Ground Shock Research Articles

Design and Testing of a Crashworthy Landing Gear

The development of a crashworthy landing gear is presented based on the civil regulations and the military specifications. For this, two representative crashworthy requirements are applied to helicopter landing gear design: the nose gear is designed to collapse in a controlled manner so that it does not penetrate the cabin and cause secondary hazards, and the main gear has to absorb energy as much as possible in crash case to decelerate the aircraft. To satisfy the requirements, the collapse mechanism triggered by shear-pin failure and the shock absorber using blow-off valve (BOV) is implemented in the nose and main gear, respectively. The crash performance of landing gear is demonstrated by drop tests. In the tests, performance data such as ground reaction loads and shock absorber stroke are measured and crash behaviors are recorded by high-speed camera. The test data show a good agreement with the prediction by simulation model, which proves the validity of the design and analysis.

Integrated Blast Resistance Model of Nuclear Power Plant Auxiliary Facilities

Standards, guidelines, manuals, and researches refer mainly to the required protection of a nuclear power plant (NPP) containment structure (where the reactor's vessel is located) against different internal and external extreme events. However, there is no consideration regarding the man-made extreme event of external explosion resulting from air bomb or cruise missile. A novel integrated blast resistance model (IBRM) of NPP's reinforced concrete (RC) auxiliary facilities due to an external above ground explosion based on two components is suggested. The first is structural dynamic response analysis to the positive phase of an external explosion based on the single degree-of-freedom (SDOF) method combined with spalling and breaching empirical correlations. The second is in-structure shock analysis, resulting from direct-induced ground shock and air-induced ground shock. As a case study, the resistance of Westinghouse commercial NPP AP1000 control room, including a representative equipment, to an external above ground blast loading of Scud B-100 missile at various standoff distances ranging from 250 m (far range) till contact, was analyzed. The structure's damage level is based on its front wall supports' angle of rotation and the ductility ratio (dynamic versus elastic midspan displacement ratio). Due to the lack of specific structural damage demands and equipment's dynamic capacities, common protective structures standards and manuals are used while requiring that no spalling or breaching shall occur in the control room while it remains in the elastic regime. The engineering systems and equipments' spectral motions should be less than their capacity. The integrated blast resistance model (IBRM) of the structure and its equipment may be used in wider researches concerning other NPP's auxiliary facilities and systems based upon their specifications.

Direct shear resistance models for simulating buried RC roof slabs under airblast-induced ground shock

Direct shear is a known response mechanism in Reinforced concrete (RC) slabs subjected to blast loads that may cause their sudden and catastrophic failure. It poses a very serious hazard to facilities subjected to blast. The empirical equations defining the direct shear resistance function for RC elements were developed in the 1970s based on results from a limited number of static tests. These equations have been used for the analyses of structural response under blast and ground shock effects since the 1980s. However, the direct shear mechanism in the short-duration dynamic domain has not been sufficiently studied, and it was not clear if those models are accurate. New static and impact test data from shear specimens with three reinforcement ratios were used to derive modified direct shear resistance functions that were different from the resistance functions proposed in the 1970s. One must determine if the new resistance functions could accurately represent the behavior of RC slabs subjected to blast loads. Furthermore, one had to understand the behavioral differences in the numerical simulations that could be associated with the two types of resistance functions, and provide recommendations on how to most appropriately represent direct shear in such analyses. This paper is focused on the assessment of the new direct shear resistance functions in RC, and the results from the parametric study were compared results obtained with the previous empirical direct shear model and with precision field test data to provide conclusions and recommendations.

Pile response subjected to rock blasting induced ground vibration near soil-rock interface

Blasting has been widely used in mining and construction industries for rock breaking. Ground vibration induced by blasting is an inevitable side effect that may cause damage to nearby structures, if not properly controlled. In this study, response and possible damage of rock-socketed pile near soil-rock interface subjected to ground shock excitations are investigated and quantified with coupled SPH-FEM method. Results indicate that the base of the pile is relatively vulnerable and that the soil properties significantly influence on response of pile subjected to a specific blast load. Furthermore, based on the numerical results, ground vibration attenuation equation is proposed.

Dynamic assessment of partially damaged historic masonry bridges under blast-induced ground motion using multi-point shock spectrum method

We studied the partial damage effects on historic masonry bridges exposed to blast-induced ground motion. For this purpose, a historic masonry bridge in Turkey was selected to estimate its shock spectral behaviour. In order to determine these results, first, various damage was created on the restored bridge finite element model. This damage was generally selected by searching for damaged historic masonry bridges in the literature. Various critical regions on an example bridge were detected and corresponding regions were removed from the restored finite element model. Thus, partially damaged historic masonry bridge models were obtained. Dynamic calculations of the bridge are presented by using the multi-point shock response spectrum method obtained from ground motions due to a blast load. Acceleration time histories of blast-induced ground motions are obtained depending on a deterministic shape function and a stationary process. Shock response spectra determined from ground shock time histories are simulated using a MATLAB-based BlastGM computer program developed by us. The frequency-varying shock response spectra are applied to each support of the two-span historic masonry bridge. The influences of various charge weights and distances from the charge centre are also investigated in the analyses. The results from the analyses demonstrate the importance of partial damage on the historic masonry bridge, blast-induced ground motion effects, and charge weight and distance from the blast centre.

