Effective Slab Width Research Articles

Assessment of effective slab widths in composite beams

This paper deals with the behaviour of composite beams with particular focus on the effective slab width, which is required for simplified structural analysis and design. Current design codes propose values for the effective width which are mostly a function of the beam span ignoring in this way the influence of other important parameters. Several 3D numerical simulations are conducted in this paper in order to illustrate these parameters and accordingly a new methodology is suggested for evaluating the effective width. The proposed approach is easier to apply in comparison with other existing methods based on stress integration, and provides effective width values which result in a more reliable representation of the actual beam state when simplified analysis is carried out. The application of the new method indicates that the effective width is mostly related to the actual slab width and, in many cases, the values obtained can significantly differ from those proposed in design codes. Validation of the new approach is carried out through comparison of simplified 2D models with the results obtained from a recent experimental investigation as well as from more complex 3D numerical simulations.

Launching of the San Cristobal Bridge

The San Cristobal Bridge in Chiapas, Mexico, is a three-span (71.5, 180, and 71.5 m) curved steel composite and orthotropic box girder erected by incremental launching. Lessons learned from the collapse during launching of the San Cristobal Bridge as well as the redesign and relaunching of the new bridge are discussed. After the collapse of the San Cristobal Bridge, T. Y. Lin International was hired by the new contractor, Ingenieros Civiles Asociados, to investigate the cause of the collapse of the original bridge, check the redesign of the bridge, and perform the erection engineering of the bridge. From the site investigation, it was concluded that the collapse of the structure was caused primarily by the failure of the shear studs and the consequent loss of composite action of the girder cross section over Pier 2. To ensure the safe erection of the structure, the redesign of the new bridge included the following changes: addition of shear studs, increase of deck posttensioning during launching, increase of the concrete slab strength, and addition of stiffeners to the bottom flange and webs. To match the predicted and measured deflections during launching, a calibration of the effective deck inertias (consistent with a 12 × tslab and contrary to the AASHTO specifications) was necessary to account for the effects of shear lag and the actual effective slab width.

Effective Slab Width in Prestressed Twin-Girder Composite Decks

The paper shows the shear-lag effect in slabs of twin-girder steel.concrete composite decks due to the main prestressing techniques such as support settlements, bonded cables inside the concrete slab, and external slipping tendons. The analysis is performed by means of a beam model taking into account the loss of planarity for the slab cross section, the flexibility of the shear connection, and the time-dependent behavior of the concrete. A linear elastic behavior is considered for the steel beams and shear connection while viscoelastic behavior is assumed for the concrete slab. A parametrical analysis is carried out on realistic bridge decks for each kind of prestressing technique, by varying the span length and the girder spacing. The distribution of longitudinal normal stresses in the slab is shown for each prestressing technique and the effective slab widths are then evaluated and compared with those suggested by ENV 1994-2 for different span lengths and for different spacing of the beams.

Effective width of a concrete slab in steel–concrete composite beams prestressed with external tendons

The finite element method is applied to evaluate the effective width of a concrete slab in composite beams prestressed with external tendons. The beams studied are simply supported, with external prestressed strands straightly and draped arranged. The effective width for the prestressed composite beams evaluated based on the finite element parametric study is compared with that of plain composite beams without prestressing, and code provisions. The influence of the shear connections on the effective width and the shear slips along the beam span, as well as the incremental stresses developed in the prestressed strands, are analyzed. The behaviors of the external prestressed composite beams subject to the shrinkage and creep in the concrete slab are also discussed.

Methodologies for Evaluation of Effective Slab Width

A composite section is made up of a steel girder and concrete slab connected by shear connectors. The shear lag phenomenon usually takes place in such a section and results in underestimation of stresses and strains at the web-to-flange intersections of the girder. With the introduction of the concept of effective slab width, the actual width can be replaced by an appropriate reduced slab width. The classical effective slab width definition does not take into account the strain variation through the slab thickness. More sophisticated definitions are introduced and used with finite element analyses. The method of finite element modeling is discussed, and the model is successfully verified with experimental results. Parametric study is conducted to investigate the effective slab width for both positive and negative moment sections. The effective slab width is computed and compared with the current AASHTO load and resistance factor design (LRFD) specifications. The results demonstrate that full width can be used as the effective slab width in the design and analysis in most cases for the design and analysis of both positive and negative moment sections. The current AASHTO LRFD specifications are found to be conservative for configurations with widely spaced girders, especially in negative moment sections.

