Slab Shear Research Articles

Experimental Study of Interior Slab-Column Connections Subjected to Vertical Shear and Cyclic Moment Transfer

An experimental investigation was conducted to study the seismic behavior of slabcolumn connections under vertical shear and cyclic lateral load. Test variables include gravity shear ratio (V /V0 g ) and flexural reinforcement ratio (ρ ) of slab within an effective slab width between lines that are one and one-half slab thickness ( c 3h 2 + ). The strength and ductility of the test specimens were evaluated in accordance with gravity shear ratios and slab reinforcement ratios. The shear strength of the test slabs was compared with the predictions by ACI 318-05.

Dry snow slab shear fracture speeds

Dry snow slab avalanches release by propagating shear fractures within thin weak layers underneath thicker, stronger planar slabs. In this paper, measured shear fracture speeds from small scale snow slabs are compared with theoretical estimates compatible with dynamic fracture mechanics. Given the important physical quantities including density and elastic shear modulus, it is concluded that estimated snow slab shear fracture speeds scale with the shear wave speed similar to estimates in other geophysical applications including shear fractures from earthquakes and in engineering materials. However, the constant of proportionality is much lower than for alpine snow than for earthquakes and engineering materials. The lower constant of proportionality may indicate the possibility of important energy dissipation mechanisms in snow avalanche fracture propagation.

Interplay of basal shear fracture and slab rupture in slab avalanche release

Dry snow avalanches release by the failure of a weak layer. Ideas from fracture mechanics have been used to study this problem. However in all but the simplest cases the problem is not analytically solvable. A computer model which allows for the spatial variability of snowpack properties and for stress redistribution between weak and strong regions has previously been designed to assess the influence of various parameters in a qualitative and semi-quantitative manner. In the present study we improve this model by including inertial effects and allowing for mode-I and II rupture of the slab (formation of crown-, side- and stauchwalls). The failure stress of a slope is investigated and the result is found to be little affected by slab rupture, indicating that slope instability is predominantly governed by basal shear failure. We then study the effect of localized perturbations in the snowpack: pre-formed ruptures in the slab such as ski tracks are found to have little effect on failure stress; static objects such as trees and rocks may stabilize the snowpack if their spacing is not much larger than the correlation length of strength variations. The model is finally used to investigate the distribution of avalanche sizes and shapes. Under certain circumstances we find power-law distributions, as observed in nature.

CFRP Strengthening for Punching Shear of Interior Slab–Column Connections

This paper presents the results of an experimental investigation studying the effect of retrofitting interior slab–column connections against punching shear failure with externally bonded carbon fiber reinforced polymer (CFRP) strips. Six full-scale, 2000 mm-square×150-mm-thick slab specimens were constructed. The effect of varying the CFRP strengthening amount and configuration on the load-carrying capacity of the slab specimens was investigated. Specimens were supported along their edges and tested to failure. Strengthened slabs showed an increase in stiffness between 29 and 60% and in punching capacity between 6 and 16% with respect to the control unstrengthened slab. An analytical model was refined to predict the punching shear capacity of the specimens strengthened with CFRP strips. The model takes into account both the configuration and amount of CFRP strips. The proposed model shows good agreement with the experimental results.

Discussion of “Punching Shear Strengthening of Reinforced Concrete Flat Plates Using Carbon Fiber Reinforced Polymers” by Baris Binici and Oguzhan Bayrak

The discussers would like to extend their appreciation to the authors for presenting their work on the use of FRP for strengthening two-way slabs in shear. This discussion is written to bring to notice the work that was carried out on this topic at the University of Toronto between 1999 and 2002 Sissakis 2000, 2002 and has not been referred to in the paper. In a pilot test series, three slab specimens retrofitted with CFRP were tested and compared with a control specimen Sissakis 2000 in an effort to validate the concept of stitching the slabs with FRP to enhance their punching shear capacity. All the slab specimens were 150

Influence of High-Strength Concrete on Punching Shear in Slabs

Influence of High-Strength Concrete on Punching Shear in Slabs

Discussion of “Ultimate Strength of Ribbed Slab Composite Beams with Web Openings” by J. W. Park, C. H. Kim, and S. C. Yang

This article comments on earlier research on composite beams with web openings (Park, Kim, Yang, 2003). The beams studied have ribbed slabs with the ribs oriented transversely. The effects of slab width and moment-shear ratio on failure mode and strength were studied and the authors found that the failure mode of concrete slabs depends on the slab width. Strength predictions of a proposed model were also compared with test results and predictions of other strength models. In this commentary, Cho focuses on the truss analogy and discusses several aspects adopted by the authors in the formulation of the shear strength equations at web holes of composite beams against the common knowledge of structural mechanics. Cho makes four points: the authors misunderstood the truss analogy proposed by Cho and Redwood (1992); in the authors' study, the full slab width was assumed to be capable of carrying the vertical shear forces, even though this is not an ordinary understanding of the slab shear behavior; comparisons and evaluations should also include the predictions by the Redwood group methods other than the truss analogy; and the truss analogy predicts better narrow slab beams, rather than wide slab beams.

