17.1 Aim of Design
The aim of design is the achievement of an acceptable probability that structures being designed will perform satisfactorily during their intended life. With an appropriate degree of safety, they should sustain all the loads and deformations of normal construction and use and have adequate durability and adequate resistance to the effects of misuse and fire.
17.2 Methods of Design
17.2.1 Structure and structural elements shall normally be designed by Limit State Method. Account should be taken of accepted theories, experiment and experience and the need to design for durability. Calculations alone do not produce safe, serviceable and durable structures. Suitable materials, quality control, adequate detailing and good supervision are equally important.
17.2.2 Where the Limit State Method cannot be conveniently adopted, Working Stress Method (see Annex B) may be used.
17.2.3 Design Based on Experimental Basis
Designs based on experimental investigations on models or full size structure or element may be accepted if they satisfy the primary requirements of 17.1 and subject to experimental details and the analysis connected therewith being approved by the Engineer-in-Charge.
17.2.3.1 Where the design is based on experimental investigation on full size structure or element, load tests shall be carried out to ensure the following:
a) The structure shall satisfy the requirements for deflection (see 22.2) and cracking (see 34.3.2) when subjected to a load for equal to the characteristic load multiplied by where shall be taken from Table 18, for the limit state of serviceability. If within of the removal of the load, the structure does not show a recovery of at least 75 percent of the maximum deflection shown during the
under the load, the test loading should be repeated after a lapse of 72 h. The recovery after the second test should be at least 75 percent of the maximum deflection shown during the second test.
NOTE — If the maximum deflection in mm, shown
NOTE — If the maximum deflection in mm, shown during 24 h under load is less than where is the effective span in m; and is the overall depth of the section, in mm, it is not necessary for the recovery to be measured.
b) The structure shall have adequate strength to sustain for 24 h, a total load equal to the characteristic load multiplied by where shall be taken from Table 18 for the limit state of collapse.
17.3 Durability, Workmanship and Materials
It is assumed that the quality of concrete, steel and other materials and of the workmanship, as verified by inspections, is adequate for safety, serviceability and durability.
17.4 Design Process
Design, including design for durability, construction and use in service should be considered as a whole. The realization of design objectives requires compliance with clearly defined standards for materials, production, workmanship and also maintenance and use of structure in service.