Copyright (c) 2009 All rights reserved. http://works.bepress.com/aremennikov Recent documents in Dr. Alex Remennikov en-us Sun, 31 May 2009 03:35:09 PDT 3600 http://works.bepress.com/aremennikov/31 http://works.bepress.com/aremennikov/31 Thu, 29 Jan 2009 21:06:11 PST This paper carries out the assessment of reliability indices of railway prestressed concrete sleepers designed in accordance with Australian Standard: AS1085.19. The current design approach of the prestressed concrete sleeper relies on the permissible stresses over crosssectional area. Loading condition acting on railway sleepers is considered from axle burden and dynamic amplification factor. On the basis of Australian design of railway prestressed concrete sleepers, only service limit states are considered; however, the design challenge is to provide adequate resistance of certain cross sections to both positive and negative bending moments. In this paper, the service limit states functions are formulated taking into account the permissible compressive and tensile stresses at both initial and final stages, and applied positive and negative bending moments at railseat and middle sections. Random variables in the reliability analysis include railway track design parameters, axle load, material and geometrical properties, prestressing force and its losses, and model uncertainties regarded to the structural resistance and load effects. Statistical properties of related parameters are adopted from previous studies. Two analysis methods are used: first-order moment reliability method (FORM) and second-order moment reliability method (SORM). Sensitivity analyses of the reliability indices for flexural capacity according to the requirements of the limit states functions are also investigated, in order to evaluate the major influences of dynamic load factors, strengths of materials, track parameters, and model uncertainties. S. Kaewunruen http://works.bepress.com/aremennikov/30 http://works.bepress.com/aremennikov/30 Thu, 29 Jan 2009 21:06:03 PST 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 in-situ prestressed 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 the prestressed concrete sleepers manufactured in Australia. This study enables and enhances the methodology to analyse and design for the prestressed concrete sleepers at ultimate limit states. S. Kaewunruen http://works.bepress.com/aremennikov/29 http://works.bepress.com/aremennikov/29 Thu, 29 Jan 2009 21:05:55 PST Both bolt profile shape and profile spacing (rib spacing) have been found to influence the bonding capacity of the grouted rock bolt. The bolt surface profile configuration has greater importance to rock bolt than the steel rebar used in civil engineering construction, because the rock bolt is subjected to greater dynamic loading than the steel rebar. The increased bonding capacity of bolts is important when supported ground is either heavily fractured, faulted or the supported ground is of soft formation, typically that of coal measure rocks. Past laboratory studies have identified the bolt profile spacing as of significant relevance to bolt resin rock bonding increase, however, no attempt has been made to determine the optimum spacing between the bolt profiles spacing. Accordingly, a series of laboratory tests were carried out on 22 core diameter bolts installed in cylindrical steel sleeve. The study was carried out by both push and pull testing. The push testing was carried out in 150 mm long sleeves while the pull testing was made in 115 mm long sleeves. Profile spacing tested include, 12.5, 25.0mm, 37.5 mm and 50 mm lengths. The profile spacing of 37.5 mm wide was found to provide the optimum bearing N. Aziz http://works.bepress.com/aremennikov/28 http://works.bepress.com/aremennikov/28 Thu, 29 Jan 2009 21:05:48 PST Commonly, railway tracks suffer with the extreme loading conditions, which are attributed 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 they are of low-possibility occurrence during the design life of the prestressed concrete sleepers. In spite of the most common use of the prestressed concrete sleepers in railway tracks, their impact responses and behaviours are not deeply appreciated nor taken into the design consideration. Up until recently, a new limit states design approach, whereas the dynamic effects are included, has been adopted in European countries, and has been proposed for the revision of Australian Standard AS1085.14.This paper presents the experimental investigations aimed at understanding the progressive collapse of prestressed concrete sleepers in railway track structures under incremental impact loading, in order to form the state of the art of the impact damage classification for prestressed concrete sleepers. Series of repeated impact tests for the in-situ prestressed concrete sleepers were carried out, ranging from a low drop height to the ultimate drop height where the ultimate failure occurred. The cumulative impact damage and crack propagation are highlighted in this paper. The effects of track environment including soft and hard tracks are also presented. By using the concept of damage accumulation, the relationships between cumulative damage of concrete sleepers and given impulse enable the predictions of residual life of the concrete sleepers under severe impact loads. It is noticed that the hard track condition rapidly