# Structural Behavior of Large-Scale I-Beams with Combined Textile and CFRP Reinforcement
## 1 Introduction  
Global mega trends such as climate change, growth of population with further urbanization, and increase of land consumption as well as further increase in mobility require great efforts from society in general and the construction sector in particular. Construction industries world-wide will struggle to meet the demands of those mega trends with established methods and incremental innovations thereof. Completely new approaches and radical innovations are called for. Carbon concrete composites or carbon reinforced concrete (CRC) and textile reinforced concrete (TRC) qualify as such disruptive innovations [1], which are atypical for the building sector. Indeed, using those materials enables a complete rethinking of established construction strategies [2; 3; 4; 5]. The higher tensile strength of reinforcement fibers such as carbon compared to typical reinforcement steel, combined with the complete insensitivity to corrosion, allows for optimization of cross-sectional designs. Often, the potential of reduction of CO\({}_{2}\)-consumption by use of CRC in new structural components is highlighted [6; 7]. This is said to be achieved through reduction of concrete mass (and especially cementitious binder) by minimization of concrete cover, member web thickness, and consequently dead load. Here, the ideaof merely replacing steel reinforcement is prevalent. Equally important is the extension of lifespan of new concrete components which is enabled by better durability of the reinforcement materials [8], especially in environments with severe exposition. The same reasoning applies for strengthening of existing structures with non-metallic reinforcement [9; 10]. By extending lifespan, the embodied CO\({}_{2}\) in concrete parts can be spread over a longer period of use, and furthermore, cost-efficiency increases. Decrease of life-cycle cost for certain applications through use of non-metallic reinforcement (see for example [11; 12]) might be the most convincing argument for most stakeholders in construction. This is typically the case when maintenance-intensive additional polymeric coatings are no longer needed [13; 14; 15]. Despite those advantages, market share of non-metallic reinforcement is still negligible, and thus the potential effect on consumption of resources is limited. One explanation next to higher initial investment costs for production of elements [16] might be the shortfall of a comprehensive set of design models and standardized test procedures based on fundamental research. World-wide, first building codes were established for use of fiber reinforced polymer (FRP) reinforcement [17; 18; 19], but in Europe, an implementation is still pending. Even then, design rules might be insufficient: New construction strategies really exploiting the potential of thin, non-metallic reinforced membranes are lacking. Instead, engineers try to keep conventional principles and cross-sections, just replacing the steel. The C\({}^{3}\)-initiative [20], a large-scale coordinated research program in Germany, examines various facets of the topic in depth: Fundamental research, potential applications, and market penetration. This study presents results from the final stage of this project, focusing on engineering models, design approaches and standardization of test methods for CRC constructions. With experimental and subsequent numerical investigations of large-scale I-beams, verification of approaches to design and calculation of members with mixed carbon fiber reinforced polymer (CFRP) reinforcement in serviceability limit state (SLS) and ultimate limit state (ULS) is possible. We should mention that the idea of combining (different) textiles and FRP-bars is not new. Previous application examples from practice are facades [21; 22], pedestrian bridges [23; 24], or precast elements [25]. [PERSON] et al. conducted studies on slender I-beams with mixed reinforcement [3]. [PERSON] [24; 26] investigated beams with CFRP prestressing strands and textile shear reinforcement. [PERSON] et al.