Semi-rigid Composite Joints Research Articles

Research on Whole-Process Tensile Behavior of Headed Studs in Steel\u2013Concrete Composite Structures

The headed studs have been widely applied in steel–concrete composite structures as shear connectors. However, the tensile performance of headed studs is also key to the structural performance in many cases such as the semi-rigid composite joints including steel beam–concrete wall joint and steel column–base joint. Therefore, this study presents experimental and analytical study on the whole-process tensile behavior of headed studs. Tests on a total of 33 pullout specimens are first conducted. The tensile capacity and load–deformation behavior of the anchorage concrete, which dominates the structural performance of headed studs, are thoroughly analyzed. In addition, test data in the literature are collected for quantitatively evaluating the influence of embedment depth, bearing area, boundary conditions, and concrete strength on the tensile behavior of the anchorage concrete. On the basis of the influence evaluation, an analytical model represented by a piecewise function is proposed to describe the whole-process load–deformation behavior of the anchorage concrete and validated through the comparison between the predicted curves and all collected experimental results. Then the proposed model is applied to simulate the rotational behavior of the typical semi-rigid joint anchored by headed studs, which takes the contribution of the anchorage concrete into consideration, and is verified by experimental results. The research findings indicate that tensile behavior of anchorage concrete is crucial to the structural performance of semi-rigid joints, even for headed studs with large embedment depth and bearing area.

How bracing and heating regimes influence the fire performance of composite frames

Purpose Unbraced one-bay composite frames are an interesting load-bearing structure for buildings with up to three storeys. However, their fire design is demanding given the lack of simplified design methods. This paper aims to deepen the understanding of the load-bearing behaviour of both unbraced and braced frames when exposed to fire. Design/methodology/approach In a previous paper, a numerical model for the fire design of these frames was established and validated with good agreement against fire tests. In the current paper, this model was used to compare the typical differences between braced, semi-braced and unbraced composite frames under fire conditions. Further studies addressed the effect of different heating regimes, i.e. partial fire exposure of the columns in the frames and varying location of the ISO standard fire. Findings Numerical investigations showed that it is necessary to take local failure and deformation limits of the fire-exposed frames into account. On this basis, unbraced composite frames can compete with braced frames as they have to endure less thermal restraints than braced frames. Originality/value In contrast to other investigations on frames, the numerical model is able to take into account the shear failure, which is especially important within the frame corners. Using this model, it is shown that limited sway is reasonable to reduce thermal restraints and hence local stresses. In this regard, the concept of semi-rigid composite joints with a distinct amount of reinforcement has proven to be very rational in fire design.

Study on the Influence of Connection Configuration on Composite Joints

Steel–concrete composite joints possess higher bearing capacity, initial stiffness and redundancy than bare steel joints. The configuration of beam-column connection would influence the behavior of composite joints, such as rigidity, rotation capacity and so on. In this paper, the test of two fully welded rigid composite joints and two flush endplate semi-rigid composite joints was introduced. The loading conditions in the tests involved sagging moment and hogging moment. The mechanical behavior of composite joints under bending moment was studied in detail, especially on the influence of connection configuration. The test results indicated that the experimental phenomena and failure mode of fully welded composite joint and flush endplate composite joint under hogging moment were similar to each other. The buckling of bottom flange of steel beam determined the behavior of composite joint under hogging moment, such as initial stiffness and bending strength. It indicated that using flush endplate connection instead of fully welded connection in composite joints had little influence on the behavior of the joint under service loads if the failure mode of joints is governed by the same component. Four models for moment-rotation relation of composite joints are compared with experimental results. Based on the comparison, a new combination model of power function expression and linear expression is developed. With proper optimum shape parameter and descending stiffness, the new model could present the moment-rotation relation of composite joints, regardless of connection configuration or loading condition.

