a. Design errors
These errors include problems in identifying the soil and foundation, ignoring the principles and foundations of earthquake-resistant building design, and errors in analysis, design, and preparation of plans, documents, and operational details. In recent years, Pekran Sazan Company has implemented a large number of strengthening projects due to design errors.
B- Executive design errors
These errors include defects in formwork, reinforcement, concrete production and formwork, concrete pouring and curing, which often occur due to unfavorable environmental conditions, lack of quality control and monitoring systems or lack of compliance in the workshop. According to the statistics of Pekran Sazan Recruitment Company, executive problems are currently the most common reason for retraining in the country.
C- Increase the load of the structure
The load on existing structures may increase over time. This increase occurs in residential buildings due to change of use and in the case of bridges due to increased traffic load and as a result the application of loads more than the expected load is another factor in strengthening and strengthening the structure.
D- Organizational changes
The behavior of reinforced concrete structures in recent earthquakes indicates the weakness of the old versions of the regulations and the need to strengthen them now. Some of these shortcomings are:
Transverse Reinforcement Hook for Transverse Reinforcement: The fixing hook is left to the end of the straps at 90 degrees in the concrete cover area, which loses restraint when the concrete breaks.
Details of the longitudinal reinforcement patch: The length of the expected foundation reinforcement patch is not sufficient for the reinforcing steel to reach a state of yielding and leads to brittle failure due to deterioration of the concrete and reinforcement joints.
Lack of surrounding steel: The lack of surrounding steel causes the concrete cover to peel off quickly and the underlying concrete does not have the necessary strength and ductility, the longitudinal reinforcement quickly buckles and the column is destroyed.
E- The impact of destructive environmental conditions
Steel has been used as reinforcement concrete for many years, but designers have always faced the problem of corrosion. This is important in coastal structures, marine structures and bridge piers that have harmful environmental factors. In recent years, several strengthening projects have been implemented by the Ministry of Oil and the Ports Organization in order to protect and strengthen marine structures in the Persian Gulf region.
F- Damage to the building due to collisions, fire, winds, earthquakes…
In these conditions, the structure needs to be recalculated, and if necessary, repair, improvement and strengthening operations must be carried out.
Operational steps for strengthening
Strengthening, evaluation stage
In order to repair and strengthen structures, a careful assessment of the existing structure must first be made. At this stage, destructive and non-destructive tests are performed to determine the quality status of the structure.
Strengthening, the stage of revelation
In the second stage of strengthening operations, which is called diagnosis, the current and future behavior of the structure is examined and it is determined whether or not the structure is in danger or will be damaged in the future.
Strengthening, the step of choosing the method
At this stage, the strength needs of the structure are determined. It is clear that the suggestions and solutions presented for the purpose of strengthening, in addition to causing the least amount of disruption to the service of the structure in question, must also be responsive in economic terms.
Factors affecting the method of strengthening
Structural value
Earthquakes in the region
Current workforce
the show length
Achievement and strengthening based on the employer’s opinion
Paying attention to the aesthetics and engineering of the structure
The historical and political importance of the structure
The strengthening method is compatible with the existing structural system
Control damage to non-structural components
Foundation bearing capacity
Restorative materials and current methods of strengthening
Methods of strengthening
Use coaxial or eccentric supports
Use of steel sheets
Use external stress
Use a shear wall
Use of interframes with building materials
Use cover papers or FRP covers
Use a layer of concrete cover
Use of reinforced mortar (Jack Frost)
Use HPFRCC cover sheets
Use of seismic isolators
Use of combined methods