The Experts below are selected from a list of 62004 Experts worldwide ranked by ideXlab platform
George S. Springer - One of the best experts on this subject based on the ideXlab platform.
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Delaminations in composite plates under transverse Impact Loads — Experimental results
Composite Structures, 2003Co-Authors: Scott R. Finn, Ye-fei He, George S. SpringerAbstract:Abstract Tests were performed measuring the locations and geometries of delaminations in Fiberite T300/976 graphite/epoxy, Fiberite IM7/977-2 graphite-toughened epoxy, and ICI APC-2 graphite/PEEK plates subjected to transverse Impact Loads. The data provide specific information on the effects of Impactor velocity, Impactor mass, material, thickness of back ply group, difference in fiber orientation between adjacent ply groups, plate thickness, and Impactor nose radius. The data were compared to the results of the Finn-Springer model. The model was found to describe the data with reasonable accuracy.
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delaminations in composite plates under transverse Impact Loads experimental results
Composite Structures, 1993Co-Authors: Scott R. Finn, George S. SpringerAbstract:Abstract Tests were performed measuring the locations and geometries of delaminations in Fiberite T300/976 graphite/epoxy, Fiberite IM7/977-2 graphite-toughened epoxy, and ICI APC-2 graphite/PEEK plates subjected to transverse Impact Loads. The data provide specific information on the effects of Impactor velocity, Impactor mass, material, thickness of back ply group, difference in fiber orientation between adjacent ply groups, plate thickness, and Impactor nose radius. The data were compared to the results of the Finn-Springer model. The model was found to describe the data with reasonable accuracy.
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delaminations in composite plates under transverse static or Impact Loads a model
Composite Structures, 1993Co-Authors: Scott R. Finn, George S. SpringerAbstract:A method is presented for calculating the locations, shapes, and sizes of delaminations which occur in a fiber reinforced composite plate subjected to transverse static or dynamic (Impact) Loads. The plate may be simply supported, clamped, or free along its edges. A model of the delamination formation was developed. This model was then coupled with a finite element analysis. The model and the finite element analysis were implemented by a computer code which can be used to estimate the load at which damage is initiated as well as the locations, shapes, and sizes of the delaminations.
Scott R. Finn - One of the best experts on this subject based on the ideXlab platform.
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Delaminations in composite plates under transverse Impact Loads — Experimental results
Composite Structures, 2003Co-Authors: Scott R. Finn, Ye-fei He, George S. SpringerAbstract:Abstract Tests were performed measuring the locations and geometries of delaminations in Fiberite T300/976 graphite/epoxy, Fiberite IM7/977-2 graphite-toughened epoxy, and ICI APC-2 graphite/PEEK plates subjected to transverse Impact Loads. The data provide specific information on the effects of Impactor velocity, Impactor mass, material, thickness of back ply group, difference in fiber orientation between adjacent ply groups, plate thickness, and Impactor nose radius. The data were compared to the results of the Finn-Springer model. The model was found to describe the data with reasonable accuracy.
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delaminations in composite plates under transverse Impact Loads experimental results
Composite Structures, 1993Co-Authors: Scott R. Finn, George S. SpringerAbstract:Abstract Tests were performed measuring the locations and geometries of delaminations in Fiberite T300/976 graphite/epoxy, Fiberite IM7/977-2 graphite-toughened epoxy, and ICI APC-2 graphite/PEEK plates subjected to transverse Impact Loads. The data provide specific information on the effects of Impactor velocity, Impactor mass, material, thickness of back ply group, difference in fiber orientation between adjacent ply groups, plate thickness, and Impactor nose radius. The data were compared to the results of the Finn-Springer model. The model was found to describe the data with reasonable accuracy.
