Papers by Keyword: Dynamic Increase Factor

Abstract: The dynamic mechanical properties (stress-strain diagram, ultimate stress, ultimate strain and strain rate) and of high strength concrete (HSC) with 5% and 10% silica fume (SF) addition at high strain rate of 10 s^-1 to 10² s^-1 (3.8 MPa, 4.1 MPa and 4.8 MPa) are determined using Split Hopkinson Pressure Bar equipment. The compressive strength of the HSC at design strength of 80 and 90 MPa is also determined. Results show that the compressive strength of the 5%SF and 10%SF HSC are 83 MPa and 92 MPa, respectively. The dynamic stress-strain diagrams show that the higher the pressure load, the higher the values of ultimate dynamic stress, σ_u and the ultimate strain rate, ἐ_u for both percentages of SF addition concrete. The ultimate dynamic stress, σ_u are between 200 – 250 Mpa and the ultimate strain rate, ἐ_u is in the range of 95 s^-1 and 160 s^-1. The ultimate dynamic strain, ε_u between 0.005-0.008 mm/mm. The dynamic increase factors (DIF) of the HSC are more than 2 compare to normal strength concrete.

Abstract: Considerable amount of studies on the ductility and flexural behaviour of normal and high strength concrete elements under static load can be found in literature. However, most of the previous theoretical investigations on moment-curvature (M-φ) relationship of concrete elements to calculate curvature ductility and flexural capacity did not take account of the strain-rate effect on the material models. M-φ analysis of concrete elements under dynamic loading are often conducted with material models developed for quasi-static load by applying Dynamic Increase Factors (DIF) to the material properties to reflect the strain-rate effect. Depending on magnitude and duration of applied dynamic load, element stiffness and boundary condition strain-rate varies over the cross section. Thus, the application of DIF to modify peak material properties often fails to reflect the strain-rate effect reliably. The improvement of using material model which incorporated strain-rate in its constitutive equations has been explored in this study. The effects of reinforcement amount, grade and concrete strength on curvature ductility for different strain rates have been studied using material models which have strain-rate effects included in theirs formulation. Based on the parametric study, a simple formula to estimate curvature ductility for concrete elements under explosive loads (high strain-rates) has been proposed.

Abstract: An explosion is defined as a large-scale, rapid and sudden release of energy. Explosions, such as a bomb explosion within or immediately nearby a building and a gas-chemical explosion, can cause catastrophic damage on the building's frames, collapsing of walls, blowing out of large expanses of windows, and shutting down of critical life-safety systems. In fact, an explosion may result in large dynamic loads, greater than the original design loads, of many structures. Blast phenomenon and blast efforts have been made during the past several decades to develop methods of structural analysis and design to resist blast loads. The analysis and design of structures subjected to blast loads require a detailed understanding of blast phenomena and the dynamic response of various structural elements. This paper introduces different methods to estimate blast loads, also presents a comprehensive overview of the effects of explosion on RC structures.

Abstract: Fiber reinforced inorganic materials, such as concrete or mortars, are expected to present good mechanical properties in case of high dynamic loading conditions, as those induced by impact or blast actions. Furthermore, basalt fibers, recently widely investigated in structural applications, are also expected to present good performance in case of high strain-rate dynamic conditions. The present paper presents the results of a dynamic characterization of basalt fiber reinforced mortar, carried out at DynaMat laboratory of the University of Applied Sciences of Southern Switzerland. Dynamic tensile failure tests have been conducted on mortar samples at selected strain rates, using a Modified Hopkinson bar apparatus.

Abstract: This paper presents a laboratory experimental study on the effect of high strain rate on compressive behavior of plain and fiber-reinforce high-strength concrete (FRHSC) with similar strength of 80-90 MPa. Steel fibers, polyethylene fibers, and a combination of these were used in the FRHSC. A split Hopkinson pressure bar equipment was used to determine the concrete behavior at strain rates from about 30 to 300 s^-1. The ratio of the strength at high strain rates to that at static loading condition, namely dynamic increase factor (DIF), of the concretes was determined and compared with that recommended by CEB-FIP code. Fracture patterns of the specimens at high strain rates are described and discussed as well. Results indicate that the CEB-FIP equation is applicable to the plain high strength concrete, but overestimates the DIF of the FRHSC at strain rates beyond a transition strain rate of 30 s^-1. Based on the experimental results, a modified equation on DIF is proposed for the FRHSC.

Abstract: The present work concentrates on the model of concrete under dynamic loading. The stochastic damage constitutive model for concrete under static loading developed by the authors’ research group is firstly reviewed in this paper. The strain rate effect is considered as viscous effect so that the dynamic generalization of the static model could be developed by analogy with viscous-plastic theory. Combined with static damage expressions, the frame work of dynamic stochastic damage constitutive relationship for concrete is established. The analytical expression of dynamic increase factor (DIF) of peak stresses under tension and compression are derived according to the present dynamic damage model. Several simulation results of concrete under static as well as dynamic loading are provided to demonstrate its capacity of reproducing the salient features experimentally observed.