Publications

This paper presents a simplified method for the design and analysis of non-prestressed, partially prestressed, and fully prestressed concrete beams subjected to pure torsion. The proposed model relates the torsional strength to the concrete compressive strength and to the amounts of transverse and longitudinal reinforcement. To check the adequacy of this simple method, the calculated strength and mode of failure are checked against the experimental results of 17 prestressed concrete 66 reinforced concrete beam tests available in the literature, and very good agreement is found. The simplicity of the method is illustrated by two examples, one for design and another for analysis.

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Five 50 MPa longitudinally reinforced beams were loaded in a four-point testing setup to study their shear behavior. The beams were three meters long, and their cross section was 150 mm by 420 mm. The testing region did not contain stirrups. The beams were shallow, with a span to depth ratio of 3. All beams were similar except for the percentages of replacement of natural coarse aggregates with recycled concrete coarse aggregates, which were 0%, 10%, 20%, 35% and 100%. The results have shown that the replacement of natural coarse aggregates with recycled ones had a negligible effect on the ultimate shear strength. However, the results on the modulus of elasticity showed a reduction of less than 10% in beams with the use of recycled aggregates.

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This paper reports the preliminary results from an experimental program aiming to gain a better understanding of the flexural behavior of GFRP-reinforced beams made of recycled aggregates concrete (RAC).Three 32 MPa concrete beams were designed to fail in flexure by concrete crushing before bar rupture and were tested in a four-point testing setup.The control beam was made of natural coarse aggregates (NCA).The second beam was reinforced similar to the control beam but was made of RAC.The third beam was made of RAC and contained a larger amount of longitudinal GFRP reinforcement.The behavior of the beams is reported.The compressive strength in the three beams was relatively similar.The RAC beam sustained noticeably larger deformation relative to the control beam made of NCA, but the ultimate flexural strength was relatively similar.The load-deflection response after cracking of the two RAC beams was relatively linear, which is typical behavior in GFRP-reinforced beams made using NCA.Hence, this property was not affected by the use of recycled aggregates.The calculations of the ACI 440.11 code for strength were conservative for the three beams.The calculations of this code for deflection at estimated service load level severely under-estimated the deflections.

The use of recycled concrete aggregates (RCA) to replace part or all of the natural coarse aggregates (NCA) in the production of concrete has been on the increase. Such use helps in the preservation of the natural resources and in the reduction in the use of landfills. Research is needed to understand the effects of using RCA on the properties of concrete. This paper reports the results of an experimental study of the pushoff shearing strength of normal-strength plain recycled aggregate concrete (RAC). A total of twenty seven pushoff specimens were cast and tested. The percentages of replacement (PR) of NCA with RCA were 0, 20%, 50% and 100%. The results showed a 7% reduction in the shearing strength for PR of 20% and 50% and a 28% reduction for PR of 100%.

This paper reports the results of an experimental investigation of the shear behavior of beams made using hybrid fiber–engineered cementitious composites (HFECC). The paper specifically deals with the shear behavior of beams made using strain hardening engineered cementitious composites that incorporate relatively low volume ratios (Vf≤2%) of discontinuous, randomly distributed hybrid fibers (steel and polyethylene) and how the strain hardening characteristics of the fiber composite impact the shear behavior of the beam. A total of 21 beams reinforced with longitudinal steel bars and with various combinations of polyethylene (PE) and steel (ST) fibers were tested in a three-point loading setup at a shear span to depth ratio of 3. The total volume fraction of the fibers in the composites ranged from 0 to 2%, and the matrix was either cementitious paste or cementitious mortar. The beams were tested in controlled deformations to enable capturing the postpeak behavior. It is shown that HFECC made using cementitious paste was effective in increasing the shear strength by up to 8 times relative to the nonfibrous matrix. In addition, the ductility, multiple cracking behavior, and shear strain capacity of the beams were considerably improved. Improvements were also observed in the HFECC beams made with cementitious mortar but to a lesser extent, in which the shear strength increased up to 3 times relative to the nonfibrous matrix. The results also showed that when used in HFECC, the PE fibers were nearly as effective as steel fibers in increasing the shear strength. The addition of fibers allowed the beams to reach or exceed their calculated flexural capacity in spite of the relatively large longitudinal reinforcement ratio used. A fiber volume of 1% is shown to be an adequate minimum shear reinforcement for beams with compressive strengths ranging from 40 to 65 MPa, irrespective of the hybridization ratio and the binding matrix.

The combination of torsion with bending and shear (T-M-V) in members with both transverse and longitudinal reinforcement is the most commonly encountered combination in practical cases. Three dimensional interaction surfaces have been suggested by Hsu in 1968, Johnston in 1971, McGee in 1974 Elfren et al. in 1974. These surfaces were basically based on the interaction curves between each two stress-resultants at a time. Due to the limitations associated with experimental testing to cover all the possible factors that influence the interaction surface, theoretical models can be effectively used to establish this interaction. Currently available models such as that developed by Ewida and McMullen in 1981 have the ability to calculate the full response members subjected to the T-V-M combinations. Other more advanced models such as those developed by Rabbat and Collins in 1978 and by Rahal and Collins in 1995 are capable calculating the full response of reinforced and prestressed concrete beams subjected to any possible combination of stress-resultants.

A simple method for predicting the ultimate strength and mode of failure of reinforced concrete beams subjected to pure torsion is presented. This method is an extension of a recently developed method for predicting the strength of membrane elements subjected to pure shear that was also applied to beams subjected to combined shearing forces, bending moments, and axial loads. The torsional strength is related to the amounts of transverse and longitudinal reinforcement and to the concrete strength. To check the adequacy of this simple method, the calculated strength and mode of failure are checked against the experimental results of 66 beam tests available in the literature, and good agreement is found. The simplicity of the method is illustrated by an example.Key words: beams, building codes, mode of failure, reinforced concrete, shear, strength, torsion.