Closure to “Ultimate Strength of Ribbed Slab Composite Beams with Web Openings” by J. W. Park, C. H. Kim, and S. C. Yang

In this brief article, Park, Kim and Yang reply to a commentary (Cho, 2005) on their research on composite beams with web openings. The beams studied have ribbed slabs with the ribs oriented transversely. The effects of slab width and moment-shear ratio on failure mode and strength were studied and the authors found that the failure mode of concrete slabs depends on the slab width. In the commentary article, Cho made four points: the authors misunderstood the truss analogy proposed by Cho and Redwood (1992); in the authors' study, the full slab width was assumed to be capable of carrying the vertical shear forces, even though this is not an ordinary understanding of the slab shear behavior; comparisons and evaluations should also include the predictions by the Redwood group methods other than the truss analogy; and the truss analogy predicts better narrow slab beams, rather than wide slab beams. The authors reply briefly to each of these points: the authors understand that the truss analogy considers the diagonal tension failure of the ribbed slab and the pullout failure of the studs interactively; the effective width of concrete slabs of composite beams was developed based on flexural behavior; in truss analogy, the resistance of the top steel tee was formulated based on the assumption of full composite action between the ribbed slab and the top steel tee; and the authors used beams with wide slabs in their tests because most beams had narrow slabs in the previous tests. The authors conclude by agreeing with the commentary author that more studies are needed for better understanding of the behavior of the studs at the bearing and anchorage zones, which are very important in the development of slab shear carrying capacity.

Dynamic Responses of Flat Plate Systems with Shear Reinforcement

Earthquake-resistant designs often use a lateral-force resisting system to resist the seismic forces and a nonparticipating system to support vertical loads. Use of flat plate floor systems consisting of a conventional or post-tensioned reinforced concrete slab-column system incorporating shear reinforcement within the slab-column connection region has become increasingly popular as a lateral-force resisting system. There is little information available to assess the dynamic responses of such systems, particularly for post-tensioned systems. This article reports on a study that consisted of shaketable tests of a conventional reinforced-concrete slab-column frame (RC specimen) and a post-tensioned slab-column frame (PT specimen). Lateral drift ratios of approximately 3 and 4% were achieved during testing for the RC and PT system frames, respectively, with relatively little loss of lateral load capacity. The damage observed at the RC connections was more significant and more widely distributed than those observed for the PT specimen. The test results indicate that use of slab shear reinforcement substantially reduces the extent of damage and prevents the dropping of the slab observed in reinforced concrete connections where shear reinforcement is not provided. The authors note that this may be an important factor in post-earthquake repairs.

Partial melting of slab window margins: genesis of adakitic and non-adakitic magmas

When a mid-ocean spreading ridge subducts, it typically splits apart at depth to form two tapered slab edges separated by asthenospheric mantle within a slab window. We examine the fate of the slab edges using simplified slab window geometries, specific thermal parameters, and assumptions regarding shear stress and slab hydration. Six fundamental zones of slab anatexis are identified and classified according to expected melt and restite compositions. Non-adakitic melts of granodioritic to tonalitic composition are generated along the plate edges at depths of 5–65 km, whereas adakitic melts form proximal to the edges at depths of 25–90 km. As anatexis proceeds, the subducted crust is converted to a migmatite of slab melt and eclogitic restite. Much of the migmatite may shear away from the slab and become incorporated into the mantle. The melts will rise and leave behind fragments of restite within mantle peridotite. If the peridotite is part of the overriding plate, then the restite fragments may become long-term residents of the continental lithospheric mantle. However, if the restite becomes entrained in the asthenosphere, it may undergo upwelling and melting, or flow away as ductile streaks to become long-term mantle heterogeneities. Slab windows are thereby identified as important sites for slab melting and geochemical replenishment of the mantle.

Repair of Slab–Column Connections Using Epoxy and Carbon Fiber Reinforced Polymer

