The wire reinforcing institute recommends the use of the subgrade drag theory for slabs up to 150 feet in length. The shear friction concept assumed that such a crack is formed when concrete will be cast at different times and that reinforcement is provided across the. Because shear cracks are inclined and the shear failure load depends on a large number of factors, shear design unlike flexural designmust consider the response of a finite length of the member, bregion. Results from direct shear tests on initially cracked specimens 21. The shear design method truss model with crack friction was implemented as a shear.
Connections such as beam bearings, daps, and corbels are some of the most critical connections in precast concrete construction because they support permanent gravity loads with little redundancy. Shear crack theory critical shear crack theory as shown in fig. The results from the experiments were used to compare the. The reinforcement in tension provides a clamping force, avf x fy across the crack faces. Unreinforced concrete slab slabs reinforced to limit crack widths. Determination of slab thickness no single design method covers every type or use of slab, so the designer should consider the use and design criteria in order to select an appropriate method. Builtup bars, composite slab, experiment, longitudinal shear, new simplified method, slipblock test, smallscale tests. Suggestions are given for construction of retrofitting method using shear bolts. Effect of flexural and shear reinforcement on the punching behavior of rc flat slabs. Shear friction, which is the subject of this paper, is a wellestablished research area,, with many applications,, and its importance to the behaviour of reinforced concrete is fully. Seismic retrofit of concrete slabs against punching shear. Distribution of shear force in concrete slabs a study of how to distribute shear force from linear fe analyses in bridge decks master of science thesis in the masters programme structural engineering and building performance design poja shams hakimi department of civil and environmental engineering division of structural engineering. Although shuibuya face slab, which is supplied with doublelayer steel mesh, has not experienced largescale shear failure, ishape cracks still appear, so the effect of shear stress cannot be ignored. Reinforced concrete design ence 355 introduction to structural design.
The shear friction model for calculating the punching shear capacity of slabcolumn connections is presented. Distribution of shear force in concrete slabs a study of how to distribute shear force from linear fe analyses in bridge decks master of science thesis in the masters programme structural engineering and building performance design. The design method used here is that proposed by moustafa. Effect of flexural and shear reinforcement on the punching.
As the shear span length increased, the longitudinal shear stress of slab decreased. Shear friction and aci 31899 the provisions for design using shear friction contained in section 11. Connections between concrete layers with different ages. Chapter 2role of shear reinforcement shear reinforcement is required to intercept shear cracks and prevent them from widening. The design longitudinal shear stress values of slabs resulting from line loads obtained by mk method is slightly higher as compared to psc method. Its value is large, and therefore, buxi power station, which is equipped with singlelayer steel mesh, shows a wide range of shear damage. Design of composite slabs with profiled steel decking. Depth of equivalent compression stress block under fire conditions acr area of crack face ae net effective slab bearing area aps area of prestressed reinforcement avf area of shear friction reinforcement b width of compression face bw net web width of hollow core slab. Mar, 2019 slab acts as a homogenous, isotropic elastic solid in equilibrium, with no discontinuities. Shear stress analysis and crack prevention measures for a. Details of these cracks in reinforced concrete beams are discussed. Evaluating the shearfriction resistance across sliding. The shear design of slab column connections is one of the.
The bending moments causes development of the flexural stress, this stress will be resisted by reinforcement provided in case of rcc beams. This example problem goes through how to design a reinforced concrete beam for shear using aci. Slab is of uniform thickness, and the neutral axis is at middepth. The ability to analyze the capacity of a slab on grade subjected to continuous wall linetype load as well as stationary, uniformly distributed live loads is also provided.
Because in site, the arrangement of reinforcement in slab and. Shearfriction design method for reinforced concrete miecz structural 27 apr 05. This thesis is brought to you for free and open access by washington university open scholarship. The shear failure load depends on numerous factors such as the dimensions, geometry, loading and structural properties of members. It should be noted that even the best design often requires reconciliation with the actual means, methods, materials, and site conditions. This has been explained by muttoni and schwartz12 as follows. Slab design reading assignment chapter 9 of text and, chapter of aci31802 introduction aci318 code provides two design procedures for slab systems. Punching shear strength of reinforced concrete slabs. Backgrounds and applications, brussels 1820 february 2008. This example uses practical design assumptions, which means using. This method of determining vn considers shear capacity of dowels as well as the friction between adjacent faces of a plane of concrete, whether the plane is the result of cracking or separate placements of concrete.
Deformation within the elements, normal to slab surface, are considered. Shearfriction truss model for reinforced concrete beams. Interface shear transfer shear friction design the purpose of this design memorandum is to provide guidance for interface shear transfer shear friction design. This paper presents an overview about the shear friction concept, design. Hate em all you want, but you cant climb some of the most classic trad routes without working through them. Under this scope, the present dissertation aims to study the behavior of connections. All forces act normal to the surface shear and friction forces are assumed to be negligible. Waffle slab analysis and design is similar to the procedure used with flat plates except that special considerations need. Types of cracks in concrete beams cracks in beams due to increased shear stress. Under this scope, the present dissertation aims to study the behavior of connections between concrete layers with different ages.
