Towards a Rational Design Procedure for Concrete Liquid Containing Structures

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Liquid containing structures (LCS) as part of environmental engineering facilities are primarily used for water and sewage treatment plants and other industrial wastes. In Canada, they are normally constructed of reinforced concrete in the form of rectangular or circular configurations. These structures are considered as lifeline facilities that require careful design and detailing to meet serviceability requirements for crack and leakage control. There are currently few guidelines and standards available in North America for the design of LCS. Only recently, the Canadian Standards Association (CSA) has developed a Standards for the design of Wastewater Treatment Plants which is due to be published very soon. The American Concrete Institute (ACI Committee 350) has developed a code and commentary for concrete LCS. There is a great deal of inconsistency among different design guidelines and standards for this important broad class of structures. This is mainly due to the lack of understanding of the seismic behavior of these structures. In recent years, the applicant has carried out extensive analytical investigations on the behavior of concrete LCS. The results have indicated that the current design codes and standards do not represent the actual behavior of these types of structures. The main issues of concern are the relationship between the crack width and leakage for members subjected to flexure and/or direct tension, effects of temperature and shrinkage due to restraints on cracking in concrete slabs and walls as well as those issues related to seismic loading. One important issue is related to the response modification factor, R, used for determining the equivalent base shear because of earthquakes. As a result, full scale experiments are planned to be performed on wall-slab connections. A steel water pressure chamber will be installed at the connection of the wall-foundation to simulate the liquid-tank interaction and to enable the detection of possible leakage within the critical regions of the tank wall. Based on the above discussion, the main objectives of the proposed research study is to develop a rational design procedure, through analytical and experimental programs, for reinforced concrete tanks that assures a safe leak resistant structure. In the experimental program, specimens while under loads which include hydrostatic, and dynamic will be simultaneously subjected to liquid pressure and leakage tests. Based on the results of this study, a performance criterion based on serviceability requirements and the level of protection will be used to establish the R values. This project also includes analytical studies which will be based on non-linear finite element method. Also, analytical investigations on the seismic behavior of concrete elevated water tanks using the finite element method will be performed in this study. It is intended to provide the necessary input for code decision making.