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Experimental study of reinforced concrete beams without stirrups under impact: performance evaluation and structural response Experiments on reinforced concrete beams without stirrups are often utilized as a simplified basis to calibrate numerical models of reinforced concrete slabs. This paper details an experimental study on the behavior of reinforced concrete beams without stirrups subjected to impact loading. For this study, the 11‐meter‐high drop tower at the Otto Mohr Laboratory of TU Dresden was used to accelerate a cylindrical impactor with a diameter of 100 mm. Compressed air accelerated the impactor to velocities between 2.7 m/s and 25.8 m/s. The impactor masses were 14.22 kg and 21.66 kg, respectively. Data on impactor and support forces, displacements, and accelerations were collected. Digital image correlation supplemented the measurements. The study revealed that the behavior of the beams exhibited different failure modes depending on the impactor velocity and mass. The shear cracks started to form at impactor velocities of approximately 11 m/s, corresponding to the lighter impactor's kinetic energy of 860 J. Furthermore, the formation of a punching cone near the loading point at impactor velocities of around 22 m/s was observed. These findings provide valuable insights for designing and thoroughly assessing the performance of shear‐deficient reinforced concrete beams under impact loading. The results serve as a foundation for enhancing the precision and reliability of numerical models, facilitating further investigations into complex structural systems. [ABSTRACT FROM AUTHOR]

Carbon concrete sandwich elements under impact load – numerical and experimental investigation This article examines the extent to which carbon concrete sandwich elements can contribute to building protection as prefabricated walls. The composite material carbon concrete enables thin‐walled constructions due to the corrosion‐resistant reinforcement. The sandwich panel consists of two 3 cm thin carbon concrete layers. Between the layers 8 cm of mineral fibre wool is placed as an insulating layer. Thanks to the layered structure, prefabricated parts can be produced that fulfil the requirements for load‐bearing capacity and building physics and can be used as wall elements in building envelopes. The article examines the extent to which such a sandwich wall element can provide structural protection against impact loads, such as those that can occur as a result of severe weather situations due to changed climatic conditions or anthropogenic causes. For this purpose, an impact test was carried out in the drop tower facility at TU Dresden. The damage caused by the impact, carried out with the compressed air‐accelerated mode of the drop tower facility, with a mass of 8.4 kg at an impact velocity of 35 m/s in the carbon concrete sandwich panel is investigated. In the experimental investigation, the fotogrammetrically determined accelerations and deflections are documented. In addition, the punching shear failure and the perforation of the carbon concrete sandwich panel are analysed in numerical simulations and the results are compared with the experimentally determined data. [ABSTRACT FROM AUTHOR]

The influence of water saturation on the compressive strength of concrete under high strain rates In this study, the influence of different water saturation achieved by different storage conditions on the static and dynamic com‐pressive strength of three different concretes were investigated. The specimens were first dried then water‐saturated and tested both under static and impact loading. The impact tests were carried out in a split Hopkinson bar. Depending on the concrete strength class, increases in the compressive strength of 200 % to 300 % at strain rates in the range of 90 to 160 1/s were observed. Compared to storage under ambient conditions, the compressive strength decreases as a result of drying due to microcrack formation. Furthermore, the concretes compressive strengths of water‐saturated specimens decrease compared to dry specimens. This decrease was observed under both static and impact loading and is independent of the strain rate. The failure of the dry specimens was more explosive with an increased number of cracks compared to water‐saturated specimens. Furthermore, two drop tower tests with an unsaturated and a water‐saturated large‐format concrete specimen showed that the increase in pore water content significantly influenced the failure pattern and decreased the reaction forces. This article was published in a similar way in [1]. [ABSTRACT FROM AUTHOR]

Mineral‐bonded composites for enhanced structural impact safety: material level investigations The Research Training Group GRK 2250/1 „Mineral‐bonded composites for enhanced structural impact safety" aims at the development of novel strengthening materials with various types of fiber reinforcement for enhancing the impact resistance of the critical infrastructure. Adequate testing methods and evaluation protocols are developed for a fundamental material characterization including the rate effects. The experimental results form an important basis for formulating numerical models for simulations of the composites, strengthening layers and concrete elements by linking different space and time scales. Finally, methods for evaluating the sustainability and resilience of the developed strengthening solutions and materials are developed. [ABSTRACT FROM AUTHOR]

