Olivia Mirza

Composite slabs for railway construction and maintenance: a mechanistic review

Australian railway networks alone require timber components in excess of 280,000 m3 per year for railway construction and maintenance. The relatively high turnover of timber sleepers (crossties in a plain track), bearers (skeleton ties in a turnout) and transoms (bridge cross beams) is responsible for producing greenhouse gas emissions six times greater than equivalent reinforced concrete counterparts. This study reviews the railway maintenance problems and solutions for the replacement of these high maintenance members. Alternative composite materials to replace timber components in railway infrastructure construction and maintenance have been developed extensively in recent years. This critical review outlined an innovative solution incorporating composite slab theory and combining with the capabilities of being precast and modular, in order to reduce the depth, weight and required installation time relative to conventional track slab systems. Systemic risks, compatibilities and compliances are highlighted to warrant real-world applicability of composite structures.

Finite element modelling of modular precast composites for railway track support structure: A battle to save Sydney Harbour Bridge

Railway networks in Australian alone require replacing a large amount of aging timber components in excess of 280,000 m3/a. The replacement of timber track components is responsible for producing greenhouse gas emissions six times greater than equivalent reinforced concrete counterparts. Sydney Harbour Bridge presently experiences similar problem. A feasibility study to develop an innovative solution for the replacement of aging timber transoms installed on the Sydney Harbour Bridge was conducted to evaluate environmental, safety and financial benefits. The development of alternative composite structure to replace the timber components overcomes some potential compatibility issues with track stiffness as well as structural and geometrical track systems. This study firstly presents a novel and resilient alterative by incorporating steel-concrete composite theory and combining the capabilities of being precast and modular, in order to reduce the depth, weight and required installation time relative to conventional concrete track slab systems. Finite element analysis of the composite structures and its behaviours incorporating the bridge system are highlighted in this paper. A three-dimensional model of steel-concrete composites was developed by using ABAQUS. Non-linear material properties and contact interfaces have been simulated to mimic actual support conditions of existing stringers on the Sydney Harbour Bridge. This investigation demonstrates the safety of the composite panels under train derailment loads.

Nonlinear Finite Element Modelling of Railway Turnout System considering Bearer/Sleeper-Ballast Interaction

Rail turnouts are built to enable flexibility in the rail network as they allow for vehicles to switch between various tracks, therefore maximizing the utilisation of existing rail infrastructure. In general, railway turnouts are a safety-critical and expensive feature to a rail system as they suffer aggressive operational loads, in comparison to a plain rail track, and thus require frequent monitoring and maintenance. In practice, great consideration is given to the dynamic interaction between the turnouts components as a failed component may have adverse effects on the performance of neighbouring components. This paper presents a nonlinear 3D finite element (FE) model, taking into account the nonlinearities of materials, in order to evaluate the interaction and behaviour of turnout components. Using ABAQUS, the finite element model was developed to simulate standard concrete bearers with 60 kg/m rail and with a tangential turnout radius of 250 m. The turnout structure is supported by a ballast layer, which is represented by a nonlinearly deformable tensionless solid. The numerical studies firstly demonstrate the importance of load transfer mechanisms in the failure modes of the turnout components. The outcome will lead to a better design and maintenance of railway turnouts, improving public safety and operational reliability.

Dynamic assessment of shear connection conditions in slab-girder bridges by Kullback-Leibler distance

Shear connectors are widely used in composite bridges that provide composite action. Their damage will reduce the load-carrying capacity of the structure. In this study, a novel method based on Kullback-Leibler distance (KLD) was developed to assess the integrity of the shear connectors. A bridge model was constructed in the laboratory and some removable anchors were specially designed and fabricated to link the beams and slab that were cast separately. Each anchor consists of a threaded bar that penetrates through the soffit of the beam and ties up into an embedded nut cap to simulate a shear connector in the real bridges. Different damage scenarios were introduced by pulling out some connectors. Vibration tests were carried out in each damage scenario. Various damage detection methods have been applied and results show that the method was able to detect all the assumed damage scenarios successfully and consistently.

Torsional effect on track support structures of railway turnouts crossing impact

AbstractThe introduction of special crossings and rail turnouts provides flexibility in the rail network as it allows for vehicles to switch between various tracks, thereby maximizing the utilizati...

Influence of shear bolt connections on modular precast steel-concrete composites for track support structures

Through extensive research, there exist a new type of connection between railway bridge girders and steel-concrete composite panels. In addition to conventional shear connectors, newly developed blind bolts have been recently adopted for retrofitting. However, the body of knowledge on their influence and application to railway structures has not been thoroughly investigated. This study has thus placed a particular emphasis on the application of blind bolts on the Sydney Harbour Bridge as a feasible alternative constituent of railway track upgrading. Finite element modeling has been used to simulate the behaviours of the precast steel-concrete panels with common types of bolt connection using commercially available package, ABAQUS. The steel-concrete composite track slabs have been designed in accordance with Australian Standards AS5100. These precast steel-concrete panels are then numerically retrofitted by three types of most practical bold connections: head studded shear connector, Ajax blind bolt and Lindapter hollow bolt. The influences of bolt connections on load and stress transfers and structural behaviour of the composite track slabs are highlighted in this paper. The numerical results exhibit that all three bolts can distribute stresses effectively and can be installed on the bridge girder. However, it is also found that Lindapter hollow bolts are superior in minimising structural responses of the composite track slabs to train loading.

