The main objectives of earthquake engineering are:
* Understand the interaction between buildings or civil infrastructure and the ground.
* Foresee the potential consequences of strong earthquakes on urban areas and civil infrastructure.
* Design, construct and maintain structures to perform at earthquake exposure up to the expectations and in compliance with building codes[1].
A properly engineered structure does not necessarily have to be extremely strong or expensive.
The most powerful and budgetary tools of earthquake engineering are vibration control technologies and, in particular, base isolation.
1.Shock Table Test Facility for Evaluating Earthquake Resistant Features in Buildings
Table acceleration response for a swing angle of 300
- Behavior of building models after 13 shocks
- Response after 5 shocks
- Shock Table Test Facility
Shock table test facility for evaluating seismic performance of buildings was designed and constructed. The table is of size 3.5m by 2.5m and is supported on 4 wheels with ability to move horizontally in one direction on rails. The table can be subjected to shocks through a swinging pendulum of 600kg mass with provision to increase the mass up to 1000kg. On the side of the table opposite to the pendulum, provision is made to generate a reverse shock through a reaction beam. The impulse force that can be given to the table can be varied by changing the swing angle of the pendulum, mass of the pendulum, the material to which the pendulum impacts. The reverse force to the table can also be varied by changing the gap between the table and the reaction beam before the start of the test. The photograph shows two brick masonry building models with different earthquake resistant features on the shock table with instrumentation to measure the table motion and the response of the building models.
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CONCEPT OF ‘CONTAINMENT REINFORCEMENT’
It is well known that most of the structures tend to undergo large deformations in the event of a strong earthquake. If the stresses caused due to lateral forces experienced by the structures exceed its strength, the structure yields, if it is ductile. If the structure is brittle, as in the case of un-reinforced masonry, it will suffer brittle failure. The pattern of failure of masonry buildings during an earthquake makes it clear that the prevention of sudden flexural failure of masonry wall is critical to ensure an earthquake resistant masonry structure. Again, since flexural tension can occur on both faces of the wall due to reversal of stresses during an earthquake, there is a need to provide ductile reinforcement on both faces. This can be accomplished by placing vertical reinforcement either on the surface or close to the surface and surrounding the wall, which is termed as “containment reinforcement”. For the containment reinforcement to be effective, it is essential for it to remain hugged to the wall at all times during an earthquake and to deform along with the masonry. In order to meet this objective the vertical reinforcements on either face of the wall have to be connected to each other, by horizontal ties/links passing through the bed joints of masonry. These horizontal ties along with the mortar in the bed joints will ensure strain compatibility between vertical reinforcement and the masonry. Earlier study on the flexure of masonry beams with longitudinal reinforcement wrapped round the beam with links through the bed joints connecting the top and bottom reinforcement has shown substantial ductility with multiple cracks before failure. Containment reinforcement is not primarily intended to increase the lateral strength of the wall, but to permit large ductile deformation and to avoid total collapse. In other words, containment reinforcement will act as main energy absorbing element of the wall which otherwise has poor energy absorption capacity.
Masonry with containment reinforcement and links/ties connecting them through bed joints.
