Push-out Test Specimens Research Articles

Push-Out Analysis on the Shear Performance of a New Type of Bellow-Sleeved Stud

For continuous steel–concrete composite girder bridges based on the post-combined method, the conventional rectangular group studs contribute to the isolation of the steel girder and the concrete slab before prestressing, leading to the majority of prestress forces being introduced to the concrete slab. However, rectangular-group stud holes cause the prestress forces to be unevenly distributed. In this study, a new type of bellow-sleeved stud (BSS) was developed to mitigate the weakening effects of rectangular group stud holes on the slab. A steel corrugated sleeve with a diameter of 60 mm was employed to cover the stud, which served as an internal formwork to prevent the concrete from bonding with the root of the stud. After prestressing was complete, the steel sleeve was filled with ultra-high-performance concrete (UHPC) to create a reliable combination between the concrete slab and the steel girder. To investigate the shear performance of this new type of connection, eight push-out test specimens were designed, and finite-element models were built. This study drew a comparison between the BSS and the ordinary headed stud (OHS). The research findings suggested that the BSS is subjected to less bending–shear coupling and offers a 4.5% increase in shear strength and a 31.9% increase in shear stiffness compared with the OHS. The study also analyzed the structural parameters influencing the shear performance of the BSS. It is found that the steel sleeve of the BSS has a negative effect on shear performance, but this can be mitigated by infusing high-strength material into the sleeve. Furthermore, the study examined the effect of construction quality on shear performance and suggested that sleeve deviation and grout leakage considerably reduced the shear performance of the BSS. Accordingly, strict control over the construction quality of the BSS is necessary.

Study on the Influence of Steel Fiber Distribution on the Mechanical Properties of Perfobond Leiste (PBL) Shear Connectors

In order to study the influence of steel fibers on the mechanical properties of Perfobond Leiste (PBL) shear connectors and improve the utilization of steel fibers in this structure, four push-out test specimens and eight finite element numerical models were produced to study PBL-type shear connector specimens with different steel fiber blending amounts and blending forms. The results show that in this structure, when the blending amount of steel fiber was 0.5% to 1.5%, the ultimate bearing capacity of the specimen improved linearly, and the steel fiber helped to give full play to the performance of the PBL shear connector. The steel fibers distributed in the Z-direction have a significant impact on the mechanical properties of the PBL shear connector, and the steel fibers distributed in this direction have a significant effect on increasing the ultimate bearing capacity of the specimen. Steel fibers distributed in the Y-direction can greatly improve the plasticity of concrete. In addition, the effective action area of steel fibers is the triangular area from the bottom of the PBL shear connector to the two tops of the concrete.

Behavior of Steel–Lightweight Self Compacting Concrete Composite Beams with Various Degrees of Shear Interaction

This study investigated the use of lightweight self-compacting concrete (LWSCC), which represents a trend in producing high-performance concrete, as slabs in steel-concrete composite beams with headed studs as shear connectors. Three push-out test specimens were fabricated and tested to assess the shear strength and behavior of M16-headed stud connectors embedded in LWSCC. Based on the push-out test results, six steel-LWSCC composite beams were manufactured and tested as simply supported composite beams. In addition, a steel-normal weight self-compacting concrete (NWSCC) composite beam specimen with full shear interaction was manufactured and tested for comparison. The main variables taken into account in this study were the degree of shear interaction and regions of bending moment (sagging or hogging). It was observed that the increase in degree of shear interaction from 50 to 100% improved the ultimate carrying capacity, the service load, and the stiffness of the tested steel-LWSCC beam specimens by a ratio reached to 96, 95, and 122%, respectively, when subjected to sagging bending moments and by a ratio reached to 57, 59, and 134%, respectively, when subjected to hogging bending moments. In addition, it was noted that the deflection and the end slip values for steel-LWSCC specimens under a sagging bending moment are smaller than those under a hogging bending moment, which have the same degree of shear interaction and at the same load level. Moreover, the experimental results show that the ultimate carrying capacity, service load, and stiffness values for the steel-NWSCC composite beam were higher than those for the steel-LWSCC beam specimens that have the same properties, while the ultimate deflection and end slip were smaller. Doi: 10.28991/CEJ-2023-09-11-04 Full Text: PDF

