The special collection on RC Structures with High and Ultrahigh-Performance Materials is available in the ASCE Library ( infrastructure enables our modern way of life and is essential to human health and happiness. During much of the 20th century, civil engineers made significant advances to improve the design and performance of buildings, bridges, and other constructed facilities under wide ranging loads and hazards, from day-to-day service conditions to extreme events such as earthquake, hurricane, fire, and impact. Advances in the area of concrete structures have been particularly significant, with concrete now being the most widely used construction material in the world.On the downside, building and maintaining our civil infrastructure have put huge demands on raw materials, natural environments, and energy supplies. With the world population exceeding 8 billion this year and the need to lift the standard of living for millions still in poverty, climate change and depletion/destruction of natural resources are two of the biggest challenges of the 21st century. Civil engineers will undoubtedly play a major role in tackling these challenges.The impact of civil infrastructure on our energy supplies and natural environments is a multifaceted issue, with different contributing factors including functional and structural design, construction, maintenance, and service life. As an important consideration, improving efficiencies in these factors is often dependent on the performance of the constituent materials that define the properties of the final product. In other words, the development and use of higher performing civil engineering materials is at the foundation of improving the sustainability and resiliency of our infrastructure. As such, this special collection of the Journal of Structural Engineering is dedicated to some of the recent advances in materials for reinforced concrete structures, showcased through 10 technical papers and one state-of-the-art review paper.Six of these papers focus on ultrahigh-performance concrete (UHPC) while five papers focus on high-strength concrete (HSC) or high-strength reinforcing (HSR) steel materials. The promise of HSC and HSR steel is significant reductions in material volumes needed to achieve the specified structural objectives, while the use of UHPC adds improved performance in durability, ductility, and toughness.Hung et al. (2021) present a state-of-the-art review of recent developments, remaining challenges, and future directions for the use of UHPC in structural applications. The potential for reinforcing UHPC with HSR bars, fiber-reinforced polymer components, and structural steel shapes is also discussed.El-Helou and Graybeal (2022) describe an experimental investigation on the shear behavior and strength of UHPC pretensioned bridge girders. The results from six bulb-tee girders demonstrate that the tensile strain-hardening of UHPC governs the shear performance of girders with little or no transverse reinforcement.A paper by Shao and Billington (2022) experimentally and numerically explores the effect of steel fiber volume on the flexural behavior and ductility of steel reinforced UHPC beams. The results from seven simply supported beams with varying reinforcing ratios and fiber volumes and two different commercially available UHPC materials are used to validate the minimum reinforcing ratio needed to achieve a target drift capacity.The seismic strengthening of concrete columns by UHPC jacketing is investigated by Hong et al. (2021). In this paper, the results from seven column test specimens demonstrate that the ductility capacity of UHPC-jacketed columns can be increased through textile reinforcing.A new type of composite member for underground structures, such as prefabricated utility tunnels, is proposed and experimentally investigated by Huang et al. (2021). In this member, conventional concrete is used between an exterior UHPC layer and an engineered cementitious composite interior layer, with perforated steel plates providing mechanical reinforcement between the different layers. The results demonstrate that a simplified theoretical method based on plane sections assumption can be used to estimate the yield and ultimate load capacities of the composite member.A paper by Tariq et al. (2021) presents a numerical study on UHPC flexural members with longitudinal reinforcement and randomly-oriented fibers. Spring-hinge numerical models are calibrated based on an experimental database and then used to conduct incremental dynamic time-history analyses of archetype frame structures with and without ductile materials in the potential plastic hinge regions of the beams. The results demonstrate the importance of system-level analyses when evaluating the seismic collapse risk of frame structures.Yang and Okumus (2021) describe a parametric numerical investigation on the seismic behavior of UHPC rectangular hollow bridge columns with HSR steel for confinement. It is demonstrated that HSR steel confinement is effective at increasing the flexural ductility of hollow UHPC columns, especially for high longitudinal reinforcement ratios and high axial loads.In a paper by Lee et al. (2021), an experimental study is presented on the use of HSR steel for the shear and torsional design of reinforced concrete structures. Through the testing of 73 specimens under shear and 42 specimens under torsion, as well as other specimens from the literature, it is concluded that the current code limit for the maximum steel yield strength can be increased for shear reinforcement, but not for torsional reinforcement.Ou et al. (2021) describe an experimental investigation on the shear design of columns with HSR steel and HSC. Based on a database of 86 column specimens, including nine large-scale columns described in the paper, a new equation is proposed for the minimum shear reinforcement required to prevent shear failure at diagonal cracking of columns with high-strength materials.A paper by Takeuchi et al. (2021) presents an experimental investigation on the seismic performance of concrete columns reinforced longitudinally with ultrahigh-strength steel bars with low bond strength. Based on the testing of nine cantilever columns, it is shown that the use of weakly bonded longitudinal bars can result in stable and ductile behavior with low residual drift, however supplemental energy dissipation may be needed to limit the peak drift response during an earthquake.Barbachyn et al. (2020) describe an experimental investigation on the use of HSR steel and HSC in stocky shear walls for safety-related nuclear building construction. It is demonstrated that nuclear shear walls with significantly reduced (around 50% for the walls tested in the study) HSR steel areas can achieve similar lateral load behavior and strength as state-of-practice shear walls with the same geometry.We hope that you enjoy reading these papers and get inspired for future directions.References Barbachyn, S., R. Devine, A. Thrall, and Y. Kurama. 2020. “Behavior of nuclear RC shear walls designed for similar lateral strengths using normal-strength versus high-strength materials.” J. Struct. Eng. 146 (11): 04020252. Huang, B.-T., J.-G. Dai, K.-F. Weng, J.-X. Zhu, and S. Shah. 2021. “Flexural performance of UHPC–concrete–ECC composite member reinforced with perforated steel plates.” J. Struct. Eng. 147 (6): 04021065. Takeuchi, T., Y. Sun, M. Tani, and P.-S. Shing. 2021. “Seismic performance of concrete columns reinforced with weakly bonded ultrahigh-strength longitudinal bars.” J. Struct. Eng. 147 (1): 04020290. Tariq, H., E. Jampole, and M. Bandelt. 2021. “Development and application of spring hinge models to simulate reinforced ductile concrete structural components under cyclic loading.” J. Struct. Eng. 147 (2): 04020322.

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