Strengthening of Masonry Arches with Fiber-Reinforced Polymer Strips Paolo Foraboschi 1 Abstract: This paper deals with masonry arches and vaults strengthened with surface fiber-reinforced polymer FRP reinforcement in the form of strips bonded at the extrados and/or intrados, considering strip arrangements that prevent hinged mode failure, so the possible failure modes are: 1 crushing, 2 sliding, 3 debonding, and 4 FRP rupture. Mathematical models are presented for predicting the ultimate load associated with each of such failure modes. This study has shown that the reinforced arch is particularly susceptible to failure by crushing, as a result of an ultimate compressive force being collected by a small fraction of the cross section. Failure by debonding at the intrados may also be an issue, especially in the case of weak masonry blocks or multiring brickwork arches. Failure by sliding has to be considered if the reinforcement is at the extrados and loading is considerably nonsymmetric. DOI: 10.1061/ASCE1090-026820048:3191 CE Database subject headings: Arches; Masonry; Fiber reinforced polymers; Reinforcement; Mathematical models; Crushing; Failure modes. Introduction Numerous historical constructions are still in service all over the world and a significant part of them are of cultural and artistic value. Many historical constructions contain masonry arches or barrel vaults, cross or groin vaults, cloist vaults, and domes i.e., masonry shells, which play an important part in public and resi- dential buildings, as well as in road, rail, and waterway infrastruc- tures. Modern-day loads are far higher than the ones initially consid- ered. A masonry shell with either tie-rods or nonslender piers only collapses if its loading is severely nonsymmetrical. The safety condition of a common masonry shell consequently depends not on the level of loading, but on the live-to-dead loads ratio. If the ratio is low, modern loads are supported because of the outstand- ing combination of mechanical properties that masonry shells can rely on to carry symmetrical loads. If the ratio is high i.e., if today’s live loads are severe, because the live loads distribution may not be symmetrical, modern loads have the potential for causing masonry shells to collapse, in fact, the failure of masonry shells is not unusual. Substantial alterations often have to be made to masonry buildings to meet present architectural requirements. Such alter- ations can lead to a significant reduction in the safety margins of masonry shells e.g., buttresses or tie-rods may be removed, new columns or walls may be rested on the shell’s extrados, openings may be cut, the spandrel fill may be removed or replaced by a lighter material, etc.. As a result, the current usage of many ma- sonry shells either satisfies present needs but fails to fulfill the requirements of modern codes, or it satisfies the codes but is unable to meet the present building, road, rail, or waterway infra- structural demands. Structural engineers consequently often have to assess masonry shells. When the safety margins of a masonry shell are no longer assured or prove inadequate for new demands, then strengthening is needed. Strengthening masonry shells poses serious concerns because the vast majority is of considerable architectural and historical value. Traditional reinforcement techniques may guarantee an ad- equate increment in strength, stiffness, and ductility, but are often short-lived and labor-intensive, and they usually violate aesthetic requirements or conservation or restoration needs. Such problems have recently led researchers Hamid et al. 1994; Modena 1994; Saadatmanesh 1994; Ehsani et al. 1997; Kolsch 1998; Triantafil- lou 1998a, b; Tinazzi et al. 2000; Albert et al. 2001; Meier 2001; Tong Li et al. 2001; Valluzzi et al. 2001 to suggest strengthening masonry shells with fiber-reinforced polymer FRP composites in the form of bonded surface reinforcements. Reinforcements epoxy-bonded to the masonry surface enable masonry structures to bear substantial tensile stresses, eliminating their greatest mechanical shortcoming at an acceptable cost. Ex- ternally bonded reinforcements may be made of steel, but they are much more effective if they are made of FRP. The benefits of FRP over conventional reinforcement materials include its adaptability to curved and rough surfaces, such as historical masonry tends to be. To ensure adequate masonry permeability and comply with restoration requirements, most of the boundary has to be left with- out reinforcement. To minimize the amount of FRP while still ensuring an adequate safety margin, reliable methods are needed for the structural analysis of reinforced shells. The main events leading to the collapse of a masonry shell include severe cracking patterns. Cracking splits the shell into slices, ultimately converting it into a one-dimensional thrusting structure, since the slices behave like arch segments. The ultimate load is therefore carried by a system of masonry arches whose geometry depends on the cracking pattern. Thus the ultimate 1 Professor, Dipt. di Costruzione dell’Architettura DCA, IUAV– Univ. degli Studi di Venezia, ex Convento delle Terese, Dorsoduro2206, 30123–Venice, Italy. E-mail: paofor@iuav.it Note. Discussion open until November 1, 2004. Separate discussions must be submitted for individual papers. To extend the closing date by one month, a written request must be filed with the ASCE Managing Editor. The manuscript for this paper was submitted for review and pos- sible publication on April 11, 2002; approved on May 14, 2003. This paper is part of the Journal of Composites for Construction, Vol. 8, No. 3, June 1, 2004. ©ASCE, ISSN 1090-0268/2004/3-191–202/$18.00. JOURNAL OF COMPOSITES FOR CONSTRUCTION © ASCE / MAY/JUNE 2004 / 191