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delaminations in composite plates under transverse static or Impact Loads a model
Composite Structures, 1993Co-Authors: Scott R. Finn, George S. SpringerAbstract:A method is presented for calculating the locations, shapes, and sizes of delaminations which occur in a fiber reinforced composite plate subjected to transverse static or dynamic (Impact) Loads. The plate may be simply supported, clamped, or free along its edges. A model of the delamination formation was developed. This model was then coupled with a finite element analysis. The model and the finite element analysis were implemented by a computer code which can be used to estimate the load at which damage is initiated as well as the locations, shapes, and sizes of the delaminations.
Alexander Remennikov - One of the best experts on this subject based on the ideXlab platform.
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on the residual energy toughness of prestressed concrete sleepers in railway track structures subjected to repeated Impact Loads
Electronic Journal of Structural Engineering, 2013Co-Authors: Sakdirat Kaewunruen, Alexander RemennikovAbstract:Installed as the crosstie beam support in railway track systems, the prestressed concrete sleepers (or railroad ties) are designed in order to carry and transfer the wheel Loads from the rails to the ground. It is nowadays best known that railway tracks are subject to the Impact loading conditions, which are attributable to the train operations with either wheel or rail abnormalities such as flat wheels, dipped rails, etc. These Loads are of very high magnitude but short duration, as well as there exists the potential of repeated load experience during the design life of the prestressed concrete sleepers. These have led to two main limit states for the de- sign consideration: ultimate limit states under extreme Impact and fatigue limit states under repeated Impact Loads. Prestressed concrete has played a significant role as to maintain the high endurance of the sleepers un- der low to moderate repeated Impact Loads. In spite of the most common use of the prestressed concrete sleep- ers in railway tracks, their Impact responses and behaviours under the repetitions of severe Impact Loads are not deeply appreciated nor taken into the design consideration. This experimental investigation was aimed at understanding the residual capacity of prestressed concrete sleepers in railway track structures under repeated Impact loading, in order to form the state of the art of limit states design concept for prestressed concrete sleepers. A high-capacity drop weight Impact testing machine was constructed at the University of Wollon- gong as to achieve the purpose. Series of repeated Impact tests for the in-situ prestressed concrete sleepers were carried out, ranging from low to high Impact magnitudes. The Impact forces have been correlated against the probabilistic track force distribution obtained from a Queensland heavy haul rail network. The Impact- damaged sleepers were re-tested under static conditions in order to evaluate the residual energy toughness in accordance with the Australian Standard. It is found that a concrete sleeper damaged by an Impact load could possess significant reserve capacity sufficient for resisting the axle load of about 1.05 to 1.10 times of the de- sign axle Loads. The accumulative Impact damage and residual energy toughness under different magnitudes of probabilistic Impacts are highlighted in this paper. The effects of track environment including soft and hard tracks are also presented as to implement design guidance related to the serviceability or fatigue limit states design.
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Dynamic crack propagations in prestressed concrete sleepers in railway track systems subjected to severe Impact Loads
Journal of Structural Engineering-asce, 2010Co-Authors: Sakdirat Kaewunruen, Alexander RemennikovAbstract:Prestressed concrete sleepers (or railroad ties) are the crosstie beam support in railway track systems. They are designed and constructed under flexural constraints in order to carry and transfer the dynamic wheel Loads from the rails to the ground. Under perfect wheel and rail conditions, the dynamic loading on railway tracks could be treated as a quasi-static load using a dynamic Impact factor. The current design method for the prestressed concrete sleepers taking into account the quasi-static effect is based on allowable stress where crack initiation is not permitted. In reality, the Impact events are often detected due to the uncertainties of wheel or rail abnormalities such as flat wheels, dipped rails, etc. These Loads are of very high magnitude but short duration. Over the design life span of the prestressed concrete sleepers, there exists the feasibility of extreme and repeated Impact loading events. These have led to two proposed limit states for the consideration of structural engineers: ultimate limit states and fatigue limit states. Prestressing techniques have been long used to maintain the high endurance of the sleepers under repeated Impact cycles. In spite of the most common use of the prestressed concrete sleepers, their Impact behavior and capacity under the repetitions of severe Impact Loads are unclear. This paper presents the experimental investigation aimed at understanding the dynamic crack propagations in prestressed concrete sleepers in railway track structures under repeated Impact loading. The Impact forces have been correlated against the probabilistic track force distribution obtained from an Australian heavy haul rail network. The effects of track environment including soft and hard tracks are highlighted in this paper.
