catch basin structural design

huangyhg

catch basin structural design
i primarily design buildings but i have a precaster client that would like to reduce the amount of reinforcing in his dot catch basins by way of engineering design.  i am curious if anyone has experience doing this or ideas for references.  he would like a stamp certifying that the reduced reinforcing is adequate, despite having less reinforcing than depicted on the standard drawing.  it seems to be a common practice, nowadays.
it doesnt appear to be directly addressed in the aashto bridge spec but comes close in the buried structures section.
any ideas?

the dot standard shall be treated as the "minimum". because of several factors involved, the analysis is not that straight forward, and you definitely will have a tough time to convince dot officials, unless this is an unique/isolate case.
i agree with kslee1000...state dot's are not quick to accept something that deviates from their standard book of details.  suggest you have your client offer them some deviation from their standard design (different configuration, dimension, etc.) that will save them money and achieve same result (smaller volume box, different traffic grate, etc.).
one reason they don't like to deviate is that then they will have to review each deviation on its own merit.  
that slows their process down (imagine that!) and they often don't have the technical expertise at a district level to do an appropriate review....so they tell everyone to make it like the standard details and don't throw a stick in the spokes.
most of the dot catch basins i have seen are relatively lightly reinforced already (except for some with concrete top slabs which are in the roadway). for example, the detail i am looking at right now (caltrans d74a) has no steel reinforcing in the walls at all unless the structure is over 8 feet deep. bottom slab is also un-reinforced. often, reinforcing is only #4 bars at 12" or 18". not sure how you will reduce this and save much money.   
the acceptance of the dot is not the basis of my question.
my client has a very clear goal and is well aware of what they accept.
assume the basin is empty, do an analysis with the following loads - soil pressure and surcharge, hydrostatic pressure (if present), traffic/wheel load if applicable. if resulted in min reinforcing, or no reinforcing required, provide t&s steel. make sure the concrete barrel meets astm requirements.
impact and wheel loads will prove that amounts of reinforcement in dot standards for top slab are minimums.
there is a astm spec (c 1433-06), "standard specification for precast reinforced concrete box sections for culverts, storm drains, and sewers".
also, california dot has a section for underground structures in their "bridge design practice manual".