TREViS: Tailoring Nano-Reinforced Elastomers to Vibrating Structures

Rubbers and other elastomers are very effective in mitigating vibrations experienced by Civil Engineering structures subjected to natural actions such as earthquakes, wind gusts or ocean waves. Following early applications in aircrafts and machineries, engineered rubbers have been successfully used in a number of energy dissipation devices and isolation bearings for buildings, bridges and other types of construction. A concerted effort has been made over the last few decades to further improve the performances of such elastomers with a variety of nano-reinforcements, e.g. carbon black, silica nano-particles and carbon-nanotubes, in so obtaining enhanced rubbers with significant nonlinearities. Despite this material complexity, manufacturers of elastomeric devices very often encourage the application of crude assumptions in the dynamic analysis of viscoelastically damped structures. Their interest is indeed to simplify as much as possible design procedures for structures equipped with their products, aimed at engaging more professional engineers. Unfortunately, such simplifications can be highly inaccurate, as demonstrated by previous investigations of the applicant in a range of design situations, e.g. buildings resisting seismic and wind forces. The TREViS project aims to demonstrate the feasibility of a radically new way of designing vibration-proof structures. According to the applicant's vision for the future, structural engineers must have the possibility to select the most appropriate mechanical properties of viscoelastic dampers and isolators, which optimise the global behaviour of new and existing structures under dynamic loadings; while the manufacturers' role should be simply to use suitable nano-reinforcements to tune structural rubbers according to the designers' specifications. As a necessary first step in this direction, an efficient computational framework will be theoretically established and experimentally validated throughout the proposed investigations; the aim is to allow accurate material information on nano-reinforced elastomeric devices to be incorporated and efficiently used to run dynamic analyses of structures equipped with such components within the limits of a reasonable computational effort. This novel strategy is intended to bridge the existing gap between academic appreciation of this challenging dynamic problem and current state of practice. A blend of experimental and computational studies will be conducted at Loughborough University along the three phases of TREViS. Orthonormal properties of Laguerre's polynomials will be used to approximate the relaxation function of elastomeric compounds containing carbon black and silica nano-particles, and special attention will be paid to strain-dependent effects and other nonlinear phenomena; an enlarged state-space model will be devised for viscoelastic beams with a sandwiched nano-reinforced core (Phase 1). Re-analysis techniques will be exploited to tackle material and geometrical nonlinearities, and a series of impulse hammer and shake table tests will be carried out for validation purposes (Phase 2). The proposed approach will be extended to frames made of viscoelastic beams with different dissipative properties, in so addressing the case of non-proportionally non-viscously damped structures (Phase 3). Each of these phases has a significant transformative aspect, namely: 1) nonlinear state-space formulation for viscoelastic materials and components, alternative to traditional characterisations in the frequency domain; 2) general computational strategy based on re-analysis techniques for enlarged state-space models, adaptable to other structural problems (e.g. flutter instability of bridge deck sections); 3) exploitation of normal modes for nonlinear structures with non-proportional non-viscous damping, providing structural engineers with physical insight and computational advantages in practical applications.

Non-academic impacts anticipated from the TREViS project can be classified in four main categories: 1) PEOPLE. In addition to Principal Investigator (Dr A Palmeri), other people will directly benefit from proposed studies. The rubber advisor (Dr A Ansarifar) will have the possibility to work on Civil Engineering applications of nano-enhanced rubbers, while his previous experience has been concentrated on Mechanical & Manufacturing Engineering problems. Additional knowledge and skills acquired by the post-doctoral Research Associate (RA) will make him/her more competitive in the job market. Demand of structural engineers with solid expertise in vibration analysis and testing is expected to rise in the next years, as dynamic investigations for health assessment and monitoring of existing structures are becoming increasingly popular in the construction industry. The ambitious publication plan will also boost the RA's CV, along with his/her chances to find a more secure job (e.g. a lectureship) in academia. Moreover, two MEng Civil Engineering students will have the opportunity to develop their final-year dissertations on complementary aspects of this research, while a PhD student will use some viscoelastic members moulded for TREViS as a case study on damage detection via dynamic tests. 2) KNOWLEDGE. Relevant technical data gained from the proposed experimental campaign will be available online for downloading. As a result, new knowledge will also be disseminated outside the academic circle, e.g. including researchers of small to medium companies with limited access to scientific journals. Web 2.0 tools such as YouTube and SlideShare will be used to engage the non-specialist audience. 3) ECONOMY. Manufacturers of elastomeric devices will benefit from the outcomes of TREViS. Specific indications will be provided to improve the performances of structural systems embedding nano-reinforced rubber. Inaccuracies of traditional strategies of analysis and design will be identified and quantified. Medium to long-term impacts of the proposed investigations include less expensive and/or more efficient elastomeric dampers and isolators being installed in vibration-proof structures. 4) SOCIETY. The ultimate impact intended for the TREViS project is common to all developments of structural protection devices against dynamic loadings, i.e. improve reliability of buildings and bridges subjected to winds and earthquakes, and increase the number of constructions benefiting from these devices. This will result in contributing towards a more resilient built environment.