The article analyses the calculation of the deflection of reinforced concrete beams strengthened with fiber reinforced polymer. This paper specifically focuses on estimating deflection when the yielding of reinforcement is reached. The article proposes a simple method for calculating deflection that was compared with the experimentally predicted deflection. The carried out comparison has showed that the proposed method is suitable not only for the strengthened beams but also for the reinforced concrete beams with a varying reinforcement ratio. The suggested calculation method is based on the effective moment of inertia, such as the one introduced in the ACI Committee 318 Building Code Requirement for Structural Concrete (ACI318). The development of deflection was divided into three stages, and equations for the effective moment of inertia were proposed considering separate stages. In addition, the put forward equations were modified attaching additional relative coefficients evaluating a change in the depth of the neutral axis.

The study analyses the behaviour of concrete and reinforced concrete columns strengthened with a High-performance Fiber-reinforced Cementitious Concrete (HPFRCC) jacket. For that purpose, experimental and nonlinear numerical analysis was accomplished. The development of deformations was divided into separate stages at each of which the behaviour of different materials was highlighted. Consequently, an analytical approach to load carrying capacity was proposed. The approach evaluates the elastic, elasto-plastic and pure plastic behaviour of a separate material. According to the proposed method, a possibility of predicting the stiffness of the strengthened element at the desired load level can be considered. The experimental results of all tested columns were compared with numerical results. A comparison of experimentally and numerically predicted deformations showed good coincidence only up to a particular load level. When the decomposition such us cracking of the material starts, inappropriate coincidence can be noticed.

The article analyses behavior of compressed concrete cylinders which were strengthened with external high performance fiber reinforced cementitious composite (HPFRCC) layer. Two different HPFRCC materials were used for the strengthening, which differed in fiber type. Two different types of loading were applied as well. The load was transferred through the whole cross section of the strengthened element and through the core – internal concrete. Loading through the whole cross section allows to validate the mixture law. Loading through the internal concrete allows to investigate the confinement effect. Comparison of theoretically calculated and experimental strength shows that mixture law and confinement effect is valid. Confinement by HPFRCC allowed to increase the strength of concrete about 4 times, but the ultimate strain remains similar. The strength of elements loaded through the whole surface has increased much more and additionally the ultimate strain has increased too. Keyword : concrete, strengthening, HPFRCC, confinement, compressive strength This work is licensed under a Creative Commons Attribution 4.0 International License.

Different strengthening technique was evaluated in order to investigate the effect of prestress. The analysed beams were strengthened with non-prestressed CFRP and prestressed CFRP at different loading levels. It has allowed a better understanding about strengthening effectiveness. Results obtained by finite element analysis were compared with experimental results obtained by other researchers. Phased nonlinear analysis was used to simulate the behaviour of the strengthened beams. Performed analysis showed that it is possible to use finite element analysis in order to investigate a real behaviour of the strengthened elements in real structure.

The paper describes the behaviour of the sandwich panels in bending. Two panels of the same dimensions are tested. The panels differ only in the layout of the inner thermal insulation layer. The thermal insulation layer is made of separate mineral wool slabs. The graphs of the strain development in the external sheets, the displacement between the layers and mid-span displacement are presented in the paper. The nature of the failure shows that only separate internal thermal insulation slabs resist the shear force. Therefore, the complete width resistance cannot be evaluated. The views of the failure are also presented.