The Experts below are selected from a list of 11082 Experts worldwide ranked by ideXlab platform
Hong Hao - One of the best experts on this subject based on the ideXlab platform.
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influence of the concrete dif model on the numerical predictions of rc wall responses to blast loadings
Engineering Structures, 2014Co-Authors: Yifei Hao, Hong HaoAbstract:Abstract Reliable prediction of structural responses to blast loadings requires an accurate dynamic material model. The dynamic strength of concrete material is normally higher than the static strength. Based on extensive experimental data, a number of empirical DIF (dynamic increase factor) relations have been proposed to model concrete material strength increment at high strain rates. Most of these empirical relations are obtained by fitting the scattered dynamic testing data. It is commonly acknowledged that the induced structural effects such as lateral inertia confinement effect are inevitable in high-speed impact tests. Therefore directly fitting the laboratory testing data may not necessarily obtain the true dynamic concrete material properties. Some recent studies investigated the contributions of lateral inertia and end friction confinement effects on DIF of concrete materials in laboratory tests, and proposed relations to remove these influences to obtain the true DIF for concrete materials. The present study carries out numerical simulations of a reinforced concrete wall under different blast loadings. Different DIF relations including CEB defined DIF, DIF proposed in previous studies after removing structural effect in laboratory tests, and NO DIF, i.e., neglecting dynamic strength increment, are considered in numerical simulations. Verification of the numerical model is made through the comparisons of the numerical simulation results with field test data. The results demonstrate that using the new DIF model yields the best prediction of the structural responses. The responses of a typical RC wall under blast loads with a 5 m stand-off Distance but different TNT explosive charge weights are also simulated using different DIF relations. The responses of RC wall obtained from numerical models with different DIF relations of concrete material are compared. From the numerical simulation results, the range of Scaled Distance that DIF relation has significant influences on the numerical simulation results is identified.
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numerical simulation of a cable stayed bridge response to blast loads part ii damage prediction and frp strengthening
Engineering Structures, 2010Co-Authors: Hong Hao, Edmond K C TangAbstract:Abstract This study investigates the blast loading effects on a large cable-stayed bridge. The results are presented in two parts. A companion paper by Tang and Hao (2010) [2] presents the numerical model of the bridge structure and simulation results of the four main bridge components (pier, tower, back span deck and main span deck) to blast load from a 1000 kg TNT explosion at a standoff Distance of 0.5 m and 1.0 m, respectively. This paper presents numerical simulation results of the four bridge components to blast loads of different Scaled Distances, and performs progressive collapse analyses of the bridge structure after damage in either one of the four main bridge components has occurred. The most vulnerable bridge component is identified. The safe Scaled Distance for bridge protection is determined. The effectiveness of FRP strengthening of concrete back span for blast load resistance is also investigated. It is found that the failure of vertical load-carrying components will lead to catastrophic bridge collapse while above deck explosion may cause severe instability of the bridge. It is also found that the minimum Scaled Distances for tower and pier for preventing catastrophic bridge collapse are approximately 1.20 m / kg 1 / 3 and 1.33 m / kg 1 / 3 , respectively. Numerical results presented in this study will help owners and engineers of similar bridges to determine appropriate measures for bridge protection against possible explosion loads.
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numerical simulation of a cable stayed bridge response to blast loads part i model development and response calculations
Engineering Structures, 2010Co-Authors: Edmond K C Tang, Hong HaoAbstract:Abstract Many researchers have conducted comprehensive experimental and numerical investigations to examine civilian structures’ response to explosive loads. Most of the studies reported in the literature deal with building structures and structure components. Studies of bridge structures subjected to blast loads are limited. This study performs numerical simulations of dynamic responses of a large cable-stayed bridge under explosive loadings. All numerical simulations are carried out using the LS-DYNA explicit finite element code. This paper describes the bridge under consideration, blast load estimation, finite element model, material model, and detailed numerical simulation results of the bridge to blast loads from a 1000 kg TNT equivalent explosion at 0.5 m from the bridge tower and pier, and 1.0 m above the deck. Damage mechanism and severity of the bridge tower, pier and deck are examined. The companion paper Hao and Tang (2010) [19] presents intensive numerical simulation results of the bridge components under blast loads of different Scaled Distances, progressive collapse analyses of the bridge after either one of the four main bridge components is damaged, and the safe Scaled Distance for bridge protection before initiating catastrophic collapse. The effectiveness of FRP strengthening of bridge concrete back span for blast load resistance is also investigated.
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numerical simulation of blast wave interaction with structure columns
Shock Waves, 2007Co-Authors: Yanchao Shi, Hong HaoAbstract:Accurate estimation of blast loads on structures is essential for reliable predictions of structural response and damage. Current practice in blast effect analysis and design estimates blast loads primarily based on empirical formulae obtained from field blast tests. Due to the limited availability of test data, those empirical formulae are usually applicable to the case that the reflection surface of the structure is big enough so that no wave diffraction around the structure exists. They will overestimate the blast loads on structure columns without infill walls around them, which are very common in the modern buildings, especially for the ground floor columns. For a standalone column, the initial reflected pressure may be quickly relieved at the edge of the column, and the column will be engulfed with the blast wave due to diffraction. Therefore, the interaction between the blast wave and structure is important for such columns. The blast loads on such columns will be different from those obtained in field blasting tests on walls. There is no method in the open literature to estimate blast loads on standalone columns. In the present study, interactions between blast waves and structure columns are simulated using AUTODYN 3D. The influence of the Scaled Distance of the blast, column stiffness, ratio of the supported mass to the column mass, and column dimension and geometry, on the blast wave–column interaction is investigated. Based on the numerical simulation results, some formulae are proposed to estimate the blast pressure, impulse, and the reflected pressure time history on standalone structure columns.
