Substituting bent plate for hot rolled steel

[MacGruber22]

I spec'd a W24x55 with half the flanges cut off for a parking barrier application. The contractor thinks it would be cheaper to use bent plate. My question is this: Does the orientation of the plate grain come into play when trying to use the newly bent plate for weak axis bending (again, parking barrier), i.e. do I take a hit on my yield stress if the grain is not parallel with the length of the member? See attached. The bent plate provides the required geometric properties to meet/exceed the original beam, and the inside bend radii exceed the minimum req. per AISC table 10-12 including footnote (1).

I am not asking in order to calculate a reduction of Fy, but rather to decide if I need to specify the grain orientation to be longitudinal.

"It is imperative Cunth doesn't get his hands on those codes."

 

[BUGGAR]

If the bent plate will be hot dip galvanized after bending, get a reading on the grain direction relative to the galvanizing also. Sorry for being vague but I remember some problem.

 

[JedClampett]

I don't like substituting a bent plate for a rolled section. The radii are usually a lot more pronounced than you think, and it never looks as good.

 

[hokie66]

I would rather have a bent plate than a W24 with the flanges cut off one side, probably resulting in a pretzel. And I fail to see the problem with orientation of grain...for this application at least.

 

[MotorCity]

For structural applications, I have not seen or heard of plate or rolled shapes accounting for grain direction. Structural steel is assumed to be an isotropic material. The only exception that comes to mind is when you deal with poisson ratio, which rarely shows up in steel design unless you are dealing with the shear modulus or tension field action. For your case, I would be comfortable in neglecting any grain direction related issues. If you were not going with a rolled shape, my preference would be to weld 3 plates together to form a channel. I am always suspicious of any residual stresses that may result from bending plate (especially to a tight radius).

 

[MacGruber22]

If the bent plate will be hot dip galvanized after bending, get a reading on the grain direction relative to the galvanizing also.

http://www.galvanizeit.org/design-and-fabrication/fabrication-considerations/bending

My original specification says that the barrier may be either painted or HDG, at the option of the owner. Based on ASTM A143 it seems that my minimum inside bend radii should be 1-5/16" if it is to be HDG after cold-bending.

The radii are usually a lot more pronounced than you think

Do you know if ASTM A6 has the tolerances for cold bent structural steel plate?

I would rather have a bent plate than a W24 with the flanges cut off one side, probably resulting in a pretzel.

I see your point.

If you were not going with a rolled shape, my preference would be to weld 3 plates together to form a channel. I am always suspicious of any residual stresses that may result from bending plate (especially to a tight radius)

Already suggested the built-up plates, and they believe that it is just as costly as the cut W24. I wasn't too concerned about residual stress, as I figured that they wouldn't be much more than those resulting from rapidly cooled hot-rolled steel. I am thinking about increasing the inside radii to 1-1/2", re-checking the weak axis moment, and calling it a day.

http://preserve.lehigh.edu/cgi/view...xt=engr-civil-environmental-fritz-lab-reports

"It is imperative Cunth doesn't get his hands on those codes."

 

[Lomarandil]

Not directly applicable here, but my one followup to MotorCity's comment (for posterity) is that in some cases, we account for different steel properties in the through-thickness direction.

 

[BUGGAR]

Also for prosperity, we've used bent plate stainless steel stair channels in reservoirs with no problems (very low stresses, low b/t and h/t).

 

[dhengr]

MacGruber22:
The yield strength and other mechanical properties do not change much, in the plane of the plate, in the x or y axis direction, or as a function of their orientation w.r.t. to the grain/rolling direction, as far as we are typically concerned in day to day structural design. The reason for some concern about through thickness (z axis) properties, and particularly through plate tension is that these stresses are perpendicular to the likeliest orientation of laminations and slag inclusions in rolled plates. The residual stresses due to cold forming are also usually within acceptable limits also, so we usually don’t include them in our design considerations. However, bending across the grain, particularly on tighter bend radii and on thicker plates usually leads to better results, for lack of cracking of the plate. When the bend line is parallel to the grain orientation the cracking/ripping potential goes up on tight bends and on thicker plates. Also, sharp edges/corners where the bend line hits the plate edges can cause a tendency to start tearing (a sheared edge, flame cut edge, etc.). The fix for that is to grind a radius on the plated corners/edges. You might want to talk to some local fabricators, as to how tight a radius they can form on whatever plate thickness you have. There will also be some fairly short length limits which most fabricators can break form and if they do have to form across the grain, these lengths will also be dependant on the width of plate they can mill order or buy.

 

[Ron]

Structural Shapes are rolled. So is plate. Grain orientation would generally be the same in longitudinal direction; however, it makes little if any difference in the strength of the material.

I've used bent plate on numerous occasions instead of rolled shapes. I don't see an issue as long as the sections are capable.

 

[Bagman2524]

Bent plate should fall under Cold Formed Steel design techniques not AISC-360

Faith is taking the first step even when you can't see the whole staircase. -MLK