Strength Of Studs Research Articles

Restoring force model of phosphogypsum-filled cold-formed thin-walled square steel tube composite wall

The phosphogypsum (PG)-filled cold-formed thin-walled square steel tube (PFCFS) composite wall is a new type of cold-formed steel (CFS) wall. The restoring force model (including the skeleton curve and hysteresis rules) is an important performance of this type of walls. Based on the characteristics of load–displacement curves of the walls, a Pinching4 model for the skeleton curve of the walls is developed. The lateral stiffness and shear capacity of the walls are calculated by theoretical formulas, while other parameters are determined through data fitting. Moreover, the hysteresis rules of the walls adopt the Pivot model, and the Pivot parameters (α and β) of the walls are determined based on the principle of equal energy. Finally, based on the above restoring force model, the energy dissipation analysis for the walls with different parameters was conducted. The results show that improving the PG strength, stud thickness, or reducing the height-width ratio of the walls significantly enhances the energy dissipation capacity of the wall; increasing the OSB thickness, axial force ratio, or reducing the screw spacing gradually improves the energy dissipation capacity of the wall; the OSB configuration and the stud strength have a smaller impact on the energy dissipation of the wall; the energy dissipation capacity of the wall when the hold-down fails is lower.

The axial tensile performance of DSCW-RC joints with lap-spliced bars

Joints formed between double-skin concrete shear walls (DSCWs) and reinforced concrete (RC) foundations commonly utilize lap-spliced bars to transfer forces. However, the behavior and design of these critical connections have not been thoroughly investigated. This study experimentally analyzes a steel-reinforced DSCW-to-RC foundation anchorage joint under monotonic uniaxial tension loading. Seven 1:3 scale specimens were tested to examine the effects of varying lap-spliced bar diameter, steel plate thickness, and stud bolt spacing. Crack propagation, load-displacement response, and reinforcement strain were measured. The results characterize two potential failure modes: ductile steel yielding and brittle stud shearing. Steel strains developed linearly up to yielding, demonstrating uniform transmission of tensile loads. Increased plate thickness and decreased stud spacing enhanced capacity. To mitigate sudden shear failures, the number and strength of studs must exceed the expected tensile demand. New design recommendations are proposed, including minimum stud bolt shear strength and the use of confining tie bars. This study provides an improved understanding of the behavior of DSCW-to-RC foundation lap-spliced connections, enabling resistance to axial demands while avoiding brittle failure modes. The experimental data will inform future analytical models and design provisions for these critical structural joints.

Shear strength damage model and damage removal FE modeling of stud shear connectors embedded in UHPC

The study conducted a series of push-out tests to study the shear strength of studs as shear connectors in steel-UHPC (ultra high-performance concrete) composite structures. The damage removal modeling was developed and utilized to simulate stud damage caused by welding defects, concrete cracking, and lifting effects. The study investigated the impact of stud damage on the static performance and shear strength of studs. Results indicated that when the root area of the stud was damaged, the shear strength and stiffness of the stud decreased with the damage degree. When the stud root was damaged within 5%h (h is the height of stud shank), it had a significant effect on the shear strength of the stud. Damage outside the 5%h range of the stud root had no significant effect on the shear strength of the stud. And a shear strength damage model was firstly proposed to reveal the damage mechanism of studs. A reduction factor K was proposed to account for the loss in shear strength caused by stud damage. Two methods for calculating K, namely the area reduction method and the equivalent area method, were developed. The calculated values of shear strength considering stud damage were obtained and verified by comparing the calculated values with the test results. The proposed method offers a better prediction of shear strength for damaged studs in UHPC.

Fatigue behavior of short-headed studs embedded in Ultra-high Toughness Cementitious Composites (UHTCC)

The multi-cracking and strain-hardening capacities of Ultra-high Toughness Cementitious Composites (UHTCC) make it feasible for orthotropic steel bridge decks (OSBDs) applications to control crack width. In this composite bridge deck, shear connectors play an important role in providing good shear strength and ensuring structural service performance. To evaluate the shear resistance of short-headed studs embedded in ultra-thin UHTCC layer, three series of push-out tests were conducted in this study. The test results including shear strength, fatigue strength, failure modes, dynamic slip, stiffness degradation, plastic slip and residual mechanical properties were all considered and carefully discussed. In this study, the shear force of shear connectors was calculated and compared with current codes. The stress amplitude-fatigue life (S-N) relationship of studs was fitted by different codes. Then the empirical formulation was developed to predict the load-slip behavior and stiffness degradation of studs during fatigue loading. The relationship between plastic slip and fatigue life was established and normalized. Furthermore, based on post-fatigue static test results and test results in previous research, a new machine learning model was proposed to predict the residual shear strength of studs and contrasted with previous model. Then Analysis of Variance (ANOVA) with two parameters (i.e. load amplitude, maximum repeated force) was conducted and revealed that the peak load significantly impacted the residual shear strength of push-out specimens compared with load amplitude. Moreover, a parametric study was conducted to further investigate the degradation of studs under various working conditions. By experimental and theoretical analysis, UHTCC could fully develop the shear strength of studs embedded in ultra-thin cover thickness. And related models were established to predict the static and fatigue behavior of steel-UHTCC push-out specimen.