exacerbates cracking in the concrete sleepers. Based on the progressive impact testing results, the damage classification of prestressed concrete sleepers has been proposed. This proposed damage index can be correlated to either increased axle load or faster train speed using an advanced dynamic analysis of railway track package. S. Kaewunruen http://works.bepress.com/aremennikov/27 http://works.bepress.com/aremennikov/27 Wed, 28 May 2008 11:26:32 PDT Ever increasing axle loads and train speeds are pressing track owners to extract as much performance as possible from their asset without wholesale or catastrophic failure. Unfortunately, there is insufficient knowledge of the static and dynamic loadings that a track may be subjected to in its lifetime, and there is widespread suspicion that track components have reserves of strength that are untapped, especially concrete sleepers. Addressing these issues has the potential for substantial savings for track owners. It's important therefore to ascertain the spectrum and amplitudes of forces applied to tracks, 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 this paper the load-carrying capacity of the selected Australian prestressed concrete sleepers is investigated under static and dynamic loading conditions. The sleepers are subjected to impact loading using a large capacity drop hammer to simulate the repeated impacts due to wheel flats or engine burns. These repeated impacts could eventually lead to cracking and failure of the sleepers, and hence are important in the context of developing the limit state design approach for the concrete sleepers. Using the impact loading technique, such phenomena as impact damage and residual strain, as well as the fracture energy as a performance indicator of damage for the selected limit states, are also quantitatively evaluated. S. Kaewunruen http://works.bepress.com/aremennikov/26 http://works.bepress.com/aremennikov/26 Wed, 28 May 2008 11:26:29 PDT Railway sleeper is a main part of railway track structures. Its role is to distribute loads from the rail foot to the underlying ballast bed. There is a widespread suspicion based on the industry experience that railway concrete sleepers have reserves of strength that are untapped. It is thus important to ascertain the spectrum and amplitudes of forces applied 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. Cracks in concrete sleepers have been visually observed by many railway organizations. The principal cause of cracking 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 philosophy for prestressed concrete sleepers is based on permissible stress principle, which are unrealistic to the actual dynamic loads on tracks. In order to devise a new limit states design concept, the research efforts are required to perform comprehensive studies of the loading conditions, the static behaviour, the dynamic response, and the impact resistance of the prestressed concrete sleepers. This paper presents the results of experimental and numerical studies aimed at predicting the dynamic responses of railway concrete sleepers. Experimental data also convey the exact failure modes for railway prestressed concrete sleepers under static and impact loadings. A high-capacity drop weight impact testing machine was constructed at the University of Wollongong to evaluate the ultimate capacity of prestressed concrete sleepers under impact loads. 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 using the Australian-manufactured prestressed concrete sleepers. A. M. Remennikov http://works.bepress.com/aremennikov/25 http://works.bepress.com/aremennikov/25 Wed, 28 May 2008 11:26:26 PDT Premature cracking of prestressed concrete sleepers has been found in railway tracks. The major cause of cracking is the infrequent but high-magnitude wheel loads produced by a small percentage of "bad" wheels or rail head surface defects which are crudely accounted for in AS 1085.14 by a single load factor. The current design philosophy, outlined in AS 1085.14, is based on assessment of permissible stresses resulting from quasi-static wheel loads and essentially the static response of concrete sleepers. In order to shift the conventional methodology to a more rational design method that involves more realistic dynamic response of concrete sleepers and performance-based design methodology, a significant research effort within the framework of the CRC for Railway Engineering and Technologies is currently underway to perform comprehensive studies of the loading conditions, the dynamic response, and the dynamic resistance of prestressed concrete sleepers. The collaborative research between the University of Wollongong (UoW) and Queensland University of Technology (QUT) has addressed such important issues as the spectrum and amplitudes of dynamic forces applied to the railway track, evaluation of the reserve capacity of typical prestressed concrete sleepers designed to the current code AS 1085.14, and the development of a new limit states design concept. This paper presents the results of the extensive investigations at UoW and QUT aimed at predicting wheel impact loads at different return periods (based on the field data from impact detectors) together with an experimental investigation of the ultimate impact resistance of prestressed concrete sleepers required by a limit states design approach. The paper also