This paper presents results of multiaxial strength tests on various high-performance concretes (HPCs) with uniaxial compressive strength from 58 to $94\mathrm{MPa}$ . A large number of stress ratios of biaxial compression-tension, compression-compression, and triaxial compression tests were investigated. Experiments were performed using a servohydraulic jack with variable stress ratios, whereas steel brushes were used to transfer the load to the specimen. With increasing uniaxial strength the obtained normalized multiaxial strength decreases. The results, along with mathematical approximations, are discussed for the description of failure. The formulated failure criteria for HPC can be used, e.g., in finite-element simulations. The increase in strength by acting a multiaxial compressive stress state or the decrease in strength by acting a compressive-tensile stress state related to the uniaxial compressive strength can be considered and enables a better material exploitation.

Today, the need for structural strengthening is more important than ever. Flexural strengthening with textile reinforced concrete (TRC) is a recommendable addition to already proven methods. In order to use this strengthening method in construction practice, a design model is required. This article gives a brief overview of the basic behavior of reinforced concrete slabs strengthened with TRC in bending tests as already observed by various researchers. Based on this, a design model was developed, which is presented in the main part of the paper. In addition to the model, its assumptions and limits are discussed. The paper is supplemented by selected application examples to show the possibilities of the described strengthening method. Finally, the article will give an outlook on open questions and current research.

Leaner, more filigree, and resource-saving constructions are the development goal of the in the building industry. In reinforced concrete construction, a ultra-high strength concrete was developed to achieve these goals. Due to its use and requirements, this very pressure-resistant material is no longer only exposed to static loads. In applications such as wide-span bridges, machine foundations and wind turbines, the susceptibility to vibration is also significant. Research into the fatigue behavior of the new building material is therefore very important. In this article we will discuss the effect of heating up of high performance concretes under fatigue stress. The thesis is that warming up, which was already observed by several research groups, has an influence on the fatigue strength. Changes in the strength of the concrete or residual stresses generated by heating can lead to early failure. The aim is to find the reasons for the heating and the grade of influence on the fatigue strength. A systematic test program was developed to investigate the influencing parameters maximum stress level, frequency, and maximum grain size of the concrete. Thirty fatigue tests were carried out; the results will be presented here. The influence on the temperature increase as well as on the heating rate for the individual parameters will be discussed. The results show that all three discussed parameters have a significant influence on the temperature rise. Whereas the maximum temperature reached depends strongly on the frequency, the other two parameters mainly influence the heating rate.