Influence of concrete shrinkage and creep on structural characteristics of precast and prestressed concrete shells

The actual concern for structural engineers is the failure of the structural material to meet the design safety and the safe service life of large span and wide floor space buildings. The main idea in this present report reflects the combination of the economical use of construction materials with the long and durable safe service life to cover large floor spaces, using precast and prestreseed concrete shell structural members. This paper describes the present ongoing numerical and experimental analysis model used to determine the structural long duration flexural and nonlinear deformation characteristics of reinforced precast elliptical paraboloid concrete shell elements, prestressed in both directions. Horizontal precast and prestressed edge beams supported on prestressed columns are provided to support the longitudinal edges of the shells. This present study has been based on nonlinear differential equations of the concrete matrix creep theory which reflects the correlation between the matrix stress and strain by its modulus of elasticity and on the well-known geometrical preconditions of the theory of elasticity concerning thin plates with small flexural deformations. For structural and crack predictions, the well-known virtual work principles have been used to estimate (a) transient bi-directional strains due to the matrix creep and shrinkage, (b) the resulting time-dependent bi-directional stress redistribution, as well as (c) bi-directional displacement variations in the structural shell elements and finally (d) bi-directional pre-stressing losses in the pre-stressed high yield tendons. The concrete shear stresses have been evaluated by the well-known principle of Juravskiy. A series of original test experiments with once evaluated strength parameters has been planned to be successfully used to provide encouraging support for the numerical evaluations.