On the fire performance of unbraced composite frames

PurposeThe purpose of this study is to gain a deeper understanding of the structural behaviour of fire-exposed unbraced composite frames. Designers to date paid little attention to unbraced one-bay composite frames as structural system. There are two main reasons for this. First, codes lack simplified methods for the fire design of these frames due to their sway and the linked P-Δ effects when subjected to fire, which complicates the design. Second, it is demanding to construct external composite joints for the regarded one-bay frames. Thus, external joints in composite constructions are mostly constructed as steel joints. Nevertheless, these frames offer advantages. These include increased usable space and flexibility in the building’s use, large spans, fast construction times and inherent fire resistance.Design/methodology/approachTo profit from these benefits, two different external semi-rigid composite joint were developed for the considered one-bay composite frames. The first solution based on concrete-filled steel tube columns and the second on concrete-filled double skin tube columns. Furthermore, a numerical model was established to study the fire performance of unbraced composite frames. The model was validated against four fire tests on isolated composite joints and two large-scale fire tests on unbraced composite frames.FindingsOverall, the predictions of the numerical model were in good agreement with the test results. Thus, the numerical model is appropriate for further investigations on the fire performance of unbraced composite frames.Originality/valueThe sequence of construction results in significant stresses in the steel section, which creates difficulties in numerical modelling and may account for the relatively few studies carried out at room temperature. For the fire design, there was, to the best knowledge of the author, to date no numerical model available that was capable of considering the sequence of construction.

Capacity of semi-rigid composite joints in accommodating column loss

In the scenario of column loss, joints would be subjected to bending moment combined with a tensile force due to large vertical displacement, where tensile force plays a critical role in resisting progressive collapse of structure by providing the catenary force. In order to study the effect of tensile force on the behavior of semi-rigid composite joints in structures in the case of column loss, six semi-rigid flush endplate connections tests were conducted, which include pure flexural tests, pure tensile tests and combined flexural and tensile tests. The experimental results indicate that under pure bending moment condition, the semi-rigid composite joint displays sufficient rotation capacity for forming “catenary action”. It is characteristic of the semi-rigid composite joint that its moment capacity decreases in a linear manner together with the increase of tensile load. Also, the capacity of semi-rigid composite joints is compared with that of the full-welded rigid composite joints. The tensile strength of high-strength bolts would not exert any effect on the initial stiffness of semi-rigid joint, but bring about decline in the moment resistance and tensile resistance of semi-rigid joint. The joints tend to fail at “catenary phase” under tensile force. A simplified M-N correlation formula for composite joint is proposed to describe the behavior of joint in structures under column loss. The finite element model with material failure criterion can predict the fracture of bolt in semi-rigid composite joint.

Seismic performance assessment of blind bolted steel-concrete composite joints based on pseudo-dynamic testing

This paper aims to investigate seismic behavior and dynamic responses of semi-rigid composite joints composed of steel-concrete composite beams and concrete-filled thin-walled steel tubular (CFTST) columns. A range of pseudo-dynamic tests (PDTs) was performed on two full-scale blind bolted end-plate joint specimens, including one flush and one extended end-plate typed joint. The input ground motion adopted for the PDTs was Ispara seismic acceleration record and scaled to represent various seismic hazard levels. Using Ispara earthquake record with different peak ground accelerations (PGAs), a lot of useful data about hysteresis behavior, stiffness degradation and energy dissipation capacity was obtained. The data was also estimated in detail to characterize the seismic performance of this kind of composite joints. Dynamic responses of beam-to-column joint including displacement and acceleration responses, and dynamic magnification factor were discussed. The experimental results indicated that the structural responses of the test joints under seismic actions coincided with the desired performances analyzed for varying damage levels. The study affirms that the blind bolted end-plate composite joints to CFTST columns possess good energy dissipation seismic performance, so they can provide sufficient ductility and adequate strength to satisfy the seismic design requirement.

