In addition, with the increase in strain rates, an increase in the energy absorption capacity is observed and this characteristic is beneficial when the foam material is used to absorb impact energy. A mesoscopic model based on the X-ray CT for the aluminium foam material is developed. The simulations and the test data agreed well for the quasi-static loading case. However, it is noted that the mesoscale model without consideration of the base material rate sensitivity and the entrapped gas underestimated the strength enhancement under dynamic loading scenario. A total of 38 specimens were prepared and tested under axial compression.
Based on the confinement level, the stress-strain behavior of FRP confined UHPFRC may experience a second ascending branch or a continuous descending branch after the sudden stress reduction or stress fluctuations. One-step raise excavation with burn cuts, where all the boreholes are pre-drilled and detonated at one time and no workers need to be underneath the freshly blasted and dangerous ground, is an important and promising method in raise excavation.
Cut parameters, especially the parameters of prime cut which used empty hole as a free surface and swelling space, have significant influence on the effect of raise formed. In this study, two small-scale experimental methods, spiral hole spacing method and observation hole method, are designed to determine the prime cut parameters such as hole spacing L , stemming length Ls1, Ls2 and air deck length La which are normally determined by empirical formula.
In order to study the feasibility of the two methods, numerical analysis and experimental tests are conducted in V zone of Sandaozhuang molybdenum mine SMM , in which there are large numbers of underground goafs need to be controlled by filled raise. Meanwhile, the field tests are carried out according to the two small-scale experimental methods.
The comparison results show that the damage zone of numerical simulation has a good agreement with the experimental data. Further, the optimal prime cut parameters obtained from experimental tests are applied in one-step filled-raise excavation, and a 23 m raise that meets the design requirements is formed through the proposed technology. The results indicate that these cut parameters determined by the small-scale experiments are suited for one-step raise excavation.
This study can provide two simple field experiments to determine the important prime cut parameters of one A mesoscale model was developed to investigate the effect of steel fiber on the thermal conductivity of steel fiber-reinforced concrete SFRC. Delaunay triangulation was employed to generate the unstructured mesh for SFRC materials. The model was validated using the existing experimental data.
Then, it was used to study how model thickness affected simulation outcomes of thermal conductivity of models with different fiber lengths, by which an appropriate thickness was determined for the later analyses. The validated and optimized model was applied to the study of relationships between thermal conductivity and factors such as fiber content, fiber aspect ratio and different parts of an SFRC block by conducting steady-state heat analyses with the finite element analysis software ANSYS.
The simulation results reveal that adding steel fiber increases thermal conductivity considerably, while fiber aspect ratio only has an insignificant effect. Besides, the presence of steel fibers has an obvious impact on the distribution of temperature and heat flux vector of the SFRC blocks. As landmarks, these types of structures can more easily be the targets of terrorist attacks than other buildings.
However, blast resistance is not taken into consideration in the design of most civil structures. Therefore, it is important to know the damage level that may be imparted to single-layer reticulated domes after a blast attack. In this study, the dynamic response of reticulated domes subjected to an interior blast was investigated with numerical simulations, and five typical failure modes were identified from the results. In addition, the effects of some important parameters were investigated with a case study.
Relationships between failure modes and interior blast impulses were summarised. Finally, the failure mechanisms were analysed, which could provide some design suggestions to decrease the probability of severe damage in spatial structures subjected to extreme dynamic loads. In recent years, a large number of studies have been carried out to investigate behaviours of concrete filled double skin steel tube CFDST members due to its increasing popularity in the construction industry. This paper firstly presents an experimental study on ultra-high performance concrete filled double-skin tubes subjected to close-range blast loading with cross section being square for both inner and outer steel tubes.
It is evident that the proposed CFDST column was able to withstand a large blast load without failure so that it has the potential to be used in high-value buildings as well as critical infrastructures. Then, to further investigate the behaviours of the proposed CFDST column, a number of parametric studies were carried out by using a numerical model which was developed and calibrated based on the data acquired from the blast test along with some laboratory tests. Parameters that affect the behaviours of concrete filled double skin steel tube CFDST members against blasts are characterised.
Using a modified split Hopkinson bar facility, a static pre-confining pressure was loaded before dynamic loading. The pull-back method is used to calculate the spalling strength and the free surface velocities of the specimen were measured by a laser detector system. The experimental results indicate that the spalling strength is related to the static pre-confining pressures.
When the impact loading and rate effect are almost the same, the results demonstrated that the spalling strength decreases with an increase in the confining pressure. Ultra-high-performance fibre-reinforced concrete has exceptional mechanical properties including high compressive and tensile strength as well as high fracture energy. It has been proved to be much higher blast resistant than normal concrete. In this article, flexural behaviours of ultra-high-performance fibre-reinforced concrete columns were investigated through full-scale tests.
Two mm 3 mm 3 mm columns with and without axial loading were investigated under three-point bending tests, and their load— displacement relationships were recorded and the moment curvatures were derived. The derived moment curvature relationships of ultra-high-performance fibre-reinforced concrete columns were then incorporated into a computationally efficient one-dimensional finite element model, which utilized Timoshenko beam theory, to determine flexural response of ultra-high-performance fibrereinforced concrete columns under blast loading.
