1,721,039 research outputs found
The effects of shear deformations of the steel member on the behaviour of composite steel-concrete bridges
No full textThis paper presents an analytical model for the analysis of composite steel-concrete bridges. The particularity of the proposed model is its ability to combine the shear deformability of the shear connection (i.e. partial interaction theory) with the one of the steel component. This is obtained by coupling an Euler-Bernoulli beam for the reinforced concrete slab to a Timoshenko beam for the steel beam. The balance conditions are derived using the principle of virtual work and the weak form of the problem is presented. The steel of the beam and the steel of the slab reinforcement are modelled by using linear elastic laws, while the time-dependent behaviour of the slab concrete is included by using a general linear viscous-elastic integral-type constitutive law. The numerical solution is obtained by means of the finite element method implementing a time-stepping procedure based on which extensive parametric study is carried out on approximately 100 realistic three-span composite beams. The numerical results obtained with the proposed model are compared to those of the composite beam model with partial shear interaction that does not include the shear deformability of the steel beam
Stochastic and recursive estimation of the hygro-thermo-chemical-mechanical parameters of concrete through Monte Carlo analysis and extended Kalman filter
No full textHygro-thermo-chemical-mechanical models, used to determine the variations over time of temperature, relative humidity and shrinkage induced deformations in concrete components, are characterised by the presence of a large number of input parameters. Some of these parameters can be evaluated on the basis of the concrete mix specifications or from literature data, while the others present a large variability and, in some cases, do not have a precise physical meaning and, for this reason, require the implementation of proper identification strategies. The experimental work involved for this characterisation can be time-consuming and costly because based on the long-term monitoring of the time evolution of the field quantities in specific positions within concrete components. The aim of this paper is to propose and validate recursive identification strategies that exploit, in a step by step fashion, the information coming from the experimentation for the identification of the model input parameters. The influence of different exposure conditions and of different concrete thicknesses are investigated and, for each scenario considered, the expected identification error of each parameter is estimated, within a stochastic context implemented through Monte Carlo analyses and Kalman Filter, as a function of the monitored time
A hygro-thermo-chemical-mechanical model for the service response of composite steel-concrete floor systems
No full textComposite steel-concrete floor systems are widely used throughout the world for building applications. This paper focuses on the service behavior of composite floors that usually consist of composite slabs in steel framed construction and of post-tensioned composite slabs in concrete structures. In the initial part of the paper, recent experimental work carried out on composite floor slabs is outlined and it includes the description of the occurrence of a non-uniform shrinkage profile through the slab thickness due to the inability of the concrete to dry from its underside because of the presence of the profiled steel sheeting. A hygro-thermo-chemical-mechanical model is then presented to predict the service response of composite floors. The proposed approach is validated against experimental data collected on post-tensioned composite samples. For this purpose, an inverse analysis procedure is applied for the characterisation of the numerous material parameters and the multi-physics model is used to predict the non-uniform shrinkage gradient. Based on this, a design model available in the literature is then used to evaluate the long-term deflections and compared the calculated values against long-term experimental measurements. Simplified models have also been used to determine the shrinkage profile for benchmarking purposes. It has been shown that the numerical and experimental deflection comparisons show good agreement when determined using a non-uniform shrinkage distribution, while the calculated values underestimate the observed deflections when obtained with a uniform shrinkage profile
Shear connection slip demand in composite steel–concrete beams with solid slabs
No full textThe objective of this work is to provide insight into the expected slip demand in the shear connection of composite steel–concrete beams through the use of a numerically efficient nonlinear beam model previously validated by comparisons with experimental tests. The results of a parametric analysis involving 1680 simply supported beams are illustrated to investigate the influence that various design parameters (i.e. span length, degree of shear connection, steel beam and concrete slab cross-section geometry, connection distribution, dead load to live load ratio, propped and unpropped construction sequences, and concrete strength) and modelling parameters (i.e. shear connection representative strength and constitutive parameters) have on the slip demand. It is observed that, for a given shear connection degree, the most important parameters are the construction sequence, the span length, and the steel section shape. In addition, the shear connection distribution can have an important effect and non-uniform shear connection distributions with more connectors near the supports might be effective in limiting the slip demand. The results illustrated in this work can be a support for more efficient designs of the shear connection in composite steel–concrete beams and a basis for possible improvements of their current design recommendations
Analysis of shear connection slip demand in simply supported steel-concrete composite beams
