20-09-2016, 03:58 PM
1455441148-CE498LectureNov16.ppt (Size: 491 KB / Downloads: 102)
INTRODUCTION
Conventionally reinforced circular concrete tanks have been used extensively. They will be the focus of our lecture today
Structural design must focus on both the strength and serviceability. The tank must withstand applied loads without cracks that would permit leakage.
This is achieved by:
Providing proper reinforcement and distribution
Proper spacing and detailing of construction joints
Use of quality concrete placed using proper construction procedures
A thorough review of the latest report by ACI 350 is important for understanding the design of tanks.
LOADING CONDITIONS
The tank must be designed to withstand the loads that it will be subjected to during many years of use. Additionally, the loads during construction must also be considered.
Loading conditions for partially buried tank.
The tank must be designed and detailed to withstand the forces from each of these loading conditions
The tank may also be subjected to uplift forces from hydrostatic pressure at the bottom when empty.
It is important to consider all possible loading conditions on the structure.
Full effects of the soil loads and water pressure must be designed for without using them to minimize the effects of each other.
The effects of water table must be considered for the design loading conditions.
DESIGN METHODS
Two approaches exist for the design of RC members
Strength design, and allowable stress design.
Strength design is the most commonly adopted procedure for conventional buildings
The use of strength design was considered inappropriate due to the lack of reliable assessment of crack widths at service loads.
Advances in this area of knowledge in the last two decades has led to the acceptance of strength design methods
The recommendations for strength design suggest inflated load factors to control service load crack widths in the range of 0.004 – 0.008 in.
Service state analyses of RC structures should include computations of crack widths and their long term effects on the structure durability and functional performance.
The current approach for RC design include computations done by a modified form of elastic analysis for composite reinforced steel/concrete systems.
The effects of creep, shrinkage, volume changes, and temperature are well known at service level
The computed stresses serve as the indices of performance of the structure.