STEP BY STEP INSPECTION ON BUILDING STRUCTURES


The concrete structure will guarantee stability and durability throughout its lifetime only if it gains an appropriate safety margin to resist and fight against the expected service forces and the environmental factors. The concrete deterioration can be studied by undergoing step by step levels of inspection.


DIFFERENT LEVELS OF ASSESSMENT ON EXISTING STRUCTURE

The different assessment levels are:

1. Preliminary Assessment 
2. Final Assessment 

PRELIMINARY ASSESSMENT OF STRUCTURES

The building codes recommend the design and practice based on Safety Factors that is chosen to minimize the risk of brittle failure. In practice, most of the failure observed in building structures will be observed initially by a warning. This warning will be either in the form of large deflections or in the form of extensive cracking. If the structure’s strength is endangered by any form of cracking, it will provide time to carry out the preliminary assessment and bring the measure to strengthen it.

During the preliminary assessment of the structure, we must evaluate whether the structure is load bearing or not. This will be continued with the quick study of drawings and the calculations together along with a preliminary inspection. This will give us a brief idea on whether the structure is overloaded or whether a reserve strength is still available. Areas wherever necessary, measure have to be provided to provide the final strengthening and the repair work.



FINAL ASSESSMENT OF STRUCTURES

The final assessment of the structure will include the careful inspection techniques for the type and the kind of deterioration that is determined from the preliminary assessment. The main objective of the assessment is to determine the residual strength of the analyzed structure and bring decisions on:

  • Ø Whether the structure possesses a residual strength or stiffness in order to behave in a safety margin. This is not a requirement for normal conditions alone but also for the exceptional events like fire, impact or earthquakes. 
  • Ø Whether special measures and methods have to be employed to perform the suitable level of safety for the structure 

Most of the structural deficiencies that affect the strength or the serviceability conditions of the structure arise from: 
  1.  The structural deficiencies like faults in material, design, and workmanship 
  2.  The changes in the environmental effects, abnormal load effects, excessive demands on the structure and fire 

In order to analyze the above conditions, a systematic approach is necessary for the structural assessment. This will include:

1. Visual Inspection

2. Study of the Existing Structure

3. Load Estimation

4. Consideration of Environmental Influences

5. Determination of steel and concrete material Properties


Visual Inspection

This inspection is carried out to detect all the symptoms of damages and defects. This must include a check on the actual dimensions of the concerned structure.



Study on Existing Structure

This inspection study will include the detailed examination of the codes, structural analysis, specification and drawings, soil investigations, the construction diary, the inspection reports and everything that is related to the quality control, design and the construction of the structure.


Load Estimation

The estimation of the loads has to be done in comparison with the actual loads and the settlement or the rotation of the foundation including the assumptions involved in the structural analysis. 

In the case of prestressed structures, the conformity of the structural analysis, the drawings, the effects of concrete shrinkage and creep, the actual stressing forces should be checked.




Consideration of Environmental Influences

These will include the effect of aggressive agents that is found in the atmosphere, temperature effects, rain and also the use of de-icing salts.


Determination of steel and concrete material Properties

The material properties of steel and concrete can be carried out using several inspection techniques and equipment available.
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