International Concrete Abstracts Portal

Chloride threshold values for steel reinforcing bars in reinforced concrete under the effect of varying temperatures and extended long-term conditions in hot climate are investigated. This investigation covers a gap in the current codes, including ACI 318, where the effect of temperature on the chloride threshold is not addressed. A total of 96 concrete specimens reinforced with carbon steel reinforcing bars sourced from two manufacturers were cast with different chloride contents and exposed to four temperatures of 20, 35, 50, and 65°C (68, 95, 122, and 149°F) for a period of more than 2 years. The chloride threshold values were determined based on corrosion potential, corrosion rate, and mass loss at the end of the exposure period. The results of the three techniques showed a consistent trend of significant dependency of the chloride threshold value on temperature. The average water-soluble chloride threshold values based on mass loss were found to be 0.77%, 0.72%, 0.47%, and 0.12% by weight of cement for temperatures of 20, 35, 50, and 65°C (68, 95, 122, and 149°F), respectively. These findings are significant as they showed a dramatic drop in the chloride threshold values at high temperature. This research highlights the need for reassessment of ACI Code limits considering hot climate.

Past investigations showed that the one-way shear strength of reinforced concrete members exhibits “size effect,” a phenomenon whereby shear strength does not increase in direct proportion to member size. However, it is unclear if the reduction in the two-way shear strength of reinforced concrete members due to size effect applies in the same magnitude as one-way shear strength. To investigate size effect in two-way shear, 12 three-pile caps were tested in three size groups: small, medium, and large. Specimens were doubly scaled from small to medium and medium to large groups, with all other key nondimensional structural parameters such as span-depth ratio, reinforcement ratio, and so on kept constant. The test results supported the existence of size effect in deep pile cap members, although the observed rate of unit shear strength reduction with depth was less severe than that predicted by size effect provisions in American and Japanese design codes. Capacity estimations made using sectional and strut-and-tie approaches prescribed by design codes, as well as the proposed analytical procedure using the softened strut-and-tie model, are presented. The proposed method produced reasonably accurate estimations at all size ranges, capturing the effect of reinforcement more efficiently resulting in an overall mean test-to-calculated capacity ratio of 1.15 with a low coefficient of variation of 11%.

Numerous shear tests on high-strength high-performance fiber-reinforced cementitious composites (HS-HPFRCCs) and ultra-high-performance concrete (UHPC) over the last three decades have enriched the understanding of their shear strength. This study integrates these experiments, which focused on specific shear strength parameters, into a comprehensive analysis. The Initial Collection Database, containing 247 shear tests, was developed for this purpose. From this, the Evaluation Shear Database was derived using specific filtering criteria, resulting in 118 beams pertinent to HS-HPFRCC and UHPC materials. These databases are accessible to the engineering community to advance the evaluation and development of shear strength formulations in structural design codes. This study concludes with an analysis of a subset of the Evaluation Shear Database, consisting of beams with reported uniaxial tensile strength. This analysis demonstrates the Evaluation Shear Database’s applicability and highlights limitations in existing design equations. Notably, their reliance on a single predictor variable constrained predictive power.

Elliptical deep beams have a peculiarity: the compression paths (struts) are neither straight nor symmetrical within the same span. The asymmetrical horizontal curvature in one span leads to the formation of asymmetrical torsional moments. The strut-and-tie method (STM), approved by ACI 318-19 and most international codes, does not take into consideration the curvature of the strut and the consequent bending and torsional moments. Therefore, eight deep elliptical specimens were cast and reinforced with variable amounts of web and flexural reinforcement to study the role and importance of each one experimentally and theoretically from the STM point of view. Only the stress paths were cast and reinforced in two other specimens to study the STM in detail and to present alternative specimens to the reference ones with less weight and cost, in addition to providing openings for services. The STM has proven its effectiveness with asymmetrical, horizontally curved deep beams due to its ease and the high safety it provides. STM development has also been presented here by adding the effect of the horizontal curvature.

Reinforced concrete (RC) structure design codes stipulate various design limits to prevent the brittle failure of members as well as ensure serviceability. In the structural design of RC walls, the maximum shear strength is limited to prevent sudden shear failure due to concrete crushing before the yielding of shear reinforcement due to over-reinforcement. Despite the increase in wall shear strength provided by a compression strut, the maximum shear strength limit for walls in the ACI 318-19 code is the same as the maximum torsional strength. Consequently, the shear strength of large-sized walls with high-strength concrete is limited to an excessively low level. The ACI 318-19, Eurocode 2, CSA-19, and JSCE-17 standards provide similar equations for estimating wall strength, but their maximum shear strength limits for walls are all different. In this study, experimental tests were conducted on nine RC wall specimens to evaluate the maximum shear strength. The main variables of the specimens were the shear reinforcement ratio, compressive strength of concrete, and the failure mode. The experimental results showed that the maximum load was reached after the yielding of shear reinforcement even when the shear reinforcement ratio was 1.5 times higher than the maximum shear reinforcement ratio specified in the ACI 318-19 code. In addition, the measured shear crack width of all specimens at the service load level was less than 0.42 mm (0.017 in.). The shear strength limits for walls in the current codes were compared using 109 experimental results failing in shear before flexural yielding or shear friction failure, assembled from the literature. The comparison indicated that the ACI 318-19 code limit underestimates the maximum shear strength of walls, and it particularly underestimates the maximum shear strength of walls with high-strength concrete or barbell-shaped cross-sections. Additionally, this study proposes an equation for estimating the maximum shear strength limit of walls based on the truss model. The proposed equation predicted the maximum shear strength of RC walls with reasonable accuracy.