A laminated steel spring, simply supported on a span of 800 mm, is required to flatten under a proof load of 10 kN with a central deflection not exceeding 50 mm. The bending stress in the leaves of the spring is limited to 450 N/mm. If the width of the plate is 10 times its thickness, determine (i) radius to which the plates should be bent, (ii) the width and the thickness of plates, and (iii) number of plates. Plates are available in multiples of mm for thickness and 2.5 mm for width. E=210 kN/mm.