We have learned that terminating a slab casting has a shear friction check to. Steel sheeting serves as a permanent formwork and as a tension bearing member after hardening of concrete. Twodirection cracking shear friction membrane model for finite elment analysis of reinforced concrete jeffrey mitchell washington university in st. The shear friction concept was initially proposed by mast 19683 and birkeland and birkeland 19664 to explain shear force transfer. These are significant variations as indicated in the following example calculation. This paper is part of an ongoing research program conducted at the concrete laboratory of the faulty of engineering, cairo university to assess the contribution of horizontal flexural reinforcement and vertical shear reinforcement on the punching behavior of reinforced concrete flat slabs. Interface shear transfer in reinforced concrete members.
The video explains the five cases for shear design and how this impacts the. Mitchell, jeffrey, twodirection cracking shearfriction membrane model for finite elment analysis of reinforced concrete 2010. The shear friction concept assumed that such a crack is formed when concrete will be cast at different times and that reinforcement is provided across the crack to resist relative displacement along it. The shear friction design method set out in section 11. Shear friction interface design is widely used in reinforced concrete design and is. Slab acts as a homogenous, isotropic elastic solid in equilibrium, with no discontinuities. Asw area of shear reinforcement in each perimeter around the col. Punching shear reinforcement on slab 39 one way joist 41 twoway slab analyzed by the direct design method 47 development length of bars in tension 50 group of headed studs in tension near an edge 52 shear strength of slab at column support 54 simple span deep beam by strutandtie model 56 continuous deep beam by strutandtie model 60. Alternatively smallscale shear tests can be used to obtain shear characteristic of the connection. Punching shear retrofit method using shear bolts for. In addition, this design memorandum presents an acceptable alternative detail for roughening existing concrete surfaces, against which new concrete will be placed.
Method 2 yieldlines may be successfully used for uniformly loaded slab. Shear friction, horizontal shear transfer, and composite. When these cracks form, it is known that shear forces can be transferred across the crack primarily in two ways, that is dowel action and shear friction. Eurocode 2 introduces the strut inclination method for shear capacity checks. Here is my understanding of the shear friction design method. This video explains a graphical approach to the aci 318 method to design for shear for reinforced concrete beams. Chiaia department of structural engineering, politecnico di torino torino, italy abstract concretetoconcrete friction contributes in many cases to the stability of a structure. For slabs, footings, shallow beams, and all other members that are generally. Twodirection cracking shearfriction membrane model for finite elment analysis of reinforced concrete.
Effect of flexural and shear reinforcement on the punching behavior of reinforced concrete flat slabs. Also, design charts from the portland cement association pca are included to provide an additional method for determiningchecking required slab thickness for flexure. A trussmodelbased design procedure is developed for transversely reinforced labs, and its application is illustrated for the case of a large transfer plate in a highrise building. Comparison of design methods for composite slabs using small. Aci 360r06, design of slabs onground, presents the designer with four basic design options. Jan 28, 2019 in this aspect we need to check for any reinforcement needed in between the construction joint to resist the shear transfer across the slab plane and any potential cracks that may occur.
Ae net effective slab bearing area aps area of prestressed reinforcement avf area of shear friction reinforcement b width of compression face bw net web width of hollow core slab c confinement factor c compressive force c seismic factor dependent on site and structure fundamental period c factor for calculating steel relaxation. Simplified shear design of structural concrete members appendixes prepared for. The intersection of shear reinforcement and cracks can be anywhere over the. Notation a crosssectional area a depth of equivalent compression stress block a. Why is shear reinforcement not provided in slabs and. For the highstrength frictional bolt shear connectors, the shear resistance is provided by the friction between steel and concrete without any bonding, so the friction coefficient of the interface plays a key role in the structural design. Detailing rules for particular situations i i informative. Aug 04, 2017 main purpose of shear reinforcement is to prevent diagonal crack. Three of the methods which are using smallscale shear tests are presented and compared in this. In this aspect we need to check for any reinforcement needed in between the construction joint to resist the shear transfer across the slab plane and any potential cracks that may occur. Twodirection cracking shearfriction membrane model for. Two separate shear friction approaches have been developed previously where these separate approaches either quantify the shear transfer capacity for a given crack displacement, normal stress and crack separation walraven approach or quantify the maximum shear. Nevertheless, this approach has several shortcomings, which have been.
Aci 360, design of slabsongrade, refers to this as a type b slab. The angle of the concrete strut varies, depending on the shear force applied see figure below. The interface between concrete layers with different ages in the given examples must assure enough shear strength as a main requirement to resist the applied actions on the structure. Shearfriction design method for reinforced concrete. Coefficient for calculation of cracked section moment of inertia shear modulus. Grdslab concrete slab on grade analysis excel spreadsheet. Aci 360, design of slabs ongrade, refers to this as a type b slab. What is the cause of shear cracks formation in concrete.
