Reinforced concrete (RC) is by far the most widely used composite material in the world. Despite the enormous economic importance of RC construction, there is a lack of viable concepts for its digital fabrication. While 3D printing of plain concrete has been pushed forward by a growing research community in recent years, methods for integration of steel reinforcement have only scarcely been researched and little attention has been payed to meet the practical requirements of construction sites and prefabrication plants. Therefore, full-scale implementations of current approaches are hardly available. Based on both, a sound review of R&D for digital fabrication of RC structures and an analysis of practical requirements, the present paper proposes a novel 3D printing process for RC structures, called Additive Manufacturing of Reinforced Concrete (AMoRC), viable for real-world application. In this hybrid process, consisting of an intermittent stud welding process and a continuous concrete extrusion process, segmented steel reinforcing bars are joined to form a three-dimensional reinforcement mesh and simultaneously encased with extruded concrete. The paper describes the conceptual design and development of the process and demonstrates the results of preliminary investigations on its feasibility. As AMoRC enables the operation of rebar welding and concrete extrusion process with synchronized feed rates, combination of both processes in one hybrid print head for digital fabrication of RC is a key-advantage of the proposed method.

The intention of this paper is to clarify the mechanisms of mixed mode fracture and shear stress transfer in plain concrete. To capture these scarcely explored phenomena, a new mechanical formulation is proposed called the fictitious rough crack model (FRCM). The FRCM considers mode I deformations to control crack formation and residual tensile stress transfer, while mode II deformations are assumed to induce shear stress transfer along the crack surfaces and compressive normal stresses attributed to aggregate interlock. The fundamental idea of the FRCM is to combine these tension-softening and shear-transfer laws and to superimpose the emerging shear and normal stresses of both mechanisms in the crack. The paper illustrates the analytical development of the FRCM and its numerical implementation. Three well-known experimental benchmark problems (concrete panel test series by Nooru-Mohamed and by Hassanzadeh as well as aggregate interlock test series by Paulay and Loeber) are numerically addressed to test plausibility of FRCM results. The numerical implementation of the FRCM is capable of simulating the transition from mode-I fracture to mixed-mode fracture in the structural response and is also able to predict the crack path with reasonable agreement.

Experimental investigations on centrically loaded column bases provide the basis for current punching shear design provisions. However, this symmetric loading condition represents an exception in daily engineering practice since usually load eccentricities occur leading to uneven shear stress distributions along the control perimeter. To account for this effect, design approaches define different factors to either increase the acting shear force or to decrease the punching shear resistance in design. New punching test results of 14 eccentrically loaded and four centrically loaded column bases now allow the evaluation of design approaches depending on different geometric boundary conditions. In this new test series, the load eccentricities were systematically graded to analyze their influence on the punching behavior. Strain measurements in the multiaxial compression zone of the concrete in the column‐footing connection reveal new insights on the punching failure of column bases. As a result, a correlation between tangential concrete strains and the reduction of punching shear strength can be recognized for increasing load eccentricities. The comparison of experimentally determined load increase factors with the design results according to Eurocode 2, Model Code 2010 and the stable version of the next generation of Eurocode 2 reveals optimization potential for deriving more advanced design provisions in the future.