Effect Of The Cracks’ Development On Reinforced Concrete Beams For Strain Distribution Around The Cracks

Stress and strain detection is one of the most effective means to detect the force and deformation of bridges. They are important indicators for evaluating structure’s usage and security status. No matter how high-tech structural analysis techniques they are, they can not replace the field testing well. Reinforced concrete bridge structures are always being with cracks in working condition, and concrete cracks will seriously affect the testing results of strain.This paper outlines the causes and classification of concrete cracks in reinforced concrete structures, introduces the traditional methods and the latest strain measurement of stress and strain measurement techniques. According to reinforced concrete experiment and the ANSYS finite element model, this paper comparatively analysis the effect of existing cracks on strain distribution, which is atound the surface of the concrete, from the aspect of crack depth, cover thickness, height of the beam cross-section and other aspects.The following preliminary conclusion can be obtained by the comparative analysis between the experiment result of reinforced concrete and the finite element model.① The crack makes the stress of concrete gets release in its vicinity, reduce strain. So, strain at the crack section is close to zero. When the distance from crack is longer than the strain’s affected area length(?s), the strain is no longer affected by the crack. That makes the strain can not reflect the real structure status in the actual project if there is crack in reinforced concrete beam.② In the condition of load do not cause cracks continue to expanding any more, the length ?s of the concrete is not concerned with load size.③ The length ?s gets increased with the increasing of crack depth. When crack extends to a certain extent, ?s changes little.④ When crack depth is the same, the larger thickness of the protective layer, the crack length of the strain affected area is greater, that is to say, strain gradient is relatively reduced when with the thickness of the protective layer is increased.⑤ With the increasing of the height of the beam section, the length of ?s a is gradually increased. When the height of beam is moderate, the length of ?s, which corresponds to different high of beam, is very close to the distance between crack section’s neutral axis and beam bottom. That is to say, the ratio between ?s and h? is close to 1.Compare with FEM calculations and the result of strain distribution under the experiment, we can obtaine basic agreement, and it indicates the use of the discrete fracture model simply simulate actual crack is feasible. That provides a reference for experiments under similar strain distribution crack, establish crack model accurately and explore a new method of measuring the distribution of strain under the crack in the future.