Partial Composite Action Research Articles

A new method for rapidly capturing the strength and full nonlinear response of partially interacting steel–concrete composite beams

A semi-analytical procedure is presented for predicting the complete flexural response of partially interacting steel–concrete composite beams up to failure. The governing equation of the Euler–Bernoulli beam theory is solved wherein concrete, steel and the shear connectors joining the concrete slab to the steel beam are assumed to have nonlinear stress-deformation relationships. The adopted constitutive relationship for the connectors allows for partial or full composite action. The solution is applicable to beams and one-way slabs subjected to concentrated or uniform load and/or their combination. The governing equation is numerically solved by satisfying the equilibrium and compatibility requirements along the member. For the reinforced concrete part of the composite beam, a nonlinear moment–curvature relationship is developed that accounts for concrete nonlinearity in compression and for cracking and tension-stiffening in tension as well as for steel reinforcement nonlinearity. The steel profile is assumed to have a bilinear elasto–plastic strain-hardening moment–curvature relationship. Comparison of the proposed model results with the corresponding experimental load–deflection curves and interfacial shear–slip curves of several beams tested by others shows good agreement. The relative simplicity, efficiency and easy application of the present solution make it possible to accurately predict the failure load, interfacial slip and full nonlinear response of partially interacting composite beams.

Structural behavior of fully prefabricated glubam-concrete composite beams constructed of innovative connectors

This study focuses on developing fully prefabricated glued laminated bamboo (glubam)-concrete composite (BCC) beams constructed of the innovative ultra-high performance concrete (UHPC)-steel composite connectors. Five mid-scale prefabricated BCC beams with different connectors and concrete slabs were tested under short-term loading conditions to evaluate the flexural behavior. Particular emphasis was placed on verifying the convenience and deconstructablity of the proposed assembly structure through a secondary assembly and loading process, revealing that the prefabricated BCC has the advantage of rapid assembly construction and appreciable reusability. This assembly structure exhibits favorable bending performance under short-term loading conditions and it shows partial composite action. Reducing spacing and enhancing shear resistance of the UHPC-steel composite connector effectively improves the flexural behavior of BCC beams. In addition, casting a layer of laminated lightweight aggregate concrete with 30 mm thick on site can enhance the bending performance of the prefabricated BCC beam with effective control of the increase in its self-weight. Typical load capacity models derived from timber-concrete composite (TCC) beam were evaluated by the test results for predicting the load capacity of the prefabricated BCC structure. A comparison and evaluation were conducted on six large-scale BCC beams connected by different connectors, indicating that the proposed fully prefabricated BCC system possesses superior competitive advantages compared with existing BCC/TCC beams and it has a good application prospect in building engineering.

Developments and bending behaviors of GFRP-concrete composite girders at low temperatures

This paper reported the experimental and theoretical studies on the low-temperature performance of GFRP box-concrete composite girders (GCCGs) under four-point bending. GFRP box section with three vertical webs was adopted to improve the shear resistance of web. The horizontal shear force at GFRP box-concrete interface (concrete on top of the GFRP box) was resisted by the combined shear connectors with T-bolts and sand coating (TBSC). The effects of low temperatures (T = 20, −30, −60, and −80 ℃) on the mechanical behaviours of composite girders under four-point bending were studied. Test results indicated that the composite girders failed in shear fracture of the GFRP web and compressive fracture of the GFRP box under sagging and hogging moments, respectively. The plane section assumption was not applicable for composite girders under sagging moment because of the shear failure of sand coating. Meanwhile, the low temperatures improved the ultimate resistance (FuT) of GCCGs under four-point bending. Finally, theoretical models with consideration of GFRP box-concrete partial composite action were developed to determine the low-temperature behaviours of GCCGs under four-point bending.

