The connections between walls of unreinforced masonry (URM) buildings and flexible timber diaphragms are critical building components that must perform adequately before desirable earthquake response of URM buildings may be achieved. Field observations made during the initial reconnaissance and the subsequent damage surveys of clay brick URM buildings following the 2010/2011 Canterbury, New Zealand earthquakes revealed numerous cases where anchor connections joining masonry walls or parapets with roof or floor diaphragms appeared to have failed prematurely. These observations were more frequent for adhesive anchor connections than for through-bolt connections (i.e. anchorages having plates on the exterior façade of the masonry walls). Subsequently, an in-field test program was undertaken in an attempt to evaluate the performance of adhesive anchor connections between unreinforced clay brick URM walls and roof or floor diaphragms. The study consisted of a total of almost 400 anchor tests conducted in eleven existing URM buildings located in Christchurch, Whanganui and Auckland. Specific objectives of the study included the identification of failure modes of adhesive anchors in existing URM walls and the influence of the following variables on anchor load-displacement response: adhesive type, strength of the masonry materials (brick and mortar), anchor embedment depth, anchor rod diameter, overburden level, anchor rod type, quality of installation and the use of metal mesh sleeve. In addition, the comparative performance of bent anchors (installed at an angle of minimum 22.5o to the perpendicular projection from the wall surface) and anchors positioned horizontally was investigated. Observations on the performance of wall-to-diaphragm connections in the 2010/2011 Canterbury earthquakes, a snapshot of the performed experimental program and the test results and a preliminary proposed pull-out capacity of adhesive anchors are presented herein.
The connections between walls of unreinforced masonry (URM) buildings and flexible timber diaphragms are critical building components that must perform adequately before desirable earthquake response of URM buildings may be achieved. Field observations made during the initial reconnaissance and the subsequent damage surveys of clay brick URM buildings following the 2010/2011 Canterbury, New Zealand earthquakes revealed numerous cases where anchor connections joining masonry walls or parapets with roof or floor diaphragms appeared to have failed prematurely. These observations were more frequent for adhesive anchor connections than for through-bolt connections (i.e. anchorages having plates on the exterior façade of the masonry walls). Subsequently, an in-field test program was undertaken in an attempt to evaluate the performance of adhesive anchor connections between unreinforced clay brick URM walls and roof or floor diaphragm. The study consisted of a total of almost 400 anchor tests conducted in eleven existing URM buildings located in Christchurch, Whanganui and Auckland. Specific objectives of the study included the identification of failure modes of adhesive anchors in existing URM walls and the influence of the following variables on anchor load-displacement response: adhesive type, strength of the masonry materials (brick and mortar), anchor embedment depth, anchor rod diameter, overburden level, anchor rod type, quality of installation and the use of metal mesh sleeve. In addition, the comparative performance of bent anchors (installed at an angle of minimum 22.5o to the perpendicular projection from the wall surface) and anchors positioned horizontally was investigated. Observations on the performance of wall-to-diaphragm connections in the 2010/2011 Canterbury earthquakes, a snapshot of the performed experimental program and the test results and a preliminary proposed pull-out capacity of adhesive anchors are presented herein. http://www.confer.co.nz/nzsee/ VoR - Version of Record
The connections between walls of unreinforced masonry (URM) buildings and flexible timber diaphragms are critical building components that must perform adequately before desirable earthquake response of URM buildings may be achieved. Field observations made during the initial reconnaissance and the subsequent damage surveys of clay brick URM buildings following the 2010/2011 Canterbury, New Zealand earthquakes revealed numerous cases where anchor connections joining masonry walls or parapets with roof or floor diaphragms appeared to have failed prematurely. These observations were more frequent for the case of adhesive anchor connections than for the case of through-bolt connections (i.e. anchorages having plates on the exterior façade of the masonry walls). Subsequently, an in-field test program was undertaken in an attempt to evaluate the performance of adhesive anchor connections between unreinforced clay brick URM walls and roof or floor diaphragm. The study consisted of a total of almost 400 anchor tests conducted in eleven existing URM buildings located in Christchurch, Whanganui and Auckland. Specific objectives of the study included the identification of failure modes of adhesive anchors in existing URM walls and the influence of the following variables on anchor load-displacement response: adhesive type, strength of the masonry materials (brick and mortar), anchor embedment depth, anchor rod diameter, overburden level, anchor rod type, quality of installation and the use of metal foil sleeve. In addition, the comparative performance of bent anchors (installed at an angle of minimum 22.5o to the perpendicular projection from the wall surface) and anchors positioned horizontally was investigated. Observations on the performance of wall-to-diaphragm connections in the 2010/2011 Canterbury earthquakes and a snapshot of the performed experimental program and the test results are presented herein. http://hdl.handle.net/2292/21050