Numerical Study of Deconstructable Flush End Plate Composite Joints to Concrete-filled Steel Tubular Columns

This paper describes a three-dimensional finite element modelling of an innovative flush end plate semi-rigid composite joint, to a concrete-filled steel tubular column, using high strength blind bolts. This innovative composite joint is formed by connecting a precast concrete slab to the top flange of a steel beam using post-installed friction-grip bolted shear connectors to facilitate the deconstructability of the entire system. A finite element model is developed using ABAQUS software to study the structural behaviour and failure modes of these prototype joints. Both geometrical and material non-linearities, as well as the non-linearity of the contacts and interfaces, are incorporated in the model. Four full-scale laboratory test specimens having deconstructable flush end plate composite semi-rigid joint to CFST columns using bind bolts are tested, with the results then used for validation of the finite element model. The proposed numerical models developed are used for conducting an extensive parametric study, in which the effects of the reinforcement ratio, thickness of the precast concrete slab, degree of shear connection, number of bolted shear connectors, size of the blind bolts in the connection zone and thickness of the flush end plate on the structural behaviour of the composite joint to concrete-filled columns are investigated. A design recommendation in the form of an empirical equation is then formulated.

Finite element analysis of HSS semi-rigid composite joints with precast concrete slabs and demountable bolted shear connectors

High-strength steel has a higher yield strength, greater corrosion resistance and superior toughness compared to mild steel, and its use can contribute to the sustainability of a steel structure by increasing its structural life whilst reducing steel usage and maintenance. In addition, using deconstructable steel-concrete composite floors can facilitate component recycling and reuse and can improve the sustainability of the building industry significantly by reducing energy consumption and construction waste at demolition. This paper investigates the structural behaviour of an innovative beam-to-column composite semi-rigid joint with deconstructable post-installed friction-grip bolted shear connectors and grade S690 high strength steel flush end plates. Non-linear continuum-based finite element models are developed and validated against results of four full-scale laboratory tests of this innovative joint. The validated finite element models are used for conducting an extensive parametric study in which the effects of the reinforcement ratio, thickness of the precast concrete slab, degree of shear connection, number of bolted shear connectors, size of the bolts in the connection zone, size of the steel beam and thickness of the flush end plate on the structural behaviour of a composite joint with deconstructable post-installed friction-grip bolted shear connectors and grade S690 high strength steel flush end plates are investigated. A simple analytical model is proposed to predict the moment capacity and rotation capacity of this type of composite joint.

Robustness analysis of 3D Composite buildings with semi-rigid joints and floor slab

Analysis of composite building structures has been performed mostly on skeleton frames or on plane frame (2D) without the presence of composite slabs and semi-rigid joints. This is because detailed modelling of non-linear behavior of steel–concrete composite joints and the floor slab is rather tedious and involves other structural components including interaction between floor beams with slab and beam-to-column joints. This paper proposes simplified composite slab and composite joint models, which can be easily incorporated within a commercial software for the analysis of three-dimensional composite building frames with less computational time. The steel concrete composite slab is modelled by representing the profile metal deck by rows of rebars with equivalent areas and the profile concrete slab is converted into an equivalent uniform concrete section. The semi-rigid composite joints in the building framework are modelled using the Eurocode's component model represented by axial and rotation spring connectors. The proposed simplified models have been verified against the established test and numerical data available in the literature and found to be accurate enough for analysing 3-D composite frames with less computational time. The robustness of moment frames and simple braced frames was then investigated under a column loss scenario. The incorporation of semi-rigid joints and composite slabs in 3D frame analysis tends to produce more realistic estimate of large scale steel–concrete composite frames subjected to accidental loads.

Experimental Investigation on the Mechanical Behavior of Semi-Rigid Composite Joints Loaded along the Minor-Axis

Today’s design of spatial steel frames requires beam-to-column connections to be checked in the direction of the minor-axis of inertia of beam section. The mechanical behavior of minor-axis connections for bare steel joints and composite joints has been investigated by experiments. A comparison of the experimental results between the bare steel joints and composite joints shows that the mechanical behavior of the minor-axis composite joint is obviously effected by the reinforcing concrete slab, which is transversely reinforced for bending and is connected to the steel beam via shear studs, this is more in line with the mechanical behavior of the frame joint. The investigation indicates that: (1) Minor-axis joints with flush end-plate connections and seat angle with double web angles connections are all typical semi-rigid joints. The bearing capacity and the rotation ability of the joints cannot be ignored in the design. (2) Due to the composite effects of the reinforcing concrete slab, sagging moment and hogging moment must be taken into consideration when the mechanical model is established using component method.