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numerical simulation of structural response and damage to simultaneous ground shock and airblast loads
International Journal of Impact Engineering, 2007Co-Authors: Hong HaoAbstract:Current practice in analysis and design of structures to withhold surface explosions considers only airblast forces on structures. A surface explosion, in fact, generates both ground shock and airblast pressure on a nearby structure. In this paper, the influences of simultaneous ground shock and airblast forces on structural responses are investigated. Blast-induced surface ground motions and airblast pressures estimated in a previous study are employed as input in the analysis. A previously developed three-dimensional homogenized material model for a masonry wall including the equivalent elastic properties, strength envelope and damage threshold is used to model masonry wall. Another material damage model developed for reinforced concrete structures is used for modelling RC behavior due to explosive loads. These material models are programmed and linked to an available computer program LS-DYNA3D through its user subroutine capability. A one-story masonry infilled RC frame is used as an example in the study. Dynamic response and damage of the example structure to simultaneous ground shock and airblast forces, or separately to ground shock only or airblast forces only are calculated. It is found that in general, airblast load governs structural response and damage when the Scaled Distance is small. However, under certain conditions, structural damage will be critically underestimated if ground shock is neglected. When the scale Distance increases, the relative importance of the ground shock on structure response increases, and ground shock will dominate the surface explosion effects on structures at large Scaled Distance. At large Scaled Distance, the ground shock and airblast force effects on structures decoupled and structure response and damage to ground shock and airblast force can be analyzed separately.
Ashok Kumar Mishra - One of the best experts on this subject based on the ideXlab platform.
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modified Scaled Distance regression analysis approach for prediction of blast induced ground vibration in multi hole blasting
Journal of rock mechanics and geotechnical engineering, 2019Co-Authors: Hemant Agrawal, Ashok Kumar MishraAbstract:Abstract The blast-induced ground vibration prediction using Scaled Distance regression analysis is one of the most popular methods employed by engineers for many decades. It uses the maximum charge per delay and Distance of monitoring as the major factors for predicting the peak particle velocity (PPV). It is established that the PPV is caused by the maximum charge per delay which varies with the Distance of monitoring and site geology. While conducting a production blasting, the waves induced by blasting of different holes interfere destructively with each other, which may result in higher PPV than the predicted value with Scaled Distance regression analysis. This phenomenon of interference/superimposition of waves is not considered while using Scaled Distance regression analysis. In this paper, an attempt has been made to compare the predicted values of blast-induced ground vibration using multi-hole trial blasting with single-hole blasting in an opencast coal mine under the same geological condition. Further, the modified prediction equation for the multi-hole trial blasting was obtained using single-hole regression analysis. The error between predicted and actual values of multi-hole blast-induced ground vibration was found to be reduced by 8.5%.
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Modified Scaled Distance regression analysis approach for prediction of blast-induced ground vibration in multi-hole blasting
'Elsevier BV', 2019Co-Authors: Hemant Agrawal, Ashok Kumar MishraAbstract:The blast-induced ground vibration prediction using Scaled Distance regression analysis is one of the most popular methods employed by engineers for many decades. It uses the maximum charge per delay and Distance of monitoring as the major factors for predicting the peak particle velocity (PPV). It is established that the PPV is caused by the maximum charge per delay which varies with the Distance of monitoring and site geology. While conducting a production blasting, the waves induced by blasting of different holes interfere destructively with each other, which may result in higher PPV than the predicted value with Scaled Distance regression analysis. This phenomenon of interference/superimposition of waves is not considered while using Scaled Distance regression analysis. In this paper, an attempt has been made to compare the predicted values of blast-induced ground vibration using multi-hole trial blasting with single-hole blasting in an opencast coal mine under the same geological condition. Further, the modified prediction equation for the multi-hole trial blasting was obtained using single-hole regression analysis. The error between predicted and actual values of multi-hole blast-induced ground vibration was found to be reduced by 8.5%. Keywords: Peak particle velocity (PPV), Blast-induced ground vibration, Scaled Distance regression analysis, Wave superimposition, Single-hole blastin
Jose A Sanchidrian - One of the best experts on this subject based on the ideXlab platform.
