City Bridge – Pt VI

Kinds of –
There are three kinds of stiffeners used:

  • The single-angle stiffener
  • The tee stiffener
  • The plate and arch or gusset stiffener

Single angle and tee stiffeners are used to assist the web to withstand buckling, the latter the most commonly used, but they have the disadvantage of upsetting the regular pitchin of the rivets.
There is no reason why single-angle stiffeners should not be used in preference to tee stiffeners, as they are quite strong enough for the purpose ..
– Note: and much easier to model single-angle stiffeners then the tees.

Gusset stiffeners are generally provided at points where concentrated loads occur…

KneeStiffProjHere’s what they are talking about re: Fig. 82,c .. Kneed stiffeners used where the flange plate projects 3″ or more past the edge of the main angle.

In the case of the girder I’m working on this is 3.84″. The problem a I see it in modeling this is simply .. how the heck to do it? Not saying it’s not possible. The example shown is based on the Evergreen .060″ angle. The question for me is .. “after cutting and gluing about 12 of these (forget the hidden side – and not even thinking of the inside) .. would I be sitting in a corner blow bubbles and making grunting sounds?” –

One way that does come to mind would be to make V-shape cuts at the two places the angle bends – leaving the ‘spine’ that touches the girder intact. That should bend well enough (I think) – the problem being making those cuts precisely enough. I think I could make a jig for that .. but ..

CornersCutting through just the one flange of the angle and bending the other to 45° – the area in blue will stretch and the area in red will compress. That *might* be ok .. the bulge of the compressed bit could be easily taken off with a scrape of an X-Acto blade .. but one of those .. hmmmm.

Of course the easiest solution would be to use a single-angle stiffener .. but it would lack that – “cool”. This is one of the places that just CALLS to be 3d printed complete with rivets .. just saying.

Note: Since I wrote this I am re-working the jogged stiffeners completely as I understand how they were made better now.

Comparing .060 Evergreen angle to REAL WORLD
ComparingThe .060″ Evergreen angle is closest in size to 3″ angle. The Engineering Toolbox – steel angles page lists six sizes of 3″ angle – from a 3/16″ to 1/2″ which I show in the drawing.

The most obvious difference is that the Evergreen shape is squared off while the ‘real world’ example is rounded off. This could be easily done with a few swipes of a file – that additional thickness of the Evergreen shape is only .004″ would be completely obscured by the rounded flange. In fact – since the ends of the angle are hidden, it would be difficult to tell what thickness the angle was.

Spacing of Web Stiffeners
The proper spacing of web stiffeners is a question to which (…) so many theories advanced.
(…) little reliance is placed in most of these theories (…) as the spacing of the web stiffeners in most cases depends on practical considerations, e.g. pitch of rivets, position of cross-girders, (…) bracing, etc.

There should always be a stiffener over the edge of a bearing plate, and at every cross-girder, or at points where any concentrated loads occur.
Okie Dokie. For my design – a stiffener at each cross-girder. Got it.

In girders over about 4 ft. deep, the distance between centres [sic] of stiffeners should not exceed the depth of the girder, with a maximum of 4 to 6 ft.1
My bridge has a girder depth of 54″. That’s 4′-6″ – which is then the maximum spacing of the stiffeners.

Near the ends, the spacing of stiffeners shall be one-third to one-half the depth. They shall be composed of two angles, one on each side of the web and shall fit tight between the legs of the flange angles.2

End Stiffeners
Fig.13-14-15The ends of plate girders are stiffened by stiffeners on each end of the bed-plates.

The arrangements usually employed are represented in Figs. 13, 14, and 15, in which c are the stiffeners; d, the sole plates; and e, the bedplates. The arrangement represented in Fig. 13 is most used, although that shown in Fig. 14 is somewhat better on account of the fact that in it the bearing of the stiffeners is not so close to the edge of the bed-plate; the pressure is therefore more evenly distributed over the area of the bedplate. In the arrangement represented in Fig. 15, the additional stiffeners d are added. The plates g are called reinforcing plates, and are added to distribute the stress more evenly over the web.3

Shearing stresses are usually provided for by web reinforcement plates or by vertical web-stiffener angles, which are often spaced very much closer together at the points of support than elsewhere.4

Final Rendering (?)
Render2Design is pretty much done. I need to figure out how I am going to do the stiffeners. The spacing was just equally spaced .. which mostly never happened evidently as placement of cross-bracing might shift them. The big question is .. that I am only showing one side. I can get away with not doing any on the hidden side of the bridge but at minimum the inside braces on the far side need doing .. and that at minimum just doing the outer and inner girder faces that you can see will be something like 24 stiffeners.

3d would be SO much easier .. and look better. I’ll think about it.

  1. The Practical Design of Plate Girder Bridges, Harold Hughes Bird, 1920 – Pg.87 []
  2. Bridge specifications: Design of plate girders, International Correspondence Schools, 1908 – Pg.15 []
  3. Bridge specifications: Design of plate girders, International Correspondence Schools, 1908 – Pg.31 []
  4. Types and Details of Bridge Construction: Plate girders, Frank Woodward Skinner, 1906 – Pg.124 []

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