On Aug 10, 2:19 pm, Louis Ohland wrote:
Interesting to see if rivets were the proximate cause. I thought that
the bridge dropped fairly straight, and if that's so, one plate failing
might cause a twisting force... Let's let the NTSB figure this one out.

Too_Many_Tools wrote:
interstate bridge were originally attached with rivets,

If the construction material is so heavy, why not pile it up off the
bridge and use a conveyor belt to move it? One benefit would be much
reduced heavy dump truck travel onto the bridge. Set the pile up on the
side opposite the construction, and work toward the pile, shortening the
conveyor belt as you go. Concrete might be moved via a pumping system
akin to what they already use with construction.

Dunno about asphalt, as I've not seen any other movement techniques
other than dump trucks.

Construction crews had piled up sand and gravel on the bridge as they
prepared to pave a 520-foot stretch of two southbound lanes



Good modern bridges CAN be designed and built, ones that endure.

The first of these modern bridges is the Brooklyn Bridge in New York
city, completed in 1883 or so. It still carries as much traffic as
ever, and originally also carried railway steam trains, which are
terribly hard on bridges due to impact loading by the stem locomotive.

Other pretty old ones are the Golden Gate bridge, and the Lions Gate
bridge in Vancouver. Both of these were built in the 1930 thus
getting close to 70 years old.

The point is that having important infrastructure designed and built
by the lowest bidder can be a receipe for disaster.

It will be interesting to find out the mode of failure; looking at
the traffic camera video clip it appears like shear failure of the
beam ends since the entire structure fell horizontally and practically
intact. Agreed that a short video is not something to base any
opinion on.... I'm guessing here, admittedly.

Whether the structure is bolted or rivetted should not make any
difference in the life expectancy of any steel structure if it is
properly designed, constructed, and maintained. Big ifs when all
three are executed by the lowest bidder.

A good bridge design can be SEVERELY overloaded, under carefully
controlled condition, without impacting the safety of the bridge. The
reason is that in the design of bridges and buildings the stress level
is kept below the endurance limit so as to eliminate the onset of
fatigue cracking. The onset of fatigue cracking is difficult to
detect and expensive to eliminate in a structure since this is
generally not allowed for in the design.

Sooo, overloading the bridge once-in-a-blue-moon is ok especially if
all other traffic is stopped for the brief transit time. This was
done on the Ambassador bridge linking Windsor and Detroit when my
employer at that time moved a 90 ton weldment over that bridge in the
early 1970.

Wolfgang