Experimental Behavior of a Steel Girder–Stringer–Floorbeam Bridge

The presented case study summarizes a quick-response project for the Tennessee Department of Transportation (TDOT), which focused on the steel-stringer behavior for a girder–stringer–floorbeam bridge. TDOT was confronted with relatively low stringer load ratings for many of their 31 similar structures. As a result, TDOT initiated this field study to ultimately produce refined load ratings. This information was then to be utilized for deciding whether an intervention (e.g., retrofit) was necessary. Diagnostic load testing was the approach selected and a representative bridge was chosen. Then load testing was comprehensively designed and executed. This included the installation of 42 strain gauges, data-acquisition quality-control testing, weighing and measuring test trucks, load testing of the structure, and then removal of the system. The load-test data provided insight into the true behavior of the bridge. The stringers were subjected to a combined interaction of the global and local response. Overall, the local demands were the largest component, but the magnitudes were well below the predicted values. This was partly because of the lateral distribution of the load. Additionally, partial composite action was identified between the steel stringers and concrete slab. Refined load ratings were calculated using the field-measured data and following the AASHTO Manual for Bridge Evaluation. The comparison of predicted to measured responses clearly indicated the conservative nature of the prior analytical calculations. The stringer load ratings were increased by 68% based on the field testing. In the end, the steel-stringer load ratings were sufficient, with no intervention necessary.

State-of-the-Art: Integrating Fastener Technology and Design Guidelines for Enhanced Performance of Cold-Formed Steel Sections

Cold-formed steel (CFS) elements have gained significant attention in the field of structural engineering due to their numerous advantages, including high strength-to-weight ratio, cost-effectiveness, and ease of assembly and prefabrication. This review paper presents a comprehensive state-of-the-art analysis of the design and analysis of CFS structures, with a specific focus on columns and beams. The primary objectives and aims of this review paper are to provide a detailed assessment of the factors influencing the behavior and performance of CFS elements, including partial composite action, fastener spacing, bolt arrangement, web aperture, stiffeners, and connection spacing, to propose and present various formulas and methodologies that accurately estimate critical buckling loads, strength, and moment resistance for CFS members, and to emphasize the significance of proper screw and bolt placement in preventing premature failure and enhancing the overall load-carrying capacity of CFS structures. Additionally, the impact of temperature on the mechanical properties and performance of CFS members is discussed. The review paper proposes different formulas and methodologies to accurately estimate critical buckling loads, strength, and moment resistance for CFS members. Moreover, the paper highlights the importance of proper screw and bolt placement to prevent early failure and improve the overall load-carrying capacity of CFS structures. The discussion also emphasizes the need for revisions in existing standards and codes to provide more practical guidelines for designers and engineers. Overall, this state-of-the-art review paper provides valuable insights and recommendations for researchers and practitioners involved in the design and analysis of CFS elements.

The influence of notch connection location on the short-term behaviour of timber-concrete composite beams, modelling of TCC beams and research for optimal locations, a numerical study

Timber-concrete composite beams, known as TCC beams, have been widely used in rehabilitation or in new buildings where several types of connections are commonly inserted to ensure partial composite action between the timber joist and the concrete slab. The notched connections represent an effective system due to their strength and ductility and it is simple to cut from timber joists. As a result, a small number is needed for the composite beam to achieve high performance in terms of bending stiffness and load-carrying capacity. This paper aims to develop a FE model for TCC beams with notched connections. It considers realistic interactions between different components. The developed FE model can satisfactorily predict the full range load-mid-span deflection curves and the failure mechanisms. The predictions agree very well with the experimental results reported in the literature, including the stiffness and the load-carrying capacity. After the validation, a numeric study was established, it aimed to research the optimal location of a notch connection between different proposed locations, to figure out which place must be installed to ensure high performance of the TCC beams. As a result of this study, the notch installed at location P3000 was found to be the optimal location to assure the highest bending stiffness. While the maximum carrying capacity was achieved at location P3750.

