Jason Ingham

Performance of Unreinforced Masonry Buildings during the 2010 Darfield (Christchurch, NZ) Earthquake

Abstract The 2010 Darfield earthquake caused extensive damage to a number of unreinforced masonry buildings. While this damage to important heritage buildings was the largest natural disaster to occur in New Zealand since the 1931 Hawke’s Bay earthquake, the damage was consistent with projections for the scale of this earthquake, and indeed even greater damage might have been expected. In general, the nature of damage was consistent with observations previously made on the seismic performance of unreinforced masonry buildings in large earthquakes, with aspects such as toppled chimneys and parapets, failure of gables and poorly secured face-loaded walls, and in-plane damage to masonry frames all being extensively documented. This report on the performance of the unreinforced masonry buildings in the 2010 Darfield earthquake provides details on typical building characteristics, a review of damage statistics obtained by interrogating the building assessment database that was compiled in association with post-earthquake building inspections, and a review of the characteristic failure modes that were observed. It was observed that structures that had been seismically retrofitted appeared to perform well, with further study now required to better document the successful performance of these retrofit solutions.

The demise of the URM building stock in Christchurch during the 2010-2011 Canterbury earthquake sequence

The progressive damage and subsequent demolition of unreinforced masonry (URM) buildings arising from the Canterbury earthquake sequence is reported. A dataset was compiled of all URM buildings located within the Christchurch CBD, including information on location, building characteristics, and damage levels after each major earthquake in this sequence. A general description of the overall damage and the hazard to both building occupants and to nearby pedestrians due to debris falling from URM buildings is presented with several case study buildings used to describe the accumulation of damage over the earthquake sequence. The benefit of seismic improvement techniques that had been installed to URM buildings is shown by the reduced damage ratios reported for increased levels of retrofit. Demolition statistics for URM buildings in the Christchurch CBD are also reported and discussed.

Diagonal Compression Testing of FRP-Retrofitted Unreinforced Clay Brick Masonry Wallettes

To address concerns regarding the seismic vulnerability of New Zealand unreinforced masonry (URM) buildings, a research program was undertaken to investigate the effectiveness of fiber-reinforced polymer (FRP) systems as a seismic retrofit intervention for in-plane loaded URM walls that are prone to fail in a shear mode during earthquakes. Seventeen URM wallettes were retrofitted with either externally bonded (EB) glass FRP fabrics, EB pultruded carbon FRP (CFRP) plates, or near-surface mounted pultruded CFRP rectangular bars. The wallettes were tested by the application of a diagonal compressive force, and data were recorded for applied force and corresponding wall drift. Results were compared with five nominally identical unretrofitted wallettes. It was determined that the FRP systems substantially increased the shear strength of the wallettes. Significant increases in the pseudoductility and the toughness were also obtained, which are all considered to be important goals of any seismic retrofit interve...

Out-of-Plane Behavior of One-Way Spanning Unreinforced Masonry Walls

An analytical model is developed to describe the out-of-plane response of one-way spanning unreinforced masonry (URM) walls by investigating the effects of various parameters. Horizontal crack height, masonry compressive strength, and diaphragm support stiffness properties are assumed as variables, and sensitivity analyses are performed to study the influence of these parameters on the cracked wall characteristic behavior. The parametric studies show that crack height significantly influences wall stability by affecting both the instability displacement and the wall lateral resistance. The reduction in cracked wall lateral resistance and in the instability displacement caused by finite masonry compressive strength is shown to be significantly amplified by the applied overburden. A study using the typical configuration of flexible diaphragms and URM walls indicates that the wall top support flexibility does not significantly influence cracked wall out-of-plane response. An existing simplified wall behavioral model is improved, and a procedure is proposed for calculation of the wall out-of-plane response envelope.

Compressive, Flexural Bond, and Shear Bond Strengths of In Situ New Zealand Unreinforced Clay Brick Masonry Constructed Using Lime Mortar between the 1880s and 1940s

AbstractThe importance of sufficient masonry mortar joint-bond strength when a structure is subjected to in-plane and out-of-plane loads has been emphasized by several researchers. However, masonry unit/mortar bond strength is difficult to predict, and performing mechanical tests on existing masonry buildings to determine masonry flexural bond and shear bond strengths is generally not practical, such that predictive expressions relating the masonry flexural bond and shear bond strengths to other masonry properties are desirable. Although relationships between brick/mortar bond and compressive strength have been investigated previously by researchers located in many different parts of the world, most of these studies were laboratory-based and did not include testing of existing masonry buildings within their scope. The writers aimed to characterize the material properties of New Zealand unreinforced clay brick masonry (URM) buildings that were generally built between 1880 and 1930, with in situ testing and...

