An experimental investigation on beam supported reinforced concrete skew slabs
K. U. Muthu, M S Ramaiah Institute of Technology, Bangalore, India M. U. Aswath, Bangalore Institute of Technology, Bangalore, India A. Prabhakara, University Viswesvaraya College of Engineering, Bangalore, India
An experimental programme has been designed to cast and test 18 beam supported reinforced concrete skew slabs subjected to distributed loading. The variables include edge rigidity, skew angle and coefficient of orthotropy. The load deflection behaviour, ultimate strength and the effect of cracking were studied and the results are presented. The current work highlights the effect of membrane action on skew slabs with lateral restraints and its signficance.
A finite element formulation for concrete structures in plane stress
G. Bertagnoli, Department of Structural and Geotechnical Engineering, Politecnico di Torino, Italy V. I. Carbone, Department of Structural and Geotechnical Engineering, Politecnico di Torino, Italy
A comprehensive, very compact non-linear finite element is proposed, which is able to describe the behaviour of two-dimensional concrete structures from serviceability conditions up to collapse. The formulation of this finite element takes into account all the material non-linearities typical of concrete structures such as cracking, non-linear behaviour in compression, tension and compression softening and shear transmission along cracks. The robustness of the finite element derives from its compactness and from the reduction of the number of input parameters that control the structural response, but whose values very often cannot be properly introduced. The proposed finite element is calibrated by reproducing a wide range of well-known experimental tests, carried out both on simple panels and complex two-dimensional structures; it is then tested with reference to three additional cases, where it shows a satisfactory capability to predict reinforced concrete two-dimensional structural behaviour.
Strength and durability of high-volume fly ash concrete
G. Baert, Magnel Laboratory for Concrete Research, Ghent University, Belgium A.-M. Poppe, Magnel Laboratory for Concrete Research, Ghent University, Belgium N. De Belie, Magnel Laboratory for Concrete Research, Ghent University, Belgium
The effects of replacing 10, 40 or 60% of the cement content by low-calcium fly ash on the compressive strength and durability of the concrete were investigated. An appropriate amount of (super)plasticiser was added to the mix to obtain good workability. At an early age the compressive strength decreases with increasing level of cement replacement. After 28 days the compressive strength increased relatively more for high-volume fly ash concrete than for the control concrete. Concrete with fly ash performed better in lactic/acetic and sulphuric acid during accelerated experiments. The chloride diffusion coefficients resulting from accelerated chloride migration tests were significantly lower for concrete with fly ash than for the control concrete, except for the mixture with 60% replacement of the cement content. The resistance to frost/thaw cycles was similar for all concrete mixtures. The carbonation depth after 9 weeks in a 10% carbon dioxide (CO2) environment increased with increasing fly ash content. High volumes of fly ash also decreased significantly the resistance against the combined action of frost and de-icing salts (3% sodium chloride (NaCl) solution). From these results it can be concluded that high-volume fly ash concrete has a potential for commercial use in particular applications.
Member analysis is the main verification method adopted for reinforced concrete (RC) beams by most codes. The verification by means of member analysis consists of comparing the design forces (bending moment, axial force and shear force) with the resisting forces, where the former are computed at ambient temperature and the latter are evaluated using simplified methods considering the prescribed fire duration. The main objection that might be raised against member analysis is that, by computing the design forces at ambient temperature, indirect actions arising in the structure owing to thermal expansion are not taken into consideration; the time-dependent response of the structure is also neglected. In this paper, the behaviour of a set of fixed-end rectangular beams with varying axial restraints is discussed. The results are used to illustrate a simplified plastic verification procedure that allows determination not only of the load-carrying capacity of the beams, but also evaluation of the deflections for any given fire duration.
Flexural response of reinforced concrete beams exposed to fire
V. Kodur, Michigan State University, USA M. Dwaikat, Michigan State University, USA
The flexural response of reinforced concrete (RC) beams exposed to fire is investigated in this paper. A macroscopic finite element model, capable of tracing the behaviour of RC beams from pre-fire stage to collapse in fire is used in the analysis. The model includes the three stages associated with fire resistance analysis, namely establishing the fire temperature - time development, calculating the heat transfer through the structure from fire and the structural analysis. The model is applied to investigate the effect of six parameters, namely the fire scenario, load level, concrete cover thickness, aggregate type, failures criteria and span length on the fire response of RC beams. Through the results of the parametric study, it is shown that the type of failure criterion, load level, fire scenario, concrete cover thickness and aggregate type have significant influence on fire resistance of RC beams. It is also shown that, while the span length has significant influence on the overall fire behaviour, it has a minor effect on the fire resistance of RC beams.
Mass transport through concrete walls subjected to high temperature and gas pressure
A. Laghcha, LGCIE, INSA-Lyon, France G. Debicki, LGCIE, INSA-Lyon, France B. Masson, EDF/SEPTEN, France
The aim of this study is the modelling of mass transport phenomena through a concrete wall, when a gas (dry air plus water vapour) at high temperature and pressure is applied to one face of the wall. The temperature of the heated wall was increased from 20 to 141 C, while the other wall was exposed to ambient conditions. A uni-dimensional numerical analysis was performed, by using the thermohydromechanic model (THM) included in theCode_Aster for the description of non-saturated porous media. Two fluid phases were considered in the material: a liquid phase (water) and a gas phase (dry air plus vapour). The vapour-to-liquid phase change was introduced as well. Owing to the progressive saturation of the wall, the porosity, the shape of the sorption isotherm and the permeability greatly influenced the results. The numerical results are compared with experimental investigation. The tests concerned three concrete cylindrical specimens, which represented core samples extracted from a concrete wall. During the tests, the specimens were subjected to the same boundary conditions found in the wall (front end-section exposed to the autoclave and back end-section exposed to ambient temperature, and the lateral surface sealed and insulated to eliminate lateral hygral and thermal flux). Three different cementitious composites were tested (two concretes with different permeability for the first and second specimens, and one with highly porous mortar for the very permeable 'flaw' created in the third specimen). The numerical results were in good agreement with the tests in terms of phenomenological evolution and flow rate through the concrete, and confirmed the necessity of having reliable data on the thermal - hydromechanical properties of the material, to guarantee the validity of the results.
