Shear Transfer Capacity Research Articles

Experimental Assessment of Shear Transfer Capacity of GFRP Reinforcement Using the Push-Off Test

Experimental Assessment of Shear Transfer Capacity of GFRP Reinforcement Using the Push-Off Test

Experimental exploration of digitally fabricated connections for structural concrete

Connections are a persistent challenge for traditional reinforced concrete construction and even more for digital fabrication with concrete (DFC). The latter, on the other hand, opens up new possibilities for producing connections with tailored geometries and surface roughness. Based on the findings of an exploratory, experimental campaign, this paper discusses the design, fabrication and structural testing of digitally fabricated joints using the DFC technology Eggshell to 3D print the formwork for joint surfaces in an additive manufacturing process. The programme includes (i) unreinforced and reinforced construction joints whose joint surface texture was varied to control the roughness and (ii) digitally fabricated dry keyed joints with varying geometry. Both, the construction joints as well as the dry keyed joints, were produced using set-on-demand concrete with a relatively small maximum aggregate size of 0 to 4 mm – i.e., strictly speaking, mortar rather than concrete – as typically applied in DFC. The experimental campaign included thorough instrumentation: a 3D scan of the joint surface before testing and high-resolution digital image correlation (DIC) combined with distributed fibre optical sensing (DFOS) during testing. The deviations from the targeted surface geometry, determined with 3D scans, were below 2 mm, with a standard deviation between 0.4 mm and 0.7 mm for keyed joints. The high-resolution DIC allowed measuring the compressive strains locally at (i) the corrugation of unreinforced or reinforced construction joints and (ii) the key chamfer of dry joints and, hence, studying strain variations over the height of the joints and the efficiency of different keys with varying dimensions. Finally, the shear transfer capacity, evaluated in a push-off test setup, showed that all digitally fabricated joints met or even outperformed the requirements defined in pertinent design codes despite the smaller aggregate size.

Flexural behaviour of full-scale precast recycled concrete sandwich panels with BFRP connectors

In prefabricated buildings, the exterior walls play an important role in the mechanical stability and thermal insulation of the structures. In this study, a new type of precast sandwich wall panel was developed by using recycled aggregate (RA) and basalt-fibre reinforced polymer (BFRP) shear connectors. A series of double shear tests were designed and conducted to evaluate the effect of the insertion angle of the BFRP connectors on their shear performance. Based on the test results, six full-scale precast sandwich panels, including two conventional panels with glass-fibre reinforced polymer (GFRP) needle connectors, were cast and tested under four-point bending loads. The tested parameters included the distribution of BFRP connectors and the RA content. In addition, the flexural performance of the new sandwich wall panel was compared with that of conventional non-composite panels. The results showed that the proposed precast sandwich wall panels exhibited better load bearing capacity and ductility. Smaller insertion angles of the BFRP shear connectors led to greater stiffness and better shear transfer capacity because they closely connected two concrete wythes in the sandwich panels. The new recycled concrete sandwich panel is also a more environmentally friendly alternative to conventional panels for use in the exterior walls of prefabricated buildings.

Effect of elevated temperature on interfacial shear transfer capacity of self-compacting concrete