Dynamic Analysis of Tunnel in Weathered Rock Subjected to Internal Blast Loading

The present study deals with three-dimensional nonlinear finite element (FE) analyses of a tunnel in rock with reinforced concrete (RC) lining subjected to internal blast loading. The analyses have been performed using the coupled Eulerian–Lagrangian analysis tool available in FE software Abaqus/Explicit. Rock and RC lining are modeled using three-dimensional Lagrangian elements. Beam elements have been used to model reinforcement in RC lining. Three different rock types with different weathering conditions have been used to understand the response of rock when subjected to blast load. The trinitrotoluene (TNT) explosive and surrounding air have been modeled using the Eulerian elements. The Drucker–Prager plasticity model with strain rate-dependent material properties has been used to simulate the stress–strain response of rock. The concrete damaged plasticity model and Johnson–Cook plasticity model have been used for the simulation of stress–strain response of concrete and steel, respectively. The explosive (TNT) has been modeled using Jones–Wilkins–Lee (JWL) equation of state. The analysis results have been studied for stresses, deformation and damage of RC lining and the surrounding rock. It is observed that damage in RC lining results in higher stress in rock. Rocks with low modulus and high weathering conditions show higher attenuation of shock wave. Higher amount of ground shock wave propagation is observed in case of less weathered rock. Ground heave is observed under blast loading for tunnel close to ground surface.

KINEMATIC ANALYSIS FOR MULTI-COPTER UAV LANDING GEAR

The multi-copter UAV landing gear is used for ground station and shock damping for landings. The materials used in the construction of landing gears are selected by using a ( ) ∑ = − − ⋅ =

Internal explosion tests for scaled subsurface magazines

A subsurface magazine is proposed to reduce the debris and the air-blast pressure caused by an accidental explosion. First, 1/20-scale indoor explosion model tests for subsurface magazines were conducted to examine the characteristics of an air-burst and ground shock vibration. It was found from the test results that the peak blast pressure ( P0) for an overburden thickness ( T) of 50 cm was 0.84–0.98 times that for T = 15 cm, and the P0 for a loading density R = 9.0 kg/m3 was 1.09–1.39 times that for R = 4.5 kg/m3. It was also found that the maximum ground shock velocity Vmax for T = 50 cm was 0.57–1.07 times that for T = 15 cm. Second, the P0 was formulated as a function of the scaled distance Z, T, and R. Third, the Vmax was formulated as a function of Z and T. Finally, these formulae were validated using the test data obtained by performing a 1/10-scale field test.

Investigations of Structural Damage Caused by the Fertilizer Plant Explosion at West, Texas. I: Air-Blast Incident Overpressure

AbstractAn explosion occurred at a fertilizer plant in the town of West, Texas, on Wednesday, April 17, 2013, devastating a populated neighborhood. A total of 15 people were killed, and approximately 160 people were injured. Approximately 150 buildings were damaged in the explosion. The damage to affected homes and businesses was estimated to exceed $100 million. The purpose of this study was to collect on-site technical data of the explosion and gain knowledge of blast loadings and structural responses from this unprecedented explosion. Specifically, this research documented the building damages caused by the West Fertilizer plant explosion and the affected buildings’ construction and materials and evaluated the technical information for the explosion, including the blast loadings, i.e., the air-blast incident overpressures and ground shocks, on different buildings with respect to the standoff distances. A total of two technical papers have been prepared. The Part I paper (this manuscript) focused on the...

Collapse Times and Resistance of the World Trade Center Towers Based on the Seismic Record of 11 September 2001