Experimental and numerical validation of a new design for three-dimensional semi-rigid composite joints

Semi-rigid composite joints not only have the advantage of optimizing the use of the material, but also of providing lateral stiffness for sway frames. By means of semi-rigid joints, the lateral stability of the structure may rely on the stiffness and ductility of the joints, thus avoiding bracing systems. These advantages may even increase when the joints are designed as semi-rigid in both axes. In this case, the joint behaves in a three-dimensional way that includes an interaction between the major and the minor axis of the column.In this paper, a new design for three-dimensional semi-rigid composite joint is proposed and tested in order to improve the behaviour and obtain the benefits of semi-rigidity when both the major and minor axis are included. Thus, the proposed design involves beams that are attached in a semi-rigid manner to both, the major and minor axes of the column.The experimental program consists in one 3D semi-rigid composite internal joint under proportional loads, another internal joint subjected to non-proportional loads and one facade joint. These tests provide information as to whether the joints satisfy the requirements of the Eurocodes 3 and 4 (EC3 and EC4) in terms of ductility, stiffness and resistance. Also the possible interactions between the major and minor axes of the proposed joint that are caused by the loads and/or the geometry are studied.Simultaneously, finite element modelling and analysis have been carried out and calibrated against the experimental results. These models have been performed with the aim of finding tools and ways to characterize and analyse the proposed joint design.Design guidelines are also provided for the use of this joint, and some additions and modifications to the Eurocode component method are proposed.

An advanced ANN model for predicting the rotational behaviour of semi-rigid composite joints in fire using the back-propagation paradigm

This paper describes an artificial neural networking (ANN) model developed to predict the behaviour of semi-rigid composite joints at elevated temperature. Three different semi-rigid composite joints were selected, two flexible end-plates and one flush end-plate. Seventeen different parameters were selected as input parameters representing the geometrical and mechanical properties of the joints as well as the joint’s temperature and the applied loading, and used to model the rotational capacity of the joints with increasing temperatures. Data from experimental fire tests were used for training and testing the ANN model. Results from nine experimental fire tests were evaluated with a total of 280 experimental cases. The results showed that the R2 value for the training and testing sets were 0.998 and 0.97, respectively. This indicates that results from the ANN model compared well with the experimental results demonstrating the capability of the ANN simulation techniques in predicting the behaviour of semi-rigid composite joints in fire. The described model can be modified to study other important parameters that can have considerable effect on the behaviour of joints at elevated temperatures such as temperature gradient, axial restraints, etc.

Seismic performance of semi-rigid composite joints with a double-sided extended end-plate. Part II: Seismic simulations

The numerical model of the double-sided extended end-plate composite joint presented in Part I of this paper is used to evaluate the seismic performance of this joint when used in moment-resisting frames. For this purpose, three frames of different heights and spans were designed and analysed. Two pushover analyses, with uniform and modal lateral load, were performed to evaluate the ultimate capacity of the frame. Incremental dynamic analyses (IDAs) were also performed to evaluate the seismic properties of each frame using accelerograms that match three types of elastic response spectra. The data provided by the simulations has allowed us to obtain the behaviour factors of the composite frames that use this type of joint, and to ensure their improved behaviour under seismic actions.

The seismic performance of a semi-rigid composite joint with a double-sided extended end-plate. Part I: Experimental research

Composite structures exhibit higher stiffness than steel structures with similar ductility, and also show better performance to fire action. These benefits have led to an increase in the number of composite structures built in high seismic areas. The main objective of the experimental tests explained in this article is to obtain useful data about the seismic behaviour of a composite semi-rigid joint with a double-sided extended end-plate. A series of monotonic and cyclic quasi-static tests was performed to characterize the behaviour of this joint type against seismic actions. The tests were performed on interior and on exterior joints, and they have provided useful data about the ductility of the joint, the amount of energy dissipated and the degradation effects. This data was used to elaborate and calibrate a component-based model of the joint that is composed of two rotational springs, one for the shear panel behaviour and the other for the connection behaviour. This model is capable of simulating the joint behaviour and damage under cyclic loads with sufficient accuracy.