Methodologies for Evaluation of Effective Slab Width

A composite section is made up of a steel girder and concrete slab connected by shear connectors. The shear lag phenomenon usually takes place in such a section and results in underestimation of stresses and strains at the web-to-flange intersections of the girder. With the introduction of the concept of effective slab width, the actual width can be replaced by an appropriate reduced slab width. The classical effective slab width definition does not take into account the strain variation through the slab thickness. More sophisticated definitions are introduced and used with finite element analyses. The method of finite element modeling is discussed, and the model is successfully verified with experimental results. Parametric study is conducted to investigate the effective slab width for both positive and negative moment sections. The effective slab width is computed and compared with the current AASHTO load and resistance factor design (LRFD) specifications. The results demonstrate that full width can be used as the effective slab width in the design and analysis in most cases for the design and analysis of both positive and negative moment sections. The current AASHTO LRFD specifications are found to be conservative for configurations with widely spaced girders, especially in negative moment sections.

Effective Slab Width Model for Seismic Analysis of Flat Slab Frames

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Reinforced concrete edge beam—column—slab connections subjected to earthquake loading

Four two-thirds-scale reinforced concrete edge beam–column–slab subassemblies (two concentric and two eccentric connections) were tested under quasi-static cyclic lateral loading. Each subassembly represented a cruciform connection in an exterior moment-resisting frame with a monolithic floor slab on one side only, loaded in the longitudinal direction of the edge-beams. The tests explored the effect of eccentricity between beam and column centrelines, and the effect of floor slabs, on the structural performance of edge beam–column–slab connections subjected to earthquake loading. Performance of the specimens was evaluated in terms of overall strength and stiffness, energy dissipation, beam plastic hinge development, joint shear deformation, and joint shear strength. All specimens underwent some beam hinging at the beam/column interfaces. However, both eccentric specimens, and one concentric specimen with a heavily reinforced floor slab, eventually failed as a result of joint shear, whereas the other concentric specimen exhibited more ductile load–displacement response. The eccentric specimens (with different eccentricities and edge-beam widths) underwent similar behaviour before they started to break down, and they also reached similar joint shear strengths. Slab participation was evaluated using slab bar strain gauge data with respect to storey drift. Actual effective slab widths were much larger than the ones typically used in design, especially for the specimens with a column wider than the edge-beams. Finally, floor slabs imposed significant joint shear demand, but they also increased joint shear capacity by expanding effective joint width.

Reinforced concrete edge beam?column?slab connections subjected to earthquake loading

Four two-thirds-scale reinforced concrete edge beam–column–slab subassemblies (two concentric and two eccentric connections) were tested under quasi-static cyclic lateral loading. Each subassembly represented a cruciform connection in an exterior moment-resisting frame with a monolithic floor slab on one side only, loaded in the longitudinal direction of the edge-beams. The tests explored the effect of eccentricity between beam and column centrelines, and the effect of floor slabs, on the structural performance of edge beam–column–slab connections subjected to earthquake loading. Performance of the specimens was evaluated in terms of overall strength and stiffness, energy dissipation, beam plastic hinge development, joint shear deformation, and joint shear strength. All specimens underwent some beam hinging at the beam/column interfaces. However, both eccentric specimens, and one concentric specimen with a heavily reinforced floor slab, eventually failed as a result of joint shear, whereas the other concentric specimen exhibited more ductile load–displacement response. The eccentric specimens (with different eccentricities and edge-beam widths) underwent similar behaviour before they started to break down, and they also reached similar joint shear strengths. Slab participation was evaluated using slab bar strain gauge data with respect to storey drift. Actual effective slab widths were much larger than the ones typically used in design, especially for the specimens with a column wider than the edge-beams. Finally, floor slabs imposed significant joint shear demand, but they also increased joint shear capacity by expanding effective joint width.

