@article {bnh-5152, title = {Laboratory testing of strengthened cavity unreinforced masonry walls}, journal = {Journal of Structural Engineering}, volume = {144}, year = {2018}, month = {03/2018}, abstract = {

An experimental campaign consisting of nine pressure-controlled quasi-static airbag tests on unreinforced masonry (URM) walls and accompanying material testing was completed to investigate methods for seismic retrofit of out-of-plane loaded cavity walls. Three control walls were tested to serve as a baseline for wall strength comparisons: (1)\ a double-leaf unstrengthened cavity wall; (2)\ a cavity wall with improved cavity connections; and (3)\ a single-leaf wall strengthened using a near-surface-mounted (NSM) fiber-reinforced polymer (FRP) strip. The experimental program was concluded by six tests that were conducted on walls strengthened using a NSM FRP strip and having cavity connections in the form of either standard bent metal ties, proprietary helical anchors, or industrial foam. The tests were designed to measure the ability of the different cavity connections to maintain the cavity gap until a ductile wall failure mechanism forms by FRP debonding. Three of the walls were previously damaged by testing in either unstrengthened or FRP-strengthened conditions. These tests were intended to study FRP retrofit effectiveness of precracked walls or the relative ability of different types of cavity connections to resist forces until a global FRP debonding occurs. For each of the six cavity connection configurations, the FRP-strengthening technique was shown to significantly improve the wall strength. The minimum strength increase was 282\% compared with that of the control cavity wall. The compiled data are presented followed by general discussions on the design of seismic retrofit for cavity walls.

}, doi = {https://doi.org/10.1061/(ASCE)ST.1943-541X.0001987}, url = {https://ascelibrary.org/doi/10.1061/\%28ASCE\%29ST.1943-541X.0001987}, author = {Hossein Derakhshan and Wade Lucas and Phillip Visintin and Michael Griffith} } @article {bnh-5153, title = {Out-of-plane strength of existing two-way spanning solid and cavity unreinforced masonry walls}, journal = {Structures}, volume = {13}, year = {2018}, month = {02/2018}, pages = {88-101}, chapter = {88}, abstract = {

An in-situ unreinforced masonry (URM) wall testing programme was conducted to study the effects of as-built wall boundary conditions on its out-of-plane strength. In total, eight pressure-controlled quasi-static airbag tests were done on 4 double-leaf cavity walls and 4 single-leaf solid walls, followed by relevant material testing. The walls were located in two 1960s URM properties in Adelaide, South Australia and had in-situ boundary conditions and construction details. Several walls included door openings at one edge and/or connected to flexible ceilings at top. Other as-built details included plaster finish on some of the internal walls and on the inner leaf of some of the external cavity walls. Additionally, the cavity walls had as-built wall ties that were damaged during construction and had irregular spacing. The main contributions of this study are to highlight the effects of these in-situ details, to make a comparison between strength predictions using an energy-based, virtual work method and an equilibrium-based method, and to improve the virtual work method for evaluation of the walls that have plaster finish. The calculations indicate that the improved virtual work method can be used to obtain a safe, lower bound, estimate of the wall strength.

}, doi = {https://doi.org/10.1016/j.istruc.2017.11.002}, url = {https://www.sciencedirect.com/science/article/pii/S2352012417300747}, author = {Hossein Derakhshan and Wade Lucas and Phillip Visintin and Michael Griffith} } @article {bnh-5261, title = {State-of-the-art review and future research directions for FRP-to-masonry bond research: Test methods and techniques for extraction of bond-slip behaviour}, journal = {Construction and Building Materials}, volume = {20}, year = {2018}, month = {10/2018}, abstract = {