Interfacial shear stress transfer may occur in structural elements across concrete or between concrete and steel. The fundamental contributing parameters which improve the shear capacities are aggregate grading, compressive strength of concrete, type and area of the interfacial zone, and interfacial reinforcement pattern. During the event of a fire, these parameters are severely affected and mainly depend on the exposure level of the temperature and its duration. In the present investigation, the effect of elevated temperature on the interfacial Shear Transfer Capacity (STC) of Self-Compacting Concrete (SCC) was evaluated using shear (push-off) specimens. SCC was developed using Fly Ash (FA) and Ground Granulated Blast Furnace Slag (GGBFS) as Supplementary Cementitious Material (SCM). The study emphasises the proper understanding of degradation in shear strength of SCC exposed to elevated temperatures. Expanded Perlite Aggregate (EPA) is utilised as a partial replacement for fine aggregate. Also, a thermal protective coating is developed with Cement Perlite Plaster (CPP) for improving the performance of SCC. The European Federation of National Associations Representing for Concrete (EFNARC) guidelines were followed to ensure the workability of the developed SCC mix. Specimens were exposed to 30, 60, 90, and 120 min of heating durations following the International Organization for Standardization 834 (ISO 834) fire rating curve and tested to examine residual compressive strength, mass loss, STC after the natural air cooling process. The SCC specimens with EPA content have exhibited higher residual compressive strength and STC. All the protected SCC specimens coated with the CPP mixture contributed to retaining the original shear capacity by resisting the temperature. An empirical relationship was proposed to predict the residual STC of SCC after exposure to elevated temperature.

Shear Transfer Capacity of Angle Connectors in U-Shaped Composite Girder: Experimental and Numerical Study

AbstractThis research investigates the shear resistance of steel angle connectors welded to the webs of U-shaped steel–concrete composite girders. First, push-out tests were conducted on the experi...

Shear friction response of lightweight concrete using bottom ash aggregates and air foams

ABSTRACT This study aimed to estimate the shear friction response of lightweight concrete made using bottom ash aggregates and air foam (LWC-BF) and determine the design parameters including shear transfer capacity, cohesion, and friction angle of such concrete at different interface conditions. The shear friction parameters were straightforwardly formulated from the extension version of the integrated mechanical models derived in our previous study based on the upper bound theorem of concrete plasticity. Eighteen non-reinforced push-off specimens (nine monolithic interfaces and nine interfaces with smooth construction joints) were tested under direct shear and the additional compressive stresses normally applied to the interfaces. The test parameters considered in different interface conditions were the compressive strength of concrete and the magnitude of compressive stresses. The experimental and analytical results showed that the addition of air foam slightly decreases the angle of friction of monolithic interfaces but insignificantly affects that of smooth construction joints. Thus, the effect of air foam added up to 20% by volume on the cohesion and friction angle of concrete was marginal. Therefore, the proposed shear friction parameters are promising to reasonably assess the shear friction strength of LWC-BF interfaces.

Innovative sandwich panels made of wood bio-concrete and sisal fiber reinforced cement composites

This paper presents the results of the development of innovative sandwich panels made by combining wood bio-concretes and long sisal fibers reinforced composites. An experimental study of the wood bio-concretes (WBC) was carried out by producing several cement-to-wood ratios (0.5, 1, 2, 2.5 and 3) in order to allow the development of panels of different density. Before producing the WBC, the influence of hot water washings of the wood shavings on the cement hydration was investigated. The effect of the cement-to-wood ratios on the density, thermal conductivity, compressive strength and elastic modulus of the WBC were also investigated. Lightweight bio-concretes were obtained with densities ranging between 700 and 1250 kg/m3 and compressive strengths within 0.44–16 MPa, after 28 days cure. The lighter and denser bio-concretes were used as cores in sandwich system with faces made of cement composites reinforced with 6% of long sisal fibers distributed in three layers. The results of compressive and flexural tests performed on the sandwich specimens revealed that the WBC2.5 were more effective in terms of promoting compressive strength, shear transfer capacity and allowing a pure bending failure, while WBC0.5 promoted core shear cracks and the inferior face crush.

