"Shrinkage is one of four phenomena that are considered as causing volume changes in concrete, the other three being creep, temperature change effects, and possible chemical disintegration. While all four are interrelated, the volume change due to loss of moisture is associated with the term shrinkage. Creep is the time-dependent change in volume resulting from external loads. A rise or fall of temperature will produce an expansion or contraction of concrete but also will affect the rate of shrinkage by increasing or decreasing the rate of moisture evaporation from the surface of the concrete.
In the design of concrete structures, the usual concern with shrinkage is to prevent its magnitude from becoming excessive. Excessive shrinkage would produce cracks of sufficient size to destroy the appearance of the concrete or permit the entrance of water. Control of the amount of shrinkage can be exercised by proper choice of materials, proportioning, and curing. Theoretically, one might eliminate all shrinkage but the requirements tor so doing would not be practical. Shrinkage does have a valuable aspect in the case of reinforced concrete in that it causes the concrete to grip the steel tightly thus reducing the possibility of bar slippage.
The size of cracks formed by shrinkage of concrete can be reduced by the use or shrinkage reinforcement. The amount of reinforcement used is not sufficient to greatly reduce the total amount of shrinkage but results in the formation of numerous small cracks rather than a few large ones.
The action of reinforcing steel in resisting the decrease in volume or concrete places the steel in compression. This pre-compression could be useful in the case of tensile steel as the stress in a bar would be that resulting from the dead load and live load minus the stress from shrinkage of the concrete.
Standard concrete design makes no allowance for this pre-compression and assumes that the bars start with zero load. If there does exist a pre-compression of a determinable and consistent amount, the present method of design requires an excess amount of tensile steel.
It is the purpose of this study to see if shrinkage does give a compression stress in the steel of sufficient magnitude to warrant a reduction in the tensile steel requirements of reinforced concrete beams"--Introduction, pages 1-2.
Best, John, 1925-2015
Civil, Architectural and Environmental Engineering
M.S. in Civil Engineering
Missouri School of Mines and Metallurgy
iv, 65 pages
© 1958 C. Raymond Nowacki, All rights reserved.
Thesis - Open Access
Reinforced concrete -- Expansion and contraction
Strains and stresses
Reinforced concrete construction -- Standards
Print OCLC #
Electronic OCLC #
Link to Catalog Record
Nowacki, C. Raymond, "Effect of concrete shrinkage on stresses in reinforcing steel" (1958). Masters Theses. 5529.