SEISMIC REINFORCEMENT OF TWO-STORY EARTHEN BUILDINGS USING A ROPE MESH: PRELIMINARY TABLE TEST RESULTS

Millions of low-income families living in earthen dwellings in seismic areas around the world are at significant risk because most of these structures are built informally and without any seismic reinforcement. Every single earthquake occurring in these areas has caused an unacceptable loss of life, injuries, and property damage. Earthquakes are recurring and construction damage is cumulative. It is urgent, therefore, to devise low-cost and easy to implement seismic reinforcement systems and to make them available to the actual dwellers. The researchers at the Pontifical Catholic University of Peru (PUCP) have been working towards that goal for almost half a century and have recently proposed design guidelines and a construction methodology for a seismic reinforcement system consisting of a mesh of nylon ropes confining all earthen walls, in order to control displacements and to prevent the overturning of wall portions that have separated due to seismic shaking. The effectiveness of this system has been validated for single-story adobe structures via shaking table tests of (almost) full-scale one-story adobe housings models. In the Andean regions, however, many families build multistory earthen houses, and it is not known whether the proposed rope reinforcing system would be effective in protecting these structures. Therefore, the PUCP researchers decided to start an experimental and analytical project devoted to the study of the seismic response of multistory earthen buildings. The main objective of the project is to assess whether the proposed rope mesh reinforcement would also be effective in providing seismic safety to multistory earthen constructions. This paper presents some preliminary results obtained during the experimental campaign, where four half-scale two-story adobe housing models were tested at the PUCP’s unidirectional shaking table under simulated strong seismic motions. The same command signal, derived from a Peruvian acceleration record, was used at different amplitudes for each shaking table test. As expected, both unreinforced models, which simulated local vernacular constructions, suffered rapid and total collapse. All the walls fractured in a few large pieces, which were not held together by the provided wooden crown beams and thus fell to the ground. The next two models were reinforced using an external nylon rope mesh, basically with the same configuration as that successfully used in the one-story models. Again, as expected, all the adobe walls fractured in large pieces, but this time the provided mesh reinforcement was able to hold the pieces together, thus maintaining structural integrity and preventing collapse. These results are encouraging, and thus the project is being continued with an analytic study of the dynamic response of big blocks of adobe masonry wall joined by elastic ropes and subjected to earthquake ground motions. The aim of this stage of the project is to attempt to explain the dynamic response of broken adobe walls, as observed during the experimental stage. The authors hope that this project will help to understand the complex response of earthen structures and that its results will lead to construction procedures for the protection of vernacular and historical earthen buildings located in seismic areas.