Bending stiffness of bamboo-concrete composite (BCC) beams under short-term loads

Bamboo-concrete composite (BCC) beams are newly-innovated products used for floor system which synergistically utilizes bamboo and concrete components. These composite beams at current technology belong to the beam characterized with partial composite action due to the existence of relative slip between bamboo segment and concrete slab. Existing investigations have demonstrated that the load bearing capacity of BCC beams depends on their bending stiffness; however, very limited prediction models are available to accurately estimate the bending stiffness of BCC beams. At present, the bending stiffness of BCC beams is predicted with the help of γ-method in Eurocode 5-Part 1-1, and available studies have demonstrated that this method overestimates the bending stiffness of BCC beams. To this end, this paper presents a novel explicit model characterized with mechanism and data mining to predict the bending stiffness of BCC beams under short-term loads. Three steps were performed to achieve the aforementioned research objective. The first step was to introduce the axial force transfer coefficient into the equilibrium equations of internal force for bamboo segment and concrete slab. Secondly, the bending stiffness of BCC beams was established by taking into account the effect of relative slip with the help of existing experimental results from the interfacial shear test and flexural test. Finally, the proposed model was validated by comparing with flexural performance results of BCC beams collected from available literature as well as those obtained from γ-method. The comparative results show that: i) the predicted bending stiffness of BCC beams is much closer to tested ones compared with γ-method; ii) the errors of proposed model predicting the bending stiffness for most BCC beams are within 10% of test results; however, nearly half of the predicted ones using γ-method have errors exceeding 10% of test results, both of which verify that the mechanism and data mining-dual driven model receives a better prediction for short-term bending stiffness of BCC beams.

Experimental testing and analytical modelling of single and double post-tensioned CLT shear walls

Post-tensioned (PT) timber technology - also called Pres-Lam technology - can provide increased strength/stiffness for mass timber seismic load resisting systems while also providing energy dissipation and re-centering capabilities. Initial experimental tests and practical implementation on PT timber structures in the past 15 years primarily utilized laminated veneer lumber (LVL), with some glulam and cross-laminated timber (CLT) prototypes and real-case applications, and their analytical prediction models were extended and adapted from precast concrete to account for unique characteristics of engineered timber. More recently, CLT has emerged into a more dominant global mass timber product. This paper presents a large-scale experimental study on 8.6 m tall PT CLT single and double wall systems. The PT double walls utilized screwed connections at the in-plane joint and U-shaped flexural plates at the foundation to provide coupling effect and energy dissipation. With screwed connections, the PT double wall partial composite action of approximately 70% was achieved and the system stiffness was almost two times that of two PT single walls without partial composite action but of equivalent length. Analytical prediction models, accounting for the peculiar controlled rocking mechanism and originally developed for PT LVL systems were adopted for PT CLT wall systems, were found to have increased compressive toe strain variability due to the increased material inhomogeneity of CLT with non-edge glued lamella. The timber compressive strains and unique ‘end effect’ bearing phenomenon was investigated for the first time with Particle Tracking Technology (PTT). Extensions to the existing PT double wall analytical prediction model were proposed and validated to capture the unique kinematic rocking mechanism where wall uplift occurs due to the strong and stiff screwed in-plane connection between individual walls.

Experimental and numerical study on the lateral torsional buckling of full-scale steel-timber composite beams

The lateral torsional buckling (LTB) of steel-timber composite (STC) beam with partial interaction was investigated in this paper. The composite beam is constructed by connecting the timber to both flanges of the H-shaped steel with bolts or screws. Twelve push-out specimens were designed to evaluate the shear performance of bolt or screw connectors. It was shown that the slip stiffness and the shear bearing capacity of the connectors increased with the thickness of timber increasing. Then, eight full-scale composite beams with lengths of 6000 mm were studied through bending tests and compared to a bare steel beam. The experimental behaviors of the specimens were identified, including the failure mode, load-deflection relationship and load-strain response. The LTB phenomenon and composite action were discussed by analyzing the strain distribution, stiffness and strength. The results demonstrated that the STC beams fastened with bolts or screws displayed partial composite action. Although the stiffness of the composite beam showed little augmentation, the maximum strength of the composite beam substantially increased by suppressing the LTB phenomenon. A finite element analysis was conducted to reveal the failure mechanism of the specimens with different geometric and physical parameters, including the number of timber layers, the interface shear stiffness and the initial imperfection. It was found that increasing the number of timber layers in the upper flange suppressed the lateral torsional buckling, and the interface shear stiffness was the key factor to control the stiffness and failure modes of STC beams.

