1,720,998 research outputs found
Progressive collapse induced by fire and blast
Full text linkComprehensive finite element modelling of key elements is essential to improve the robustness assessment of structures subjected to a coupled effect of fire and blast. Focusing the attention on steel structures, a method for a realistic multi-hazard approach is presented. The problem has been investigated at the material level first and then at the structural level. The material level was studied performing a detailed experimental investigation in a wide range of strain rates and temperatures. A typical structural steel, namely S355, has been studied. A Split Hopkinson Tensile Bar equipped with a water-cooled induction heating system was used for the mechanical characterisation at high strain rates (300 1/s, 500 1/s and 850 1/s) and in a wide range of temperatures (20C, 200C, 400C, 550C, 700C and 900C). A Hydro-Pneumatic machine and a universal electromechanical testing machine were used for intermediate (5 1/s and 25 1/s) and quasi-static (0.001 1/s) strain rate tests at room temperature, respectively. Results showed that the S355 structural steel is strain rate sensitive, keeping its strain hardening capacity with increasing strain rates. The temperature effect was studied by means of the reduction factors for the main mechanical properties. Results at high strain rates highlighted also the blue brittleness phenomenon between 400C and 550C. The link between the material and the structural level is a material constitutive law able to take into account the strain rate sensitivity and the thermal softening. The widely used constitutive law proposed by Johnson and Cook was calibrated using the experimental results. A critical review of this material model highlighted a perceptible variation of the thermal softening parameter at different temperatures. Following a fitting approach, a modification of the dimensionless temperature (T*) has been proposed.The structural level was numerically investigated adopting the calibrated material model. Explicit non-linear dynamic analyses of a steel column under fire conditions and followed by an explosion were performed. The commercial code LS-DYNA was used. A method for a realistic multi-hazard approach has been proposed by studying the residual load bearing capacity. The results can be also of great interest to establish the initial conditions that could potentially lead to the onset of progressive collapse in steel framed structures under a combined effect of fire and blast. As expected, the results indicated that the load bearing capacity is influenced by the stand-off distance, the charge size as well as the column boundary conditions. The time of fire loading at which an explosion is triggered is a critical parameter as well
Strain rate effects on reinforcing steels in tension
No full textIt is unquestionable the fact that a structural system should be able to fulfil the function for which it was created, without being damaged to an extent disproportionate to the cause of damage. In addition, it is an undeniable fact that in reinforced concrete structures under severe dynamic loadings, both concrete and reinforcing bars are subjected to high strain-rates. Although the behavior of the reinforcing steel under high strain rates is of capital importance in the structural assessment under the abovementioned conditions, only the behaviour of concrete has been widely studied. Due to this lack of data on the reinforcing steel under high strain rates, an experimental program on rebar reinforcing steels under high strain rates in tension is running at the DynaMat Laboratory. In this paper a comparison of the behaviour in a wide range of strain-rates of several types of reinforcing steel in tension is presented. Three reinforcing steels, commonly proposed by the European Standards, are compared: B500A, B500B and B500C. Lastly, an evaluation of the most common constitutive laws is performed
Influence of the temperature on the tension behaviour of EUROFER97 alloy at high strain rate
No full textThis paper presents an experimental investigation on the influence of the temperature on the reduced activation steel Eurofer97 under uniaxial tensile loads at high strain rate. Round undamaged specimens of this material having gauge length 5 mm, diameter 3 mm, were tested in universal machine to obtain its stress-strain relation under quasi-static condition (0.001s−1), and in modified Hopkinson bar to study its mechanical behaviour at high strain rates (300 s−1, 1000 s−1) respectively. The tests at high strain rate were carried out at 450 °C and at nitrogen temperature. Finally, the parameters of the Zerilli-Armstrong constitutive material relationship were obtained
Strain rate behaviour in tension of austenitic stainless steel used for reinforcing bars
No full text
Mechanical properties of s355 under extreme coupled effect of high temperatures and high strain rates
No full text
Experimental analysis of the UHPFRCs behavior under tension at high stress rate
No full textThe results of experimental investigation on the tensile response of UHPFRCs under high stress rates are presented. The dynamic tests are carried out on notched cylindrical specimens using a Split Hopkinson Tensile Bar. The material behavior of UHPFRC and its matrix (UHPC) is investigated at four high stress rates (from 400 to 1000 GPa/s). The rate sensitivity of the UHPFRC and UHPC in tension is evaluated in terms of Dynamic Increase Factor (DIF) of their peak strength. Finally, two different coring orientations on UHPFRC having 3, 4 and 5% fiber content are considered
- …
