International Concrete Abstracts Portal

End hooks of steel fibers provide a stronger bridging force across the concrete matrix in steel fiber-reinforced concrete (SFRC). In this work, SFRC beams were prepared with steel fibers of the same length and diameter but different types of end hooks (straight, three-dimensional [3D], four-dimensional [4D], and fivedimensional [5D]) at increasing fiber volumes (0.0, 0.5, 1.0, 1.5, and 2.0%). Four-point bending tests conducted on each SFRC beam yielded load-deflection curves, from which the first cracking strength, flexural strength, and fracture toughness up to certain deflection-to-beam length ratios were obtained. The test results showed that the presence of end hooks remarkably enhanced the flexural strength and toughness of the SFRC beams, and this enhancement was amplified with an increasing number of hooks. Quantitative analysis revealed the hooking index, a factor introduced herein to delineate the efficiency of various types of hooks, was 1.00, 1.30, 1.60, and 2.10, respectively, for straight, 3D, 4D, and 5D steel fibers used in the present study. Lastly, empirical models for predicting flexural strength and toughness were established with high prediction accuracy.

In the present study, shear-friction tests were conducted under cyclic loading to investigate in-plane shear transfer across a thin and long interface between new and existing concrete slabs. For shear reinforcement across the interface, concrete shear keys and steel shear plates were used in combination with adhesive anchors (that is, post-installed reinforcing bars). Test results showed that the shear behavior of the thin slab interfaces was significantly affected by the types and details of interface reinforcements. The concrete shear keys and shear plate effectively restrained relative slip across the interface during the initial behavior and increased the peak strength, while the adhesive anchors contributed to the peak strength and post-peak residual strength. Failure modes were concrete failure around the concrete shear keys (that is, local crushing and shearing-off) and in the anchorage zone of the shear plate (that is, cracking and spalling-off). The nominal shear strengths of the thin slab interfaces were calculated by summing the shear-friction strength of adhesive anchors, local crushing strength around concrete shear keys, and shear yield strength of shear plates. The predicted strength agreed with the test results. Based on the results, design considerations of shear transfer across an interface between thin concrete slabs were discussed.

An effective moment of inertia (Ie) unified for reinforced concrete (RC) and reinforced steel fibrous concrete (RSFC) one-way slabs was presented. Two model parameters for the degree of tension stiffening and plasticization of concrete in compression (PZC), where the relationships of concrete stresses and strains deviate from its linear elastic stage, were calibrated using 26 test results of RC and RSFC slabs, including eight slabs tested in this study for three different reinforcement ratios (ρ) and fiber contents (Wf). Comparisons with test results revealed that underestimated deflections were predicted with the Ie currently adopted as basic formats in different codes, for RC slabs having relatively lower or higher ρ values and RSFC slabs with wide ranges of ρ typical to one-way slabs. However, regardless of the magnitudes of ρ and Wf, reasonable deflections were predicted with the unified Ie, which was constituted with linearized weight functions of the ratio of cracking moment to moment in service and modified to include the effects of ρ, PZC, and Wf.

This paper presents the implications of creep-fatigue interactions for the long-term behavior of bulb-tee bridge girders prestressed with either steel strands or carbon fiber-reinforced polymer (CFRP) tendons. A large amount of weigh-in-motion data incorporating 194 million vehicles are classified to realistically represent live loads. Computational simulations are conducted as per the engagement of discrete autonomous entities in line with time-dependent material models. In general, the properties of the CFRP tendons insignificantly vary over 100 years; however, the stress range of CFRP responds to fatigue cycles. Regarding prestress losses, the conventional method with initial material properties renders conservative predictions relative to refined approaches considering time-varying properties. The creep and fatigue effects alter the post-yield and post-cracking responses of the steel- and CFRP-prestressed girders, respectively. From deformational capability standpoints, the steel-prestressed girders are more vulnerable to fatigue in comparison with the CFRP-prestressed ones. It is recommended that the fatigue truck and the compression limit of published specifications be updated to accommodate the ramifications of contemporary traffic loadings. Although the operational reliability of both girder types is satisfactory, the CFRP-prestressed girders outperform their steel counterparts in terms of fatigue safety. Technical findings are integrated to propose design recommendations.

This paper presents a numerical study that simulates the behavior of squat reinforced concrete (RC) shear walls with high-strength reinforcing steel and high-strength concrete. The finite element models are critically evaluated based on previous experiments of four deep-beam specimens and four squat shear-wall specimens with varied material strengths, base moment-to-shear ratios, and section shapes (rectangular and flanged). Monotonic lateral load analyses provided reasonable predictions of the peak lateral strength for squat walls tested under reversed-cyclic loading. However, reversed-cyclic models were necessary for more accurate predictions of the cyclic lateral load versus drift behavior, including cracking, stiffness degradation, lateral load-resistance mechanism, peak strength and corresponding drift, and energy dissipation. Importantly, the model predictions for specimens using high-strength materials were as good as or better than those using normal-strength materials with the same base moment-to-shear ratio. Thus, the use of higher-strength materials did not negatively impact the ability of the models to predict wall behavior.