Effective Slab Width Research Articles

Analysis of the Behaviour of Composite Connections in Multi-Storey Buildings Under Earthquake Loading

In the past years, number of beams and slabs in steel structures that are executed as composite steel – concrete elements has significantly increased. In moment-resisting frames with composite steel – concrete slabs, slab reinforcement in tensile zone needs to be considered in design of composite steel – concrete beam – to – column connections with steel plates and bolts in tensile zone. However, the number of reinforcement bars that should be taken into account in connection design significantly depends on the effective width of the concrete slab. Moreover, directions for calculation of the effective width of the concrete slab are still not unambiguous as they can be calculated either according to recommendations from Eurocode 4 or Eurocode 8. In this paper, composite connections are briefly explained and main differences between composite steel – concrete beam – to – column connections and corresponding steel connections are summarized. Furthermore, behaviour of a composite steel – concrete beam – to – column connection under bending moment and shear force induced by earthquake loading is investigated using finite element analysis in software package Abaqus. Finally, a parametric study is carried out in order to examine the suitability of two code recommendations for determination of the effective width of concrete slab in case of seismic loading.

Slab Reinforcement Contributions to Negative Moment Strength of Reinforced Concrete T-Beam with High Strength Steel at Exterior Beam-Column Joints

Previous studies have revealed that the contribution of slab reinforcement to the T-beam flexural strength in negative moment regions are not negligible for the seismic capacity design. An effective slab width (i.e., effective width of flanged section) has been proposed, within which the slab reinforcement needs to be included in the calculation of the beam nominal flexural strength in negative moment regions. These studies mainly focused on the cases using normal-strength steel in moment resisting frames. However, recently high-strength steel has been widely used in reinforced concrete moment resisting frames in high seismic regions to avoid congestion near beam-column joints. The use of high-strength steel may affect the beam stiffness due to the fact that it will require less amount of reinforcement, and result in a different normal stress distribution compared to the case with normal-strength steel. Therefore, this paper investigates the slab reinforcement contribution to the flexural strength of the reinforced concrete T-beam designed with high-strength steel in negative moment regions at exterior beam-column joints, for which nonlinear pushover analyses were conducted. Beam reinforcement grade was considered as a primary parameter with several other design variables including slab thickness, height, and span length of the beam. Analytical results show that the use of high-strength steel can result in a wider effective slab width than the case of normal-strength steel for calculating the beam nominal flexural strength under the negative moment. Based on these results, new design equations were proposed.

Finite element analysis of RC moment-resisting frames to assess effective slab width; a parametric study

In reinforced concrete (RC) moment-resisting frames (MRFs) with cast-in-situ slabs, the slab action as tension flange during lateral loading enhances the flexural capacity of beams in negative moments. This enhancement may lead to strong beam-weak column unfavorable failure mode in these structures. Field observations of RC MRFs during strong ground motion indicated that the effective slab width values considered by the seismic provisions of the design codes are not adequate to guarantee the achievement of the design method of weak beam-strong column. An accurate estimation of effective slab width needs to assess factors such as geometrical characteristics of connection, continuity of models, and imposed story drift level. A 3D spatial two-story RC MRF was developed using finite element analysis (FEA) to explore the effect of mentioned factors on effective slab width. For finite element (FE) modeling of RC MRF, the concrete damaged plasticity (CDP) model is applied. The CDP model parameters are defined using a mesh-independent methodology introduced in the literature. Comparing the FEA results and results obtained from three half-scale RC MRFs, tested under reversed cyclic loading conditions showed an excellent correlation. The results predicted by the FE model in terms of lateral load–displacement response, reinforcement yielding sequence, crack patterns, and failure modes had a considerable agreement with test observations. The validated FE model was used to develop the other models to conduct a parametric study in the next step. Geometric parameters studied in this paper through numerical modeling were longitudinal and transverse beam length and height, and cross-sectional column dimension. Results of the parametric study showed that the effect of the ratio of transverse beam length to height is significantly more than the ratio of longitudinal beam length to height. The trend of effective slab width versus story drift depends on connection geometry, especially the ratio of transverse beam length to transverse beam height. Finally, an equation was driven to predict the effective slab width using linear regression analysis.

