Leaderboard

The lower ratio leads to stable structure, but it does not mean that one cannot ensure stability with larger ratios. For larger ratios, you will need nonlinear analysis to ensure that. The ratio of 6 is too much, check if the ratios are correctly calculated by ETABS; it is possible that one of the displacement may correspond to horizontal members. Cantilever horizontal members will have more displacements in horizontal plane than VLLR (vertical lateral load resisting) elements and ETABS can include those values in calculation of drift which is misleading.

it considers ,go to flexural design

So looks like today, I came across the same problem that is being discussed here. I had to provide a design criteria for a buried concrete pit. I will summarize my findings below for the benefit of everyone. This applies to structural members that are subjected to environmental exposure conditions or that are required to be liquid tight. 1) The first step is to calculate flexural demand in the walls of concrete pit/ water tank based on all possible conditions. For the case of buried concrete pit, it included, empty condition (no fluid in the pit) , operating condition (full of liquid), test condition (no backfill around the pit and it is full of liquid) etc. Buoyancy checks should also be performed. 2) Compare required flexural reinforcement against minimum reinforcement ratio = 0.006 per ACI 350, Table 7.12.2.1 & ACI 224 , Section 3.5 and provide whichever is the maximum. The ratios provided are basically temperature and shrinkage reinforcement ratios based on gross section so provide half of the reinforcement at each face. 3) Satisfy maximum crack width of water-retaining structure = 0.10 mm, ACI 224R-01 Table 4.1 based on the reinforcement already provided. If the reinforcement is inadequate, increase the reinforcement till this requirement is met. To meet this requirement, smaller bars should be used with close spacing. Now a few comments on the the excellent discussion above. @Khawaja Talha post above is applicable for all normal cases where there is a restraint to shrinkage and temperature movements only. If you have a condition like that, you need to provide 0.45% reinforcement ratio in your slabs. Example of a situation where this would be applicable will be a structure where movement or expansion joints haven't been provided at industry standard spacing. But if you want to meet liquid tight start with 0.6% as a minimum and work your way as suggested above. Other posts above explain the same things in a slightly different manner but all good. Thank you