Concrete beams reinforced with a combination of steel and fiber-reinforced polymer (FRP) bars can provide increased strength, serviceability, and durability. However, the amounts of FRP and steel necessary to ensure sufficient strength and ductility are unclear. Because of the linear elastic behavior of FRP bars before failure, the deformation characteristics of hybrid reinforced concrete beams differ from those of conventional steel reinforced concrete beams and pure FRP reinforced concrete beams. Conventional ductility indices are not suitable for concrete beams in hybrid reinforcement approaches. To ensure the ductile failure of beams, proper reinforcement ratio limits are proposed. In addition, a new ductility index is defined in terms of deformability and energy absorption capacity. Various comparisons between experimental results and theoretical predictions show that the developed models can accurately predict the load capacity and ductility. In addition, the influences of various parameters...

Concrete beams reinforced with a combination of steel and glass fiber-reinforced polymer (GFRP) bars exhibit promising strength, serviceability, and durability. The fatigue performance of concrete beams with hybrid reinforcement has not been studied previously. This paper designs an experimental program to investigate the fatigue flexural performance of concrete beams with longitudinal tension reinforcement of steel and GFRP bars. One static flexural specimen and three fatigue flexural specimens are tested. The influences of the fatigue load and reinforcement ratio on the fatigue behaviors are investigated. The fatigue loading level and the effective reinforcement ratio influence the fatigue life. The fatigue loading has little influence on the neutral axis depth. The curvature and midspan deflection increase significantly with the fatigue cycles before 0.01 million cycles and then increase slightly with the fatigue cycles after 0.01 million cycles. During the majority of the fatigue life, crack widths develop slowly. Different theoretical models for the midspan deflection of the concrete beams with hybrid reinforcement subjected to fatigue loading are developed and compared with the test results, and the selected model shows satisfactory accuracy.

Through direct shear tests, this paper aimed to research the effect of fine marble aggregate on the shear strength and fractal dimension of the interface between soil and concrete corroded by sulfuric acid. More realistic concrete rough surfaces than the artificially roughened surfaces were formed by immersing four concrete plates in plastic buckets filled with sulfuric acid for different periods of time. The sand was adopted to imitate the soil. 3D laser scanner was employed to obtain the digital shapes of concrete plates subjected to sulfuric acid, and the rough surfaces were evaluated by fractal dimension. Large direct shear experiments were performed to obtain the curves of the interface shear stress and shear displacement between sand and corroded concrete plate. The method of data fitting was adopted to calculate the parameters of shear strength (i.e., friction angle and the cohesive) and the parameters of the Clough–Duncan hyperbolic model. The results indicated that as the corrosion days increased, the surface of the concrete plate became rougher, the surface fractal dimensions of the concrete corroded by sulfuric acid became bigger, and the interface friction angle became greater. The friction angle of the interface and the fractal dimensions of the surface of the concrete plate containing crushed gravel and marble sand were smaller than that of the concrete plate containing crushed gravel and river sand.

When exposed to sulfuric acid environments, the service life of concrete structures would be reduced due to the high alkalinity of concrete. The influence of three factors including water/cement ratio, the pH value of the solution, and the chemical composition of the aggregate on the resistance of concrete subjected to sulfuric acid has been widely investigated by previous researchers. This paper aims to investigate the influence of these three factors on the durability evaluation indicators including mass loss and surface fractal dimension through orthogonal experiments, which has been reported rarely in previous research. Four combinations of coarse and fine aggregate including gravel and river sand, gravel and crushed marble sand, crushed marble stone and river sand, and crushed marble stone and marble sand were adopted, and three water/cement ratios including 0.35, 0.45, and 0.55 were selected, and the sulfuric acid solution pH values 0.95, 2, and 4 were chosen in this paper. The results showed that the larger the water/cement ratio, the smaller the mass loss and the surface fractal dimension of the specimens, and with the decrease of the pH value of the sulfuric acid solution, the mass loss and the surface fractal dimension of the specimens would be increased. The concrete specimen containing gravel and river sand had the greatest surface fractal dimension and greatest mass loss, while the concrete specimen containing crushed marble sand had a smaller surface fractal dimension and a smaller mass loss. The dominant and secondary order of three factors on mass loss and surface fractal dimension of concrete subjected to sulfuric acid was the pH value of the solution > the chemical composition of the aggregate > the water/cement ratio.

This paper discusses the latest progress in research on ant nests and explores innovative scientific concepts associated with underground ant nests from the perspective of bionics. The methods used by scholars to study the structure of ant nests and the interaction between the structure itself and the individual ants are investigated. The structural characteristics of the ant nest, its internal environment and ventilation characteristics are discussed in detail. In addition, this paper presents an innovative project in which the effect of underground ant nests on soil geotechnical properties and the effect of calcined ant nest soil powder, from the perspective of civil engineering, are addressed. Practical examples of the application of the structural and inter-relational aspects of subterranean ant nests in the field of architectural bionics are also provided, from the perspectives of construction, morphology, function and material. This review attempts to integrate civil engineering, architecture and biology, enlighten architects and biologists on converging their thinking, provide new ideas regarding underground ant colony nests, and provide references for long-term human habitation.