Elastic Analysis of Steel-Concrete Composite Beams with Partial Interaction

The paper presents an exact analytical method for the elastic analysis of steel-concrete composite beams with partial interaction. Accepting the basic assumptions of the Newmark analytical model and adopting the axial force in the concrete slab as the main unknown, the second order nonhomogeneous differential equation of the steel-concrete composite element with partial interaction is derived. Further, the complete solutions for simply supported and fixed-ended composite beams subjected to concentrated and uniform loads respectively, are developed. The solution of the homogeneous equation is determined by imposing proper Dirichlet or Neumann boundary conditions depending on the static scheme of the element. The particular solutions are then derived for the considered loading conditions. It is shown that the internal axial force in concrete slab associated to composite beams with partial interaction can be expressed as a fraction of the axial force in concrete slab under full interaction through a non-dimensional function f(aL) which takes into account the connection’s stiffness, the mechanical properties and also the length of the element. Moreover, the solutions are included in a flexibility-based approach to derive the force-displacement relations of the beam element with partial interaction. For the resulted 2-noded beam-column element with 6DOF, the stiffness matrix is derived, showing that the partial composite action may be included at the element level by means of a series of correction factors applied to the standard full-interaction stiffness matrix coefficients. A numerical example is provided to demonstrate the accuracy and performance of the proposed method. Within the elastic range, the predicted load-midspan deflection curve is in very good agreement with both experimental and other numerical results retrieved from international literature. A parametric study was conducted to investigate the influence of the shear connection degree on the beam’s midspan deflection and the results were compared with those computed by using code provisions.

Composite behaviour of wide sandwich panels with thin high performance recycled aggregate concrete wythes with fibre reinforced polymer shear connectors

ABSTRACT The traditional means of using precast concrete sandwich panels are restrictive in terms of applications, where thick wythes result in heavy panels which are often unsuitable in retrofitting domestic and commercial buildings. As concrete sandwich panel technology has evolved to make it more widely accessible, recent research work has demonstrated that it is possible to achieve thermally efficient partial composite action within a thin wythe panel provided non-conductive shear connectors are used. This paper examines high performance recycled aggregate concrete in heavily insulated non-load-bearing panels for retrofitting domestic and commercial buildings. A series of concrete mixes were tested to develop one which would be more sustainable than the widely accepted standard mixes for wythes. Different 220 mm thick concrete sandwich panels were tested consisting of 20 mm thick fibre-reinforced recycled aggregate concrete wythes and a 180 mm layer of XPS insulation. Unconnected and shear connected panels were tested in flexure in a displacement control test. The effects of composite action and post-cracking toughness were examined and it was concluded that a shear connected panel comprising sustainable thin recycled aggregate concrete wythes enclosing a thick layer of insulation is a feasible product to use for light high-performance sandwich panels.

Cyclic Loading Test for Two-Story RC Moment Frames Retrofitted with Internal Steel Frames

An internal steel frame–retrofitting method without diagonal braces was studied to strengthen existing reinforced-concrete (RC) moment frames with nonseismic details. For better constructability and structural capacity, a novel shear connection method was developed and verified by cyclic shear testing. To evaluate the seismic performance of retrofitted frames, three two-story moment frames with and without strengthening were tested under cyclic lateral loading. The test results showed that, despite partial composite action between RC and steel members, the proposed retrofit method significantly increased the stiffness and strength of the RC moment frame, achieving a satisfactory deformation capacity greater than 2% drift ratio. On the basis of the test results, the failure mechanism of the retrofitted frame was discussed, considering the shear connection behavior. The test strengths of the frame specimens were compared with the predictions based on a simple plastic mechanism. Further, the degree of partial composite action between the RC and steel members developed by shear connections was addressed to improve the strength predictions.

