THE CHARACTERISTIC VALUES OF DESIGN SHOULD BE BASED ON STASTICAL DATA AND IF SUCH DATA ARE NOT AVAILABLE ,THEY SHOULD BE BASED ON EXPERIENCE.

SAFETY AND SERVICEABILITY REQUIREMENTS FOR THE STRUCTURAL DESIGN :-- In the method of design based on limit state concept, the structure shall be designed to withstand Safely all loads to liable to act on it through out its life , it shall also satisfy it's serviceability requirements,such as limitations on deflection and cracking.The acceptable limits for the safety and serviceability requirements before failure occurs is called a limit state .The aim of design is to achieve acceptable probabilities that the structure will not become unfit for the use for which it is intended , that is ,that it will not reach a limit state .All relevant limit states shall be considered in design to ensure an adequate degree of safety and serviceability.In general the structure shall be designed on the bases of the most critical limit state and shall be checked for other limit states .For ensuring the above objective, the design should be based on characteristics values for materials strength and in the loads to be supported .The characteristic values should be based on stastical data if available and where such data are not available they should be based on the experience .The design values are derived from the Characteristic values through the use of partial safety factors, one for materials strength and the other for loads .In the absence of special considerations these factors should be 95 percent probability of not being exceeded during the life of the structure .The limit state of collapse of structure or part of the structure could be assessed from the rupture of one or more critical sections and from buckling due to elastic or plastic instability (including the effects sway where appropriate ) or overturning.The resistance to bending,shear ,torsion and axial loads at every section shall not be less than the appropriate value value at that section produced by the probable most unfavorable combination of loads on the structure using the appropriate partial safety factors .