Showing papers in "International Journal of Protective Structures in 2012"

Laboratory Test on Dynamic Material Properties of Annealed Float Glass

Abstract: In this study, laboratory tests were conducted to investigate the dynamic material properties of annealed float glass, which is widely used in building applications. The influence of strain rate effect on glass strength and Young's modulus is studied. Quasi-static tests were performed first to determine the glass static strength and Young's modulus; then dynamic compressive tests were carried out at the strain rates from 98/s to 376/s using a modified Split Hopkinson Pressure Bar. Tensile tests were performed in the strain rate range of 35/s to 990/s through splitting tensile test (Brazilian test). Test results reveal that the compressive and tensile strengths of annealed glass are very sensitive to strain rate. Dynamic increment on glass compressive strength is found more significant than its tensile strength, a phenomenon different from other brittle materials such as concrete. The Young's modulus is found relatively insensitive to strain rate in the testing range, and is slightly larger in compressive ...

Pounding Damage to Buildings and Bridges in the 22 February 2011 Christchurch Earthquake

Abstract: This paper addresses the damage to buildings and bridges resulting from relative movements between adjacent structures observed by the authors from building inspections and in-the-field investigations in Christchurch and surroundings carried out two weeks after the devastating earthquake of 22 February 2011. Relative structural response is often initiated by the different dynamic characteristic of the participating structures. Pounding induced damage might occur when the closing relative response is larger than the gap between adjacent structures. In the Central Business District (CBD) of Christchurch City many adjacent buildings have inadequate gaps between them or in many cases even no gap. Consequently, a large number of buildings, already weakened by the previous main shock of 4 September 2010 and its several thousand aftershocks, suffered further damage due to the strong February aftershock. The reoccurrence of excessive soil liquefaction caused particularly heavy damage to bridge sites along Avon Ri...

Experimental Modeling of Extreme Hydrodynamic Forces on Structural Models

Abstract: This paper presents the results of a comprehensive experimental program focused on the impact of extreme hydrodynamic forces on structural models generated by a turbulent hydraulic bore. The parameters investigated include: (1) bore depth-time history; (2) initial flume-bed conditions (dry bed versus wet); and (3) damping effect of mitigation walls on the hydrodynamic forces. At impact, the maximum inundation (bore) depths varied between 250 mm and 450 mm and the bore front velocity ranged from 2.6 m/s to 5.0 m/s. High-speed video recordings of the bore-structural model interaction were captured simultaneously with the base shear force-, pressure-, base overturning moment-, and top lateral displacement-time histories experienced by the structural models. Three force components were identified in the bore-induced force-time histories: impulsive, run-up (transient hydrodynamic force), and quasi-steady hydrodynamic. The impulsive or run-up force was the maximum force component experienced by the structural m...

Numerical Modeling of the Impact with Structures of Tsunami Bores Propagating on Dry and Wet Beds Using the SPH Method

Abstract: In this paper, the simulation of the impact with structures of tsunami-like bores rapidly advancing on dry and wet beds is performed using a three-dimensional numerical model based on the Smoothed Particle Hydrodynamics (SPH) method. Firstly, to validate the numerical model, physical experiments are simulated and a quantitative comparison between experimental and numerical results is presented. Secondly, numerical results of the propagation of bores on dry and wet beds are compared to the analytical solution of the shallow water equations. Furthermore, the resulting time-histories of the pressures and net force acting on a square column and a vertical wall due to the impact of these bores are compared qualitatively. To better understand the development of the hydrodynamic forces, a detailed analysis of the velocity field and of the water surface elevation is also incorporated. This study is part of a comprehensive interdisciplinary research program whose purpose is to help develop design guidelines for ts...

On Blast Pressure Analysis Due to a Partially Confined Explosion: III. Afterburning Effect

Abstract: This paper aims at extending our understanding with regard to some characteristics of an interior explosion within a room with limited venting. An interior explosion may be the result of an ammunition storage explosion, or an explosive charge as part of a terrorist action or a warhead explosion that follows its penetration into a closed space in a military action. Full scale experiments have been performed with a TNT charge detonated at the center of a single room sized space with rigid boundaries. The room has a limited size opening for venting at the ceiling. Numerical simulations of the problem have been performed using AUTODYN Ver. 12.1 and compared with the experimental measurements. Some deviations between the measured pressure and the predicted pressure motivated the present study in an attempt to study the effect of the additional energy released due to the burning of the detonation products reacting with the surrounding oxygen. The study that is described in this paper enhanced our understanding....

