The made. Bridges can also be destroyed

The large and violent movements of the ground caused by an earthquake will generally disrupt many of the services we come to rely upon for our comfort  Electric light poles are always vulnerable to damage and in most cases, after a serious tremblor, electric service will be severed.  No electricity means no lights, heat (in most cases), and no water – assuming that the water mains are still intact.  Those who use land-line phones will probably be without service, as may those with cell phones if the relay towers have been damaged or toppled.  Natural gas pipelines could be broken, as well, presenting a danger of fire or explosion.Nearly all of our stores, including grocery stores, rely on food and other supplies being brought in by truck.  When an earthquake has struck, and supply lines may be impacted, you will probably be startled at how quickly the shelves are stripped bare.  A major quake can also damage local airports and train facilities, making it impossible for supplies to be brought in until repairs have been made.  Bridges can also be destroyed or damaged to such an extent that they will be unusable. Other sections of the infrastructure can also be negatively impacted by an earthquake, such as power plants, especially nuclear power plants where the possibility of harmful radiation being released is present.  Dams are another possible danger source, and if you live downstream of a dam while living in an earthquake zone, you might want to make sure that your plans for evacuation have been made.  Facilities that process either sewage or hazardous industrial waste are other spots that might cause problems should an earthquake occur. Permanent ground deformations can tear a structure apart. Some foundation types are better able to resist these permanent ground deformations than others. For example, the use of pile foundations, with the piles extending beneath the anticipated zone of soil liquefaction, can be effective in mitigating the hazard’s effects. The use of heavily reinforced mats can also be effective in resisting moderate ground deformation due to fault rupture or lateral spreading. Most earthquake-induced building damage, however, is a result of ground shaking. When the ground shakes at a building site, the building’s foundations vibrate in a manner that’s similar to the surrounding ground. Brittle elements tend to break and lose strength. (Examples of brittle elements include unreinforced masonry walls that crack when overstressed in shear, and unconfined concrete elements that crush under compressive overloads.) Ductile elements are able to deform beyond their elastic strength limit and continue to carry load. For economic reasons, building codes permit buildings to be damaged by the infrequent severe earthquakes that may affect them, but prevent collapse and endangerment of life safety. For buildings that house important functions essential to post-earthquake recovery, including hospitals, fire stations, emergency communications centers, etc., codes adopt more conservative criteria that’s intended to minimize the risk that the buildings would be so severely damaged they could not be used for their intended function. To be earthquake proof, buildings, structures and their foundations need to be built to be resistant to sideways loads. The lighter the building is, the less the loads. This is particularly so when the weight is higher up. Where possible the roof should be of light-weight material. If there are floors and walls and partitions, the lighter these are the better, too.If the sideways resistance is to be obtained from walls, these walls must go equally in both directions. They must be strong enough to take the loads. They must be tied in to any framing, and reinforced to take load in their weakest direction. They must not fall apart and must remain in place after the worst shock waves so as to retain strength for the after shocks.If the sideways resistance comes from diagonal bracing then it must also go equally all round in both directions. Where possible, it should be strong enough to accept load in tension as well as compression: the bolted or welded connections should resist more tension than the ultimate tension value of the brace (or well more than the design load) and it should not buckle with loads well above the design load.And the loads have got to go down to ground in a robust way. If the sideways load is to be resisted with moment resisting framing then great care has to be taken to ensure that the joints are stronger than the beams, and that the beams will fail before the columns, and that the columns cannot fail by spalling if in concrete. Again the rigid framing should go all around, and in both directions.If the building earthquake resistance is to come from moment resisting frames, then special care should be taken with the foundation-to-first floor level. If the requirement is to have a taller clear height, and to have open holes in the walls, then the columns at this level may have to be much stronger than at higher levels; and the beams at the first floor, and the columns from ground to second floor, have to be able to resist the turning loads these columns deliver to the frame.Alternatively, and preferably, the columns can be given continuity at the feet. This can be done with ‘fixed feet’ with many bolts into large foundations, or by having a grillage of steel beams at the foundation level able to resist the column moments. Such steel grillage can also keep the foundations in place.If the beams in the frame can bend and yield a little at their highest stressed points, without losing resistance, while the joints and the columns remain full strength, then a curious thing happens: the resonant frequency of the whole frame changes. If the building was vibrating in time with shock waves, this vibration will tend to be damped out.This phenomenon is known as ‘plastic hingeing’ and is easily demonstrated in steel beams, though a similar thing can happen with reinforced concrete beams as long as spalling is avoided.All floors have to be connected to the framing in a robust and resilient way. They should never be able to shake loose and fall. Again all floors should be as light as possible. They should go all round each column and fix to every supporting beam or wall, in a way that cannot be shaken off.One way of reducing the vulnerability of big buildings is to isolate them from the floor using bearings or dampers, but this is a difficult and expensive process not suitable for low and medium rise buildings and low cost buildings.Generally it is wise to build buildings that are not too high compared to their width in Earthquake areas, unless special precautions are taken.  

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