After that, the one-dimensional finite element model was validated with the real blast testing data. The results show good correlation between the advanced finite element model and experimental results. The feasibility of utilizing the one-dimensional finite element model for simulating both high-strength reinforced concrete and ultra-highperformance fibre-reinforced concrete columns against blast loading conditions is confirmed.
Ultra-high performance steel fibre reinforced concrete is assumed to be a two-phase model consisting of concrete matrix and steel fibres. The concrete matrix is modelled with homogeneous material and the straight round steel fibres are assumed to be dispersed with random locations and orientations in the matrix. The interfacial transition zone ITZ effect is studied based on the single fibre pull-out tests, and parameters describing the fibre-matrix one dimensional bond-slip behaviour are obtained and discussed based on both experimental and theoretical results.
After the three-dimensional model is validated with static split tensile tests, split Hopkinson pressure bar SHPB split tensile tests are numerically modelled and the stress-time history is interpreted in the mesoscale level. The proposed model qualitatively and quantitatively predicts the material static and dynamic behaviours, and also gives insights on the fibre reinforcement effect in the concrete matrix.
A total of 8 CFST columns, including 4 with circular cross sections and 4 with square cross sections, were tested under close-range blasts. LVDTs were used to record displacement histories and pressure sensors were used to measure pressure histories. The influence of explosive charge weight, steel tube thickness and cross section geometry on dynamic response of CFST columns was analyzed and failure modes of CFST columns were also investigated.
Following the blast tests, an experimental study was conducted to investigate residual strength of blast-damaged CFST columns. It was found that the CFST columns were still able to retain a large portion of their axial load capacities even after close-range blast events. Steel ogive-nosed projectiles with an average mass of g are launched to penetrate UHPC cylinder targets with mm diameter and mm length.
In order to accurately predict depth of penetration DOP and cratering damage of UHPC cylinder targets, uniaxial compressive and four-point bending testing results are used to validate 3D finite element material model. Moreover, an empirical formula to predict DOP is derived according to the simulated data. Key load-carrying elements such as concrete columns are probably the most critical structural components for structural protection against bomb threats. Failures of columns may trigger catastrophic progressive collapse if there is insufficient structural redundancy.
Field blast tests on columns made of this material were performed. Test results showed that UHPC columns had excellent blast resistant capability, only small mid-height deflection and minor concrete damage was observed after the blasting tests. In the present study, to quantify blast-induced damage and assess residual loading capacity of UHPC columns, static axial loading tests on post-blast UHPC columns were carried out.
Undamaged control samples were tested to provide benchmarks. Damage index and residual loading capacity of UHPC columns after various blast loadings were obtained. Structural responses and damages under blast loading environments are critical to structural and personnel safety. The blast scenarios involving close-in detonations are attracting increasingly more attentions over the last few decades due to the rising of terrorism. Under close-in detonations, structural elements tend to fail in a brittle mode including shear, concrete crater and spall.
In such loading scenarios, the structural designated loading capacity which is usually based on flexural deformation assumption is not fully developed. To provide high-level structural protection, high performance concretes with varying fibre additions are now widely investigated and used in blast resistance designs. In the present study, field blast tests results on reinforced concrete slabs under close-in detonations are presented.
Performances of slabs made of normal strength concrete and steel fibre reinforced concrete are compared and discussed. Besides conventional steel rebar reinforcement, new reinforcement scheme i. Furthermore, a numerical study based on Multi-Material ALE and Lagrangian algorithm is carried out to further investigate the field tests' phenomenon. The most common failure mode of structures subjected to blast loading is progressive collapse which is mainly resulted from the failure of load bearing columns.
The numerical model is firstly validated against a series of laboratory and field tests and then used to derive pressure-impulse diagrams for UHPCFDST columns in terms of their residual axial load-carrying capacity after being subjected to blast loading. Different parameters are studied to investigate the effects of axial load ratio, steel tube thickness, column dimension and concrete strength on the pressure-impulse diagrams. Retrofitting technology and high performance construction material are now widely investigated so as to increase structural ductility and robustness under extreme loading conditions.
In the present study, some recent developments in structural protection against blast loads are compiled. Metallic foam materials with varying foam density and gradient are used in the cladding design, their energy absorbing capacities and stress-strain relationships are studied based on uniaxial compression tests. These foam material are used to cast sacrificial claddings on the concrete slabs in the field blast tests. Damage and structural deformation are measured to check the effectiveness of the claddings.
Besides sacrificial foam cladding, concrete material with new reinforcement scheme including steel wire mesh and micro steel fiber is developed, and the static test results indicates the excellent ductility and crack control ability of this novel design. In the field blast tests, concrete slabs with different steel wire mesh reinforcement are exposed to varying blast loads. The effectiveness of the slab reinforcing design is discussed based on field performance. The impact responses observed in the tests, including depth of penetration DOP , crater diameter and volume loss, were investigated and discussed, which indicates an effective impact resistance of steel wire mesh reinforced RPC in comparison with the previous studies on ultra-high performance based cement composites UHPCC with additions of fibres and basalt aggregates.