Experimental study of innovative bolted shear connectors in demountable cold-formed steel–concrete composite beams

Although cold-formed steel (CFS) members have been widely used in structures, their application is limited due to the buckling and instability of these members. To enhance their strength and stiffness, they are often combined with other materials like concrete or timber. One of the main challenges in composite structures is ensuring proper connection between different components to facilitate safe shear load transfer. This is achieved through various types of shear connectors. Bolted shear connections are preferred over headed shear studs because they offer greater strength and can be easily dismantled. Headed shear studs welded onto a steel section are unsuitable for CFS members due to their low thickness.In this paper, we propose a novel demountable composite connection specifically designed for prefabricated CFS structures. The behavior of this connection was evaluated through fifteen push-out test specimens, with key variables including CFS section thickness and bolt diameter/strength. The ultimate load, stiffness, ductility, and failure modes of all specimens were determined. The results revealed that specimens with a higher thickness of CFS members experienced bolt fracture, exhibiting superior effective stiffness, strength, and ductility. Conversely, specimens with a lower thickness of CFS members failed due to distortional buckling of the CFS members. The test results underscore the importance of carefully designing and providing a proportionate CFS section thickness to ensure shear connectors fracture before the CFS members. This significantly improves the shear strength capacity of the composite connection with CFS sections and precast concrete slabs. Furthermore, the deconstructability of the connection at the end of its service life was investigated. The steel–concrete composite connection with precast concrete slabs and demountable bolted shear connections was also modeled using a 3D finite element method. The numerical model’s accuracy in simulating the observed structural behavior was confirmed against experimental data. Finally, appropriate and straightforward formulations for predicting the ultimate load of the CFS-concrete composite connection were proposed. It was concluded that the predictions of ultimate shear load capacity values by EC4, AISC, and AISI provisions for this composite connection are significantly less accurate.

Experimental study on a highly efficient shear transfer system for square CFST

A new shear transfer system for CFST columns is studied, which is an application of the patent EP2305911B1 into the square CFST columns. The new optimized system, called UPCCFST, consists of crown-shaped protrusions on the steel sheet oriented towards the side that remains in contact with the concrete. Initial tests have been conducted to study the failure modes and optimize the design. The optimized design is considered the default characteristic of the experimental campaign, consisting of 56 push-out test specimens. The following parameters have been analyzed: connection system, punch density, concrete type, punch arrangement and cross-section dimensions. The UPCCFST system with the optimum punch density (HD) has shown a steel-concrete shear strength, τu, 12.31 and 2.95 times higher than the conventional flat CFST in 200 × 4 and 110 × 2 specimens, respectively. Regarding the slip energy, the UPCCFST specimens absorbed 8.1 and 3.6 times more energy than the respective flat CFST specimens.

Post-fire bond behaviour in elliptical concrete filled steel tubes: Experiment and simulation

The post-fire bond behaviour between the steel tube and core concrete in elliptical concrete filled steel tubes (ECFST) is studied in this paper. A total of 15 post-fire push-out test specimens, including 9 elliptical, 3 circular and 3 square CFSTs, were designed and tested. The testing parameters included: (a) target temperatures (Ttar = 20 °C, 600 °C and 800 °C); (b) high temperature duration time (td = 30 min, 60 min, 180 min and 300 min); (c) length of long axis of elliptical section (2a = 200 mm and 300 mm); (d) section type (elliptical, circular and square). The test results indicated that the target temperature and high temperature duration time affected the post-fire bond strength of ECFSTs significantly, and the post-fire bond strength of ECFSTs could be increased with the increasing values of the two parameters. Based on the test data, a two-linear stage bond stress versus slip constitutive model considering the influence of both the temperature and fire-exposed surface area was proposed and verified to capture the post-fire bond behaviour in ECFSTs, which could be used in the refined bond behaviour numerical analysis of ECFSTs.

