Blast Design and Modelling Forum 2008

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    24th July 2008, Hotel Realm, Canberra

    In today’s world, knowledge of modern protective structures is vital. This workshop will provide participants with a valuable overview of the research projects conducted in this area in Australia. The leading researchers in Australia will be presenting their research during the forum. There will be a special presentation which will allow the participants an insight into the issues associated with load assessment, response analysis, available tools and factors that must be addressed in developing a successful blast resistant building design.  Prof. Andrew Whittaker, a leading researcher in USA will discuss the present research related to blast resistant design in USA.

    Program
    9:00 Workshop registration
    9:30 Introduction
    Professor Priyan Mendis, University of Melbourne
    9:40 Blast R&D in USA and performance of nuclear structures
    Andrew Whittaker
    10:20 An Investigation of Impact and Blast Performance of Steel Sections with Infill Materials for Critical Infrastructure Protection
    Alex Remmenikov and Brian Uy – Abstract
    10:40 Risk-based Optimisation of Protective Measures Against Terrorist Threats to Infrastructure
    Mark G. Stewart – Abstract
    11:00 Morning Break
    11:20 Numerical Analysis of Fiber Reinforced Polymer Composit Strengthened RC Walls with Anchorages Against Blast Loads
    A. Mutalib and H. Hao – Abstract
    11:40 Numerical Modelling of High-Speed Impact Tests of Concrete Material Properties
    Hong Hao, Xiaoqing Zhou, Zhong-Xian Li – Abstract
    12:00 Application of Distributed Nonlinearity for Progressive Collapse Analysis of Reinforced Concrete Frames
    Hamid R. Valipour and Stephen J. Foster – Abstract
    12:20 Polymer Reinforced Concrete Panels to Resist Blast Loads
    Sudharshan Raman, Tuan Ngo, Priyan Mendis – Abstract
    12:40 Lunch
    1:20 Facade and Structural Systems Project
    Ken Dale
    1:40 Blast Resistance of FRP Retrofitted RC Slabs
    Chengqing Wu, DJ Oehlers, M. Rebentrost, J. Leach, A. Whittaker – Abstract
    2:00 Behaviour of Glass Facade Panels
    Raymond Lumantarna, Harry Susiswo, Priyan Mendis, Tuan Ngo – Abstract
    2:20 Challenges in High-Speed Impact Tests of Dynamic Concrete Material Properties
    Yifei Hao, Hong Hao, Boris Tarasov – Abstract
    2:40 An Improved Procedure for Progressive Collapse Analysis of RC Frames to Blast Loading
    Yanchao Shi, Hong Hao, Zhong-Xian Li – Abstract
    3:00 Behaviour of FRP Reinforced Concrete Panels
    Ganchai Tanapornraweekit, N. Haritos, Priyan Mendis, Tuan Ngo – Abstract
    3:20 Closing Remarks by Professor Priyan Mendis
    Abstracts

    An Investigation of Impact and Blast Performance of Steel Sections with Infill Materials for Critical Infrastructure Protection
    Alex Remennikov, Brian Uy

    Understanding the performance of energy absorption characteristics of critical structural elements is necessary for the development of design guidelines for protecting critical infrastructure facilities against acts of terrorism. This research experimentally and numerically studies the adequacy of high performance steel tube columns with and without infill materials under impact and blast loadings.

    The paper describes the results of experimental studies of steel sections both filled and unfilled subjected to high intensity impact loads. The results from the impact tests are compared with the results from high-fidelity physics-based numerical models for high-performance steel sections and infill materials. The potential advantages of using infill materials to increase the energy absorption capacity of steel sections are identified and discussed.

    Risk-Based Optimisation of Protective Measures Against Terrorist Threats to Infrastructure
    Mark G. Stewart

    A decision support analysis considers fatality risks and cost-effectiveness of protective measures expressed in terms of expected cost spent on risk reduction per life saved for terrorist threats to infrastructure. The analysis is applicable to any item of infrastructure, but in this paper is applied to commercial buildings. Risks may be compared with risk acceptance criteria in the form of quantitative safety goals. The risk acceptability and cost-effectiveness of protective measures includes cost of the protective measures, attack probability, reduction in risk due to protective measures, probability of fatality conditional on successful terrorist attack and number of exposed individuals.

    The risk-based approach developed herein provides a means for initial risk screening based on the broad levels of risk and its acceptability. It was found that the annual fatality risks are very low for small and large commercial buildings without protective measures subject to a non-specific threat. It was also suggested that expenditure typically needed to provide substantial protection to buildings is not cost-effective for new and existing commercial buildings subject to a non-specific threat. However, for a specific threat the provision of protective measures is more likely to be cost-effective.