Numerical studies based on validated material and element models are also conducted to simulate the impact responses of reinforced RPC targets against high-velocity proj ectile penetration in explicit hydro-code LS-DYNA. The impact responses, especially for the DOP, are well predicted by using the numerical models. Moreover, further investigation based on the verified numerical models is discussed in the present paper to explore the influence of mechanical and physical properties of steel wire mesh reinforcement on the resistance of projectile penetration. All right reserved. The numerical accuracy and stability of the MFS is verified by examining the boundary conditions and comparison with other methods.
Subsequently, the amplification effects on displacement, surface hoop stress and fluid pore pressure around a cavity in a three-layered poroelastic half-plane are investigated. Numerical results indicate that the scattering characteristics strongly depend on parameters including the incident frequency and angle, soil-layer porosity and boundary drainage condition.
The amplification effects of a cavity in the poroelastic layered half-plane appear to be more significant than the corresponding case of a homogenous half-plane. The amplitude of the fluid pore pressure on the surface of the cavity is amplified up to five times that of the free field, which also considerably aggravates the dynamic stress concentration around the cavity. Aluminium foam is widely known as an energy absorptive material which can be used as a protective cladding on structures to enhance blast resistance of the protected structures.
Previous studies show that higher density provides larger energy absorption capacity of aluminium foam, but results in a larger transmitted pressure to the protected structure. To lower the transmitted pressure without sacrificing the maximum energy absorption, graded density foam has been examined in this study. An analytical model is developed in this article to investigate the protective effect of linear density foam on response of a structure under blast loading. The model is able to simulate structural deformation with reasonable accuracy compared with experimental data.
The sensitivity of density gradient of foam cladding on reinforced concrete structure is tested in the article. In conclusion, increasing steel ratio is an effective way for improving the impact behaviors of RACFST, but resulting in higher cost for practical application.
Library Of American University Of Madaba Catalog › Details for: Modern protective structures /
For the impact design of RACFST, steel strength and steel ratio are two essential factors in terms of impact behavior enhancement and cost efficiency. Based on a series of cyclic loading tests on 14 UHPSFRC specimens subjected to combined static axial loading and cyclic lateral loading, the investig ation and analysis have been carried out on crack status, failure modes, hysteretic loops, skeleton curves, strength and stiffness degradation, energy dissipation capacity and ductility of UHPSFRC columns.
The influence of stirrup spacing, type of stirrup, axial compression ratio and shear span ratio on the seismic performance of UHPSFRC columns was also investigated in details. The experiment results show that three typical failure modes are observed, i. The existence of steel fiber could prevent the cracked concrete from spalling efficiently and delay the bulking of longitudinal reinforcement further. It noteworthy that the limit plastic drift ratio of all columns changes from 0. The explosion test of four full-scale circular cross section and four full-scale square section concrete-filled steel tubular columns was researched.
The strain variation of the concrete-filled steel tubular columns was analyzed. The load-strain curve of the circular concrete-filled steel tubular column has obvious yield plateau, indicating the circular concrete-filled steel tubular column has better ductility than square concrete-filled steel tubular column. After the test, six concrete-filled steel tubular columns were ripped four specimens were tested for the residual bearing capacity while the other two components were not.
The destruction performance of the circular and square concrete-filled steel tubular columns was studied before and after the residual bearing capacity test, showing consistent failure modes before and after the test. Using a unified theoretical formula which was modified by the task group, the damage degrees of the four specimens were assessed.
Three specimens were damaged slightly, and one specimens was severely damaged, but no collapse occurred. Columns are essential load carrying structural components and may experience accidental loads such as terrorist bombing attacks during their service life. Damages to columns may trigger structural collapse and it is therefore very important to protect critical load-carrying columns. In recent studies, a novel ultra-high performance concrete UHPC material was developed and static loading test results revealed its outstanding mechanical strengths and ductility.
The present study investigates the blast load-carrying capacities of columns made of UHPC. Concrete columns built with UHPC were blast tested in the field first; then brought back to laboratory and subjected to static load tests to determine their residual load-carrying capacities after experiencing varying levels of blast damage. The results from the field blast tests and laboratory static load tests for residual load-carrying capacities are presented and discussed in this paper.
Numerical models for simulating responses and residual strengths of the UHPC columns after blast loadings are also developed in commercial hydro-code LS-DYNA and presented in the paper. Comparisons between the test data and numerical results are made and the accuracy of the numerical model is validated. Conventional concrete works as an important construction material. However, conventional concrete is known to be brittle and prone to tensile failure and cracks. To overcome such defects and improve the dynamic performance of concrete against extreme loading conditions, concrete with different additions and formulae have been developed.
In a recent study, to develop ultra-high performance concrete UHPC material with better strength and crack control ability, super fine aggregates with high pozzolanic effect were mixed into the steel fibre reinforced concrete instead of the traditional graded coarse aggregates. Furthermore, to achieve high early age strength, nanoscale additives which can accelerate the hydration process of the ordinary Portland cement were also introduced into the concrete composite.
