Structural Concrete, Vol. 5, no. 3, September 2004

Written on 19 August 2011.

Spatial variability of concrete deterioration and repair strategies

Y. Li, Delft University of Technology, The Netherlands
T. Vrouwenvelder, Delft University of Technology, The Netherlands
G. H. Wijnants, Netherlands Organisation for Applied Scientific Research, Delft, The Netherlands
J. Walraven, Delft University of Technology, The Netherlands

This paper presents an improved and more realistic approach to evaluate the deterioration process and optimise the repair strategy of concrete structures. It is based on the commonly used probabilistic-based reliability analysis methods, but takes into account the spatial variability of concrete properties that has great impact on the design and maintenance decisions of structures. The developed approach is exemplified by the concrete bridge 'Wilpsedijk' in the Netherlands to show the service lifetime prediction based on spatial variability of concrete deterioration including initiation and propagation period. With respect to an established repair criterion, available repair options and the corresponding repair costs, the optimal lifetime repair strategy is determined. In comparison with most of the studies that neglect the variables with random spatial variability, the approach reflects the actual situation more realistically and can produce useful information as the proportion or percentage of the surface area that shows concrete deterioration during the whole period of time. It enables the planning of different repair and maintenance strategies for the structure from a practical point of view. 

Structural Concrete, Vol. 5, no. 4, December 2004

Written on 19 August 2011.

Direct design of hollow reinforced concrete beams. Part I: design procedure

A. S. Alnauimi, Sultan Qaboos University, Sultanate of Oman
P. Bhatt, University of Glasgow, UK

This paper, Part I, presents a general 'direct design procedure' for the design of reinforced concrete hollow beams subjected to a combined load of bending, shear and torsion. Elastic stress field in conjunction with Nielsen's twodimensional yield criterion for reinforced concrete subjected to in-plane forces were used in the design of reinforcement. This procedure is based on and satisfies the lower bound theorem of the classical theory of plasticity. The main features of this procedure are the precluding of the use of empirical equations as is the case with existing codes of practice and in addition to satisfying the requirements of the theory of plasticity it reduces the ductility demand assumed by this theory. Comparison between the direct design procedure and the truss analogy showed that the direct design procedure leads to steel requirements close to those of the truss analogy when the angle of inclination of the struts is 458. The direct design procedure produced much less reinforcement than the American Concrete Institute and the British Standards Institute codes.

Structural Concrete, Vol. 5, no. 3, September 2004

Written on 19 August 2011.

Modelling effect of corrosion on bond strength of plain bar reinforcement

T. Pregartner, Engineering Office Eligehausen & Asmus, Stuttgart, Germany
J. Cairns, School of the Built Environment, Heriot-Watt University, Edinburgh, UK
J. Ozbolt, Institute for Construction Materials, University of Stuttgart, Germany

In the present paper a simple approach to model the effects of corrosion on bond between plain bar reinforcement and concrete with the finite element method (FE method) is shown. With the combination of a non-linear FE-solver and a discrete bond model it is sufficient to simulate corrosion by radial expansion of a concrete cylinder. The bond model used accounts for the effects of confinement and stresses in the vicinity of the reinforcement bar. Hence the effects of corrosion could be investigated with this simple approach. The model is calibrated on pull-out tests with RILEM specimen. Calculations conducted on beam end specimen containing plain surface bars show a plausible agreement with test results and with results known from literature. 

Structural Concrete, Vol. 5, no. 2, June 2004

Written on 19 August 2011.

Studies on strength and permeability characteristics of blended cements in lowand mediumstrength concretes

R. Vedalakshmi, Corrosion Science and Engineering Division, Central Electrochemical Research Institute, Karaikudi
S. Srinivasan, Corrosion Science and Engineering Division, Central Electrochemical Research Institute, Karaikudi
K. Ganesh Babu, Department of Ocean Engineering, Indian Institute of Technology, Madras, India

In the present investigation the strength and permeability characteristics of blended cements such as Portland pozzolana cement and Portland slag cement were evaluated in 20, 30 and 40 MPa concretes. The cements were produced by intergrinding mineral admixtures such as fly ash and slag with clinker and gypsum in the plant. The compressive strength over a period of 1 year and water permeability at the end of 7, 28 and 90 days were evaluated and the results were compared with ordinary Portland cement. Thermo-gravimetric analysis was also carried out to assess the pozzolanic reaction of blended cements. The results show that blended cement concretes have lower strength than Portland cement concrete at all ages in all of the grades of concrete studied. Porosity in terms of water absorption of blended cement concretes is less than Portland cement concretes in 20 MPa concrete but was not significantly different in 30 and 40 MPa concretes. Thermo-gravimetric and differential thermal analysis reveals that there is a reduction in Ca(OH)2 content in blended concretes indicating the consumption of hydroxide in pozzolanic reaction. 

Structural Concrete, Vol. 5, no. 2, June 2004

Written on 19 August 2011.

The infuence of the parameter φ/ρeff on crack widths

A.W. Beeby, The University of Leeds, UK

Many formulae for the prediction and control of crack widths in reinforced concrete members assume that the transfer length over which force is transferred by bond from the reinforcement to the concrete on either side of a crack is proportional to the parameter φ/ρeff, where φ is the bar diameter and ρeff is an effective reinforcement ratio. This paper aims to examine the validity of this assumption by comparing the predictions of the theory which leads to the derivation of the parameter φ/ρeff to data from experimental programmes where crack widths were measured. These comparisons strongly suggest that φ/ρeff has minimal influence on crack widths. 

Structural Concrete, Vol. 5, no. 3, September 2004

Written on 19 August 2011.

Thinking about codes

J.C. Walraven, Delft University of Technology, The Netherlands, former President of fib

Codes have always played an important role in the design of structures. In the past, CEB and FIP devoted considerable attention to the actualisation of codes, especially by writing the so-called 'Model Codes for Concrete Structures', which were intended to be future-oriented. Those codes were intensively used as a basis for updating national codes and as a source for providing a new international code: the Eurocode. Nowadays, code writing is again at the centre of interest. On the one hand, the new Eurocode for Concrete Structures has been completed and accepted as an ENV (draft). On the other hand it is felt that new developments ask for new ideas about the basis and the content of codes in the future. Within fib, preparations have started for a new Model Code. In this paper some general reflections are given to the renovation of codes. This paper was devoted to the 60th birthday of Professor Eligehausen.