The Experts below are selected from a list of 1731 Experts worldwide ranked by ideXlab platform

Mark G. Stewart - One of the best experts on this subject based on the ideXlab platform.

  • Risk-based assessment of blast-resistant design of ultra-high performance concrete columns
    Structural Safety, 2021
    Co-Authors: Mark G. Stewart
    Abstract:

    Abstract In conventional structural protective design against blast loads conservative structural designs are anticipated. However, unknown factors that include threat uncertainty, blast load variation, construction methods, material quality, etc., could impact the accuracy of assessment and design, sometimes even leading to an overestimation of structural capacity to explosive blast effects or an underestimation of actual blast Pressures. In the present study, structural safety and reliability analyses of Ultra-high Performance Concrete (UHPC) columns under varying blast scenarios are performed. The variation in column dimensions, steel reinforcement, UHPC material strength, explosive range and mass, and numerical and blast load model errors are considered. The Peak Reflected Pressure and impulse from the selected blast scenarios are derived based on variation in the explosive mass and standoff distance. Failure probabilities of columns made of this emerging high performance concrete material are then estimated. It was found that for a UHPC column designed for blast the probability of major damage given an explosive blast load varies from 1 × 10−2 to 1 × 10−5 for explosive ordnance and terrorism blast scenarios. This provides a reasonable margin of safety against major structural damage. It was also found that the risk reducing benefit of blast-resistant UHPC columns can be considerable.

  • Blast Load Variability and Accuracy of Blast Load Prediction Models
    International Journal of Protective Structures, 2010
    Co-Authors: Michael D. Netherton, Mark G. Stewart
    Abstract:

    A statistical analysis of explosive blast loading field (test) data has revealed a high level of variability of Peak Reflected Pressure, impulse and time of positive phase duration for repeatable tests where variability would be expected to be a minimum. The model error (accuracy) of a widely used predictive blast load model is also assessed. A probabilistic model of blast loading is then developed that considers variability and/or uncertainty of explosive mass, net equivalent quantity of an explosive in terms of TNT mass, stand-off distance, air temperature, air Pressure, inherent variability and model error. Two widely used explosives are considered: Tritonal (military) and ANFO (terrorism). This type of statistical and probabilistic analysis is essential for structural reliability analysis of structures subject to explosive blast loading where load variability is an important contributor to damage and safety risks. It was found that the TM5-1300 design values for Peak Reflected Pressure and time of positive phase duration adequately represent median values of the probability distribution of blast loads. The TM5-1300 design values for Peak Reflected impulse were 40% higher than median values with probabilities of exceedance of only 4% to 23%. This over-estimation of actual blast loads on a structure may lead to conservative design outcomes.

Liu Wenxiang - One of the best experts on this subject based on the ideXlab platform.

  • Fiber optic method for obtaining the Peak Reflected Pressure of shock waves
    Optics express, 2018
    Co-Authors: Zhao Wang, Guangrui Wen, Wu Zutang, Yang Jun, Chen Liqiang, Liu Wenxiang
    Abstract:

    Most of fiber-optic Pressure sensors used in shock wave measurements are based on deformations of sensing elements. These approaches result in low dynamic Pressure ranges for these sensors used in the air. A novel fiber-optic method based on the relationship between Pressure and the acceleration of a diaphragm is proposed to obtain Peak Reflected Pressure of shock waves in the air. The optical sensor is designed with a thin circular diaphragm as the sensing element, and the Fabry-Perot optical interferometry is used to detect the acceleration of the diaphragm. Shock tube and explosive-blast experiments prove that the proposed fiber optic method is feasible and has the advantages of no calibration, high precision and fast response time. The proposed fiber-optic Pressure method has potential in practical applications for shock wave measurements.

Hong Hao - One of the best experts on this subject based on the ideXlab platform.

  • Characteristics of Free Air Blast Loading Due to Simultaneously Detonated Multiple Charges
    International Journal of Structural Stability and Dynamics, 2014
    Co-Authors: Nimasha Weerasingha Mohottige, Hong Hao
    Abstract:

    Extensive research has been conducted to investigate the characteristics of blast load due to single charge explosion, including numerical simulations and experimental blast tests in both unconfined and confined environments. Further, available guidelines for blast resistant design such as UFC-3-340-02 (2008) and ASCE 59-11 (2011) provide details to predict blast loads on a structure subjected to single charge explosion. However, blast load characteristics due to multiple charge explosions are poorly discussed in available literature. In this paper, commercially available Hydrocode, AUTODYN is calibrated for single charge explosions. Based on a comparison between numerical simulation and UFC prediction, correction factors for Peak Reflected Pressure and positive Reflected impulse as a function of charge weight, scaled distance and mesh size of the numerical model are proposed to minimize the errors in simulations. The calibrated AUTODYN model is then used to conduct parametric studies to investigate the effects of charge weight, scaled distance, number of charges and distance between the charges on the characteristics of free air blast load due to simultaneous detonated multiple charges. Numerical simulation results are used to derive analytical formulas for predictions of Peak Reflected Pressure ratio and positive Reflected impulse ratio between single and multiple explosions. The discussion is made on characteristics of free air blast load due to simultaneous detonated multiple charges.

