Residual stresses in Steel sections
The stresses remaining in unloaded steel sections are of importance in column style as they lead to reduction of flexural stiffness of the columns and consequently during a lower buckling strength .Although residual stresses area unit self-equilibrating, the effective moment of inertia of the cross section are going to be modified once elements of the section, that have residual compressive stresses, area unit yielded. It is noticed that the magnitude of most residual stresses in hot-rolled sections of a moderate steel strength is about up to 30 % of the yield strength and area unit uniformly distributed across the thickness of the plate. A longitudinal residual stress gradients will if truth be told be found in cold-formed HSS tubes. One gradient is thought because the perimeter (membrane) residual stress and is developed parallel to the tube wall. The opposite gradient is thought because a thorough thickness residual stress is developed across the tube wall face and on the cross sectional perimeter. The most dominant parameter that affects the tangent modulus and supreme strength of HSS column is the residual stress gradient. The magnitude of this kind of residual stresses varies from twenty five to 70 % of the fabric yield strength.
Retrofit of existing structures is usually required once live masses increase on the far side of those structures that were originally designed. it may also be needed due to the associate degree of inadequate style, damage, fatigue cracking, or deterioration like corrosion. The subsequent steps for upgrading steel bridges are:
1. Fastening cowl plates to the crucial rim areas of the bridge floor beams.
2. Once rim material is supplementary, the present bolting system could become light. This could be corrected by adding additional bolts or subbing larger bolts.
3. Bearing stiffeners is also strengthened by bolting or fastening angles or by fastening plates.
4. Intermediate stiffeners can also be supplementary by bolting or fastening plates.
5. If the net wasn’t originally spliced to resist moment, it’s going to be spliced by adding facet plates.
6. Tension truss members are often strengthened by the addition of adjustable bars or cowl plates. cowl plates should, however, be welded to the gusset plates.
7. Compression truss may be brought into effect by adding cowl plates, either to convert unsymmetrical cross sections or to cut back the width-to-thickness magnitude relation of the plates that comprise the cross section, so as to avoid native bucking and totally utilize their yield strength.
The usually mentioned ways of retrofitting steel bridges (and structures) generally involve bolting or fastening further steel plates to the structure. These ways, however, have variety of constructability and sturdiness drawbacks. In several cases, fastening isn’t a fascinating answer because of fatigue issues related to weld defects. On the opposite hand, mechanical (bolted) connections that have higher fatigue life, area unit time intense and expensive. Drilling holes for fast connections conjointly ends up in a cross sectional loss further because the introduction of stress raisers. In addition, structural steel designing courses in kerala plates need work instrumentality and will add hefty dead masses to the structure that reduces their strengthening effectiveness. The supplementary steel plates also are prone to corrosion that may lead to a rise in future maintenance prices.
There is a requirement for adopting sturdy materials and cost-efficient retrofit techniques to beat a number of the drawbacks of standard techniques explicit earlier. One among the potential solutions is to use high performance non-metallic materials like FRPs. In general, FRP materials give superior strength-to-weight ratios for retrofit of structures. FRP rigid plates and versatile sheets area unit obtainable and may simply be applied to the surface. FRP versatile sheets especially supply a singular advantage of having the ability to adapt to complicated and hook like surfaces.