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An Experimental Evaluation of the Attenuation Effect of Rail Pad on Flexural Behaviour of Railway Concrete Sleeper under Severe Impact Loads
2008Co-Authors: Sakdirat Kaewunruen, Alexander RemennikovAbstract:Interactions between the wheel of rolling stocks and the rail often generate interfacial Impact forces to railway tracks. The dynamic Impact Loads are of very high magnitude but short duration, and are caused by either wheel or rail abnormalities such as flat wheels, dipped rails, etc. Although the possibility of the large Impact loading to cause an extreme failure to an insitu concrete sleeper could be very low about once or twice in the design life cycle, the damage of track components especially for the concrete sleepers is often observed. The railway sleeper is a major component of railway tracks. Its role is to distribute the load from the rails to the underlying ballast bed. Up to current knowledge, the behaviour of the insitu pre-stressed concrete sleepers under the Impact loading has not yet been thoroughly comprehended. In order to evaluate the resistance of railway concrete sleepers to Impact Loads, a high-capacity drop-weight Impact testing machine was thus constructed at the University of Wollongong. It is currently the largest one of its kind in Australia with the maximum drop height of 6m. This paper demonstrates the experimental investigations, in order to evaluate the attenuation effect of rail pads on the Impact behaviour of railway concrete sleepers. The Impact tests were carried out using pre-stressed concrete sleepers manufactured in Australia. This study enables and enhances the methodology to analyse and design for the pre-stressed concrete sleepers at ultimate limit states.
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Experimental and Numerical Studies of Railway Prestressed Concrete Sleepers Under Static and Impact Loads
2007Co-Authors: Sakdirat Kaewunruen, Alexander RemennikovAbstract:Railway sleeper is an important component of rail-way track structures. Its role is to distribute Loads from the rail foot to the underlying ballast bed. There is a widespread notion based on the industry experi-ence that railway concrete sleepers have reserves of strength that are untapped. It is thus important to ascertain the spectrum and amplitudes of forces ap-plied to the railway track, to understand more clearly the manner in which track components respond to those forces, and to clarify the processes whereby concrete sleepers in particular carry those actions. In addition, cracks in concrete sleepers have been visually observed by many railway organizations. As noted in the review [1], the principal cause of crack-ing is the infrequent but high-magnitude wheel Loads produced by a small percentage of “bad” wheels or railhead surface defects. Those Loads are of short duration but of very high magnitude. For instance, the typical loading duration produced by wheel flats is about 1-10 msec, while the force magnitude can be over 400 KN per rail seat. Current design philos-ophy for prestressed concrete sleepers is based on permissible stress principle taking into account only the static and quasi-static Loads, which are unrealistic to the actual dynamic Loads on tracks. In order to de-vise a new limit states design concept, the research efforts are required to perform comprehensive stud-ies of the loading conditions, the static behaviour, the dynamic response, and the Impact resistance of the prestressed concrete sleepers [2-5]. A ma-jor research effort at the University of Wollongong is to evaluate and compare the ultimate capacities of concrete sleepers under static and Impact Loads. There have been only a few studies related to the modelling of prestressed concrete sleepers. Most of them predicted the rail seat flexural behaviour of the concrete sleepers, as shown in Figure 1 [2, 6]. Also, since high-capacity Impact tests require signifi-cant amount of resources and are time consuming, a convenient means to develop an understanding of the Impact behaviour is to use the numerical Impact simulations.Finite element analysis (FEA) provides a tool that can simulate and predict the responses of reinforced and prestressed concrete members. A three-dimen-sional non-linear finite element model of a railway prestressed concrete sleeper was developed using the general purpose finite element analysis package, ANSYS10 [7]. The concrete section was modelled using SOLID65 solid element where the compres-sive crushing of concrete and the concrete cracking in tension zone can be accommodated [8-10]. In thecurrent practice, the railway concrete sleeper is de-signed to resist prestressing force fully throughout the whole cross section as the force/moment redis-tribution can be seen in Figure 1. The static full-scale experiment was conducted to validate this FE model [5]. The experimental details were based on the associated Australian Standards [10, 11]. Com-parison with experimental load-deflection response is then presented. The calibrated finite element model was extended to include ballast support and was linked to LS-Dyna [12] for Impact analysis and validation against the drop Impact tests.
