Tests on Reinforced Partially Prestressed Concrete Tank Walls

Current practice for structural design of environmental concrete structures such as water reservoirs and sewage treatment tanks follows one of two philosophies. The tanks are either fully prestressed or non-prestressed. In one case, the design philosophy is to prevent cracks by keeping the concrete in compression. In the other case, the design philosophy is to allow cracks but limit steel stresses to ensure that the cracks do not become too wide. This paper presents the results of the experimental phase of a research program that aims to investigate the concept of partial prestressing in liquid containment structures. Understanding the behavior of partially prestressed tanks is the key for providing rational solutions ranging from reinforced concrete at one end of the design spectrum to fully prestressed concrete at the other. In the experimental phase, a total of eight full-scale specimens, representing segments from typical tank walls, were subjected to load and leakage tests. The test specimens covered a range of prestressed and non-prestressed reinforcement ratios and were subjected to various combinations of axial tension and bending. Partially prestressed specimens clearly showed improved crack width and distribution under both pure flexure and pure tensile loadings. While the specimens were under load, leakage tests were conducted to obtain leakage rates through the cracks. The flexural compression zone prevented leakage in all specimens tested under flexure. In addition, through-cracks demonstrated autosealing provided the crack widths were below a certain limit. These two aspects are important design parameters that are not explicitly recognized in current design standards.