Experimental investigation of headed studs in steel-ultra-high performance concrete (UHPC) composite sections

Featuring high compressive and tensile strengths, ultra-high performance concrete (UHPC) is an efficient and durable alternative for conventional concrete in steel–concrete composite sections. However, few experimental studies to date have involved large diameter (≥ 25 mm) headed studs, UHPC with compressive strengths larger than 130 MPa, and relatively low strength but cost-effective UHPC. This study investigates the shear performance of steel headed studs embedded in UHPC through pushout tests with 24 specimens. Specimens included headed studs with diameters of 16 mm, 19 mm, 22 mm, and 25 mm, and either UHPC with compressive strength of 152.5 MPa or a cost-effective UHPC with a strength of 85.7 MPa (named as HPC hereafter). The results showed that smaller-diameter specimens (16 or 19 mm) failed with stud shank fracture, while the larger-diameter specimens (22 or 25 mm) failed at welding lines. Compared to HPC, UHPC did not notably increase the performance of headed shear strength. The load response consisted of a linear stage, a softening stage, and a post-peak stage lasting up to a slip of 10 mm or greater, with high variability in post-peak response among specimens with identical parameters. A global database of 120 push-out test specimens from this study and references was established, covering concrete strengths from 23.5 MPa to 152 MPa. The formulae given by AASHTO LRFD Bridge Design Specification, Eurocode-4, and Chinese code GB50017-2003 overestimated the shear capacity of headed studs by 52 %, 5 % and 53 %, respectively. The equation for the slip modulus slightly overestimated the slip modulus of headed studs. In conclusion, this study broadened the ranges of concrete strength and diameter of headed shear studs, and revealed that the existing equations of predicting shear capacity and slip modulus need improvement.

Shear Strength of Headed Stud Connectors in Self-Compacting Concrete with Recycled Coarse Aggregate

This study investigated the use of self-compacting concrete (SCC) made with recycled coarse aggregates (RCAs), which represents a trend of producing environment-friendly concrete, integrated with hot-rolled steel sections by means of headed stud shear connectors in composite structures. Therefore, thirty-six push-out test specimens were examined to assess the shear strength and behavior of the headed stud connectors embedded in RCA-SCC, with the concrete compressive strength, stud diameter, and RCA ratio as the main variables. Four ratios of RCAs ranging from 0 to 60% were used to produce concrete with three different compressive strengths (25, 33, and 40 MPa) for each one. It was found that the use of SCC with RCAs had a negative effect on the shear strength of headed stud connectors. This negative effect could be reduced by increasing the concrete compressive strength and/or the stud diameter. Similarly, a reduction in the shear stiffness of the tested specimens was inversely proportional to the RCA ratio, while the ultimate slip was directly proportional to the RCA ratio. An evaluation of the test results was made by comparing them with those determined by Eurocode 4 and AASHTO LRFD.

Feasibility and performance of novel tapered iron bolt shear connectors in demountable composite beams

The performance of tapered iron bolt (TIB) shear connectors and their feasibility to be used in demountable composite beams are investigated in this study. The typical TIB shear connector consists of six components, i.e., a connecting bolt, conical iron plug, top covering plate, top fixing bolt, retaining washer and inner sleeve. The connectors are expected to 1) reduce the initial slip between the concrete slab and steel beam, which generally exists for steel-concrete composite beams using bolted shear connectors, and 2) be capable of being replaced for composite beams in-situ without damaging other components. Two series of pushout tests were conducted on the specimens with TIB shear connectors in accordance with Eurocode 4 (EC4). The demountability of TIB shear connectors after severe corrosion induced by accelerated corrosion, i.e., wet-dry cycles, was examined. All pushout test specimens failed in shear fracture at the bolts while the concrete slabs remained undamaged. The test results demonstrated that the replacement of TIB connectors would not affect the failure mode of TIB connectors but have a moderate influence on the shear capacity. Therefore, a reduction factor was proposed to account for the influence of replacement in design. The design equations of TIB shear connectors under bolt shear and local concrete failure were proposed. The proposed design method is able to provide a reasonably accurate prediction for the failure mode and shear strength of the TIB connectors.

