Hossein Derakhshan

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.

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.

Influence of Diaphragm Flexibility on Seismic Response of Unreinforced Masonry Buildings

The effects of diaphragm flexibility on the seismic response of low-rise unreinforced masonry buildings are examined using one-way stiffness- and strength-eccentric single-story systems subjected to unidirectional ground excitation. A wide range of diaphragm stiffnesses are considered. Results show that diaphragm flexibility can induce different effects depending on the configuration of the system and the level of diaphragm flexibility. When diaphragm is relatively stiff, amplified displacement demands can be imposed on the flexible side of the structure. When diaphragm is relatively flexible, peak displacements of in-plane loaded walls generally reduce. A diaphragm classification is developed to capture these salient effects.

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.

Simulation of Shake Table Tests on Out-of-Plane Masonry Buildings. Part (I): Displacement-based Approach Using Simple Failure Mechanisms

ABSTRACT A displacement-based (DB) assessment procedure was used to predict the results of shake table testing of two unreinforced masonry buildings, one made of clay bricks and the other of stone masonry. The simple buildings were subject to an acceleration history, with the maximum acceleration incrementally increased until a collapse mechanism formed. Using the test data, the accuracy and limitations of a displacement-based procedure to predict the maximum building displacements are studied. In particular, the displacement demand was calculated using the displacement response spectrum corresponding to the actual shake table earthquake motion that caused wall collapse (or near collapse). This approach was found to give displacements in reasonable agreement with the wall’s displacement capacity.

Laboratory testing of strengthened cavity unreinforced masonry walls

AbstractAn experimental campaign consisting of nine pressure-controlled quasi-static airbag tests on unreinforced masonry (URM) walls and accompanying material testing was completed to investigate ...