Kinematics-Based Modelling of Compact Footings
Promotor(s) : Mihaylov, Boyan
Date of defense : 26-Jun-2019/28-Jun-2019 • Permalink :
|Title :||Kinematics-Based Modelling of Compact Footings|
|Author :||Spada, Giorgia|
|Date of defense :||26-Jun-2019/28-Jun-2019|
|Advisor(s) :||Mihaylov, Boyan|
|Committee's member(s) :||Denoël, Vincent
De Miranda, Stefano
|Number of pages :||134|
|Keywords :||[en] two-Parameter Kinematic Theory|
[en] concrete compact foootings
[en] one-way shear behavior
|Discipline(s) :||Engineering, computing & technology > Civil engineering|
|Target public :||Researchers|
Professionals of domain
|Institution(s) :||Université de Liège, Liège, Belgique|
|Degree:||Master en ingénieur civil des constructions, à finalité spécialisée en "civil engineering"|
|Faculty:||Master thesis of the Faculté des Sciences appliquées|
[en] The main objective of this thesis work is the extension and validation of a Two-Parameter Kinematic Theory (2PKT) for shear behavior of deep beams to concrete compact footings. The foundations have the purpose to transfer the load of the superstructure and its weight to the soil layers. Generally, reinforced concrete footings are designed without shear reinforcement; therefore, these elements are susceptible to brittle failure according to the amount of diagonal cracking due to shear stresses. Large-scale tests provided by Uzel (2003) are the starting point for the analysis. It is known that there is a significant size effect in shear strength of lightly reinforced slender members without shear reinforcement, for that it is important to simulate during the test the real size of this kind of elements in order to correctly evaluate the influence of the size on the shear behavior of large concrete footings; therefore only large-scale tests of the Uzel’s series are considered. One-way shear is studied, thus the footings were modelled to represent a strip of the element subjected to point load (simulating the load coming from the column footing) and uniformly distributed load imposed by a set of hydraulic jacks equally spaced (which reproduce the simplified soil pressure, in practice it is not uniform, but it varies according to the soil type).
Then, Finite Element Models (by using program VecTor2) of tests are performed in order to obtain reliable and accurate predictions and enlarge the footings database, for which, in the literature, few suitable tests are available. Simultaneously, the 2PKT for shear behavior in deep beams was developed for footings, adapting the loading conditions and the shear resistance contributions. By means of the 2PKT it is possible to predict the shear failure load, the crack widths near failure, and the complete deformed shapes. The two parameters used in the models are the ultimate vertical displacement of Critical Loading Zone (CLZ) and the average tensile strain in the longitudinal reinforcement on the flexural tension side. In order to show the validity of the theory, a parametric study is developed by using FEM models. The parameters included in the study are the concrete strength, the longitudinal reinforcement ratio and the length of the footing. Based on the use of non-linear finite element calculations validated against experimental results, it is possible to validate the 2PKT extended to concrete compact footings. The 2PKT method reproduces well the observations and the measurements during the large- scale laboratory tests. The average experimental-to-predicted strength ratio obtained with the extended 2PKT calculations for the footings database and the FEM models is 1.04 and the Coefficient of Variation (CoV) is 14.2%. The shear resistance components, thus critical loading zone and aggregate interlock for footings without shear reinforcement, underline that the size effect for deep concrete footings is principally produced by the aggregate interlock mechanism. Specifically, increasing the dimension of the element, the critical loading zone deforms more, and the diagonal cracks are wider, therefore the shear stresses transmitted throughout the cracks reduce.
This thesis work is just the starting point for the validation of the 2PKT. The FEM models created for the parametric study could be actually validated by means of real laboratory large- scale tests, in order to experimentally demonstrate the shear predictions of the theory and enlarge its validity.
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