Publications

The 1994 CSA-A23.3 standard "Design of concrete structures" includes a new shear design method based on the equations of the modified compression field theory (MCFT). This "general method" is a simplification which casts the MCFT in the traditional "V c + V s " format resulting in a set of six general equations and two tables. This new method unifies the treatment of reinforced, partially prestressed and fully prestressed concrete and accounts, in a rational manner, for the effects of axial load and bending moment on shear capacity. Simplifying the MCFT while maintaining acceptable generality and accuracy involved a number of considerations and assumptions. This paper gives the background to the development of these shear design equations and tables of the general method.Key words: beams, building codes, crack width and spacing, diagonal cracking, reinforced concrete, shear strength, size effect in shear, structural design.

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A simplified method for the analysis and design of membrane elements subjected to in-plane shearing and normal stresses is presented. The method proposed is capable of calculating the ultimate strength and the mode of failure of membrane elements. The strength curves in the method are also cast in a tabular format to further simplify the method. The results of the proposed method compare well with experimental results of 14 membrane elements reported in the literature and with the results of the modified compression field theory. Comparisons with the general method and the American Concrete Institute code are also presented. Use of the method is illustrated by two examples, one for design and the other for capacity calculation.

The behaviour of and design requirements for the transverse stiffeners of transversely stiffened web plates in plate and box girders has been studied using a fully non-linear finite element package. Using nodal line representation of the transverse stiffeners, the form and magnitude of the forces applied to the stiffeners during the collapse of the web plates were investigated. Analyses were also carried out with discrete stiffeners so that the variation in strength with stiffener size could be determined and the effect of the deflection of the stiffener assessed. A limited study was also carried out with a complete girder arrangement including flanges, so that the contribution of the transverse rigidity of the flanges to girder shear strength could be established. Analyses were undertaken for webs in shear, bending and direct compression. Using the results of the finite element study for validation purposes, a simple beam model was formulated with the stiffener and associated width of web plate acting as a beam spanning between the girder flanges, subjected to a lateral load resulting from the destabilising action of the buckling web plates. This simple design model can be used to optimise the stiffener size and is compatible with the basic approach adopted in the British Code BS5400, Part 3, which can therefore be modified to allow for the findings of this study. (A) For the covering abstract see IRRD 864118.

This paper describes a study conducted to investigate the effects of increasing the thickness of the concrete side cover on the behavior of reinforced concrete beams tested in shear. Seven test results are reported. The thickness of the concrete side cover ranged from 5-75 mm (0.2-3 in.) for beams with a target concrete strength of 25 Mpa (3600 psi), and from 25-75 mm (1-3 in.) for beams with a target concrete strength of 40 MPa (5800 psi). The beams were reinforced in the longitudinal and transverse directions. The specimens with 75 mm (3 in.) side cover developed a sharp increase in diagonal crack width upon cracking and showed less favorable behavior. However, at estimated service stresses all specimens either remained uncracked or developed crack widths smaller than a suggested 0.3 mm (0.012 in.) limit. Spalling was observed in the specimens with larger covers near ultimate conditions, but was limited to corners of the section, leaving a considerable part of the cover on the vertical side intact. The ACI shear method and general method provided conservative estimates of the strength.

The contribution of shear strains to the vertical deflections in reinforced concrete (RC) beams is typically neglected for two main reasons.First, this contribution is relatively smaller than the contribution from flexure.Second, the calculation of the shear strains in cracked RC beams is complex and requires iterations.This paper presents a simple model for the calculation of the shear stress-strain response of beams after cracking of the concrete and before yielding of the steel.It represents this part of the response using a straight line whose slope and intercept stress are related to the ratios of the reinforcement and to the concrete compressive strength respectively.The results of the proposed model are shown to be simple and to compare well with experimental results.

Keywords SURREY UNIVERSITY TRANSVERSE, WEBS, LOADS, FORMULATION, ANALYTICAL, CLAUSES, FIELD, INTERMEDIATE, STIFFENED, SHEAR, STIFFENERS, NUMERICAL, MODELS, STANDARDS, METHODS, FORCES, LINEAR, GIRDERS, LOADS, DESIGN, STUDIES, PARAMETRIC, CODES, TENSION, BEAMS, SIMPLE UK... Show All

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The contribution of the shear strains to the overall deformations of reinforced concrete (RC) elements is typically neglected. However, when RC cracks in shear, its shear modulus is significantly reduced, and the contribution of the shear strains to the overall deformations of the elements is increased. Experimental testing has shown that shear deformations can be significant. Under service conditions, RC can be cracked in shear and hence, a simple method for the calculation of the effective cracked shear modulus is desired. Research has shown that the part of the shear response after cracking and before yielding can be well modeled using a straight line. This paper uses existing experimental data and the equations of the modified compression field theory (MCFT) to examine this part of the response in RC membrane elements and to develop two simple equations that can be used to characterize the straight line. The proposed equations are evaluated by comparing their results with existing experimental data on the shear response of thin RC membrane elements. The comparison includes the post-cracking response and the shear strains at estimated service level loading. A very good agreement is obtained between the experimental and the calculated results. The simplicity of the proposed equations is illustrated using a numerical example.

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This paper present the results of an experimental investigation of the shearing strength of plain concrete based on pushoff type of tests. Twenty pushoff specimens with compressive strengths ranging from 19 to 66 MPa were cast and tested to failure. The results indicate that the cracking shearing strength increase with the increase in compressive strength. However, the rate of increase diminishes as the compressive strength increases. An equation relating the cracking shearing strength to the compressive strength of the concrete is proposed. This equation can be used to calculate the cracking shear stresses in elements which are commonly designed using the shear-friction model.