Design Considerations: Earthquake Loads versus Wind Loads

Several methods are available for designing structures subjected to seismic loads: the response spectrum method and the equivalent horizontal force method. The response spectrum method is widely used for irregular shaped and important structures, the second method consists in replacing the influence of the acceleration during an earthquake by equivalent horizontal forces. This method is only suited for regular structures with two axis of symmetry. The equivalent horizontal forces are based on the dynamic behaviour of the structure (geometry, stiffness and mass) and the acceleration during an earthquake (given in the response spectrum). The equivalent horizontal forces depend on the mass and are therefore much larger for heavy structures than for lightweight structures. In reducing the mass of the structure the earthquake forces can be reduced. Therefore lightweight structures are a valid answer for reducing the horizontal earthquake loads. Structures are not only designed for vertical loads due to gravity but also for horizontal forces due to wind. These wind forces depend on the velocity of the wind and the shape of the structure. The velocity of the wind is a function of the location and the surroundings. In general buildings withstand even exceptional wind loads without much damage. For lightweight structures the horizontal loads due to earthquake are smaller than the wind loads and the building is resistant enough to withstand also earthquakes. Therefore reducing the mass of the structure adds additional safety.

Keywords:

Lightweight structures , earthquake loads , wind loads , behaviour of structures