Critique of critical shear crack theory csct for fib model code. However, artificial manmade cracks several orders of magnitude longer and wider than natural flaws have required a correction factor term y that can be up to about 3 times the recorded experimental value. Applications of the critical shear crack theory to punching of rc. Critical shear crack theory 7 aureliomuttoni,originally developed the critical shear crack theory in 1985, at the technical university of zurich. Applications of critical shear crack theory to punching of.
Nonlinear finite element modeling of shearcritical. Experimental investigation of the shear behavior of a. Validation of the critical shear crack theory for punching of slabs. The critical shear crack theory csct is a consistent approach used for shear design of one and twoway slabs failing in shear and punching shear respectively. Effect of point loads on reinforced concrete slabs without. Applications of critical shear crack theory to punching of reinforced concrete slabs with transverse reinforcement. Recent improvements of the critical shear crack theory for. Evaluation of shear strength of concrete flat plates. The shear stress needed to cause slip in a given direction along a given crystallographic plane of a single crystal explanation of critical shear stress. Complex nature of diagonal tension accompanied by the formation of new cracks as well as closing and propagating preexisting cracks has deterred researchers to achieve an analytical and mathematical procedure for accurate predicting shear behavior of reinforced concrete, and there is the lack of a unique theory accepted universally.
Critique of critical shear crack theory csct for fib model. Fracture mechanics is the field of mechanics concerned with the study of the propagation of cracks in materials. The failure of a material is usually classified into brittle failure or ductile failure. First of all, the scpt is used to analyze the critical shear crack of sc70, which is located at a distance of about 2700 mm from the support the method of section 4. Punching strength is a critical point in the design of flat slabs and due to the lack of a theoretical method capable of explaining this phenomenon, empirical formulations presented by codes of practice are still the most used method to check the bearing capacity of slabcolumn connections. Shear strength of concrete members without transverse. For stirrup design, the section located a distance d from the face of the support is called the critical. Accurate critical stress intensity factor griffith crack.
Critique of critical shear crack theory csct for fib model code articles on shear strength and size effect of rc beams. This paper outlines the theoretical background of the punching shear provisions implemented in the fib model code 2010 and presents a practical example of its applica tion. Re shear cracks in pt members, a principal tensile shear crack would not extend to the tension face, as a flexure shear crack would. Faculty of engineeringuniversity of sulaimani, kurdistan region of iraq accepted 19 oct 2014, available online 25. Cracks in concrete beams due to increase in shear stress appears near the support such as wall or column.
The limitations of such an approach are discussed in this paper and a new theoretical model, based on the critical shear crack theory, is presented to investigate the strength and ductility of shearreinforced slabs. Pdf application of critical shear crack theory to punching of. Figure 32 position of critical shear crack developing through compression strut from engineerin 101 at abant izzet baysal university. An important feature of this theory is the critical shear crack csc, which is suitably defined as follows. Failure criterion based on critical shear crack theory critical shear crack theory as shown in fig. In theory the stress at the crack tip where the radius is nearly zero, would tend to infinity. Applications of the critical shear crack theory to. Fatigue crack initiation normally occurs due to repeated plasticity on shear planes in individual grains. Critical plane approach an overview sciencedirect topics. Faculty of engineeringuniversity of sulaimani, kurdistan region of iraq accepted 19 oct 2014, available online 25 oct 2014, vol. The theoretical principles of the critical shear crack theory for punching shear failures and derivation of consistent closed.
A comparison between the treatments of punching by ec2 and. This paper presents a study on the shear behavior of concrete beams without web reinforcement strengthened by external vertical prestressing rebars evprs. Nucleation of a cleavage crack occurs when a critical value of effective shear stress is attained due to a critical grouping ideally a pileup of dislocations which can create a crack nucleus, i. Punching strength of reinforced concrete flat slabs. Thus shear wave splitting opens a window into the analysis of small variations of the rock mass that probably no other geophysical measurement can match, and is the underlying reason why shear wave splitting is the key to monitoring the crackcritical crust discussed in, below. Critical shear crack theory csct was first developed for punching failures of slabcolumn connections without shear reinforcement muttoni. With no shear reinforcement provided, the member failed immediately upon formation of the critical crack in the highshear region near the right support. Results of the refined calculation of the failure criterion of critical shear crack theory csct. The traditional approach of codes of practice for estimating the punching strength of shearreinforced flat slabs is based on the assumption that. As previously shown,3,4,6 the width of the critical shear crack can be correlated to a physical parameter a reference. How to distinguish between a shear force crack and a bending. By integration of the stresses at the critical shear crack, 86 the contribution of each shear transfer action is determined as well as its governing parameters. The critical shear crack theory for punching design. Critical shear stress article about critical shear.