Performance of grouped stud connectors in precast steel-UHPC composite bridges under combined shear and tension loads

Ultra-high performance concrete (UHPC) becomes an innovative resolution for facilitating the construction and structural performance of prefabricated bridges. Head stud shear connectors are commonly applied in prefabricated steel–concrete composite bridges and can withstand uplift forces as well as shear forces. In this paper, six standard push-out tests (SP-Test) and ten modified push-out tests (MP-Test) are prepared and tested. In the MP-Test, stud connectors are subjected to shear and tensile forces simultaneously. The stud diameter, stud aspect ratio and the ratio of tension to shear are considered for their effects on shear resistance, shear stiffness and ductility. Besides, the finite element (FE) analysis and parametric analysis are conducted to further investigate the behavior of stud connectors under combined loads. The formulas for predicting the shear-tension interaction strength and shear resistance of stud connectors in UHPC under combined loads are proposed. The results show that the stud connectors exhibit both shear and tension failure characteristics under combined loads. The lower ratio of tension to shear has less effect on the shear resistance and ductility. Meanwhile, the stud aspect ratio is positively related to shear resistance and ductility but has no effect on shear stiffness under combined loads. As the ratio of tension to shear increases, a considerable reduction is observed in the shear resistance and relative slip as well as shear stiffness of stud connectors. However, the attenuation effect of tensile stress on the shear strength of studs can be neglected when the tensile shear ratio is less than 0.17. The unevenness of the force on single stud in stud connectors can be ignored and excessive strength of UHPC has limited effect on improving the strength of studs under combined shear and tension loads. The proposed shear strength reduction factor takes into account the ratio of tension to shear and gives more reasonable predictions of shear resistance under combined loads. Besides, compared with other available equations, the proposed shear-tension interaction model predicts the interaction strength more accurately.

Experimental and finite element investigations on shear behaviors of stud connectors embedded in Engineered Cementitious Composite (ECC)

Engineered Cementitious Composite (ECC) exhibits superior mechanical properties such as high tensile strength, ductility, and toughness, which enable using thinner sections in steel-ECC composite structures. Existing design equations for the shear capacity of stud connectors were derived by regression analysis of test data from push-out specimens using normal concrete, which often have stud height-to-diameter ratios above 4. This research investigates the shear behaviors of stud connectors, with different height-to-diameter ratios from 2.73 to 4.62, embedded in ECC. Push-out tests showed that the height-to-diameter ratio is important for the shear capacity of studs. Finite element analysis was performed to evaluate the effects of the diameter, height-to-diameter ratio, and tensile strength of studs as well as the compressive properties of ECC on the shear behaviors. Regression analysis was performed using the analysis data to modify the equations for predicting the shear capacity of studs embedded in ECC for steel-ECC composite structures.

Numerical investigation of steel-concrete composite (SCC) beam subjected to combined blast-impact loading

Existing literatures on combined effects of blast-impact loadings on steel-concrete composite beams are limited. In this study, behavior of steel-concrete composite beam subjected to combined blast-impact loading was investigated using LS-DYNA nonlinear FEA software program. The accuracy and reliability of developed FEA model was validated using experimental data reported in literature. Parametric studies were performed on impacting speed, concrete strength, various characteristics of H-structural steel, yield strength of studs and steel rebars to get insight into performance of composite beam subjected to combined blast impact loading. FEA results revealed that increase in specified cylindrical compressive strength of concrete, yield stress, flange and web thicknesses of H-type structural steel beam significantly improved dynamic response of a steel-concrete composite beam under combined impact-blast load case whereas yield stress of studs, and reinforcement steel bars showed insignificant contribution. Moreover, increasing impactor’s initial velocity significantly affects dynamic response of a SCC beam under combined blast-impact loading.

