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.
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.
Y. Gholipour, Department of Civil Engineering, University of Tehran, Iran
Structures are often subjected to various types of dynamic loads and the need to accurately predict the structural response and reserve capacity under such loading has led to an interest in the properties of composite materials. Fibre reinforcement improves the dynamic behaviour of reinforced concrete and ferro cement under impact loading. This paper reports an experimental investigation of the dynamic behaviour of composite slab panels under impact loads. Impact tests were carried out on various types of fibre-reinforced cement concrete slabs and fibre-reinforced ferro-cement slabs to study the influence of fibres on the energy absorption. The response of all the above specimens were examined and compared. Analytical solutions were obtained from a finite element analysis and the results are also compared.
Experimental and numerical assessment of the dynamic behaviour of a stress-ribbon footbridge
E. Caetano, Faculty of Engineering of the University of Porto, Portugal A. Cunha, Faculty of Engineering of the University of Porto, Portugal
This paper describes the experimental and numerical study of the dynamic behaviour of a stress-ribbon footbridge constructed at the campus of the Faculty of Engineering of the University of Porto, Portugal. This bridge has not displayed any vibration problem, as yet, but significant levels of vertical oscillation have been observed under pedestrian use. Therefore, a site observation programme was developed in order to assess the main dynamic characteristics and levels of vibration of the bridge, to compare them with limit values recommended by structural codes, and to validate a numerical model to be used in predicting the bridge response under extreme loadings.
Effects of fly ash on chloride migration in concrete and calculation of cover depth required against the corrosion of embedded steel reinforcement
N. Shafiq, Department of Civil Engineering, University Technology Petronas, Tronoh, Perak, Malaysia
This study investigated the effects of fly ash on chloride migration in concrete and calculation of cover depth in order to protect the embedded steel reinforcement against the occurrence of severe corrosion. A rapid chloride migration test was conducted for determination of the coefficient of chloride diffusion. The resulting coefficient of chloride diffusion was used for calculation of minimum cover depth required for a specified service life of concrete structure. Concrete made of 40 and 50% fly ash as partial replacement of cement resulted in a lower coefficient of chloride diffusion and hence a cover depth of 75 mm or less was calculated for a specified service life of 120 years. On the other hand a higher value of the coefficient of chloride diffusion was determined for 100% ordinary Portland cement (OPC) concrete, therefore a thick concrete cover such as 150 mm was calculated for a similar life span.
Chloride profiles and diffusion coefficients in structures located in marine environments
A. A. Di Maio, CONICET-LEMIT, Argentina L. J. Lima, University of La Plata, Argentina L. P. Traversa, CIC-LEMIT, Argentina
Steel corrosion is one of the main causes of damage in reinforced concrete structures. Recent studies carried out in Argentina indicate that the percentage of damage in concrete structures induced by corrosion of reinforcement is 16%. In structures located in marine environments the corrosion is due fundamentally to the action of chlorides. Chlorides penetrate concrete by different processes; in structures exposed to atmosphere, the ingress process is by diffusion. Ingress depends on the characteristics of concrete and of its distance to the sea (marine environment). In this paper, assessment of durability of concrete structures exposed to marine (Atlantic Ocean coast) environments is reported. The ages of the evaluated structures, bridges and buildings, vary between five and 67 years. Surface chlorides concentration (environmental loads) and the effective diffusion coefficient, calculated using Fick's second law, are included. Furthermore, the quality of the cover concrete is characterised by means of the specific gravity and porosity accessible to water methods.
