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Methods for numerical analysis of soil-structure interaction

Lager, Elias and Karlsson, Pontus LU (2019) In TVSM-5000 VSMM01 20191
Structural Mechanics
Department of Construction Sciences
Abstract
All buildings need a foundation that supports the structure. Since a layer of soil is most often in between a structure and the bedrock, a soil-structure interaction between the foundation and the soil beneath occurs. This interaction is of great importance when it comes to predicting the sectional forces that will arise in a structure, along with the settlement that occurs. Therefore the need to conduct accurate calculations when it comes to soil-structure interaction is evident.

One problem with modelling a soil-structure interaction using a full FE-analysis of the soil is that it requires a large amount of computational effort along with a significant effort in building the models, and a rather deep understanding of soil modelling.
... (More)
All buildings need a foundation that supports the structure. Since a layer of soil is most often in between a structure and the bedrock, a soil-structure interaction between the foundation and the soil beneath occurs. This interaction is of great importance when it comes to predicting the sectional forces that will arise in a structure, along with the settlement that occurs. Therefore the need to conduct accurate calculations when it comes to soil-structure interaction is evident.

One problem with modelling a soil-structure interaction using a full FE-analysis of the soil is that it requires a large amount of computational effort along with a significant effort in building the models, and a rather deep understanding of soil modelling.

For this reason commercial software programs are available for conducting calculations regarding the soil-structure interaction. In this thesis the software RFEM and Abaqus have been used in order to evaluate the accuracy and efficiency of modelling the soil using the Winkler method and the Pasternak method. The Winkler method models the soil as uniformly distributed springs beneath the structure. The Pasternak method uses the same spring bed as the Winkler model, but with added shear springs between the main springs making up the Winkler bed. These springs are added in order to capture the transfer of shear forces that occurs in a soil. These methods were compared to full FE-analyses using Abaqus with varying degrees of complexity when it comes to modelling the soil.

Four different types of foundations were analysed in a parametric study along with a case study of a real structure. The types of foundations studied during the parametric study were a pad-, strip-, raft- and basement foundation. In the case study a seven story office building in Malmo, Sweden, called Eminent, was studied.

Result shows that when the Winkler method is used, both the shape and the magnitude of the settlement differ significantly from the results of the full FE-analyses where the soil is modelled using 3D elements and plasticity of the soil is considered. The major reasons for this are that the soil surrounding the structure is not taken into account and that the shear transfer that takes place in a soil is neglected. Neglecting shear in the soil results in a convex shape of the settlement when in reality the structure takes more of a concave shape. The sectional forces calculated using the Winkler method differ from the ones obtained using the full FE-analyses. In particular the tensile stress at the top of the
foundations tend to be exaggerated.

The Pasternak model implemented in RFEM yields sectional forces that are similar to the ones obtained when modelling the soil with linear elastic solid elements. It does, however, underestimate the settlements of the foundation in relation to the full FE-analyses. The difference in results between modelling the soil using a linear elastic material or an elastoplastic material tend to decrease when the size of the foundation increases. Therefore the Pasternak method yields rather similar results for the sectional forces, to a full FE-analysis with elasto-plastic material model on foundations such as rafts and basements. (Less)
Popular Abstract (Swedish)
När grundläggningen för en byggnad ska dimensioneras är snittkrafter och sättningar som kommer att uppstå i konstruktionen av stor betydelse. Det finns därför ett behov av att kunna beräkna dessa krafter och sättningar på ett säkert och relativt enkelt sätt.
Please use this url to cite or link to this publication:
author
Lager, Elias and Karlsson, Pontus LU
supervisor
organization
alternative title
Numeriska analysmetoder för samverkansgrundläggningar
course
VSMM01 20191
year
type
H3 - Professional qualifications (4 Years - )
subject
publication/series
TVSM-5000
report number
TVSM-5242
ISSN
0281-6679
language
English
id
8996064
alternative location
http://www.byggmek.lth.se/english/publications/tvsm-5000-present-2014/
date added to LUP
2019-10-04 13:40:01
date last changed
2019-10-04 13:40:01
@misc{8996064,
  abstract     = {All buildings need a foundation that supports the structure. Since a layer of soil is most often in between a structure and the bedrock, a soil-structure interaction between the foundation and the soil beneath occurs. This interaction is of great importance when it comes to predicting the sectional forces that will arise in a structure, along with the settlement that occurs. Therefore the need to conduct accurate calculations when it comes to soil-structure interaction is evident.

One problem with modelling a soil-structure interaction using a full FE-analysis of the soil is that it requires a large amount of computational effort along with a significant effort in building the models, and a rather deep understanding of soil modelling.

For this reason commercial software programs are available for conducting calculations regarding the soil-structure interaction. In this thesis the software RFEM and Abaqus have been used in order to evaluate the accuracy and efficiency of modelling the soil using the Winkler method and the Pasternak method. The Winkler method models the soil as uniformly distributed springs beneath the structure. The Pasternak method uses the same spring bed as the Winkler model, but with added shear springs between the main springs making up the Winkler bed. These springs are added in order to capture the transfer of shear forces that occurs in a soil. These methods were compared to full FE-analyses using Abaqus with varying degrees of complexity when it comes to modelling the soil.

Four different types of foundations were analysed in a parametric study along with a case study of a real structure. The types of foundations studied during the parametric study were a pad-, strip-, raft- and basement foundation. In the case study a seven story office building in Malmo, Sweden, called Eminent, was studied.

Result shows that when the Winkler method is used, both the shape and the magnitude of the settlement differ significantly from the results of the full FE-analyses where the soil is modelled using 3D elements and plasticity of the soil is considered. The major reasons for this are that the soil surrounding the structure is not taken into account and that the shear transfer that takes place in a soil is neglected. Neglecting shear in the soil results in a convex shape of the settlement when in reality the structure takes more of a concave shape. The sectional forces calculated using the Winkler method differ from the ones obtained using the full FE-analyses. In particular the tensile stress at the top of the
foundations tend to be exaggerated.

The Pasternak model implemented in RFEM yields sectional forces that are similar to the ones obtained when modelling the soil with linear elastic solid elements. It does, however, underestimate the settlements of the foundation in relation to the full FE-analyses. The difference in results between modelling the soil using a linear elastic material or an elastoplastic material tend to decrease when the size of the foundation increases. Therefore the Pasternak method yields rather similar results for the sectional forces, to a full FE-analysis with elasto-plastic material model on foundations such as rafts and basements.},
  author       = {Lager, Elias and Karlsson, Pontus},
  issn         = {0281-6679},
  language     = {eng},
  note         = {Student Paper},
  series       = {TVSM-5000},
  title        = {Methods for numerical analysis of soil-structure interaction},
  year         = {2019},
}