Push-out tests on studs with UHPC cover embedded in UHPC-NSC composite slab

To cope with the volumetric cost of the ultra-high-performance concrete (UHPC) and enhance performance of studs in steel–concrete composite bridges, a novel bridge slab system has been developed. In this system, the slab was made of UHPC and normal strength concrete (NSC), and the studs were covered with UHPC. Since the static behavior of studs with UHPC cover embedded in UHPC-NSC composite slab is different from in the NSC or UHPC slab, an experimental study is needed to investigate the ultimate strength of studs, as well as the relative slip and failure patterns. The mainly parameters considered include stud diameter, stud height, and stud root with or without UHPC cover. The experimental results reveal that the mechanical behavior of studs in the proposed composite slab system was successfully improved. The ultimate strengths of the studs with a diameter of 19 mm and 22 mm covered with UHPC embedded in UHPC-NSC composite slab are only 3.8 % and 2 % less than that in UHPC slab, respectively. The relative slips of stud with UHPC cover in the UHPC-NSC composite slab are larger than 6 mm, which satisfy the ductility demand in EC4. The results also show that the current design codes underestimate the actual shear strength of the stud with UHPC cover in the UHPC-NSC composite slab. Finally, an equation is proposed to predict the shear stiffness of a stud with UHPC cover embedded in the UHPC-NSC composite slab based on the energy equivalent model, and verified by the experimental results. The calculation value agrees well with the experimental result for a stud diameter≥16 mm.

Finite Element Modeling on Shear Performance of Grouted Stud Connectors for Steel–Timber Composite Beams

Steel–timber composite (STC) systems are considered as an environmentally friendly alternative to steel–concrete composite (SCC) structures due to its advantages including high strength-to-weight ratio, lower carbon footprint, and fully dry construction. Bolts and screws are the most commonly used connectors in STC system; however, they probably make great demands on the accuracy of construction because of the predrilling in both the timber slabs and steel girder fangles. To address this issue, the STC connections with grouted stud connectors (GSC) were proposed in this paper. In addition, stud connectors can also provide outstanding stiffness and load-bearing capacity. The mechanical characteristic of the GSC connections was exploratorily investigated by finite element (FE) modeling. The designed parameters for the FE models include stud diameter, stud strength, angle of outer layer of cross-laminated timber (CLT) panel, tapered groove configurations, and thickness of CLT panel. The numerical results indicated that the shear capacity and stiffness of the GSC connections were mainly influenced by stud diameter, stud strength, angle of outer layer of CLT panel, and the angle of the tapered grooves. Moreover, the FE simulated shear capacity of the GSC connections were compared with the results predicted by the available calculation formulas in design codes and literatures. Finally, the group effect of the GSC connections with multiple rows of studs was discussed based on the numerical results and parametric analyses. An effective row number of studs was proposed to characterize the group effect of the GSC connections.

Analytical model for the Load-Slip behavior of headed stud shear connectors

Extensive push-out tests have been conducted to obtain the formulas for the strength, stiffness, and load-slip curve of headed stud shear connectors through curve regression for parameters including concrete strength, stud strength, and stud diameter. However, due to the limitation of conditions in tests, the application range of these formulas is limited and there is a lot of discrepancies among them. This work proposes an analytical model to describe the shear behaviors of headed stud shear connectors by analyzing the load-slip curves and failure modes in the literature. The stud and surrounding concrete are idealized as a model of beam rested on foundation, whose equivalent stiffness is analytically determined by a function of the stud diameter, stud length, and parameters reflecting material properties of the stud and concrete. Therefore, the whole load-slip curve is directly obtained according to the material and geometric parameters of the headed stud shear connector. Numerical examples show that the present model can predict the load-slip curve in good agreement with the existing experimental data. Finally, the effects of material and geometry of shear connectors on their shear behaviors are discussed parametrically.

Shear behavior of short headed studs in Steel-ECC composite structure

Engineering cementitious composite (ECC) is a promising candidate as the overlay material of orthotropic steel bridge deck (OSBD), to improve the durability and extend the service life. The mechanical performance of short headed stud connectors in steel-ECC composite structure has been limited studied. This study investigated the shear behavior of short headed studs embedded in ECC through experimental push-out tests and validated finite element (FE) analysis. The experimental and analytical results were analyzed accordingly in terms of shear strength, shear stiffness and failure mode. The push-out testing results showed that the existence of natural interfacial bond was beneficial for improving the initial stiffness of the specimen. The FE simulation results agreed well with the experimental ones. Base on the validated FE model, a parametric analysis was then conducted to investigate the influence of the stud diameter, stud height, stud strength, corrosion of stud, and compressive strength of ECC on the shear capacity of short headed studs. The analysis indicated that the diameter and tensile strength of headed stud had a significant improvement on the shear strength of headed studs, while the stud height and compressive strength of ECC exhibited the opposite trend. The corrosion of stud drastically reduced the shear performance of headed studs in terms of shear strength and ductility. It was also observed that AASHTO LRFD specification overestimated the shear strength of short headed studs embedded in ECC, while the Eurocode 4 and Chinese code were relatively conservative.

