Currently in several countries, as is the case of Venezuela, many structures designed in accordance with the guidelines established in the standards of that country are not really capable of achieving the desired performance, so it has been convenient to study new design methods that allow decrease the vulnerability of structures, hence the implementation of seismic design based on performance.
This seismic design allows the selection of appropriate design criteria, structural systems and configuration; the dimensioning and detailing of a structure as well as its non-structural elements, in addition to the guarantee and quality control during construction and long-term maintenance, so that at specified levels of terrain movement and with predefined levels of reliability , the structure will not be damaged beyond certain limit states or other states of utility. (SEAOC, 1995).
Source: El Mundo Newspaper
The ATC-40 states that there are three seismic levels of design which describe a limit state of damage, which represents a limit or tolerable condition established based on the possible physical damage to the building, the threat to the safety of the occupants of the building. the building induced by these damages and the functionality of the building after the earthquake. Once these levels have been defined, it is necessary to propose a numerical (analytical) representation for each of these levels, so that the designer can establish against the design of the structure.
The design levels proposed in the performance design are: service earthquake, design earthquake and maximum earthquake.
Service earthquake: this level has a 50% probability of being exceeded in a period of 50 years. It has a return period of 75 years.
Design earthquake: this level has a 10% probability of being exceeded in a period of 50 years. It has a return period of 475 years.
Maximum earthquake: this level has a 5% probability of being exceeded in a period of 50 years.
There are also some performance criteria that are responsible for describing the desired behavior of the structure during the different seismic levels of design. These criteria are usually established depending on the level of damage acceptable in the structural elements, non-structural elements, and content of the structure, which varies according to the importance and function of it, these levels are:
Complete operation: establishes that the structure remains with its original strength and rigidity, however some cracking may occur in dividing walls, facades or panels.
Immediate occupation: it establishes that the structure suffers deterioration of little consideration. Greater damage is accepted, compared to the previous limit state, in facades, dividing walls, and there may be minor failures in the equipment and content that is not essential for the operation of the structure.
Life safety: To satisfy this level, the safety of the life of the user public must be guaranteed. From the point of structural damage, it implies that the structures lose a considerable percentage of their rigidity, resistance and energy dissipation capacity. It is possible that part of the non-structural elements suffer serious damage and have to be replaced in their entirety.
Incipient collapse: In this case the overall stability of the structure is maintained, even when the structural and non-structural damage is very serious, so that the physical integrity of the occupants is not guaranteed.
Source: Vision 2000 Committee
The future vision of seismic design of structures, consists of verifying the performance in structural, non-structural and economic terms that the building will have for each of the seismic levels of design according to the use thereof. This verification is carried out on the basis of the maximum allowed drifts, based on the degree of local and global damage of the structure and based on the performance index.