The shear performance of concrete beams is known to be an important mechanical feature; hence, enhanced shear resistance is critical for determining a beam’s performance in terms of security and service life. This paper presents a study on the shear behavior of concrete beams without web reinforcement strengthened by external vertical prestressing rebars (EVPRs). Experimental data were obtained from seven test beams with varying influencing factors (stirrup ratio ρsEP, arrangement spacing s, prestressing force Fp, and compressive stress degree γp of the EVPRs) to determine their effects on the shear behavior. The results reveal that the EVPRs can significantly improve the shear capacity and ductility of concrete beams without web reinforcement. Furthermore, the failure mode is changed from brittle diagonal tension to relatively ductile shear compression, and the flexural cracks and shear cracks are more fully developed. The shear capacity becomes enhanced as the ρsEP and γp are increased; vertical compressive stress provided by the EVPRs can reduce the principal tensile stress of the concrete structure to prevent the shear cracking and enhance the shear resistance of the concrete. Meanwhile, in the stage from the formation of the critical shear crack (CSC) to the shear failure, the EVPRs can be used as stirrups to share the shear load. It can be concluded that EVPRs can effectively improve the shear performance of concrete beams.
The ultimate load capacities of steel fiber-reinforced concrete beams were determined by experiments conducted on steel fiber-reinforced concrete beams under the action of a two-point symmetrical concentrated load. Accordingly, failure modes and experimental data were obtained for 19 sets of test beams with varying concrete strength, longitudinal reinforcing bars, shear span ratio, and steel fiber volume content to determine their effects on steel fiber-reinforced concrete beam behavior. An optimization model reflecting the contributions of all tested factors to the shear capacity of a steel fiber-reinforced concrete beam is then derived and its accuracy is demonstrated by a comparison against the test results.
In order to analyze the causes of cracking in abutments subject to concrete shrinkage and temperature variation during the construction process and to determine factors affecting the mechanical properties of the abutment, nonlinear calculations capturing abutment behavior are conducted with Midas/FEA software. Using these calculations, the cracking mechanism is identified, and the influence of the evaluated factors is analyzed. It is concluded that the deformation between the pile cap and abutment backwall as constrained by a pile foundation when subjected to concrete shrinkage and temperature changes is the basic cause of abutment cracks during construction; these cracks form over the piles and develop upward. For a given reinforcement ratio, the distribution of horizontal crack-control steel using small, closely spaced bars is more beneficial. When pile-bearing capacity meets the standard, the width of the generated cracks tends to decrease with the decrease in the diameter of the piles. e existence of a postcast strip in the abutment backwall also contributes to the decrease in the depth of the crack. Finally, the impact of age difference between the pile cap concrete and abutment backwall concrete on cracking is inconsequential.
Abstract. The actual bearing capacity of a bridge in active service is crucial to the structure, but such data is generally difficult to obtain. In order to obtain the actual ultimate bending capacity of the used hollow slab, a destructive test of a hollow slab, which has been used ten years, has been carried out. Moreover, based on the experimental analysis of the material parameter data, a three-dimensional finite element nonlinear analysis model of the used hollow slab was established. Through the experiment and finite element analysis of the used hollow slab, the comparisons of the failure mode, crack propagating and ultimate bending capacity were focused on. The main conclusions obtained through the study are as follows: (1) Strand is a kind of stable prestressed material, which can maintain good mechanical properties for a long time; (2) The used hollow slab still maintains good ultimate bending capacity, although underwent a decreased rigidity due to long-term cumulative damage; (3) The total strain fracture model is qualified for simulating the nonlinearity of concrete material, and can obtain the ultimate bearing capacity of reinforced concrete structure effectively as well as simulates the development of cracks well.
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