Precast concrete technologies are widely used in construction, due to their advantages in terms of economy, quality control, speed in erection and architectural flexibility. Precast structures are used in most industrial facilities, and in many shopping centres, schools, gyms and public buildings. Despite their widespead use, the design of precast concrete structures is only partially covered in the current version of Eurocode 8 - one of the Eurocode series of European standards (EN) related to construction, which describes how to design structures in seismic zones - and in many national design codes. This news article describes how EU research results have played an important role in the recent release of a new international standard - namely, ISO 20987:2019 (“Simplified design for mechanical connections between precast concrete structural elements in buildings”) - filling an important gap between previously existing standards. The derived design rules are being implemented in the ongoing revision of Eurocode 8.
Some concerns about the seismic safety of such precast industrial buildings have been expressed in the past, mainly after the problems highlighted by recent earthquakes (Bournas et al., 2014). Whereas it has been demonstrated that precast solutions can offer the same (if not superior) safety of ordinary “cast-in-situ” constructions, the need to develop design rules for the connections between precast elements has been stated by the industry sector and by the related research community.
This problem was addressed by a dedicated 7th Framework Programme for EU research (FP7) project called SAFECAST (Performance of Innovative Mechanical Connections in Precast Buildings Structures under Seismic Conditions), which ran from 2009 to 2012, and in which many European experts participated, also collaborating with Chinese laboratories. The precast construction industry - represented by five National Associations of precast concrete producers - played a key role in the SAFECAST project, which was coordinated by ASSOBETON (the National Italian Association of Precast Concrete Producers).
The problem of reliably designing, dimensioning, installing and maintaining appropriate connection devices between the structural elements, able to guarantee predefined levels of performance under different loading situations, is the fundamental prerequisite for precast structures to be fully competitive in terms of safety and reliability of behaviour and performance.
The activities of the SAFECAST project included a large numerical and experimental campaign on existing and new / improved connections, culminating in the testing programme conducted at the European Laboratory for Structural Assessment (ELSA) at the European Commission’s Joint Research Centre (JRC) in Ispra, Italy, on a large building mock-up - quite possibly the largest building ever seismically tested to failure (see Figure). The size of the mock-up was motivated to the need to include in the test many different solutions as for the design of connections.
The results of the ELSA tests (which are described by Negro et al, 2013), complemented by the findings of the experimental activities performed in other European and Chinese laboratories and by the numerical studies conducted by the Consortium, resulted in a set of guidelines for the seismic design of connections, both traditional and innovative. The duty of translating those guidelines into standardized norms was undertaken by the JRC. A dedicated Working Group was set up within the relevant Technical Committee of the International Standard Organization (ISO). After the necessary technical discussions at international level, in October 2019 a new ISO Standard – namely ISO 20987:2019 (“Simplified design for mechanical connections between precast concrete structural elements in buildings”) - was released.
At present, several partners of the SAFECAST project are working on the implementation of the derived design rules into the revision - currently under way - of Eurocode 8 (Design of structures for earthquake resistance). Rules for the correct dimensioning of connections between precast elements could be drafted directly into the European design codes, or as a reference to ISO 20987.
Antonella Colombo, ASSOBETON (Italian Association of Precast Concrete Producers) and Paolo Negro, European Commission, Joint Research Centre (JRC)
For more information:
* Bournas, D.A., P. Negro and F.F. Taucer. 2014. Performance of industrial buildings during the Emilia earthquakes in Northern Italy and recommendations for their strengthening. Bulletin of Earthquake Engineering, 12 (5): 2383-2404. https://doi.org/10.1007/s10518-013-9466-z
* Negro P., D.A. Bournas, and F.J. Molina. 2013. Pseudodynamic tests on a full-scale 3-storey precast concrete building: Global response. Engineering Structures; 57: 594-608. https://doi.org/10.1016/j.engstruct.2013.05.047