Building Architecture Towards Seismic Action
The response towards an earthquake force is different for a different building. Some building may stand still for an earthquake but another won't stays stable for the same earthquake. In addition to the way the earthquake force is carried to the region ,it also depends on the
- Overall shape
This is an emphasis on the importance of planning that has to be conducted by the structural engineers and the architects together in order to ensure that maximum stable design is put forward. Here they have to avoid all unfavorable features that will contribute towards the instability of the structure when subjected to earthquakes. This practice would help to develop a building with a good configuration without compromising strength and stability.
Late Henry Degenkolb, a famous earthquake engineer of U.S.A, summarised the importance of building configuration as,
" If we have a poor configuration to start with, all the engineer can do is to provide a band-aid- improve a basically poor solution as best as he can. Conversely, if we start - off with a good configuration and reasonable framing system, even a poor engineer cannot harm its ultimate performance too much.''
The concern of architectural features of a building has made architects to concentrate more on the aesthetics and functionality. This has lead to much wonderful as well as imaginative structures. The structural are found marvelous either because of the reason of shape of the building or because of the structural system of the building or a combination of both. But whatever be the choice architects go far, they have a great influence on the performance of the building under the strong earthquakes. A study conducted on various kinds of damages happened to many buildings around the world had bought us information on which building architecture is best desirable and which is not under seismic circumstances.
We will look into certain architectural features which were found greater influence in building performances during earthquake motion.
Building size can be tall or too long or too larger in the plan. Tall buildings , which have the larger height to the base ratio as shown in figure 2, when subjected to a ground motion experiences larger horizontal movement for the floors.
|Fig.1: Effect of Size of Building Towards Earthquake|
In short buildings with a very long length along x direction as shown in figure 4 have many other damaging effects due to the earthquake. Now the buildings with larger plan area , for example, buildings like warehouses and all the horizontal seismic forces are carried by the columns and wall in excessive amount.
It has been found that the buildings with simple layout or geometry have performed well during the earthquakes. There exist building configuration like U, V, H, and plus shaped in a plan that has undergone significant damage. The formation of interior corners in this geometry is mostly avoided by separating the building into two parts.
For example, we can make use of a separation joint at the junction formed by breaking an L-shaped building into two rectangles, as shown in figure below,
|Fig.2. Buildings With Simple Plan Respond Well With Earthquake|
Another main problem seen in architecture is the unequal distribution of columns or walls in the plan. This would result in twisting of the building during earthquake motion.
During an earthquake, internal forces are formed in each floor levels in the building that has to bring down. For this, the shortest path is selected. Any discontinuity in this load transferring would affect the load transferring and hence results in poor performance of the building. It means any vertical irregularity would adversely affect the building. Many forms of irregularities are shown below,
Buildings that are situated over a sloped ground also have an unequal height of columns moving through the slope. This results in twisting and damage for short columns.
As shown in the figure above the structures with columns that hang or float on beams at an intermediate story have discontinuities in the load transfer path. The story displacements increase when floating columns are introduced in the building
Gap Between Adjacent Building
This is essential criteria to be regarded in buildings designed in a thickly populated area. Where engineers are forced to built buildings adjacently. The cause of this is pounding which in turn is caused due to lateral motion of the building. The building height is a governing factor of large story drift. With the increase in height of the building, the collision of the adjacent buildings are higher. The figure below shows a picture depicting seismic pounding.
As shown in the figure the buildings vibrate in their own characteristics. The roof of the shorter buildings may undergo pounding at the mid-height of the taller building. This is found to be a very dangerous phenomenon of earthquake response.