Shear friction or aggregate interlock behaviour across sliding planes in concrete is now a wellestablished area of research. Shear performance of optimizedsection precast slab with. Punching shear retrofit method using shear bolts for reinforced. Similarities between punching and shear strength of steel.
Shear design example university of wisconsinplatteville. Full structurally continuity is assumed in the design at a construction joint with the reinforcement is fully continuous across the joint. With some limitations, reinforcement for slabs can be sized using the subgrade drag theory in order to increase the spacing of control or construction joints. Contractor how to write a construction method statement from scratch design. Shear crack in concrete beam concrete design eurocode. Refer to aci 223 for procedures for the design and construction of shrinkagecompensating concrete slabs onground.
This paper presents an overview about the shearfriction concept, design. All the slabs were supported along their perimeter and tested by pushing down on the center of. Punching shear does notuse the variable strut inclination method. The beams are subjected to bending moments and shear forces when it is loaded. Concrete slab on grade analysis the engineering community. Shear forces are carried across concretetoconcrete interfaces through three mechanisms including. The failure load predictions of this model are compared to over 100 tests on slabs found in the literature and to three tests recently conducted at the university of calgary. Given that bridge deck deterioration occurs due to the formation of cracks on the top surface, a costeffective yet highly durable composite bridge deck could be. Required area of reinforcement for shear friction according to cl. Twoway joist waffle slab design approach and methodology twoway joist slab often called twoway ribbed slab or waffle slab is an economical floor system when the spans are long andor loads are high. Comprehensive design example for prestressed concrete psc girder superstructure bridge design step 5 design of superstructure design step 5. Design methods for composite slabs still require fullscale bending tests which are expensive and space demanding.
Experimental study of friction resistance between steel and. The result is a lightly reinforced slab designed to offset the effects of temperature and shrinkage of the concrete. In fact, the shear friction stresses almost linearly increase to a certain. Main purpose of shear reinforcement is to prevent diagonal crack. Comprehensive design example for prestressed concrete psc. Comparison of design methods for composite slabs using. Its common to find slab sections leading into and out of perfect cracks in places like yosemite and lumpy ridge, colorado. In slab and foundation, shear stress is generally kept below the allowable shear stress or shear strength of concrete. The punching shear strength calculation method is based on the previous formulation, with some. Since we are casting the slab at different times, shear transfer and a potential crack may occur and thus shear friction check should be performed. Examination of shear friction design provisions scholars mine.
Strains in flexural rebars in the slabs, crack widths, lateral loads. However, shear forces will develop between the slabs. The shear friction method is used in the design of precast concrete structural connections for estimating the shear capacity of interfaces between precast members and castinplace concrete and for calculating the residual shear capac ity of cross sections which are weakened by cracking. How to seal or repair cracks in concrete walls, floors or. Design provisions applicable when shear is transferred across a specific plane are set out in aci 31899, section 11. This mechanism occurs as a consequence of the crack. Similarities between punching and shear strength of steel fiber reinforced concrete sfrc slabs and beams 2. Simplified shear design of structural concrete members. The slab must then be proportioned on the basis of the most adverse combination of all of the stresses that are likely to occur, not just those resulting from patch or point loads. This assumption is in keeping with the application of shear friction in the design of connec. Loads were applied until failure while cracks were marked at each load step of 50 kn, 75 kn, and 100 kn. Cracks in concrete beams due to increase in shear stress appears near the support such as wall or column.
Effect of point loads on reinforced concrete slabs without transverse reinforcement r. Effect of point loads on reinforced concrete slabs without. Pdf design of slabs using shear friction researchgate. The dowel action of longitudinal reinforcement and the uncracked compression zone contribute to the prevention of excessive opening of the inclined shear cracks, and are included in the shear friction mechanism. Dec 18, 2015 in an odd way, friction slabs are like wide cracks. Investigation of suitable shear friction interface between. Pdf the shear friction model for calculating the punching shear.
These cracks are also called as shear crack and are inclined at 45 degrees with the horizontal. Reinforced concrete buildings series design booklet rcb2. Testing and modelling 319 dritan topuzi, maria anna polak, sriram narasimhan a new method for postinstalled punching shear reinforcement 337 rupert walkner, mathias spiegl, jurgen feix punching failure of slabcolumn connections reinforced with headed shear studs 353. Twoway joist waffle slab design approach and methodology. Concrete shear friction interface behavior oregon state university. Predicting shear type crack initiation and growth in. Theyre characterized by a low angle between roughly 65 and 80 and a dearth of holds think. This method makes use of the shear friction provisions of aci 318 with the friction coefficient, being equal to 1. However, with the relatively low percentage of steel provided by this method, it is recommended that only. The design of suspended floors should conform to requirements of aci 318 and aci 421. In this method the shear is resisted by concrete struts acting in compression and shear reinforcement acting in tension.
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