In circular tanks (fixed at the bottom-in this case D=16m, H=5m), the main ring forces come from the water load acting on the walls (calculating the tension forces along the height of the wall using Portland Cement Association tables).....
A friend of mine (Dr. in engineering) says that the major ring forces comes from the hydration heat of the concrete in the first 3 days and the stresses due to shrinkage. He claims that according to the European codes, these forces are greater than the tension forces results from the water load; and the tank walls' reinforcement will be determined upon these forces. As a result the amount of ring rebar is 2 times the amount of reinforcement needed to take the tension forces.
I read the ACI code #350 and 318 , a book issued by PCA (design of concrete circular tanks)and another book called Handbook of concrete engineering/Fintel- ALL these Books and codes do not mention what the Dr said.
According to the handbook of concrete engineering, the shrinkage reinforcement shall be 0.65% when control joints are eliminated...but using a ratio of 0.45% as minimum is acceptable (in our case ; using 0.45% will be the same amount of the required rebar and will be 50% less of his results- according to his design the amount of reinforcement is 0.88% of Ac)
According to ACI code #350 , the maximum stress in reinforcement for elements in direct tension shall not exceed 20,000psi (steel grade 60).
According to PCA (portland Cement Assosiation) book- low steel stresses tend to make concrete crack because the lower the allowable steel stress, the greater the area of steel provided to carry the tensile loads; it is desirable to use higher allowable steel stress so that less steel is used , resulting is less restraint shrinkage and smaller tensile stresses in concrete.
Do you have an Idead about these huge stresses?
A friend of mine (Dr. in engineering) says that the major ring forces comes from the hydration heat of the concrete in the first 3 days and the stresses due to shrinkage. He claims that according to the European codes, these forces are greater than the tension forces results from the water load; and the tank walls' reinforcement will be determined upon these forces. As a result the amount of ring rebar is 2 times the amount of reinforcement needed to take the tension forces.
I read the ACI code #350 and 318 , a book issued by PCA (design of concrete circular tanks)and another book called Handbook of concrete engineering/Fintel- ALL these Books and codes do not mention what the Dr said.
According to the handbook of concrete engineering, the shrinkage reinforcement shall be 0.65% when control joints are eliminated...but using a ratio of 0.45% as minimum is acceptable (in our case ; using 0.45% will be the same amount of the required rebar and will be 50% less of his results- according to his design the amount of reinforcement is 0.88% of Ac)
According to ACI code #350 , the maximum stress in reinforcement for elements in direct tension shall not exceed 20,000psi (steel grade 60).
According to PCA (portland Cement Assosiation) book- low steel stresses tend to make concrete crack because the lower the allowable steel stress, the greater the area of steel provided to carry the tensile loads; it is desirable to use higher allowable steel stress so that less steel is used , resulting is less restraint shrinkage and smaller tensile stresses in concrete.
Do you have an Idead about these huge stresses?