Earthquake effect on building
For reference, malaysia is located outside from the volcanic area and earthquake zone which ease our structure engineer in design process. The earthquake effect today cannot be neglected as some part around malaysia is feeling the seismic activity. As reference, some of the well known country that often exposed to the seismic activity is Taiwan and Japan. But Indonesia, our neighbour is also exposed to the seismic activity and malaysia can feel the aftershock even the earthquake happens thousands of kilometers away.
During an earthquake the foundation of the building moves with the ground and the superstructure shakes and vibrates in an irregular manner due to inertia of their masses (weights).
As the ground moves, the building will tends to move in the opposite direction as if being pushed by an imaginary force.
The building structure attempts to resist this force and in doing so absorbs the energy released. Weaker construction will provide less resistance and energy absorption and thus result in damage to the structure and in certain cases failure.
Main causes of failure of a building include, but not limited to, heavy roof, excessive opening in walls, deficient foundations, poor interlocking of walls and poor site conditions.
Below is some of the cases of damage due to earthquake activity towards building defect around the world
Damage due to soil liquefaction in apartment buildings in Niigata, Japan, Niigata. (Earthquake magnitude 7.5), June 16, 1964. Liquefaction is a phenomenon that happens when the strength of saturated soil is reduced by the earthquake’s sudden movements and as a result the soil behaves like a heavy liquid
Soft story damage in a building during Loma Prieta Earthquake (magnitude 6.9), October 17, 1989
The Agassiz statue, Stanford University,San Francisco Earthquake (magnitude 7.8), April 18, 1906
Damage due to ground deformation in a school in Anchorage, Alaska Earthquake (magnitude 9.2), March 28, 1964.
San Francisco Bay Bridge 2nd level collapse,Loma Prieta Earthquake (magnitude 6.9), October 17, 1989
Severe damage in a concrete parking structure, California State University, Northridge, Northridge Earthquake (magnitude 6.7), January 17, 1994
Massive earthquake and fire damage in San Francisco, San Francisco Earthquake (magnitude 7.8), April 18, 1906. The fire resulting from the earthquake was a major contributor to the losses
Soft story damage in a building during Northridge Earthquake (magnitude 6.7), January 17, 1994. Soft story is typically the result of one the stories being laterally softer than the others due to large window and door openings or parking garages
The information above shows all the building defects and even failure. For additional knowledge, the information belows shows some of the precaution steps in design to prevent the seismic activity for causing critical damage to the building.
Measures for Achieving Seismic Safety
SITE SELECTION
Site Investigations will assist in identifying potential danger of sliding, erosion, land subsidence or liquefaction during an earthquake. The local practice of managing any such hazard should be given due considerations. A safer site is the one having
- No danger of landslides
- Sufficient plantation on slope
- Trees not too close to the house
- Mild slope
- Far from river banks
Potential hazardous sites
Steep and unstable slopes
Building should not be constructed near steep and unstable slopes. Cliffs made of soft or crumbly, clay loam; deposits materials, etc. should be avoided.
Areas susceptible to landslides and rock fall
Landslides or rock fall areas should be avoided while selecting a site for building
construction. Some slopes may look stable, but failure could be started by
an earthquake. The building could be completely damage by the landslide.
However, building in these areas can be constructed after providing proper retaining
walls and green barriers.
Fill Areas
Building should not be constructed on loose fill. In a filled ground, the bearing capacity of foundation subsoil is low and settlement of foundation may occur.
Geological fault and Ruptured areas
Geological fault and ruptured areas that are usually visible, permanent, deep and active should be avoided for construction. Buildings should be constructed at least 250 m away from these lines
Forest and trees
The forests are really useful to stop landslides. But for safety consideration, buildings should not be constructed close to any big tree, as there might be a possibility of falling of the trees during earthquake.
Too Close building
Building should not be constructed close to another building: there might be a possibility of falling of building during earthquake. Pictures below clearly indicated that harms may comes from building which built too close together.
APPROPRIATE PLANNING
The shape, size and layout of the building is important for its seismic safety. Constructions with asymmetrical plan and elevation are more vulnerable to earthquake than those having symmetrical plans elevations
Regular shape
Regular shaped buildings like square, rectangular, or circular resist the earthquakes more effectively as compared to irregular buildings and are therefore preferable in earthquake prone areas. During the earthquake movements the corners of non-uniform buildings are stressed more and may be damaged. Complex shaped buildings, shall therefore be made simple by providing gaps at appropriate locations. Some complex shapes and their simplified solutions are shown
Short walls
In long and narrow buildings, longer wall is weak against earthquake forces and can easily fall down during an earthquake. Therefore, if long and narrow buildings are constructed, they should be divided into two or more blocks with sufficient gap between them. The foundation of these blocks may be connected to each other and separation can be made only in the superstructure. The other alternatives include provision of cross walls and buttresses as shown below.
Box Effect
One of the essential principles of earthquake-resistant construction is to use a compact,
box-type layout. Furthermore, all the components of the building such as walls, floor
and roof structure, should be well tied up with each other, so the building could act as a
box during earthquake vibration. The maximum length of wall between cross walls shall
preferably be limited to 15 ft for an effective box action
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