Numerical and analytical investigations on the flexural behaviours of composite beams of inverted-T steel section and ultra-high-performance concrete (UHPC) slab

This study numerically and analytically investigates the flexural performance of a new form of steel–concrete composite beam, where an inverted-T section is connected to ultra-high-performance concrete (UHPC) slab that serves as the compression chord. Such arrangement eliminates the necessity for the top flange and absorbs the compressive stresses when the beam is under construction. Thus, the aim of this study is to develop a comprehensive finite element (FE) model for the proposed inverted-T steel-UHPC composite beam in ABAQUS by considering both geometric and material nonlinearities. The developed FE model was validated against the existing experimental results, and afterwards the validated FE model was employed to conduct an extensive parametric study. In the parametric study, the effects of different design parameters including slab thickness, concrete compressive strength, stud spacing, stud diameter, effective width of slab and web penetration depth were investigated in terms of the load–deflection, bond-slip, and damage patterns. Furthermore, the load–deflection and load-slip behaviors of the proposed beam were compared with the conventional steel–concrete composite beam. Finally, an analytical procedure was developed to determine the flexural resistance of the inverted-T steel-UHPC composite beam. The results of this study will pave the way toward a practical application that is expected to decrease the construction time and cost.

Assessment of Effective and Minimal Slab Widths for Evaluating the Shear Capacity of RC Overhang Slabs

Abstract The effective width is a relevant parameter for the design of bridge overhang slabs under concentrated loads. Experimental tests have been used to assess expressions for its calculation. However, the load capacity increases with the width until a transition area is reached. Test specimens may have lacked enough width to reach full shear capacity, affecting thus the evaluation of the results. On the other hand, within the transition area, a threshold value has been hypothesized to match the effective width. This paper aims to provide recommendations for minimal widths that guarantee the full capacity of overhang slabs and to assess the calculation of the effective width by means of the threshold value and other formulations. The effect of the edge beam is also considered. A campaign of validated non-linear FE-simulations based on experiments on range of width-span ratios was performed. The results suggest using a width-span ratio of at least 4.0 for slabs without an edge beam and 5.3 for slabs with an edge beam for the experimental practice. The efficiency of the formulation for the effective widths is diffuse and the use of threshold value leads to unsafe predictions. Instead, linear-elastic FE-analyses are recommended for the design practice.

Negative bending capacity of web-embedded U-shaped steel-concrete composite beams

This paper discusses the negative bending behavior of a new type of web-embedded U-shaped steel-concrete composite beams (WUSCBs). Considering the effective width of the concrete slab, a negative bending moment test was performed on eight WUSCB specimens. The web-embedded shear connector in the WUSCB has been shown to have good shear connection performance and maintain the overall function of the WUSCB. The failure process of the specimen was categorized by the cracking, yielding, and buckling loads which correspond to 0.29 Pu, 0.79 Pu, and 0.90 Pu, respectively. Negative bending failure was observed in the WUSCB, evidenced by the steel plate yielding and concrete slab cracking. The WUSCB was found to have good ductility and deformability under negative bending. A finite element model was established to verify with the experimental results. The calculation method for negative bending capacity is proposed; and the calculation results are in good agreement with the test results.

Evaluation of base sliding response and effective slab width in ten-storey tests

Evaluation of base sliding response and effective slab width in ten-storey tests

CYCLIC BEHAVIOR OF COMPOSITE CONNECTIONS IN COMPOSITE FLOOR DIAPHRAGMS

AbstractThis research explores the cyclic behavior and strength of the composite concrete‐filled steel deck diaphragm system through experimental pushout and cantilever diaphragm tests. This work is part of the Steel Diaphragm Innovation Initiative (SDII), a multi‐institutional project that is investigating the behavior of composite steel deck diaphragms in steel buildings structures in high seismic zones. Sixteen unique pushout tests were conducted at Northeastern University as part of SDII. These specimens had variations in the orientation of the steel deck, concrete density, effective slab width, shear stud position and grouping. Additionally, seven of these tests were cyclic. Eight cantilever diaphragm tests were conducted at Virginia Tech as part of SDII. The parameters included deck height, slab thickness, concrete density, layout of shear studs, and reinforcement. These experimental tests provide valuable knowledge that aids in the characterization of the behavior and strength prediction of this structural system.

Accuracy of Seismic Response Evaluation of Two-Dimensional Analysis Model with Rigid Joints for RC Frame Buildings.

