Andrzej Seruga

In the paper there are presented the selected mechanical properties of granite concrete used to construction of Rędziński Bridge. Based on the compressive strength and the modulus of elasticity values, resulted from the experimental investigations, it was evaluated the commonly used relationship for prediction the modulus of elasticity based on the compressive strength.

The paper gives a detailed description of strengthening of reinforced concrete beams with CERP materials. A review of the building structure, the results of monitoring its technical state and the methods used to strengthen it are included. The strengthened beams are a part of an industrial hall roof support structure. The beams were strengthened with pretensioned carbon fiber strips in flexure and composite fabrics in shear. It was the first implementation in Poland of strengthening an RC structure by pre-stressing with CFRP strips. Nonlinear FEM analysis has been used to evaluation the effectiveness of strengthening method.

The paper presents researches, which were conducted in the world on torsional behavior of prestressed concrete elements. Particular attention is paid to researches carried out in the North America and the Middle East. Some experiments, which took place before 1978 are mentioned. More recent researches from 1978–2011 are discussed. Older experiments were conducted on typical elements, which did not contain any strengthening. Researches on elements with openings, and specimens made of concrete containing steel fibers or strengthened with CFRP sheets are also presented. Experiments connected with sustained torque are discussed.

Nowadays reinforced concrete bending elements are strengthened most often using post-tensioning technology with unbonded steel tendons or CFRP materials. Type of material used to strengthen of the building structure is selected based on the real conditions of structure exploitation as well as structural solution, accessibility to element and anticipated strengthening effectiveness. Values of post-tensioning forces are known based on measured jack pressure, concrete strains in selected cross sections and girder deflection. In case of strengthening the cracked elements, the cracks should be injected with epoxy resin before start to strengthen. The method of injection should be suitable to values of crack widths. In case of many cracks, some of them (small cracks) are unfilled. It can be supposed their presence have influence for strengthening effectiveness evaluation of reinforced concrete elements.

In the paper there are discussed the problems dealing with the calculation of transmission length, development length and anchorage length in prestressed concrete elements according to codes: Model Code 1990, 2010; PN-EN 1992-1-1:2008. Additionally the codes DIN 1045-1 and ACI 318 were taken into consideration. Calculation example for prestressed concrete tank wall panel under construction, has pointed the serious difference in obtained values of transmission length from experimental investigation and from codes relationship.