Deep Precast Grease Trap Design

[nader666]

Hi everyone,

I am the review engineer of a new sewer pump station project which has a 23' deep & 10' diameter grease trap. The contractor has submitted a shop drawing for the grease trap (copy attached) with a monolithic base and solid rings on top, the submitted shop drawing shows 4" thick wall with 6X6-w4xw4 WWM reinforcement (copy attached). I request structural calculation because I did my calculation and it did not even come close to that wall thickness and reinforcement. I have attached the calculation submitted by the project design engineer. He argued that ASTM C478 is not the proper standard because there is ASTM C1613 which is specifically for Concrete precast grease trap ( copy attached). The structural design requirement on ASTM C1613 has stated to use ACI 318 Strength Design Method or Alternate Design Method. I think because the grease trap is an environmental concrete structure, ACI 350 is the right code to design the grease trap. The project engineer still insist that his calculation is correct and because the grease trap is already available at the precast yard, he is fighting to get the shop drawing approved and have the contractor use it. I think he has used the minimum reinforcement for non-bearing wall and I think As should be calculated to resist the maximum tension( As = Tmax/0.9 Fy).
Please advice if the attached calculation acceptable.

Thanks

 

[nader666]

ASTM 1613 & ASTM 890

 

[nader666]

The specification has called to use ACI 350 for sanitary structures. ASTM C478 is also listed in the precast section of the specification but for precast manholes and the project engineer has refereed to ASTM C1613 because the grease trap has a 6' liquid at the bottom section and it is not a regular manhole but if we use ASTM C 478 , the minimum thickness of the wall would be 1/12 of the interior diameter.

 

[nader666]

Attachments have been reattached here, please check the treat attachments.