This procedure is applicable for conventionally reinforced cast-in-place concrete, precast-prestressed concrete and post-tensioned cast-in-place concrete. The evaluation of an existing concrete building is usually performed for stability, strength, safety and future expected life. Evaluation of a structure may be required in the following situations:
Structures are subjected to excess or improper loading, vibrations, fire, etc.
Structures having visible signs of distress / deterioration such as excessive cracking or spalling of the concrete, reinforcing bar corrosion, member deflection or rotation, etc.
Structures with doubt about design, detail, material, or construction.
Doubts exist about safety against future loading and the original design criteria.
After a change in use or occupancy.
After repair or strengthening.
Evaluation of a structure can be performed at various levels as under:
Stability of the entire structure and the stability of individual components of the structure.
Strength and safety of individual structural elements.
Stiffness of the entire structure and the stiffness of individual structural elements.
Susceptibility of individual structural elements to excess long-term deformation.
Dynamic response of individual structural elements.
Durability of the structure.
Fire resistance of the structure
Serviceability of the structure
Most common steps for structural evaluation are as follows:
Defining the existing condition of the building, including:
a) Reviewing available information on the building.
b) Conducting a condition survey of the building.
c) Determining the cause and rate of progression of existing distress.
d) Determining the degree of repair required.
Selecting the structural elements which require detailed evaluation.
Assessing past, present, and future loading conditions to which the structure has and will be exposed under the anticipated use.
Conducting the evaluation.
Evaluating the results. The results may be reported in one of the following forms:
a) The structure is adequate for normal use over its expected life if maintained properly
b) The structure, although adequate for present loading and existing conditions, may not remain so in the future
c) The structure is inadequate for its current or intended use, but may be adequate for alternative use
d) The structure is inadequate or unsafe, and needs remedial work
e) The structure is unsafe and beyond repair
f) The information or data are not sufficient to reach a definitive conclusion
The evaluation report must cover the following topics:
Preliminary investigation
Methods for material evaluation
Assessment of loading
Selection of evaluation method
The evaluation
Fig: Structural Evaluation
The strength of existing concrete buildings may be evaluated analytically or by load tests. The observations such as type and extent of cracking, excessive deflections, deterioration of concrete, and history of loading, construction record, design record, and results of evaluation are used to precisely determine why the structure has undergone distress. The reasons and mechanisms that caused the problem may be single or multiple. The cause, effect, and degree of influence of problems on serviceability and safety of the structure must be studied. The repair system must be as cost-effective as possible. Before starting a repair work, the cost of repair and the expected life of the structure after repair must be compared with the cost of fresh construction and a logical conclusion as to whether repair is the solution must be made.