Investigation and Optimization of Protective Properties of Metal Multi-Layered Shields: A Review

Abstract: Effort to enhance protective properties of shields against high speed impact triggered investigations of the ballistic performance of multilayer barriers having different structure, their comparison with each other and with the monolithic barriers. In spite of a large number of publications on these topics there are no comprehensive surveys of this field. The goal of the present review is to close this gap. This review includes analytical, numerical and experimental investigations which can be useful for elucidating general properties of multi-layered metallic shields, e.g. effect of layering, spacing and change of the order of the plates on the protective performance of shields, and also studies which suggested analytical methods for optimization of multi-layered shields.

Impact & Energy Absorption of Road Safety Barriers by Coupled SPH/FEM

Abstract: Road safety barriers are used to minimise the severity of road accidents and protect lives and property. There are several types of barrier in use today. This paper reports the initial phase of research carried out to study the impact response of portable water-filled barrier (PWFB) which has the potential to absorb impact energy and hence provide crash mitigation under low to moderate speeds. Current research on the impact and energy absorption capacity of water-filled road safety barriers is limited due to the complexity of fluid-structure interaction under dynamic impact. In this paper, a novel fluid-structure interaction method is developed based on the combination of Smooth Particle Hydrodynamics (SPH) and Finite Element Method (FEM). The sloshing phenomenon of water inside a PWFB is investigated to explore the energy absorption capacity of water under dynamic impact. It was found that water plays an important role in energy absorption. The coupling analysis developed in this paper will provide a pla...

Numerical Simulations on the Collapse Behaviors of High-Rise Towers:

Abstract: In this paper, several numerical simulations of framed structures were performed to identify the specific structural cause of the high-speed total collapse of the World Trade Center (WTC) towers, which occurred during the 9/11 terrorist attacks. A full-scale aircraft impact simulation of the WTC tower 2 was conducted to examine the dynamic unloading phenomena that occurred in the core columns during impact, which may have caused the destruction of the splices between column sections. Fire-induced progressive collapse analyses of a high-rise tower with an outrigger truss system were carried out to qualitatively demonstrate the effects of fire patterns and structural parameters on the behavior of this tower's collapse. In general, the tower remained standing for a longer period of time due to the catenary action of the outrigger truss system only if the load paths in the tower were protected and if the member connections were strong enough. However, in these analyses, the collapse speed never reached a valu...

Using P-I Diagram Method to Assess the Failure Modes of Rigid-Plastic Beams Subjected to Triangular Impulsive Loads

Abstract: This paper puts forward a simplified method for assessing the failure modes of rigid-plastic beams by solving the governing partial differential equation with defined initial conditions based on five previously developed transverse velocity profiles. It is found that there are twelve different response patterns possible for a rigid-plastic beam subjected to a triangular pulse shape impulsive load. As developed in this paper, the P-I diagram is based on the derived deformation pattern such that selected failure criteria can be used to identify and differentiate various failure patterns. The shear-to-bending ratio, the boundary conditions, and the load pulse shape, all influence the response of the rigid-plastic beams, and are discussed in detail. Although the peak pressure and the shear-to-bending ratio together determine the response pattern, it is also found that the combination of peak pressure, impulse, and shear-to-bending ratio define the failure type and sequence. Fully clamped beams are relatively ...

Collapse Mechanisms of Seawall Due to the March 2011 Japan Tsunami Using the MPS Method

Abstract: On March 11 2011 a huge tsunami was caused by a magnitude 9.0 earthquake, which devastated the sea defenses in the Tohoku coastal region of Japan. We investigated one of the disaster areas, the Taro district, which had been very famous for having a 10m high seawall. This paper focuses on why the seawall in the Taro district collapsed during the tsunami. To this end the present work involves (1) the field disaster investigation, (2) the scale of the March 11 tsunami by performing its run-up calculation, (3) the overflowing effects of the tsunami on the seawall by using the MPS (Moving Particle Semi-implicit) method, (4) the overflowing model test of a seawall and (5) the possible collapse mechanisms of the seawalls, in which they were mainly destroyed by the overflowing and the ensuing draw down wave of the tsunami.

Pounding Response of Adjacent Concrete Rods: An Experimental Study:

Abstract: This paper presents results of the first stage of an experimental research program on the pounding response of adjacent concrete structures during earthquake. It shows experimental results for longitudinal impact of concrete rods. The impact of concrete to concrete surfaces of the rods was studied and the coefficient of restitution was experimentally determined. Acceleration time histories were recorded and characteristics of the impact pulse was determined. The study was extended to include filling materials that had been placed in the joint between the impacting concrete surfaces to study their effect on the impact.

On the Impact Force and Energy Transformation in Ship-Bridge Collisions

Abstract: Taking ship-bridge collision as an example, how the wave propagation and the dynamic behavior of materials influence the impact force and energy transformation are studied from the impact dynamics viewpoint. By using a new flexible, energy-dissipating crashworthy device developed by the authors, both the impact force and energy transformed can be markedly reduced, which is much conductive to protect both bridge and ship.