Mechanical Behaviour of Aluminium-Timber Composite Connections with Screws and Toothed Plates.

This paper presents an investigation of the load-slip behaviour of aluminium-timber composite connections. Toothed plates with bolts are often used for connecting timber structural members with steel structural members. In this paper, toothed plates (C2-50/M10G, C2-50/M12G or C11-50/M12) have been used as reinforcement in aluminium-timber screwed connections for the first time. The push-out test specimens consisted of laminated veneer lumber slabs, aluminium alloy beams, and hexagon head wood screws (10 mm × 80 mm and 12 mm × 80 mm). Of the specimens, 12 additionally had toothed plates as reinforcement, while 8 had no reinforcement. The load carrying-capacity, the mode of failure and the load-slip response of the strengthened and non-strengthened screwed connections were investigated. The use of toothed plate connectors was found to be effective in increasing the strength of aluminium-timber composite connections and ineffective in improving their stiffness. The examined stiffness and strength of the connections can be used in the design and numerical modelling of aluminium-timber composite beams with reinforced screwed connections.

Experimental study on the bond-slip behavior and stress transfer mechanism between shaped steel and high-performance fiber-reinforced concrete

In light of the weak bond strength between the two materials in steel reinforced concrete (SRC) and the brittleness of high-strength concrete, the use of high-performance fiber-reinforced concrete (HPFRC) was proposed with the addition of cellulose fiber and rice husk ash (RHA) in high-strength concrete. The purpose of this study is to investigate the bond behavior of shaped steel embedded in HPFRCs. Thirteen push-out test specimens of steel high-performance fiber-reinforced concrete (SHPFRC) were cast. The test parameters considered in this study were the HPFRC strength, cover thickness, embedment length, and stirrup ratio. The experimental process and failure modes were analyzed, and the influence of various test parameters on the average bond strength was studied. The average effective bond stress was introduced to study the whole process of bond failure and the stress transfer mechanism. Then, a method for calculating the bond stress was established. The results showed that the failure modes of the specimens were classified into bond splitting failure, bond anchorage failure, and mixing failure. The parameters have various effects on the average bond strength. The introduction of the average effective bond stress reflected the transfer mechanism of bond stress at the interface. The largest component of bond stress was chemical adhesion, and mechanical interaction was the smallest.

Parametric study of I-shaped shear connectors with different orientations in push-out test

A great deal of research has been conducted to improve the understanding of the behavior of new types of shear connectors. This article presents the study of I-shaped connectors behavior under monotonic load welded in four different orientations in order to get the position which gives the high shear strength and the best ductility. For this purpose, eight push-out test specimens with I-shaped shear connectors with different orientations and dimensions were tested in C20/25 and C30/37 concrete classes. The load-slip behavior and failure modes of the tested connectors are presented and discussed. Furthermore, a non-linear 3D finite element modelling of the push-out test is performed in order to further investigate the influencing parameters on the I-shaped connectors behavior. Hence, a parametric study is carried out by using the established 3D finite elements model to study the influence of concrete strength, connector’s steel grade, reinforcements, height and length of the connector. Both experimental and numerical results show that there is a privilege orientation for which the shear strength of an I-shaped shear connector is significantly higher than that of all other tested orientations.

