End of testing, full report on this tests : large-scale vibrating table trials of Santosh Yadav, doctoral student CDP Risk@UGA

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Santosh Yadav, doctoral student at CDP RISK, is working on 1/2 scale tests of seismic resistance of buildings. As his Grenoble laboratory burned down in a fire last winter, his tests have been carried out over the last two weeks on the vibrating table at the FCBA in Bordeaux.

DYNAMIC TEST ON THE REDUCED SCALE MASONRY STRUCTURE WITH SEISMIC BAND SUCCESSFUL

After completion of construction work for the three reduced scale houses using adobe brick and mud mortar- one without band, one with timber and one with reinforced concrete seismic band on 6th November, it was another challenging job to safely move and place the house on the shake table. The temperature and relative humidity of the FCBA lab where the models were constructed is maintain at 23.5°C and 46.5%, which help in uniform drying of the specimen.

HOW TO INSTALL A 6 TON BUILDING ON A VIBRATING TABLE?

On the week of 16- 20th November, the platform (Figure 1) to move the house on the shake table were assembled. The conceptualization of this platform is made by Laurent Debove, 3SR and was based on ancient Egyptian technique.

Fig 1. Platform to move the house on the shake table

The house model was rolled to get close to the shake table with the help of 10 rollers attached to the metal frame structure on which our house were constructed. This metallic frame also helps in connecting with the shake table. After getting the house close and parallel to the table, we used farm jack to lift the house as shown in Figure 2.
 

Fig 2. House elevated using farm jack to place the platform

When the level of shake table was reached using farm jack, the platform was placed under the house so that the roller on the metallic frame aligned perfectly on the rail on the top of the platform. Later, the house was smoothly guided to the centre of the shake table with the help of tension cable as shown in Figure 3 and the rollers were removed and properly connected to the shake table with the help of bolts.

Fig 3. Rolling the house with RC seismic band on the shake table

The roof was later placed on the top of the house and the model analysis of the structure to obtain the mode shape and natural frequency were carried out with the help of accelerometer.

STARTING THE TESTS

As we were testing the reduced scale model, the applied earthquake signal was modified using similitude law.
The first test with RC band was carried out on 26th November, where we applied 50%, 100%, 150%, 200% and 300% of Guadeloupe earthquake signal. Even after the application of 300% of signal, the structure was still standing with repairable damages. We can observe the crack generated at the mortar-brick interface can also pass through brick but is limited between the two seismic band region, preventing the structure to collapse.
From this dynamic test, we could clearly observe the sliding phenomenon at the interface of the seismic band and brick, control of the crack propagation, limiting the damage on the structure. There are many more interesting finding, which was not able to detect with the naked eyes but will be interesting to observe those phenomena once we process all the results obtained using the DIC technique for in-plane and out-of-plane behavior of the masonry structure.
We are going to test the remaining two models with timber and without band this week.

Texts: S. Yadav ; photos: S. Yadav & Y.Sieffert ; edition : S. Perrier