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Experimental determination of energy absorption capacity for prestressed concrete sleepers under Impact Loads
2007Co-Authors: Alexander Remennikov, Sakdirat KaewunruenAbstract:Extreme loading conditions on railway tracks may include dynamic Impact Loads with very high magnitude but short duration. These loading conditions are caused by wheel or rail abnormalities such as flat wheels, dipped rails, etc. A high-capacity drop weight Impact testing machine was constructed at the University of Wollongong, in order to evaluate the ultimate capacity of prestressed concrete sleepers under Impact Loads. This paper presents the experimental investigations to evaluate failure modes, flexural toughness, and energy absorption mechanisms for railway prestressed concrete sleepers under static and Impact loadings. Energy absorption capacity of the prestressed concrete sleepers was also evaluated to determine the amount of energy required to fail the sleeper under Impact load. Static and Impact tests were carried out on the Australian-manufactured prestressed concrete sleepers. The residual capacity of the prestressed concrete sleepers after Impact has also been highlighted. Figure 1. Typical components of railway tracks. ties, contact zone stiffness, frequency of loading, precision of Impact, and locally energy-absorbed area (Hughes and Al-Dafiry, 1995). Regarding to railway sleepers, Ye, et al. (1994) and Wang (1996) investigated the resistance of concrete railroad ties to Impact loading. Their study focused on the effect of material uses on the ultimate capacity of prestressed concrete sleepers. However, it was unclear whether strain rate has an effect on the behaviors of concrete sleepers or not, and whether there could be a simplified prediction for the ultimate capacity of concrete sleepers. The key hindrance was about how rail pad really affect the system Impact responses and how much of that effect. Wakui and Okuda (1999) have later proposed a simplified technique to predict the ultimate capacity of concrete sleepers but they failed to prove it. In the proposal, strain rate and loading rate have been taken into account in moment capacity calculation on the basis of sectional analysis and only steel tendons’ failure mechanisms. So far, the ultimate behaviors of prestressed concrete sleepers under Impacts are currently unclear and there is no method to predict the ultimate moment capacity under Impact loading. This paper examines the ultimate behaviour of railway prestressed concrete sleepers subjected to static and Impact loading. The prestressed concrete sleepers were designed complied with Australian Standard: AS1085.14 (2003). The test specimens were kindly supplied by an Australian manufacturer, ROCLA. Static energy absorption capacity can be obtained from the static tests. Drop-weight Impact hammer was used to apply extreme Impact loading to the specimens at certain drop heights on the basis of the test arrangement. The Impact pulses were recorded using the high capacity load cell connected to the National Instrument data acquisition system. After applying the ultimate Impact load, the sleeper was re-tested for residual capacity and energy absorption. The comparative study of both static and Impact energy absorption of prestressed concrete sleepers was carried out. The damage and failure modes were identified in this paper. 2 EXPERIMENTAL OVERVIEW 2.1 Testing specimens The typical full-scale prestressed concrete sleeper, which is often used in broad gauge tracks, was selected for these tests. The dimensions and shape of the prestressed concrete sleeper are shown in Table 1. The high strength concrete material was used to construct the prestressed concrete sleepers, with design compressive strength at 28 days of 55 MPa, and the prestressing steels used were the high strength with rupture strength of 1860 MPa. The cored samples, drilled from the sleepers, were taken and tested, as per the Australian Standard AS1012.14, as shown in Figure 2. It was found that the average compressive strength at the test age of about two years was 80 MPa. It is believed that the high strength prestressing wires are of high quality and the strength will not change during time. Cross section of the prestressed concrete sleepers at railseat can be seen in Figure 3. 