Question

8. There exists an old steel frame structure (two-story) under original load P, the beam and column have H type cross sections as shown below, frame span is L, material Q235b, height is h1 and h2 respectively, this steel frame is symmetrical structure. supposed that the maximum tension stress of this steel frame is at a point (upper flange) and this work stress value is ok, Since the work environment changes, the steel frame will be asked to be loaded additional external load AP, based on structural analysis, if the combined force (P+AP) is loaded to the frame and no any reinforcement measures are set, the stress at a point will surpass or be larger than the strength limit of 215Mpa, that will not be allowed. Up to now, the additional load AP has not be loaded to the frame and original load P cannot be removed in the future construction. Our question is: (1), please give one method to reinforce the second steel beam near the steel column (2), if using your reinforcement way, how to know whether or not the tension stress at a point is smaller than the strength limit of 215Mpa after enlarged force (P+AP) acting? (3) , what aspects do you pay attention to in reinforcement construction operation? point upper fiber of steel bo 30.000 ground surface) two story steel frame

Answer 1

For the given loading condition, the 2nd beam can be reinforced by using vertical stiffeners.

over its span L.

Providing equal number of stiffeners on both sides of the beam, the 2nd beam's tensile strength can be increased.

Since, the ultimate strength of the initial beam was 215 Mpa, after reinforcement, its strength increases more than 50%.

So, provided the force $\Delta$ P is less than increase in beam strength, the beam will be able to withstand the force (P + $\Delta$ P).

Important points to include during reinforcement for steel beams is if it is welded, it has to be minimum 6mm, there should be a gap of 3t -5t in the unattached end, toe weld should be at least 10mm from edge of flange.