One-way shear strength of large footings

Results are presented from 23 shear tests on 1-m deep specimens made of low-strength concrete and tested with shear span-to-effective depth ratios between 1.4 and 2.4 to obtain information that is relevant to the one-way shear strength of footings. Based on these results and other test results from the literature, an amendment is proposed to the 1994 Canadian concrete code one-way shear strength provisions for members without stirrups. In order to account for the beneficial effects of strut-action in deep members such as footings, it is proposed that the reduction in shear strength due to size not be applied to sections located less than 2d from the face of a support or concentrated load when the applied shear introduces compression into the member. The strut-and-tie provisions in the Canadian code, which has stress limits to prevent concrete compression failures, normally should be used to design deep members, but should not be used to design members without minimum stirrups. The proposed revision eliminates the unnecessary increase in footing depths that is needed to meet the one-way shear strength requirements of the 1994 Canadian concrete code.Key words: building codes, footings, reinforced concrete, shear strength, structural design, tests. </jats:p

Flexural behaviour of concrete-steel hybrid bridge girders

The experimental results from a full-scale test are compared with analytical predictions in order to investigate the behaviour of a hybrid bridge girder with a reinforced concrete web and steel flanges. A linear analysis indicates that restrained shrinkage had a significant influence on initial cracking of the concrete web. The longitudinal strains, predicted by a nonlinear flexural analysis accounting for shrinkage and construction stages, compare well with the strains measured during the test. The average widths of the flexural cracks at the service load level are predicted using an empirical average crack spacing approach. The modified compression field theory is used to predict the diagonal cracking of the web due to combined shear and bending moment. A rigorous nonlinear analysis indicates that the effects of creep, load-cycles, and shear deformation must be accounted for in predicting the displacement of the girder. Finally, sectional strength calculations indicate that the distributed longitudinal reinforcement in the web contributes significantly to the flexural capacity of the hybrid girder. Key words: bridges, composite, cracking, girder, hybrid, reinforced concrete, structural design, tests. </jats:p

Shear strength of members without transverse reinforcement

The variable angle truss model is extended to members without transverse reinforcement by introducing concrete tension ties perpendicular to concrete compression struts. The modified compression field theory approach of limiting the shear transfer across diagonal cracks is combined with the variable angle truss model to develop equations for the shear capacity of members without transverse reinforcement. These equations are the theoretical basis of tabulated values for members without stirrups in the general shear design method of the 1994 Canadian concrete code. This paper also presents the results from an experimental study in which 27 narrow (beam-like) wall elements, with significant longitudinal reinforcement and little or no transverse reinforcement, were subjected to combined axial tension, bending moment, and shear. The experimental results are compared with predictions from the 1994 Canadian concrete code, as well as the American Concrete Institute building code. Key words: building codes, reinforced concrete, shear strength, structural design, tension, tests, truss model. </jats:p

Full-scale test of concrete-steel hybrid bridge girders

A full-scale laboratory test was conducted on a unique hybrid bridge girder with a reinforced concrete web and steel flanges. Half-width precast concrete deck panels were compositely attached to the top steel flange of a 17.1 m long hybrid girder to construct a "half-bridge" that was tested to study the service load behaviour and the behaviour under increasing load until failure. It was observed that the concrete web of the hybrid girder cracked because of the combination of dead weight and restrained shrinkage. Under the service loads, the concrete web had numerous closely spaced cracks that were reasonably well controlled - the maximum crack width was 0.20 mm. Although there was significant diagonal cracking in the web of the girder, the ultimate behaviour was dominated by flexure. This paper presents the methods used to construct and test the half-bridge, and a summary of the important results. A companion paper presents a detailed analysis and discussion of the test results. Key words: bridges, composite, cracking, girder, hybrid, reinforced concrete, structural design, tests. </jats:p

Repair of an 18-Story Shear Wall Building Damaged in the 2010 Chile Earthquake

Three transverse shear walls at one corner of an 18-story building in Santiago failed in flexural compression just below grade, causing the ground floor to drop 75 mm and the corner of the roof to displace laterally 185 mm. Cracking of walls and floor slabs caused significant building distortions. Nonlinear analyses of shear walls and floor slabs were used to understand the measured residual displacements and determine effective stiffnesses needed for a three-dimensional (3-D) model of the building. This model was used to estimate jacking forces needed to reposition the building. Existing cracks in shear walls were injected with epoxy, and fiber reinforced plastic (FRP) fabric was used to control new cracks. Instrumentation was used during jacking to monitor building movements, inclinations of walls and slabs, maximum compression and tension strains in walls, and crack widths. The building was repaired for less than 25% of the replacement cost and with much less impact on building habitants and the surrounding community. </jats:p