International Concrete Abstracts Portal

Eleven large-scale reinforced concrete coupling beam specimens were tested under reversed cyclic displacements of increasing magnitude. The main variables included yield stress (fy) of the primary longitudinal reinforcement (Grade 80, 100, or 120 ksi [550, 690, or 830 MPa]), span-depth (aspect) ratio (1.5, 2.5, or 3.5), and layout of the primary longitudinal reinforcement (diagonal [D] or parallel [P]). Specimens had the same nominal concrete strength (8000 psi [55 MPa]) and cross section (12 x 18 in. [310 x 460 mm]) and were designed for nominal shear stresses of 8 √__f c′ psi (0.67 √__f c′ MPa) for D-type beams and 6√ __f c′ psi (0.5 √ __f c′ MPa) for P-type beams. Transverse reinforcement was Grade 80 (550) in all but one beam (D120-2.5), which had Grade 120 (830) reinforcement. Test results show that, on average, D-type beams had chord rotation capacities in excess of 5%, 6%, and 7% for beams with aspect ratios of 1.5, 2.5, and 3.5, respectively. P-type beams with Grade 80 or 100 (550 or 690) longitudinal bars, tested only for an aspect ratio of 2.5, had chord rotation capacities of approximately 4%. Based on these results, the authors recommend permitting the use of high strength steel, Grade 80 (550) and higher, in D-type and P-type coupling beams for earthquake-resistant design. The spacing of confining reinforcement should be limited to 5db for fy = 80 ksi (550 MPa) and 4db for fy = 100 or 120 ksi (690 or 830 MPa). Consistent with prior findings, the results show that deformation capacity is correlated with span-depth ratio and more sensitive to spacing of the confining reinforcement than to uniform elongation of the longitudinal reinforcement. Finally, the test results illustrate the effects of reinforcement grade on stiffness and energy dissipation of pseudostatically loaded coupling beams.

In this study, five reinforced concrete (RC) beam specimens with transverse web openings and one specimen without openings were prepared. Diagonal steel bars were arranged around the web openings in the beam specimens so as not to fail at the section with the openings. The specimens were subjected to static reversed-cyclic shear loading of double curvature, and those specimens failed in shear at a different part than the section with the web openings. This paper provides a simple model of the relationship between stress in the diagonal reinforcement around the openings and the applied shear load considering the shrinkage of concrete. Moreover, an evaluation method of the ultimate shear capacity of the beam using the upper-bound solution of the limit analysis was also provided. These models showed good agreement with the test results. The study contributes to the crack control and safety of RC beams with openings.

Although estimating the post-cracking torsional stiffness is vital for distributing the torsional moment in analyzing statically indeterminate reinforced concrete (RC) structures, none of the North American codes provide an analytical approach for determining the torsional stiffness after cracking. Moreover, the scarcity of experimental work has resulted in the lack of torsion design provisions for concrete box girders reinforced with glass fiber-reinforced polymer (GFRP). Therefore, the purpose of this research was to study the stiffness characteristics of RC box girders reinforced with GFRP reinforcement and to provide a simple analysis technique that can be used to predict post-cracking torsional stiffness. Fourteen concrete box girders were fabricated and tested under a pure torsional moment. In addition, data on 10 solid rectangular RC beams with GFRP reinforcement was collected from the literature. The test results indicate that the concrete strength, as well as the ratio, type, and configuration of the web reinforcement, substantially affected the post-cracking torsional stiffness of the tested specimens. An analytical model was developed for estimating the torsional stiffness after cracking. This model was based on a thin-walled tube and space truss analogy using a concept of postcracking shear modulus. The proposed model considers the effect of concrete strength, the configuration and ratio of the GFRP web reinforcement, and the ratio of the GFRP longitudinal bars. In addition, an equation to calculate the ultimate twist of the GFRP-RC members was developed. The validity of the proposed model was investigated by analytically regenerating the torque-twist curves of the tested box girders and the other specimens available in the literature.

Under earthquake load, as the inelastic deformation increases, the shear strength of reinforced concrete coupling beams is degraded by diagonal cracking. In the present study, for the performance-based design of short coupling beams (l/h ≤ 2.5), a shear strength degradation model based on diagonal strut and truss mechanisms was developed, addressing the effects of the target chord rotation, longitudinal reinforcing bar ratio, length-to-height ratio, ratio and details of transverse reinforcement, distributed longitudinal web bars, and diagonal bars. Based on the proposed method, a simplified moment-rotation relationship of plastic hinges was developed for the nonlinear numerical analysis of coupling beams. For verification, the proposed method was applied to existing coupling beam specimens with a conventional reinforcing bar layout, distributed longitudinal web bars, and/or diagonal reinforcement. The predicted moment-rotation relationships generally agreed with the test results. Thus, the proposed plastic hinge model is applicable to the nonlinear analysis of short coupling beams to describe the shear strength degradation after flexural yielding. Design recommendations for the practical application of the proposed method were discussed. The proposed model revealed that the use of distributed longitudinal reinforcement and diagonal reinforcement is effective for high ductility.

The purpose of this study is to assess the feasibility of using a non-metallic basalt fiber (BF) pellets to enhance the ductility of glass fiber-reinforced polymer (GFRP) reinforced concrete deep beams. In addition, the ability of BF pellets to supplant conventional web reinforcement was evaluated. To achieve the goals of this study, seven large-scale concrete deep beams reinforced with GFRP headed-end bars were constructed and tested to failure under three-point loading over a span of 1390 mm. The beams had a rectangular section of 250 x 590 mm with overall length of 2100 mm. Experimental variables included the volumetric percentage of BF pellets and transverse web reinforcement. The addition of fibers improved the post-peak behavior by increasing the ductility index by more than 50%, when compared to the counterpart control beam. The results provide support for replacing conventional web reinforcement in deep beams with a layer containing BF pellets in the tie zone.