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Precast concrete construction represents a viable alternative to construction methods utilizing cast-in-place concrete. Advantages related to the use of precast techniques include higher quality control that can be obtained in the precast plants, speed of erection, and freedom in the architectural shape of the members. Despite these well-recognized advantages, the use and development of precast concrete structures in seismic areas have been typically limited, by the lack of confidence and knowledge about their seismic performance.
The crucial missing link in modelling of precast buildings is adequate knowledge about the behaviour of connections. The empirical evidence from past earthquakes is sparse, incomplete, not quantified and often controversial. Some reports show excellent behaviour of precast systems and connections other reports identify catastrophic collapses of connections in precast structures. This is not surprising, since seismic response clearly depends on the specific structural system, type of connections and quality of the design and construction. Some collapses due to connection failures were reported during the 1977 Vrancea earthquake (Tzenov et al, 1978), the 1979 Montenegro earthquake (Fajfar et al, 1981) and the Northridge earthquake (EERI, 1994). Failures of welded and poorly constructed connections were also the main cause of extensive collapses in Armenia (1989) and during the 1976 Tangshan earthquake in China (Anicic et al, 1982). These bad experiences have generated mistrust to precast systems in general. In some countries this practically preclude the use of precast structures (i.e. Chile; Park et al, 2003) and in many codes all precast systems were penalized with high seismic forces related to the reduced competitiveness in the market.
With the support from both European Commission and Chinese Government, a series of collaborative research activities on the seismic behaviour of precast reinforced concrete structures have been organised under the PRECAST EC8 project. The project included a number of European and overseas Partners, from academia and other research institutions as well as from the precast construction industry organised into 4 research groups. The project PRECAST STRUCTURES EC8 was successfully carried out and concluded in early 2007, after 4 years of activity.
The main objectives of the project were:
The co-normative research programme "Seismic behaviour of precast concrete structures with respect to EC8” (PRECAST STRUCTURES EC8) was aimed at assessing and possibly calibrating, by means of experimental and numerical investigation, the design rules provided by Eurocode 8 with reference to precast reinforced concrete structures. The results of the project were meant to be used to support the European Commission policy in the field of standardization, both for the Eurocode programme and for the revision and completion of the harmonized product standards issued by CEN/TC 229, under Construction Product Directive provisions and mandate M100 Precast Concrete Products.
For logistical reasons, the work was distributed to four National Groups (Greek Group, Italian-Slovenian Group, Portuguese Group and Chinese Group) with the three competencies of production, testing and research. The main results obtained by the Italian-Slovenian and the Chinese Group are reported here.
As the core activity of the Italian-Slovenian group, the design and construction of two full-scale structure prototypes were carried out. The prototypes have been designed according to EC8 in order to be submitted to pseudo-dynamic and cyclic tests. They consisted (figure 3) either of two beam spans-one roof bay or two roof bays-one beam span (with beams and roof elements spanning 8 m each), supported by six 5 m high columns. The experimental campaign foreseen in the project included both pseudo-dynamic and cyclic tests on both prototypes. The seismic ground motion in pseudo-dynamic tests was imposed by means of a real signal, modified
A first research project was aimed at comparing the global ductility supplies of cast-in-situ and precast equivalent structures, and was based on a series of full-scale pseudodynamic tests conducted at ELSA and at SKLDRCE. It was concluded that the ductility capacities of precast structures can be comparable to those of ordinary constructions.
Another research programme was aimed at investigating the global behaviour of single and multi-storey precast structures, and was based on pseudodynamic full-scale tests conducted at ELSA and shaking-table tests conducted at SKLDRCE. The structural systems proved to be much more efficient than it was assumed in distributing the horizontal forces, as long as connections are adequately designed.
The design of connections and the contribution of connections to the global behaviour is the main focus of the recently activated research programme SAFECAST, funded by the European Commission, which will be conducted in close contact with the Tongji University.
European Commission,Joint Research Centre
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The project consisted of 10 partners organised in 4 local working groups. The activities were co-ordinated by the Technical University of Milan (Prof. G. Toniolo) and the project had established external collaboration with the Technical University of Istanbul (Prof. F. Karadogan).
The four local working groups were organised as follows:
Technical University of Milan (Prof. G. Toniolo), co-ordinator
Larco Astori SpA
University of Ljubljana (Prof. M. Fishinger)
Laboratorio Nacional de Engenharia Civil (Dr. E. Coelho)
Civibral Sistemas de Construcao s.a.
National Technical University of Athens (Prof. P. Carydis)
Proet s.a. Prefabrications
Tongji University, Shanghai (Prof. X. Lu)