A series of uniaxial compression and four-point bending tests had been performed in the laboratory to get the material properties of this innovative concrete material. Great improvement of the concrete uniaxial compressive strength and flexural tensile strength was observed. Field blast tests were carried out on columns made of this UHPC material. Superior blast resistance performance was observed.
In the current study, based on the available test data, numerical models are developed and numerical simulations are carried out. The simulation results are found to comply well with the experimental results. In recent years, concrete filled double skin steel tube CFDST members have gained interest due to its attractive properties such as ease of construction, light weight, high strength and good seismic resistance, and thus it is expected that these members have the potential of being used in construction of buildings.
However, there is lack of understanding about the inelastic behaviors of CFDST members under blast loads. In this paper, based on the ConWep airblast loading model, the blast resistance of typical circular CFDST columns used in engineering field is investigated and the multiple failure modes of CFDST columns under blast loading are analyzed.
The influence of explosive charge weights and column axial loading condition on the response of CFDST columns are investigated through parametric study. Finally, the direct shear and flexural failure modes of CFDST columns are analyzed, and uncoupled P-I pressure-impulse diagrams are obtained based on an equivalent single degree of freedom SDOF system. A load-cladding-structure LCS model was used to study the mitigating effect provided by metallic foam cladding against blast loading on reinforced concrete RC structural members.
The model considered the interactions between an external blast load, a protecting foam cladding, and a target RC structural member. The effectiveness of the LCS model was validated by field blast tests conducted in The validated model was then used to derive pressure impulse diagrams of the foam-protected RC members. Afterwards, two nondimensional parameters representing the relationship between the foam cladding and the target RC member were characterized. Using the suggested nondimensional parameters, normalized pressure-impulse p-i diagrams for the foam-protected RC members were generated.
The effects of the two nondimensional parameters on the p-i diagrams were investigated by comparing the corresponding asymptotes. Based on the predicted results, an optimized design of the foam cladding for RC structural members was suggested. Due to the threat of terrorist activities worldwide, research on the protection of building structures from the effects of explosions is critical in order to avoid catastrophic damage to buildings.
Protecting our infrastructures means protecting lives. Metallic foam is an economical, light-weight and recyclable material used as a sacrificial cladding to protect structures. Its efficient energy absorption enables metallic foam to mitigate the blast energy acting on the protected structure.
Serials Currently Covered in the TRID Database
This paper describes our numerical investigation of the protective performance of metallic foam cladding on reinforced concrete RC structural members using LS-DYNA. The numerical model was validated by field blast testing results. Using the validated numerical model, parametric studies were conducted to assess the influence of different foam properties on the pressure-impulse P-I diagrams of the foam-protected RC slabs. The influence of the thickness of the RC members was also investigated. The derived P-I diagrams will prove useful in the preliminary design of the foam cladding on RC members.
A common approach for predicting member response under blast loading is through the use of a finite element software package. Such an analysis typically requires the implementation of a three dimensional mesh and, therefore, requires significant computational effort. Then, results determined using the approach are compared against those obtained from blast experiments and the numerical efficiency of the model is discussed.
There has been an extensive amount of research into determining the compressive stress-strain properties of concrete for design. Difficulty has arisen in quantifying the softening or descending stress-strain relationship as it has been found to depend on the size and shape of the specimen being tested as well as on the confinement and eccentricity of compressive load applied to the specimen.
This difficulty has restricted the development of design rules for reinforced concrete members not only for strength but also for ductility particularly for confined members. In this paper, a meso-scale model, which divides concrete into a three phase composite material consisting of the mortar matrix, aggregate and interfacial transition zone, is used to explain and quantify the softening mechanism of concrete specimens.
It is shown that this meso-scale model can both simulate the cracking patterns and deformations which are seen to occur in concrete while softening and also quantify and explain the effects of size, shape, confinement and eccentricity of load. This realistic simulation of the softening mechanism should allow a better understanding and quantification of the compressive failure mechanism of concrete which should lead to the development of better design rules particularly for confined concrete.
Pressure-impulse P-I diagrams based on the equivalent single-degree-of-freedom approach SDOF have been used during building design in order to assess the effects of blasts on structures. They provide an easy way to describe the likely outcome of the combination of blast pressures and impulses on a particular structural element in a building at the moment an explosion occurs. However, only P-I diagrams of structural members under external blasts have been addressed in current guidelines and previous studies.
Due to the complexity of confined scenarios, confined blast pressure-time histories cannot be approximated by simplified representations of pressure-time histories used for external blasts, such as triangular shapes representing linear decay or curves indicating exponential decay. Rather, they should be simplified as bilinear pressure-time histories. Thus, SDOF models which incorporate bilinear blast loads were developed to predict the response of a member with a bilinear, elastic-plastic-hardening, resistance-deflection function.