Cohesive stress transfer and shear capacity enhancements in hybrid steel and macro-polypropylene fiber reinforced concrete

The link between the fracture behavior and shear capacity of fiber reinforced concrete composite is investigated. The synergy between hooked steel fibers and continuously embossed macro-synthetic fibers in providing improved fracture and post-cracking shear resistance is experimentally evaluated. The fracture responses of plain concrete, concrete with discrete hooked ended steel fibers at two volume fractions (0.5% and 0.75%) and concrete with hybrid blend of steel and macro-synthetic polypropylene fiber (0.3% steel and 0.2% macro-synthetic) are evaluated. The cohesive stress-crack separation relationships of the different composites are obtained from the fracture test responses of notched beams in flexure. There is an improvement in the early fracture response of concrete containing hybrid fiber blend when compared with steel fiber reinforcement, which is due to the higher crack closing stresses produced at small crack openings immediately after cracking. The load carrying capacity in shear obtained from the concrete composite with hybrid blend is significantly higher than the concrete with steel fiber reinforcement at identical fiber volume fraction and is identical to the response obtained from steel fiber composite with a higher volume fraction of fibers. From the full-field displacements obtained using digital image correlation (DIC), the in-situ dilatant behavior of the shear crack is established. Influence of the high early crack opening resistance seen in blends provides better crack control for the shear crack and leads to a significant improvement in the shear resistance derived from stress transfer across the rough crack faces. A mechanistic model for predicting the shear capacity of reinforced fiber composite beams, which considers the crack profile information of the shear crack obtained from DIC and the cohesive stress-crack separation relationship obtained from the fracture tests is presented. The model predicts an increase in the contact stresses on the crack faces in the fiber-reinforced composite with the inclusion of fibers, which increases the shear transfer capacity of the crack.

Shear transfer of concrete strengthened using bolted steel plates

Abstract Reinforced concrete (RC) with steel bars set across a shear plane was strengthened using bolted steel plates to transfer shear force. Nineteen Z-series specimens were tested to investigate shear transfer behavior with bar ratios varying from 0.46 to 1.2% and steel plate ratios ranging from 3.57 to 10.42%. Nine D- and B-series specimens were tested to assist to understand shear transfer mechanism by means of a shear component model. In this model, the shear transfer resistance was provided by different sources, i.e., friction, aggregate interlock, adhesion, shear dilation, dowel action, and steel plate resistance. Results found that the ultimate shear transfer capacities increased by 15–57% with a ductile failure mode. The increase of the shear transfer resistance was primarily due to two factors: 1) the increase of the shear components of friction, aggregate interlock, and shear dilation caused by the additional transverse clamping force provided by the steel plates and 2) steel plate resistance. Expressions were developed to predict the ultimate resistance of shear transfer of strengthened RC with approximate accuracy.

Experimental study on flexural behaviour of partially encased cold-formed steel composite beams using rebar as shear connector

This paper focuses on the composite action of two samples each consisting of two composite beams and a composite slab with bent up rebar as a shear connector. The specimens were knowingly adapted to have different shear transfer capacities along the interfaces with different geometries of the composite beams. By using the four-point bending tests of the two full-scale specimens, the authors experimentally evaluated the flexural behaviour of the partially encased composite beams. Therefore, this paper presents experimental works on the structural performance of composite beams consisting of cold-formed steel (CFS) section with self-compacting concrete (SCC) by means of the shear connection mechanism of the proposed using deformed reinforcement bar. “The results have shown that the theoretical value of flexural capacities designed agrees well enough with the experimental results. Based on the present beam tests results it was realised that the new composite system showed slightly higher results than predicted with ultimate moment ratios between 0.89-0.91% and 0.83-1.08% for the 250 mm and 150 mm beam respectively. According to the experimental bending test results, the composite section can reach the ultimate strength without compression buckling failure or local shear when the proposed shear connector was presented in the composite action. Analysis and design of composite beams are studied to validate the present test results.”

Shear transfer behavior at the circular tubed column-steel beam interface

This paper discusses the shear transfer behavior at the interface between circular tubed column and steel beam. Five beam-column connection specimens with crossing diaphragm were tested under monotonic loads, considering the key parameters of joint tube thickness, embedded diaphragm width, and crossing diaphragm thickness. Based on the experimental results, typical failure modes and load-displacement curves were obtained and discussed in details. A simplified finite element model was developed and validated with the experimental results. Parametric studies on the shear transfer capacity were carried out and analyzed. Lastly, practical formulas for estimating the shear transfer capacity are suggested.

