Apparently it wasn't designed for vehicle loads. I thought it was common practice to design them for H-10 loads for maintenance vehicles and ambulances.
I would seriously doubt that bridge was ever cleared by hand. I grew up and still have a ton of family ~40 mins away and about the only DPW snow removal done by hand is the entryways to older buildings. Even the walk-behind snowblower is a rare sight anymore as municipalities have gone to using blower and plow attachments on larger zero-turn mowers and UTVs for doing sidewalks and other narrow areas.
Back in the 50s-60s that plowing would've likely been done by a small tractor with a plow. A friend of my father's is a retired Sussex County DPW worker whose service actually predates the DPW. As a teenager he (or his father?) collected a small stipend to maintain their section of road, when he was hired into the newly formed DPW his service as a local farm kid operating the old Chalmers "G" was counted toward his pension.
This is one of those situations where I think "There's gotta be a better way". I'm an avid cyclist. There are bicycle routes (and pedestrian routes) that NEED bridges like that over busy freeways, etc. What we need is something light and cheap, easy to put up, that'll support the few cyclists or pedestrians that bother using it. But, I've been watching them build one over I-30 on my commute. I know it's been six months since they started on it. And here lately, they've been using a Bobcat or similar vehicle on it. So what should be light and quick and cheap and easy turns into some monster bridge that's required to support tons and tons of weight and likely costs a couple of million dollars just so I can ride across on a bicycle. It's like if you had to design the roof of every house to support a bulldozer. And the consequence is, the things are so danged expensive, they are few and far between.
A neutral steer is where one track tread rotates one direction and tho opposite track rortates the other, causing the vehicle to turn in circles in place.
It can also be done by locking one track and engaging the other, but this move is not a true neutral steer.
Bobcats don't use 'tracks' but is rather a wheeled vehicle. Granted, and I don't know this for sure, but it's possible that they can independently control the rotational direction of one set of wheels relative to the other.
It could be a waste of time to suggest what design changes can be done to this pedestrian bridge. The reason being all pedestrian bridge must be designed to the national standard and for USA it is the AASHTO. In it you find the live load, that is the load created by "pedestrians" crossing it, is about 5N/m2 or 104.8 pounds per square foot (psf) used internationally. The Florida FIU footbridge which collapsed in March 2018 before it could be opened to the public (before live load could be applied) has a live load of 90 psf stipulated in the design brief (FIU-UniversityCity Prosperity
Project - Pedestrian Bridge).
If someone designs a bridge not according the national standard he could lose the PE license and prosecuted if error were uncovered.
AASHTO is a good engineering practice representing our current state of the knowledge. The only way one can make the above bridge to carry a Bobcat is to specify it as a road bridge.
It is very simple to solve the snow problem. One of them would be to cast heating elements inside the concrete as some of the roads.
Some Bobcat models come equipped with tracks as OE. The "T" series models, for instance. Looks like there's tracks for over the wheels of many of the other models, as well.
And due to the 'truss' effect, would have probably been stronger to start with. Of course, the bridge didn't actually collapse, just the 'roadway' failed.
A Skid Steer will have a hydraulic drive motor driving each side. Each motor is fed by a variable displacement pump that is reversible.
When the control handle for either side is in the center position the pump is not pumping. The further back the control handle is moved, the more volume the pump delivers and the motor runs faster. When the control handle is moved ahead, the pump pumps in the opposite direction and the motor runs in the opposite direction.
To turn in place one control handle is pushed forward and the other control handle is pulled back.
Bill
--------------------
"Why not the best?"
Jimmy Carter
Modern machines have an integrated electronic control between the operator and the machine, taking operator inputs and outputting data via CAN and proprietary networks to control engine, hydraulics, and other systems. Aside from a few foreign manufacturers, drive controls today are typically standardized on one electronic joystick and loader controls the other. This improves everything from driver comfort to component life as it prevents machine abuse, the downside being that amateur operators are no longer as entertaining to watch as controls no longer need a deft touch. When I was still at Earthworm I worked on a few integration projects on similar machines, between logic and electrical troubleshooting its almost enough to make one long for the days of mechanical linkages and direct hydraulic control.
Good point, ProEpro. To improve the lifting capacity, the empty balance of those loaders is already shifted toward the rear wheels. Get it tilted back far enough, and the center of gravity would shift even more.
From what I've seen, mechanical linkage skid-steer machines are in wide use. On Bobcats website they say that the mechanical controls are still the most popular.
