A study on earth pressure on abutment walls of portal frame bridges
(2024) In TVSM-5000 VSMM01 20241Structural Mechanics
Department of Construction Sciences
- Abstract
- Portal frame bridges are one of the most popular types of bridges in Sweden. These
bridges consists of a framework structure that mitigates the use of bearing supports
and expansion joints which in turn makes them economically viable, efficient and
robust. The structure makes use of having vertical surfaces such as abutment walls
that are in contact with soils, meaning that braking forces, thermal expansion and
adjacent loading can be transmitted through the structure into the surrounding soil.
This creates intricate soil structure interaction which require careful consideration of
how these earth pressures impact the structure.
When calculating increased earth pressure due to horizontal loading, following the
Swedish Transport... (More) - Portal frame bridges are one of the most popular types of bridges in Sweden. These
bridges consists of a framework structure that mitigates the use of bearing supports
and expansion joints which in turn makes them economically viable, efficient and
robust. The structure makes use of having vertical surfaces such as abutment walls
that are in contact with soils, meaning that braking forces, thermal expansion and
adjacent loading can be transmitted through the structure into the surrounding soil.
This creates intricate soil structure interaction which require careful consideration of
how these earth pressures impact the structure.
When calculating increased earth pressure due to horizontal loading, following the
Swedish Transport Authority (STA) regulations was necessary. However, the current
process was both time-consuming and flawed, neglecting crucial soil mechanics. Com-
mercial software like Dlubal’s RFEM offered tools for soil-structure interaction analysis
which this thesis employed. Various spring model theories are modelled and compared
with STA regulations.
Eight different types of portal frame bridge designs, with five different modelling the-
ories were analysed. Parameters such as span, width, height, thickness and soil char-
acteristics were examined. Each bridge design had a variation of bridge models with
varying values of key parameter to derive a result to discern patterns, similarities, and
discrepancies across the bridge designs. All spring models were implemented in RFEM
with springs that deactivate under tension to simulate soil mechanics more accurately.
A few bridges implemented passive earth pressure springs to analyse the impact.
The results showed that all the spring models have movement in the bottom slab unlike
the assumptions the STA states. The results also showed that all the spring models
had similar contact stresses, with a maximum value at the surface of the abutment
wall which decreased with depth reaching a minimum value at the foundation slab.
Predictably, the earth pressure distribution of STA models aligned with regulatory
standards.
The spring bed models simulated more realistic behaviour of the structure and the
distribution of the earth pressure. This lead to a depth varied distribution of sectional
forces, which left room for optimizable structural design. The lack of an iterative
process decreased the computational time to process a design.
In summary, this master thesis aimed to initiate discussion concerning the necessity
of revising the STA, since the methodology to model the earth pressure lacks phys-
ical connection. The triangular stress distribution with its peak in the centre of the
abutment wall and the restricted movement of the foundation slab inadequately rep-
resented the structural behaviour. Moreover, this necessitated a force equilibrium
process through an iterative procedure, leading to a time-consuming methodology.
The regulation needs reconsideration and refinement of current practises. (Less) - Popular Abstract (Swedish)
- Vid dimensionering av plattramsbroar, som är en av Sveriges vanligaste brotyper, utgör det ökade jordtrycket mot rambenet på grund av horisontella laster en viktig faktor i dimensioneringsprocessen. Dagens regelverk framtaget av Trafikverket innebär en process som är tidskrävande för konstruktören samt underskattar jordens horisontella stabiliserande effekt. Detta kan leda till en låg utnyttjandegrad av rambenet, som i sin tur leder till onödigt höga materialkostnader och miljöpåverkan.
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9167959
- author
- Lewis, Philip LU and Ahadi, Deniz
- supervisor
- organization
- alternative title
- En studie om jordtryck på ramben i plattramsbroar
- course
- VSMM01 20241
- year
- 2024
- type
- H3 - Professional qualifications (4 Years - )
- subject
- keywords
- Portal frame bridge, Integral bridge, Springbed, foundation, RFEM, Trafikverket, Winkler, Pasternak, Brigade, Earth pressure, soil pressure
- publication/series
- TVSM-5000
- report number
- TVSM-5272
- ISSN
- 0281-6679
- language
- English
- id
- 9167959
- alternative location
- http://www.byggmek.lth.se/english/publications/tvsm-5000-present-2014/
- date added to LUP
- 2024-06-26 08:40:00
- date last changed
- 2024-06-26 08:40:00
@misc{9167959,
abstract = {{Portal frame bridges are one of the most popular types of bridges in Sweden. These
bridges consists of a framework structure that mitigates the use of bearing supports
and expansion joints which in turn makes them economically viable, efficient and
robust. The structure makes use of having vertical surfaces such as abutment walls
that are in contact with soils, meaning that braking forces, thermal expansion and
adjacent loading can be transmitted through the structure into the surrounding soil.
This creates intricate soil structure interaction which require careful consideration of
how these earth pressures impact the structure.
When calculating increased earth pressure due to horizontal loading, following the
Swedish Transport Authority (STA) regulations was necessary. However, the current
process was both time-consuming and flawed, neglecting crucial soil mechanics. Com-
mercial software like Dlubal’s RFEM offered tools for soil-structure interaction analysis
which this thesis employed. Various spring model theories are modelled and compared
with STA regulations.
Eight different types of portal frame bridge designs, with five different modelling the-
ories were analysed. Parameters such as span, width, height, thickness and soil char-
acteristics were examined. Each bridge design had a variation of bridge models with
varying values of key parameter to derive a result to discern patterns, similarities, and
discrepancies across the bridge designs. All spring models were implemented in RFEM
with springs that deactivate under tension to simulate soil mechanics more accurately.
A few bridges implemented passive earth pressure springs to analyse the impact.
The results showed that all the spring models have movement in the bottom slab unlike
the assumptions the STA states. The results also showed that all the spring models
had similar contact stresses, with a maximum value at the surface of the abutment
wall which decreased with depth reaching a minimum value at the foundation slab.
Predictably, the earth pressure distribution of STA models aligned with regulatory
standards.
The spring bed models simulated more realistic behaviour of the structure and the
distribution of the earth pressure. This lead to a depth varied distribution of sectional
forces, which left room for optimizable structural design. The lack of an iterative
process decreased the computational time to process a design.
In summary, this master thesis aimed to initiate discussion concerning the necessity
of revising the STA, since the methodology to model the earth pressure lacks phys-
ical connection. The triangular stress distribution with its peak in the centre of the
abutment wall and the restricted movement of the foundation slab inadequately rep-
resented the structural behaviour. Moreover, this necessitated a force equilibrium
process through an iterative procedure, leading to a time-consuming methodology.
The regulation needs reconsideration and refinement of current practises.}},
author = {{Lewis, Philip and Ahadi, Deniz}},
issn = {{0281-6679}},
language = {{eng}},
note = {{Student Paper}},
series = {{TVSM-5000}},
title = {{A study on earth pressure on abutment walls of portal frame bridges}},
year = {{2024}},
}