Periodic Reporting for period 1 - IRESCO (Innovative REtrofitting for Substandard COnstruction)
Reporting period: 2016-09-01 to 2018-08-31
Much of the existing building stock in Europe and developing countries was designed according to old standards using poor material and construction practices. These buildings have deficient lateral load resistance that can lead to extensive damage and collapse during strong earthquakes as observed in recent major events (e.g Haiti 2010, Lorca 2011, Nepal 2015). In the last 15 years, loss of human life due to earthquakes was over 60,000/year with $300 Billion/year estimated economic loss. Deterioration of structural elements due to ageing and aggressive environmental conditions is another factor that can significantly increase the vulnerability of reinforced concrete (RC) structures. The retrofit of deteriorated or seismically deficient structures provides a feasible and economic approach to improving their load carrying capacity and reducing their vulnerability. Different conventional retrofitting techniques have been examined in the past to enhance the performance of substandard structures. However, these methods can be highly invasive, labour intensive and they usually increase the mass of the building. In recent years, the use of composite materials in retrofitting of existing structures has been increased substantially and proved to be efficient in accommodating deterioration of structural elements or damages observed after strong earthquakes. Externally bonded Fibre Reinforced Polymers (FRP) applications have gained ground due to the advantages such as high resistance to corrosion, excellent durability, high strength to weight ratio and adaptability of the technique to different types of structural members. However, high initial cost of FRP materials and their fire protection requirements are major obstacles to their wide application, especially in developing countries. Therefore, there is a pressing need to develop more cost-effective retrofitting solutions for substandard structures. This action aimed to develop a novel and economic method for strengthening of substandard RC structures by using a new generation of environmentally friendly mortar-based composite materials using recycled high strength steel cords/fabrics embedded in an inorganic grout matrix. This novel technique can be efficiently used for flexural, axial and shear strengthening of reinforced concrete (RC) members and it is cost effective, fire resistant, sustainable, and has low environmental impact. The main objectives of the project is to: (i) develop a better understanding of the characteristics of mortar-based composite materials with inorganic matrix and bond-slip behaviour between steel cords and grout to develop design-oriented models for the novel strengthening system; (ii) develop design-oriented models and performance-based design guidelines so that this new technique can be introduced in practice; (iii) evaluate analytically the efficiency of the novel strengthening system at improving the seismic performance of representative substandard buildings through non-linear time-history analyses; and (iv) develop practical design guidelines for adoption by European standards to use the new technology for strengthening of deficient RC members.
Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far
The work performed was both experimental and analytical. An experimental characterization of R-SRG was carried out based on multi scale testing at material and structural level. The mechanical characteristics of the recycled steel cords obtained from Anagennisi project (Project ID: 603722) were further processed in order to classify the different types of recycled steel cords and their corresponding behaviour. Pull-out tests on R-SRG were conducted to characterize the bond-slip mechanism developed between the mortar and the recycled steel cords to simulate the actual behaviour of the new composite material. The bond behaviour of multi-ply SRG composites applied to concrete substrates was studied by performing lap-splice and single-lap bond tests. The efficiency of steel-reinforced grout jackets and of jackets made by spirally running steel cords and inorganic matrix when applied on plain concrete cylindrical columns using different design parameters was investigated. Full-scale cantilever columns representative of the pre-1970s old-type detailing in southern Europe were retrofitted with the novel jacketing system and tested under reversed cyclic loading simulating earthquake effects. The test results were utilized for the needs of the analytical study of the novel mortar-based composite system. Reliable finite element models of circular and prismatic concrete columns confined with the SRG composite system in order to investigate the effects of different design parameters on the performance of the jacketed members were developed. A comprehensive experimental database of SRG-confined columns was developed and used to develop new design-oriented models to predict the strength and ultimate strain of SRG confined concrete columns by taking into account the confinement stiffness of the jackets. The effectiveness of SRG composites to improve the seismic behaviour of substandard RC frame buildings under different levels of earthquake excitations was investigated analytically. Design recommendations were developed to use the novel mortar-based composite for displacement ductility and shear strength enhancement of deficient RC members. A practical example-guide was prepared for structural engineers to use R-SRG strengthening systems.
Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)
This project aimed to develop an innovative and cost-effective strengthening solution by using a novel mortar-based composite, which comprises recycled high strength steel cords, by-product of tyre recycling, embedded in an inorganic grout matrix. The results have demonstrated the feasibility of using the novel method in enhancing both strength and deformation capacity of deficient RC structural members. Design-oriented models and performance-based design guidelines have been developed which will allow the use in practice. The very positive outcomes of this project can lead to a new generation of low-cost and efficient retrofitting systems for deteriorated or seismically deficient structures with high impact on both economy and society. This is especially important since about 30% of the total European construction output is invested in rehabilitation and maintenance of housing and infrastructure with composites materials playing a leading role. The proposed retrofit solution uses high strength steel fabrics as by-product of tyre recycling will benefit society by reducing the CO2 emissions, and improve the quality of life, health and safety of those who live in earthquake prone regions. The output of this project will be directly exploitable by researchers in the field of material, structural and earthquake engineering, contractors, infrastructure owners, code developers and practicing engineers. Further research should address issues related to the durability and fire resistance of the proposed strengthening system. Moreover, additional experimental studies should examine the efficiency of the system at global level. Finally, design guidelines need to be further developed to enable engineers and contractors to specify and design such a novel retrofitting technique.