ISBN 978-9937-0-9019-3 Seismic Strengthening Of Stone Masonry Wall Using Horizontal Bands Paras Khati Department of Earthquake Enginering IOE Thapathali Campus Kathmandu, Nepal [email protected]a) Abstract— This paper introduces a technically feasible and economically affordable horizontal bandage retrofitting technique for low earthquake resistant masonry structures in developing countries as Nepal. An unreinforced masonry wall section has been tested for lateral strength before and after introduction of horizontal bands. The wall thus seismic strengthened by introduction of horizontal bands using section modifier. The Stresses developed in wall of retrofitted model are decreased by 50- 90% than its original modal. The analysis demonstrates introduction of horizontal bands can mitigate the risk to unreinforced masonry wall buildings in future scenario earthquakes. This method improves the in-plane and out-of- plane mechanism of unreinforced masonry wall. Keywords— Horizontal bands, Retrofitting, Stone Masonry, Section modifier. I. INTRODUCTION Nepal lies in earthquake prone zone. Nepal has encountered many earthquake in past. Nepal has suffered 16 major earthquakes, including recent Gorkha Earthquake of 25 April 2015 in which more than six lakhs houses were fully damaged, three lakh houses were partly damaged among which most were traditionally constructed unreinforced stone masonry with mud mortar. Unreinforced stone masonry with mud mortar is mostly used construction materials in the Nepal. Here the construction practice of masonry system is non-engineered. It is also most vulnerable against earthquakes. The unreinforced masonry is a brittle material. Hence, if the stress state within the wall exceeds masonry strength, brittle failure occurs, followed by possible collapse of the wall and the building. Based on post-earthquake damage surveys, the major types of masonry failure modes have been identified as: a. Failure of In-Plane Walls It depend on the geometry of the wall (Height/Width ratio), quality of materials and on boundary restraints and loads acting on the wall. In-plane loads usually exhibit three modes of failure: Sliding Shear: In case of low vertical load and poor quality mortar. Shear: Wall loaded with significant vertical load as well as horizontal forces can fail in shear with diagonal cracking. Diagonal cracking of piers either start from corners of openings or in solid walls, from the wall ends Bending: this type of failure can occur if walls are with improved shear resistance. Crushing of compression zones at the ends of the wall usually takes place b. Failure of Out-plane Wall Occur due to the lack of adequate wall ties, bands or cross walls. When ties are adequate, failure mode is out of plane bending horizontally. Slender walls are more likely to suffer this type of damage. c. Corner Separation Failure is due to lack of lateral support at two ends of the wall during out of plane loading. Separation of orthogonal walls due to in-plane and out-of-plane stresses at corners. d. Delamination of Walls Caused by lack of integrity of two wyths of the wall. Openings in the masonry walls will form short piers, which will experience concentrations of shear stresses and hence diagonal cracks. The corners of the openings, tension cracks may appear due to the reverse cyclic stress induced by lateral loading. Major deficiencies of masonry buildings: i. Lack of Strength and Stiffness ii. Lack of Integrity between Walls Roof and Floor iii. Absence of Vertical and Horizontal Bands KEC Conference 2021, April 18, 2021 “3 rd International Conference On Engineering And Technology” Kantipur Engineering College, Dhapakhel, Lalitpur, Nepal KEC Conference 2021 220
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In Nepal construction practice of masonry system is
non-engineered which are most vulnerable against
earthquakes. This can be mitigated by improving
seismic performance of the existing low strength
masonry structures. A suitable retrofitting technique
for Stone masonry structures with mud mortar is
introduction of bands which, increases it's
compressive and shear strength significantly and
provides safety against failure in compression and
shear. It shows:
1. Increase in permissible compressive stress
and shear stress in wall by 11.4 and 5.2
times of original model respectively.
2. Improvement of the in-plane and out-of-
plane strength of the wall by introduction of
horizontal bands.
REFERENCES
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KEC Conference 2021, April 18, 2021“3rd International Conference On Engineering And Technology”