Then using the developed SDOF model, normalised P-I Diagrams for structural members with bilinear resistance-deflection functions under bilinear blasts were generated. These results were then used to undertake a parametric study to investigate the influence of varying blast load shapes and varying bilinear resistance-deflection function shapes on the normalised P-I curves. Also, comparisons against other techniques employed to eliminate pulse load shape effects were also undertaken for bilinear pulse loads and bilinear resistance-deflection function shapes.
This paper describes an investigation into the effectiveness of using spray-on nano-particle reinforced polymer and aluminium foam as new types of retrofit material to prevent the breaching and collapse of unreinforced concrete masonry walls subjected to blast over a whole range of dynamic and impulsive regimes. Material models from the LSDYNA material library were used to model the behaviors of each of the materials and its interface for retrofitted and unretrofitted masonry walls.
Available test data were used to validate the numerical models. Using the validated LS-DYNA numerical models, the pressure-impulse diagrams for retrofitted concrete masonry walls were constructed. The efficiency of using these retrofits to strengthen the unreinforced concrete masonry unit CMU walls under various pressures and impulses was investigated using pressure-impulse diagrams.
Comparisons were made to find the most efficient retrofits for masonry walls against blasts. Wu, C , 'Research development on protection of structures against blast loading at University of Adelaide', Australian Journal of Structural Engineering , vol. This paper presents a review of research into the protection of structural members against blast loading at The University of Adelaide, including experimental, analytical and numerical studies on characteristics of blast loading, blast resistance of structural members and mitigation of blasts effects on structural members using retrofitting techniques.
Explosive blasts are investigated experimentally and numerically to study the distributions of peak overpressure and impulse generated from spherical charges and cylindrical charges with different orientations in unconfined and confined environments. A series of blast tests on reinforced concrete RC slabs, ultra-high performance concrete UHPC slabs, and aluminium foam protected RC slabs was conducted to investigate the performance of those slabs under blast loads.
With the blast testing data numerical models including single degree of freedom model, finite difference model and final element model, have been developed and validated and those numerical models are then used to analyse the blast effects of RC, UHPC and foam protected RC slabs. Investigation of mitigation of blast effects on masonry structures is also addressed. Objective: To investigate the role of sector laser photocoagulation for prevention of macular edema after plaque radiotherapy for uveal melanoma. Methods: Noncomparative, pilot interventional case series. The main outcome measure was optical coherence tomography-evident macular edema.
Results: A total of 29 patients had sector laser photocoagulation sector panretinal photocoagulation and sub-Tenon triamcinolone injection. The median tumor thickness and base was 3. The median radiation dose and rate to the macula was 2, cGy and There were no major side effects registered. Conclusion: Sector panretinal photocoagulation in combination with sub-Tenon triamcinolone appears to show potential as a safe and beneficial intervention for the prevention of macular edema after plaque radiotherapy for uveal melanoma in this series.
Objective: To study the cost benefit analysis of using a telemedicine-based digital retinal imaging evaluation compared to conventional ophthalmologic fundus examination of diabetic patients for diabetic retinopathy. The costs for the standard of care ophthalmic examinations were calculated based on Medicaid reimbursement rates. The process of telemedicine-based diagnosis was based on a take-store-forward-visualize system.
The cost of telemedicine-based digital retinal imaging examination included cost for devices, training, annual costs and a transportation fee. Current Medicaid reimbursement, transportation, and stafflabor costs were used to calculate the conventional retinal examination cost as a comparison.
It has become a critical issue that the human life and civil facility have been threatened by the increasing terroristic explosive attack. The application of cellular materials is an effective and feasible measure to mitigate blast and impact loading on buildings due to their energy absorption capacity. However, most of numerical models regarded the cellular materials as homogeneous materials on the macro level which may affect the accuracy of simulation, because none of them can reflect the pore structure of cellular materials, especially for the irregular metallic foam structures.
In the microstructure model of metallic foam, the cell walls were represented by thin shell elements and the solid wall material of the cells is modelled as bi-linear stressstrain relationship based on the material properties of the cell wall material of metallic foam. The numerical models were validated through comparing simulated results with analytical values of plateau phase stress-strain response under static condition.
With the validated microstructure models, a series of parametric studies were conducted, in order to have a better understanding about the mechanical properties of closed-cell metallic foam. The emphases of this study were on the differences between static and dynamic performances of closed-cell metallic foam specimens in both 2D and 3D cases, the relationship between dynamic increase factor and nominal strain rate.
Protection of infrastructure against blast loading has been receiving more attention in recent years due to occasional engineering explosion accidents, e. An effective solution to mitigate blast effects on these buildings is to protect them with sacrificial foam claddings for absorption of blast energy.
However, little research has been conducted to analyze the effectiveness of metallic foam protected reinforced concrete RC structural members under airblast loads. This paper is to develop a numerical model to analyze the mitigation of blast effects on foam cladding protected RC members with consideration of interaction of blast load, foam layer and protected structural member. This numerical model is a simplified SDOF system where the deformability of the RC flexural member is considered in the form of the supporting spring. The stiffness of the spring K is estimated from the resistance deflection function of the RC member which is derived from combined moment curvature and moment rotation models.
