Archive | July 2014

Building blocks for an earthquake resistant building!

Earthquakes have various types of effects on constructions. It is therefore difficult to design a house that is earthquake proof and ensure that it will resist all possible kinds of earthquakes. However, it is possible to employ a lot of earthquake resistance features using earthquake resistant engineering techniques while building your house. This will increase the chances of survival of both building and occupants manifold.

As we talk about the safety of the building during the earthquake it is important to understand ‘why does a building fall in an earthquake?’ Earthquake is a sudden movement of the ground due to a series of shock waves at short intervals. It can move the land up or down or from side to side. Every building no matter how poorly it is made, it can carry some load, so they can survive the up and down motion of an earthquake. However, not all buildings can survive a side to side earthquake, unless this has been taken into account during structural design and construction phase and some earthquake resistant measures are used to avoid such situations.

Another reason of buildings collapsing in an earthquake is excessive load on the building in the form of another floor, extra walls and partitions or even rocks piled on roof to stop them from blowing away. This leads to weakening of the reinforcement of steel bars with the concrete as a consequence of which the bars bend outwards moving away from the columns taking away all the strength of the building. You can see this effect in the form of cracks that appear in the concrete.

Buildings constructed on loose soil or ground are more prone to damage during an earthquake. The soft soil turns into a sort of quicksand during an earthquake, leading to the complete sinking of building in the soil. The taller buildings will stay intact or fall in entirety. The chances of taller buildings to fall apart completely are higher especially if some liquefaction of the soil underneath has caused the building to tilt.

While designing a building one needs to ensure a few things like the configuration (plan and elevation) of the building is as simple as possible. The structure should be built on firm and uniform ground, while the building should be dynamically simple and definite. In addition to required strength the frame of the building should also have adequate ductility.

To make earthquake resistant buildings, structures and foundations, it is important to note that the lighter the building, the lesser the load will be. Therefore, one needs to ensure that while constructing a building, the roof, floor, walls and partitions are of light weight. To achieve the sideways resistance, it is necessary that the walls go equally in both the directions. The walls should be strong enough to take the loads and must be tied in to any framing, and reinforced to take load in their weakest direction. They should not fall apart but rather remain in place after the worst shock waves to retain strength after shocks.

Vertical reinforcement is another method to make earthquake resistant buildings. Vertical reinforcement bars can be embedded in the wall piers, foundation at the bottom and in the roof band at the top. This will force the slender building or structure to bend instead of rock when an earthquake strikes. These reinforcement bars enhance the capability of walls when the earth shakes from side to side and delays the X-cracking. It also protects the wall from sliding or collapsing in the weak direction.

A few more earthquake resistant design tips will include the following :

  • Use regular shapes like square or rectangle while designing the building plan.
  • The length of the walls in a room should not exceed 6m in length, while in hilly terrains it should not exceed 3.5m in length. Consider using pilasters or cross walls for longer walls.
  • The height of each storey should be kept below 3.2m.
  • Ensure that  solid and sound bricks/concrete blocks should be used for construction. Bricks with crushing strength less than 35kg/cm2 for single storey building and of 50kg/cm2 for 2-3 storey building should not be used.
  • Provide a R.C.C band of 4” thickness throughout the run along wall at lintel level passing over doors and windows.
  • Make sure that the thickness of load bearing wall should at least be 200mm.
  • The clear width between a door and nearest window should be at least 600mm.
  • A door or window should be placed at least at a distance of 600mm from the edge of the wall.

Keep these little things in mind while constructing a building to safeguard them from earthquakes. Happy building!