2.2 Experimental program In the experiments, a steel plate was used to distribute Impact load to concrete sleepers. The width of the plate is equivalent to railseat and effective zone described in AS1085.14 (2001). The supports were considered as a simple support with influential span due to elastic support. These supports provide restraints to the translational and rotational deformation. The weight of the projectile was set as 5.81 kN, and therefore, the drop height becomes the only variable. The experimental setup thus required for specific energy absorption capacity for particular sleeper, in order to back calculating for the optimum drop height. A sleeper was performed the static tests in the conventional manner as shown in Figure 4. An electronic load cell was used to measure the applied load in order to keep load accurate and consistent, while LDVT was mounted at the mid-span to obtain the corresponding deflection. The device was connected to computer for recording. Figure 2. Cored concrete samples Figure 3. Cross section of sleepers at railseat Figure 4. Static test setup. Figure 5. Impact test setup. Table 1. Dimensions and masses of the test sleepers At railseat (m) At centre (m) Mass
Sakdirat Kaewunruen - One of the best experts on this subject based on the ideXlab platform.
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on the residual energy toughness of prestressed concrete sleepers in railway track structures subjected to repeated Impact Loads
Electronic Journal of Structural Engineering, 2013Co-Authors: Sakdirat Kaewunruen, Alexander RemennikovAbstract:Installed as the crosstie beam support in railway track systems, the prestressed concrete sleepers (or railroad ties) are designed in order to carry and transfer the wheel Loads from the rails to the ground. It is nowadays best known that railway tracks are subject to the Impact loading conditions, which are attributable to the train operations with either wheel or rail abnormalities such as flat wheels, dipped rails, etc. These Loads are of very high magnitude but short duration, as well as there exists the potential of repeated load experience during the design life of the prestressed concrete sleepers. These have led to two main limit states for the de- sign consideration: ultimate limit states under extreme Impact and fatigue limit states under repeated Impact Loads. Prestressed concrete has played a significant role as to maintain the high endurance of the sleepers un- der low to moderate repeated Impact Loads. In spite of the most common use of the prestressed concrete sleep- ers in railway tracks, their Impact responses and behaviours under the repetitions of severe Impact Loads are not deeply appreciated nor taken into the design consideration. This experimental investigation was aimed at understanding the residual capacity of prestressed concrete sleepers in railway track structures under repeated Impact loading, in order to form the state of the art of limit states design concept for prestressed concrete sleepers. A high-capacity drop weight Impact testing machine was constructed at the University of Wollon- gong as to achieve the purpose. Series of repeated Impact tests for the in-situ prestressed concrete sleepers were carried out, ranging from low to high Impact magnitudes. The Impact forces have been correlated against the probabilistic track force distribution obtained from a Queensland heavy haul rail network. The Impact- damaged sleepers were re-tested under static conditions in order to evaluate the residual energy toughness in accordance with the Australian Standard. It is found that a concrete sleeper damaged by an Impact load could possess significant reserve capacity sufficient for resisting the axle load of about 1.05 to 1.10 times of the de- sign axle Loads. The accumulative Impact damage and residual energy toughness under different magnitudes of probabilistic Impacts are highlighted in this paper. The effects of track environment including soft and hard tracks are also presented as to implement design guidance related to the serviceability or fatigue limit states design.