Three- or two-dimensional (2D) numerical models are used for the evaluation of the seismic performance of reinforced concrete (RC) buildings. This study examines a 2D numerical model for a specimen used in a full-scale four-story RC shaking-table test and evaluates the accuracy of the seismic response of the 2D numerical model, which is composed of a square fiber section model for the columns, a T-shape fiber section model for the beam and slab, and a rigid joint model for the beam-column joint. A parametric analysis of the effective slab width is performed to analyze its effects on the modal shape and natural period. The results suggest that the primary natural period of the considered model is almost identical to that associated with the experimental results. The applicability of the 2D numerical model for estimating the seismic response of the structure is established. By comparing the results of the seismic analysis and the experiment in the 50% amplitude of the JMA-Kobe wave, which corresponds to slightly exceeding VII on the modified Mercalli intensity scale, the root-mean-square percentage error of the 2D numerical model is 1.03% for the floor acceleration and 4.7% for the inter-story drift. Thus, the analytical model used in this study has sufficient accuracy in evaluating the seismic performance of buildings constructed in regions with a maximum seismic intensity of VII.

Shear lag effect of twin I-shaped composite girders in cable-stayed bridges

The five loading cases for experimental models were designed to investigate the shear lag effects in composite girders of a cable-stayed bridge at the action of the positive or negative moment combined with axial and shear forces. The governing differential equations were established for the composite girder in cable-stayed bridges. The finite segment model considering the slip effect was developed using the differential equations solutions as displacement patterns. And the applicability of the finite segment model was calibrated with experimental results. The key influencing factors of effective width were analyzed by the full-scale parametric study. The slab width and cable spacing are the key factors controlling the effective slab width in composite cable-stayed bridges.

Experimental behavior based on effective slab width acting as a flange with supporting steel beams in composite floors with openings

An experimental study with many variables was carried out to investigate the effective width of simply supported composite beams (T&L sec. beams) with & without slab opening. Three full-scale composite slab models with six different carrier simply supported composite beams (three with T-sec. & three with L-sec.) with constant slab rectangularity was tested. Each model loaded by uniform load (in the elastic zone) then loaded by means of two-concentrated load system acting at equal distances from supports till failure. One of them without slab opening and the others with two symmetric slab openings and constant opening horizontal position. All standard tests were performed and all instructions and precautions were followed as perfect as the laboratory instruments permitted. All experimental steps were executed in a manner such that meeting practical conditions as exactly as could. In this research, the tested model features, materials properties and measurement instrumentations are described in brief. The maximum load carrying capacity; crack patterns, generated strains and deflections at different positions were experimentally investigated. For the sake of analysis generalization and error minimization, all results were analyzed by means of dimensionless relations. The results were recorded and analyzed guided by their mechanical behavior. Interesting gained results, conclusions and recommendations are introduced.

Numerical simulation and simplified calculation of the effective slab width for composite cable-stayed bridges

With the advent of progressively large and complex structures, the simultaneous presence of axial forces and bending on bridge decks is emerging as a recurring and increasingly concerning phenomenon. In the design of steel–concrete composite cable-stayed bridges, the combination of the axial force, mainly induced by the inclination of the cables, and bending is being increasingly considered to realize long spans that can bear the weight of the structure while ensuring a high rigidity of the deck. Despite its importance, this aspect is not sufficiently treated in the design codes, e.g., Eurocode specifications do not consider the axial force and its shear lag effects; therefore, the design rules are specified exclusively for the case of bending. From a practical standpoint, this deficiency can entail design complications due to the use of complicated FE models (shell and brick elements), which incur significant computational loads and design effort. In this study, a simple methodology for the design and verification of a girder composite deck subjected to combined compression and bending is developed. The methodology is based on a parametric study performed using finite element (FE) models that are valid for a generic girder composite deck. The stress distribution on the composite deck can be assessed while accounting for the axial force and bending moments associated with the deck by considering the results obtained using universal beam models. The proposed methodology is applied to an existing cable-stayed bridge.