An alternative design for internal and external semi-rigid composite joints. Part I: Experimental research

An experimental program has been carried out to test and characterize an innovative design for internal and external semi-rigid composite joints. Three tests are performed on semi-rigid composite joints with flush end plates. One of the tests deals with an internal joint with asymmetric loads, and the other two with external joints. When compared with the usual configuration of this type of joint, the proposed alternative design introduces an innovation which consists in inserting the central reinforcement bars through the column flanges in order to achieve an improved behaviour. In addition, in the case of external joints, the cantilever normally needed to ensure sufficient anchorage length for the reinforcement can be dispensed with. The experimental results are used to calibrate the finite element models. These are used to conduct a parametric study and to propose some modifications to the Eurocode 4 component method, as can be seen in the companion paper.

An alternative design for internal and external semi-rigid composite joints. Part II: Finite element modelling and analytical study

Tests on semi-rigid composite joints with the alternative configuration proposed in Part I of this paper are simulated by using the finite element method. The finite element models are adjusted, compared and validated with the experimental results until reliable and robust models are achieved. These models are used to compare the performance of the conventional joints with the alternative design that has been proposed. The internal joints with the proposed design show improved resistance and stiffness, more acutely as the moments on either side of the joint become increasingly unbalanced. On external joints, the same values are obtained as with the conventional design, but without the need for a cantilever. A parametric study is also carried out on external and internal joints following the alternative design in order to define the components which intervene in it as well as to develop the corresponding analytical model.

Experimental study on semi-rigid composite joints with steel beams and precast hollowcore slabs

The concept of semi-rigid composite connection has been widely researched in the past; however, most of the researches are limited to composite joints with metal deck flooring and solid concrete slabs. Composite construction incorporating precast concrete hollowcore slabs (HCU) is a recently developed composite floor system for buildings. The research on the structural behaviour of the semi-rigid composite joints with HCU is new and without any previous experimental database. In this paper, eight full-scale tests of beam-to-column semi-rigid composite joints with steel beams and precast hollowcore slabs are reported. The variables are stud spacing, degree of the shear connections, area of the longitudinal reinforcement and slab thickness. The test set-up and instrumentation is described in detail. The experimental behaviour is analysed and based on the test data the structural behaviour of these semi-rigid composite joints is discussed. Based on the experimental data, a simplified method to predict rotation and moment capacity for this type of composite connection is proposed.

Analysis of rigid and semi-rigid steel-concrete composite joints under monotonic loading - Part II: Parametric study and comparison with the Eurocode 4 proposal

Analysis of rigid and semi-rigid steel-concrete composite joints under monotonic loading - Part II: Parametric study and comparison with the Eurocode 4 proposal

Analysis of rigid and semi-rigid steel-concrete composite joints under monotonic loading - Part I: Finite element modelling and validation

The paper concerns the modelling of rigid and semi-rigid steel-concrete composite joints under monotonic loading through use of the Abaqus program, a widespread finite element code. By comparing numerical and experimental results obtained on cruciform tests, it is shown that the proposed modelling allows a good fit of the global joint response in terms of moment-rotation law. Even the local response in terms of stresses and strains is adequately predicted. Hence, this numerical approach may represent a useful tool for attaining a better understanding of experimental results. It may also be used to perform parametric analyses and to calibrate simplified mechanical models for practical applications. rn

Finite element modelling of semi-rigid composite joints

Semi-rigid joints in steel and composite construction are, at present, a frequently discussed topic. In framed structures, joints are located at points of intersection between beams and columns. In the semi-rigid joint concept, the actual stiffness and resistance of joints are considered thereby influencing the overall performance of the framed structure. The advantages of the semi-rigid joint concept are well known; many experimental studies have been conducted on the behaviour of semi-rigid joints. The contribution described herein outlines a possibility for simulating the behaviour of semi-rigid composite joints using the finite element method. A two-dimensional joint model based on the current state-of-the-art knowledge is introduced that can be analysed using existing finite element programs. Comparisons between simulation and test results show good agreement.