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Dynamic crack propagations in prestressed concrete sleepers in railway track systems subjected to severe Impact Loads
Journal of Structural Engineering-asce, 2010Co-Authors: Sakdirat Kaewunruen, Alexander RemennikovAbstract:Prestressed concrete sleepers (or railroad ties) are the crosstie beam support in railway track systems. They are designed and constructed under flexural constraints in order to carry and transfer the dynamic wheel Loads from the rails to the ground. Under perfect wheel and rail conditions, the dynamic loading on railway tracks could be treated as a quasi-static load using a dynamic Impact factor. The current design method for the prestressed concrete sleepers taking into account the quasi-static effect is based on allowable stress where crack initiation is not permitted. In reality, the Impact events are often detected due to the uncertainties of wheel or rail abnormalities such as flat wheels, dipped rails, etc. These Loads are of very high magnitude but short duration. Over the design life span of the prestressed concrete sleepers, there exists the feasibility of extreme and repeated Impact loading events. These have led to two proposed limit states for the consideration of structural engineers: ultimate limit states and fatigue limit states. Prestressing techniques have been long used to maintain the high endurance of the sleepers under repeated Impact cycles. In spite of the most common use of the prestressed concrete sleepers, their Impact behavior and capacity under the repetitions of severe Impact Loads are unclear. This paper presents the experimental investigation aimed at understanding the dynamic crack propagations in prestressed concrete sleepers in railway track structures under repeated Impact loading. The Impact forces have been correlated against the probabilistic track force distribution obtained from an Australian heavy haul rail network. The effects of track environment including soft and hard tracks are highlighted in this paper.
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An Experimental Evaluation of the Attenuation Effect of Rail Pad on Flexural Behaviour of Railway Concrete Sleeper under Severe Impact Loads
2008Co-Authors: Sakdirat Kaewunruen, Alexander RemennikovAbstract:Interactions between the wheel of rolling stocks and the rail often generate interfacial Impact forces to railway tracks. The dynamic Impact Loads are of very high magnitude but short duration, and are caused by either wheel or rail abnormalities such as flat wheels, dipped rails, etc. Although the possibility of the large Impact loading to cause an extreme failure to an insitu concrete sleeper could be very low about once or twice in the design life cycle, the damage of track components especially for the concrete sleepers is often observed. The railway sleeper is a major component of railway tracks. Its role is to distribute the load from the rails to the underlying ballast bed. Up to current knowledge, the behaviour of the insitu pre-stressed concrete sleepers under the Impact loading has not yet been thoroughly comprehended. In order to evaluate the resistance of railway concrete sleepers to Impact Loads, a high-capacity drop-weight Impact testing machine was thus constructed at the University of Wollongong. It is currently the largest one of its kind in Australia with the maximum drop height of 6m. This paper demonstrates the experimental investigations, in order to evaluate the attenuation effect of rail pads on the Impact behaviour of railway concrete sleepers. The Impact tests were carried out using pre-stressed concrete sleepers manufactured in Australia. This study enables and enhances the methodology to analyse and design for the pre-stressed concrete sleepers at ultimate limit states.
