Load-slip Relationship Research Articles

CONNECTION BEHAVIOR IN COMPOSITE PROFILED STEEL SHEET WITH FERROCEMENT (PSSF) SYSTEM

This paper concerns with the behavior of the connections in the composite Profiled Steel Sheet with Ferrocement (PSSF) systems. The PSSF panels is a light weight composite panel consists of a profiled steel sheet (PSS) and ferrocement panel connected together by either mechanical fasteners or by epoxy adhesive resin. Ten push-out specimens were tested. The veriables were the strength of morter and the volume friaction of wire mesh for ferrocement panels, and types of connection between the two components. The ultimate load, the load slip relationship, and modes of failure were recorded. The results showed that the specimens connected by using* bolts of 10 mm diameter can sustain load greater by 64% than those connected by using bolts of 5 mm diameter. The ultimate load was found not to be inflenced** when the strength of ferrocement is increased from 35 MPa to 45 MPa. Also the effect of volume fraction of wire mesh was observed to enhance slightly the ultimate load when the layers of wire meshs is increased from 2 to 3 layers. For the specimens made by connecting the ferrocement components to the PSS by adhesive epoxy layer, a rigid connection was obtained and sudden separation occurred between the ferrocement component and steel sheet after local buckling of PSS.

Experimental and numerical study on static behavior of grouped large-headed studs embedded in UHPC

The static behavior of grouped large-headed studs (d = 30 mm) embedded in ultra-high performance concrete (UHPC) was investigated by conducting push-out tests and numerical analysis. In the push-out test, no splitting cracks were found in the UHPC slab, and the shank failure control the shear capacity, indicating the large-headed stud matches well with the mechanical properties of UHPC. Besides, it is found that the shear resistance of the stud embedded in UHPC is 11.4% higher than that embedded in normal strength concrete, indicating that the shear resistance was improved. Regarding the numerical analysis, the parametric study was conducted to investigate the influence of the concrete strength, aspect ratio of stud, stud diameter, and the spacing of stud in the direction of shear force on the shear performance of the large-headed stud. It is found that the stud diameter and stud spacing have an obvious influence on the shear resistance. Based on the test and numerical analysis results, a formula was established to predict the load-slip relationship. The comparison indicates that the predicted results agree well with the test results. To accurately predict the shear resistance of the stud embedded in UHPC, a design equation for shear strength is proposed. The ratio of the calculation results to the test results is 0.99.

Numerical and analytical modeling of fiber-matrix bond behaviors of high performance cement composite

Use of steel fiber in high performance cement composite (HPCC) can enhance its strength and toughness, which is achieved through stress transfer from fiber to matrix at interface. In this study, a numerical model in Finite Element Method and three analytical models were proposed to predict bond behaviors between HPCC matrix and three different shaped (straight, hooked, and corrugated) steel fibers at different ages. The proposed numerical model considered an enhancement factor based on the modified interfacial friction law (MIFL). In the analytical models, frictional force following a power function was considered. Predicted results from those numerical and analytical models were compared with existing models and corresponding experimental results. The comparisons indicated that the enhancement factor employed in the MIFL efficiently reflected the change in fiber-matrix bond properties with age. The predicted pullout load-slip relationships and energies from those proposed models showed higher accuracy than those from the existing models.

Study of single perfobond rib with head stud shear connectors for a composite structure

The head stud connector and the perfobond rib connector are the most common forms of ductile and rigid shear connector, respectively, but have strengths and weaknesses. This study evaluates the behaviour of a single perfobond rib with head stud shear connector that combines the advantages of both. First, a shear resistance equation is proposed to predict the strength of the single perfobond rib with head stud shear connector based on equations for the head stud connector and the single perfobond rib shear connector. Five groups of single perfobond rib with head stud shear connectors, ten push-out test specimens in total, were used to investigate the fracture failure mode, load–slip relationship, shear capacity and ductility of the specimens. Based on the test results, the influences of the parameters of the shear connector on shear capacity are discussed. The experiments show that the single perfobond rib with head stud shear connector is superior in terms of shear resistance and ductility. Shear capacity and corresponding relative slip of the specimens increase with increasing diameter of the head stud and transverse rebar, whereas ductility decreases. The accuracy of the proposed shear-capacity equation is verified by comparison with the test results.

