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Messages - BCota
31
« on: April 17, 2010, 09:09:14 PM »
not really....I would assume everywhere; I know that most of it was/is recycled steel rather than raw ore.
32
« on: April 17, 2010, 10:39:38 AM »
Vermont is actually an excellent state with respect to their oversight of construction operations; Many of the other state DOT's that we do work for will outsource quality assurance inspectors to observe means and methods and ensure that everything is to spec while VAOT sends actual state employees (which I imagine is probably cheaper too). The use of outsourced inspectors is kinda like letting a valet park your car for you -- on a couple levels.
33
« on: April 17, 2010, 07:09:00 AM »
When the Chinese were gearing up for the Olympics they bought up all of the steel (recycled and otherwise) which caused gross inflation of the steel market.
34
« on: April 17, 2010, 07:03:52 AM »
The purpose of prestressing is to prevent cracking due to flexure...the early age cracking that you are referring to is due to temperature; when concrete gets strong fast it tends to be really hot too and that can cause it to crack when it cools down -- these beams got to 5000# in about 16 hrs (type III cement) but it was achieved through careful, deliberate proportioning of the ingredients rather than high curing temperature -- they will never crack under any foreseeable circumstances.
35
« on: April 16, 2010, 02:18:22 PM »
28 Day compressive strength of companion cylinders is over 9000# per square inch. For some perspective, thats about triple the strength of a typical slab or basement. Beams will continue gaining strength forever (with diminishing returns) but will top out around 10,000# at 90 days or so (you'll be driving on it by then). 6000# is the required strength per the design calculations but we end up with a lot higher because we need to get the strength quick in order to remove the beams from the forms on a daily basis.
36
« on: April 16, 2010, 02:09:16 PM »
I is!
37
« on: April 15, 2010, 03:54:45 PM »
38
« on: April 14, 2010, 01:26:04 PM »
Unless class sizes have increased significantly since '03 that appears to be upwards of 1/2 the class receiving honors! Well done to all...especially the teachers!
39
« on: April 13, 2010, 09:40:12 AM »
One reason that the edge of the pavement tends to do that is from lack of adequate compaction. Typically it is a roller compactor and it is not uncommon for the operator to pass just shy of the edge of the roadway. Also, if the road is crowned, the compactor may not put as much pressure on the edge as it does toward the middle of the road. Both of these conditions will result in reduced density & higher permeability of the edge of the pavement. This allows water to get in there which freezes and thaws and eventually causes the pavement to fail like you are observing. In addition to this, stress induced from wheel loads at the edge of the roadway are always higher because there is not as much area to distribute the weight of the vehicle; in comparison to the middle of the road where there could be 8-14 feet of pavement to spread out the weight in each direction, the edge may only have a few inches in one direction.
40
« on: April 12, 2010, 09:59:13 AM »
careful....I am one of the engineers 
41
« on: April 10, 2010, 11:51:15 AM »
Just like all previously male dominated professions, the balance is becoming more equalized. My civil class of '07 at UNH was about 20% female. Women tend to have better natural (as opposed to learned) organizational skills which is definitely beneficial in engineering & many other occupations.
42
« on: April 10, 2010, 11:43:32 AM »
"Epoxy coated rebar is such a joke.
It is a waste of money."
x2
43
« on: April 10, 2010, 11:41:48 AM »
Two of the beams on a trailer is nearly 25 Tons + trailer + tractor <= 40T (has to be without special permitting). Just like logging trucks during spring break-up we can't ship on certain roads until after VT-trans lifts the weight restrictions.
44
« on: April 10, 2010, 11:37:47 AM »
preaching to the choir with me on that one, Mike. The only reason we use it is because it is required for all state jobs (any state, not just VT). By the sarcasm I'd bet you know this too, but if not kept completely free of flaws, epoxy rebar will get localized rust concentrations (provided that moisture can infiltrate through the concrete) which is actually worse than balanced rust formation like what has happened to the steel bridge on McNall Rd. The reason Mike considers it wasteful is because once the steel is encased in 'crete it wont matter whether it is epoxy or not because the beams will never crack and the concrete is extremely dense which will prevent moisture from penetrating anywhere close to any of the mild steel reinforcement or prestressing strands. Epoxy coated rebar is almost always required when bars must project our of the beam (in this case to attach the sidewalks and curbs) because they are not protected by the concrete until the sidewalk is cast. It is expected that this bridge will be around for quite some time so the increased upfront expense of the coated bars will be offset by increased longevity of the structure.
45
« on: April 05, 2010, 09:27:38 AM »
Checked it out yesterday....plate steel girders w/ cast in place concrete deck; in need of a paint job too. Looks identical in size & design to the bridge going south on 128 leaving Westford village and probably constructed within 5-10 years of each other based on the accumulation of surface rust on the girders. I'm surprised that VAOT has built so many steel bridges over water .... don't they know that water + steel = rust?
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