    Numerical Analysis of Fiber Reinforced Polymer Composite Strengthened RC Walls with Anchorages against Blast Loads
    A. A.Mutalib, H. Hao

    Since the early 1990s, accidental explosions and terrorist events have greatly heightened the awareness of building owners and designers of the threats of explosive loadings. Extensive research has been conducted into blast effects on building structures and the protective design methods using the Fiber Reinforced Polymer (FRP) strengthening concepts in resisting progressive collapse, structural damage and preventing injuries against dynamic explosive impacts.

    Both numerical and experimental studies have proved the effectiveness of the FRP in strengthening structures to resist blast loads. However, problems subjected to end anchorage, bond length, and premature peeling has been a concern when strengthening structures in flexure or shear using the FRP. In this paper, numerical analyses of dynamic response and damage of FRP composite strengthened RC walls with anchorages are carried out to examine the structural response under blast loads.

    The research illustrated that an anchor system could be necessary when using externally FRP laminates for strengthening RC walls to prevent premature peeling. This study presents three simulations of RC walls that are unstrengthened RC wall, FRP composite strengthened RC wall with end anchorage and FRP composite strengthened RC wall with both end anchorage and anchors applied at a minimum spacing across the width and height of RC wall under different blast loads. Commercial software LS-DYNA is used to carry out the structural response analysis. Numerical results show that both anchors enhance the capacity of the externally bonded FRP by preventing the peeling phenomenon.

    Numerical Modelling of High-Speed Impact Tests of Concrete Material Properties
    Hong Hao, Xiaoqing Zhou, Zhong-Xian Li

    This paper discusses the challenges in dynamic impact tests of concrete specimens to determine the concrete material properties at high strain rates, and presents numerical models that are developed to conduct numerical simulations of concrete material properties. The numerical models developed include a homogeneous concrete material model and a three-phase mesoscale concrete material model with distinctive modeling of aggregates, mortar matrix and interfacial transition zone (ITZ) between aggregates and mortar matrix. Different material models, including damage model, strength model, Equation of State and strain rate enhancement, are used for different materials. These models are used to simulate impact tests to determine the compressive and tensile properties of concrete materials at high strain rates. Numerical results are compared with actual test data. The feasibility of using numerical simulations to supplement physical tests in determining the concrete material properties at high strain rate is demonstrated.

    Application of Distributed Nonlinearity for Progressive Collapse Analysis of Reinforced Concrete Frames
    Hamid R. Valipour, Stephen J. Foster

    This paper presents the formulation of a novel 1D frame element with distributed nonlinearity and its application for progressive collapse assessment of reinforced concrete frames. The force interpolation method is adopted to formulate the element. The material nonlinearity including the softening of concrete under compression is taken into account and the problem of objectivity associated with concrete softening is resolved by using a non-local damage formulation. Geometrical nonlinearity is taken into account by satisfying the equilibrium equations for the deformed element, however, the strains and slope are assumed to be small.

    A composite Simpson integration scheme, accompanied with a parabolic piecewise interpolation of curvature function is used to establish the deformed shape of the element required for the geometrical nonlinearity analysis. The effect of strain rate on the material strength and stiffness is taken into account by adopting dynamic increase factor (DIF) approach. The efficiency and accuracy of the formulation compared with available analytical and experimental results is verified by some numerical examples.

    Polymer Reinforced Concrete Panels to Resist Blast Loads
    Sudharshan Raman, Tuan Ngo, Priyan Mendis

    A review and preliminary investigations on the use of polymer coatings to enhance the blast resistance of reinforced concrete (RC) structures will be presented. A RC panel was constructed, and then subjected full scale blast tests in Woomera, South Australia in March 2007. The same panel was then modelled with an explicit finite element (FE) code, to simulate the experimental testing. Subsequently, modified designs of the panel were modelled by applying polyurea coatings in order to evaluate the efficiency of the proposed retrofitting technique in enhancing the blast resistance of the RC panels. The findings of the FE analysis indicate that RC panels coated with polyurea perform much better than the unretrofitted RC panel under the blast loading conditions.

