Analytical derivation of the effective creep coefficients for timber-concrete composite structures (original) (raw)
Related papers
2011
The paper presents analysis of the stress and deflections changes due to creep in statically determinate composite steel-concrete beam. The mathematical model involves the equation of equilibrium, compatibility and constitutive relationship, i.e. an elastic law for the steel part and an integral-type creep law of Boltzmann-Volterra for the concrete part. On the basis of the theory of the viscoelastic body of Arutyunian-Trost-Bažant for determining the redistribution of stresses in beam section between concrete plate and steel beam with respect to time 't', two independent Volterra integral equations of the second kind have been derived. Numerical method based on linear approximation of the singular kernal function in the integral equation is presented. Example with the model proposed is investigated. The creep functions is suggested by the ACI 209R-92 model. The elastic modulus of concrete Ec(t) is assumed to be constant in time 't'. The obtained results are compared...
Behaviour of creep of timber beams under natural environmental conditions
WIT Transactions on the Built Environment, 2014
The current research is devoted to the investigation of relationships in creep behaviour of timber beams under natural environmental conditions with the purpose of detecting the factors significantly affecting such parameters as the variable moisture content of wood, temperature, stress level, span-depth ratio, macrostructure of wood and other factors, and to establish a mathematical model applicable for determining parameters related to prognosis of deflection of timber beams under variable loads. This study includes the analysis of experimental test results in static bending of 17 softwood (Pinus Sylvestris L.) beams with different span and span/depth ratios regarding a variation of moisture content, relative humidity and air temperature. The mathematical model examined in this study for the description of creep has been developed on the basis of the Burger body concept. A sufficiently good compatibility of average experimental and modelled strain values of timber beams was observed in the results. These results testify that the developed creep model may be used for predicting deformation of timber beams, and constants involved are applicable for natural environmental conditions. This study is part of extensive research that is aimed at contributing to the determination of accurate model parameters and to establishing an adequate and practically applicable mathematical model for more accurate predictions of final deflection of timber beams for design purposes. Keywords: timber beams, deflection in bending, development of creep under natural environmental conditions, mathematical model of creep.
Creep functions for wood composite materials
Wood and Fiber Science, 2007
Two related functions used to describe the creep of non-wood materials were fitted to data for wood composite materials. The first function, which is linear in its constants, was unsatisfactory for representing the creep of plywood, oriented strandboard, laminated timber, and dry-process hardboard under the given loading and environmental conditions. The second function is nonlinear in its constants. Creep of plywood and oriented strandboard were moderately well represented by this function, while creep of laminated timber and hardboard were exceptionally well represented. Experimental creep data and estimates of empirical constants are presented.
Creep behaviour modelling of a composite steel–concrete section
Journal of Constructional Steel Research, 2009
Long term behavior modelling of steel-concrete composite beams requires the use of the time variable and the taking into account of all the sustained stress history of the concrete slab constituting the cross section. In this context, a research contribution of the time-dependent behavior of composite sections under the creep influence of a concrete slab is presented in the present work. The concrete creep influence upon the composite section strength is taken into account as part of the concrete linear viscoelasticity. Thus, by considering the assumption of a complete composite connection made up of a steel beam and concrete slab, with no slip at the interface, and owing to the irreversible law of concrete, we obtain an analytical model, based upon a system of two differential linear equations governing the long term behavior of composite beam cross sections in bending. Results obtained from the application of the suggested model to a steel-concrete composite beam are satisfactory.
Parametrical Analysis of Long-Term Behaviour of Timber – Concrete Composite Bended Elements
2014
The article presents results of the parametric study in which influence of several properties of wood-concrete beams changes to their final resistance under long-term loading was investigated. Influence of concrete and wood strength changes, concrete shrinkage and effect of various environmental conditions was analysed. The changed parameters on two types of timber concrete elements with different structural systems, on beam-type and plate-type element were studied. For the analysis mathematical model derived in analytical terms was used, which takes into account viscous-elastic creep of concrete and wood, mechano-sorptive creep of wood, creep of shear connection, concrete shrinkage and the changes of environment under the long term loading.
An Effective Analytical Model for Predicting Creep Coefficient
2013
Time dependent (long–term) effects of concrete are greatly influenced and governed by creep of concrete. As a part of the study on effect of time dependent factors on the cracking behaviour of reinforced concrete flexural members, the effect of creep on the serviceability of concrete structures is studied. Based on a survey of published experimental data, equations were developed to calculate the creep coefficient of concrete at any time‘t’. This paper presents a new analytical model to predict creep of concrete, considering the main controlling independent parameters that affect creep. A parametric study of the proposed model is also included in this paper.
Recent compilation of data on numerous large-span prestressed segmentally erected box girder bridges revealed gross underestimation of their multi-decade deflections. The main cause has been identified as incorrect and obsolete creep prediction models in various existing standard recommendations, and is being addressed under a separate study. But previous analyses of the excessive deflections of the the Koror-Babeldaob (KB) Bridge in Palau and of four Japanese bridges further have shown that a more accurate method of multi-decade creep analysis is also required. Its systematic and comprehensive presentation, appropriate not only for bridges but also for any large creep-sensitive structure, is the objective of this paper. For each time step, the solution is reduced to an elastic structural analysis with generally orthotropic elastic moduli and eigenstrains. This analysis should normally be three-dimensional. It can be accomplished A member of the National Academy of Sciences and the National Academy of Engineering, he is the founding Past Chair and a member of Joint ACI-ASCE Committee 446, Fracture mechanics of Concrete. He is also a member of ACI Committees 209, Creep and shrinkage in Concrete; 348, structural safety; and Joint ACI-ASCE Committees 334, Concrete shell design and Construction; 445, shear and torsion; and 447, Finite element analysis of reinforced Concrete structures. He is a licensed structural engineer in Illinois.
Terms in the Application of Stress-strain Relations for Concrete Creep (Version 2
The application of concrete creep and shrinkage coefficients should facilitate and eliminate the dilemmas that are now present in the practice and theory of 2 RC, 3 PC and Composite structures. The first part of the paper points out the possible difficulties that arise in obtaining experimental data and the exact definition of the creep coefficient and the function of measure concrete creep. The largest part of this paper deal with how to get the expression and value of creep coefficients and measures of creep and shrinkage of concrete. The paper is intended for researchers in laboratories for testing the behavior of concrete under long-term loads. The work can be usefully informative for designers and builders. In the new version 2 of the paper, typing errors and other observed differences were eliminated for the previous version.