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Experimental and Numerical Studies of Railway Prestressed Concrete Sleepers Under Static and Impact Loads
2007Co-Authors: Sakdirat Kaewunruen, Alexander RemennikovAbstract:Railway sleeper is an important component of rail-way track structures. Its role is to distribute Loads from the rail foot to the underlying ballast bed. There is a widespread notion based on the industry experi-ence that railway concrete sleepers have reserves of strength that are untapped. It is thus important to ascertain the spectrum and amplitudes of forces ap-plied to the railway track, to understand more clearly the manner in which track components respond to those forces, and to clarify the processes whereby concrete sleepers in particular carry those actions. In addition, cracks in concrete sleepers have been visually observed by many railway organizations. As noted in the review [1], the principal cause of crack-ing is the infrequent but high-magnitude wheel Loads produced by a small percentage of “bad” wheels or railhead surface defects. Those Loads are of short duration but of very high magnitude. For instance, the typical loading duration produced by wheel flats is about 1-10 msec, while the force magnitude can be over 400 KN per rail seat. Current design philos-ophy for prestressed concrete sleepers is based on permissible stress principle taking into account only the static and quasi-static Loads, which are unrealistic to the actual dynamic Loads on tracks. In order to de-vise a new limit states design concept, the research efforts are required to perform comprehensive stud-ies of the loading conditions, the static behaviour, the dynamic response, and the Impact resistance of the prestressed concrete sleepers [2-5]. A ma-jor research effort at the University of Wollongong is to evaluate and compare the ultimate capacities of concrete sleepers under static and Impact Loads. There have been only a few studies related to the modelling of prestressed concrete sleepers. Most of them predicted the rail seat flexural behaviour of the concrete sleepers, as shown in Figure 1 [2, 6]. Also, since high-capacity Impact tests require signifi-cant amount of resources and are time consuming, a convenient means to develop an understanding of the Impact behaviour is to use the numerical Impact simulations.Finite element analysis (FEA) provides a tool that can simulate and predict the responses of reinforced and prestressed concrete members. A three-dimen-sional non-linear finite element model of a railway prestressed concrete sleeper was developed using the general purpose finite element analysis package, ANSYS10 [7]. The concrete section was modelled using SOLID65 solid element where the compres-sive crushing of concrete and the concrete cracking in tension zone can be accommodated [8-10]. In thecurrent practice, the railway concrete sleeper is de-signed to resist prestressing force fully throughout the whole cross section as the force/moment redis-tribution can be seen in Figure 1. The static full-scale experiment was conducted to validate this FE model [5]. The experimental details were based on the associated Australian Standards [10, 11]. Com-parison with experimental load-deflection response is then presented. The calibrated finite element model was extended to include ballast support and was linked to LS-Dyna [12] for Impact analysis and validation against the drop Impact tests.
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Experimental determination of energy absorption capacity for prestressed concrete sleepers under Impact Loads
2007Co-Authors: Alexander Remennikov, Sakdirat KaewunruenAbstract:Extreme loading conditions on railway tracks may include dynamic Impact Loads with very high magnitude but short duration. These loading conditions are caused by wheel or rail abnormalities such as flat wheels, dipped rails, etc. A high-capacity drop weight Impact testing machine was constructed at the University of Wollongong, in order to evaluate the ultimate capacity of prestressed concrete sleepers under Impact Loads. This paper presents the experimental investigations to evaluate failure modes, flexural toughness, and energy absorption mechanisms for railway prestressed concrete sleepers under static and Impact loadings. Energy absorption capacity of the prestressed concrete sleepers was also evaluated to determine the amount of energy required to fail the sleeper under Impact load. Static and Impact tests were carried out on the Australian-manufactured prestressed concrete sleepers. The residual capacity of the prestressed concrete sleepers after Impact has also been highlighted. Figure 1. Typical components of railway tracks. ties, contact zone stiffness, frequency of loading, precision of Impact, and locally energy-absorbed area (Hughes and Al-Dafiry, 1995). Regarding to railway sleepers, Ye, et al. (1994) and Wang (1996) investigated the resistance of concrete railroad ties to Impact loading. Their study focused on the effect of material uses on the ultimate capacity of prestressed concrete sleepers. However, it was unclear whether strain rate has an effect on the behaviors of concrete sleepers or not, and whether there could be a simplified prediction for the ultimate capacity of concrete sleepers. The key hindrance was about how rail pad really affect the system Impact responses and how much of that effect. Wakui and Okuda (1999) have