Yuya HAYASHI

Simplified Assesment Method of Steel I-Girder�fs Ultimate Bending Strength

Masatsugu NAGAI,Eiji IWASAKI

In recent years, in the bridge construction enterprise, reduction of construction cost is desired strongly and positive correspondence is performed by various organization.�@Although "multi main Girder", the " multi stiffener thin board", the "complicated width stiffener system", and the "non-composite design" have been a fundamental design concepts until now recently, a new design so called "Rationalization girder" is developed the bridge as an extremely simple structural form. As for this type of bridge, the "few main girders" and "few stiffeners" become the main design concepts.
Now, by road-bridge specification, as for ultimate bending strength of simple steel I-Girder, the yield moment is defined as the maximum.
If the height of girder and the material are chosen, the thickness of the web is decided by selecting the number of horizontal stiffener materials.
It is decided whether to set up the horizontal stiffener material by thinking about the balance of weight and the processing. When the load is increased, it is said that the greatest strength of I girder will become yield moment if this technique is observed strictly though the compression buckling of the web is early. The web to which the yield moment of I girder is required can be called the technique of design few degrees of freedom though it supplements by stiffener system. If the designer arbitrarily sets thickness of plate and the stiffener system of the web and ultimate strength is appreciable or if the safety performance is checked by using the close strength, it can be expected for expanding the design degree of freedom to become possible and to lead to an economic design. An actual section of I girder is checked for the bending strength evaluation method of steel I girder of proposed three techniques, in this study, it is examined which technique to be going to adopt in the future by comparing the accuracy of each method.

These conclusions are summarized as follows
�EIn the Nishimura�fs formula, when the web compression area is narrow, the problem that the stress at the lower flange position cannot be specified happens.
�EThough the PART-A of Nishimura�fs type tends to high evaluate strength from the Mikami�f formula, it is possible that both are using the evaluation formula with a high powerful horizontal torsion as this cause.
�EThough the difference of 7% or less is in the Mikami�fs formula in the model employed here for the Nishimura�fs formula, a good agreement is comparatively shown in other cases excluding Case-4, 6, and 8.
�EIt is thought that the Mikami�fs formular can be used for the difference between the techniques extremely greatly on the safety side.
�EThe tendency that the simple evaluation technique becomes an evaluation of the safety side was obtained from the comparison with the experiment result