Structural performance of steel-concrete composite bridges utilising innovative blind bolt shear connectors

The purpose of this research is to identify more efficient and reliable connection methods to design a composite steel/concrete structural system with a focus on sustainability. While using innovative blind bolt shear connectors into substitute for the welded stud brings several benefits regarding constructability and sustainability, research contributions on the high strength blind bolt shear connector are very limited. Therefore, in this study, several push-out test specimens were carried out, in accordance with the Eurocode 4 standards, for both the traditional welded stud and the blind bolt shear connector, to determine the ultimate capacity, ductility, stiffness, stress-strain and load versus slip performance. In addition, finite element analysis has been done on the two types of shear connectors to determine the factors influencing static strength of shear connectors. The feasibility and accuracy of the 3-D finite element model developed in this work was validated by comparing with experimental results obtained from push-out tests. Experimental and finite element modelling results revealed that the blind bolt shear connectors would be an appropriate alternative to the traditional welded stud for sustainable purposes under static loading conditions.

Composite Steel and RPC Testing

Reactive powder concretes are a set of ultrahigh-strength concrete reinforced with fibers. Their compressive strength is greater than 100 MPa. For assuring connection of steel beams and a concrete slab, steel stud connectors are used. The investigation of that kind of shear connection efficiency, in the case of this higher strength concrete deck using standard push-out test specimens has been executed. The experimental results are presented in the paper.

Mechanical Testing of Composite Steel and Reactive Powder Concrete Structural Element.

Reactive powder concrete (RPC), typically with higher compressive strength, is particularly attractive to structural engineers to apply them in infrastructures for enhancing their resistance under severe environments and loads. The main objective of the initial study presented in the paper was to investigate the behavior of two types of these new cementitious materials differing in the nature of microfibers. The RPC mixes were reinforced with steel and then with basalt microfibers. To evaluate the structural performance of developed unconventional materials, properties were investigated experimentally and compared with the control normal concrete mix. Mechanical tests indicated that dispersing fine fibers for making RPC, a mean compressive strength of 198.3 MPa and flexural strength 52.6 MPa or 23.2 MPa, respectively, were developed after 28 days of standard curing at ambient temperatures. In composite structures consisting of steel girders and a concrete slab, it is necessary to prevent the relative slip at the steel and concrete interface using shear connectors. The very high RPC strength enabled a material saving, weight-reduced application of precast construction, and particularly effective joint to steel beams. The investigation of such shear connection efficiency, in the case of the higher strength concrete deck, using standard push-out test specimens was executed. Finite element numerical models were developed. The outputs of the studies are presented in the paper.

Experimental investigation of composite floor system with thin-walled steel trussed beams and partially prefabricated concrete slab

The present investigation addresses the structural behavior of steel and concrete composite floor systems, composed of thin-walled trussed members, usually adopted in the steel frame constructional technology. The floor systems of typical light-weight frame constructions are generally constituted by thin-walled beams (or open-web joist), wood-based panels (Oriented Strand Boards – OSB) and self-drilling screws connecting both materials (steel and wood). In some situations, concrete slabs are cast over the OSB panels and no shear connectors are adopted to ensure the composite action between the steel members and the concrete. In this context, one of the objectives of this work aims at presenting three new innovative solutions for shear connectors, composed of thin-walled members and attached to the top chord of the trusses by means of self-drilling screws (4.2 mm diameter). A series of experimental tests were performed in the Structures Laboratory of Federal University of Rio de Janeiro (COPPE/UFRJ), in order to provide reliable information in terms of shear strength, deformation capacity and mechanisms of collapse associated with eight push-out test specimens, according to recommendations established by Eurocode 4. Also, the performance of the referred connectors was investigated with the help of three full-scale bending tests, which revealed important characteristics regarding the structural behavior of the composite floor systems in terms of bending capacity, flexural stiffness, degree of interaction between the steel trusses and the concrete slabs, as well as strain distribution at mid-section.

