To meet the demand for cutting-edge technological solutions to strengthen structures and upgrade their seismic capability, MAPEI S.p.A., in collaboration with DiSt – Department of Structural Engineering and Architecture of the Federico II University of Naples, has developed an innovative, low-impact, rapid FRP system for strengthening non-confined beam-pillar joints in reinforced concrete, which only needs to be applied externally.
This innovative application technique reduces the amount of disruption typical of more invasive, traditional systems, avoids having to remove portions of external cladding, reduces the overall cost of the work and minimizes the amount of disturbance to occupants of the building.
From a functional point of view, the external FRP strengthening system, which consists of quadriaxial carbon fiber fabric applied around a non-confined joint, is similar to horizontal clamps positioned inside a joint and prevents brittle-type failure in the joint panel in favor of more yield in the longitudinal rebar in the adjoining beam.
The validity of the system was verified by carring out an experimental test campaign in the DiSt test lab on two beam-pillar joints: The first one in its original, as-built configuration and the second one in a strengthened configuration, representative of reinforced concrete buildings typically found in medium-risk seismic zones designed according to construction norms and standards, which are commonly found, but no longer practiced. These test configurations were characterized by their lack of clamps in the hinge panel and poor transversal reinforcement in the beams and pillars.
The failure mode of the as-built joint was typical of the type of failure found in existing buildings with diagonal shear cracks in the joint panel, while the joint strengthened with FRP on the external side only confirmed the effectiveness of the strengthening system. The tests demonstrated that initial stiffness was more or less similar to that of the as-built joint, which means this application may be considered to be a “localized” type. The effectiveness of the system was confirmed by it achieving the main objective: To modify the failure mode from brittle-type (shear failure in the joint panel) to ductile-type (flexural yield of the beam).
To summarize, the experimental test campaign demonstrated the validity of this new strengthening system that increases the shear strength of the joint panel and favors the development of ductile yield failure in the beam. This results in a significant increase in the amount of energy dissipated, leading to an increase in the performance characteristics and seismic capability of a building.
Founded in 1937 in Milan, MAPEI now has 90 subsidiaries, including the parent company, in 57 countries and 83 production facilities in 36 countries spread across 5 continents, a consolidated turnover in 2019 of €2.8 billion and more than 10,500 employees worldwide.
The foundations for the success of the Company are Specialization in the world of building by offering certified products and systems to meet the requirements of clients and market demand; Internationalization to be more in tune with local needs and to reduce transport costs to a minimum; and Research & Development, which receives the most support from the Company in terms of both investments and human resources. MAPEI has always been fully aware of the impact the Company has on the environment and on society in general and, over the years, the three cornerstones of the MAPEI philosophy have been joined by Sustainability as an essential driver behind the continuous development of the Company.
About MAPEI North America
Headquartered in Deerfield Beach (Florida), MAPEI North America consists of the subsidiaries MAPEI Corporation (for the USA), MAPEI Inc. (for Canada) and MAPEI Caribe (for Puerto Rico and other Caribbean islands), whose 18 facilities collectively have a workforce of more than 1,700 employees. MAPEI facilities have been certified to ISO 9001 and ISO 14001 standards. An environmentally conscious manufacturer that reinvests 5% of its revenue into R&D, MAPEI offers training for architects, contractors, installers and distributors through the MAPEI Technical Institute. For more about MAPEI, visit www.mapei.com or call 1-800-42-MAPEI (1-800-426-2734).