1,721,038 research outputs found
Behaviour of High Performance Fibre Reinforced Cementitious Composites under high dynamic loading and fire for safe tunnels
No full textIn this paper are described the results of an experimental study on the behavior of High Performance Fibre Reinforced Cementitious Composites under static and dynamic tension loading. This material has been developed for new segment tunnel resisting to fire and explosion. Results have shown the influence of the high temperature and the strain rate. The dynamic strength is increased by high temperature exposure, and the the toughness is progressively reduced. A change in the failure mechanism has been observed in dynamic increasing the exposure temperature
Experimental analysis on the tensile dynamic behavior of existing concrete under high strain-rates
No full textThe presented research is part of a wider research project involving the study of the dynamic behavior under extreme loads of the Tenza Bridge, a concrete arch bridge located in southern Italy. The dynamic behavior of the concrete of the bridge under tensile loads is herein investigated. Several dynamic tensile tests under different strain rates were performed on concrete specimens at the DynaMat laboratory of the University of Applied Sciences of Southern Switzerland using modified Hopkinson bars. The results were then processed in terms of strength dynamic increase factor-strain rate relationships. These are fundamental to assess constitutive laws of concrete to be implemented in analytical models of the bridge under dynamic loads. The results are compared with existing analytical formulations that attempt to predict the dynamic tensile strength of concrete. The comparisons show that, even though tested concrete was taken from an existing structure, the relationships found in the literature accurately describe its tensile dynamic behavior
Tensile High Strain-Rate Behavior of Reinforcing Steel from an Existing Bridge
No full textAs part of a research project focusing on the blast assessment of bridges, a dynamic characterization was carried out on reinforcing steel belonging to an existing structure. The steel was from a reinforced concrete (RC) arch bridge, namely, the Tenza Bridge, built in the 1960s in southern Italy. The behavior of both concrete and reinforcing steel under dynamic loading rates was investigated; the results of a test campaign on reinforcing steel are presented herein. Tensile failure tests were performed on steel specimens at different strain rates using a modified Hopkinson bar device. Data from the tests were processed to obtain stress-strain relationships under different strain-rate conditions, and the results were compared with existing formulations, providing the dynamic properties of reinforcing steel
Dynamic Behaviour of UHPFRCC in Tension
No full textUltra High Performance Fiber Reinforced Cementitious Composites belong to a new class of structural materials characterized by high strength and ductility. Thanks to the high energy absorbed during the fracture process, due to multiple cracking and pull-out phenomena, they are often suggested for dynamic loading applications. Current understanding of the dynamic response is very limited because of very few investigations have been actually carried out. An experimental research aimed at contributing to the understanding of the behaviour of advanced fiber-reinforced cementitious composites subjected to low and high strain rates was carried out. The material investigated is a Ultra High Performance Fiber Reinforced Cementitious Composites. Straight high carbon steel micro-fibers were used. The material behaviour was investigated at several strain rates and the tests results were compared with their static behaviour. Tests at intermediate strain rates were carried out by means of a hydro-pneumatic machine (HPM), while high strain rates were investigated by exploiting a Split Hopkinson Tensile Bar (SHTB). A comparison between static and dynamic tests highlighted several relevant aspects regarding the influence of fibers on the peak strength and post-peak behaviour at high strain rates. Finally, this material will be employed in the construction of an innovative tunnel segment designed for extreme conditions (high temperature and shock)
Strain-rate sensitivity of a pultruded e-glass/polyester composite
No full textStructural analysis of composite structures subjected to dynamic loads requires detailed knowledge of the mechanical behavior of component materials under high strain-rates. This paper presents the results of tests to investigate the tensile dynamic behavior of a pultruded E-glass/polyester composite used in a steel-less blast protection barrier. The described activity is part of the Security of Airport Structures research project, focusing on structural protection of airport infrastructures against disruptive action. Modified Hopkinson bars and hydropneumatic machine devices were used to conduct strain-rate controlled tensile failure tests on glass fiber-reinforced polymer specimens. The results are discussed and then implemented within a viscoplasticity constitutive model and a strain-rate-dependent failure criterion in order to simulate the exhibited mechanical behavior
Analysis of the strain-rate behavior of a basalt fiber reinforced natural hydraulic mortar
No full textFiber reinforced inorganic materials, such as concrete or mortars are expected to present good mechanical properties under high dynamic loading conditions, such as those induced by earthquakes. Furthermore, basalt fibers, which are being increasingly investigated in structural applications, are also expected to present good performance under high strain-rate conditions. This paper presents the results of a dynamic characterization of a basalt fiber reinforced natural hydraulic mortar, in order to verify its capability to withstand high dynamic loading conditions. In particular, the reinforced mortar was morphologically characterized by SEM and mercury intrusion porosimetry; then, quasi-static flexural and tensile tests were conducted. Finally, dynamic tensile failure tests were carried out at medium and high strain-rates, using a Hydropneumatic machine and a Modified Hopkinson bar apparatus, respectively. The results were elaborated to derive Dynamic Increase Factors for the tensile strength. The fiber addition leads to a bridge action effect, and consequently to a more ductile behavior and higher toughness of the fiber reinforced mortar compared to a plain mortar. In addition, the fiber reinforced mortar appears to be highly strain-rate sensitive, as the tensile strength DIF increased up to 5.1, for a high strain-rate of about 102 s-1
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