Fully composite beams with U-shaped steel girders: Full-scale tests, computer simulations, and simplified analysis models

This paper focuses on the fully composite beam consisting of the U-shaped steel girder and angle connectors. Through the four-point bending tests of six full-scale specimens, the authors experimentally evaluated the flexural behavior of the fully composite beams. The specimens were intentionally varied to have different shear transfer capacities along the interfaces between the concrete slabs and the U-shaped girders and different geometries of the U-shaped girders. Test results show that all the specimens were fully composite and exhibited the favorable ductile flexural behavior. Computer models were then developed for the experimental specimens. It was found that the computer models were able to replicate the nonlinear behavior of the experimental specimens observed during the tests. Based on the computer models, parametric analyses were performed to investigate the influences of the residual stresses in the U-shaped girder, the strengths of construction materials, the geometries of the U-shaped girder and concrete slab on the strength of the fully composite beam. Beyond the computer models, simplified analysis models that are based on the assumed strain and stress diagrams and can be implemented through hand calculations were developed to capture the nonlinear moment-curvature responses of the composite beams. It is found that the results from the simplified analysis models agree well with the computer models. The simplified analysis models are thus recommended for future practice.

Design properties of insulated precast concrete sandwich panels with composite shear connectors

Researchers have developed various types of shear connectors to enhance shear transfer in insulated concrete sandwich panels. The shear transfer capacity of a precast concrete sandwich panel (PCSP) system that is composed of two precast reinforced concrete wythes separated by a layer of insulation wythe is influenced by the degree of composite behavior/action. This paper presents experimental results of push-out tests of concrete sandwich panels that use a grid type of glass fiber-reinforced polymer shear connector and then compares these results with previous research results that are based on corrugated shear connectors. A design equation (ICC-ES) was modified for this work to determine the shear strength of PCSPs with various configurations. For this study, 22 double-shear (push-out) specimens were fabricated and tested using two types of insulation materials, three insulation wythe thicknesses, and two grid spacings for the shear connectors as the variables. The test results were used to calculate toughness index and shear modulus values and to calibrate the modified ICC-ES equation. Increasing the thickness of the insulation wythe had a decreasing effect on the maximum shear flow and shear modulus of the PCSP system.

Unidirectional GFRP composite connections between precast concrete wall panels under simulated seismic loads

A method of connecting precast concrete walls with Glass Fiber Reinforced Polymer (GFRP) composite sheets is investigated. The method can be used either as a seismic retrofit of existing welded steel plate connections or in new construction. The specimens consisted of two precast concrete wall panels connected with either two or four layers of unidirectional GFRP composite sheets. Eight specimens were subjected to quasi-static cyclic loads to explore the effect of the following variables on the connection capacity: concrete surface preparation; application of surface pressure to the GFRP laminate; number and orientation of GFRP composite layers; and use of carbon fiber reinforced polymer (CFRP) spike anchors. The performance of the composite connection was acceptable in terms of lateral load, lateral displacement, and shear transfer capacity. Application of surface pressure during curing of the GFRP laminate and the use of CFRP spike anchors improved the lateral load and displacement capacity of the composite connection significantly. An empirical expression is proposed to determine the capacity of the composite connection.

Shear behavior of reinforced concrete basement walls with consecutive convexo-concave-shaped bars as shear reinforcement

ABSTRACTThis study examined the significance and shortcomings of the consecutive convexo-concave shaped shear reinforcement (CCSR) developed as an alternative for transverse crossties in basement walls. Three wall specimens prepared under a full scale were tested under constant axial load and out-of-plane lateral load. In the tests, the CCSR was classified into two types including S-type for the S-curve bending and B-type for approximately 90° bending. To investigate the shear transfer capacity of the CCSR, a mechanism model was driven on the basis of the upper-bound theorem of concrete plasticity. Test results revealed that the CCSR is more favorable to restrict the opening of the inclined cracks and enhancing the shear capacity of the basement wall when compared with the conventional crossties. Wall S (with S-type of CCSR) and Wall B (with B-type of CCSR) possessed 1.21 times and 1.12 times higher shear capacity, respectively, than wall C (with the conventional crossties). The wall S exhibited least rapid descending branch after the peak load, maintaining 80% of the peak load until the wall drift ratio reached 5.4%. The American Concrete Institute (ACI) 318-14 equations extremely underestimate the shear capacity of the basement wall, whereas the predictions obtained from the proposed mechanical model are in better agreement with the test results.

