International Concrete Abstracts Portal

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.

Nonplanar reinforced concrete (RC) core walls form the backbone of millions of mid- and high-rise buildings, resisting both gravity and lateral loads from wind and earthquakes. The latter inevitably induces torsional demands, even in the case of full plan-wise symmetric structures, which add to bending, shear, and axial deformations. Unfortunately, current international building codes are not applicable for the design of nonplanar sections governed by warping torsion rather than circulatory torsion. This lack of information and guidance in building codes has resulted in a very limited number of structures being designed to account for warping stresses, even though the latter can be of a similar order of magnitude to bending stresses and, therefore, of major significance. A simple procedure is herein presented to estimate the ultimate warping moment and ultimate torque of nonplanar RC sections based on “warping-equivalent” ultimate bending moments from sectional analysis. A circular and bilinear bending moment-torque interaction relationship is proposed and compared to the existing, albeit limited, experimental and numerical results available in the literature.

This research examines the performance of quality-controlled recycled concrete aggregates (QRAs) with fly-ash-based cement. Compared to concrete made from untreated recycled concrete aggregates (URC), quality-controlled recycled aggregate concrete (QRC) has superior physical, mechanical, and durability properties. Except for sorptivity, the physical, mechanical, and durability properties of QRC are almost identical to those of natural aggregate concrete (NC). The compressive strength, splitting tensile strength, flexural strength, fracture energy, and modulus of elasticity of QRC are higher than those of URC by 18.0%, 16.8%, 60.0%, 27.17%, and 43.46%, respectively. The abrasion resistance of QRC is approximately 60% higher than URC. Scanning electron microscope (SEM) image and energy-dispersive X-ray (EDX) analysis prove that quality control produces denser old interfacial transition zones (OITZ) with fewer microvoids. The QRA improves not only the pore structure but also the weak mortar structure attached to the aggregate. There is also a strong correlation between the compressive strength and splitting tensile strength, flexural strength, fracture energy, and modulus of elasticity of QRC. QRA can be used to compute the mixture proportions for concrete (certainly up to medium-strength concrete) according to either the Indian standard or the international standard. It is challenging to improve the sorptivity of recycled concrete aggregates closer to NC. In addition, QRC has an initial sorptivity of two times (initial) and a final sorptivity of 1.8 times higher than NC, whereas URC has an initial sorptivity of 3.5 times (initial) and a final sorptivity of 2.35 times higher than NC.

Basalt fiber-reinforced polymer (BFRP) composite is one of the promising structural materials recently introduced to the construction industry as internal reinforcement for the purpose of prestressing concrete. In this study, experimental and analytical investigations have been carried out to assess the flexural performance of BFRP-prestressed concrete (PSC) beams designed as over-reinforced, under-reinforced, and significantly under reinforced, as well as non-prestressed concrete beams. The assessment has been made based on the flexural strength, serviceability, and deformability/ductility. The current findings have revealed that even though the non-prestressed beams have exhibited a comparable flexural strength and good deformability, they did not satisfy the serviceability requirements of deflection and crack width. On the other hand, the significantly under-reinforced PSC beams have satisfied the serviceability and strength requirements, however, exhibited reduced cracking and poor deformability. The over- and under-reinforced PSC beams have performed reasonably well in strength and serviceability performances. The partial prestressing of the beams with multiple layers of tendons has been found effective in improving the ductility by introducing a kind of progressive failure based on sequential rupturing of the BFRP tendons. Thus, it is concluded that the proposed under-reinforced design may offer the potential to avoid the sudden or catastrophic failure typically experienced by the single-layered fully prestressed concrete beams, and may hence be considered besides the over-reinforced design recommended in most of the international codes/standards.

When using a plastic hinge analysis, an estimate of the ultimate displacement capacity of reinforced concrete (RC) structural wall buildings is highly dependent on the assumed plastic hinge length. A plastic hinge length equal to 0.5 times the wall length has typically been regarded to provide a safe and lower-bound estimate and has subsequently been used in building codes internationally. Recent numerical and experimental research has shown that the typical design plastic hinge length of 0.5 times the wall length can give an overestimate of the actual length, which would provide false indication of the ultimate displacement capacity of the wall. This research uses a large database of planar and nonplanar experimental and numerical research results with a wide range of design parameters to investigate the plastic hinge length and efficacy of some of the empirical expressions that exist in the literature. A simple expression is derived that can be used by design engineers to calculate a conservative estimate of the plastic hinge length of planar and nonplanar RC walls.