concrete slender beams, yet limited studies have investigated this phenomenon in steel fiber-reinforced lightweight concrete (SFRLC) members without shear reinforcement. ACI CODE-318-19 restricts the use of deformed steel fibers as an alternative to minimum shear reinforcement to normalweight concrete members with a compressive strength not exceeding 41 MPa (6000 psi) and a member height not exceeding 610 mm (24 in.). The provision does not permit deformed steel fibers to be used as minimum shear reinforcement in lightweight concrete members, regardless of member height. This study addresses this gap by examining the size effect and the influence of longitudinal reinforcement ratios on the shear behavior of large-scale SFRLC beams. Six slender beams with effective depths of 700 mm [27.6 in.], 800 mm [31.5 in.], and 1000 mm [39.4 in.] were tested under a constant shear span-to-depth ratio (𝑎/𝑑=3.5) and longitudinal reinforcement ratios of 1% and 1.5%. Hooked-end steel fibers were added at 0.5% of the concrete volume to evaluate their contribution to shear capacity. The results revealed that the experimental shear stresses at failure loading decreased as the effective depth increased, confirming the size effect in SFRLC beams. Beams with a longitudinal reinforcement ratio of 1.5% exhibited significantly higher shear capacities than those with a 1.0% reinforcement ratio, with increases of approximately 52.8%, 23.4%, and 39.0% for effective depths of 700 mm (27.6 in.), 800 mm (31.5 in.), and 1000 mm (39.4 in.), respectively. The inclusion of steel fibers enhanced the shear capacity and provided an effective alternative to the minimum shear reinforcement specified by ACI CODE-318-19 for lightweight concrete members. This study highlights the potential of steel fibers to improve the structural performance of lightweight SFRC beams and offers insights to inform design practices for large-scale members.

Six large-scale reinforced concrete column-foundation connections, designed to represent interior connections of a continuous foundation slab, were subjected to reversed-cyclic displacements to investigate the effects of foundation longitudinal reinforcement ratio (ρ), foundation thickness (h), column hooked-bar embedment length (ℓe), and foundation shear reinforcement on connection deformation capacity. The specimens were designed to be nominally similar to a specimen from an earlier study, except for the variables of interest. In all specimens, strength was limited by column bar yielding and deformation capacity was governed by concrete breakout, even though the embedment length was adequate to yield the column bars. ACI CODE-318-25 was published late in the course of this study, so specimens did not satisfy ACI CODE‑318-25 Section 25.4.11 requirements for anchorage of bar groups in tension. Test results indicate that improved drift ratio capacity can be achieved by either: a) delaying column-bar yield strain penetration into the foundation with increased foundation longitudinal reinforcement ratio ρ or column longitudinal bar embedment length ℓe; or b) increasing concrete breakout resistance with longer ℓe or foundation shear reinforcement that has a shear strength exceeding the shear demand associated with 40% of the transfer moment based on the eccentric shear stress model assuming vc = 0. The concept of transfer width (based on ℓe instead of h) is useful for designing foundations to resist column moment transfer, but foundation flexural reinforcement for moment transfer should be placed near the top of the foundation instead of divided between the top and bottom mats. Column longitudinal bars should be extended to the bottom mat of foundation reinforcement because terminating the bars near foundation middepth resulted in earlier breakout and lower deformation capacity.