Experimental investigation of perfobond hoop shear connector’s bearing capacity and slip

Perfobond hoop (PBH) is a type of shear connector specifically promoted from perforated steel plate connectors (PBL) with relatively higher bearing capacity and ductility. However, there is limited information on the effect of the parameters on PBH’s bearing capacity and slip, such as concrete compressive strength, opening diameter on perfobond plate and hoop diameter. To investigate the mechanical behavior of PBH, push-out tests were conducted under static loading. Corresponding failure modes, bearing capacity and load-slip relationship were obtained. In this paper, the shear-friction theory and the method of multivariate linear regression analysis are employed to analyze the experimental results and a simplified formula for PBH bearing capacity is proposed based on the test results of eighteen specimens. By fitting the normalized results of specimens, an empirical equation for the load-slip relationship of PBH within the whole loading process is obtained, which is in an exponential form. The proposed formulae are both validated with the verification results and can provide good references for the design and applications of PBH.

Experimental and Theoretical Study on the Flexural Performance of GFRP-Concrete-Steel Composite Beams

A novel GFRP (glass fiber-reinforced polymer)-concrete-steel composite beam bridge was proposed to prolong the service life of bridges. In order to investigate the flexural behavior of the composite beams, four-point bending tests and push-out tests were conducted. First, GFRP-concrete-steel composite beams with different interface types were fabricated and tested. Experimental results indicated the concrete ultimate strain and the ultimate deflection were increased because of the confining effect provided by GFRP plates. The GFRP-concrete interface had no obvious effect on flexural stiffness and flexural capacity. The slip effect of GFRP-concrete-steel beams was similar to that of steel-concrete beams. The failure process of GFRP-concrete-steel beams was different from that of steel-concrete beams due to the effect of the GFRP plate. Then, push-out specimens were tested to investigate the slip effect between GFRP-concrete decks and steel beams. The effect of GFRP plates on the studs was insignificant because of the large stud hole, and a regression formula of load-slip relationship was presented based on the experimental results. Finally, finite element model and theoretical model were employed to analyze the deflection calculation method and the flexural capacity calculation method, respectively.

Bending performance of composite bridge deck with T-shaped ribs

This paper proposes a new type of steel-concrete composite deck, which is composed of orthotropic steel deck (OSD) with T-shaped ribs, concrete plate and studs connecting OSD and concrete plate. The OSD can act as framework for concrete plate and contribute to load bearing capacity at the same time, which could save construction time. Compared with conventional OSD system, this new type of composite bridge deck can also improve fatigue performance. Considering that this type of composite deck is not yet applied in practical engineering and its mechanical performance is not revealed in previous literatures, two full-scale specimens were designed and manufactured in this research. The mechanical performance, particularly, bending capacity in positive and negative region was carefully tested and analyzed. The load-deflection curve, load-slip relation, strain distribution in concrete and steel were obtained. The test results showed that the plastic performance of this kind of composite bridge deck was satisfying and the bending capacity was high.

On the early-age bond-slip behavior of an eccentric bar embedded in a grouted sleeve

Grouted-sleeve connections are widely used to connect prefabricated concrete members. The bond stress-slip behavior is an essential issue to be considered when assessing the performance of a grouted-sleeve connection loaded in tension. This paper presents an experimental investigation regarding the local and global bond stress-slip behavior of grouted-sleeve connections. Three parameters were investigated: the embedment length, construction eccentricity, and loading time after grouting, respectively. The specimens were subjected to a monotonic tensile load, and the slip between the bar and the grouted-sleeve was measured during the test. Moreover, to evaluate the confinement effect, the circumferential strain at the surface of the grouted-sleeve was measured. The results reveal that the maximum local bond stress increases with the age of the grout, whereas it decreases as the construction eccentricity of the bar increases. Moreover, the influence of the construction eccentricity is mitigated by a longer bonded length. The load-slip relationship is approximately linear for the specimen with an embedment length-to-bar diameter ratio equal to ten, loaded at the age of seven days. Based on the experimental results, an analytical model, including the local and global bond stress-slip relationship, is proposed to evaluate the maximum slip and to describe the strain distribution in the long specimens (lb/d = 6, 10). The agreement among the experimental and calculated bond stress, the maximum slip and strain distribution at the surface of the sleeve demonstrates the validity of the proposed model.

Performance Evaluation of Different Types of Shear Connectors in Steel–Concrete Composite Construction

AbstractShear connectors are designed in steel-concrete composite construction to transmit the longitudinal shear, to prevent separation of steel and concrete slabs, and also to increase the structural efficiency of the whole system. In this study, the performances of different types of shear connectors in steel-concrete composite specimens are evaluated by conducting push-out tests under monotonic loading conditions. An ISMB 200 @ 25.4 kg/m universal steel beam measuring 400 mm and a reinforced cement concrete slab measuring 300 mm with a breadth of 200 mm and a thickness of 200 mm reinforced with 8 mm diameter steel rods are used for the experimental study. The results reveal that the load-slip relationships for various types of shear connectors and failure mechanisms are obtained to identify those shear connectors which are more relevant to the steel - concrete composite members.