No full textThe objective of this study is to provide insight into the expected slip demand in composite steel-concrete beams through numerical simulations. A wide parametric analysis is carried out evaluating the partial interaction performance of simply supported beams designed considering a variety of floors, i.e. span length, slab thickness, shear connection strength, dead load to live load ratio, slab concrete strength. For each of these beams, the slip demand required to achieve the expected design capacity is evaluated. In this process, key parameters influencing the slip requirements are identified. These also include the construction sequence (propped or unpropped) and the shear connection distribution (uniform or non-uniform with different layouts)
Service and ultimate behaviour of composite steel-concrete beams subjected to combined bending and shear
No full textThis paper describes the behaviour of composite steel-concrete beams subjected to combined bending and shear at both service and ultimate conditions. In particular, it is shown that for realistic composite bridge arrangements it is important to account for the shear deformability of the steel beam for an accurate prediction of the instantaneous and long-term deflections, which otherwise might be underestimated. At the ultimate limit state conditions, it is highlighted that for an adequate evaluation of the composite response subjected to significant actions of combined moment and shear force, it is necessary to consider the shear behaviour of the steel and slab components. This is accomplished comparing the results of three composite beam models accounting for the deformability of the shear connection at both service and ultimate conditions, while varying the beam models adopted to represent the response of the slab and the steel beam. The proposed formulations could be used to complement the analysis tools available to bridge designers
A steel-concrete composite beam model with partial interaction including the shear deformability of the steel component
No full textThis paper presents an analytical model for the analysis of steel–concrete composite beams with partial shear interaction including the shear deformability of the steel component. This model is obtained by coupling an Euler–Bernoulli beam for the reinforced concrete slab to a Timoshenko beam for the steel beam. The composite action is provided by a continuous shear connection which enables relative longitudinal displacements to occur between the two components. The balance conditions are derived using the principle of virtual work and the weak form of the problem is presented. The steel of the beam and the steel of the slab reinforcement are modelled by using linear elastic laws, while the timedependent
behaviour of the slab concrete is included by using a general linear viscous–elastic integral-type constitutive law. The numerical solution is obtained by means of the finite element method implementing a time-stepping procedure. The derived displacement-based finite elements are
tested and their performance is discussed. Extensive numerical simulations are carried out on approximately 200 realistic simply supported and three-span composite beams to evaluate the effects of the shear deformability of the steel member on the overall structural response. The numerical results obtained with the proposed model are compared to those of the composite beam model with partial shear interaction that does not include the shear deformability of the steel beam to determine under which conditions shear deformations of the steel component need to be considered in the analysis of composite systems and to evaluate how these are affected by the shear connection stiffness and by the redistributions due to the time-dependent behaviour of the concrete slab
Beam tests of composite steel-concrete members: a three-dimensional finite element model
No full textModern construction makes frequent use of composite steel-concrete beams for bridge and building applications. This paper describes a three-dimensional finite element model in which all components forming the composite member are modelled by means of solid elements. The proposed approach is developed using the commercial software Abaqus and is able to model the composite response without requiring information from push-out tests commonly performed to define the constitutive relationship for the shear connectors. All materials are assumed to behave in a nonlinear fashion. Contact between the elements is simulated using surface-to-surface and embedment techniques. The adequacy and accuracy of the proposed modelling approach are validated against experimental results available in the literature on simply-supported and continuous beam tests with both solid and composite slabs
Long-term behaviour of composite steel-concrete structures: an overview of the state of the art
No full textThis paper presents the current state of the art on the modelling and experimental work dealing with the long-term behaviour of composite steel-concrete structures and how this affects the response at service and ultimate conditions. The structural elements considered include columns, slabs and beams. In the latter case, only H-shaped or box steel sections with a solid and composite slabs have been considered. In the initial part of the paper considerations on the time-dependent behaviour of the concrete are provided for each structural element to account for the different drying conditions which, for example, occur in the presence of the hollow sections in columns and of the steel deck in floor systems. When presenting previous work on the long-term response of composite columns particular attention is placed on the influence of time effects on the ultimate response, considerations on confinement at service conditions and creep buckling. Only brief considerations are provided for the long-term response of composite slabs because of the very limited work carried out in this area. Despite this, recent research dealing with the development of shrinkage gradients through the thickness of slabs cast on profiled sheeting is provided. Considerations on the work carried out to date on composite beams are presented with particular focus given to design related issues, such as the determination of the concrete slab effective widths, shear-lag effects, influence of time effects on the ultimate response, prestressing and buckling. The paper concludes with recommendations for future research work to be carried out in this area
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