You might try wood, especially if you want to test the dimensions to see
if they are adequate. A 3 by 8, ie 2 2 by 8s held together, has about the
same flex as the 3 by 3 by .25 steel tubes and shows around 500 psi max
stress with a 1000 lb load. You might put some iron channel stock on the
top of each bar to make it last a little longer.

Hul

wrote:
On Friday, February 10, 2017 at 5:13:43 PM UTC-6, lakeside bob wrote:
Want to build a gravel screen to sort out over size rocks from sand.
The gravel and rocks would be dumped on grizzly bars on a 40 degree incline and the gravel and rocks would slide down the slope rocks sliding off the top of the grizzly bars, and sand falling between the grizzly bars under the grizzly bars to be picked up and moved to usage area. the rocks moved to waste area. Spacing between bars would be 3 inches.
Question which would bend the least when the gravel and rocks are dumped on the grizzly bars?
Rocks would be up to 18 inches round so about 150 pounds each. Dropped about 18 inches on to the bars.
Size of wheel loader bucket is 1.75 cubic yards so total weight to be slowly dumped on the grizzly bars would be 1.75 x 2800 lbs in yard = 4,900 pounds.
Data
grizzly bars angle 2 inch x 2 inch and 3/8 inch thick.
grizzly bars angle 2.5 inch x 2.5 inch and 1/2 inch thick
grizzly bars 3 inch x 3 inch x 1/8 inch thick square tube
grizzly bars 3 inch x 3 inch x 1/4 inch thick square tube
all 36,000 pound strength steel

thank you for replying it is much appreciated.

OK some more information.
Bars will be 8 feet long with a support under each one three feet down from the top of the sloping deck. The bars will be welded to cross tubes of 3 x 3 x 1/4 inch steel at the top of the frame and bottom along with one at 3 ft down from the top of frame.
the 36,000 pound steel is what the local shop sells.
the wheel loader bucket is 8 feet long or wide, so with the cap between bars at 3 inches and each bar being say 3 inches wide the gravel will be dumped on 16 or 17 bars.