Structural Concrete, Vol. 10, no. 2, June 2009

Written on 19 August 2011.

Information-based formulation for Bayesian updating of the Eurocode 2 creep model

W. Raphael, École Supérieure d'Ingénieurs de Beyrouth, St. Joseph Univeristy, Riad El Solh Beirut, Lebanon
R. Faddoul, École Supérieure d'Ingénieurs de Beyrouth, St. Joseph Univeristy, Riad El Solh Beirut, Lebanon
D. El-Asmar Selouan, École Supérieure d'Ingénieurs de Beyrouth, St. Joseph Univeristy, Riad El Solh Beirut, Lebanon
A. Chateauneuf, LGC-UBP Polytech Clermont Ferrand, Aubière, France

The disparity between theoretical and experimental results reveals that the creep of concrete is often underestimated by most, if not all, codes of design; this is particularly true in the case of Eurocode 2. Thus it is necessary to calibrate the present code models. Bayesian-type inferences turn out to be an especially suitable tool for the work needed in revising and updating design codes. This is by virtue of their capability to incorporate additional information resulting from current practice and research so as to improve existing models. In this paper, corrective coefficients are proposed for the Eurocode model, allowing better estimation of the long-term creep of concrete. To achieve this aim, the authors rely on a large database of experimental results compiled by collecting data from several research institutions in Europe. Two descriptive statistical methods are applied in order to compare the experimental results from the above-mentioned database with results calculated using the Eurocode 2 model for the same input parameters. A Bayesian-type statistical inference is then performed to evaluate the corrective coefficient for different categories of concrete strengths using various prior distributions. The approach presented here has proven to be an effective and systematic framework for the consideration of all possible types of uncertainties in model calibration. The results obtained are very interesting for engineers involved in design and supervision of structures. The adoption of such a design approach would improve long-term serviceability of structures subjected to creep. 

Structural Concrete, Vol. 10, no. 2, June 2009

Written on 19 August 2011.

Peeling failure in beams strengthened by plate bonding. A design proposal

E. Oller Ibars, Civil Engineering School, Technical University of Catalonia, Barcelona, Spain
D. Cobo del Arco, Tec-Cuatro, SA, Barcelona, Spain
A. R. Marí Bernat, School of Civil Engineering, Technical University of Catalonia, Barcelona, Spain

Existing experimental research has shown that the application of externally bonded laminates to strengthen reinforced concrete (RC) structures can lead to brittle failures involving debonding of the laminate before the design load is reached and a classical failure mode occurs. In an externally bonded RC beam, this peeling failure can initiate either near mid-span owing to the effects of flexural or shear cracks, or at the laminate end as a result of stress concentration at the laminate cut-off point. The design procedure to obtain the laminate area to strengthen a RC element should avoid these premature peeling failures. Therefore, there is a need to understand the mechanics of the laminate debonding process in order to prevent it. The evolution of the debonding process can be analysed by using non-linear fracture mechanics assuming a bilinear constitutive law for the interface. The crack propagation process is described through the evolution of different stages, in which the interfacial shear stresses can be obtained. As the transfer of stresses from laminate to concrete through the interface is a critical parameter in the correct performance of externally bonded structures, the transferred force should be limited to a maximum value in order to prevent peeling failure. A shear-bending interaction diagram based on this maximum transferred force associated with peeling failure is the main point of the design proposal presented in this paper. 

Structural Concrete, Vol. 10, no. 1, March 2009

Written on 19 August 2011.

The effects of diagonal web reinforcement on cyclic behaviour of lightweight structural walls

W. Raongjant, Department of Civil Engineering, Rajamangala University of Technology, Thanyabuli, Thailand
M. Jing, Department of Civil Engineering, Rajamangala University of Technology, Thanyabuli, Thailand

This study focuses on the seismic behaviour of lightweight reinforced concrete shear walls with different web reinforcement modes, with the aim of discovering an optimised web reinforcement mode to increase ductility and shear resistance. The paper describes a comprehensive experimental programme involving four lightweight concrete shear wall specimens with the same shear span ratio of 1.43. The wall specimens are reinforced against shear, either conventionally (orthogonal grids of web reinforcement) or with diagonal bars. The different deformation characteristics, hysteretic response, stiffness attenuation and energy dissipation capacity between four wall specimens are investigated. The test results clearly show that diagonal web reinforcement results in lower shear strains near the wall base and improved energy dissipation characteristics.

Structural Concrete, Vol. 10, no. 1, March 2009

Written on 19 August 2011.

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.

Structural Concrete, Vol. 10, no. 1, March 2009

Written on 19 August 2011.

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. 

Structural Concrete, Vol. 10, no. 1, March 2009

Written on 19 August 2011.

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.