The collapses of the World Trade Center north tower (WTC1) and south tower (WTC2), struck by terrorist attacks on 11 September 2001, produced ground tremors discernable at nearby seismic stations (Kim et al. , 2001) and, as will be shown, other stations throughout the northeastern United States. Although seismic signals produced by building collapses are not unusual (Holzer et al. , 1996), the mass of the falling World Trade Center (WTC) towers and traumatic circumstances were extraordinary. This study determined the collapse durations of the towers with unique precision from the precise timing of seismic station records. Collapse duration is a pivotal indicator of the collapse resistance of the towers (Bažant and Verdure, 2007) and, as such, might inform future building design. WTC1 was the first struck, at 12:46:30 UTC (8:46:30 a.m. local time) at its 96th floor by a hijacked airliner, but remained standing longer than WTC2, struck ∼16 min later, at 13:02:59 UTC at its lower 81st floor. The burning WTC2 abruptly collapsed ∼56 min after being struck. WTC1 collapsed similarly ∼102 min after it was struck (Shyam‐Sunder, 2005). The detailed structural analysis of the collapsing towers (Hamburger et al. , 2002; Bažant and Verdure, 2007) revealed the top floors of each tower, above the strike/combustion zone, descended as a unit, successively crushing floors beneath while pushing ahead an accumulating zone of compacted material. During this progressive collapse, peeled structural fragments fell loosely ahead of the more slowly descending upper‐tower segments, which were mostly obscured by opaque dust, smoke, and debris (Hamburger et al. , 2002). Small‐magnitude ground shocks were likely produced by the loosely falling fragments, as well as high‐velocity elastic impulses transmitted into the remaining structure beneath the descending upper segment; …

Investigations of Structural Damage Caused by the Fertilizer Plant Explosion at West, Texas. II: Ground Shock

An explosion occurred at a fertilizer plant in the town of West, Texas, on Wednesday, April 17, 2013, devastating a populated neighborhood. A total of 15 people were killed, and approximately 160 more people were injured. Approximately 150 buildings were damaged in the explosion, and the damage to affected homes and businesses was estimated to exceed $100 million. This research documents the building damages caused by the unprecedented explosion and evaluates the technical information for the explosion. The Part I paper of this research focused on the building damage documentation and air-blast incident overpressure calculations. As a companion paper, this manuscript (Part II) primarily focuses on the study of blast-induced ground-shock effects. The ground shock–induced building damages and ground vibration peak particle velocities (PPVs) are analyzed. With a combined consideration of these two types of blast loadings, the air-blast incident overpressures and ground shocks, the field investigated damages caused by the West Fertilizer plant explosion are explained in a more precise manner. The air-blast incident overpressure is identified as the dominant factor for the damages of both wood light-frame buildings and engineering buildings. The ground shock is the secondary factor but is still important. Concluding the research outcomes in the Part I and Part II papers, this study proposes a four-scale blast-induced damage severity evaluation system, demonstrates efficient blast-loading calculation methods for both the air-blast incident overpressure and ground-shock PPV, and provides a correlation between the blast loadings and the blast-induced damages for the West Fertilizer plant explosion case. The documentation and analyses that resulted from this research could serve as a good case study for better understanding of the blast loadings and building structural responses.

Multi-point response spectrum analysis of a historical bridge to blast ground motion

In this study, the effects of ground shocks due to explosive loads on the dynamic response of historical masonry bridges are investigated by using the multi-point shock response spectrum method. With this purpose, different charge weights and distances from the charge center are considered for the analyses of a masonry bridge and depending on these parameters frequency-varying shock spectra are determined and applied to each support of the two-span masonry bridge. The net blast induced ground motion consists of air-induced and direct-induced ground motions. Acceleration time histories of blast induced ground motions are obtained depending on a deterministic shape function and a stationary process. Shock response spectrums determined from the ground shock time histories are simulated using BlastGM software. The results obtained from uniform and multi-point response spectrum analyses cases show that significant differences take place between the uniform and multi-point blast-induced ground motions.

Differences in Ground Reaction Forces and Shock Impacts Between Nordic Walking and Walking

The regular practice of Nordic walking (NW) has increased in recent years, in part thanks to the health benefits described by the scientific literature. However, there is no consensus on the effects of shock-impact absorption during its practice. Purpose: The aim of this study was to compare the levels of impact and ground reaction forces (GRF) between NW and walking (W). Method: Twenty physically active and experienced participants were assessed using a dynamometric platform and accelerometry analysis. Results: The results show statistically significantly higher levels of acceleration in the tibia (12%) and head (21%) during NW compared with W. Equally, GRF were significantly higher (27%) at the instant of strike compared with W, and a reduction of the forces at the instant of takeoff (8%) was observed. Conclusions: During NW, shock impacts and GRF levels increased compared with W, an aspect that should be considered when prescribing health improvement programs.

A geophysical shock and air blast simulator at the National Ignition Facility.

The energy partitioning energy coupling experiments at the National Ignition Facility (NIF) have been designed to measure simultaneously the coupling of energy from a laser-driven target into both ground shock and air blast overpressure to nearby media. The source target for the experiment is positioned at a known height above the ground-surface simulant and is heated by four beams from the NIF. The resulting target energy density and specific energy are equal to those of a low-yield nuclear device. The ground-shock stress waves and atmospheric overpressure waveforms that result in our test system are hydrodynamically scaled analogs of full-scale seismic and air blast phenomena. This report summarizes the development of the platform, the simulations, and calculations that underpin the physics measurements that are being made, and finally the data that were measured. Agreement between the data and simulation of the order of a factor of two to three is seen for air blast quantities such as peak overpressure. Historical underground test data for seismic phenomena measured sensor displacements; we measure the stresses generated in our ground-surrogate medium. We find factors-of-a-few agreement between our measured peak stresses and predictions with modern geophysical computer codes.

