Masonry structures occupy a significant share of the current building stock due to widespread material availability and cost-effectiveness. Regions with high seismicity, like the Himalayas, have typically developed local seismic culture over the centuries. This has led to improved construction techniques providing an enhanced seismic performance, as evident from post-earthquake surveys. Bhatar is a building typology found in the Himalayas, featuring embedded horizontal timber bands in masonry walls, enhancing the box-behaviour and in turn avoiding their premature out-of-plane failure.
This work aims to quantify the improvement of the out-of-plane performance of masonry walls due to the presence of horizontal timber bands. Numerical analyses were conducted in DIANA FEA software starting from the few experimental results available in literature on this typology. These were used to calibrate the properties of masonry, which was represented as a homogeneous isotropic continuum, with nonlinearities considered by means of a total strain rotating crack model.
Firstly, a U-shaped masonry wall having the same geometry and boundary conditions as the experimental tests was simulated using 3D modelling approach. Non-linear static analyses were performed exploring two different strategies, with minor variations in analysis parameters. Very good agreement was obtained with the results from literature for both strategies with one able to simulate local cracks better, while the other was able to simulate global failure mechanism better. The calibrated numerical model was then employed to conduct sensitivity analyses for precompression load and aspect ratio.
Further refinements to the calibrated model were done. The influence of the frictional behaviour between timber and masonry was explored through discretely modelled interface elements. The timber-to-timber connection was modelled as a hinge. The improvement in the behaviour of the wall due to timber bands connected throughout the frontal wall was also evaluated.
Finally, the calibrated numerical model was employed for the pushover analysis of a full-scale structure representing the geometry of a typical Bhatar house. The results from the numerical analysis were used for seismic assessment using Capacity Spectrum Method. The assessment demonstrated the capability of a Bhatar structure to resist ground acceleration specified for the highest earthquake category defined by Indian Standard Criteria for Earthquake Resistant Design of Structures. Contrarily, an unreinforced masonry structure did not possess the required ductility to resist such an earthquake.
Inclusion of timber bands at corners of a U-shaped masonry wall resulted in an increase of lateral resistance by 40%. Walls with timber bands connected throughout the front wall presented a further increase of 35% in the force capacity. The corresponding improvement in force capacity for a full-scale Bhatar house was even more remarkable at 109% compared to an identical unreinforced house. There was also a noticeable increase in the ductility.
This work constitutes a further step towards a better understanding of the behaviour of Himalayan masonry structures under earthquakes, promoting better seismic risk reduction strategies. This improved understanding into the role of timber in greater seismic resilience of masonry structures also informs better maintenance, conservation and preservation of heritage and historical masonry structures in the Himalayas.

A large share of the buildings today is still masonry buildings, both reinforced and unreinforced. Post-earthquake reconnaissance studies have shown a remarkable difference between the performance of reinforced and unreinforced masonry buildings. While the unreinforced masonry buildings tend to suffer severe damage, even collapse, resulting in loss of innumerable and invaluable life; reinforced masonry buildings have often been reported to perform remarkably well under seismic events. Sometimes, this performance has exceeded performance of engineered buildings as well.

Himalayas are a highly seismic region in South Asia with multiple major earthquakes recorded across the past two centuries. The remoteness of the region and abundant availability of local materials along with frequent earthquakes has resulted in the development of a seismic culture of earthquake-resistant, timber-reinforced masonry buildings. Though these buildings have shown superior performance under seismic actions, little scientific research has been done to understand and analyse the reason behind this superior performance.

Across the different regions of Himalayas, timber has been used in different structural configurations to increase the seismic resistance of the masonry structures. These traditional building systems remain popular in the Himalayan region for their cheap and easy availability locally. This additional graduation project is a step towards understanding the behaviour of these masonry structures, and the role of timber in preventing catastrophic failure in the former.

In this study, different building typologies in the Himalayas that use timber as a structural element are identified and described. Failure mechanisms of masonry structures are widely studied and a brief overview is presented. In-plane, out-of-plane, combined in-plane and out-of-plane and local failure mechanisms of unreinforced masonry are discussed in detail. Furthermore, a literature review of post-earthquake reconnaissance surveys is conducted to understand different mechanisms through which masonry structures fail.

A review of state-of-the-art on experimental, analytical and numerical studies conducted on resistance of some of the building typologies of Himalayan region (for example, Bhatar, Dhajji Dewari, Ikra, Kath Kuni) is done in this study to understand work done previously. Finally, an analytical analysis is conducted on single room, one-storeyed Bhatar building to investigate the response of an in-plane wall to a lateral load exerted by earthquake excitation.