Analytical Model for Load⁻Slip Relationship of Perfobond Shear Connector Based on Push-Out Test.

In composite structures, the perfobond connector is an alternative type of shear connector which consists of a steel plate with a certain number of holes. The load–slip relationship is critical for structural analysis and numerical simulation of composite structures using perfobond connectors. In this study, push-out tests were conducted on 72 specimens to obtain the load–slip behaviors of perfobond connectors. Based on the test results, parametric study was performed to analyze the effects of changing the hole geometry, the concrete strength, the configuration of the rebar in hole, the dimensions of the perfobond rib, and the size of the concrete slab. Furthermore, the characteristics and physical meanings of the load–slip curves were analyzed, and the limits and conditions for theoretical expressions were derived. Finally, an analytical model was proposed to express the load–slip relationship of perfobond connectors covering a wide range of design variables.

Experimental and numerical analyses on nonlinear behaviour of wooden parallel chord trusses composed of self-tapping screws

Five different wooden parallel chord trusses were made of Canadian spruce 2 by 4 lumbers. Chord–web nodal points were composed of self-tapping-screws (STS) whose numbers per nodal point and allocations in nodal point were considered as the main experimental parameters which were varied from 2rows-2lines till 2rows-4lines. Load–slip relationships at nodal point were evaluated using the joint specimens made of similar materials. These parallel chord trusses were modeled using a finite element method (FEM) program by taking not only nonlinearity of nodal point joints but also material nonlinearity of chord members using fiber model into consideration. Strength properties of the chord members were deduced via specific gravity of chord member based on the regression equations given by a literature. Static monotonic central point loading tests were conducted on five specimens to investigate nonlinear behaviors of wooden parallel chord trusses. Comparisons between observed results by experiments and computed ones by FEM calculations showed a tendency that material nonlinearity gave less effect on the total nonlinear behaviour of the specimens when joint performance was inferior, on the other hand, as the joint performance increased material nonlinearity gave dominant effect on the total nonlinear behaviour of the specimens.

Whole-process Bond Characteristics of FRP-to-concrete Joint under Pressure

Lateral anchoring can effectively inhibit the premature debonding of FRP (Fiber-Reinforced Polymer) plate bonds to concrete. To effectively improve the efficiency of reinforcement, the bond characteristics of FRP-to-concrete joints under pressure through the entire debonding process were analyzed via a theoretical model, experimental evaluation, and parameter studies. The results show that the load-slip behavior of a bonded joint features an elastic stage, an elastic-softening stage, an elastic-softening-residual stage, a softening-residual stage and a residual stage. Moreover, the trilinear bond-slip model reveals changes in interface bonding properties under pressure. The experimental analysis of the load-slip relationship and bond stress distribution prove the accuracy of the theoretical model. Both load capacity and slip increase with increasing bond length or lateral pressure, while increasing the plate stiffness results in an increased load capacity and a reduction in ductility.

Epoxy interlocking: A novel approach to enhance FRP-to-concrete bond behavior

This paper presents a novel approach which can enhance the interfacial bond behavior between fiber reinforced polymer (FRP) composite material and concrete. Epoxy ribs are formed by grooving on the concrete surface before epoxy is applied. The dowel action from the epoxy ribs leads to an “epoxy interlocking” effect. The mechanism of the proposed epoxy interlocking approach was analyzed in this paper from both adhesion and interlocking aspects. Furthermore, the partial interaction of the epoxy interlocking was quantified and calibrated by experimental results. The epoxy interlocking in the tested specimens led to an 88.8% increase in bond strength on average. An analytical approach was proposed to quantify the average partial interaction for the individual epoxy ribs. The load-slip relationship for individual epoxy ribs was found to be related to concrete compression behavior. A parametric study was conducted analytically on the effects of groove depth and spacing, concrete strength and epoxy rib location. The reasonable results in the parametric study further verify the efficiency of the epoxy interlocking to enhance the bond performance between FRP and concrete.