Uniaxial Compressive Strength and Stiffness of Field-Extracted and Laboratory-Constructed Masonry Prisms

AbstractMasonry material characteristics such as compression stress-strain behavior and the relationships between brick, mortar, and masonry compressive strengths are required for the detailed analysis and assessment of masonry structures. These properties have been investigated previously, but most past studies were laboratory based and did not include within their scope the testing of existing masonry buildings. This study aimed to characterize the compressive strength and the compression stress-strain relationship of vintage clay brick masonry used in New Zealand unreinforced masonry (URM)-bearing wall buildings that were generally constructed between 1880 and 1940. Testing was performed on 45 masonry prisms that were extracted from eight New Zealand historic URM buildings and on 75 masonry prisms that were constructed in the laboratory using 14 different brick/mortar combinations. It was found that the laboratory-constructed sample test results adequately replicated those from the field-extracted samp...

Using Recycled Concrete Aggregates in New Zealand Ready-Mix Concrete Production

Motivations for adopting recycled concrete as an aggregate source include the preservation of natural resources, effective utilization of a growing waste stream, and financial and energy savings. Although current New Zealand practices include some use of crushed concrete in road construction, use of recycled concrete aggregate (RCA) in low specification concrete is currently infrequent and the use of recycled concrete as an aggregate source in structural concrete applications is rare. To make such recycling feasible, the properties of RCA must be related to the properties of new concrete that utilizes the recycled aggregates. In response to this need, a study was undertaken to investigate the feasibility of using RCA as a viable alternative to natural aggregate (NA) in the production of concrete manufactured in a conventional New Zealand ready mix concrete plant. Aggregate properties and hardened and fresh concrete properties of RCA concrete were studied and compared with the associated properties derived from NA concrete. Results indicated that RCA is a viable alternative to NA in the production of concrete. Furthermore, it was confirmed that the properties of RCA dictate the hardened properties of the reconstituted concrete and that RCA from certain strength placements limited the resulting possible strengths of concrete produced from it.

Statistical Assessment of Damage to Churches Affected by the 2010–2011 Canterbury (New Zealand) Earthquake Sequence

The Canterbury Region of New Zealand experienced an extensive earthquake sequence during 2010–2011, with two particularly severe events being on September 4, 2010 and February 22, 2011. The present work entails a statistical analysis of the data collected for 112 churches in the affected region, including in situ damage observed by the authors and the structural assessment classification assigned by local authorities. The seismic performance of these churches is discussed and compared with both the structural classifications used in Italy, where a specific survey form for churches is used, and with the building damage classifications assigned by the local authorities.

Seismic Zonation and Default Suite of Ground-Motion Records for Time-History Analysis in the North Island of New Zealand

A seismic zonation to be used in the selection of ground-motion records for time-history analysis of buildings in the North Island of New Zealand is presented. Both deaggregations of the probabilistic seismic hazard model and the seismological characteristics of the expected ground motions at different locations were considered in order to define the zonation. A profile of the records expected to apply within each zone according to the identified hazard scenarios is presented and suites of records are proposed for each zone, based on region-wide criteria, to be used in time-history analysis in the absence of site specific studies. A solution for structures with fundamental periods of between 0.4 and 2.0 seconds is proposed, considering a 500-year return period and two common site classes (C and D, according to the New Zealand Loadings Standard).

In-Plane Orthotropic Behavior of Timber Floor Diaphragms in Unreinforced Masonry Buildings

AbstractA full-scale experimental program consisting of testing four as-built diaphragms and four retrofitted diaphragms in both principal loading directions is presented. As-built configurations were typical of those found in historic unreinforced masonry buildings in North America and Australasia, whereas retrofitted diaphragms consisted of plywood panel overlays with stapled sheet metal blocking systems (SMBS). Test results were characterized using bilinear representations to establish recognizable performance parameters such as shear strength, shear stiffness, and ductility capacity, which were then used for comparative analysis. The nonlinear and low stiffness behavior of as-built diaphragms was confirmed in each principal loading direction. The plywood overlay and SMBS dramatically improved as-built diaphragm shear strength and shear stiffness and were shown to perform satisfactorily from a serviceability perspective. The orthotropic nature of as-built diaphragms was proven, with perpendicular-to-jo...