Shear transfer of concrete strengthened with externally bonded CFRP strips inclined to shear plane

Concrete with steel reinforcement across a shear plane was externally bonded using carbon fiber-reinforced polymer (CFRP) strips with different inclination angles to find optimal strengthening effect of shear resistance. Thirty-five Z-type specimens were tested and classified into two groups, i.e., the shear transfer group and shear component group, to investigate shear resistance and shear transfer behavior based on a component model. In this model, the shear resistance was contributed by six shear components, i.e., friction, aggregate interlock, adhesion, shear dilation, dowel action, and resistance parallel to the shear plane provided by CFRP strips. Results found that inclination angles of about 70 and 45° were optimal and associated with the maximum shear resistance for specimens with CFRP reinforcement ratios of 0.298% and 0.149%, respectively. Compared to the cases of CFRP strips perpendicular to the shear plane, additional percentage increases of the maximum shear resistance in a range of 8–23% were obtained in the cases using CFRP strips with optimal inclination angles. These extra benefits were mainly attributed to the increases in the friction and aggregate interlock, shear dilation, and resistance parallel to the shear plane provided by CFRP strips. A best-fitting expression was also proposed to predict the ultimate shear transfer capacities of strengthened reinforced concrete using CFRP strips with optimal inclination angles.

Shear transfer capacity of reinforced concrete exposed to fire

Shear transfer capacity of reinforced concrete elements is a function of concrete compressive strength and reinforcement yield strength. Exposure of concrete and steel to elevated temperature reduces their mechanical properties resulting in reduced shear transfer capacity of RC elements. The objective of present study is to find the effect of elevated temperature on shear transfer capacity of reinforced concrete. For this purpose pushoff specimens were casted using normal strength concrete. After curing, specimens were heated to 250°C and 500°C in an electric furnace. Cooled specimens were tested for shear transfer capacity in a universal testing machine. It was found that shear transfer capacity and stiffness (slope of load-slip curve) were reduced when the specimens were heated to 250°C and 500°C. Load level for the initiation of crack slip was found to be decreased as the temperature was increased. A simple analytical approach is also proposed to predict the shear transfer capacity of reinforced concrete after elevated temperature.

Direct Shear Behavior of Fiber Reinforced Concrete Elements

Improving the accuracy of load-deformation behavior, failure mode, and ultimate load capacity for reinforced concrete members subjected to in-plane loadings such as corbels, wall to foundation connections and panels need shear strength behavior to be included. Shear design in reinforced concrete structures depends on crack width, crack slippage and roughness of the surface of cracks.
 This paper illustrates results of an experimental investigation conducted to investigate the direct shear strength of fiber normal strength concrete (NSC) and reactive powder concrete (RPC). The tests were performed along a pre-selected shear plane in concrete members named push-off specimens. The effectiveness of concrete compressive strength, volume fraction of steel fiber, and shear reinforcement ratio on shear transfer capacity were considered in this study. Furthermore, failure modes, shear stress-slip behavior, and shear stress-crack width behavior were also presented in this study.
 Tests’ results showed that volume fraction of steel fiber and compressive strength of concrete in NSC and RPC play a major role in improving the shear strength of concrete. As expectedly, due to dowel action, the shear reinforcement is the predominant factor in resisting the shear stress. The shear failure of NSC and RPC has the sudden mode of failure (brittle failure) with the approximately linear behavior of shear stress-slip relationship till failure. Using RPC instead of NSC with the same amount of steel fibers in constructing the push-off specimen result in high shear strength. In NSC, shear strength influenced by the three major factors; crack surface friction, aggregate interlock and steel fiber content if present. Whereas, RPC has only steel fiber and cracks surface friction influencing the shear strength. Due to cementitious nature of RPC in comparisons with NSC, the RPC specimen shows greater cracks width.
 It is observed that the Mattock model gives very satisfactory predictions when applied to the present test results with a range of parametric variations; ranging from 0 % to 0.5 % in steel fibers content; from 0 % to 0.53 % in transverse reinforcement ratio; from 15 to 105 MPa in compressive strength of concrete. While it gives a poor prediction for a specimen with 1% steel fiber.