Numerical Investigation of the Nonlinear Composite Action of FRP-Concrete Hybrid Beams/Decks

Interfacial slip can cause rigidity degradation and stress concentration in fiber-reinforced polymer-concrete hybrid beam (FCHB). Therefore, precisely evaluating the composite action between fiber-reinforced polymer (FRP) and concrete of FCHB plays a pivotal role in structural analysis and design. Previous push-out tests showed that most connections for FCHB behave nonlinearly in load-slip relationships even at a low load level. However, existing analytical equations have their limitations due to the assumption of linear load-slip interfacial relationship which is not suitable for FCHB. The originality of this paper is to propose a finite difference method (FDM) to elaborate the interfacial slip and shear stress. FDM agreed well with the analytical solutions of the linear load-slip relationships for connections. Results indicate that higher accurateness can be obtained by using more elements. And 40 elements for half span of FCHB can reduce the error of numerical results to 1%. Then, the proposed FDM was expanded to predict the interfacial behavior of FCHB considering nonlinear interfacial load-slip relationships. It was found that perforated FRP rib connections can ensure nearly full composite action and the bolted connection can lead to a very high slip level. The use of ultra-high performance concrete (UHPC) results in a higher degree of composite action than normal concrete. The deflection considering slip was computed by adding deformation under full composition action and that caused by the slip effect. It was suggested that high strength steel bolts are effective both in normal concrete and UHPC. When the slip modulus is suggested to be larger than 20 kN/mm, the capacity per bolt should be larger than 20 kN.

Push-Out Tests on Large Diameter and High Strength Welded Stud Connectors

In recent years, steel-concrete composite cable-pylon anchorages are increasingly employed in the construction of long-span cable-stayed bridges, especially in China. Welded stud connectors, typically 19 mm and 22 mm in diameter, are usually densely arranged at the interface between the steel anchorage box and the wall of the concrete pylon to transfer the huge cable force into the concrete pylon. However, dense welded stud arrangements at the interface have some disadvantages, such as the shear strength reduction of stud connectors and the difficulties in arranging reinforcements and pouring pylon concrete. Larger diameter and higher strength welded studs may be excellent alternatives since they both could increase the shear strength of a single stud connector and thus reduce the required number of welded studs. In this paper, push-out tests were implemented on four groups of welded stud connector specimens, including conventional 22 mm welded studs, 22 mm welded studs with much higher strength, 25 mm welded studs, and 30 mm welded studs. The shear strength, shear stiffness, and ductility of these welded stud connectors were investigated and compared with the predictions by the equations recommended in existing design codes. The results show that the shear strength of welded stud connectors could be conservatively determined by Eurocode 4, while AASHTO LRFD will produce a suitable estimation. The load-slip relationships proposed by Ollgaard and Buttry can be used to predict the load-slip curves of large diameter and high strength welded stud connectors.

Static behavior of grouped large headed stud-UHPC shear connectors in composite structures

Accelerated bridge construction (ABC) utilizing precast systems offers many benefits such as faster onsite construction and lower traffic impacts. Ultra-high performance concrete (UHPC) becomes an innovative solution that facilitates some types of ABC. This paper proposes a novel steel-UHPC composite system and large studs with diameter of 30 mm. Push-out tests are conducted to investigate the shear behavior of large studs embedded in UHPC and compared with normal strength concrete (NSC). A total of 6 single stud and 18 grouped studs specimens are used to investigate the effects of casting method, precast deck strength, infilling material strength and transverse reinforcement in the shear pocket. Test results showed that grouped stud effect in the UHPC specimen was insignificant. Ultimate strength of grouped stud in precast UHPC deck was 10% higher than that of NSC precast slab while interfacial slip of UHPC specimen was 17% lower. Noting that grouped large studs better match with UHPC since no visible crack was observed at failure in UHPC slab while NSC slab displayed a number of cracks. Finally, load-slip relationship for large grouped studs embedded in UHPC was proposed based on experimental results and comparisons between the test results of strength and codes predictions were made.

A theoretical solution for the pullout properties of a single FRP rod embedded in a bond type anchorage

ABSTRACTThis paper proposes a theoretical solution for predicting the pullout properties of a single fiber-reinforced polymer (FRP) rod embedded in a bond type anchorage based on a trilinear bond–slip model. The radial variation of the shear stress and reaction of the steel sleeve are considered in the solution. Pullout procedure with elastic, elastic-softening, elastic-softening-debonding, pure softening, softening-debonding, and debonding stages, as well as the corresponding critical stages, are analyzed. In this theoretical solution, the maximum pullout load, shear stress along the rod–grout interface, axial tensile stress of the FRP rod, and load–slip relationship are derived with explicit formulations. Effective bond length of bond type anchorage is also discussed. The solution is validated against experimental results available in literature. The theoretical solution reveals that the anchorage may attain its maximum pullout load in the elastic-softening, pure softening, or elastic-softening-debonding stage. Moreover, the effects of embedded length, ultimate shear stress, and residual shear stress on maximum pullout load closely related with the stage in which the anchorage attains its maximum pullout load. However, the effect of radius of FRP rod on the maximum pullout load increases with the embedded length, no matter in which stage the anchorage attains its maximum pullout load.