Behavior of High Ductility Cement Composite Beams under Low Impact

Abstract: This paper describes part of a study that examines possible material compositions aiming at increasing and controlling the ductility of cementitious composities under dynamic loading. The work described herein focuses on the influence of adding micro or macro scale steel fibers to the cementitious composite mix on the hardened specimen's mechanical properties. Small beam specimens made of 14 types of mixes were tested under static and dynamic loads, where the low-velocity dynamic loading was generated in a free-fall hammer. Variables that were examined included compression strength, single and hybrid usage of different types of steel fibers and the fibers volume ratios. The main conclusions indicate enhanced mechanical properties of the hybrid HSC specimens under dynamic loading. The results show that an enhanced material behavior, and therefore also structural response, can be engineered by designing different fiber reinforced cement composite mixes with similar compressive strengths.

Design Concept for Local Damage of Concrete Plates Subjected to High Velocity Impact

Abstract: Local damage of concrete structures, i.e. spalling, scabbing and perforation, would occur when concrete structures are impacted by high velocity projectiles. To propose protective design of concrete structures against high velocity impact, failure mechanism of local damage of concrete plates should be investigated. The authors have studied on failure mechanism of the local damage through impact tests and numerical analyses. This study presents a design concept for the local damage of a concrete plate subjected to high velocity impact. In the design procedure, occurrence of scabbing is judged based on comparison between maximum impact load and scabbing resistant capacity of the concrete plate. Impact load history and penetration depth are calculated using the modified theoretical model, and scabbing resistant capacity is estimated by applying a modified formula for punching shear resistant capacity.

Finite Element Analysis of 3-D Problems of Deformation and Failure of Masonry under Explosive Loading:

Abstract: A finite-element procedure is developed for solving three-dimensional non-steady problems of deformation and fracture of brickwork reinforced by composite plates, including rigid and soft layers.

Terminal Strength and Energy Capacity of RC Beams During Progressive Collapse of Multistory Buildings

Abstract: The objective of this work is to create a set of engineering formulas approximating structure response to a loss of one of supporting columns. Those expressions are created for the beam mode, arching mode, and the cable mode of a beam losing the column support. The correction coefficients are derived on the basis of experimental results. To assess the design load for an isolated beam subjected to a test, it is proposed to use the safety factor as a guide, the factor that can easily be calculated for any real project. The response to dynamic column removal is quantified and the Dynamic Factor is determined. This is helpful in the initial assessment of RC elements. The proposed column failure mechanism has two phases; the first one can be slow, but the second is usually fast, because of the altered configuration. The energy criterion presented provides another check of the capacity of a beam to withstand a column removal.

Experimental impact characterization on a Structurally Dissipating Rock-shed (SDR) structure

Abstract: The estimate load by direct measures for structures that are in actual use is in practice very difficult or even impossible because the impact location is inaccessible, or the projectile is deformable so can not be instrumented. The problem of identifying impact force on mechanical structures is the inverse of the direct problem: the use of measured responses on a given structure to try to identify the causes, i.e. the impact forces that are at the origin.In this study, we developed an experimental method to identify the impact force on a reinforced concrete slab. A transfer function obtained experimentally between the acceleration response and the force history applied to a point of the structure was used. To regularize the solution obtained with this inverse problem, we used the Tikhonov method. To locate the impact force, we used an experimental method based on the minimization of an objective function created from the transfer functions between several impact locations, forming a mesh structure, and s...

Method to Analyze the Effect of the Shock-Wave Loading on Building Elements

Abstract: During designing of some modern industrial and civil buildings it is necessary to consider influence of the intensive impact-wave loadings. The strain rate deformation of building and structural elements takes place both in the elastic and in plastic stage. In such tasks, it is necessary take into account presence of finite deformations as well as dynamic properties of materials. The calculation of above nonlinear task, including dynamic stress-strain states in elements, is carried out by the method of finite differences. Thus, an adaptive net is used on space and temporal to co-ordinates. Accuracy of numerical simulation is verify on every step of calculation, and if necessary change of step is involved.

A Simplified Model for Explosion Venting Due to the Separation of a Heavy Protective Cover

Abstract: The paper presents a study aiming at simulation and understanding of some characteristics of an interior explosion within a room with an opening, that is initially being closed by a heavy cover, and may open gradually due to the effect of the explosion products. An effective simplified model of explosion venting due to separation of the protective cover has been developed. The developed model with lumped parameters is based on the Bernoulli equation and describes the quasi-stationary phase of the vented interior explosion. The initial internal gas pressure induced by the very short non-stationary phase is predicted by the developed approximate analytical formula, based on the full energy conservation law. The formula yields very good agreement with experimental data and with numerical analysis results. The simulation of the unsteady outflow from a cylindrical high-pressure vessel upon a sudden separation of the cover has shown that the developed simplified model yields the integral characteristics of the ...