Determining the effective slab width of composite joint with the weak-axis connection for ultimate bearing capacity

Extensive brittle failures on the weld zone of beam bottom flange in composite joints of SMRFs were observed during the Northridge earthquake. One of the main reasons is the sizeable tensile strain demand generated at the beam bottom flange zone under sagging bending. The key to accurately understanding the mechanical properties of composite joints is the effective width of the slab. However, the previous research is all aimed at the I-section composited joints with column strong-axis connection or CFST column connection. Therefore, the research conclusions may not suit the composited joint with the weak-axis connection. Beam column weak axis connection is as universal as the strong axis connection. Therefore, this paper used ABAQUS software to investigate the effective width of the slab in composited joints with the weak-axis connection. Firstly, it defines the ultimate state of bearing capacity corresponding to the analysis in this paper. Secondly, it investigates the influence factor on the effective width of the slab under the ultimate sagging moment and hogging moment. Thirdly, it uses Gray Correlation Theory and MATLAB to fit the calculation formula of the effective width of the slab under the ultimate sagging moment and hogging moment. Fourthly, it compares the slab's effective flange width in the previous experiment and the formula presented in the paper. Finally, analyze the applicability of the fitting formula to the strong axis rigid composite joints and T-shaped rigid composite joints of the I-shaped column and H-beams.

Prediction model for load effective distribution width of slab in composite box girders using gene expression programming

To determine the loading condition of the deck slab in girder bridges, the concept of the load effective distribution width is widely accepted in practical design. However, effective models for calculating the load effective distribution width of deck slab in steel–concrete composite box girders (SCCBG) are still lacking, which may bring about significant errors in slab design. In this study, a rational model to calculate the load effective distribution width of deck slabs in SCCBG in both the elastic and elastoplastic stages is proposed using the gene expression programming (GEP). First, four loading tests were conducted and elaborate finite element (FE) models were developed to investigate the load distribution of the slab in SCCBG. The FE models were validated by the test results and then applied to conduct a comprehensive parametric study to obtain the influences of the design parameters and the database for the GEP model. On this basis, formulas forthe load effective distributionwidth in the elastic and elastoplastic stages were proposed by using the GEP algorithm. Furthermore, extra testing data were applied to verify the validity of the proposed models. By comparing the results given by several bridge codes, it is demonstrated that the proposed models can provide more accurate and reliable predictions and are quite simple and useful for pre-design applications.

Numerical evaluation for the effective slab width of continuous composite beams

Basic beam bending theory and the effective width concept are commonly used in the design and analysis of steel–concrete composite beams to evaluate deflections, stresses, and strengths. The shear-lag effect is partially accountedfor by adopting a reduced “effective” slab width rather than the actual slab width. Besides the precise numerical values obtained via numerical analysis of a composite beam, Code provisions should provide a simplified practical techniquefor calculating effective slab width that is both simple and precise. Current design codes propose effective width values that are essentially a function of the beam span, ignoring the effects of other essential factors. Finite element analysis of continuous composite beams is a complex task, as large numbers of contacts and meshing elements are required to catch all the physical phenomena; this leads to potential convergence difficulties using a general static analysis. In this paper, several 3D numerical simulations of a composite continuous beam are conducted using the RIKS method available in ABAQUS. Comparisons to available experimental results are used to validate the proposed FE model. Then, the so-validated numerical model is utilized to perform a parametrical study to assess the effect of the longitudinal reinforcement at the hogging moment region and the influence of the concrete slab width on the effective width evaluation. Finally, the proposed finite element model and EC4 specification results are compared to draft a useable design guide.

A Proposal for a Simple Method for Determining the Concrete Slab Width of Composite Beam-to-Column Joints

Extensive brittle failures in the weld zone of the beam bottom flange in composite joints of SMRFs were observed during the Northridge earthquake and the Kobe earthquake. One of the main reasons is the large tensile strain demand generated at the beam bottom flange zone under positive bending. The key to accurately understanding the mechanical properties of composite joints is the effective width of the slab. However, researchers have no consensus on the flange slab’s effective width for composite joints, even with the simplest solid concrete slab. Therefore, the best way to design the composite joint specimen is by following the current design specifications. However, each specification implements different ideas and approaches for specifying an effective slab width. This paper presents comparisons of the effective flange width provisions in China, the United States, Australia/New Zealand, and the European Union. The characteristics of each provision are briefly described and summarized. Numerical comparisons for positive and negative moment regions of continuous spans follow. Based on the commonalities and main differences among all these provisions, we propose a recommended equation for calculating the effective width of a solid concrete slab, reflecting the specification differences. The reliability of the recommended equation was verified with ABAQUS software analysis. The recommended equation can meet the fast and secure design requirements for composite joints in tests with concrete slabs.