Mechanical Model for Shear Friction Capacity of Concrete at Construction Joints

This study examined the reliability and limitations of code equations for determining the shear friction strength of a concrete interface with construction joints. This was achieved by examining the code equations (ACI 318‐14, AASHTO, and fib 2010) and comparing the results predicted by equations with experimental data compiled from 207 push‐off specimens (133 rough and 74 smooth construction joints). The integrated mechanical model for the monolithic interface, derived from the upper‐bound theorem of concrete plasticity, was also modified to estimate the shear friction strength of the construction joints. The upper limit for shear friction strength was formulated from a concrete crushing failure limit on the strut‐and‐tie action along the interfacial plane, to avoid overestimating the shear transfer capacity of transverse reinforcement with a high clamping force. Code equations are highly conservative and dispersive in predicting the shear friction strength of rough construction joints and yield large scattering in the data for the ratios between the measured and predicted shear friction strengths. The predictions obtained using the proposed model agreed well with test results, indicating correlating trends with the test results for evaluating the effects of various parameters on the shear friction strength of rough construction joints. According to the proposed model, the values of cohesion and coefficient of friction for concrete could be determined as 0.11 and 0.64, respectively, for smooth construction joints and 0.27 and 0.95, respectively, for rough construction joints, where is the compressive strength of concrete.

08.02: Experimental research of multiple perfobond connectors for composite girders

ABSTRACTExtensive research has been carried out in recent years focusing on the behaviour of innovative connectors for steel and concrete composite girders. Those elements exhibit large resistance and adequate behaviour under different load types, and at the same time are easy to fabricate and to erect on site. Among these types, the Perfobond connector or Perfobond rib, consisting of a perforated steel plate welded to the steel beam flange, has been extensively studied by numerous authors, due to its particularly convenient efficiency, behaviour and ductility characteristics.Although many connector types have been studied in the past, few studies focused on the behaviour of groups of special connectors, a typical arrangement used in conventional headed stud connectors.This paper focuses on the behaviour of multiple Perfobond connectors placed side‐by‐side on a steel girder and immersed in the reinforced concrete slab. This quite innovative arrangement enhances the resistance from a single connector classic layout, but the proximity to other connectors may significantly change the behaviour of individual connectors that interact with each other.Fourteen push‐out tests on groups of Perfobond connectors were carried out at the Civil Engineering Department of the University of Coimbra, Portugal, while this paper reports and discuss the results.The investigated variables were: the number of connectors, ranging from one (the basic arrangement) to three; the spacing between connectors; the transverse reinforcement within the connector's holes; and the concrete strength. The results are presented and discussed concentrating on the connector's structural response for shear transfer capacity, ductility and collapse modes. A comparative assessment of these properties focusing on the number of connectors and its spacing is presented and discussed, aiming at establishing preliminary conclusions about the behaviour of Perfobond groups. In addition, a brief comparison of the experimental results with existing analytical models for Perfobond connectors is also presented to establish the most convenient model for this particular geometry. Finally, some adapted models referred in the literature to cope with Perfobond groups are applied to the tested geometries and the analytical and experimental tests are compared and discussed.