Rapid Simulation of Blast Wave Propagation in Built Environments Using Coarse-Grain Simulation

Abstract: The paper discusses the first stage in a study concerned with the development and evaluation of a fast, accurate, and versatile method of simulating blast wave propagation within complex built environments (comprising any configuration of structures such as buildings and blast barriers). Existing methods of modeling the propagation of a blast wave each fail in at least one of the speed, accuracy or versatility requirements. Conventional computational fluid dynamic (CFD) simulations, for example, typically take several days to complete a single run. An alternative, novel method proposed here is to use a simulation approach implemented within a coarse spatial and time framework, where the mesh elements and time steps are orders of magnitude larger than those used in conventional CFD simulations. The approach requires the use of intelligent modeling techniques to capture the behavior of elements at the coarse level. Specifically hybrids of artificial neural networks and multivariate linear predictors are use...

Experimental Investigation of Aluminum Foam Lined Suppressive Shield Containment Vessels

Abstract: Manufacture, transport, and storage of dangerous goods, especially energetic materials, in Canada and around the world pose serious challenges to explosives regulators and inspectors. Currently siting of manufacturing and storage facilities are in accordance with quantity-distance principles designed to mitigate effects of accidental explosions. The land requirements to satisfy these principles are imposing financial burdens on the explosives sector.This paper presents an experimental program designed to investigate the effectiveness of suppressive shield containers in reducing the blast pressure outside of the container while eliminating fragments thus reducing the distance requirement for the stored amount of explosives. Several suppressive shield panels including aluminium foam-lined panels were tested to study their effect on blast pressure and impulse. In addition computational fluid dynamics techniques were used to study suppressive shields effects on blast environment. The results show reduction of...

Response Prediction of Foam-Insulated Concrete Sandwich Panels Subjected to Blast Loads using Bilinear Weighted-Resistance SDOF Models

Abstract: This paper presents the development and validation of a single-degree-of-freedom (SDOF) methodology that can be used for the analysis and design of foam-insulated concrete sandwich panels subjected to blast loads. The experimental program used for validation involved both static and dynamic testing of full-scale wall panels. Static testing demonstrated that the degree of composite action provided depends greatly upon the shear connector used and that the internal shear resistance mechanisms change as the panel undergoes large deflection. Given the extreme complexities involved, a simplified bilinear resistance definition was developed using weighted averages between the composite and non-composite resistances. The weighting values were based upon equating the averaged energy absorption capacity measured during the large deflection static testing with that of the analytical definition. The analytical resistances were then used in SDOF models to examine their applicability through comparison to full-scale b...

Does Stronger Concrete Make Stronger and More Resilient Elements

Abstract: Over the last few decades multistory buildings have been designed using gradually stronger and stronger concrete. The obvious advantage of increasing the material strength is the ability of the designer to reduce section area of some members without sacrificing strength. This paper takes a broader view in that it examines a number of mechanical characteristics of a structural member that had been thinned-down because of stronger concrete. Apart from nominal strength there is the elementary quantity of elongation at failure, which limits the deflection that can be attained. Other properties of concern are: Natural frequency, deflection under static and dynamic lateral loading, dynamic bending moment response under lateral loading and, above all, the amount of energy absorbed prior to the beginning of failure. The importance of the latter comes from the fact that when some elements are subjected to extreme loads, they are certain to fail, but the amount of energy absorbed by their destruction may be decisiv...

Earthquake Engineering – Reconnaissance and Assessment of Existing Buildings

Abstract: Most existing built infrastructure, especially historical monuments, has not been designed in accordance with earthquake resistant standards. Earthquake engineering as a specific field of science and practice has only been developed over the past fifty years. Therefore, many buildings across the globe need to be inspected and to be assessed in order to determine their resistance against earthquakes based on today's knowledge. Based on safety standards and a risk assessment, the earthquake engineer provides information to the owner as to use the building in the future in order to fulfill economic as well as safety demands. This paper outlines the inspection procedure, defines the methodology of reconnaissance on site and describes the subsequent assessment of buildings from the practical point of view.

A Numerical Study on Impact Damage Assessment and Dynamic Behaviour of Concrete Bridges by Pounding Effect

Abstract: The South Hyogo prefecture earthquake indicated that various kind of damage was incurred under severe ground motion. Some of the reported damage cases are caused by pounding between bridge girders and between a superstructure and an abutment. To establish the reasonable and safe seismic design for bridges, it is necessary to evaluate the damage level of bridge abutment under impact of bridge girder and to clarify dynamic behaviour of whole bridge under pounding. So the main objective of this study is to evaluate the damage level of an abutment by pounding. To achieve this, impact response analyses of pounding effect were conducted by using 3-dimensional FEM. Furthermore, to clarify dynamic behavior of whole bridge under pounding, frame analyses were conducted.