The Effect of Slenderness Ratio on Seismic Performance of Unreinforced Masonry Walls Pritha Chudal Graduate Studemt Institute of Engineering, Thapathali Campus Kathmandu, Nepal prithachudal@gmail.com Prem Nath Maskey Professor of Civil Engineering Institute of Engineering, Pulchowk Campus Kathmandu, Nepal pnmaskey@live.com Abstract—During Gorkha Earthquake 2015, most of unreinforced masonry buildings were partially or fully collapsed. Unreinforced brick masonry buildings (URBM), have relatively high compressive strength but low tensile strength. Its lateral load carrying capacity is relatively low by which it is highly vulnerable to earthquake. In this paper a brief study of the capacity of URM walls on the basis of slenderness ratio is carried out and a limiting slenderness value is suggested in reference with literature reviews. It is observed that slenderness ratio affects stability of URM walls during an earthquake and hence is an appropriate parameter to address out-of–plane stability. Increment of slenderness ratio showed the decrement of the load carrying capacity of URM walls. The paper also suggests the value of slenderness ratio of URM wall shall be within 9 to 20. Keywords—unreinforced masonry, loading eccentricity, slenderness ratio, out-of-plane I. INTRODUCTION Unreinforced brick masonry (URBM) has been the principal construction material for buildings in Nepal for a long time. Bricks most commonly used in Nepal are of size 230mm × 110mm × 55mm. Unreinforced brick masonry has high compressive strength but is much lower in tensile or shearing strength. Hence, the lateral load resisting capacity of masonry construction is low. In an earthquake, the heavy mass of masonry walls contributes to high earthquake forces. Inertial forces are the product of the mass of an object and the acceleration of its motions; thus, heavier the buildings, higher the forces they are shaken with. Unreinforced masonry buildings perform poorly in earthquake. The walls aligned along the direction of seismic load are subjected to in-plane forces and the walls perpendicular to the loads to out-of-plane forces. The walls perpendicular to the lateral loads have much lesser resistance compared to the walls along the direction. The concrete if present, floor acts as a rigid floor diaphragm in its own plane. Hence the lateral forces acting are distributed to walls in accordance to their stiffness. The loads distributed are transmitted through shearing action to the foundation. Due to heavy mass of masonry wall leading to high inertial forces, poor connection between the walls and diaphragms be separated from roof leading to the collapse of the building. Unreinforced masonry is weak in resisting such lateral forces. (FEMA, 774) The study highlights the need for enhancement of the research on the URM buildings behavior under earthquake loading. The extensive studies with the action of the tests and researches of URM have focused on in-plane walls. Although walls perpendicular to the direction of earthquake are not the direct path to the loads, they need to be able to resist the force exerted. Since URM walls have low tensile strength, slender masonry walls are vulnerable to out-of-plane failure and belongs to one of the most controlling modes of failure Out of plane failures are most vulnerable in case of masonry during earthquake. It causes greatest risk to the safety of people inside and outside of the building as it causes collapse of the walls leading to partial or complete collapse of the building. Here this study focuses on the effect of slenderness ratio, eccentricity of load on the stability of URM wall. II. NEED TO STUDY Seismic activities in Nepal are very frequent, which are caused by the continental collision of Indian plates and Eurasian plates. On 25th April 2015, an earthquake of moment magnitude Mw 7.8 with a focal depth of <15km struck about 80km northwest of the capital, Kathmandu (USGS 2015). The earthquake caused thousands of deaths as well as damaged a huge number of buildings. The large scale of damage has indicated that the study and research of the general practice of building construction in Nepal and the assessment of their capacity of such buildings are necessary to understand. Brick masonry is one of the most popular construction materials in developing countries like Nepal. Unreinforced masonry structures normally have high compressive strength by which there are strong in gravity loads but are very weak in tensile strength i.e. lateral forces causing are high vulnerable in earthquakes. During earthquakes, in plane forces cause sliding or shearing whereas out-of-plane causes bending leading to flexural strain. KEC Conference __________________________________________________________________________________________ 209 KECConference2019, Kantipur Engineering College, Dhapakhel Lalitpur