In Situ Out-of-Plane Testing of As-Built and Retrofitted Unreinforced Masonry Walls

Abstract

Draft ManuscriptAuthors may post the final draft of their work on open, unrestricted Internet sites or deposit it in an institutional repository when the draft contains a link to the bibliographic record of the published version in the ASCE Library or Civil Engineering Database. "Final draft" means the version submitted to ASCE after peer review and prior to copyediting or other ASCE production activities; it does not include the copyedited version, the page proof, or a PDF of the published version. varied from 80 to 130 years, and all but one were constructed using clay brick masonry with 6 timber floor and roof diaphragms. The fourth building was a reinforced concrete frame structure 7 with pre-cracked clay block partition walls in addition to partition walls that appeared 8 undamaged. The test program was comprised of testing five one-way vertically spanning solid 9 URM walls from the group of three URM buildings and testing four two-way spanning URM 10 partition walls from the reinforced concrete frame building. All walls were tested with their 11 original support conditions, but three one-way spanning walls were additionally re-tested with 12 modified support conditions. These additional tests allowed the effects of wall support type to be 13 investigated, including the influence of a concrete ring beam used at the floor levels and the 14 influence of wall to timber diaphragm anchorage by means of grouted steel rods. Several walls 15 were next retrofitted by adding either near-surface mounted (NSM) carbon fiber reinforced 16 polymer (FRP) strips or NSM twisted steel bars (TSB), and were then re-tested.

In Situ Out-of-Plane Testing of Unreinforced Masonry Cavity Walls in as-Built and Improved Conditions

“…Note, however, that RC bond beams or RC slabs in buildings with URM load-bearing cavity walls [28] may not effectuate significant arching action of the walls if no vertical frame elements are present to restrain these elements vertically [11]. The method currently recommended by ASCE [9] for determining the OOP force capacity of previously undamaged URM infill walls assumes arching action based on a compressive strut method proposed by Angel et al [12] as follows:…”

“…Based on experimental testing [10,11] and previous model iterations [24,25], Derakhshan et al [13] proposed an assessment procedure for determining the OOP response of simply-supported URM load-bearings walls in vertical flexure based largely on the consideration of a semi-rigid rocking wall mechanism developing post-cracking as follows:…”

“…However, vertical frame elements are generally required to vertically restrain topside bounding frame elements in order to effectuate arching action (i.e., RC bond beams atop loadbearing URM walls are unlikely to effectuate much arching action). Furthermore, buildings in Australasia with load-bearing URM walls typically have timber diaphragms [7] which have been experimentally shown to provide little to no arching action to URM walls [9,11]; • Displacement-based performance criteria (with appropriate capacityreduction factors as proposed by Derakhshan et al [13]) should generally be considered for URM cavity walls without arching action, and force-based performance criteria should be considered for infill cavity walls with arching action; • URM cavity walls without arching action at all storey levels and walls with arching action at higher storey levels are susceptible to OOP strength exceedance when subjected to DBE demands in regions of either moderate seismicity (e.g., Auckland) or high seismicity (e.g., Hastings) (see Table 5); • Existing OOP assessment methods may be viable for assessing cavity walls in vertical flexure provided that the equivalent solid wall thickness is determined firstly. However, the determined equivalent solid wall thickness is only directly applicable to the analytical model being considered (see Tables 6 and 7), and a limited range of material properties and component geometries were tested in this experimental program for validation; and • Cavity tie retrofits with adequate spacing, as well as adequate compressive and shear stiffness, can greatly improve the OOP capacity of URM cavity walls, especially for infill walls experiencing OOP arching action (see Fig.…”

“…Buildings in Australasia with load-bearing URM walls typically have timber diaphragms [7] which have been experimentally shown to provide little to no arching action to URM walls [9,11]. For simplysupported walls with no significant overburden load or without arching action, Derakhshan et al [25] recommended that the crack height be assumed to occur such that h 1 = 0.67(h 1 + h 2 ), wherein the variables h 1 and h 2 represent the height (m) of the individual wall segments below and above, respectively, the primary horizontal crack.…”

“…URM cavity walls were physically tested in two different buildings utilising an approach wherein lateral forces were applied using a system of airbags to simulate distributed OOP seismic forces. This approach was consistent with the testing procedures recommended by ASCE [9] and previously utilised by Derakhshan et al [10,11] and Angel et al [12]. The URM cavity walls were tested in vertically-spanning, one-way bending (herein referred to as "vertical flexure") to facilitate comparison of the results with existing predictive models that assume vertical flexure only for estimating OOP behaviour [12,13].…”