  • Prediction of airblast loads on structures behind a protective barrier
    International Journal of Impact Engineering, 2008
    Co-Authors: Xiao-qing Zhou, Hong Hao
    Abstract:

    Experimental results and numerical simulations have demonstrated that a protective barrier can effectively reduce blast load and, therefore, protect structures from an external explosion. However, there are no formulae in the open literature that can be used to estimate the blast loads on a structure behind a barrier. In this paper, pseudo-analytical formulae based on numerical results are derived to estimate the Reflected Pressure-time history on a rigid wall behind a protective barrier. Numerical simulations of blast wave propagation are carried out to estimate the Peak Reflected Pressure and the impulse on a rigid wall behind a blast barrier. The shock wave front arrival time and positive phase duration are extracted from the numerical results. Pseudo-analytical formulae, which are derived from the best-fitted curves of the numerical results, are suggested. These formulae can be used with those given in TM5-1300 or other methods for blast Pressure estimation in the no-barrier case, to estimate Pressure-time histories at various building locations behind a protective barrier.

  • Reliability analysis of direct shear and flexural failure modes of RC slabs under explosive loading
    Engineering Structures, 2002
    Co-Authors: Hsin Yu Low, Hong Hao
    Abstract:

    Two loosely coupled SDOF systems are used to model the flexural and direct shear responses of one-way reinforced concrete slabs subjected to explosive loading. Incorporating the effects of random variations of the structural and blast loading properties, as well as the strain rate effect caused by rapid load application, failure probabilities of the two failure modes are analyzed. The model is capable of predicting the failure probability of the slab with random material and geometrical parameters and subjected to random blast loading. Considering the random variations of structural properties and blast loading, the failure probabilities of one-way RC slab designed according to BS 8110 (Stuctural use of concrete, parts 1 and 2 (1985)) are calculated. The effect of span length of the slab on its failure probability to blast loading is also investigated. Based on numerical results, a semi analytical boundary that separates the slab's flexural and shear failure modes is derived as a function of Peak Reflected Pressure and duration of blasting wave.

Zhao Wang - One of the best experts on this subject based on the ideXlab platform.

  • Fiber optic method for obtaining the Peak Reflected Pressure of shock waves
    Optics express, 2018
    Co-Authors: Zhao Wang, Guangrui Wen, Wu Zutang, Yang Jun, Chen Liqiang, Liu Wenxiang
    Abstract:

    Most of fiber-optic Pressure sensors used in shock wave measurements are based on deformations of sensing elements. These approaches result in low dynamic Pressure ranges for these sensors used in the air. A novel fiber-optic method based on the relationship between Pressure and the acceleration of a diaphragm is proposed to obtain Peak Reflected Pressure of shock waves in the air. The optical sensor is designed with a thin circular diaphragm as the sensing element, and the Fabry-Perot optical interferometry is used to detect the acceleration of the diaphragm. Shock tube and explosive-blast experiments prove that the proposed fiber optic method is feasible and has the advantages of no calibration, high precision and fast response time. The proposed fiber-optic Pressure method has potential in practical applications for shock wave measurements.

John R. Lacourse - One of the best experts on this subject based on the ideXlab platform.

  • The Effects Of Stenosis Geometry On The Reflected Pressure Waveform
    Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society Volume 13: 1991, 1
    Co-Authors: D.l. Lizotte, John R. Lacourse
    Abstract:

    Using a one-dimensional single artery model, the effects of varying stenosis geometry on Peak Reflected Pressure are considered. The Peak Reflected Pressures are most sensitive to stenosis length and percent constriction and not detailed stenosis shape. The results fall within a range determined earlier for axially and longitudinally symmetric stenoses of two simple shapes incorporating abrupt and gradual transitions into and out of the stenosed region. Atherosclerosis as a progressive disease requires early, preferably noninvasive, detection in order to minimize complications due to developing lesions. Early detection requires instrumentation to assess the status of the disease before symptoms are apparent. To aid in instrumentation development, the effects of varying stenosis geometries on the Reflected Pressure waveform are investigated. The basic model used is the transmission line analog developed by Noordergraaf [l]. The resulting onedimensional equations are solved using finite difference techniques [2]. Pressure and flow are calculated for each position over time in a single artery. A single stenosis is simulated within this artery of variable (axisymmetric) geometries. The aortic Pressure pulse serves as input. For the results presented, a 30 cm