    Blast Resistance of FRP Retrofitted RC Slabs
    Chengqing Wu, Oehlers DJ, Rebentrost M, Leach J, Whittaker AS

    Tests were conducted to investigate the performance of two conventionally reinforced slabs augmented with FRP (fibre reinforced polymer) under near-field blast loading. The FRP was externally bonded (EB) to the compressive (loaded) face of the 2000 1000 100mm slabs. Two normal reinforced concrete (NRC) slabs were also tested as control specimens.. The response of each slab was monitored with an accelerometer, a LVDT and two pressure transducers. The pressure sensors located at the centre and at one edge of the slabs measured airblast pressure that varied significantly from those estimated using traditional procedures such as those in TM5-1300. The tests indicated that the addition of the EB CFRP plates to the compressive face improved the ductility and blast resistance of the slabs. Pressure loadings, crack patterns, failure mode(s) and permanent displacement are reported for each specimen and compared.

    Behaviour of Glass Façade Panels
    Raymond Lumantarna, Harry Susiswo, Priyan Mendis and Tuan Ngo

    This presentation reports part of a study on the vulnerability of window facade units under blast loads. Glazing unit is the weakest part of a façade system which can be easily breached if subjected to extreme loads such as blast or impact. In the past, fragility curves have been used as vulnerability assessment tools for the glazing element, while the predominantly deterministic pressure impulse curves has been used effectively to characterise damages on both structural and façade elements. The work presented in this forum highlight the framework required to develop an effective vulnerability assessment tool based on principles used in pressure impulse and fragility curves. The numerical analysis was performed with LS-DYNA explicit finite element analysis code.

    Challenges in High-Speed Impact Tests of Dynamic Concrete Material Properties
    Yifei Hao, Hong Hao, Boris Tarasov

    This paper discusses the challenges in conducting the high-speed impact tests of dynamic concrete material properties. These include the limitations of the commonly used test equipments such as the drop hammer, Split Hopkinson Pressure Bar (SHPB) and light gas gun, and the problems related to dynamic testing such as the axial inertial confinement, stress wave propagation, lateral inertial confinement, and end friction. For concrete materials, effect of aggregate size is another problem that needs be investigated since most previous high-speed impact tests were conducted using mortar specimens without aggregates, owing to the equipment limitation.

    With the newly developed blast/impact simulator in UWA and numerical simulations, these problems will be systematically investigated in this work. In particular, the aggregate size effect, lateral inertial confinement effect, and end friction effect will be quantified based on both the laboratory test data and numerical simulation results. The axial inertial confinement and stress wave propagation problem will also be investigated and some correction factors will be introduced to correct the strain readings to eliminate their influence in order to get the true dynamic concrete material properties.

    An Improved Procedure for Progressive Collapse Analysis of RC Frames to Blast Loading
    Yanchao Shi, Hong Hao, Zhong-Xian Li

    After the September 11 event, there has been a sharp increase in research activities related to structural progressive collapse. The US GSA and DoD also provide guidelines for structural progressive analysis. All the previous studies, as well as the GSA and DoD guidelines assume structural progressive collapse starts from zero initial conditions. Although the blast-loading phase is very short and the structural progressive collapse usually occurs after the loading phase, when a structure starts to collapse progressively, it will not start from zero initial condition. Moreover, if the blast load is big enough to knock down one or a few key vertical load-carrying members, it is very likely that it would cause damage of different degrees to adjacent structural members. Neglecting the nonzero initial conditions and damage of adjacent structural members in analysis might lead to inaccurate prediction of structural progressive collapse.

    In this paper, an improved procedure for progressive collapse analysis of reinforced concrete (RC) frames under blast loading is proposed. The method takes into account the nonzero initial conditions and structural member damage. A three-storey two-span RC frame is used as an example to demonstrate the method. Numerical results are compared with those obtained using the GSA and DoD method, and with those from a comprehensive numerical simulations by directly applying the blast loads on the frame. It is found that the proposed method is efficient and reliable in simulating the progressive collapse of RC frames as compared to the direct numerical simulations, and gives more accurate predictions of structural progressive collapse process as compared to the US GSA and DoD guidelines.

    Behaviour of FRP Reinforced Concrete Panels
    Ganchai Tanapornraweekit , N. Haritos, P. Mendis, T. Ngo

    Strengthening of RC structures is a major task in protective structural design. Improvements in the blast resistance of structures by means of Fibre Reinforced Polymers (FRP) has been shown to be effective, experimentally from a review of the literature. From the modeling point of view, however, it would appear that the strain rate effects of FRP material have not been taken into account in studies appearing in the literature which might result in differences in the predicted behavior of a composite structure under blast. An extensive review of experimental results related to the stress-strain relationship of FRP under high strain rates has been conducted to develop a universal constitutive model of FRP material for a range of strain rates. This research will finally combine the developed FRP constitutive model with non-linear FE modeling to verify the resultant numerical model predictions against available experimental results. A summary of these results will be presented in the forum.