Field Test and Rating of Arlington Curved-Steel Box-Girder Bridge: Jacksonville, Florida

A load capacity rating procedure and the results of field tests conducted on the Arlington curved-steel box-girder bridge are presented. Two Florida Department of Transportation (FDOT) test trucks with a total weight of up to 117 tons provided the static loading. One FDOT test truck with a total weight of 52.7 tons applied the dynamic loading. The actual behavior of the bridge was ascertained by comparing the field test results with those obtained from three different theoretical mechanical models. Analysis demonstrates how the actual mechanical behavior and load capacity of a curved-steel box-girder bridge can be well predicted by a proper finite element method based on as-built bridge plans. Some important parameters, such as impact factors, the effective width of the concrete slab, and the structural effect of barriers, are discussed. Finally, the load rating factors for a variety of Florida's rating vehicles were determined on the basis of a finite element model generated from field test results and analytical modeling of the bridge. The current capacity ratings are approximately 17% to 27% higher than those determined in 1988 using a conventional analytical method. The capacity increase is due mostly to the conservativeness of traditional methods and codes. The research results are instructive and applicable to bridge design and bridge load rating.

Real strength of high-performance concrete bridge deck slabs

Deterioration of bridge deck slabs due to corrosion of reinforcement has become increasingly evident over the past 40 years and continues to be the cause of costly repair programmes. Detailing to reduce the risk of corrosion is simpler if the percentage of reinforcement is low. It is now recognised that laterally restrained slabs exhibit strengths far in excess of those predicted by most design codes. This increase in strength can be attributed to arching or compressive membrane action (CMA), and by recognising it in design, lower percentages of reinforcement can be specified. CMA has been incorporated into a small number of design standards. However, problems still exist in translating the arching theory into slabs in practice. The problem is in the assessment of the degree of external lateral restraint inherent in slab structures. This paper presents the results of tests on eight one-third-scale bridge deck edge panel models with target compressive strengths of 100 N/mm2. The test programme aimed at realistically modelling the restraint conditions intrinsic in the edge panel of a real bridge deck slab. A method for assessing the real restraint in such a slab was incorporated into an existing arching theory by using an effective slab width concept. The procedure showed good correlation with the test results and with other results reported in the literature.

The behaviour of through-deck welded shear connectors: an experimental and numerical study

This paper describes a study of the behaviour of shear connection between steel beams and composite slabs, which use through-deck welded shear connectors. An experimental study involving three push-out test specimens was carried out and these test results were discussed. A push-out test specimen was simulated and analysed in both two and three-dimensions. The effect of the inclusion of profiled steel sheeting, the effect of the width of a concrete slab, and the effect of different loading and support conditions have been discussed. The pull-out strength of the concrete has also been studied and compared with the experimental results of tests carried out by the authors and others. A new expression based on wedged cone failure has been developed for the effective width of a concrete slab in a two-dimensional numerical analysis.

頭付きスタッドの弾塑性性状を考慮した合成梁架構の弾塑性平面骨組解析

The authors propose the elasto-plastic frame analysis on steel frames with composite beams, focusing on the structural non-linearity of headed studs. The structural non-linearity was experimentally investigated while the slip rigidity was theoretically calculated. This analytical method showed a good agreement with the results of tests on steel frames with continuously spanned or long-spanned composite beams, leading to the fact that the effective width of slab on long-spanned beams should be taken shorter than designed, while the one for short-spanned beams may be taken as the same as designed.

Seismic Reliability Assessment of Existing R/C Flat-Slab Buildings

The reliability of existing reinforced-concrete flat-slab buildings, designed and detailed to resist gravity loads only, was studied for punching failure at connections under earthquake-type loading. Two flat-slab buildings, three and 10 stories in height, designed according to the ACI 318-56 building code, were used in the nonlinear dynamic analysis and reliability calculations. Results from previous experimental results on the seismic resistance of slab-column connections were employed to establish the effective slab widths, unbalanced moment-transfer capacity of connections, and their punching strength. The member dimensions, material strengths, and live load were treated as random variables and the effect of model uncertainty was included in the calculations of reliability indices. Random earthquake time histories were generated with the Kanai-Tajimi power spectrum. The limit-state function was based on the punching failure capacity of the interior slab-column connections. Based on the reliability analysis, the probability of failure of existing flat-slab buildings are presented for different soil conditions and peak ground accelerations varying from 0.05 g to 0.2 g .

Experimental and Numerical Studies of Composite Beams Exposed to Fire

The development of appropriate computer models to predict the response of buildings to fire is now making it possible to analyze specific structures under realistic fire‐exposure conditions. By means of experimental tests carried out at the University of Braunschweig on simply supported composite beams connected to reinforced concrete slabs, a theoretical study for estimating the effective slab width of composite concrete beams exposed to fire has been set up using a finite‐element analysis. The satisfactory agreement between the experimental and the calculation results confirms the efficiency of the finite‐element theory for determining the fire resistance of composite beams. The influence of the top transverse reinforcement in the concrete slab on the fire resistance and crack propagation are examined. The application of the results in designing fire safety of buildings is also discussed.

