“Here in this blog, we will try understand the difference between earthquake load & wind load & which one is more dangerous.
Author: Mohammad Sohel Akhtar(Sr. Structural Engineer,Specialist in design of building for earthquake & cyclone)
Before understanding the severity of wind and earthquake loads & wind load, we need to have a clarity between how earthquake and wind load acts.
Wind load is directly acting on the exposed potion of building or structure. As per the opening in the building,internal wind pressure is developed in the building. The net force on the wall or roof a building will be the relative difference of external wind wind pressure & internal wind pressure.
On the other hand,earthquake load is an induced load at the upper floors. However, as we all know, earthquake waves reach to the ground level of building in the form of transverse waves, compression waves or rotational waves. These wave create a heavy shear force or lateral force at the ground level but this load is distributed to the upper floor due to inertia of the buildings. However, no earthquake load directly act on the upper floor but occupant at upper floor feels jolting. Hence, we can say earthquake load is an induced load. As per the newtons first law,every object wants to be in the same state until and unless it is subjected with an external loads.We can say,earthquake load is an inertial load.
A person seating on the car at back seat feels backward push.However he /she was not directly pushed back by any external force. We can analogue this with force experienced at the upper floor however there is no direct load is acting on that floor.Either backward push felt by a person seating on the car when it start moving forward or jolting felt by a person in building during earthquake,both the forces are inertial forces.
Which one is more dangerous: Earthquake force or Wind Load:
Although both the forces are dynamic in nature. In case of cyclone, as people like fisherman or people working at the seashore are warned in advance.Also, people residing in any building can be moved to safer place if their buildings are not able to withstand the strong wind. But prediction for earthquake is not possible.It’s exact occurrence in terms of date, time & place is still under investigation among the Geologist & Scientist.No body can predict the exact date & time of dislocation of faults & relative moment of tectonic plates.Therefore, if earthquake occurs with Tsunami,many people are died at the seashore.People at the seashore cane be saved if it is possible to predict. But i am sorry to say, till date,we are not at that level to predict the exact date & timing of occurrence of earthquakes. Although Geologist can give a hint for it’s occurrence due the past seismic activity and the presence of fault planes or tectonic plate boundaries.
On the basis of intensity of wind and earthquake, any of the two may be more severe and life threatening but as earthquake can not be predicted with exact date and timing, we can say it is more dangerous.
Whichever is more dangerous, people are advised to construct building which can withstand safely for any earthquakes & strong winds which have been specified as per the earthquake zone & wind zone for a particular area.