Permeability of OPC-FA-SF self-compacting concrete
H. Y. Leung, Hong Kong College of Technology, Hong Kong A. Nadeem, Hong Kong College of Technology, Hong Kong G. K. W. Tse, Hong Kong College of Technology, Hong Kong
This paper examines the water permeability and chloride penetrability of self-compacting concrete with fly ash and silica fume as admixtures. The influence of 28-day concrete strength on concrete permeability is also investigated. It was found that addition of fly ash and silica fume was effective in reducing the concrete permeability. Most self-compacting concrete specimens showed low to very low water permeability and chloride penetrability. Test results also indicated that the 28-day concrete strength should not be used as an indicator for concrete permeability.
Offshore concrete platforms for the Sakhalin II development
S. Hetland, Aker Solutions, Lysaker, Norway
Sakhalin II is an integrated oil and gas development in the Russian Far East. It involves the installation of a large offshore platform at the Piltun sector of the Piltun-Astoskhskoye field (PA-B) and a single large platform at the Lunskoye gas field (LUN-A). These platforms, together with the existing Molikpaq drilling and production platform, are equipped to export their output by pipeline to Sakhalin. From here it is transported by way of an onshore link of 800 km to Prigorodnoye, Aniva Bay at the south of the island, which is the location for a major liquefied natural gas (LNG) storage facility and terminal, and oil handling terminal. The two fields contain an estimated 1.2 billion barrels (190 000 000 m3) of crude oil and 500 billion m3 of natural gas. Output is scheduled at up to 9.6 million of LNG per year and about 180 000 barrels per day (29 000 m3/day) of oil. The project partners are Gazprom (50% plus one share), Shell (27.5%), Mitsui (12.5%) and Mitsubishi (10%). The GBS contracts were issued on 1 July 2003 and both platforms were installed during the summer of 2005.
Crack widths near reinforcement bars for beams in bending
K. Tammo, Division of Structural Engineering, Lund Institute of Technology, Sweden S. Thelandersson, Division of Structural Engineering, Lund Institute of Technology, Sweden
Earlier research performed on axially loaded concrete prisms shows that crack widths close to reinforcement are smaller and less dependent on concrete cover than crack widths at the concrete surface. To check practical applicability of these results a similar experimental investigation of cracking behaviour has been undertaken for beams loaded in bending. The influence of steel stress and concrete cover on crack widths close to the reinforcement and at the concrete surface has been investigated. The results show that the main features of cracking behaviour for axially loaded prisms and beams are similar. Beams resemble axially loaded prisms in that cone-shaped concrete failure occurs in the bond zone where the bar meets a crack. At higher steel stresses this concrete cone follows the displacement. For this reason crack widths close to the bar are significantly smaller and much less affected by the thickness of concrete cover than at the concrete surface. Surface crack widths consequently are poor indicators of the potential for exposure to corrosive attacks on reinforcement and current design methods can be counter-productive for service life of concrete structures.
The improved n-method for the calculation of stresses in service
M. Taliano, Politecnico di Torino, Italy
This paper reports the main results of a parametric analysis which is based on the calculation of stresses on concrete and steel of r.c. rectangular sections subjected to bending under quasi-permanent and characteristic loads. Two calculation methods are used: a general method and a simplified one, namely the n-method. The main parameters that influence the calculation of stresses are then discussed and the differences that are produced by the n-method using the classical values found in the literature compared with the general method are evaluated. By varying only some of the involved parameters, appropriate new values of the modular ratio, called 'improved modular ratios', are determined and two equations for the assessment of the improved modular ratios are proposed, one for each considered load combination. In this way, applying the 'improved' n-method, it is possible to calculate the stresses on concrete and steel with good accuracy.
Engineering the construction of the Stonecutters Bridge concrete backspans
G. Morgenthal, Principal Engineer, Maunsell AECOM, Shatin, Hong Kong R. Sham, Executive Director, Maunsell AECOM, Shatin, Hong Kong K. Yamane, Engineering Manager, Maeda-Hitachi-Yokogawa-Hsin Chong Joint Venture
One of the most challenging aspects in the construction of Stonecutters Bridge, Hong Kong, was the erection of the concrete backspan structures. At a height of about 70 m a geometrically complex grillage deck was to be constructed. The superstructure cannot support its own weight before the stay cables are installed; it was thus constructed on a unique falsework system required until stressing of the stays. The paper describes the development of the construction procedures, the construction engineering and the design of the temporary works. The work involved the accurate stage-by-stage modelling of the entire construction process to assess the structural adequacy throughout and to facilitate geometry control. The different strands of work were highly interactive and optimised erection methodologies, developed together with the contractor, led to a successful implementation of the project.
Fatigue life of short-span reinforced concrete railway bridges
M. Pimentel, Laboratory for Concrete Technology and Structural Behaviour (LABEST), University of Porto, Portugal E. Brühwiler, School of Architecture, Civil and Environmental Engineering, École Polytechnique Fédérale de Lausanne (EPFL), Switzerland J. Figueiras, Laboratory for Concrete Technology and Structural Behaviour (LABEST), University of Porto, Portugal
In this paper a parametric study on the fatigue life of short-span reinforced concrete railway bridges is presented. Only reinforcement steel fatigue damage is considered. The objective of this work is to assess the factors that may have a decisive influence on reinforcement fatigue life, to evaluate the consequences of the increasing traffic loads and to identify the research needs so as to allow more accurate fatigue examinations of existing bridges under more demanding traffic conditions. It is concluded that reinforcement fatigue life is mainly governed by the existence of heavy traffic (freight trains) and that it is highly sensitive both to the axle loads increase and to the accuracy in the reinforcement stress range calculation. It is also shown that the current analysis procedures may suffice for economic design of new bridges, whereas in the case of existing bridges more elaborate analysis procedures may be necessary to prove fatigue safety.
