Guide for the Design and Construction of Externally Bonded Fiber-Reinforced Polymer Systems for Strengthening Unreinforced Masonry Structures

Description

Masonry is a generic term used to describe a type of construction where clay, or concrete masonry units, or natural stones are bonded together to form a load-bearing structure or a component in a structure. Non-load-bearing masonry includes partitions and veneers. Although masonry is used in flexural applications such as retaining walls, roof and floor beams, and lintels, it is more frequently used in load-bearing walls primarily resisting compression loads. Reinforced and unreinforced masonry(URM) walls have been used in constructing structural load-bearing components. In buildings, masonry walls can serve effectively as part of the lateral load-resisting system to resist wind and earthquake loads. Infill masonry walls play a significant role in enhancing in-plane stiffness and shear resistance of both reinforced concrete (RC) and steel frames, if properly connected to the structural frame.

Unreinforced masonry structures have shown their vulnerability to major events such as earthquakes, severe wind, blast, and impact. In addition, factors such as change in occupancy, deterioration, or an increase in lateral-load demand, may create the need to perform structural retrofit. ACI 530 covers the design and construction of new masonry; the repair, retrofitting, and rehabilitation of masonry struc-tures are not included in that code. The repair and retrofit/rehabilitation of existing masonry structures have traditionally been accomplished using conventional materials and construction techniques. Externally bonded steel plates, RC overlays, grouted cell reinforcements, and post-tensioning are just some of the many traditional techniques available.

Fiber-reinforced polymer (FRP) (ACI440R) composites have emerged as an alternative to traditional materials for strengthening masonry structures. Fiber-reinforced polymer materials are lightweight and noncorrosive. They exhibit high tensile strength and elastic modulus(carbon FRP), and are impact resistant with electromagnetic transparency. These materials, which are available in a variety of forms, including flat sheets and plates and reinforcingbars and prestressing tendons of typically round crosssection, provide the licensed design professional with flexibilityin achieving desired performance. Fiber-reinforced polymersystems can be used in seismic, wind, or blast strengtheningof URM structural elements.