Numerical investigations on the influence of transverse beams and slab on the seismic behavior of substandard beam-column joints

The paper investigates the seismic performance of non-seismically designed reinforced concrete exterior and interior beam-column joints. The study focuses on the influence of transverse beams and slab on the sub-assemblies which are failing due to a joint shear failure. In the case of exterior joints, top and bottom longitudinal deformed bars of the loaded beam are anchored with a 90° bend in the joint, where no transverse reinforcement is available. The work is carried out in the framework of a 3D finite element analysis, where the microplane model with relaxed kinematic constraint is used for the constitutive law of concrete. First, the numerical approach is validated against an experiment from the literature carried out on an exterior edge joint with transverse beams and monolithically cast slab. The verification of the modeling approach is done in terms of cyclic load–displacement behavior and crack pattern. The validated modeling approach is then used to further analyze various configurations of exterior and interior joints without and with transverse beams and slab. The results of the numerical study show that the presence of transverse beams leads to an increased joint shear strength due to the confining action, whereas the slab substantially affects the flexural behavior of the loaded beam as well as the overall load transfer in the sub-assembly. It is found that the presence of slab leads to an unsymmetric load–displacement behavior under positive and negative moments, particularly when a relatively high effective slab width is contributing under negative moments. The results are evaluated to obtain the values of critical principal tensile stresses for joint shear strength that might be appropriate for the analysis of joints of different configurations considering the presence of transverse beams and slabs.

Flexural behavior of web embedded steel-concrete composite beam

This paper discussed a new web-embedded steel–concrete composite beam (WTSCB). The WTSCB consists of an inverted T-section steel section and a concrete slab. Five kinds of new shear connectors were designed at the web top and embedded in the concrete slab. In comparison with the conventional composite beam, shear connector welds are not necessary in the WTSCB. Push-out tests were conducted to investigate the shear property of the connectors, in which the load transferring mechanism of shear connector was researched and the calculation method of shear resistance was proposed. Then bending tests, considering effective width of concrete slab and shear connection types, were conducted on ten WTSCB specimens. Bending failure mode and excellent deformability were presented in WTSCB specimens. Moreover, the design methods including shear connection degree, bending capacity and elastic bending stiffness were proposed based on Eurocode 4.

Negative bending behavior of novel U-shaped steel and concrete composite beams

The negative bending behavior of the reinforcement stiffened cold-formed U-shaped steel and concrete composite beams (RCUCBs) is discussed in this paper. The negative bending experiment on 10 specimens were conducted and the damage process and corresponding static behavior in each stage are defined. Two distinct failure modes were found depending on whether the inverted U-shaped reinforcement (IUR) is installed or not: ductile plastic failure mode (when installed) and sudden elastic failure mode (when not installed). The IUR was observed to keep the integral action and improve the bending capacity and ductility of a RCUCB. The closed steel U-section stiffened by the reinforcement truss provides significant confinement to the encased concrete and even maintains its integrity after concrete cracking. The study results show that the plastic hinging of the framed RCUCB under vertical loads spreads to about L0/6 and suggest that the effective slab width in the negative moment zone is Be = L0/3 + b, similar to the positive moment case. Lastly, a negative bending design method was proposed, giving good calculations compared to the test results. The slab reinforcement, steel U-section, encased concrete, and bottom reinforcement contribute 53%, 30%, 11%, and 6% respectively to the negative bending capacity on average.

Experimental study of steel-concrete composite beams with slab opening

This study investigates experimentally the effect of openings in the concrete slab of the composite beams. Composite beams consisted of concrete slab connected with steel I-beams by steel headed stud connectors is used in the study with eleven specimens. The test specimens are designed to test and failed in flexure. The test specimens are classified depending on the variable parameters into the following groups: control sample; opening ratio; ratio the short to the long dimension of opening; thickness of the concrete slab; grade of compressive strength; strengthen of opening by steel plate. The results of the study indicate that the general trend in the ultimate load is to increase with increasing thickness of the concrete slab and increasing the compressive strength of concrete. While the ultimate load decreased when increasing the opening ratio because decreasing the effective width of the concrete slab and the cracks develop when the opening was near to the applied loads. Also, the distribution of shear connectors in place of opening on both sides and present the diagonal reinforcing rebars about the opening minimize from the significant decrease for the ultimate load.