The effectiveness of FRP retrofits is heavily reliant on the shear bond that can be developed between the FRP and masonry substrate, which has been the focus of experimental research for almost two decades. This paper collates and critically reviews previous experimental work on the shear bond between FRP composites and masonry substrates, identifying 1583 individual pull-tests across 56 published studies. Whilst the pool of existing data is significant in terms of number of tests, it encompasses a rather narrow range of substrate material, FRP material and retrofit configuration. Most notably, the majority of tests have been undertaken on clay brick substrates, carbon FRPs and externally-bonded retrofits. By contrast, testing of natural stone substrates and near-surface-mounted retrofits has been limited. Significantly, the review identifies considerable inconsistency in the test arrangements, instrumentation methods, and data processing techniques for extracting local bond-slip properties, which has undoubtedly hindered the development of a unified bond model and codifiable design rules. Methods of extracting bond-slip behaviour from test data are critically reviewed, and importantly it is shown through numerical examples that without adequate instrumentation it is not possible to reliably extract this behaviour from standard pull-tests. Finally, suggestions for adequate instrumentation and a framework for undertaking bond-slip behaviour extraction through inverse analysis are presented. Significantly, the experimental database compiled as part of this work-thought to be the largest of its kind to date{\textemdash}is made openly available as an accompanying Data in Brief article with the intent that it will facilitate development of bond-strength models for FRP bonded to masonry.

}, doi = {10.1016/j.conbuildmat.2018.06.103}, url = {https://www.sciencedirect.com/science/article/abs/pii/S0950061818314934}, author = {Jaroslav Vaculik and Phillip Visintin and Michael Griffith and N.G.Burton and R.Seracino} } @article {bnh-5154, title = {Case studies of material properties of late nineteenth-century unreinforced masonry buildings in Adelaide}, journal = {Australian Journal of Civil Engineering}, volume = {15}, year = {2017}, month = {11/2017}, abstract = {

An experimental programme was developed to improve our understanding of the actual\ in situ\ strength of non-structural components in typical South Australian unreinforced masonry (URM) construction. The focus was on testing URM walls and chimneys in out-of-plane direction, and in the course of this study 132 as-built URM material specimens were collected. The specimens were tested either\ in situ\ or in laboratory. In total, four URM houses located in Darlington, a southern suburb of Adelaide, South Australia, were studied. Three of the buildings were built in the 1960s and the fourth was built in the 1980s. A comparison between the buildings material strength and the default values recommended in the Australian Masonry Standards, AS3700, suggests that the code specified default lower 5\% characteristic values were often greater than the measured characteristic strength. The collected data are presented for documentation and some comparison between this and other studies are also made.

}, doi = {https://doi.org/10.1080/14488353.2017.1401196}, url = {https://www.tandfonline.com/doi/abs/10.1080/14488353.2017.1401196}, author = {Hossein Derakhshan and Phillip Visintin and Michael Griffith} } @article {bnh-3804, title = {Final report: seismic retrofit tests of URM cavity walls}, number = {249}, year = {2017}, month = {07/2017}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

University of Adelaide researchers were engaged by Bushfire and Natural Hazards CRC to undertake an experimental campaign aiming to identify and develop seismic retrofit methods for out-of-plane loaded cavity walls. The research is a part of a broader project titled "Cost-effective mitigation strategy development for building related earthquake risk". This report presents the details of the tested cavity walls, trialed retrofitted schemes, obtained results, and discussion. The report concludes with recommendations on the seismic retrofit of this type of wall construction.

A review of the masonry literature suggested that retrofit methods have already been developed and widely researched for solid unreinforced masonry (URM) walls, but that the methods cannot be readily applied to cavity walls due to the cyclic nature of the seismic loads and the limited access to the cavity gap. The methods generally require access to both faces of the wall to attach fiber-reinforced-polymer (FRP) strips to masonry.

The broad retrofit concept for cavity walls was conceived to be using NSM FRP technique on the exposed surfaces of the cavity wall skins, e.g. to one face of each wall skin, but with the provision that the wall ties be verified/upgraded to maintain the cavity gap. For this purpose, 6 different alternatives of cavity structure were investigated. Two options involved the use of standard wall metal ties with different densities. Two other options included the use of proprietary helical mechanical anchors with different densities, and finally two configurations of expanding foam was used to partly or wholly fill the cavity gap. All of the FRP strips were near-surface-mounted (NSM).

