SANCHEZ LOPEZ DARIO EUGENIO

INFLUENCE OF THE INITIAL DEFLECTION FORM ON BUCKLING RESISTANCE CAPACITY OF STEEL PLATES 

Iwasaki Eiji

Since the main steel girder is composed of thin plates, it is necessary to evaluate the buckling resistance capacity precisely. It is known that buckling resistance capacity decreases, since thin plates have residual stress due to the welding and gas cutting, and flat plates have an initial deflection as consequence of production and assembly. 
In the analysis of steel plate’s buckling resistance capacity, to evaluate on the safe side, in many cases is used the maximum value or a value close to the maximum value of the variation of residual stress and initial deflection. However, in case a steel plate has many stiffeners and ribs attached, a sinusoidal shape is often assumed there is an insufficient knowledge about initial deflection.
Buckling resistance capacity analysis is performed using the first mode of buckling obtained from linear buckling as initial deflection and is compared with the case of using a sine wave shape. This modeling considers the reduction in plate thickness due corrosion and stiffener height due to residual stress. When doing an elasto-plastic nonlinear analysis, for the initial deflection of flat plate, is used the following 2 types(S1，S2) for compare the strength. For S1 type, the first buckling mode from linear buckling analysis that occurs when forced displacement is applied is used as the form of initial deflection. For S2 type, the form describing a trigonometric function is used as the initial deflection form.
In conclusion Reducing the dimensions of the height of the stiffener and the thickness of the web of the plate, it is clearly seen that with shape S1, the buckling resistance capacity is greatly reduced in relation to the load capacity that it has with shape initial deflection S2. On the other hand, with the plates with the horizontal length greater than the vertical, a sudden decrease in load capacity is observed after reaching the maximum stress, this with the initial deflection of the first linear buckling mode. Therefore, it can be concluded that this type of deflection has a greater influence on the reduction in buckling resistance.