Iš anksto įtemptųjų gelžbetoninių elementų įtempių ir deformacijų apskaičiavimo sluoksnių modelis

Abstract

Application of refined ultimate state theories and use of high strength materials have resulted in longer spans and smaller depths of reinforced and prestressed concrete structures. Consequently, the condition of the limiting deflection rather than the strength requirement often is the governing design criterion. Long-term deflections might be up to 3 to 4 times larger than the short-term deflections. Such increments are caused by complex physical effects such as concrete creep, shrinkage and cracking, bond defects, etc. Long-term concrete creep and shrinkage deformations govern prestress losses. Structural analysis can be carried out either by traditional design code methods or numerical techniques. Although design code methods ensure safe design, they have significant limitations. Different techniques are used for strength, deflection, crack width and prestress loss analyses. Besides, most of the simplified approaches do not assess such factors as concrete shrinkage, cracking or tension stiffening. Based on a large number of empirical expressions and factors, they lack physical interpretation and do not reveal the actual stress-strain state of cracked structures. On the other hand, numerical techniques are universal and can take into account each physical effect. However, inadequacies made in the prediction of each effect might lead to significant inaccuracies when integral magnitudes such as deflection are to be assessed. Consequently, the predictions by the numerical techniques might be even less accurate than those obtained by the code methods. A new statistically verified constitutive model, called the Flexural, has been developed at Vilnius Gediminas technical university for deformational analysis of flexural reinforced concrete members subjected to short-term and long-term loading. In the present research, the Flexural deformational model has been extended for case of prestressed members. The analysis includes concrete creep, shrinkage, cracking and tension stiffening effects. It is based on the classical techniques of strength of materials, extended to application of layered approach and the use of the material diagrams of the Flexural constitutive model.