Modelling Transition Zones and Optimal Design Adjoining Tunnels and Bridges

Sajjad, Muhammad Babar

Modelling Transition Zones and Optimal Design Adjoining Tunnels and Bridges

Sajjad, Muhammad Babar

Permalink

Publication Type:: Thesis
Issue Date:: 2023

Open Access

Copyright Clearance Process

Recently Added
In Progress
Open Access

This item is open access.

The embargo period expires on 30 Sep 2024

Adobe PDF

Download thesisAdobe PDF (10.2 MB)

View statistics

Full metadata record

Field	Value	Language
dc.contributor.author	Sajjad, Muhammad Babar
dc.date.accessioned	2023-11-20T01:46:47Z
dc.date.available	2023-11-20T01:46:47Z
dc.date.issued	2023
dc.identifier.uri	http://hdl.handle.net/10453/173475
dc.description	University of Technology Sydney. Faculty of Engineering and Information Technology.	en_US.UTF-8
dc.description.abstract	Track transitions, such as bridge approaches, road crossings, and shifts from slab track to ballasted track, are known to be locations where track degradation accelerates due to dynamic and high impact forces. As a result, there is a higher differential settlement, which can cause an abrupt change in the structural response of the track due to variations in stiffness and track damping. This can cause accelerated deterioration of track material and geometry, leading to reduced efficiency, compromised track longevity, increased passenger discomfort, and elevated maintenance costs. In order to mitigate these issues, transition zones are provided at sudden discontinuities of track stiffness to minimize instability and reduce vibrations, and to ensure a smoother train passage over sections of significantly different track characteristics. By ensuring a smooth and gradual transition between flexible (less stiff) and rigid (stiff) track substructure, a well-designed transition zone can mitigate the impact of dynamic loads generated by moving trains. This study proposes a novel approach to smoothen the abrupt stiffness variation along railway transitions and provides a step-by-step design of a multistep transition zone comprising adjoining segments with changing stiffness values, and design optimization guidelines. The influence of stiffness on the track dynamic response applied to transition zones is investigated analytically, considering a beam on elastic foundation. Vertical track displacements for varying stiffness values under different combinations of axle loads and speeds are calculated analytically and numerically, and they are found to be in good agreement. The results indicate that stiffer tracks undergo lesser settlements compared to those having smaller stiffness. Furthermore, the effect of abrupt stiffness variation at transition sections is analysed under four-carriage loading causing considerable differential settlement, which is further exacerbated by increased train speeds. A mathematical process is introduced to determine the optimum stiffness of each segment to ensure a gradual change in stiffness while minimizing the corresponding differential settlement to allowable limits. The proposed methodology is further validated through Finite Element Modelling (2D & 3D) approach and worked-out examples, considering multiple loading conditions, epitomizing the effects of stiffness variation along the number of transition steps. From a practical perspective, this study significantly extends the design rejuvenation of transition zones by minimizing the differential settlement at any two consecutive transition segments. The proposed approach can be implemented to improve the durability and effectiveness of railway tracks during both their construction and upkeep, resulting in decreased passenger discomfort and reduced expenses for maintenance.	en_US.UTF-8
dc.format	Thesis (PhD)
dc.language.iso	en_US	en_US.UTF-8
dc.relation	https://opus.lib.uts.edu.au/bitstream/10453/173475/1/thesis.pdf
dc.rights	info:eu-repo/semantics/openAccess
dc.rights	The author owns the copyright in this thesis including all reproduction and reuse rights for the work. The work may not be altered without the permission of the copyright owner. Attribution is essential when quoting or paraphrasing from this thesis.
dc.rights	© 2023 Muhammad Babar Sajjad
dc.rights	au.edu.uts.lib/cph
dc.title	Modelling Transition Zones and Optimal Design Adjoining Tunnels and Bridges	en_US.UTF-8
dc.type	Thesis
utslib.copyright.status	open_access	*
utslib.copyright.embargo	2024-09-30T00:00:00+1000

Abstract:

Track transitions, such as bridge approaches, road crossings, and shifts from slab track to ballasted track, are known to be locations where track degradation accelerates due to dynamic and high impact forces. As a result, there is a higher differential settlement, which can cause an abrupt change in the structural response of the track due to variations in stiffness and track damping. This can cause accelerated deterioration of track material and geometry, leading to reduced efficiency, compromised track longevity, increased passenger discomfort, and elevated maintenance costs. In order to mitigate these issues, transition zones are provided at sudden discontinuities of track stiffness to minimize instability and reduce vibrations, and to ensure a smoother train passage over sections of significantly different track characteristics. By ensuring a smooth and gradual transition between flexible (less stiff) and rigid (stiff) track substructure, a well-designed transition zone can mitigate the impact of dynamic loads generated by moving trains. This study proposes a novel approach to smoothen the abrupt stiffness variation along railway transitions and provides a step-by-step design of a multistep transition zone comprising adjoining segments with changing stiffness values, and design optimization guidelines. The influence of stiffness on the track dynamic response applied to transition zones is investigated analytically, considering a beam on elastic foundation. Vertical track displacements for varying stiffness values under different combinations of axle loads and speeds are calculated analytically and numerically, and they are found to be in good agreement. The results indicate that stiffer tracks undergo lesser settlements compared to those having smaller stiffness. Furthermore, the effect of abrupt stiffness variation at transition sections is analysed under four-carriage loading causing considerable differential settlement, which is further exacerbated by increased train speeds. A mathematical process is introduced to determine the optimum stiffness of each segment to ensure a gradual change in stiffness while minimizing the corresponding differential settlement to allowable limits. The proposed methodology is further validated through Finite Element Modelling (2D & 3D) approach and worked-out examples, considering multiple loading conditions, epitomizing the effects of stiffness variation along the number of transition steps. From a practical perspective, this study significantly extends the design rejuvenation of transition zones by minimizing the differential settlement at any two consecutive transition segments. The proposed approach can be implemented to improve the durability and effectiveness of railway tracks during both their construction and upkeep, resulting in decreased passenger discomfort and reduced expenses for maintenance.

Please use this identifier to cite or link to this item:

http://hdl.handle.net/10453/173475