Sub-Project 6: Development and manufacturing of energy dissipation devices and seismic isolators 

The current earthquake codes for conventionally protected structures, though they prevent collapse, allow even severe damage under strong earthquakes. In fact, the seismic resistance of the conventionally protected structures relies on their capacity to undergo significant inelastic deformations in strong earthquakes, namely on their ductility. Moreover, the conventional techniques provide no protection to the contents of a building nor to secondary structural features. The prevention of earthquake damage to contents such as sensitive equipment is vital for hospitals and other critical facilities like museums.

Passive control systems of seismic vibrations (e. g. seismic isolation and energy dissipation) are innovative techniques which are worldwide considered to be already fully mature for providing mitigation of seismic damage for civil structures and components or equipment and have proven to be reliable and cost-effective for bridges and viaducts, civil buildings, cultural heritage and critical facilities. The main objectives of Sub-Project 6 are:

• the development of innovative low stiffness isolators (LSIs) to be used in civil applications characterized by light structures (residential houses) or for light industrial equipment;
• the development of innovative electro-inductive devices (DECS) to be used in civil applications characterized by heavy structures (bridges and viaducts);
• the evaluation of the benefits, as well as ascertaining the limitations, of two important types of devices actually available on the market: sliders coupled with hysteretic elements and friction pendulum systems.

Activities related to the first two objectives will be carried out by ALGA, while those related to the third one will be performed by MAURER. Some contribution to these activities will be also provided by STAP and VCGP, in the role of technical consultants. The abovementioned objectives will be accomplished by testing the devices on the shaking table of the ENEA Laboratories of Casaccia (near Rome), using a suitable mock-up. The design, development and qualification of the devices will be supported by numerical analyses, which will be carried out by developing original non-linear mathematical models.

Particular efforts will be paid in the dissemination of the results; to this aim, a User Manual will be prepared by all the partners in the last part of the project with the aim of helping the Designers and other potential End User to design structures incorporating such devices. The results of Sub-Project 6 activities will also provide input for the development of European standards for the antiseismic devices and structures provided with them.

Sub-Project 6 is coordinated by ENEA, featuring also the participation of ALGA, MAURER, STAP and VCGP.

Disseminated material related to this Sub-Project can be found by clicking each of the links below:

Deliverables

Presentations

Reports

Publications

Events

Meetings

A summary of each of the tasks involved in this Sub-Project is provided below:

Task 2.2a.1: Development, manufacturing and qualification of low stiffness HDRBs and DECSs

The proposal concerns alternative, innovative seismic design approaches, in particular, a novel SI system based on low stiffness HDRBs. These devices are complementary to the existing HDRBs and will have a great potential for application to a large number of structures and situations for which the latter are not a viable option, and to the direct protection of industrial equipment.

Most of the SI projects based on HDRBs utilise bearings with a damping varying between 10 and 15%, whose stiffness is such to obtain a natural period of vibrations ranging between 2 and 2.5 seconds. Under these circumstances, the design displacement of the structure during earthquake mainly depends on the response spectrum and therefore on the seismicity level and soil conditions. Normal values of the design displacements normally range between 100 mm for very low seismicity levels (for instance, in Italy for category 3) up to 400 mm, or even more, for very high seismicity areas (for instance, in Turkey).

HDRBs’ geometrical dimensions usually grant a sufficient stability of the bearing itself. However, it may happen that, if the weight of the structure is relatively low (for instance, for 2 or 3 storey buildings), even using very soft rubber compounds it is not possible to obtain the required horizontal stiffness with a suitable geometrical dimension.

The aim of the research activities to be carried out in this Task is to develop a new type of HDRB that provides a very low horizontal stiffness while ensuring stability under extreme displacements. The development of the novel system will also duly consider the need to become an industrial product, competitive, in term of costs, to similar devices available on the market.

The results of the activities will also provide input for the development of European standards for the anti-seismic devices and structures provided with them. The development of the novel HDRB requires activities on the following topics:

• development of a new concept of HDRB with low stiffness and high stability;
• definition of performance needs for such an innovative anti-seismic device;
• development of improved materials, functional mechanisms, geometry, and life of the device;
• design verification and optimisation through numerical models;
• development and realisation of manufacturing techniques and tools for the construction of the device;
• manufacturing of the prototypes.

For activities in the infrastructure field, in order to overcome the performance of presently available dampers, ALGA already started theoretical and industrial studies aimed at the development of an innovative damper (DECS), based on electro-inductive phenomena. Such activities have been carried out in the framework of a research program partially funded by the former Italian Ministry of the University and Research (MURST). As a result of these activities, some first prototypes of DECS have been manufactured. The study led to very promising results, which strongly encourage a further substantial development and a full validation of such devices for practical industrial applications, especially to bridges and viaducts.

The main technical advantages of the DECS devices, as well as the enhancement with respect to the existing dampers performances are hereinafter summarised: energy dissipation is the only viable system to reduce the effect of the earthquake, while simultaneously controlling the relative displacements of the structural components. Until now, the physical principles used in the wide variety of existing energy dissipating devices are based on (i) yield of metals, (ii) viscosity of fluids or elastomers and (iii) friction.

As a consequence, all the existing ED devices are characterised by one or more disadvantages such as limited cycle life, response dependence on temperature and ageing, high scattering of the response and heat generation which may alter the response or damage the devices.