Effect of Soil Properties on the Response of Pile to Underground Explosion

This paper develops and presents a fully coupled nonlinear finite element (FE) procedure to treat the response of piles to ground shocks induced by underground explosions. The Arbitrary Lagrange Euler coupling formulation is used in the study with proper state material parameters and equations. Pile responses in four different soil types, viz, saturated soil, partially saturated soil, and loose and dense dry soils are investigated and the results compared. Numerical results are validated by comparing them with those from a standard design manual. Blast wave propagation in soils, horizontal pile deformations, and damages in the pile are presented. Pile damage presented through plastic strain diagrams will enable vulnerability assessment of the piles under the blast scenarios considered. The numerical results indicate that the blast performance of single pile foundations embedded in saturated soil and loose dry soil are more severe than those embedded in partially saturated soil and dense dry soil. The present findings can serve as a benchmark reference for future analysis and design.

The Dynamic Response of Shallow Buried Structure under the Action of Explosion Load

Simulating and analyzing the dynamic response of the shallow underground structure under the ground explosions by LS-DYNA. The results show that the ground shock under ground explosions contains two different forms, one is direct impact ground shock and the other is indirect impact ground shock; with the increasing of depth, the ground shock decreases. The effective stress of the upper part of the roof is larger than other parts of the shallow underground structure; the effective strain of the corner of the roof is larger than other parts of the shallow underground structure.

Shock Response Analysis of Soil-structure Systems under Seismic Environment

Shock response analysis of the soil-structure systems induced by near-fault pulses is investigated. Vibration transmissibility of the soil-structure systems is evaluated by Shock Response Spectra (SRS). Medium-to- high rise buildings with different aspect ratios located on different soil types as well as different foundations with respect to vertical load bearing safety factors are studied. Two types of mathematical near-fault pulses, i.e., forward directivity and fling step, with different pulse periods as well as pulse amplitudes are selected as incident ground shock. Linear versus nonlinear Soil-Structure Interaction (SSI) condition are considered alternatively and the corresponding results are compared. The results show that nonlinear SSI is likely to amplify the acceleration responses when subjected to long-period incident pulses with normalized period exceeding a threshold. It is also shown that this threshold correlates with soil type, so that increased shear-wave velocity of the underlying soil makes the threshold period decrease.

Blast response and failure analysis of pile foundations subjected to surface explosion

This paper presents the response of pile foundations to ground shocks induced by surface explosion using fully coupled and non-linear dynamic computer simulation techniques together with different material models for the explosive, air, soil and pile. It uses the Arbitrary Lagrange Euler coupling formulation with proper state material parameters and equations. Blast wave propagation in soil, horizontal pile deformation and pile damage are presented to facilitate failure evaluation of piles. Effects of end restraint of pile head and the number and spacing of piles within a group on their blast response and potential failure are investigated. The techniques developed and applied in this paper and its findings provide valuable information on the blast response and failure evaluation of piles and will provide guidance in their future analysis and design.

Containment evaluation against ground shock in rock

Structures, systems and components that are essential for the safe operation and shutdown of a nuclear power plant may be subject to a variety of impulsive loads. This paper presents an experimental and numerical evaluation of the influence of ground shock and airblast forces on the structural response of a 1:8 scale reactor containment structure founded on schist. The numerical model, including both free air and schist properties, was programmed and linked to finite-element software as its user-provided subroutines. The numerical and experimental scaled model results demonstrate good agreement with each other. The full-scale simulation of typical reactor containment was subjected to surface explosions through the developed relationship for structural response analysis. The proposed methodology can be employed to evaluate the blast response of a concrete shell type containment structure and to estimate the integrity of containment.

Experimental and Numerical Investigation of the Ground Shock Coupling Factor for Near-Surface Detonations

This paper presents the results of recent ground shock experiments conducted by the U.S. Army Engineer Research and Development Center to further investigate the adequacy of the coupling factor approach to shallow-buried or near-surface detonations. Comparisons between these recent experimental results and results of numerical simulations of the ground shock propagation in soil are presented. It was found that the coupling factor curve currently adopted in design of buried structures does not accurately represent the actual ground shock propagation in soil and that different coupling factor curves are needed for different physical quantities of interest in design. The results presented in this paper also suggest that the coupling factor curves are functions of several parameters in addition to the depth of burial and that numerical simulations can capture reasonably well the ground shock propagation of soil stresses and particle velocities.