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Publication: Out-of-plane Proof Testing of Masonry Infill Walls (2018)
Preparation and upload by:
Filip Anic, Faculty of Civil Engineering and Architecture, University of Osijek
List of test setups
Publication abstract (click to enlarge):
Publication abstract (click to shrink):
Proof testing of multiple fired-clay-brick unreinforced masonry (URM) infill walls set within reinforced concrete frames was undertaken using airbags to simulate out-of-plane (OOP) loading. The proof testing was conducted to provide engineers in various research and practitioner roles with verified wall behaviour for the purpose of seismic assessment of buildings. A total of 19 tests were perfo
Proof testing of multiple fired-clay-brick unreinforced masonry (URM) infill walls set within reinforced concrete frames was undertaken using airbags to simulate out-of-plane (OOP) loading. The proof testing was conducted to provide engineers in various research and practitioner roles with verified wall behaviour for the purpose of seismic assessment of buildings. A total of 19 tests were performed in six buildings. It was observed that two-way OOP flexure can substantially improve the OOP load-carrying capacity of tested infill walls compared to one-way vertical OOP flexure and that boundary restraints and presumed "arching" action from the building frame can significantly increase the OOP capacity of URM walls. In addition, the effects of simulated in-plane damage on the OOP capacity of a URM infill wall were investigated, and it was found that the damage reduced the OOP strength by up to 40%. On-site proof testing is demonstrated as a simple and cost-effective way to establish actual wall lateral capacities in cases where boundary conditions cannot be clearly established and existing analytical models predict low lateral capacities.
The objectives of the OOP airbag proof testing reported herein were to provide a basis of knowledge regarding:
- The execution of and benefits to engineers and building owners of proof testing masonry infill/partition walls as part of a larger detailed seismic assessment programme;
- The OOP behaviour of masonry infill/partition walls in one-way vertical flexure as well as two-way flexure and the effects of boundary restraint conditions on the OOP behaviour of masonry infill/partition walls;
- Comparisons of experimentally attained capacities to anticipated seismic demands in regions of moderate to high seismicity;
- The effects of in-plane shear damage on OOP initial stiffness and ultimate strength and drift capacities of masonry infill/partition walls.
AIM AND SCOPE
Experimental results attained from proof tests may lead to more efficient retrofit design of building components and subsequent reductions in cost, time, energy, solid waste production, and other resources associated with deconstruction, partial reconstruction/replacement, or retrofit solutions that are relatively costly and invasive (e.g., steel-framed strongbacks).
DESIGN AND CONSTRUCTION OF THE TEST SPECIMENS:
The experimental proof testing programme consisted of 19 tests performed on 16 walls. A summary of geometric details and boundary conditions of the test wall specimens is given in table below. Note that walls with test identifications (IDs) ending with a letter (e.g., A, B, or C) were tested multiple times with different levels of simulated damage or changes in boundary conditions.
Most of the test walls in the WR building (WR1, WR2B, WR3, WR4, WR6) were tested unrestrained on the side (vertical) edges utilising either saw cuts made prior to testing or tall door openings to conservatively simulate one-way vertical flexure for purposes of analysis elsewhere in the building. Plaster was retained on both sides of the test walls in the WH and WO buildings and on various other walls in this testing programme but otherwise ignored in analysis (based on the assumption that the plaster's marginal contribution to OOP strength would be approximately equally offset by its marginal self-weight). Hence, for purposes of estimating the self-weight of the test walls, only the brick thicknesses listed in Table above were considered, as all test walls in this programme consisted of a single brick wythe.
Summary of measured and estimated masonry material characteristics (all strength values in MPa unless noted otherwise):
A total of 19 URM infill walls located in six buildings in New Zealand were tested for OOP behaviour. The testing procedures, measured material strength, recorded lateral wall behaviour, and observed wall damage are presented and discussed. The following significant results can be drawn:
- The testing showed that the walls are capable of resisting seismic demands in regions with moderate to high seismicity (e.g., Wellington, New Zealand) despite some simplified predictive methods suggesting lower strengths for some walls. Considered predictive models are applied in greater detail in a companion article (Walsh et al. 2018);
- Restraint at the walls' vertical edges (horizontal boundaries), resulting in two-way OOP flexure as compared to one-way vertical OOP flexure, can substantially improve the OOP load-carrying capacity of tested infill walls;
- Topside fixed restraint and presumed 'arching' action from the building frame can greatly increase the OOP capacity of URM walls;
- In-plane damage was found to reduce the OOP capacity of URM infill walls by up to 40%;
- Material strength related to brick compression, mortar compression, masonry bed joint shear, and cavity tie pull-out, as well as other properties, were determined for a range of buildings in this typology, providing evidence for engineering consultants on the merits of conducting site investigations to make more accurate assumptions when performing future building analyses;
RECOMMENDATIONS FOR FUTURE RESEARCH
Further research in this area should involve advanced data processing to define more accurately the effects of different boundary conditions on URM infill wall performance. Further testing will preferably involve an examination of retrofit techniques. Some walls, for example, may be retrofitted with vertical near-surface-mounted carbon fibre strips, which is a cost-effective and minimally-invasive seismic retrofit technique for some scenarios where cavity ties are not appropriate, particularly for walls that are propped at the top.
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The creation of these resources has been funded by the ERASMUS+ grant program of the European Union under grant no. 2016-1-DE01-KA203-002905. Neither the European Commission nor the project‘s national funding agency DAAD are responsible for the content or liable for any losses or damage resulting of the use of these resources.