Stochastic assessment and structural reliability of spatially variable unreinforced masonry walls subjected to in-plane shear loading

Gooch, Lewis John

Title: Stochastic assessment and structural reliability of spatially variable unreinforced masonry walls subjected to in-plane shear loading
Creator: Gooch, Lewis John
Relation: University of Newcastle Research Higher Degree Thesis
Resource Type: thesis
Date: 2024
Description: Research Doctorate - Doctor of Philosophy (PhD)
Description: The introduction of limit state design methodologies and capacity reduction factors for the design of engineered structures has resulted in a focus on understanding the probability of failure of structural elements under various load effects, be they permanent or imposed gravity loads, wind events, or earthquakes. Accurate, reliability-based calibrations have previously been performed for steel and concrete structures, though there are few such studies focusing on the probability of failure of structural masonry elements. To address this research gap, this dissertation presents a detailed study focusing on the determination of the structural reliability of unreinforced masonry (URM) walls subjected to in-plane shear loading. This research into the structural reliability of URM shear walls utilised a combination of an extensive experimental program and a series of stochastic finite element analyses (SFEAs), in order to produce suitable probabilistic models that describe the variability of the peak in-plane shear capacity of URM walls. The laboratory investigation presented in this dissertation focused on the accurate quantification of the statistical properties of masonry material behaviour, including the direct and flexural tensile bond strengths, and the shear bond and shear frictional resistances of the unit-mortar interface, the composite masonry compressive strength, and the direct and flexural tensile strengths of clay brick masonry units, through the application of 776 material characterisation tests. In addition to this, a total of sixteen full-scale masonry walls tests were constructed and tested under a cyclic, displacement-based, in-plane shear loading. These wall specimens were devised such that a set of four theoretically identical wall specimens were intended to fail in one of the unique failure mechanisms URM shear walls are susceptible to. The results of this experimental program found that the peak in-plane shear capacities of URM walls to resist flexural failure modes, i.e.: flexural tensile and flexural compressive failures, are highly invariable, with coefficients of variability (COVs) equal to 0.023 and 0.003 for the ultimate shear capacity of a flexural tensile and flexural compressive failure, respectively. Furthermore, it was observed that the COVs for shear failure modes (shear sliding and diagonal tensile failures) were higher, with a value equal to 0.028 for shear sliding and 0.090 for diagonal tensile. However, these variabilities are still relatively small given the typically large COVs of masonry material properties. In contrast to the finding for peak shear capacity, there was a significant amount of observed variability in the ultimate displacement capacity of the experimentally tested walls. COVs for the displacement capacity ranged from 0.245 to 0.655 across the four sets of wall specimens. Further to the above, the results of the experimental material characterisation program allowed for the derivation of probabilistic models that described the material properties typically expected to govern the in-plane shear capacity of URM walls. These models were derived by fitting probability density functions (PDFs) to the experimentally recorded data. Assessing the accuracy of a Normal, Lognormal, Weibull (Extreme Value Type III), Gumbel (Extreme Value Type I) and Gamma distributions for each material property produced an extensive set of results, consistent with previous statistical investigations of masonry behaviour presented in literature. Considering the experimental results of the full-scale laboratory wall tests, as well as the PDFs of URM material behaviour, a series of seven SFEAs were produced to represent the laboratory specimens. It was initially found that the application of a monotonic, displacement-based loading produced results inconsistent with experimental observations. As such, a detailed, cyclic loading scheme, consistent with that applied in the laboratory tests was examined. This more comprehensive loading model significantly exacerbated the computational expensive of each numerical simulation, however, it was observed that the damage to the structural elements under the initial, small displacement cycles was significant enough to reduce the prediction of in-plane shear strength by up to 13%. This reduction produced numerical models significantly more consistent with experimental observations. As a result, probabilistic models of the model error (ME) associated with the SFEA predictions of the peak in-plane shear capacities of each of the four failure mechanisms considered in this dissertation were derived. Average values of ME were observed to range from 0.94 to 1.12. Finally, four SFEAs of structural configurations typical of Australian masonry walls panels were performed using probabilistic models of masonry material properties derived from the literature. From the results of these SFEAs, as well as the previously derived probabilistic models of ME, structural reliability analyses of each of the four failure mechanisms that URM shear walls are susceptible to were performed in accordance with the AS 3700 (2018) requirements for design. These results indicated that, for flexural tension and diagonal tension failures, the current AS 3700 provisions are consistent with the AS 5104 (2018) requirements for the structural reliability of commercial buildings. In the case of a flexural compressive failure, the larger capacity reduction factor specified by AS 3700 (2018) for a compression failure, derived from the consideration of permanent and imposed gravity loads, produced annual reliability indices below the target index determined from AS 5104 (2018). Furthermore, for a shear sliding failure, tensile cracking resulting from the application of cyclic loading resulted in annual reliability indices less than the AS 5104 (2017) provisions. Thus, a revised design methodology for a shear sliding failure has been proposed for AS 3700 that considered a cracked section under in-plane lateral load effects. Furthermore, additional clauses outlining the design methodology for shear walls subject to flexural tensile cracking, overturning and flexural compression failures have been proposed.
Subject: unreinforced masonry; structural reliability; finite element analysis; spatial variability; shear wall; laboratory testing; material characterisation
Identifier: http://hdl.handle.net/1959.13/1511105
Identifier: uon:56466
Language: eng
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