HLRF-BFGS-Based Algorithm for Inverse Reliability Analysis

This study proposes an algorithm to solve inverse reliability problems with a single unknown parameter. The proposed algorithm is based on an existing algorithm, the inverse first-order reliability method (inverse-FORM), which uses the Hasofer Lind Rackwitz Fiessler (HLRF) algorithm. The initial algorithm analyzed in this study was developed by modifying the HLRF algorithm in inverse-FORM using the Broyden-Fletcher-Goldarb-Shanno (BFGS) update formula completely. Based on numerical experiments, this modification was found to be more efficient than inverse-FORM when applied to most of the limit state functions considered in this study, as it requires comparatively a smaller number of iterations to arrive at the solution. However, to achieve this higher computational efficiency, this modified algorithm sometimes compromised the accuracy of the final solution. To overcome this drawback, a hybrid method by using both the algorithms, original HLRF algorithm and the modified algorithm with BFGS update formula, is proposed. This hybrid algorithm achieves better computational efficiency, compared to inverse-FORM, without compromising the accuracy of the final solution. Comparative numerical examples are provided to demonstrate the improved performance of this hybrid algorithm over that of inverse-FORM in terms of accuracy and efficiency.

Experimental investigation of an existing and new retrofitted steel bridge girder due to fatigue failure

N response history analysis (NRHA) represents nowadays the more accurate method for prediction of the seismic response of structures because it incorporates in the analysis model the non-linear material and geometry behavior. In NRHA a key issue is the input modeling. A research aiming to find out a selection criterion for different sets of accelerograms, all of them satisfying the spectrum compatibility criteria imposed by the code, that enable a reliable assessment of the seismic demand is performed. The analysis is based on a preliminary evaluation of correlation among parameters for ground motion intensity measure (IM) and cinematic, energetic and damage parameters describing structure nonlinear responses. To this aim, a modified expression of the effective peak acceleration (EPA) is proposed, defined over the range of structure fundamental period referring to undamaged and damaged model would help this recognition. Subsequently, a method of selecting accelerograms has been proposed, able to take into account the two components of each seismic accelerations capable of providing sets of accelerometers compatible with a predetermined response spectrum and which effects on the analyzed structure are individually consistent with the seismic intensity presented by the spectrum. The selection criterion for accelerogram sets is based on the minimum value of the coefficient of variation (CoV) of the EPA. It reduces the dispersion of the effects of each accelerograms on the structure that has to analyze or designed, that is one of the most relevant drawbacks of the selection criterion available in literature. Validation of the criterion is carried out analyzing the response of the three plane multi-stored moment resisting frames (MRFs) to a set of 60 different accelerograms and analyzing the value of the correlation coefficient between input intensity measure and structure response parameters. The effectiveness of a selection criterion is proved by evaluation of average values and COV of NRHA response parameters of MRFs.O construction methods such as prefabrication method have been developed to improve productivity in construction and to reduce cost. SEN Engineering Group, a Korea-based structural productivity solution provider, introduces new productivity enhancing construction methodologies, including the Form Prefab Steel Reinforced Concrete (F-PSRC) column and Thin Steel Concrete beam system. This system can dramatically augment onsite productivity by reducing or eliminating the usage of temporary scaffolding works and form-works. The F-PSRC column and TSC beam system has been successfully applied in more than 50 projects in Korea, especially in those involving super-fast-track IT industry factories and offices. In terms of productivity, it was identified through the previous study that F-PSRC columns technology was 42.45% more productive than the conventional SRC columns without increasing of overall cost including fabrication and on-site construction. And now this system is about to be introduced in Singapore through a large-scale inland container deposit project. This system focuses to enhance productivity on site by reducing temporary on-site works and pursuing factory prefabrication. Hence, it is imperative that those in the industry learn about how the F-PSRC column and TSC beam system practices and design are able to shorten the construction periods of projects.

Effect of strain profiles on the behavior of shear connectors for composite steel-concrete beams

In composite steel-concrete construction applications, the behavior of the shear connectors is paramount to the overall system performance. The most common method for evaluating shear connector strength and its behavior is through the use of a push test. Push tests have been used as early as the 1960s to predict the strength and behavior of shear studs in solid slabs. The performance of steel-concrete composite structures is greatly dependent on the load-slip characteristics of shear connectors. Significant research work has been performed on composite beams in regard to their stiffness and ductility of the shear connectors for both solid and profiled slabs. This paper describes the strength and ductility of the shear connectors in composite beams with both the solid and profiled steel sheeting slabs when different strain regimes were implemented in the concrete element. An accurate non-linear finite element model using ABAQUS is developed herein to study the behavior of shear connectors for both solid and profiled steel sheeting slabs. The reason for employing different strain regimes in push tests is to properly simulate the behavior of shear connectors in composite beams where trapezoidal slabs are used. The pertinent results obtained from the finite element analysis were verified against experimental results from other researchers. Based on the finite element analysis and experimental results, it has been determined that the strength and the load-slip behavior of composite steel-concrete beams is greatly influenced by the strain regimes existent in the concrete element.