Steel profile sections dimensions limitations- web and thickness to Flange and its thickness 1

[Dokmah]

Does any one know what are the limitations for the Steel profile sections dimensions web and thickness to Flange and its thickness. such as PEB what the max. height of the web to the flange width and relation to their thickness..

 

[driftLimiter]

Not sure if your talking about the limitations of the rolled profiles from the mill, if you mean Welded plate girders. There are slenderness limits of the elements. However there are adjustments for non-compact and slender elements under compression due to flexure. I don't know that there are any hard limits, but lets say you want to avoid having a lot of stiffeners to resist shear and improve slenderness, you could derive a limit based on the compact requirements AISC 360-10 Chapter B.(for example).

I would be willing to bet that the Metal Building guys have some rules of thumb about these things.

 

[bugbus]

Most rolled sections tend to be near the limit of plate slenderness where they can develop the full plastic section capacity and undergo a certain amount of rotation without local buckling occurring prematurely (Class 1 or 2 based on Eurocode). This would be close to the most efficient distribution of material for a given cross-section area. Any more slender than that and the efficiency of the section drops off quickly. Any stockier and you are not getting the full potential out of the given amount of material you have.

 

[centondollar]

Efficiency (measured in stiffness or strength per unit of weight) is not highest with compact sections - it is actually quite the opposite. Class 3 sections, for example, rarely require transverse or longitudinal stiffeners, but the larger web depth acquired with them far offsets any issues relating to elastic section capacity or local buckling. Cold formed steel design is the easiest example of efficiency through slenderness, but the same applies to principles used for design of ships, aeroplanes, offshore structures, vehicles or bridge plate girders.

To answer the original poster: there are no limits if you do fancy calculations and experiments. For ordinary design, the code-prescribed slenderness limits can be an easy way to churn out cookie-cutter designs which doesn´t involve consideration for shear buckling, local buckling, crippling etc.

 

[Dokmah]

i still believe there is a limitation between in web-height & thickness to Flange-Depth & thickness, such as in plate girder for bridges

 

[centondollar]

There are guidelines in the codes to define "slender" and "compact webs and flanges, yes, but there is seldom an upper slenderness limit specified. Stiffeners were invented to overcome the problems brought on by slender girders. If the code applied in your country specifies hard limits on slenderness, you should of course abide by those regulations.

In practice, you cannot provide e.g., a web 1mm thick and 1000mm tall in a bridge, but any reasonable dimensions can usually be proven to work by applying structural analysis and steel design principles.

 

[271828]

If you're in AISC Land, check out the AISC Specification Chapter F, specifically F5 and F13.2. There are some limits on h/tw, flange-to-web area ratio aw, etc.

 

[BridgeSmith]

In AASHTO, the web depth (D) is limited to 6 times the minimum flange width (bf).

The flange thickness (tf) has to be greater than 1.1 times the web thickness (tw).

There's a flange proportion limit of bf / 2*tf <= 12, and limits defining for compact and noncompact flanges for buckling.

There's also limits for the web that define compact, non-compact, and slender, which are a bit more complicated than a straight depth to thickness ratio. The upper limit for webs without longitudinal stiffeners is D / tw <= 150. With longitudinal stiffeners, the limit is 300.


Rod Smith, P.E., The artist formerly known as HotRod10