JUNG J. KIM ⁽¹⁾, TAI FAN ⁽²⁾; TAHA REDA, M. MAHMOUD ⁽³⁾; NIGEL G. SHRIVE ⁽⁴⁾

⁽¹⁾ Research Professor, Sejong University, Civil & Environmental Engineering, jungjkim@sejong.ac.kr

⁽²⁾ Post-Doctoral Fellow, University of New Mexico, Civil Engineering Department, tfan01@unm.edu

⁽³⁾ Professor & Regents’ Lecturer, University of New Mexico, Department of Civil Engineering, mrtaha@unm.edu

⁽⁴⁾ Professor, University of Calgary, Civil Engineering Department, ngshrive@ucalgary.ca

ABSTRACT

Many historic masonry structures consist of an inner core of rubble masonry or grout (inner leaf) and an outer layer of brickwork (outer leaf). Cracks in various directions might be observed in these structures. Global inclined cracks are typically caused by externally applied loads such as earthquakes or uneven soil settlement. On the other hand, local vertical and horizontal cracks can be caused by compressive overload, or constrained tensile stresses which develop as a result of differential creep and shrinkage in the different masonry components. Environmental effects such as temperature and weathering can also induce stresses and degrade a structure. Local cracks can be associated with non-apparent interface debonding between the core and the brickwork. Such interface debonding alters the horizontal strain compatibility between the core and the brickwork and can lead to local buckling: the horizontal cracks widen and the brickwork moves out-of-plane. Observation of horizontal and vertical local cracks and evidence of interface debonding can be considered as a sign/indicator that the historical masonry structure has experienced long-term stress redistribution due to differential creep. Such stress redistribution can lead to global failure of the masonry structure as some of its components become overstressed. In this paper we demonstrate that the sequence of crack development described can lead to structural collapse. We suggest that recognition of these signs might be useful for planning and executing retrofitting work to prevent collapse of historical masonry structures.

Keywords: Cracking, debonding, creep, historic masonry