Behaviour of Unreinforced Masonry

Abstract

Unreinforced Masonry (URM) structures can simply defined as structure without any reinforcement. URM is a common material for building construction but is known for its seismic vulnerability due to its heavy weight, high stiffness and negligible strength. URM structures are commonly used in developing countries like India for low rise building up to two story in rural area. Damage to those structures results in loss of life and cultural heritage.

The main objective of the present thesis is to know the lateral behaviour of URM structure, and understand the concept of equivalent frame modelling (EFM). In the present work inverted triangular and uniform distribution lateral loads are used to study the nonlinear behaviour of masonry. There are several methods to carry out Static Pushover (SPO) analysis of URM, but Equivalent Frame Modelling is the simple one. EFM is being used for modeling the non-linear behavior of masonry by providing flexural and shear hinges in the model. EFM is nothing but assuming wall with opening as combination of horizontal and vertical members. The plastic hinges were used in SPO analyses since they allow the user to accurately follow the structural performance beyond the elastic limit at each step of the incremental analysis. Perfectly rigid plastic hinges were assumed as recommended in literature reviews and modelling is done in SAP2000 software.

In order to know which property of masonry is sensitive to lateral behaviour, sensitivity analysis is carried out. Sensitivity analysis was carried out by varying all parameters with 5%, mean and 95% value. Tornado diagram is used to represent the results of sensitivity. It was found that except compressive strength all other parameters are affecting the lateral behaviour.

The fragility can be regarded as one of the most important tool for performance based design of structures. The fragility curves are developed by using HAZUS methodology. Different damage levels such as slight, moderate, extensive and complete damage state are considered to represent variability in seismic performance of building and finally fragility curves were obtained for three damage state quality levels of masonry based on spectral displacements and damage probability. It is observed that the building have more probability for moderate damage. Different brick masonries are considered, to compare the results of the pushover.