Research
Research Papers
Methodology for the Assessment of Face-Loaded Unreinforced Masonry Walls under Seismic Loading
E L Blaikie, Opus International Consultants Limited
In the early 1980s, US researchers (ABK, 1982) subjected full-scale specimens representing a face-loaded wall element spanning between two adjacent floor diaphragms, to earthquake motions. They found that a single horizontal crack tended to form near mid-height of the test specimens and another crack formed at the test bed floor, and that the walls were able to sustain large displacements, comparable with the wall thickness. This ability to withstand large displacements without collapse resulted in the walls having a significant post cracking seismic resistance. The term "dynamic stability" was used to distinguish this type of behaviour from the behaviour that might have been expected from static force calculations.
Subsequently this concept was used to develop the current New Zealand Society of Earthquake Engineering (NZSEE) guidelines for the assessment of face-loaded walls. These guidelines are based on the equal energy method and the initial elastic stiffness of the wall (Priestly, 1985). However, in this study the current NZSEE guidelines were shown to be an unreliable, and often very unconservative, method of predicting the seismic resistance of URM walls.
In this study a more reliable method of assessing the seismic behaviour of face-loaded URM walls, originally proposed in a previous EQC Research Foundation funded project (Blaikie, Spurr, 1992), has been developed to a stage that is suitable for design office use. A computer model was used to test and refine the methodology, and full size walls sample were laboratory tested to calibrate the computer model. The influence of "near fault" earthquake motions on the wall response was included as this may become an important consideration for locations near to active faults such as Wellington.