Experimental and analytical study of the shear strength and stiffness of studs embedded in high strength concrete

Push-out test was carried out to investigate the influence of the ratio of the stud height to the concrete slab thickness and the reinforcement layout on the shear performance of the headed stud embedded in high strength concrete (HSC). Test results indicated that the influence of the ratio of stud height to concrete slab thickness on the shear stiffness should be taken into consideration. A shear stiffness prediction formula, which has clear physical meaning and simple expression, was proposed and validated. The predicted shear stiffness by the proposed equation is in good agreement with experimentally determined value. According to this formula, the shear stiffness of studs is affected by the stud diameter, compressive strength and elastic modulus of HSC. In addition, a formula to predict the shear strength of a stud embedded in HSC considering both the interaction between stud and concrete and the enhancement effect of the welded collar was also proposed and evaluated. The mean ratio of predicted results obtained from the proposed formula to experimental results is 0.98.

Experimental investigation of shear connector behaviour in composite beams with metal decking

Presented are experimental results from 24 full-scale push test specimens to study the behaviour of composite beams with trapezoidal profiled sheeting laid transverse to the beam axis. The tests use a single-sided horizontal push test setup and are divided into two series. First series contained shear loading only and the second had normal load besides shear load. Four parameters are studied: the effect of wire mesh position and number of its layers, placing a reinforcing bar at the bottom flange of the deck, normal load and its position, and shear stud layout. The results indicate that positioning mesh on top of the deck flange or 30 mm from top of the concrete slab does not affect the stud\' s s strength and ductility. Thus, existing industry practice of locating the mesh at a nominal cover from top of the concrete slab and Eurocode 4 requirement of placing mesh 30 mm below the stud\' s head are both acceptable. Double mesh layer resulted in 17% increase in stud strength for push tests with single stud per rib. Placing a T16 bar at the bottom of the deck rib did not affect shear stud behaviour. The normal load resulted in 40% and 23% increase in stud strength for single and double studs per rib. Use of studs only in the middle three ribs out of five increased the strength by 23% compared to the layout with studs in first four ribs. Eurocode 4 and Johnson and Yuan equations predicted well the stud strength for single stud/rib tests without normal load, with estimations within 10% of the characteristic experimental load. These equations highly under-estimated the stud capacity, by about 40-50%, for tests with normal load. AISC 360-16 generally over-estimated the stud capacity, except for single stud/rib push tests with normal load. Nellinger equations precisely predicted the stud resistance for push tests with normal load, with ratio of experimental over predicted load as 0.99 and coefficient of variation of about 8%. But, Nellinger method over-estimated the stud capacity by about 20% in push tests with single studs without normal load.

Numerical simulation of shear capacity of lightweight aggregate concrete stud connectors

In order to study the mechanical properties of the stud connectors in lightweight aggregate concrete (LWAC), the finite element software ABAQUS was used to establish the push test models of ordinary concrete and LWAC, respectively. Through parameter analysis of 21 models, the influence of different parameters on the shear performance of LWAC stud connector was studied. Among them, concrete strength, stud diameter and stud strength have strong effects. Compared with stud connector in ordinary concrete, the LWAC stud connector enters the elastoplastic working stage earlier, the ultimate slip is slightly larger, the ductility is better, and the shear capacity is about 11% lower. Regression analysis was performed on the finite element calculation results, and the method for shear bearing capacity calculation of the stud connectors in LWAC is given.

Load sharing mechanism between shear studs and profiled steel sheeting in push tests

Push tests as suggested in Eurocode 4 have been widely used to determine the shear strength of stud shear connectors. In the presence of profiled steel sheeting, however, the push load is jointly resisted by both types of components, i.e., shear studs and sheeting. As a result, the exact load carried by a shear stud remains unknown. This paper intends to study the load sharing mechanism between the shear studs and sheeting in push tests through the development of a three-dimensional finite element model. It is found that the sheeting itself can carry 20–65% of the push load when the thickness of the sheeting is in the range of 0.9–1.5 mm. Accordingly, the actual load resisted by the shear studs is much lower than the prediction of Eurocode 4, which does not exclude the strength contribution from the sheeting. A parametric analysis is conducted to check the influence of a wide range of parameters including sheeting orientation, stud position and layout, diameter and height of studs, concrete grade, rib height, sheeting thickness, yield stress of sheeting, and level of transverse loading on the load sharing between studs and sheeting in composite slabs with trapezoidal steel sheeting. Finally, the ultimate push load and the actual stud strength obtained from parametric analysis are compared with the predictions from Eurocode 4. The comparison indicates that the accuracy of Eurocode 4 in predicting the ultimate push load can be improved. Meanwhile, new models are required to predict the actual shear strength of studs.