In addition, the currently available ED devices need for a rather frequent maintenance for ensuring their prescribed performances and frequently for replacement during the structure life. The DECS supersede all the above-mentioned disadvantages and in addition, can really provide a maintenance-free performance. The basic idea of the DECS consists in an electric generator that produces current exploiting the movements generated by the earthquake. The current is then dissipated in a short circuit, so that all the mechanical energy supplied to the device is converted into heat.

Task 2.2a.2: Development, manufacturing and qualification of elastoplastic devices and friction pendulum

The industrial partner MAURER will manufacture some typical existing isolators of different kinds with the aim of:

1.  evaluating the benefits and limits of such devices, so as to develop possible improvements, and in particular, assessing and validating the recently proposed criterion for evaluating the re-centring capability of the isolation systems;

2.  experimentally substantiating claimed characteristics and advantages of some overseas products such as friction pendulum.

It is noted that Item 1 represents an important novelty since, at present, the re-centring matter is only dealt within the AASHTO “Guide specifications for seismic isolation design”. However, the latter adopts a very controversial and questionable criterion, now disclaimed by the scientific community, and which in fact prevents the use in the USA and other countries of important types of seismic devices developed in Europe.

Item 2, on the other hand, deals with a subject of topical interest that is presently debated within the framework of technical associations. The subject is particularly important for seismic retrofit projects. Both items of activity require important experimental activities (e.g. shaking table tests) that will be carried out at the ENEA Laboratories (see Task 2.2a.4).

Task 2.2a.3: Implementation and Validation of Numerical Tools

The exploitation and dissemination of the innovative anti-seismic systems developed within Cluster 2.2a, then the number of future applications, will also depend on the availability of reliable Numerical Tools capable of correctly describing the behaviour of the devices of such systems. As a matter of fact, the Designers and other potential End Users are usually not familiar with these technologies: moreover, they generally use commercial structural codes (e.g. Finite Element codes), which often are not suitable for describing highly non linear elements.

The main objective of Task 2.2a.3 is the implementation and the validation, through the shaking table tests and other laboratory activities performed in the framework of Task 2.2a.4, of suitable numerical models of the devices developed within Tasks 2.2a.1 and 2.2a.2 and the structures and mock-ups provided with them. These models will then be described in the User Manual (Task 2.2a.5). The aforesaid numerical activities of Task 2.2a.3 will help the manufacturers to optimise the device characteristics and designing the shaking table tests.  

In the framework of Task 2.2a.3, the acceleration time-histories to be used for both the numerical activities and the shaking table tests (see Task 2.2a.4) will also be defined. The first step of this activity is the identification of the maximum credible earthquake within an accepted return period (design earthquake) and site characterization in terms of shear-waves profiles, local intensity and epicentral distance as applicable to a selected site. The definition of the design earthquake is mainly based on a seismotectonic approach, which takes into account both the seismic history of the region and the seismogenetic potential of relevant neotectonic structures. Earthquake parameters and site conditions with a fixed scatter will then be used to sort out accelerograms recorded during events and sites the parameters of which are in the selected ranges of the site.

Task 2.2a.4: Shaking table tests

The manufactured prototypes will be installed in a mock-up and tested on the shaking table facility of ENEA Laboratories of Casaccia. The ENEA shaking table measures 4m ´ 4m and can support up to 300 kN: its maximum overturning moment is 300 kNm. It can be controlled in 6 degrees of freedom, but the tests described here will mainly be carried out in the horizontal direction only, so as to simplify the evaluation of the results and the comparison among the different devices.

The test mock-up will be quite a simple structure (e.g. a rigid mass) and will be the same for all the anti-seismic systems developed within the Cluster. This will allow for a better comparison of the performances of the different systems and their improvement. Based on the input characterization (see Task 2.2a.3) two main series of tests will be carried out. The first series will be carried out on the model subjected to a set of 4 different synthetic earthquake inputs generated to match the same design acceleration spectrum (AST type) characterized by a PGA (peak ground acceleration) of 0.41 g, according to AASHTO specifications. The design spectrum, established by a specific seismic hazard study, will be associated to an average return period of 900 years, and has a 7.5% probability of exceedance in the expected structural life (i.e. 70 years) for infrastructure and a design spectrum, established by a specific seismic hazard study, associated to an average return period of 475 years, and has a 10% probability of exceedance in the expected structural life (i.e. 50 years) for urban areas.

The second series will be carried out on the same model subjected to time-histories recorded during the most severe earthquakes in Europe (i.e., Campano-Lucano Earthquake, 23rd December 1980, Friuli Earthquake, September 1976, etc.). The corrected acceleration time-histories from records obtained during the main shock will be collected from the CD-ROM “European Strong-Motion Database”. The CD-ROM was created with the support of the European Commission, ENVIRONMENT (contract ENV4-CT97-0397). 

Task 2.2a.5: User manual

At the conclusion of the Project, an User Manual will be prepared by all partners involved in Cluster 2.2a, in particular by the manufacturers. The User Manual is quite an important document, which will be particularly addressed to potential End Users, with the aim of providing them with practical tools to design structures equipped with the devices developed in the framework of the Project. This document will also help the manufacturers in the dissemination of this technology. It will contain descriptions of the main features and performances of the devices, and comparisons among different type, so as to help the User to choose the most suitable device. In the framework of Task 2.2a.5, manufacturers can also produce their own brochures.