Predicting bond behavior of HB FRP strengthened concrete structures subjected to different confining effects

This paper presents an analytical model to predict the bond behavior of hybrid bonded (HB) fiber reinforced polymer (FRP) strengthened concrete structures considering different confining effects. The bond strength of HB-strengthened concrete structures subjected to uniaxial loading is attributed to the friction-type bond from steel plate and the chemical bond provided by epoxy-based resin. The friction-type bond is assumed to develop before any interfacial slip occurs, and remain constant when the interfacial slip is nonzero; for the chemical bond between FRP and concrete, a tri-linear bond-slip relation is adopted. The loading process of HB-strengthened structures consists of three stages, and the stage-wise solution to slip, bond stress, and axial force of HB FRP are derived based on a governing ordinary differential equation (ODE). In this study, the experimental program includes twelve HB-strengthened concrete specimens, using different confining effects (twisting moments on the steel bolts). Test results indicated that the ultimate pullout strength increases and the failure mode switches from debonding to FRP rupture as the twisting moment increases. Moreover, by comparison to three series of experimental results, the proposed model can precisely predict failure mode, ultimate strength, load-slip relation and bond stress distribution. The twisting moment on bolts is found to have the most significant improvement on the ultimate tensile strength. Finally, the critical twisting moment without yielding FRP rupture is derived.

Experimental Study on Welded Headed Studs Used In Steel Plate-Concrete Composite Structures Compared with Contactless Method of Measuring Displacement

Steel plate-concrete composite structures are a new innovative design concept in which a thin steel plate is attached to the reinforced concrete beam by means of welded headed studs. The comparison between experimental studies and theoretical analysis of this type of structures shows that their behaviour is dependent on the load-slip relationship of the shear connectors used to ensure sufficient bond between the concrete and steel parts of the structure. The aim of this paper is to describe an experimental study on headed studs used in steel plate-concrete composite structures. Push-out tests were carried out to investigate the behaviour of shear connectors. The test specimens were prepared according to standard push-out tests, however, instead of I-beam, a steel plate 16 mm thick was used to better reflect the conditions in the real structure. The test specimens were produced in two batches using concrete with significantly different compressive strength. The experimental study was carried out on twelve specimens. Besides the traditional measurements based on LVDT sensors, optical measurements based on the digital image correlation method (DIC) and pattern tracking methods were used. DIC is a full-field contactless optical method for measuring displacements in experimental testing, based on the correlation of the digital images taken during test execution. With respect to conventional methods, optical measurements offer a wider scope of results and can give more information about the material or construction behaviour during the test. The ultimate load capacity and load-slip curves obtained from the experiments were compared with the values calculated based on Eurocodes, American and Chinese design specifications. It was observed that the use of the relationships developed for the traditional steel-concrete composite structures is justified in the case of ultimate load capacity of shear connectors in steel plate-concrete composite structures.

EXPERIMENTAL RESEARCH ON TENSILE AND SHEAR BEHAVIOUR OF THE INTERFACE BETWEEN NON-STEAM-CURED UHPC AND STEEL PLATE STRUCTURE

Ultra-High Performance Concrete (UHPC) has a great potential for the application in composite construction and steel structure strengthening. The interface between UHPC and steel plate is important to the composite behaviour of the entire structure. In this paper, five kinds of interface between non-steam-cured UHPC and steel plate were investigated through a series of pure-tensile and push-out tests. The interface treatments included smooth plate; embossed plate; epoxy based adhesive with sprinkled-in aggregates, pre-bent steel rebar welding; and headed stud connecting. The results shows that UHPC has low and unreliable adhesion to the steel plate; the embossed steel-plate interface and the epoxy based adhesive interface have higher adhesion strength but brittle failure under tensile or shear loads without constraint; the pre-bent steel rebar welding and headed stud connecting treatments demonstrate evident regularity and ductility after initial interface adhesive failure, but little increase on shear capacity is observed by imposing constraint. Furthermore, the behavior of stud connection interface was specially discussed in this paper. It was found that classic theory and current codes of practice significantly underestimate the capacity of cone failure of UHPC, and an assumption of variable angle failure surface was suggested. In addition, an exponential function model for the load-slip relationship of headed studs in UHPC was calibrated and verified by the test results.