Structural dynamic behavior of reinforced concrete slabs under impact loads for variable velocities The present paper describes essential results of comprehensive experimental investigations of the analysis of rc‐slabs under impact loads. The presented work was done in collaboration between the Fraunhofer Institute for High‐Speed Dynamics – Ernst‐Mach‐Institut (EMI) and the Technical University of Dresden (TUD) in the national research project "impact on concrete structures – experiment and simulation" sponsored by the DFG (Deutsche Forschungsgemeinschaft). In a comprehensive test series the loading of a so‐called hard impact – that means the kinetic energy is almost completely introduced in the structure – was studied for different velocity ranges (4.2–6.0 m/s; 44–67 m/s and 200–274 m/s). The resulting damage phenomena and the dynamic structural response were measured by extensive instrumentation (strain gauges, pressure sensors, laser and high‐speed cameras). The received data for low and high strain rates serves for the general understanding of the relations between local transient loading and global structural response. It is the basis for the adaption of existing material models, the development of engineering models and the validation of numerical calculations. [ABSTRACT FROM AUTHOR]

Non-destructive testing of protective components by using the impact echo method Military facilities of the German Armed Forces are a possible target for attacks when deployed in an area of conflict. For this reason, the protection of operational facilities by means of massive protective components is of great importance. Contact detonation tests were conducted on test specimen made from reinforced concrete as well as steel fibers reinforced concrete, aiming at developing engineering models for the dimensioning of the components with respect to impacts with high load velocities. The damage caused by the contact detonation in the component was determined by using a method of nondestructive testing. The aim of this study is to evaluate the impact echo (IE) method for this particular field of application. The investigations showed that the IE-method was suitable for determining the size of the damaged area, but not for detecting the exact damage depth at each individual measuring point. Hence future experimentations with further nondestructive test equipment, such as the georadar, will be conducted and evaluated. [ABSTRACT FROM AUTHOR]

Bond between concrete and reinforcement under high dynamic loading In addition to the well-planned loads during life-cicle in usual structures, buildings such as embassies, military infrastructure or nuclear power plants must withstand also threads like impact and explosion due to terrorist atacks. These dynamic loads are leading to high strain rates in the construction materials. It is well known, that the mechanical properties of concrete and steel as well as their interaction change with an increase of the loading rate. The knowledge of the rate dependent bond behavior is the condition for the nonlinear analysis of high-dynamic stressed reinforced structural components, if system reserves should be activated by the formation of plastic hinges, a sealing effect against fluids and gases has to be ensured and the crack width or the deformation should be limited. The bond behavior between steel and concrete under high loading rates has been investigated. Different test configurations have been developed and an extensive test program has been performed. The results served as a basis for the development of a model for the bond behavior, where the influence of high strain rates is considered. [ABSTRACT FROM AUTHOR]

Defects in laminated composite structures like voids and impact damages have a major influence on the fatigue behaviour. These defects may occur in the manufacturing process and during lifetime of composite parts and lead to matrix cracks within single layers and to delaminations between adjacent layers with different fibre orientations. We investigated the relationship between voids and impact damage and fatigue lifetime. Specimens made of a glass fibre non-crimp fabric were produced by vacuum assisted resin infusion. Voids were introduced by air-bypass simulating a leakage during the vacuum assisted resin infusion-process. Impact damage was induced using a canon. Stringer-panels with the basic dimensions of 1000 mm × 1200 mm and a radius of 1980 mm were tested under multiaxial load situations in a hexapod test rig and a tension/compression-shear test rig. [ABSTRACT FROM AUTHOR]

Metrological challenges analyzing high dynamic impact on reinforced slabs The comprehension of high dynamic impact processes on reinforced concrete structures is of essential importance for the dimensioning of structures regarding exceptional loading scenarios like airplane impacts. Since, for high strain rates in comparison with quasi-static conditions an altered material behavior appears, an adequate methodology and application of appropriate measurement is required to assess the structural behavior of building components. The present paper describes the metrological methodology and the challenges of the experimental investigations of reinforced concrete slabs under impact with loading periods of only a few μs or ms. The determination of time history curves of impact velocities, bearing forces, displacements and the determination of sound wave velocities inside the structure requires an appropriate high sampling rate with the signal recording. The results lately lead to a holistic assessment of the structural behavior and the damage phenomena of such processes. [ABSTRACT FROM AUTHOR]

