Modelling of temperature profiles in a concrete slab under climatic exposure
O. Larsson, Lund University, Sweden
Effects of surrounding climate impose temperature variations in both time and space for concrete structures. The associated thermal strains may give rise to stresses and cracking due to external or internal restraint. This will affect the performance of the structure. It is therefore important to analyse the temperature variations and the extreme situations that can occur. To predict the dynamic thermal conditions in concrete structures a finite-element model has been developed. The ability of the model to describe correctly the various boundary conditions such as solar radiation, outgoing long-wave radiation and convection is investigated in this paper. Field temperature measurements in a concrete slab placed outdoors are used for the validation. The necessary climatic input data for the model were obtained from measurements in the vicinity of the slab. The results show that the model can describe with good accuracy the effects of different climatic factors in extreme situations and is well suited to use in further studies.
Metakaolin: a versatile material to enhance the durability of concrete - an overview
A. K. Parande, Central Electrochemical Research Institute, Karaikudi, Tamilnadu, India R. H. Chitradevi, Central Electrochemical Research Institute, Karaikudi, Tamilnadu, India K. Thangavel, Central Electrochemical Research Institute, Karaikudi, Tamilnadu, India M. S. Karthikeyan, Central Electrochemical Research Institute, Karaikudi, Tamilnadu, India B. Ganesh, Central Electrochemical Research Institute, Karaikudi, Tamilnadu, India N. Palaniswamy, Central Electrochemical Research Institute, Karaikudi, Tamilnadu, India
The utilisation of calcined clay in the form of metakaolin as a pozzolan for concrete has received considerable interest in recent years. The use of metakaolin as a mineral admixture for concrete is a well-documented practice. Metakaolin is a quality enhancing pozzolan for concrete. In this review paper the work done by various researchers on the effect of the addition of metakaolin to modify the properties of concrete are documented; source and manufacture, fresh concrete properties, hardened concrete and durability. From the survey it is concluded that metakaolin enhances early strength in concrete through a filler effect. Metakaolin also enhances long-term strength and durability of concrete and corrosion resistance. Less work has been carried out in corrosion studies and some of these works are highlighted in this review paper.
Failure analysis of hollow-core slabs tested in shear
G. Bertagnoli, Politecnico di Torino, Italy G. Mancini, Politecnico di Torino, Italy
Many experimental campaigns on hollow core slabs put into evidence critical shear behaviour of such structures. Widespread perplexities on the actual shear resistance of such members took place in the scientific community when the results of these experimental campaigns were published. As a first result the model proposed in the Model Code 90 and in the Eurocode to evaluate the uncracked shear capacity of prestressed elements was supposed to overestimate the real ultimate strength of the members. A more careful interpretation of the shear design of such structures is presented in this paper and shows that there is no safety risk if these slabs are designed with care. The ultimate behaviour of hollow core slabs mainly subjected to shear actions is related to many different phenomena such as prestressing dispersion, anchorage of prestressing strands, cracking bending moment and, of course, shear resistance. The mutual interaction of such phenomena asks for a multi-criteria design approach which is presented in the following and which gives very good results when compared to experimental campaigns output.
Extreme strength criterion and design of RC elements
V. P. Mitrofanov, Poltava National Technical University, Ukraine
This paper presents an improved design of reinforced concrete elements (RCE) subjected to flexure and eccentric compression or tension. The disadvantages of the traditional deformational strength criterion of concrete as confirmed by experimental data are noted. Emphasis is put on the difficulties in determining ultimate concrete strain experimentally, as well as in accounting for the influence of many conditions and factors. To remove these disadvantages, the extreme strength criterion (ESC) is proposed and used. The ESC expresses the determination of the maximum load parameter as a function of the extreme fibre compression compressive strain ecu in a RCE section at failure. On the basis of the ESC, a new general design method is developed for RCEs under bending and eccentric compression/tension. In addition to the constitutive relations for concrete and steel, the plane sections hypothesis and the balance equations, the proposed method includes the ESC, which replaces the traditionally used concrete strength criterion. The advantages of the proposed method are demonstrated to be generality, completeness, exactness, reliability and systematic accounting of a large number of factors. The proposed method does not require the experimental determination of the ultimate concrete strain, because the ecu is found during solution of the RCE strength problem as one of the unknowns of the equation system.
Concrete structure ownership and management: part 2
S. L. Matthews, Building Research Establishment, UK J. Jacobs, Technial Approvals and Standardisation Division, BBRI, Belgium I. Stipanovic Oslakovic, Civil Engineering Institute of Croatia, Zagreb, Croatia D. J. Cleland, Queen's University, Belfast, UK
With correct design, specification and construction, concrete structures provide high-performance durable assets with long service lives. Owners can maximise the benefits to be gained from concrete structures, while minimising through-life cost and sustainability impacts, by taking a through-life perspective on the design, specification and management of their structures; rather than simply focusing on first cost. This second part of a two-part paper provides an overview of the advice given in the fib guide to good practice entitled Concrete Structure Management - Guide to Ownership and Good Practice (fib Bulletin 44)
Design equation for predicting fire resistance of reinforced concrete columns
V.K.R. Kodur, Michigan State University, East Lansing, MI, USA N. K. Raut, Michigan State University, East Lansing, MI, USA
An empirical equation for evaluating the fire resistance of reinforced concrete (RC) columns is presented. Data from a large set of experimental studies are analysed to study the influence of various parameters on the fire resistance of RC columns. The fire test data are utilised to develop a simplified equation for expressing the fire resistance of RC columns as a function of influencing parameters. The validity of the equation is established by comparing the predictions from the empirical equation with data obtained from fire resistance experiments and analytical studies. Predictions from the proposed equation are in good agreement with the test results and computer models, and provide better estimates of fire resistance than those predicted from current codes of practice. The proposed equation also incorporates parameters such as load eccentricity, which is not included in the current equations available in the literature. Furthermore, the proposed equation expresses the fire resistance in terms of conventional structural and material design parameters, and thus facilitates easy calculation of fire resistance.
