Modelling bond strength of corroded plain bar reinforcement in concrete
G. Xu, Huazhong University of Science & Technology, China J. Wei, Huazhong University of Science & Technology, China T. Tan, Huazhong University of Science & Technology, China H.Q. Liu, Huazhong University of Science & Technology, China
In this paper, the corrosion influence on bond strength between plain bar and concrete without confinement is studied at the time of cracking and before cracking occurs, and causes of bond strength increment are analysed quantitatively. A new calculation model for corrosion pressure and corrosion depth at the time of cracking is proposed. Considering the change of bar surface and increment of corrosion pressure, a new calculation model for bond strength at the time of cracking and before cracking occurs is given. Additionally, the theoretical model is verified using different test results.
Cost optimisation of lattice-reinforced joist slabs using genetic algorithms
V.C. Castilho, Universidade Federal de Uberlândia, Brazil M.C.V. Lima, Universidade Federal de Uberlândia, Brazil
Genetic algorithms (GA), a search method inspired by Darwin's theory of evolution, offer an optimisation tool that has been used very successfully to solve a variety of engineering problems. The search process it implements starts with a set of one or more chromosomes (initial population) and, by applying selection and reproduction operators, iteratively 'evolves' the population into better ones, until a stopping criterion is reached. This article investigates lattice-reinforced joist slab cost optimisation problems using a GA with continuous variables. The problem considered concerns one-way slabs, continuous over two spans, in which only the in situ concrete characteristics and joist spacing are varied. The design variables are: concrete layer thickness, concrete layer strength, reinforcement, distance between joists and degree of redistribution of the continuous slabs' negative moments. The search for a solution includes an investigation into the use of discrete variables for data representation. To obtain results that allow for a comparative empirical analysis, these problems are also evaluated by a conventional optimisation method. The results indicate that the GA method is a viable optimisation tool for solving lattice-reinforced joist slab cost minimisation problems.
The use of prestressed concrete piles to support integral abutments
E.G. Burdette, University of Tennessee, Knoxville, USA S.C. Howard, University of Tennessee, Knoxville, USA J.H. Deatherage, University of Tennessee, Knoxville, USA D.W. Goodpasture, University of Tennessee, Knoxville, USA
The Tennessee Department of Transportation (TDOT) in the United States has become the national leader in the design and construction of jointless bridges with abutments which are integral with the bridge deck. While TDOT criteria call for limits of length of 152 m (500 ft) and 244 m (800 ft) for steel and concrete bridges, respectively, they have on more than one occasion exceeded these limits significantly. TDOT's desire to address any questions raised about the efficacy of using prestressed concrete piles to support integral abutments and perhaps to extend the limits on bridge length led to the tests reported in this paper. Four full-size abutments, 3.05 m (10 ft) wide, were built and tested in the field. The description and results of these tests are reported and discussed. Of particular interest are the testing of one pile to failure and the cyclic tests performed on one pile. The conclusions drawn were, first, that prestressed concrete piles are appropriate to use to support integral abutments and, second, that the TDOT criteria for bridge lengths are reasonable and conservative.
Shear strength in the new Eurocode 2. A step forward?
A. Cladera, University of Balearic Islands, Palma de Mallorca, Spain A.R. Mari, Technical University of Catalonia, Barcelona, Spain
The shear strength of reinforced concrete beams with stirrups has been a highly controversial matter since Ritter and Mörsh proposed the first truss models. Since then, different analytical models have been discussed, such as truss models with concrete contribution, shear/compression theories, truss models with variable angle of inclination, and compression field theories. However, some of these models were too complex to be implemented in a code of practice and they had to be simplified. As Regan has pointed out, for simpler models the problem is mostly that of the need to neglect some factors, considered secondaries. However, what is secondary in one case may be primary in another. With the release of the new Eurocode 2 (prEN 1992-1-1:2003) the controversy has been raised again. The EC-2 proposes a very simple formulation based on a truss model. However, the authors think that it is a gross oversimplification of a complex problem as it neglects important key variables. In this paper the new EC-2 shear procedure predictions are compared to empirical tests and to other simplified formulations. It is concluded that the EC-2 procedure is very easy to use by practising engineers but it presents a great scatter of results. On the one hand, it may be too conservative for slightly shear-reinforced beams or for prestressed beams. On the other, it may be slightly unconservative for heavily reinforced members.
Output-only dynamic testing of bridges and special structures
Á. Cunha, University of Porto, Portugal E. Caetano, University of Porto, Portugal F. Magalhães, University of Porto, Portugal
This paper stresses the important role that output-only dynamic testing of bridges and special structures can play in the assessment of dynamic structural behaviour by presenting a set of applications recently performed at several Portuguese bridges (railway, roadway and pedestrian bridges), as well as at the new Braga Sports Stadium suspended roof, and briefly referring to the most important tools developed for that purpose at the Laboratory of Vibrations and Monitoring at the Faculty of Engineering of the University of Porto.
Shear and torsion in prestressed hollow core units: finite element analyses of full-scale tests
H. Broo, Chalmers University of Technology, Göteborg, Sweden K. Lundgren, Chalmers University of Technology, Göteborg, Sweden B. Engström, Chalmers University of Technology, Göteborg, Sweden
The present calculation methods for shear and torsion in prestressed hollow core slabs add stresses from various influences without taking into account deformations and compatibility, the softening of cracking concrete, or restraint at the boundaries; therefore, they are most likely conservative. The main purpose of this work is to establish three-dimensional finite element models, which can be used both to analyse the effect of parameters that influence the shear and torsion response and to be included in global models of complete floors. An important aspect was therefore to simplify the models to avoid time-consuming analyses. Coarse meshes with solid elements were combined with beam elements. The established models were validated by simulating a series of full-scale tests conducted on both 200 mm and 400 mm thick hollow core units subjected to various combinations of shear and torsion. In general, although very coarse meshes were used, the finite element analyses of the tests succeeded in describing the overall behaviour, crack pattern, failure mode, and maximum load, with a reasonably good agreement.
