1- lack of old code’s validation
Many old buildings have been designed according to codes that nowadays are not valid anymore and require seismic retrofitting to function properly. Another important point is study and investigate the past earthquackes.
2- Change in Use
There is another group of buildings around us that needs to be changed in use. Change in use of building results in greater internal forces than before which may not be able to withstand as before and it cause various load bearing and lateral members to fail. Therefore, its necessary to investigate properly before presenting the suitable retrofitting design.
3- Damages to building
Another factor that requires us to submit a building retrofit and seismic remediation plan is the damages that occur during the construction period. common damages in steel buildings include:
- Buckling in the compressive members
- Oxidation and corrosion of members
- Fatigue Complications
- Destruction and oxidation of welding
Common damages in concrete buildings are as follows:
- The emergence of cracks in the elements
- Loss of concrete cover
- Buckling of reinforcing bars
- Corrosion and oxidation of bars
- Occurrence of creep in concrete
4- Weakness in Materials
There are many factors that contribute to the poor quality of materials used in buildings such as weaknesses in steel systems and factories, weakness in cement production, inadequate water to cement ratio, and so on.
5- Design and Construction flaws
These problems are to be occured when an earthquake strikes and in many cases cause the buildings to collapse. These flaws include molding, reinforcement and concrete casting.
In order to carry out a retrofitting plan at the request of the client, retrofitting experts evaluate the existing status of the structure and, if necessary, map the existing structure, conduct field surveys and retrieve information from the structure using retrofit tests as well Numerical modeling of the structures available in specialized software will analyze and compare various retrofit schemes in terms of performance and economic aspect and finally the most cost-effective execution plan will be proposed to the client for implementation.
The economic and financial issues of the retrofit plan are one of the most important factors in choosing and executing a retrofit plan. These will directly and indirectly affect the cost of the project. As an example, running a concrete jacket around one-story columns (for example, parking) leads to an increase in the cross-sectional area and, as a result, the space between the columns is reduced. In this case, in addition to the direct costs associated with the design and implementation of the retrofitting strategy, the free space and distance between the pillars on the parking floor will be reduced and the likelihood of occupying one or more of the parking spaces in this floor will be lost. As a result, in addition to the problems and costs of implementing the plan, indirect costs that may be imposed on the structure in question in the future should be considered.
Retrofitting procedure is as follows:
- Adding or replacing reinforced structural members
- Erosion Control
- Reinforcement using FRP composites
- Seismic recovery and reinforcement