A Study on the Behavior of Composite Concrete and Open Web Steel Joists

In this research, the results of three composite open web steel joist static tests are presented along with the results of companion pushout tests. The effect of shear connection degree and span-to-depth ratio on the behavior of composite open web joists under distributed static loading is reviewed and discussed, followed by a comparison of results of the shear stud strength from push-out tests, back-calculated from the ultimate capacity of the composite joist tests, and to the provisions in the AISC, EC4, NZS, SJI, and BS5950. Specimen test results of the studied span-to-depth ratios showed that the load-deflection behavior was similar to ultimate capacity difference less than 10%, but they experienced different failure modes and deflection. And when the test results were compared based on the shear connection degree, they revealed that the composite open web joist designed with partial shear connection suffered from severe deformation and deflection accompanied with higher ultimate capacity

Monotonic shear strength of headed studs in reinforced infill walls

Headed studs are key components of structures which facilitate composite behavior between steel and concrete elements. In steel building structures, reinforced concrete infill walls surrounded by a stiff steel frame is a common example of a composite structure used to resist horizontal loads such as those produced by earthquakes or wind. To this end, these types of concrete walls need to be anchored to the steel frame with headed studs which must withstand shear and tensile forces (AISC 360). To properly design headed stud anchors in concrete walls, it is first necessary to understand their behavior when subjected to monotonic shear forces considering edge conditions and reinforcing details that may influence the stud strength.Few tests have examined headed studs subjected to monotonic shear with typical boundary effects in reinforced infill walls, so a new experimental study on 17 specimens explores the behavior of headed studs exposed to monotonic shear loading with group effects. The experiments showed that the strength of studs installed in infill walls with edge conditions is well predicted (average error in prediction is smaller than 10%) by ACI 318, AISC 360 and EC-4. However, when group effects of anchors are included in the analysis of infill walls, only the ACI 318 is able to predict the behavior.

STUDY OF THE COMPOSITE ACTION OF HOLLOWCORE PANELS USED IN GIRDER-SLAB SYSTEM

Floor construction with precast hollowcore panels produced by Lafarge Precast Edmonton results in a commonly used girder-slab system. Continuity between the elements is ensured by bent rebars and shear studs. Once all these elements are installed, a structural concrete is poured between the reinforced concrete panels and over the entire floor. The extent of composite action between the rigid diaphragm and the steel beams is not known. Therefore, its potential benefit is not taken into account in the current design procedures for the steel structure. The main components of this research project are the following: an experimental program consisting of a series of 6 large-scale shear tests were carried out. The outcome of this research shows that there is a potential for a composite action between a hollowcore plank and a standard hot rolled W shape. It was found that there is enough confinement to develop the steel stud strength when the beam is connected to the precast prestressed concrete panels using a 1/2" shear stud embedded between the planks and under two to three inches of concrete topping.

Behaviour and Modeling of the Bearing Capacity of Shear Stud Connectors

The bearing capacity of shear stud connectors from the simplified design equations in different building codes tends to be underestimated because of a relatively large safety factor. Finite element analysis using ABAQUS was carried out to simulate the force–deformation response of shear stud. The finite element model was verified by using push-out tests, and detailed parametric numerical studies were conducted to investigate the force–deformation response of different shear stud configurations. A new design equation was derived from linear regression based on the results of the parametric studies. The presented equation shows better agreement with the experimental data. Detailed comparison between the proposed equation and existing design equation in China code for shear stud strength was carried out. The results show significant reduction in the construction cost when the new equation is used.

Deterioration in strength of studs based on two-parameter fatigue failure criterion

In the concept of two-parameter fatigue failure criterion, the material fatigue failure is determined by the damage degree and the current stress level. Based on this viewpoint, a residual strength degradation model for stud shear connectors under fatigue loads is proposed in this study. First, existing residual strength degradation models and test data are summarized. Next, three series of 11 push-out specimen tests according to the standard push-out test method in Eurocode-4 are performed: the static strength test, the fatigue endurance test and the residual strength test. By introducing the "two-parameter fatigue failure criterion," a residual strength calculation model after cyclic loading is derived, considering the nonlinear fatigue damage and the current stress condition. The parameters are achieved by fitting the data from this study and some literature data. Finally, through verification using several literature reports, the results show that the model can better describe the strength degradation law of stud connectors.