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'[OT] OK to operate at the absolute max rating?'
On Mon, Jul 14, 2008 at 2:25 PM, Carl Denk <alltel.net> wrote: cdenk
> I think this thread belongs at [OT], and am duplicate posting there.
> The factor of safety on structures (not necessarily bridges) is commonly
> 1.4 on the dead load, 1.7 on the live load. These are there to account
> for both variability of dimensions of members, actual strength
> differing from the assumed design strength and variability of the
> loading.There may be a factor of 0.9 or 0.85 applied to allowable
> stresses to allow for certain types of loading.
So you're telling me that they don't keep driving bigger and bigger
trucks over it until it collapses, then build an exact replica of the
|That's the way it's not supposed to happen, but: A few years back the
Ohio state patrol stopped a load in Central Eastern Ohio with a 200 ton
load (not including the truck, etc.) enroute from Indiana to Some
Eastern State (that was more than 2/3 the way across Ohio. The load was
not permitted to move further, just happened that was next to a railroad
track. It took the railroad some weeks to schedule a special flat car,
and then the load proceeded. The item of interest is that a legal
maximum load in Ohio is around 40 - 45 ton, and this was 5 times that
had overloaded many facilities in both Indiana and Ohio. Every once in a
while we hear of a bridge in the back roads collapsing due to overload,
usually destroying the bridge, but no one hurt.
Many years ago, I was part of a small crew inspecting railroad bridges
at the Republic Steel Co. Youngstown steel mill. One day the bridge
creaked more than usual as a train carrying molten steel passed overhead
while we were underneath. The dispatcher later said he sent several
loaded cars next to each other with the locomotive close coupled with no
empties as standard procedures required. If those several hundred tons
of molten steel would have ended in the river below, the explosion would
have be huge!
85% of structural failures are due to details, and not main members like
beams or columns. The I-35 bridge in Minn. failure was due to a gusset
plate (small plate joins several main members). Several years ago, Ohio
closed a large bridge on I-90 near Painesville, Oh. for a similar plate
failing. The plate had rusted to where it actually buckled lowering one
end of the bridge several inches, and crews were investigating the bump
when they found the problem.
Alex Harford wrote:
Correction: The legal Ohio load is 40,000 lbs. - 45,000 lbs (20 - 22.5
tons) not as stated below, sorry, misplaced decimal and units. ~)
Carl Denk wrote:
Carl Denk wrote:
> Correction: The legal Ohio load is 40,000 lbs. - 45,000 lbs (20 - 22.5
> tons) not as stated below, sorry, misplaced decimal and units. ~)
Was the truck really carrying 200 tons?
|200 ton is what I recall the media reported. The stopped location was
about 100 miles South of us. We were going to drive down and see it, but
schedule didn't allow us. Later thinking, a typical truck axle allowable
load is 12,500 lbs. and if we take 20,000 lbs. as a maximum overloaded,
that's 20 axles and if 4' apart, that's 76' between front and rear axles
as a minimum. Probably a lot more weight on an axle than that. Sounds
like kind of a high weight to me now, but 100 ton isn't worth talking
of, and there was a lot of media coverage. :)
Reading of trucks cited for overweight in the 50 ton range is fairly
common. My experience at work includes handling installation and
dismantling and shipping out large stamping presses and other
Here's a link to one of those recent back roads collapse:
And here's a link to pictures of some mid sized equipment:
> Carl Denk wrote:
>> Correction: The legal Ohio load is 40,000 lbs. - 45,000 lbs (20 - 22.5
>> tons) not as stated below, sorry, misplaced decimal and units. ~)
> Was the truck really carrying 200 tons?
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