Cost Optimization of Steel-concrete Composite Floor Systems with Castellated Steel Beams

Performance of cost optimization program of composite steel deck-slabs (DS) and supporting castellated beams (CB) consisting of interior beams, edge beams and girders is proposed in this paper. The program applies the vibrating particle system (VPS) meta-heuristic algorithm, which imitates the free vibration of ideal one-story frame structures with viscous damping. The program is also furnished with an advanced cost function, which takes into account both material and fabrication costs of all parts of the floor system. The effect of four major cost reduction procedures and additional cost-saving techniques are studied on the cost function. Considering various DS profiles, altering the dimensions of hexagonal openings, different number of floor divisions and choosing costlier DSs except the optimal deck are the major cost reduction procedures. Inclusion of partial composite action for CBs, infilling certain openings of CBs and applying camber are the supplementary economizing techniques. To realize the economy of LRFD method, a meticulous design theory of composite CBs in adherence with LRFD principles of AISC 360-16 specifications is applied to the formulation of the strength constraints. Due to excessive deflections and due emphasis on vibration control of CBs, we implement accurate design procedures for the formulation of the serviceability constraints. Performance and superiority of the proposed optimization program is validated by studying three distinct real-size design examples taken from the literatures.

Third-point flexural test on concrete-filled rectangular tubular flange girders

The influence of shear stud connectors on the horizontal displacement brought about by the occurrence of shear stress at the interface between the rectangular steel tube and in-filled concrete on Concrete-filled Rectangular Tubular Flange Girders (CFRTFG) was investigated. As a composite structure, providing shear stud connectors allow stress transfer between steel and concrete which may result for the two (2) components to work as a single unit. Accordingly, a three-dimensional finite element software called SOLIDWORKS® was employed. Static linear analysis was performed using the finite element (FE) models to study the effect of shear stud connectors on the resulting stresses and slip on CFRTFGs. Results showed that the maximum slip occurred at CFRTFG without shear stud connectors while CFRTFG under full composite action had the least slip. Correspondingly, the maximum shear stress for both CFRTFG under full and partial composite action occurred at the shear stud connectors, while the maximum shear stress for CFRTFG without shear connectors occurred at the supports. Conducting finite element analysis using SOLIDWORKS® proved to be theoretically accurate as in the case of this study.

Thermal-Structural Analysis and Thermal Bowing of Double Wythe UHPC Insulated Walls

Ultra-high performance concrete (UHPC) was recently introduced to the precast concrete sandwich panel (CSP) industry, resulting in significantly thinner and lighter panels than those with conventional concrete. As exterior walls, they are expected to endure a wide range of seasonal temperatures, causing thermal bowing. A robust thermal-structural coupled finite element (FE) model, capable of modeling the partial composite action, was developed for the UHPC CSPs to assess their thermal bowing behavior. Three CSP designs, differing mainly in configuration and quantity of shear connectors, have been studied. Thermal loading was introduced by subjecting one surface to a constant room temperature, and the other to a variable temperature range of -50 °C to +60 °C. The model predictions were validated using panels tested under thermal and structural loading. The analysis revealed that panel deflections increased with the degree of composite action but satisfied serviceability requirements for the full range of temperatures. Cracking of the UHPC wythe occurred when the temperature differential (ΔT) between the two surfaces was equal to or less than -7 °C. The maximum tensile stress in the connector was less than 12% of its tensile strength, and occurred in the first connector from the panel end, which is consistent with the maximum relative slip between wythes.

Experimental and analytical studies on shear behaviors of FRP-concrete composite sections

The design of FRP profile-concrete composite sections, including beams and decks, is usually governed by the shear strength of the FRP profiles. However, analytical methods that can precisely predict the shear capacity of the composite sections have not been well developed, because there is lack of knowledge of the FRP-concrete composite action and distribution of shear stress along the FRP. This paper investigates the shear behaviors of FRP-concrete composite sections and develops formulae to predict the shear capacity of the composite sections. First, flexural tests of three FRP-concrete composite beams were conducted to investigate the shear failure mode and interface behaviors. All the beams failed in FRP shear fracture along horizontal direction. Then, push-out tests were used to determine the slip property for the FRP-concrete interface which reveals that FRP stay-in-place form and steel bolts can ensure full and partial composite action, respectively. Based on the experimental study, closed-form equations to compute the maximum shear stress are derived and validated against experimental data in this paper and literature. Finally, simple yet reliable equations of shear capacity are derived and recommended for engineers to design the FRP-concrete composite sections.

