ASIAN JOURNAL OF CIVIL ENGINEERING (BUILDING AND HOUSING)
Year:2005 | Volume:6 | Issue:5|Papers Count:6

Deterioration of steam-cured concrete specimens made with laumontite containing aggregates, under marine submerged, tidal, and atmospheric exposures for 30 years, was investigated. The expansion of the specimens exposed to the marine submerged and tidal exposures ranged from complete disintegration to the moderate deterioration. The deteriorated regions contains little calcium hydroxide as well as calcium silicate hydrates, but rich with ettringite, brucite, and calcite. At the deteriorated region, white rim of ettringite crystal is found around the aggregates. Ettringite, brucite, and calcite are also found at the voids as well as along the cracked path. No visible crack was found on the surface of the atmospheric specimens. It is clearly understood that exposure condition is a governing factor related to the expansion caused by the laumontite mineral. No expansion of 30 years old atmospheric and tidal specimens is found after further wetting and drying exposure utilizing natural seawater of temperature 60°C.      

This paper reviews the results of some recent works conducted by the author on new methods of retrofitting the RC frames. On the local retrofit of RC members, it includes the work on the application of a new high performance fibre-reinforced cementitious composite material. The composite can be applied either as a wet mix to the desired thickness or attached as precast sheets or strips to the face of the member using a suitable epoxy adhesive. The suitability of this technique of member retrofit to enhance the strength and ductility of the retrofitted member compared with other methods of local retrofit, such as steel plates and FRP laminates, is discussed. Other works reviewed in this paper include those carried out recently on global retrofit of RC frames using direct internal steel bracing. Results of inelastic pushover tests on scaled models of ductile RC frames, directly braced by steel X and knee braces are presented which indicate that such bracings can increase the yield and strength capacities and reduce the global displacements of the frames to the desired levels. Also, the results of direct tensile tests on three full scale models of three different types of brace/RC frame connections are presented. Finally, the values of seismic behaviour factor, R, for this type of brace/frame system, evaluated from inelastic pushover analysis of dual systems of different heights and configurations are presented.      

Developed in a European Brite-Euram research project, a new service life design concept for reinforced concrete structures has been established. This new concept allows the design of reinforced concrete structures for a defined lifetime related to limit state formulations. The result of the durability design is a limit state-based failure probability of the structure. This new approach has been used for the design against reinforcement corrosion in uncracked concrete regions for various new structures as well as for the redesign and estimation of remaining service life of existing structures. These practical applications demonstrated the appropriateness of the approach. Within this publication the application of the approach to a bored tunnel construction in the Netherlands (Western-Scheldt project) will be presented. The construction consists of two different elements, the ramp and the bored tunnel itself (reinforced concrete and steel members). The tunnel has two tubes with an external diameter of 11.0 m and a length of 6.5 km. All elements have been designed according to the new performance based durability design procedure.      

A study on RC deep beams behavior is conducted in this paper by means of finite element analysis along with experimental evaluation of analytical simulation. The beams have shear span to depth ratio between 0.5 and 1.5 and effective depth from 400 mm to 1400 mm. Lateral reinforcement ratio varies by 0.0%, 0.4% and 0.8% in shear span. A fracture type analysis is employed to simulate RC members through smeared rotating crack approach. The results showed reliability of analysis in predicting deep beams behavior in terms of failure load, failure mode as well as crack propagation. The objective of this study is to investigate capabilities of the finite element simulation for further study on deep beam behavior instead of conducting expensive time consuming experimental works. This includes particularly members with possibilities of failing in shear as well as size effect by means of large-scale structures numerical simulation.    

Future demands for performance of concrete structures pose multidisciplinary challenges on the designer. He must master the integration of structural design, durability and service life design, and the rapidly growing demands for sustainability. However, such designs required to fulfill the long-term performance of structures poses also challenges to the owners or clients. They will have to define their service life demands in a factual and verifiable manner, and to agree to the acceptance criteria to be fulfilled. This new integrated approach to service life design of concrete structures identifies a new design procedure - a change in design paradigm-which shall be followed, if real improvements shall be achieved. The changes in design paradigm are not at all dramatic, but the consequences of adopting such changes may well be dramatic regarding improved performance, service life and reliability - and will greatly increase the competitiveness of structural concrete. With this new perspective in mind such demands for service life designs will also reflect on revised engineering university curricular.      

There is a growing worldwide perception that the built environment, both historic and of recent construction, is characterized by an unacceptably high level of seismic risk. Given the technical, economical and social problems involved, mitigation of this risk cannot be but a long-term objective, whose achievement requires the availability of efficient normative documents allowing for rational and cost-effective interventions. The paper illustrates the main features of a recently released European code (Eurocode 8 Part 3) devoted to the subject. The document is aligned with the present international trend of explicitly stating and pursuing the sought performances, but contains also elements of novelty. These latter regard essentially the introduction of so-called "levels of knowledge", as a factor for deciding type of analysis and use of newly defined confidence factors in member verification, plus a set of entirely new capacity expressions for the ultimate and damage states of the members.