Following the 2010/2011 Canterbury, New Zealand earthquakes, a detailed door-to-door survey was conducted in the Christchurch region to establish the earthquake performance of lightweight timber-framed residential dwellings with a masonry veneer external cladding system. The post-earthquake survey involved documenting the condition of dwellings in areas that had experienced different levels of earthquake shaking, allowing comparison between the performance of different veneer systems and different shaking intensities. In total, just fewer than 1,100 residential dwellings were inspected throughout the wider Christchurch area. The survey included parameters such as level of veneer damage, type of veneer damage, observed crack widths, and level of repair required. It is concluded that based on observed earthquake performance at the shaking intensities matching or exceeding ultimate limit state loading, the post-1996 veneer fixing details performed satisfactorily and continued use of the detail is recommended without further modification. AM - Accepted Manuscript
During the 2010/2011 Canterbury earthquakes, several reinforced concrete (RC) walls in multi-storey buildings formed a single crack in the plastic hinge region as opposed to distributed cracking. In several cases the crack width that was required to accommodate the inelastic displacement of the building resulted in fracture of the vertical reinforcing steel. This type of failure is characteristic of RC members with low reinforcement contents, where the area of reinforcing steel is insufficient to develop the tension force required to form secondary cracks in the surrounding concrete. The minimum vertical reinforcement in RC walls was increased in NZS 3101:2006 with the equation for the minimum vertical reinforcement in beams also adopted for walls, despite differences in reinforcement arrangement and loading. A series of moment-curvature analyses were conducted for an example RC wall based on the Gallery Apartments building in Christchurch. The analysis results indicated that even when the NZS 3101:2006 minimum vertical reinforcement limit was satisfied for a known concrete strength, the wall was still susceptible to sudden failure unless a significant axial load was applied. Additionally, current equations for minimum reinforcement based on a sectional analysis approach do not adequately address the issues related to crack control and distribution of inelastic deformations in ductile walls.
Unreinforced masonry (URM) is a construction type that was commonly adopted in New Zealand between the 1880s and 1930s. URM construction is evidently vulnerable to high magnitude earthquakes, with the most recent New Zealand example being the 22 February 2011 Mw6.3 Christchurch earthquake. This earthquake caused significant damage to a majority of URM buildings in the Canterbury area and resulted in 185 fatalities. Many URM buildings still exist in various parts of New Zealand today, and due to their likely poor seismic performance, earthquake assessment and retrofit of the remaining URM building stock is necessary as these buildings have significant architectural heritage and occupy a significant proportion of the nation’s building stock. A collaborative research programme between the University of Auckland and Reid Construction Systems was conducted to investigate an economical yet effective solution for retrofitting New Zealand’s existing URM building stock. This solution adopts the shotcrete technique using an Engineered Cementitious Composite (ECC), which is a polyvinyl alcohol fibre reinforced mortar that exhibits strain hardening characteristics. Collaborations have been formed with a number of consulting structural engineers throughout New Zealand to develop innovative and cost effective retrofit solutions for a number of buildings. Two such case studies are presented in this paper. http://www.concrete2013.com.au/technical-program/
As a result of the 4 September 2010 Darfield earthquake and the more damaging 22 February 2011 Christchurch earthquake, considerable damage occurred to a significant number of buildings in Christchurch. The damage that occurred to the Christchurch Roman Catholic Cathedral of the Blessed Sacrament (commonly known as the Christchurch Basilica) as a result of the Canterbury earthquakes is reported, and the observed failure modes are identified. A previous strengthening intervention is outlined and the estimated capacity of the building is discussed. This strengthening was completed in 2004, and addressed the worst aspects of the building's seismic vulnerability. Urgent work was undertaken post-earthquake to secure parts of the building in order to limit damage and prevent collapse of unstable parts of the building. The approach taken for this securing is outlined, and the performance of the building and the previously installed earthquake strengthening intervention is evaluated.A key consideration throughout the project was the interaction between the structural securing requirements that were driven by the requirement to limit damage and mitigate hazards, and the heritage considerations. Lessons learnt from the strengthening that was carried out, the securing work undertaken, and the approach taken in making the building "safe" are discussed. Some conclusions are drawn with respect to the effectiveness of strengthening similar building types, and the approach taken to secure the building under active seismic conditions. AM - Accepted Manuscript
