Concrete shrinkage

Deformation of concrete can occur due to temperature or humidity changes. When the deformation is restrained, stresses are induced in the concrete. Shrinkage produced by drying out or cooling is of particular interest with regard to durability of... 

When the shrinkage cannot take place due to internal (e. g. the reinforcement) or external restraints, tensile stresses arise in the concrete that can lead to cracking if they exceed the tensile strength of the concrete. Shrinkage is more harmful when it takes place at early ages, i. e. when the tensile strength of concrete is extremely low. 

Figure 8. The course of shrinkage for mortars modified with SBR polymer and control concrete and next view of laboratory stand for measuring of the concrete shrinkage strains...

Prestressing loads allow for slip at anchorage, elastic shortening of concrete, creep of concrete, shrinkage of concrete, relaxation of steel stress, and frictional losses in the tendon ducts. Load factors are in accordance with the AQ/ASME Code. 

Afs = loss of prestress in steel Tendon due to concrete shrinkage (ksi)... 

The analytical determination of the gravity load distribution between the frame and the infill wall requires several considerations. First, a part of the gravity loads may be applied onto the RC columns before the construction of the infill walls because these walls could be constructed after the frame has been completed. Second, long-term effects such as concrete and masonry creep, concrete shrinkage, and brick masonry expansion with time due to water absorption can significantly affect the gravity load distribution. While refined finite element models with viscoelastic material properties can be employed for the determination of the gravity load distribution, the increased computational burden of such analyses may not necessarily produce results of increased accuracy due to lack of experimental data to allow the cahbration of multiaxial viscoelastic constitutive models. 

Concrete Shrinkage Effect Concrete shrinkage can considerably affect the performance of strengthened elements with additional layers or jackets. Tensile stresses are induced to the new concrete of the layer or jacket while there is also an induced slip at the interface between the old and the new concrete. Denarie and Silfwerbrand (2004) presented a model where the tensile stresses of the new concrete due to restrained concrete shrinkage are proportional to coefficient R. Coefficient R is characteristic of the connection between the old and the new concrete and the degree of restraint (Eq. 14). 

In the tested square prism specimens, the reduction of the concrete strength was found to range from 20 % to 30 %. This reduction was more significant for larger values of tensile stresses caused by the restrained concrete shrinkage (Lampropoulos et al. 2012a). 

Concrete Shrinkage Concrete shrinkage effect can be simulated by applying volumetric strain to the elements of the jacket. The effect of concrete creep should also be included to take into account the tensile stress relaxation. In a previous study (Lampropoulos and Dritsos 2010), in order to include creep effects, application of a volumetric strain equal to half of the free concrete shrinkage strain was proposed. 

For the modeling of the strengthened specimens, it is essential to simulate the interface between the old and the new concrete and the shrinkage effect of the new concrete. The interface can be simulated using contact elements, while concrete shrinkage effect can be simulated by applying a volumetric strain to the elements of the jacket. 

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