Material testing was conducted on aluminum foam specimens to obtain the stress stain curve which was idealised as a rigid-perfectly plastic-locking model. The resistance deflection curve of the RC slab and the idealised rigid-perfectly plastic-locking model for foam specimen were incorporated into the coupled SDOF interaction model for dynamic analysis. A field blast testing on foam protected RC slab was conducted and the accuracy of the coupled SDOF interaction model was validated by experimental data from the blast testing of the foam protected RC slab.
Confined blast loading occurs in many scenarios and the effects of confined blast loading may result in more serious damage to buildings due to multiple shock reflections Shi et al.
- Organic Syntheses An annual publication of satisfactory methods.
- Modern Protective Structures.
- Modern Protective Structures (Civil and Environmental Engineering)?
However, spherical charges are assumed for all confined explosive-effects computations in modern standards for blast-resistant design such as UFC and the soon-to-be published ASCE Standard for the Blast Protection of Buildings ASCE forthcoming without consideration of effects of charge shape on the distribution of reflected overpressure and impulse. As confinement is an aggravation factor of explosion effects, analysis and design of infrastructure under critical scenarios of confined blast loading should take the aggravation factor into consideration.
This paper is to develop a numerical model for prediction of blast loads inside unvented structures as a result of variation of the charge shape, charge orientation, geometries and volumes of confined chambers. A finite element program, AUTODYN Century Dynamics, , is utilized extensively to generate a model which is capable of being calibrated with the experimental results conducted by Wu et al. The calibrated AUTODYN model is then used to conduct parametric studies to analyze the effects of the variation of charge shape, charge orientation, chamber geometry and chamber volume on the peak reflected overpressure and impulse on the walls of the chamber.
The quasi-static overpressure for fully confined blast loading is characterized and the simulated results are used to derive the relationships between the quasi-static overpressure and scaled distance for the fully confined blast loading. Discussion is made on characteristics of fully confined blast loading inside chambers. Population stratification is an important issue in case-control studies of disease-marker association.
Failure to properly account for population structure can lead to spurious association or reduced power. In this article, we compare the performance of six methods correcting for population stratification in case-control association studies. We also include the uncorrected Armitage test for comparison. In the simulation studies, we consider a wide range of population structure models for unrelated samples, including admixture. The Armitage test does not adjust for confounding due to stratification thus has inflated type I error. Among all correction methods, EMMAX has the greatest power, based on the population structure settings considered for samples with unrelated individuals.
Genetic studies of midgut carcinoid cancer have exclusively focused on genomic changes of the tumor cells. We investigated the role of constitutional genetic polymorphisms in predisposing individuals to ileal carcinoids. Given the small sample size, our findings warrant an independent cohort for a replication study. Owing to the rarity of this disease, we believe these results will provide a valuable resource for future work on this serious condition by allowing others to make efficient use of their samples in targeted studies.
Although the distributions of peak incident overpressure and impulse generated from spherical charges and cylindrical charges of the same weight can differ greatly close to the point of detonation, spherical charges are assumed for nearly all explosive-effects computations per modern standards for blast-resistant design such as UFC and the soon-to-be published ASCE Standard for the Blast Protection of Buildings.
A blast-testing program was performed using a reinforced concrete slab as the target to investigate the reflected peak overpressure and impulse distributions as a function of charge shape, orientation, and scaled distance. The charge shapes were cylindrical and spherical, and the charge mass varied from 0. Nine pressure transducers were installed on the surface of the slab to record the distribution of pressure histories over the face of the target.
A finite element model of the explosive and the target was validated using the experimental data. The validated model was then used to undertake a parametric analysis to more broadly study the effects of detonation point, ratio of charge length to charge diameter, charge orientation and standoff distance on the distribution of reflected overpressure. Numerical results are compared with predictions of UFC For cylindrical charges, the ratio of charge length L to diameter D , the orientation of the longitudinal axis of the charge, and detonation point within the charge affected the distributions of reflected peak overpressure and impulse in the immediate vicinity of the explosive.
The UFC underpredicts substantially the reflected peak overpressure and impulse on a target aligned with the vertical axis of a cylindrical charge with an aspect ratio of 1. Receiver operating characteristic ROC curve, plotting true positive rates against false positive rates as threshold varies, is an important tool for evaluating biomarkers in diagnostic medicine studies. By definition, ROC curve is monotone increasing from 0 to 1 and is invariant to any monotone transformation of test results. And it is often a curve with certain level of smoothness when test results from the diseased and non-diseased subjects follow continuous distributions.
Most existing ROC curve estimation methods do not guarantee all of these properties. One of the exceptions is Du and Tang which applies certain monotone spline regression procedure to empirical ROC estimates. However, their method does not consider the inherent correlations between empirical ROC estimates. This makes the derivation of the asymptotic properties very difficult. In this paper we propose a penalized weighted least square estimation method, which incorporates the covariance between empirical ROC estimates as a weight matrix.