It was found that with NSM FRP retrofit, the existing wall ties may be sufficient to maintain cavity gap depending on the location of the wall in Australia. For walls in regions with relatively higher seismic hazard, helical anchors can be added, and the anchor spacing can be proportional to seismic hazard but need not be less than 260 mm, i.e. every 3rd course.

}, issn = {249}, author = {Hossein Derakhshan and Wade Lucas and Phillip Visintin and Michael Griffith} } @article {bnh-4406, title = {Modelling FRP-to-substrate joints using the bilinear bond-slip rule with allowance for friction - Full-range analytical solutions for long and short bonded lengths}, journal = {International Journal of Solids and Structures}, year = {2017}, month = {11/2017}, abstract = {

Methods for simulating the mechanics of debonding and predicting global load-slip (P-Δ) response from local bond stress versus slip (τ-δ) relationships can vary significantly in their complexity. It is generally accepted that an adequate representation of intermediate crack debonding can be achieved by considering only mode-II (shear) fracture along the interfacial bond, a problem that can be solved by accounting for one-dimensional fields of elastic stress and strain in the substrate and plate, and nonlinear interfacial slip and shear stress along the bond. In this paper, full-slip-range analytical solutions are presented for the bilinear τ-δ rule with allowance for residual friction. The procedure is capable of modelling the entire debonding process over both long and short bonded lengths. This is an extension of previous works which are either inapplicable to all bonded lengths or do not allow for residual strength. Applicability of the formulation can range from externally-bonded or near-surface-mounted FRP plates, to embedded bars or bolts in brittle substrates such as concrete, rock or masonry. The versatility and low computational effort required to apply the developed formulation makes it ideal for both directly predicting the\ P-Δ relationship from known τ-δ parameters, or conversely for extracting a τ-δ relationship from a reference\ P-Δ curve using inverse calibration. While it is not the purpose of this paper to propose a bond model for any specific type of system, a framework is proposed for doing so. Significantly this framework addresses the difficulty in identifying a unique solution of local properties from experimental data, and highlights that the bonded length has an important influence on the reliability of extracted results.

}, doi = {10.1016/j.ijsolstr.2017.11.024}, url = {https://www.sciencedirect.com/science/article/pii/S0020768317305279}, author = {Jaroslav Vaculik and Sturm, Alexander B. and Phillip Visintin and Michael Griffith} } @article {bnh-2695, title = {Fundamental Mechanics Governing FRP-Retrofitted RC Beams with Anchored and Prestressed FRP Plates}, journal = {Journal of Composites for Construction}, volume = {20}, year = {2016}, month = {04/2016}, type = {Refereed}, abstract = {

It is often found that a major limitation to retrofitting RC beams by adhesive bonding fiber-reinforced polymer (FRP) plates is premature debonding, which restricts the FRP strains to well below that at fracture. Tests have shown that the FRP peak strains can be increased by anchoring the plate ends of adhesively bonded plates and also by prestressing the anchored plates before adhesive bonding, both of which make the system much more efficient. In this paper, a mechanics-based numerical approach is developed that quantifies the stiffness, strength, and ductility of FRP retrofitted RC beams, in which the FRP plates are anchored, prestressed, and adhesively bonded. The approach can cope with any degree of anchorage and prestress and whether adhesively bonded or not. The approach is generic as it can be applied to any type of RC beam, anchor, and FRP plate and any distribution of load. Furthermore, it allows for discrete flexural cracks and for the formation of softening hinges should these occur. Worked examples are given as a possible design approach. This paper provides a design tool for engineers to develop and quantify their own FRP retrofitting systems for beams with anchored plates.

}, doi = {10.1061/(ASCE)CC.1943-5614.0000710}, url = {http://ascelibrary.org/doi/abs/10.1061/(ASCE)CC.1943-5614.0000710}, author = {D. J. Oehlers and Phillip Visintin and Wade Lucas} }