Dmytro Dizhur

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.

Field Testing of Flexible Timber Diaphragms in an Existing Vintage URM Building

AbstractIt is well known that the in-plane behavior of flexible timber diaphragms has a large influence on the global earthquake response of unreinforced masonry (URM) buildings. The type and the activation of out-of-plane URM wall failure mechanisms are strictly related to diaphragm stiffness, which is a property that also governs the effectiveness of the diaphragm to distribute earthquake-induced loads between lateral load resisting wall elements. However, there is a lack of reported experimental campaigns pertaining to these issues, and in particular, few experimental data have been published on the in situ behavior of existing vintage flexible timber floor diaphragms such as single straight sheathed diaphragms that are typically encountered in New Zealand URM buildings. To address this paucity of available in situ test data, an experimental campaign was executed to investigate the as-built cyclic and dynamic behavior of full-scale vintage flexible timber floor diaphragms with the outcomes being presen...

In-Plane Shear Improvement of Unreinforced Masonry Wall Panels Using NSM CFRP Strips

AbstractThe large number of earthquake-prone vintage unreinforced masonry (URM) buildings in many seismically active parts of the world results in a need for minimally invasive and cost-effective strengthening techniques to enhance the poor earthquake performance of such buildings. The objective of the research reported here was to investigate the applicability of using near-surface-mounted (NSM) carbon fiber–reinforced polymer (CFRP) strips as a retrofitting technique for improving the in-plane shear strength and displacement capacity of multi-leaf URM walls constructed using solid clay brick masonry. The use of this technique for repairing earthquake damaged URM walls was also investigated. Ten multileaf wall panels measuring approximately 1,200×1,200  mm were constructed using recycled vintage solid clay bricks and retrofitted using NSM CFRP strips with varying reinforcement ratios. These panels were loaded in diagonal compression, and the results were compared with those obtained from testing of nomin...

Observed performance of residential masonry veneer construction in the 2010/2011 Canterbury earthquake sequence

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.

In-situ testing of a low intervention NSM seismic strengthening technique for historic URM buildings

Due to the poor seismic performance of unreinforced masonry (URM) buildings there is a need for a cost effective minimally-invasive seismic retrofit technique. Most research considering out-of-plane seismic retrofit of URM walls has been conducted using laboratory-based studies with well defined but artificial boundary conditions, using constituent construction materials that attempt to simulate the material properties of masonry found in historic URM buildings. Thus, in-situ testing of retrofitted URM walls is required to provide data with which to validate the accuracy of laboratory-based studies. An experimental campaign was executed to investigate the performance of a near-surface mounted (NSM) carbon fibre reinforced polymer (CFRP) seismic retrofit solution. This campaign involved testing of five masonry walls loaded out-of-plane in four different buildings located in New Zealand. Testing confirmed that the CFRP retrofit technique is an excellent minimally-invasive and cost effective option for seismic strengthening of URM buildings. Details of the history of the buildings, and the methods used to undertake the field tests are reported, and experimental results are presented.

Post-Earthquake Reconnaissance of Unreinforced and Retrofitted Masonry Parapets

Unrestrained unreinforced clay brick masonry (URM) parapets are freestanding wall elements found atop a large number of vintage URM buildings. Parapets are considered to be one of the most vulnerable nonstructural components that are prone to out-of-plane collapse when subjected to earthquake induced shaking. Using data collected during the earthquake reconnaissance efforts, 959 URM parapets were identify to be in existence in the Christchurch (New Zealand) area prior to 2010, with 60% (580) of them having collapsed during the 2010/2011 Canterbury earthquake sequence. Construction details and observed performance of both as-built and retrofitted parapets were documented. The reported study provides an inventory of observed parapet failure modes and a critical review of commonly encountered parapet retrofits and their respective seismic performance.

Performance of Posttensioned Seismic Retrofit of Two Stone Masonry Buildings during the Canterbury Earthquakes

AbstractSeismic retrofitting of unreinforced masonry buildings using posttensioning has been the topic of many recent experimental research projects. However, the performance of such retrofit designs in actual design-level earthquakes has previously been poorly documented. In 1984, two stone masonry buildings within The Arts Centre of Christchurch received posttensioned seismic retrofits, which were subsequently subjected to design level seismic loads during the 2010/2011 Canterbury earthquake sequence. These 26-year-old retrofits were part of a global scheme to strengthen and secure the historic building complex and were subject to considerable budgetary constraints. Given the limited resources available at the time of construction and the current degraded state of the steel posttension tendons, the posttensioned retrofits performed well in preventing major damage to the overall structure of the two buildings in the Canterbury earthquakes. When compared to other similar unretrofitted structures within Th...

In-Plane Assessment of Existing Timber Diaphragms in URM Buildings via Quasi-Static and Dynamic In Situ Tests

Mechanical and dynamic in-plane properties of timber diaphragms are known to be key parameters when determining both the local and global seismic response of unreinforced masonry (URM) buildings. However, few data pertaining to experimental campaigns on this issue are available in the literature, especially regarding existing floors. In this work, the outcomes of a field testing campaign on full-scale old timber diaphragms are presented. Two specimens, whose size was 5.6 x 9.6 m2 and 4.7 x 9.6 m2 were obtained from a 17 x 9.6 m2 floor and were subjected to a series of both cyclic and snap back tests in the direction orthogonal to the joists. Since the original anchoring system was deficient, new epoxy-grouted anchors were installed before starting the testing procedure. So as to reproduce the inertial load distribution, an ad hoc loading system was developed by means of wire ropes and steel pulleys. After testing the diaphragms in the as-built condition, the effect of different refurbishment techniques was also investigated. From the results, it seems that even simple and cost-effective solutions such as the re-nailing of the flooring are sufficient to achieve a significant increase in the equivalent shear stiffness.

Earthquake Performance of Two Vintage URM Buildings Retrofitted Using Surface Bonded GFRP: Case Study

AbstractAs part of a seismic retrofit scheme, surface bonded glass fiber-reinforced polymer (GFRP) fabric was applied to two unreinforced masonry (URM) buildings located in Christchurch, New Zealand. The unreinforced stone masonry of Christchurch Girls’ High School (GHS) and the unreinforced clay brick masonry Shirley Community Centre were retrofitted using surface bonded GFRP in 2007 and 2009, respectively. Much of the knowledge on the seismic performance of GFRP retrofitted URM was previously assimilated from laboratory-based experimental studies with controlled environments and loading schemes. The 2010/2011 Canterbury earthquake sequence provided a rare opportunity to evaluate the GFRP retrofit applied to two vintage URM buildings and to document its performance when subjected to actual design-level earthquake-induced shaking. Both GFRP retrofits were found to be successful in preserving architectural features within the buildings as well as maintaining the structural integrity of the URM walls. Succe...

Lateral Performance of As-Built and Retrofitted Timber Diaphragm Fastener Connections

AbstractThe in-plane stiffness of timber diaphragms commonly found in vintage unreinforced masonry (URM) buildings is largely determined by the rigidity of the fastener connections. Currently in th...