later proposed a simplified technique to predict the ultimate capacity of concrete sleepers but they failed to prove it. In the proposal, strain rate and loading rate have been taken into account in moment capacity calculation on the basis of sectional analysis and only steel tendons’ failure mechanisms. So far, the ultimate behaviors of prestressed concrete sleepers under Impacts are currently unclear and there is no method to predict the ultimate moment capacity under Impact loading. This paper examines the ultimate behaviour of railway prestressed concrete sleepers subjected to static and Impact loading. The prestressed concrete sleepers were designed complied with Australian Standard: AS1085.14 (2003). The test specimens were kindly supplied by an Australian manufacturer, ROCLA. Static energy absorption capacity can be obtained from the static tests. Drop-weight Impact hammer was used to apply extreme Impact loading to the specimens at certain drop heights on the basis of the test arrangement. The Impact pulses were recorded using the high capacity load cell connected to the National Instrument data acquisition system. After applying the ultimate Impact load, the sleeper was re-tested for residual capacity and energy absorption. The comparative study of both static and Impact energy absorption of prestressed concrete sleepers was carried out. The damage and failure modes were identified in this paper. 2 EXPERIMENTAL OVERVIEW 2.1 Testing specimens The typical full-scale prestressed concrete sleeper, which is often used in broad gauge tracks, was selected for these tests. The dimensions and shape of the prestressed concrete sleeper are shown in Table 1. The high strength concrete material was used to construct the prestressed concrete sleepers, with design compressive strength at 28 days of 55 MPa, and the prestressing steels used were the high strength with rupture strength of 1860 MPa. The cored samples, drilled from the sleepers, were taken and tested, as per the Australian Standard AS1012.14, as shown in Figure 2. It was found that the average compressive strength at the test age of about two years was 80 MPa. It is believed that the high strength prestressing wires are of high quality and the strength will not change during time. Cross section of the prestressed concrete sleepers at railseat can be seen in Figure 3. 2.2 Experimental program In the experiments, a steel plate was used to distribute Impact load to concrete sleepers. The width of the plate is equivalent to railseat and effective zone described in AS1085.14 (2001). The supports were considered as a simple support with influential span due to elastic support. These supports provide restraints to the translational and rotational deformation. The weight of the projectile was set as 5.81 kN, and therefore, the drop height becomes the only variable. The experimental setup thus required for specific energy absorption capacity for particular sleeper, in order to back calculating for the optimum drop height. A sleeper was performed the static tests in the conventional manner as shown in Figure 4. An electronic load cell was used to measure the applied load in order to keep load accurate and consistent, while LDVT was mounted at the mid-span to obtain the corresponding deflection. The device was connected to computer for recording. Figure 2. Cored concrete samples Figure 3. Cross section of sleepers at railseat Figure 4. Static test setup. Figure 5. Impact test setup. Table 1. Dimensions and masses of the test sleepers At railseat (m) At centre (m) Mass
William Allsop - One of the best experts on this subject based on the ideXlab platform.
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evaluation of wave Impact Loads on caisson breakwaters based on joint probability of Impact maxima and rise times
Coastal Engineering, 2011Co-Authors: Giovanni Cuomo, R Piscopia, William AllsopAbstract:When waves break against seawalls, vertical breakwaters, piers or jetties, they abruptly transfer their momentum into the structure. This energy transfer is always spectacular and perpetually unrepeatable but can also be very violent and affect the stability and the integrity of coastal structures. Over the last 15 years, increasing awareness of wave-Impact induced structural failures of maritime structures has emphasised the need for a more complete approach to dynamic responses, including effects of impulsive Loads. At the same time, movement of design standards toward probabilistic approaches requires new statistical tools able to account for uncertainties in the variability of wave loading processes. This paper presents a new approach to the definition of Loads for use in performance design of vertical coastal structures subject to breaking wave Impacts. Based on conservation of momentum and joint probability of non-dimensional wave Impact maxima and rise times from large-scale test measurements, a new set of equations have been derived to characterise design Impact Loads at different non-exceedance probability levels and guidance is given for the estimation of the static-equivalent design Loads to be used in early-stage feasibility studies. Predictions of static equivalent design Loads and corresponding safety factor against sliding using the proposed methodology are found to be in very good agreement with both predictions by most established deterministic methods and field observations reported in literature.