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air blast resistance of full scale slabs with different compositions numerical modeling and field validation
International Journal of Impact Engineering, 2015Co-Authors: Ricardo Castedo, Pablo Segarra, A Alanon, Lina M Lopez, Anastasio P Santos, Jose A SanchidrianAbstract:Abstract This paper investigates the advantages and accuracy of a finite element simulation of a blast loaded full-scale slab by validating the results with the corresponding field tests. For this modeling, a 3D pure Lagrangian approach using LS-DYNA with appropriate blast load routine (CONWEP), material models and suitable boundary conditions is developed. Eight full-scale slabs were cast and tested. Three standard reinforced concrete slabs with the explosive at a Scaled Distance of 0.79 m/kg1/3 were used to calibrate the numerical model. Two normal reinforced concrete (RC) slabs with the explosive charges located at Scaled Distances of 0.41 and 0.20 m/kg1/3, and three more with different constructive solutions, such as fiber reinforced concrete (steel and polypropylene fibers) or reinforced concrete protected with a steel sheet at the center of the slab, aim to study the sensitivity of the model to these changes. Field data obtained with accelerometers and pressure transducers are compared with results obtained from the numerical modeling for the calibration tests. For the others, the results from numerical model match those from field blast tests in terms of damage pattern and percentage of surface damage. The model is sensitive to the effect of Scaled Distance (explosive at lower Scaled Distance produced higher surface damage and different fracture patterns) and to different construction patterns. Reinforced concrete slabs with steel or polypropylene fibers had better blast resistance under tensile stress (bottom part of the slabs) than simple reinforced concrete. The slab with the steel sheet on top had higher surface damage on both faces than the others for the same Scaled Distance.
C H Lim - One of the best experts on this subject based on the ideXlab platform.
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re examination of peak stress and Scaled Distance due to ground shock
International Journal of Impact Engineering, 2007Co-Authors: Eng Choon Leong, Santhanam Anand, H K Cheong, C H LimAbstract:Abstract Ground motions associated with the passage of blast transients are important in two respects. Firstly, they develop as a result of the dynamic pressure pulse and are integrally related to the strains suffered by the soils. Secondly, ground motions subject nearby structures, buried or aboveground, to possible damaging vibrations. An accurate assessment of ground shock parameters, especially peak stresses, is thus essential for a reliable design against blast loading. Reliable ground shock parameters can be obtained from full-scale tests or small-scale tests complemented by numerical analyses. The US Army Corps of Engineers TM5-855-1 manual is widely used for estimates of ground shock parameters. This paper examines the TM5-855-1 estimation of the peak stresses in the light of small-scale field explosion tests in Singapore residual soils. The TM5-855-1 equations for ground shock predictions are not dimensionally consistent and become cumbersome when the need for units conversion arises. To overcome this problem, dimensionless parameters are proposed. A better understanding of the peak pressure–Scaled Distance plot in TM5-855-1 is provided using the dimensionless parameters.
Hemant Agrawal - One of the best experts on this subject based on the ideXlab platform.
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modified Scaled Distance regression analysis approach for prediction of blast induced ground vibration in multi hole blasting
Journal of rock mechanics and geotechnical engineering, 2019Co-Authors: Hemant Agrawal, Ashok Kumar MishraAbstract:Abstract The blast-induced ground vibration prediction using Scaled Distance regression analysis is one of the most popular methods employed by engineers for many decades. It uses the maximum charge per delay and Distance of monitoring as the major factors for predicting the peak particle velocity (PPV). It is established that the PPV is caused by the maximum charge per delay which varies with the Distance of monitoring and site geology. While conducting a production blasting, the waves induced by blasting of different holes interfere destructively with each other, which may result in higher PPV than the predicted value with Scaled Distance regression analysis. This phenomenon of interference/superimposition of waves is not considered while using Scaled Distance regression analysis. In this paper, an attempt has been made to compare the predicted values of blast-induced ground vibration using multi-hole trial blasting with single-hole blasting in an opencast coal mine under the same geological condition. Further, the modified prediction equation for the multi-hole trial blasting was obtained using single-hole regression analysis. The error between predicted and actual values of multi-hole blast-induced ground vibration was found to be reduced by 8.5%.
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Modified Scaled Distance regression analysis approach for prediction of blast-induced ground vibration in multi-hole blasting
'Elsevier BV', 2019Co-Authors: Hemant Agrawal, Ashok Kumar MishraAbstract:The blast-induced ground vibration prediction using Scaled Distance regression analysis is one of the most popular methods employed by engineers for many decades. It uses the maximum charge per delay and Distance of monitoring as the major factors for predicting the peak particle velocity (PPV). It is established that the PPV is caused by the maximum charge per delay which varies with the Distance of monitoring and site geology. While conducting a production blasting, the waves induced by blasting of different holes interfere destructively with each other, which may result in higher PPV than the predicted value with Scaled Distance regression analysis. This phenomenon of interference/superimposition of waves is not considered while using Scaled Distance regression analysis. In this paper, an attempt has been made to compare the predicted values of blast-induced ground vibration using multi-hole trial blasting with single-hole blasting in an opencast coal mine under the same geological condition. Further, the modified prediction equation for the multi-hole trial blasting was obtained using single-hole regression analysis. The error between predicted and actual values of multi-hole blast-induced ground vibration was found to be reduced by 8.5%. Keywords: Peak particle velocity (PPV), Blast-induced ground vibration, Scaled Distance regression analysis, Wave superimposition, Single-hole blastin