The resulting estimator satisfies all the aforementioned properties, and we show that it is also consistent. Then a resampling approach is used to extend our method for comparisons of two or more diagnostic tests. Our simulations show a significantly improved performance over the existing method, especially for steep ROC curves. We then apply the proposed method to a cancer diagnostic study that compares several newly developed diagnostic biomarkers to a traditional one.
We propose and examine statistical test-strategies that are somewhat between the maximum likelihood ratio and Bayes factor methods that are well addressed in the literature. The paper shows an optimality of the proposed tests of hypothesis. We demonstrate that our approach can be easily applied to practical studies, because execution of the tests does not require deriving of asymptotical analytical solutions regarding the type I error.
However, when the proposed method is utilized, the classical significance level of tests can be controlled. Currently, there are adequate guidelines available for FRP retrofitting RC structures against static and seismic loads. However, there is still limited information on retrofitting RC structures against short-duration dynamic loading effects such as blast loading. Due to the increasing threat of terrorism in recent years, retrofitting of RC structures against blast loading is of paramount importance in structural engineering.
In this paper, a dynamic model that is based on single-degree-of-freedom SDOF approach is developed for the analysis of the response of retrofitted fixed end supported RC slabs subjected to blast loads. A previously validated layered capacity analysis method is used to determine the yielded and ultimate blast resistant capacity of a cross-section of a RC slab which allows varying strain rates with time along the depth of the member.
The corresponding deflections are determined by plastic hinge analysis. To simplify the calculation process, a tri-linear resistance-deflection function which consists of elastic, elasto-plastic and plastic region for fixed end supported RC slabs is converted to an equivalent bilinear function. This developed model can adequately predict the retrofitted members' response to blast loading. It is then is used to conduct a parametric study to optimise the retrofitting of RC slabs subjected to blast loading by varying the quantity, material type and technique of retrofitting.
If the maximum deflection of the designed member under airblast loads is less than the allowable deflection, the designed member is considered to be safe. Although the displacement-controlled design method is easy to use, it may not result in a design having maximum energy-absorption capacity against airblast loads, especially for a design of a reinforced ultra-high performance fibre concrete RUHPFC member which is of both high strength and high ductility, that is, high energy-absorption capacity.
- Professor Chengqing Wu?
- I Banged My Step Sister II.
- The Modern Thai House: Innovative Designs in Tropical Asia?
- American Spyplanes.
- Black Ethnics: Race, Immigration, and the Pursuit of the American Dream.
- Continuous Media with Microstructure 2.
- Theodor Krauthammer?
In this paper, a layered analysis model allowing for varying strain rates with time as well as along the depth of the member was used to calculate energy-ab sorption of a simple supported RUHPFC slab under airblast loads. An optimal reinforcement ratio of the slab was achieved by maximizing the energy absorption of the slab under different reinforcement ratios. The energy-controlled design method was validated by field blast tests. Using the validated design method, a designed slab with the optimal reinforcement ratio was also tested and the effectiveness of the design was demonstrated.
We consider a specific classification problem in the context of change-point detection. We present generalized classical maximum likelihood tests for homogeneity of the observed sample in a simple form which avoids the complex direct estimation of unknown parameters. This paper proposes a martingale approach to transformation of test statistics. For sequential and retrospective testing problems, we propose the adapted Shiryayev-Roberts statistics in order to obtain simple tests with asymptotic power one.
An important application of the developed methods is in the analysis of exposure's measurements subject to limits of detection in occupational medicine.
Since the middle of the twentieth century, the problem of making inferences about the point in a surveyed series of observations at which the underlying distribution changes has been extensively addressed in the economics, biostatistics and statistics literature. Cumulative sum-type statistics have commonly been thought to play a central role in non-sequential change point detections.
Alternatively, we present and examine an approach based on the Shiryayev-Roberts scheme. We show that retrospective change point detection policies based on Shiryayev-Roberts statistics are non-asymptotically optimal in the context of most powerful testing. An effective solution to mitigate blast effects on URM wall is to retrofit URM walls with metallic foam sheets to absorb blast energy.
However, mitigation of blast effects on metallic foam protected URM walls is currently in their infancy in the world. In this paper, numerical models are used to simulate the performance of aluminum foam protected URM walls subjected to blast loads. A distinctive model, in which mortar and brick units of masonry are discritized individually, is used to model the performance of masonry and the contact between the masonry and steel face-sheet of aluminum foam is modelled using the interface element model.
The aluminum foam is modelled by a nonlinear elastoplastic material model. The material models for masonry, aluminum foam and interface are then coded into a finite element program LS-DYNA3D to perform the numerical calculations of response and damage of aluminum foam protected URM walls under airblast loads.
Discussion is made on the effectiveness of the aluminum foam protected system for URM wall against blast loads. Road side barriers are constructed to protect passengers and contain vehicles when a vehicle crashes into a barrier. In general, full-scale crash testing needs to be carried out if a geometrically and structurally equivalent barrier has not previously been proven to meet the requirements of containing the vehicle and dissipating sufficient impact energy for passenger protection. As full-scale crash testing is very expensive, the number of data that can be measured in a test is usually limited, and it may not always be possible to obtain good quality measurements in such a test, a reliable and efficient numerical simulation of crash testing is therefore very useful.