Equivalent Frame Analysis of Flat Plate Buildings for Seismic Loading

An equivalent frame approach is presented for nonlinear seismic analysis of reinforced‐concrete flat plate buildings. The approach employs a parametric hysteretic model and is based on the effective slab‐width concept. Unlike in the previous equivalent frame approaches, the proposed method targets both the moment‐transfer capacity as well as stiffness of the interior and exterior slab‐column connections. The hysteretic parameters and the effective slab width factors are determined from results of laboratory tests on slab‐column connections for the class of flat plate buildings constructed prior to the 1960s with reinforcing detail typical of gravity load design. The validity of the approach is justified by comparing the calculated and the measured responses of two‐bay flat plate subassemblies tested under earthquake‐type loading. With the proposed equivalent frame approach, the response of flat plate buildings for seismic loading could be predicted more realistically over a wide range of lateral drift levels.

Seismic response of reinforced concrete frame subassemblages — a Canadian code perspective

The 1984 CSA standard for the design of concrete structures for buildings provided new seismic design and detailing requirements for concrete structures. Full-scale, reversed cyclic loading tests of reinforced concrete beam–slab–column subassemblages were carried out to investigate the seismic performance of frame structures designed with the latest Canadian code. The test results indicate the importance of including the influence of slab reinforcement in computing the beam capacity as well as the need to carefully design the joint regions for shear. The test results indicate the excellent performance of frame components designed with K = 0.7 (R = 4.0) and the poor performance of those designed and detailed with K = 2.0 (R = 1.5). The performance of subassemblages designed with K = 1.3 (R = 2.0) depends on the column to beam strength ratio and on the shear strength of the joints. Models to predict the flexural response as well as the shear response of key elements are described and the role of the spandrel beam in limiting the effective slab width is explained. Key words: seismic design, reinforced concrete, detailing, structures, codes.

Contribution of R/C Floor Slabs in Resisting Lateral Loads

The effective width of slab to be used for the case of lateral loading has not been explicitly addressed in design codes. Ignoring the slab contribution to the flexural capacity of the beams leads to a significant underestimation in structural strength. It may also lead to a failure mechanism different than that anticipated. Tests were conducted on three one‐half scale reinforced concrete beamcolumn‐slab subassemblages to determine the influence of the torsional stiffness of the transverse beam elements on the effective width of slab participating as a tension flange to the longitudinal beam. The effect of initial damage due to loading in the transverse direction was also investigated for one of the models. All of the models were subjected to the same cyclic lateral load history. It was concluded that the effective width of slab was greater for the models with increased transverse torsional stiffness. The difference in strength among the models was larger at the earlier loading cycles. At the maximum load...

Effective widths of composite beams with ribbed metal deck

The effective width of the concrete slab of a composite beam is used in the determination of its moment resistance and service load moment for the purposes of structural design of the composite beam. It is usually assumed that the same effective width of the concrete slab may be used for both ultimate strength and elastic stage calculations.This paper presents the results of an analytical investigation of the variation of the effective width of composite beams and ribbed slabs formed by ribbed metal deck in both the elastic and inelastic stages and at ultimate load. A layered finite element method is used to model the composite beam. The influence of four variables on the effective width of the composite beams was studied, namely, type of loading, beam span to actual concrete slab width, ultimate compressive strength of the concrete, and steel beam size.It was found that the effect of the compressive strength of the concrete and the size of the steel beam have negligible influence on the effective width of the concrete slab. The effective width of the slab at ultimate load is of the order of 4% larger than that in the elastic range.The effective width used for the design of composite beams under a uniformly distributed load, which is the practical loading in most cases, is significantly different from that which should be used for any other type of loading.

合成ばり端部鉄骨フランジのひずみ性状に関する数値解析的研究 その1 : ハイブリッド型応力法に基づく合成ばりの解析法について

In this paper two numerical methods for analyzing a composite beam are proposed, which are based on the hybrid stress model. One assumes changeable effective width of concrete slab. The other assumes two dimensional stress distribution in a concrete slab. Both considers interface slip between top flange of a steel beam and a concrete slab. And these numerical methods are applied to predict the plastic behavior of two composite beams (CB 5-D, CB 5-DV) whose experimental results are reported by Dr. Igarashi et. al. (13)