Shear characterisation of pultruded superstructural FRP-concrete push-outs

In this paper, an investigation aimed at characterising the behaviour of headed shear studs in push-out testing is presented. The study aims to contribute to the limited knowledge of Pultruded Fibre Reinforced Polymer (PFRP)-concrete composites, highlighting the predominant failure mode and the underlying variables relevant for predictive analytical equations. Two phases of experimental push-out tests were carried out on composite slabs comprising of normal density concrete (NWC), and PFRP connected using steel headed studs. Phase one focused on studying the effects of headed shear stud configuration on the load capacity of the composite slabs, adopting 19 mm diameter studs. Phase two of the study was aimed at characterising the behaviour of the composite slab by varying the headed stud diameters. Two push-out test specimens adopted 12 mm diameter studs, and a third specimen within this phase adopted the 16 mm stud diameter. The dominant failure mode was bearing, net tension and shear out failures of the FRP plates. These modes of failure were distinctly different from those prevalent in the conventional steel-concrete composite, which is either stud shank failure or concrete pull out. The test investigation suggested a successive increase in shear capacity with increased stud sizes. Specimen with stud size of 16 mm attained higher shear strength per stud, approximately 29.4% in comparison to those with 12 mm diameter studs. The study observed that PFRP-concrete composites could mobilise between 40 and 50% shear resistances to that of their steel-concrete counterpart’s. However, the intensity of bearing failure increases with increase in stud size, thereby compromising the ductility of shear connection.

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.

Push-out tests on three innovative shear connectors for composite cold-formed steel concrete beams

The composite action between concrete and steel makes the use of composite beams in buildings more economical than the use of typical hot-rolled steel beams. This can be attributed to the beam’s lower depth, which significantly reduces the weight of steel. Composite beams can be constructed by lipped C-channels made from cold-formed steel, concrete, and different shear connectors (which exhibit behaviours that are not yet well understood). In this study, the behaviour of three innovative shear connectors used in composite cold-formed steel concrete beams made of lipped C-channels with profiled metal decking was experimentally examined. Experimental tests aimed to determine the maximum resistance of the proposed shear connectors; these results were then compared with the predicted values and the values for other shear connectors investigated in other studies. Likewise, the ductility and the strength capacity of the shear connectors were investigated. Twelve push-out test specimens were prepared and tested in accordance with Eurocode 4. It was found that a shear connector’s strength capacity considerably depends on its deformation and on the crushing of concrete. The ductile behaviour of all the tested shear connectors satisfied the ductility requirements of Eurocode 4. In this study, it is concluded that the proposed shear connectors were suitable for use in the construction of composite beams, as they were stronger than the standard headed studs and the other available shear connectors; they were also sufficiently strong to perform composite actions.

Long-term behaviour of steel-timber composite (STC) shear connections

The long-term behaviour of steel-timber composite (STC) connections under sustained loading is studied both experimentally and theoretically. The laboratory work involved applying a sustained load to twelve STC push-out test specimens and monitoring the load-slip behaviour of the shear connection (including the interaction between timber, steel beam, and shear connector) over a 16-month period in a Service Class 2 environment in accordance with EC5. The mechanical shear connectors utilised to connect the hot-rolled steel sections to cross-laminated timber (CLT) panels were coach-screws, dog-screws, post-tensioned high strength bolts, and high strength bolts located in cementitious grout pockets. In addition to the testing programme, a 3D moisture diffusion analysis considering the effects of temperature was conducted to predict the moisture content of the timber panels. The results of the experiments and diffusion analysis were employed to calibrate a long-term rheological model for the shear connection which considers the effect of the stiffness change caused by variations of the moisture content, creep, mechano-sorption and inelastic shrinkage. The rheological model was used to predict the slip and thereby to calculate the creep coefficient of the STC members over a service life of 50 years. An average creep coefficient of 2.5 for the STC joints tested was obtained. The high strength bolts in grout pocket shear connectors had the lowest creep coefficient of 0.6, whilst the post-tensioned high strength bolts exhibited the highest creep coefficient of 3.9, owing to the loss of post-tensioning.