describes the reliability concepts and rationales associated with the development of limit states format codes and the issues pertaining to conversion of AS 1085.14 to a limit states design format. A. M. Remennikov http://works.bepress.com/aremennikov/24 http://works.bepress.com/aremennikov/24 Wed, 28 May 2008 11:26:23 PDT In recent years, the explosive devices have become the weapon of choice for the majority of terrorist attacks. Such factors as the accessibility of information on the construction of bomb devices, relative ease of manufacturing, mobility and portability, coupled with significant property damage and injuries, are responsible for significant increase in bomb attacks all over the world. In most of cases, structural damage and the glass hazard have been major contributors to death and injury for the targeted buildings. Following the events of September 11, 2001, the so-called "icon buildings" are perceived to be attractive targets for possible terrorist attacks. Research into methods for protecting buildings against such bomb attacks is required. Several analysis methods available to predict the loads from a high explosive blast on buildings are examined. Analytical and numerical techniques are presented and the results obtained by different methods are compared. A number of examples are given. A. M. Remennikov http://works.bepress.com/aremennikov/23 http://works.bepress.com/aremennikov/23 Wed, 28 May 2008 11:26:21 PDT The repeated impact of train wheels over sleepers can reduce the lifetime of a sleeper and degrade ballast. In more extreme cases it can lead to the breakdown of the concrete sleeper. Concrete sleepers are rigid compared to steel and wooden sleepers and therefore it is necessary to provide impact attenuation to prevent premature breakdown of the concrete. One of the measures employed to attenuate the effect of the impact loads on concrete sleepers has been the use of the resilient rail seat pads. Numerous analytical and numerical models have been formulated to investigate the dynamic behaviour of railway track substructures. All models require careful selection of the track component properties to satisfactorily represent track vibration response. However, there is currently no standard method available that can be used to evaluate the dynamic properties of the rail pads. At the University of Wollongong, an instrumented hammer was used to excite an equivalent single degree-of-freedom system (SDOF), incorporating a rail pad as a resilient element, to determine the dynamic properties using methods of modal analysis. The analytical SDOF dynamic model was applied to best fit the experimental modal measurements that were performed in a frequency range of 0-500 Hz. The curve fitting gives such dynamic parameters as the effective mass, dynamic stiffness, and dynamic damping constant, all of which are required for numerical modelling of a railway track. A. M. Remennikov http://works.bepress.com/aremennikov/22 http://works.bepress.com/aremennikov/22 Wed, 28 May 2008 11:26:17 PDT Impact loads applied to concrete sleepers, either due to the wheel flats of a train or rail abnormalities, may cause the sleepers to crack. The rail pads have been used to attenuate the effect of these impact loads on concrete sleepers and on the substructures in ballasted railway tracks. The rail pads experience high intensity loads due to wheel impacts and, as a result, the pad properties deteriorate during the service life. The consequences can be significant for the dynamic behaviour of railway tracks, interaction of vehicle and track, and impact forces on track components. However, there is currently no standard method available that can be used to evaluate the dynamic characteristics of the pads. In this paper, the degradation of rail pad properties as a function of their in-service life is studied with a view of developing a technique for predicting the optimum period of track maintenance with regard to pad replacement. Identification of structural properties using methods of experimental modal analysis provides a means for investigation of the deterioration of dynamic pad characteristics. A technique using an instrumented impact hammer is employed in this study. The pad samples were collected from the railway lines in Sydney Electrified Network, Australia, which are operated by Rail Corporation New South Wales (RailCorp). Through testing of pads in a recently developed rail pad testing machine, the vibration responses were measured in the frequency range from 0 to 1000 Hz using the Bruel & Kjaer PULSE Vibration Analyser system. The analytical solution was derived to estimate the dynamic stiffness and damping constants of the worn pads from the obtained experimental data. The rates of deterioration based on limited data are proposed to predict the useful lifetime of pads and the period of pad replacement. In this study, the type of rail pad used was the high-density polyethylene (HDPE) pad with 5.5 mm thickness. All worn pads were sourced from RailCorp tracks with approximately 22 MGT (million gross tons) annual tonnage. Based on linear regression analysis, it has been determined that at 20 kN preload (equivalent to PANDROL e-Clip fastening system clamping force) degradation of dynamic stiffness and damping is about 2.2 MN/m and 19.6 Ns/m per MGT, respectively, for the particular track conditions. A. M. Remennikov