Dynamic Testing of Seismic Resistant Cob Structure for Post-Earthquake Reconstruction

ABSTRACT

This paper presents the details of shaking table tests on a seismic-resistant cob structure. The seismic resistance of the model was increased using bamboo strips and steel wire mesh. A one-third scale model of a prototype cob building was used to observe its dynamic performance using a shaking table. The model was subjected to different levels of acceleration time history record of the 1940 El Centro earthquake. These levels were varied from 25% (R25) to 200% (R200) in increment of 25%. The data of acceleration of both the in-plane and out-of-plane loaded walls and displacement of the model were recorded. The damage to the model began with the appearance of cracks in the in-plane loaded wall at R100 level of dynamic excitation that changed the structure’s dynamic characteristics. The size and numbers of cracks increased in the walls of the model with increased levels of peak ground acceleration (PGA) and the structure became heavily damaged at R200 level of test run. The acceleration response and its amplification were higher for the in-plane loaded wall as compared to the out-of-plane loaded wall. The maximum acceleration for the in-plane and out-of-plane loaded walls was recorded as 0.65 g and 0.57 g, respectively, in the prototype domain. The torsion effects caused unequal structure displacement at its east and west ends at roof level. The energy dissipation of the wall continued until the end of testing. The observed structural damages corresponded to four performance levels that were correlated with the damage limit states.

KEYWORDS:

• Cob Structure
• In-Plane Wall
• Interstory Drift
• Inertia Force
• Seismic Strengthening
• Natural Frequency
• Damage State

Acknowledgments

The authors wish to acknowledge the financial support provided by the Government of Balochistan for this project. Help from all the laboratory technical staff members is also acknowledged.