How to distinguish between a shear force crack and a. In the critical shear crack theory csct 21 22 23 the shear stress transferred across the crack is an explicit function of the crack width in the critical shear region. This theory, based on a mechanical model, is shown to provide a unified approach for one and twoway shear in slabs, leading to simple design expressions for estimating the. The most important factor as to whether a crack will propagate past the first grain and go on to cause fatigue failure is the microscopic shear stress in critical grains. An analysis of the critical shear crack development on the basis of test results f cavagnis, mf ruiz, a muttoni engineering structures 103, 157173, 2015. In this paper, the fundamentals of the critical shear cracktheory csct are introduced. Shear crack in concrete beams structural engineering. Principal tensile shear cracks happen in low flexural stress zones normally fully compressive near points of contraflexure or at free ends where there will. The limitations of such an approach are discussed in this paper and a new theoretical model, based on the critical shear crack theory, is presented to investigate the strength and ductility of shear reinforced slabs. If an initial crack size is known, then a critical stress can be determined using the strain energy release rate criterion. Background to fib model code 2010 shear provisions part. Critical stress intensity factor bulk material values mpam 12 3.
The theoretical principles of the critical shear crack. Application of critical shear crack theory to punching of reinforced concrete slabs with transverse reinforcement. Re shear cracks in pt members, a principal tensile shear crack would not extend to the tension face, as a flexureshear crack would. This paper discusses the limitations of the traditional approach for estimating the punching strength of shear reinforced flat slabs and proposes a new theoretical model, based on the critical shear crack theory, to investigate the strength and ductility of shear reinforced slabs.
Request pdf on apr 1, 2017, aurelio muttoni and others published the critical shear crack theory for punching design. Validation of the critical shear crack theory for punching. Critique of critical shear crack theory for fib model code articles on. The theory is based on a mechanical model allowing to determine the amount of shear force that can be carried by cracked concrete accounting for the opening and roughness of a critical shear crack leading to failure. These cracks are also called as shear crack and are inclined at 45 degrees with the horizontal. The shear performance of concrete beams is known to be an important mechanical feature. Punching resistance of internal slabcolumn connections. In that document, donmez and bazant raise a number of criticism on the hypotheses critical shear crack theory csct. Comprehensive design example for prestressed concrete psc girder superstructure bridge design step 5 design of superstructure design step 5. This theory was based on the hypothesis that the shear strength of concrete slabs without transverse reinforcement depends on the width and roughness of a crack that. Criteria for formation of diagonal cracks in concrete beams v ave v bd can be regarded as rough measure of stress distribution of v is not known exactly, as reinforced concrete is nonhomogeneous.
These elementary effects are exemplarily sketched in fig. Punching strength of reinforced concrete flat slabs without. The critical shear crack theory csct was developed following a scientifically. Shear crack propagation theory scpt the mechanical. Nucleation of a cleavage crack occurs when a critical value of effective shear stress is attained due to a critical grouping ideally a pileup of dislocations which can create a cracknucleus, i. Based on the experimental data that include maximum shear crack width, residual shear crack width, angle of the main crack and shear drift ratio, a simplified equation are proposed to predict the shear deformation of the highstrength reinforced concrete hsrc beam member. The theory is developed with a clear link to experimental observations, explaining the observed phenomena and calculating their response.