This paper presents finite element simulations of a 3-rail steel road traffic barrier under vehicle impact. The numerical simulations show that the barrier is able to meet low performance levels. However, the maximum deceleration is higher than the acceptable limit for passenger protection.
If present, a kerb launches the vehicles into the barrier, allowing for the possibility of overriding the barrier under certain circumstances, but it redirects the vehicle and reduces the incident angle, which reduces impact force on the barrier. Further investigation into all common kerb profiles on roads should be carried out, as only one kerb profile is investigated in this study.
Current guidelines recommend using single-degree-of-freedom SDOF method for dynamic analysis of reinforced concretec RC structures against blast loads, which is not suitable for retrofitted members. Thus, a finite difference procedure developed in another study was used to accurately and efficiently analyze the dynamic response of fibre reinforced polymer FRP plated members under blast loads.
It can accommodate changes in the mechanical properties of a member's cross section along its length and through its depth in each time step, making it possible to directly incorporate both strain rate effects which will vary along the length and depth of a member and non-uniform member loading to solve the partial differential equation of motion. The accuracy of the proposed method was validated in part using data from field blast testing.
The finite difference procedure is implemented easily and enables accurate predictions of FRP-plated-member response. Considered in the paper is the problem of selecting a diagnostic biomarker that has the highest classification rate among several candidate markers with dichotomous outcomes. The probability of correct selection depends on a number of nuisance parameters from the joint distribution of the biomarkers and thus can be substantially affected if these nuisance parameters are misspecified.
A two-stage procedure is proposed to compute the needed sample size that achieves the desired level of correct selection, as so confirmed by simulation results. Investigated in this paper is the point estimation and confidence intervals of the treatment efficacy parameter and related secondary parameters in a two-stage adaptive trial. Based on the minimal sufficient statistics, several alternative estimators to the sample averages are proposed to reduce the bias and to improve the precision of estimation.
Confidence intervals are constructed using Woodroofe's pivot method.
Numerical studies are conducted to evaluate the bias and mean squared error of the estimators and the coverage probability of the confidence intervals. Little information is available on the intra-individual variability of oxidative stress biomarkers in healthy individuals and even less in the context of the menstrual cycle. The objective of this study was to characterize the analytical and biological variability of a panel of 21 markers of oxidative damage, antioxidant defence and micronutrients in nine healthy, regularly menstruating women aged years.
Analyses included measurement of lipid peroxidation, antioxidant enzymes and antioxidant vitamins. Blood specimens were collected, processed and stored using standardized procedures on days 2, 7, 12, 13, 14, 18, 22 and 28 in one cycle for each subject. Replicate analyses of markers were performed and two-way nested random effects ANOVA was used to describe analytical, intra-individual and inter-individual variability.
Analytical variability was the smallest component of variance for all variables. The ICC among replicates ranged from 0. These results provide important initial information on the variability of biomarkers of oxidative stress, antioxidant defence and micronutrients across the menstrual cycle. Comparative diagnostic studies usually involve comparison of the area under receiver operating characteristic curves when biomarkers are measured on a continuous or ordinal scales.
In designing such studies, specification of a number of nuisance parameters is often required to compute sample sizes. When these parameters are incorrectly specified, statistical power to detect a meaningful difference in area can be substantially adversely affected. We propose an adaptive method to calculate the sample size and show these procedures to be effective in controlling error rates. We consider evaluation and comparison of the diagnostic accuracy of biomarkers with continuous test outcomes, possibly correlated due to repeated measurements.
We develop nonparametric group sequential testing procedures to evaluate and compare the area of biomarkers under their receiver operating characteristic curves, with either independent or paired test outcomes. Theodor Krauthammer. In today's world, reasonably predictable military operations have been replaced by low intensity conflicts-less predictable terrorist activities carried out by determined individuals or small groups that possess a wide range of backgrounds and capabilities.
Because of the threats posed by this evolving type of warfare, civil engineers and emergency personnel face new challenges in designing facilities to protect lives and property and in conducting effective rescue operations and forensic investigations.
Addressing these needs, Modern Protective Structures develops realistic guidelines for the analysis, design, assessment, retrofit, and research of protected facilities. After introducing a comprehensive risk management approach, the author provides a general background on explosive devices and their capabilities as well as explosive effects and the processes that generate them. He then discusses the effects of conventional and nuclear explosions. The book subsequently considers the significant design differences between conventional and nuclear loads and between existing design procedures and state-of-the-art information from recent research.
It also summarizes existing blast-resistant design approaches and describes the dynamic responses of structural systems to blasts, shocks, and impacts. Additional coverage includes the behavior of specific structural connections, the traditional concept of P-I diagrams, and progressive collapse. The book concludes with a systematic and balanced protective design approach.
Tackling the analytical, design, assessment, and hazard mitigation issues associated with short-duration dynamic loads, this book examines how impulsive loads affect various types of buildings and facilities. It provides the necessary material to help ensure the safety of persons, assets, and projects. Chapter 2 Explosive Devices and Explosions.