The crack band model is applied to the problem of crack shear in concrete. The constitutive law for concrete within the crack band is provided by the microplane model, in which the microstrains on weak planes of various orientations (the microplanes) are assumed to conform to the same macroscopic strain tensor, and the microstresses from all the microplanes are superimposed. Due to the neglect of shear stiffness on individual microplanes, the material behavior is completely characterized by the relation between the normal stress and strain for each microplane. To simulate crack shear, the law for unloading contribution on the microplanes after previous tensile strain‐softening is important, since the shear stresses resisting crack shear, as well as the normal confining stresses and crack dilatancy, result from compression along lines inclined with regard to the crack plane. A satisfactory agreement with the existing results from shearing tests of cracked concrete blocks (i.e., aggregate interlock tests) i...

Crack Shear in Concrete: Crack Band Microflane Model

It is not correct to state that the collapse of the Wilkins Air Force Base depot building occurred without warning. The structure was known to be extensively cracked in shear well before the collapse, and it is the discusser’s understanding that some beams in the building were already being braced with shoring consisting of various wooden poles. The observer was in fact looking for additional trouble at the time of the collapse, although it must be argued that the fact that the failure occurred while he was present was coincidence. The record of cracking for the particular design at Wilkins was so bad that a revised design had already been prepared and was used in some similar buildings. The January 1957 issue of the ACI Journal had several articles dealing with the failure and with the repairs to other structures of the same group that had not failed but that were showing significant shear cracking.

Recent Approaches to Shear Design of Structural Concrete

An experimental study on a series of composite beams combining a 250 mm (9.84 in.) deep reinforced concrete (RC) element and a 50 mm (1.97 in.) thick reinforced ultra-high-performance fiber-reinforced concrete (R-UHPFRC) element is presented. The specimens are tested in a cantilever-beam setup with the R-UHPFRC element acting as an additional tensile reinforcement. The test parameters include the span length and the ratio and type of the steel reinforcing bars, including stirrups. Most of the beams fail in flexure at a force that is 2.0 to 2.8 times higher than the resistance of the reference RC beams. The medium-span cantilevers with a low stirrup content failure along a flexure-shear crack. Near-interface concrete cracking softens the bond between the elements and enhances the member deformation capacity. The R-UHPFRC element contributes significantly to the shear resistance.

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Experimental Investigation on Reinforced Ultra-High-Performance Fiber-Reinforced Concrete Composite Beams Subjected to Combined Bending and Shear

Shear in one-way reinforced concrete (RC) members is transferred in cracked concrete members by a number of actions such as aggregate interlock, residual tensile stresses, dowelling action, inclination of compression chord and transverse reinforcement (if available). The amount of shear transferred by each action is significantly influenced by the cracking pattern (shape of shear cracks) and by the kinematics at failure (opening and sliding of the cracks). In this paper, the activation of the various shear-transfer actions is investigated for one-way RC members. This is done by using a set of detailed measurements on the cracking pattern and actual kinematics at failure recorded on a number of specimens (beams) with a very low amount of transverse reinforcement. The amount of shear transferred by each action is estimated on the basis of available physical models and compared for the various specimens. The results show rather good predictions in terms of strength by following this approach. Consistent explanations of the shear transferred by each action are provided.

Analysis of shear-transfer actions on one-way RC members based on measured cracking pattern and failure kinematics

1. Mechanics of fracture and progressive cracking in concrete structures.- 1.1 Introduction.- 1.2 Blunt crack band theory.- 1.3 Finite element implementation.- 1.4 Energy considerations.- 1.5 Applications and practical analysis.- 1.6 Crack development.- 1.7 General model for progressive fracturing.- 1.8 Conclusion.- References.- 2. Scale effects in fracture of plain and reinforced concrete structures.- 2.1 Introduction.- 2.2 Dimensional analysis applied to plain and reinforced concrete structures.- 2.3 Fracture stability in plain and reinforced concrete elements.- 2.4 Hysteretic behaviour of reinforced concrete elements.- 2.5 Appendix: Dimensional independence.- References.- 3. Numerical methods to simulate softening and fracture of concrete.- 3.1 Introduction.- 3.2 The behaviour of concrete in a tension test.- 3.3 A comparison between concrete and steel.- 3.4 Tensile fracture zones.- 3.5 A general model for the tensile fracture of concrete.- 3.6 Material properties.- 3.7 FEM analysis of a fracture zone: coincident with predetermined crack path.- 3.8 FEM analysis of a fracture zone: not coincident with predetermined crack path.- 3.9 Some comparisons with test results.- 3.10 Summary and conclusions.- References.- 4. Numerical modeling of discrete crack propagation in reinforced and plain concrete.- 4.1 Introduction.- 4.2 Discrete crack models for concrete.- 4.3 The linear model.- 4.4 The nonlinear model.- 4.5 Crack propagation modeling: the future.- References.- 5. Fracture of steels for reinforcing and prestressing concrete.- 5.1 Introduction.- 5.2 Fracture.- 5.3 Fracture under extreme conditions.- 5.4 Fatigue.- 5.5 Environment sensitive cracking.- References.- Author's index.

T. Paulay

Papers

Horizontal Construction Joints in Cast-In-Place Reinforced Concrete