How to make efficient structural design with model & load tests
Structural design of concrete and steel structures is based on the results of load tests on model or prototypes. Here, tests are conducted on models formed with materials like Perspex or micro-concrete. Therefore,
1. These tests are utilized to provide an excellent physical idea of the action concerning these structures, or
2. The outcomes of examinations of deflections and strains explained by principles of model analysis can be applied directly for design, or
3. The outcomes of the experimental model tests are utilized to define the boundary conditions and develop the basis for complicated computer analysis of the complete structure.
The structural tolerability of reinforced concrete members which are developed in factory or precast in huge quantities can also be examined for performance through laboratory tests on prototypes.
These tests provide the results for the strength as well as the deflection and cracking performance of the structure in any specified loading. Several products, which are developed in factory, like pre-stressed concrete sleepers are produced with prototype testing.
In case of finally approving the design and construction depending on preliminary load tests on prototypes, they should fulfill the essential requirements of deflection and cracking, based on conditions under which the product is expected to be used. Therefore, pre-stressed concrete sleepers which are dependent on a large number of repetitive loading all through their life must be examined under numerous cyclic loads other than static tests.
IS 456, clause 18.3 provides the following approvals for design subject to experimental basis:
1. The structure must fulfill the indicated requirements for deflection and cracking based on a load of 1.33 times the factored design load for usability conditions for 24 hours. Besides, there must be 75 percent retrieval of deflection once 24 hours of loading is completed.
2. The structure should contain adequate strength to withstand 1.33 times the factored load for collapse for 24 hours.
All the above tests must be carried out thorough knowledgeable persons by trustworthy equipments. Analysis of structures for acceptance should be conducted according to IS 456: clause 16.