Hochduktile Betone mit Kurzfaserbewehrung (meist Polyvinilalkohol‐ oder hochmodulige Polyethylenmikrofaser) sind neue zementgebundene Hochleistungswerkstoffe, die unter Zugbeanspruchung eine Verfestigung aufweisen und eine im Vergleich zu gebräuchlichen Faserbetonen mehr als einhundertmal höhere Bruchdehnung besitzen. Neben ihrer großen Verformungsfähigkeit sowie hohen Biegezug‐ und Schubfestigkeit weisen hochduktile Betone bis zur Bruchdehnung sehr geringe Rissöffnungen auf. Diese besonderen Eigenschaften machen diese neue Betonart für spezielle Anwendungen sowohl bei Neubau als auch bei Verstärkung und Instandsetzung von bestehenden Bauwerken interessant. Dieser Aufsatz gibt einen Überblick über die baustofflichen Grundlagen, die Eigenschaften und Anwendungsmöglichkeiten der neuen Faserbetonart. Strain‐hardening cement‐based compositesMaterial design, properties and applications in construction Strain‐hardening cement‐based composites (SHCC) are new, high‐performance materials reinforced in most cases with either polyvinyl‐alcohol or high‐density polyethylene fibre. These composites exhibit strain‐hardening behaviour under tensile loading. They have a strain capacity on an order of magnitude of more than one hundred times that of ordinary fibre‐reinforced concrete. SHCC have relatively high tensile and shear strengths and up until reaching strain capacity yield only very narrow, multiple cracks. These specific features make this new type of concrete attractive for a number of practical applications both in new construction and in the repair and strengthening of existing structures. The article at hand provides an overview of SHCCs' material design as well as of their mechanical performance, durability and fields of application. [ABSTRACT FROM AUTHOR]

Der vorliegende Beitrag beschäftigt sich mit hochdynamischen Einwirkungen auf das Material Beton und auf Stahlbetonkonstruktionen. Zunächst werden die Grundlagen zu den hochdynamischen Einwirkungen Explosion und Impakt kurz beschrieben. Materialien verhalten sich unter diesen Einwirkungen anders als unter statischen Einwirkungen, weshalb auf die Materialmodellierung eingegangen wird. Verfahren der Strukturdynamik können bei Einwirkungen, die lediglich über Millisekunden wirken, gar nicht oder nur in Ausnahmefällen eingesetzt werden. Die sogenannten Hydrocodes sind hier besser geeignet. Anschließend wird gezeigt, wie Stahlbetonkonstruktionen im baulichen Schutz eingesetzt und dimensioniert werden. Um die Anforderungen an die Schutzelemente zu erfüllen, ist die konstruktive Durchbildung von besonderer Bedeutung. Hierfür werden Beispiele aufgeführt. Concrete and Reinforced Concrete Structures Subjected to Explosion and Impact The present paper deals with high dynamic loads acting on concrete material and on reinforced concrete structures. First the explosion and impact events are described briefly. The behavior of materials subjected to high speed loading is different from the behavior under static loads. Therefore concrete material modeling will be shown. Methods of structural dynamics can usually not be applied because high dynamic loads only act over a time period of milliseconds. Therefore a class of hydrocodes will be used. Further the design of reinforced concrete structures which are subjected to explosion and impact is presented. In order to meet the design requirements the corresponding structural detailing has to be considered. Examples will be presented. [ABSTRACT FROM AUTHOR]

In diesem Beitrag werden der Entwurf und der Aufbau eines zweiaxialen Split-Hopkinson-Bars und erste experimentelle Ergebnisse vorgestellt. Um das Verhalten von Materialien unter stoßartigen also dynamischen Belastungsbedingungen zu ermitteln, ist der Split-Hopkinson-Bar eine etablierte Versuchsmethode. Dabei ist es möglich, Proben definiert einaxial und mit Verzerrungsraten von 50 bis 150 1/s zu belasten. Mit dem zweiaxialen Versuchsstand soll das Materialverhalten von Betonen unter zweiaxialen dynamischen Belastungszuständen untersucht werden. Daher muss die zu entwickelnde Versuchsanlage hinsichtlich der zu untersuchenden Betone, hinsichtlich der zu untersuchenden Verzerrungsraten bzw. Belastungsgeschwindigkeiten sowie hinsichtlich einer synchronen zweiaxialen Belastung konzipiert werden. Design and construction of a biaxial Split-Hopkinson-Bar The Split-Hopkinson-Bar setup is a widely used method to determine the dynamical properties of materials under high loading rates. From these experiments, a rise of the concrete compression strength with increasing loading rate is known. Furthermore, an increase of compression strength under multiaxial static loading conditions is known. For the purpose to study the effect of multiaxial compression and concurrently high loading rates, a biaxial Split-Hopkinson-Bar has been designed and built up. With this test facility strain rates up to 150 1/s can be reached. The design of this biaxial Split-Hopkinson-Bar requires the consideration of the material strength of the test specimens, the loading rates and the synchronisation of two gas guns. [ABSTRACT FROM AUTHOR]