Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.13/935794
- Title
- Earthquake protection of masonry shear walls using fibre reinforced polymer strengthening
- Author/Creator
-
Chaminda Konthesingha, Konthesingha Muhandiramlage
- Institution
- University of Newcastle. Faculty of Engineering & Built Environment, School of Engineering
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Unreinforced masonry (URM) buildings are highly vulnerable to damage during earthquakes, due to their high mass, limited ductility and low tensile strength. However, being economical, durable, easy to procure and good for thermal and sound insulation ensures that URM is widely used both for low-rise structural walls and for infill to framed structures. In addition to that, many of the existing historically and culturally important buildings have been identified as URM constructions. Therefore, strengthening of URM buildings to resist earthquake damage has a remarkable importance. URM shear wall strengthening with near surface mounted (NSM) fibre reinforced polymer (FRP) strips is a relatively new and effective seismic retrofitting technique to improve their earthquake resistance. This technique involves inserting thin FRP strips into grooves cut into the surface of the wall. The aesthetic impact to the structure is minimal due to this strengthening technique compared with attaching FRP reinforcement to the surface of the wall (External Bonding (EB) technique). The other advantages of NSM FRP are the ability to develop higher strains in the FRP before debonding compared to EB techniques, and protection from vandalism, to some extent from fire and other environmental influences. In this research study an extensive experimental study along with numerical analyses were carried out to investigate the cyclic in-plane shear behaviour of unreinforced masonry (URM) walls retrofitted/strengthened with near surface mounted (NSM) fibre reinforced polymer (FRP) strips. Carbon FRP (CFRP) strips were used in this technique and were designed to enhance the performance of URM walls which fail by diagonal cracking or bed joint sliding within the height of the wall. The bond-slip behaviour between NSM FRP strips and clay brick masonry was investigated using six experimental pull tests under cyclic loading. The results including bond strengths, critical bond length and the local bond-slip behaviour were determined and were compared with a similar monotonically loaded pull test results. The bond-slip curves for monotonic and cyclic loading cases were approximately similar. Two major experimental investigations were carried out in this project to investigate the effectiveness of retrofitting/strengthening of URM walls panels with NSM CFRP strips using previously damaged and newly constructed undamaged wall panels. The effectiveness of NSM CFRP strip retrofitting applied to damaged URM walls was investigated using sixteen previously damaged wall panels with two different damage levels (lightly and highly) subjected to vertical pre-compression combined with increasing reversing cycles of in-plane lateral displacement. The damaged walls were partially repaired, retrofitted with NSM FRP strips and retested. The study assessed the effect on strength, displacement capacity, energy dissipation and ductility achieved by FRP retrofitting compared to the undamaged URM panels under different pre-compression levels. The retrofitted walls displayed higher displacement capacities compared with URM walls. The ultimate loads were not enhanced due to retrofitting under higher pre-compression levels. However the presence of the reinforcement restored the ultimate loads to those observed for the original undamaged URM state. The improvements in the behaviour of the URM walls due to retrofitting were generally similar irrespective of the amount of pre-existing damage in the URM walls. A new test setup representing realistic boundary conditions to simulate the earthquake behaviour of shear walls in actual buildings was designed and built for the series of experiments with newly constructed wall panels. It was designed to impose zero in-plane rotation (fixed-fixed) boundary conditions at the top and bottom of the masonry wall specimens. A representative finite element (FE) model was used to obtain the actual dimensions of the test setup. The design parameters for the experimental series, including test specimen dimensions and pre-compression loads to achieve diagonal cracking failure modes, were obtained using the same FE model. A total of twenty three wall panels constructed with two wall aspect ratios (height : length = 1 and 0.5) were tested. They were strengthened with NSM CFRP strips in six different reinforcement arrangements including vertical, horizontal and a combination of both. Four panels were tested under monotonically increasing in-plane lateral displacement and the others under increasing reversing cycles of in-plane lateral displacement combined with a vertical pre-compression. The expected zero in-plane rotation (fixed-fixed) boundary conditions were achieved from the new setup with classic diagonal failure occurring through the test walls. The displacement capacity, energy dissipation and ductility of the wall panels were enhanced due to the NSM FRP strengthening. The maximum load of the strengthened walls was increased compared to URM when the strengthening contained vertical FRP strips. The reinforcing scheme which used a combination of vertical and horizontal FRP strips performed the best. A finite element model was developed to validate the experimental results. The micro-modelling approach was used in this masonry model. The FRP strips were attached to the masonry model using the bond-slip relationship established from the experimental pull tests. The key behaviours of the experimental test results could be reproduced by the developed FE model.
- Relation
- University of Newcastle Research Higher Degree Thesis
- Date
- 2012
- Keyword(s)
-
masonry;
cyclic;
shear;
near surface mounted (NSM);
fibre reinforced polymer (FRP)
- Resource Type
- thesis
- Rights
- Copyright 2012 Konthesingha Muhandiramlage Chaminda Konthesingha
- Identifier
- http://hdl.handle.net/1959.13/935794
- Language
- eng
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