PRECASEISMIC

Abstract

Precast concrete structures have been shown to be safe, durable, reliable and cost-effective structural systems, however, their full implementation in seismic regions has been limited. One of the main reasons for this situation is the lack of reliable design strategies for precast reinforced concrete member connections especially when earthquake actions are considered. In the USA, New Zealand and Japan, the Precast Seismic Structural Systems Research Program (PRESSS) has focused on this lack of development. With this research program, new beam-column connections were developed and new design methods were adopted. In this program the adopted philosophy was to control the damage, allowing the structures to stay operational after an earthquake or economically reparable. It is expected that, in the near future, the standards will consider the structural and economic advantages of precast buildings in seismic regions.

In Europe the new standard for structures in seismic regions Eurocode 8 (EN1998-1:2004) is not as conservative as its predecessor (ENV1998-1-1:1994) but still is cautious with respect to the seismic performance of precast concrete structures, compromising its economical competitiveness.

Some experimental research was, meanwhile, done in Portugal at the Faculdade de Ciências e Tecnologia of the Universidade Nova de Lisboa (FCT-UNL) by Lúcio, Ebeling et al, Marreiros et al and Reguengo et al at the Instituto Superior Técnico (IST) by Proença, Lúcio, Reis et al, Camara et al and at Laboratório Nacional de Engenharia Civil (LNEC) by Mendes et al in the Cordis FP5 Project "Precast Structures EC8 - Seismic behaviour of precast concrete structures with respect to Eurocode 8". However, there is still much work to be done involving optimization and the study of various parameters, using numerical and experimental analysis on the development of new and more efficient structural connections and definition of structural guidelines. Some of this work is already going on with the works of Marreiros and Reguengo from Concremat company.

Experimental testing of reinforced concrete structural elements is an expensive and time consuming process. It requires specimens manufacture, well-equipped laboratory, specialized technical staff to run the tests and academic staff to analyze the results. Large number of equally conditioned tests must be performed in order to obtain a representative behaviour of the structural member. In certain circumstance in-situ testing is necessary, involving other expenses. Tests must be destructive if analyses involving ultimate stages of structural elements bearing capacity are required.

Reliable software, able to reproduce the structural elements testing, would reduce significantly the number of necessary tests and would allow for optimization of the structural members shape and reinforcement and the analysis of diverse parameters, which is almost impossible to do in a pure experimental way.

There are several approaches for modeling of destructive tests available. Some of them are already implemented in commercial or freeware software, however, their practical applications still remains very limited. They can mostly reproduce only purely academic problems with very simple underlying constitutive models. When applied to more complicated structures subject to complex loading, they exhibit pathologies that are not properly understood. This discourages practitioners from adopting such techniques.

The objective of this proposal is to:
i) design and verify experimentally new construction solutions for connections of reinforced concrete precast elements;
ii) develop reliable numerical strategies to reproduce the experimental testing;
iii) link the two previous objectives and perform numerical optimization of the suggested solutions;
iv) establish structural guidelines for an optimized design of such connections.

Two main Portuguese civil engineering research units and a precast company, FCT-UNL, IST-UTL and Concremat SA, are together in this project and it is in the sequence of the previous POCI/ECM/61017/2004 "SAFE_PC - Safety of Precast Structures: General Design, Connections and Seismic Behaviour", financed by the Fundação para a Ciência e Tecnologia.

The knowledge interchange of the results, with the national and international professional and scientific community, will be ensured though members of Commission 6 - Prefabrication, and of the Task Group 6.10 - "Precast concrete buildings in seismic areas - Practical aspects", of the fib - fédération internationale du béton. The Principal Investigator of this project proposal is member of fib Commission 6 and some members of the project team participate in the Works of Task Group 6. In this project it is expected that specialists from fib Commission 6 will come to Portugal as consultants and co-operate in the research.