Foundation, Concrete and Earthquake Engineering

Need for Structural Safety

A structural failure, in some cases, would merely be an inconvenience. In other cases, loss of life and significant loss of property may be involved. This occurrence is considered in proportioning and designing structural member seriously. The methods of designing has been developed to have sufficient warning before failure before failure. Safety is provided to the structures to develop adequate strength against all loads that may foreseeable act on it.

If the strength of a structure, built as designed, could be predicted accurately, and if the loads and their internal effects (moments, shear, and axial forces) were known accurately, safety could be ensured by providing a carrying capacity just barely in excess of the known loads. However, there are a number of sources of uncertainty in the analysis, design and construction of reinforced concrete structures. These sources of uncertainty, which require a definite margin of safety, may be listed as follows:

1. The assumed intensity of load may not be same as that of actual intensity.

2. Actual loads may be distributed in a manner different from that assumed.

3. The assumptions and simplifications inherent in any analysis may result in calculated load effects-moments, shears etc. different from those that, in fact, act in the structures.

4. The actual structural behavior may differ from that assumed , owing to imperfect knowledge.

5. Actual member dimensions may differ from those specified.

6. Reinforcement may not be in its proper position.

7. Actual material strength may be different from that specified.

It is evident that the selection of an appropriate margin of safety is not a simple matter. But, considering the consequence of failure, the design codes are developing rational safety provisions.

No comments:

Post a Comment