Repair, strengthening, and retrofit of reinforced and prestressed concrete members have become increasingly important issues as the World's infrastructure deteriorates with time. Buildings and bridges are often in need of repair or strengthening to accommodate larger live loads as traffic and building occupancies change. In addition, inadequate design and detailing for seismic and other severe natural events has resulted in considerable structural damage and loss of life, particularly in reinforced concrete buildings. Numerous buildings and bridges suffer damage during such events and need to be repaired. The use of carbon fiber reinforced polymer (CFRP) composite fabric bonded to the surface of concrete members is comparatively simple, quick, and virtually unnoticeable after installation. The use of composites has become routine for increasing both the flexural and shear capacities of reinforced and prestressed concrete beams. Earthquake retrofit of bridge and building structures has relied increasingly on composite wrapping of columns, beams, and joints to provide confinement and increase ductility. This article presents the results of cyclic testing of three large-scale reinforced concrete slab-column connections. Each of the specimens was a half-scale model of an interior slab-column connection common to flat-slab buildings. The specimens were reinforced according to ACI-318 code requirements and included slab shear reinforcement. While supporting a slab gravity load equivalent to dead load plus 30 percent of the live load, the specimens were subjected to an increasing cyclic lateral loading protocol up to 5 percent lateral drift. The specimens were subjected to the same loading protocol after they were repaired with epoxy crack sealers and CFRP sheet on the surfaces of the slab. Repair with epoxy and CFRP on the top surface of the slab was able to restore both initial stiffness and ultimate strength of the original specimen.

Variations in snow strength and stability on uniform slopes

This research investigated whether single snowpits could reliably represent snowpack strength and stability conditions throughout apparently ‘uniform’ slopes. Seven slopes were selected by experienced avalanche forecasters, three each in the Bridger and Madison Ranges of Southwest Montana (USA), and one in the Columbia Mountains near Rogers Pass, British Columbia (Canada). Teams performed 10 quantified loaded column tests in each of five snowpits within a 900 m 2 sampling site on each ‘uniform’ slope, measuring shear strength in a single weak layer. Collection of slab shear stress data enabled the calculation of a stability index, S QLCT. Altogether, eleven trials were performed during 2000/2001 and 2001/2002, testing several weak layer types exhibiting a wide range of strengths. Weak layer strength and slab stress conditions varied widely across the sampling sites, with coefficients of variation in weak layer shear strength ranging from 10% to 50%, coefficients of variation in shear stress from 2% to 48%, and stability indices ranging from 1.8 to 5.7. Of the 54 snowpits completed, 10 pits were empirically rejected as unrepresentative of the stability index at their sampling sites. Of the remaining 44 statistically analyzed pits, 33 pits were statistically representative of their site-wide stability index, and the other 11 pits were found statistically unrepresentative of their site. All five snowpits at a site were statistically representative of their site-wide stability index in three of the eleven trials. The frequent inability of single pits to reliably represent stability on those eleven 900 m 2 sampling sites, located on apparently ‘uniform’ slopes, highlights the importance of improving our understanding of the processes affecting the variability of snowpack stability on any given day and the uncertainties associated with ‘point’ stability data.

Standardized composite slab systems for building constructions

The use of steel deck slabs has proved over the years to be one of the most economic structural building systems. Despite this affirmative, mainly for various historic reasons beyond the scope of the present paper, the Brazilian construction industry has not fully exploited the considerable potential of this structural solution. The first part of this paper presents and discusses the analytical and experimental results of a wide-rib composite steel deck developed at the Structural and Materials Laboratory of PUC-Rio. The steel decks results are centred on the steel/concrete longitudinal shear ultimate limit state, load vs. slab strain curve responses and on steel deck design and detailing recommendations. The final part of the paper focuses on an innovative composite slab system made of a steel deck and a styrofoam plate, side by side, filled with reinforced concrete also developed at PUC-Rio. A parametric analysis of the steel deck profile was first performed. When an optimum steel deck profile was established, the investigation proceeded with a series of full-scale-experiments to access the system’s ultimate and serviceability limit states. The experiments also comprised the study of the concrete vs. steel deck interlocking or mechanical shear transfer devices.

Slablike ion temperature gradientdriven mode in reversed shear tokamaks

The ion temperature gradient driven (ITG) mode in reversedshear tokamaks is analysed using a gyrokinetic toroidal particlecode. It is found that the ITG mode in the reversed shearconfiguration shows a coupled mode structure between the slaband toroidal ITG modes. Especially in the qmin-region, aslablike feature due to the reversed shear slab ITG mode(Idomura Y, Tokuda S and Wakatani M 1999 Phys. Plasmas6 4658) becomesstrong. This coupled eigenmode structure is changed from a slabmode to a toroidal mode depending on ηi = Ln/Lti andLti. Results show that in reversed shear tokamaks the ITGmode is determined from a competition between the slab andtoroidal ITG modes.

Punching shear of slabs: crack size and size effects

Fictitious crack model assumptions and equilibrium equations were used to develop a numerical model in order to predict the punching load and the deformations of reinforced concrete slabs. Concrete strength, aggregate type, reinforcement ratio as well as the fracture strength properties were taken into account in developing the new model. In spite of the low tensile strength of concrete, it has considerable fracture energy, therefore the fracture process zone in front of a growing crack can contribute to the flexural concrete strength. The proposed model adopted the fictitious crack model principles. The three equilibrium equations were used on a radial segment of the slab and the effect of crack size and size effect were incorporated in the formulation. The model results were compared with the experimental results and currently available shear design formulae to investigate the effect of the fracture properties on the predicted punching load. The model provided consistent and improved results compared to the existing codes.

