Behaviour of Unreinforced Masonry

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

Implications of importance factor on seismic design from 2000 SAC-FEMA perspective

The seismic design of buildings uses global ductility factor and occupancy importance factor (IF) as two major fixed parameters in defining the safety of the structure. The study of performance variation of the structure with global ductility factor is available but there is hardly any study that provides information regarding the increase in the level of safety achieved by increasing the IF values. Being a building categorical dependent parameter, IF is used by the international seismic design codes for increasing the design loads of the structure. The change in the level of safety achieved through the variation in the value of the IFs for reinforced concrete (RC)–framed buildings will perhaps be an important and useful representation of the stakeholders for the approximate damage cost estimation. This article performs the structural safety assessment against seismic load using a standard structural reliability method with second-order hazard approximation to evaluate the effect of the IF on the level of safety and the cost associated with the building. Results show that an overall reduction of 50%–60% in the damage index of the selected buildings can be achieved by increasing the IF from a value of 1.0–2.0 with a consequent increase in the cost of the building

Variability of mechanical properties of cellular lightweight concrete infill and its effect on seismic safety

Cellular lightweight concrete (CLC) block masonry has gained popularity in the masonry market with the growing demand in the modern construction industry due to its various advantages, including a positive impact on the environment. Subsequently, the detailed characterization of its vital engineering properties should be studied for the development of the mathematical model, analysis, evaluation, and design of structures made of CLC block masonry. The present study investigates the variability in two important strength properties of CLC block masonry and proposes the most appropriate models for their statistical distribution to support probability-based structural analysis and design. This study shows that the assumption of a normal distribution in the absence of an appropriate uncertainty model can result in an inaccurate estimate of the seismic risk of an RC frame building infilled with CLC block masonry. The paper further assesses the seismic safety of a typical RC framed building infilled with CLC block masonry in relation to traditional brick masonry, considering the proposed uncertainty model. Although CLC block masonry results in a higher seismic risk compared with traditional brick masonry, it can be used as an infill material in high seismic areas because it results in a probability of failure within the acceptable limit