Despite the intensive efforts dedicated in the last decades to better understanding punching shear failures, there is still no consensus on the. Applications of the critical shear crack theory to punching. Principal tensile shear cracks happen in low flexural stress zones normally fully compressive near points of contraflexure or at free ends where there will not be a flexural crack at all. The theoretical principles of the critical shear crack theory. Today, it is the critical stress intensity factor k ic, found in the plane strain condition, which is accepted as the defining property in linear elastic fracture mechanics. Critique of critical shear crack theory csct for model. Critical stress intensity factor k ic has been an approximation for fracture toughness using only loadcell measurements. Effect 1 is the crack localization within the fracture process zone fpz. Aug 23, 2016 the main variable considered in the study is the shear span to depth ratio. Pdf some specific documents related to punching shear provisions in draft proposal of model code 2010 can be downloaded from the following links.
The method is based on an estimate of the crack width in the shear critical region and provides a rational basis for the evaluation of the shear and punching shear strength of members without stirrups. The method is based on an estimate of the crack width in the shear critical region and provides a rational basis for the evaluation of the shear and punching shear strength of. The aspects criticized have however been largely discussed in previous works of the csct, proving the validity of the theory. Material failure theory is the science of predicting the conditions under which solid materials fail under the action of external loads. This paper discusses the limitations of the traditional approach for estimating the punching strength of shearreinforced flat slabs and proposes a new theoretical model, based on the critical shear crack theory, to investigate the strength and ductility of shearreinforced slabs. Free online education presentations on applications of critical shear crack theory to punching of reinforced concrete slabs with transverse reinforcement videos there are no web sessions on applications of critical shear crack theory to punching of reinforced concrete slabs with transverse reinforcement. This document compiles such previous knowledge as a reply to the authors of the report. A critical section is one where a critical or maximum stress occurs. Critique of critical shear crack theory csct for model code. The proposed approach is based on a physical model and overcomes most limitations of current codes of practice. Normally, the failure of the concrete specimen is mainly caused by the opening of the csc, but. Critical shear stress article about critical shear stress.
The mechanical model of the critical shear crack theory csct has been used in the past to investigate a number of shearrelated problems, such as punching. The critical shear crack theory for punching design american. It uses methods of analytical solid mechanics to calculate the driving force on a crack and those of experimental solid mechanics to characterize the materials resistance to fracture. Shear strength of members without transverse reinforcement as. There are no online learning courses on applications of critical shear crack theory to punching of reinforced concrete slabs with transverse reinforcement. The theory is based on a mechanical model that allows the amount of shear force that can be carried by cracked concrete to be determined, accounting for the opening and roughness of a critical shear crack leading to failure.
Shear cracks are diagonal and flexural cracks are vertical. The mechanical model of the critical shear crack theory csct has been used in the past to investigate a number of shear. Punching shear strength of reinforced concrete slabs. Background to fib model code 2010 shear provisions part ii. A comparison between the treatments of punching by ec2. Critique of critical shear crack theory for fib model code. This has been explained by muttoni and schwartz12 as follows. Punching resistance of internal slabcolumn connections with.
Shear failures in reinforced concrete members without transverse reinforcement. The theoretical principles of the critical shear crack theory for. The shear failure process of rc members without shear reinforcement includes several interacting effects of material behavior. Critique of critical shear crack theory csct for b model code articles on shear strength and size e ect of rc beams abdullah d onmez1 and zden ek p. Figure 32 position of critical shear crack developing.
Online learning aci university on applications of critical shear crack theory to punching of reinforced concrete slabs with transverse reinforcement. The theory is based on a mechanical model that allows the amount of shear force that can be carried by cracked concrete to be determined. The theory is based on a mechanical model that allows the amount of shear force that can be carried by cracked concrete to be determined, accounting for the opening and roughness of a. This theory, based on a mechanical model, is shown to provide a unified approach for one and twoway shear in slabs, leading to simple design expressions for estimating the strength and deformation capacity of such members. A comparison between the treatments of punching by ec2 and the critical shear crack theory csct slabs without shear reinforcement rizgar amin agha. The main variable considered in the study is the shearspan to depth ratio. It is 51 noticeable that, although different models account for different governing shearcarrying actions 52 and for the strain and size effects in different manners, the final design expressions account for. The critical shear crack theory for punching design researchgate. The theory was first developed for punching design of slabcolumn connections without shear reinforcement. Critique of critical shear crack theory csct for fib. Sometimes they do happen at other locations when stresses are reversed during dynamic loads.
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