he new minnesota i35w bridge unveiled

huangyhg

the new minnesota i35w bridge unveiled
here's a couple of links:
looks like pt concrete box girder design with new piers.   
mike mccann
mccann engineering
i think, concrete is the way to go in this kind of environment!
not much to look at. i wonder what the less costly options looked like.
i also wonder if they will design it as single spans so that if one span goes the entire structre doesn't fall down again.
jlnj,
mndot is concerned about the built in redundancy in the design. continuous multiple spans in concrete in a part provide this redundancy. single simple span does not have any redundancy.
didn't the failure of the central span cause the failure of the outer spans? maybe we don't know yet.
we may not be talking about the same type of redundancy.
for the collapsed bridge-
i think, the main truss by itself did not have any redundancy. if one   
the other options are on the mndot website.  also there are visualizations available for each team.
after seeing the proposal, i can say that the one item which probably won so many technical and innovative points is the system monitoring equipment for distress.  this is new structural health monitoring and is innovative and, in my opinion, not used on this scale before.  
that said, i can't help but wonder if it will pan out to be all that it is cracked (no pun intended) up to be.  concrete cracks and that is a fact, but this bridge should be post-tensioned longitudinally and transversly so what is the point of monitoring for cracks?  or even if the tendons are monitored....
what is the baseline going to be and will the contractor be liable for any and all deviations from the baseline for how many years if ever?  
lots of issues to dig out.
regards,
qshake
eng-tips forums:real solutions for real problems really quick.
i think, highly sophisticated structural health monitoring is a good thing.  once the longitudinal and transverse post tensioning is introduced to the bridge, the concrete will go thru volumetric changes due to creep etc.
during this process it is not unheard of few cracks popping up in the bridge here and there due to restraint from other sources like reinforcement, bearing system, etc. this usually happens in the first few years of the life of the bridge. if these cracks are visible earlier, restoration can happen sooner and further degradation can be minimized. some times the size of these cracks can be small and not visible to the naked eyes.
i briefly reviewed all the proposals, without regard to the engineering details, since i would assume the competing engineers all were capable.
i was struck by the difference in the approaches taken. with the exception of the selected proposal, the others were just a typical rehash of the old design, low bid, and build to specifications. - nothing really wrong with that. the unsucessful firms were just outsold based on the presentation and ability to address the local requirements and situations.
there is no doubt the selected proposal had far more "glitz" and polish, especially with the options. it was directed to address the established rating system and to be more accepatable to the locals, especially the city of minneapolis that tried to ban any shrine circus that had wild animals.
cosmetic options (a different pier shape and a few pound of coloring in the concrete) did not really raise the cost and started the project off on a good first foot forward. the presentation of the aesthics was very good. having built a notable bridge about 10 miles downstream in conjuction with a local engineering firm also helped.
the schedule is an important factor now, but in 14 months, just getting it done by the end of the year is all that will be important then since many of the access problems would have found a stabilized "temporary" solution. like all projects, if the contractor finishes it on time, it will be a good project. any early completion bonuses allowed can be justified by the savings to the public. any delays in awarding will just cost the public more in terms of commerce, work disruptions.
i expect to be able to fish the rock bottoms and outcroppings around/under the old bridge for walleys and smallmouth bass this weekend before the cold and construction.