Punching shear of slabs: crack size and size effects

Fictitious crack model assumptions and equilibrium equations were used to develop a numerical model in order to predict the punching load and the deformations of reinforced concrete slabs. Concrete strength, aggregate type, reinforcement ratio as well as the fracture strength properties were taken into account in developing the new model. In spite of the low tensile strength of concrete, it has considerable fracture energy, therefore the fracture process zone in front of a growing crack can contribute to the flexural concrete strength. The proposed model adopted the fictitious crack model principles. The three equilibrium equations were used on a radial segment of the slab and the effect of crack size and size effect were incorporated in the formulation. The model results were compared with the experimental results and currently available shear design formulae to investigate the effect of the fracture properties on the predicted punching load. The model provided consistent and improved results compared to the existing codes.

Reliability analysis of direct shear and flexural failure modes of RC slabs under explosive loading

Two loosely coupled SDOF systems are used to model the flexural and direct shear responses of one-way reinforced concrete slabs subjected to explosive loading. Incorporating the effects of random variations of the structural and blast loading properties, as well as the strain rate effect caused by rapid load application, failure probabilities of the two failure modes are analyzed. The model is capable of predicting the failure probability of the slab with random material and geometrical parameters and subjected to random blast loading. Considering the random variations of structural properties and blast loading, the failure probabilities of one-way RC slab designed according to BS 8110 (Stuctural use of concrete, parts 1 and 2 (1985)) are calculated. The effect of span length of the slab on its failure probability to blast loading is also investigated. Based on numerical results, a semi analytical boundary that separates the slab's flexural and shear failure modes is derived as a function of peak reflected pressure and duration of blasting wave.

EVALUATION OF TRANSVERSAL FORCE INFLUENCE IN LAYERS OF REINFORCED CONCRETE WITH SURVIVAL MOULDS/SLUOKSNIUOTŲJŲ GELŽBETONINIŲ KONSTRUKCIJŲ SU LIKTINIAIS KLOJINIAIS STIPRUMO SKERSINIŲ JĖGŲ ATŽVILGIU ĮVERTINIMAS

Bending composite reinforced concrete slabs have horizontal concreting joints and this is their main difference from monolithic constructions. During initial bending stage of loaded composition slab compression and shear stresses appear, therefore they should be treated as monolithic ones. Nevertheless, with the augmentation of deflection the influence of transversal forces increases. Depending on the distance between concentrated force and support force, corresponding shear stresses are caused in the contact zone of the layered slab. Vector trajectories of those stresses correspond to the curve of compression layers in imaginary internal arches. The distance between the support and shear force, and the number of repetitive static heights (a=1…2…5d) of the slab have been evaluated, some cases have been observed and noted when forces influencing the detachment of monolithic and precast slab are the greatest ones. It has been noticed that the augmentation of distance between the support and vertical force causes the decrease of leaning angle of successive shear stresses in reinforcement bars.

Behavior of Composite Bridge Decks with Alternative Shear Connectors

An experimental study of composite bridge decks with alternative shear connectors has been performed. The alternative shear connector consists of concrete filled holes located in the webs of grid main bars and friction along the web embedded in the slab, which enables shear transfer between the concrete slab and steel grid. Results of static and fatigue tests on full-scale prototype decks indicated that composite action between the concrete slab and steel grid is maintained well above the service load range even after fatigue loading, the eventual loss of composite action at overload is gradual, failure was controlled by punching shear of the concrete slab and was unaffected by the shear connectors, and no significant change in behavior was observed due to fatigue loading. Further, the measured stress range at the shear connection location would not control the fatigue behavior of the deck in positive bending, and no fatigue cracking of the steel grid was observed in negative bending.

EVALUATION OF TRANSVERSAL FORCE INFLUENCE IN LAYERS OF REINFORCED CONCRETE WITH SURVIVAL MOULDS

Summary Bending composite reinforced concrete slabs have horizontal concreting joints and this is their main difference from monolithic constructions. During initial bending stage of loaded composition slab compression and shear stresses appear, therefore they should be treated as monolithic ones. Nevertheless, with the augmentation of deflection the influence of transversal forces increases. Depending on the distance between concentrated force and support force, corresponding shear stresses are caused in the contact zone of the layered slab. Vector trajectories of those stresses correspond to the curve of compression layers in imaginary internal arches. The distance between the support and shear force, and the number of repetitive static heights (a=1…2…5d) of the slab have been evaluated, some cases have been observed and noted when forces influencing the detachment of monolithic and precast slab are the greatest ones. It has been noticed that the augmentation of distance between the support and vertical...