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.