Predicting the Demand of Shear Tab Connections with Composite Beams in Fire

Shear tab connections are one of the most commonly used simple beam-end framing connections. Simple connections are designed to resist shear forces at ambient temperature. This study aims at identifying the key parameters that affect the behavior of composite beams with shear tab connections under fire. Large axial forces are generated during a fire event due to the thermal expansion of the materials. These forces, which are not considered in the design, could lead to connection failure. In this study, finite element (FE) models are developed in Abaqus and validated against experimental data available in the literature. The strength degradation of the steel material at elevated temperatures is accounted for using retention factors. Concrete damage plasticity is implemented to model the concrete behavior at high temperatures. FE simulations are then performed to investigate the effect of different parameters on the behavior of shear tab connections in composite beams subjected to fire. The main parameters are: load ratio, concrete slab temperature, shear tab thickness, setback distance, bolt diameter, in addition to the creep in the concrete and the partial composite action. This proposed research provides more guidance on the effect of thermally induced forces and deformations of shear tab connections with composite beams. It also provides the basis for developing simple methods of analysis.

Behavior of adhesively bonded engineered wood – Wood chip concrete composite decks: Experimental and analytical studies

In this study, epoxy and polyurethane (PUR) were used to glue five medium-sized (i.e. length of 2300 mm and width of 215 mm) engineered timber-concrete composite decks to investigate their composite action and flexural behavior under four-point bending tests. Cross laminated timber (CLT), laminated veneer lumber (LVL), plain concrete (PC) and an innovative type of wood chip concrete (WCC) were used. The five specimens were WCC-Epoxy-LVL, WCC-PUR-LVL, WCC-Epoxy-CLT, WCC-PUR-CLT and PC-Epoxy-LVL. All the specimens showed linear load-deformation responses approaching the final failure. Ultimately, all the decks failed by either compressive crushing of concrete or wood parts, rather than the debonding at the wood-concrete interface, indicating a good composite action of the timber-concrete composite decks. Compared with the specimens made of PC, the flexural stiffness and load-carrying capacity of the specimens made of WCC reduced by around 20%. Nevertheless, the thermal conductivity of WCC could be reduced by 30%, interpolated from the chart in an independent study. Lastly, the authors analytically predicted the effective bending stiffness and mid-span deflection for each specimen, considering the shear flexibility of transvers layers (stressed perpendicular to fiber direction) in engineered wood as partial composite action and assuming a perfectly rigid bond at wood-concrete interface.

Partial Composite-Action and Durability Assessment of Slab-on-Girder Highway Bridge Decks in Negative Bending Using Long-Term Structural Monitoring Data

AbstractThis paper uses long-term bridge monitoring data to quantitatively assess the composite action exhibited in slab-on-girder highway bridges and investigates the potential relationship betwee...

Shear tab connection with composite beam subjected to transient-state fire temperatures

Purpose This study aims to develop a rational model to predict the thermal axial forces developed in shear tab connections with composite beams when subjected to transient-state fire temperatures. Design/methodology/approach Finite element (FE) models are first developed in ABAQUS and validated against experimental data available in the literature. Second, a parametric study is conducted to identify the major parameters that affect the behavior of shear tab connections with composite beams in the fire. This includes beam length, shear tab thickness, shear tab location, concrete slab thickness, setback distance and partial composite action. A design-oriented model is developed to predict the thermal induced axial forces during the heating and cooling phases of a fire event. The model consists of multi-linear springs that can predict the stiffness and strength of each component of the connection with the composite beam. Findings The FE results show that significant thermal axial forces are generated in the composite beam in the fire. This is prominent when the beam bottom flange comes in contact with the column. Fracture at the toe of the welds governs the behavior during the cooling phase in most FE simulations. Also, the rational model is validated against the FE results and is capable of predicting the thermal axial forces developed in shear tab connections with composite beams under different geometrical properties. Originality/value The proposed model can predict the thermal axial force demand and can be used in performance-based approaches in future structural fire engineering applications.