1 

Inklemeffecten bij steenzettingen op dijken: Eindigeelementenstudie naar geometrisch en
fysisch nietlineair gedrag van blokkenmodellen

[PDF]

2 

Computational Modelling of Masonry Structures

[PDF]

3 

Computational Reuse Optimisation
Application development for reusing structural stadium elements in a new project and configuration through implementation of a genetic algorithm.

file embargo until: 20170620
[Abstract]

4 

Numerieke modellering van steenzettingen
In dit rapport wordt verslag gedaan van een numeriek onderzoek naar steenzettingen op dijken. De steenzetting van een dijk kan door een golfaanval worden beschadigd. Dit wordt veroorzaakt door een opwaartste druk aan de onderzijde, die verantwoordelijk is voor het uitlichten van de stenen. Als er een sterkteberekening wordt uitgevoerd, blijkt dat er zogenaamde inklemeffecten optreden. Dit is het gevolg van het geometrisch en fysisch nietlineair gedrag. Er is dus een grotere kracht dan het eigen gewicht nodig om een steen uit de zetting te trekken. Het gunstige effect van deze inklemkrachten kan echter nog moeilijk worden gekwantificeerd en dus niet in de praktijk worden toegepast. Het doel van het afstudeerproject is meer inzicht te verkrijgen in de rol die de verschillende parameters spelen bij het inklemgedrag. Hiertoe wordt steeds de maximaal toelaatbare belasting pmax op het moment van bezwijken van de rij blokken beschouwd.

[PDF]
[Abstract]

5 

Sequentially linear modelling of combined tension/compression failure in masonry structures
The modelling of brittle fracture is essential for the assessment of structural safety. It remains a challenge due to sharp material softening after realization of the material strength. Standard nonlinear finite element analysis techniques using incrementaliterative solution procedures have been adapted to deal with the sharp softening curves associated with brittle materials, but convergence difficulties have stimulated the development of alternative modelling methods. The sequentially linear analysis method is an attractive alternative approach, since it is driven by increments of damage instead of increments of displacements, force or time. Consequently, this noniterative procedure circumvents the aforementioned convergence difficulties.
This method is still in its development stage and needs to be augmented, verified with tests and validated with experimental results with respect to multiple situations.
In this thesis the recent sequentially linear analysis software is verified and combined tensioncompression failure is validated with the aid of a masonry deep wallframe structure.

[PDF]
[Abstract]

6 

The stability of a facetted glass shell structure
The Master’s thesis has focussed on the stability of a facetted shell structure. The research contributes to a Ph.D. research currently carried out at the Technical University of Denmark (DTU), which investigates the possibilities to design and build a shell structure from flat glass panels. The structure is a socalled plate (facetted) structure, which is a relatively unknown, though very efficient structure type. By combining this structural typology with laminated float glass, a very transparent structure becomes possible.
Since smooth shell structures are prone to buckling, it is very important to assess the behaviour of the glass facetted structure in this respect. During the research different aspects that are important for the stability of the structure have been investigated using a finite element model. Important was for instance the sensitivity of the structure to imperfections. Furthermore, the influence of the stiffness of the joints between the glass facets turns out to play an important role in the behaviour of the structure. Especially the normal stiffness (k_n) is vital, while the bending stiffness (k_m) is less important. Other aspects that have been considered are the robustness of the structure and the influence of the stiffness of the panels. The research has shown that the structural system and its combination with laminated float glass looks very promising.

[PDF]
[Abstract]

7 

Analysis of MixedMode Fracture in Concrete

[PDF]

8 

Computational modeling of concrete fracture

[PDF]

9 

Analysis of MixedMode Fracture in Concrete  Closure

[PDF]

10 

Numerical Study on Crack Dilatancy Part 2: Applications

[PDF]

11 

Numerical Study on Crack Dilatancy Part 1: Models and Stability Analysis

[PDF]

12 

Analysis of concrete fracture in "direct" tension

[PDF]

13 

Building response due to ground movements

[PDF]

14 

Extension and Verification of Sequentially Linear Analysis to Solid Elements
When analyzing threedimensional problems with nonlinear finite element analysis (NLFEA) often problems are encountered such as bifurcation and divergence of the solution. In particular, cases subjected to tension softening tend to encourage the emergence of multiple equilibrium paths. In order to overcome these problems the Sequentially Linear Analysis (SLA) method has been developed for threedimensional solid elements. SLA is an alternative for incrementaliterative solution schemes to model the nonlinear fracture behavior of quasibrittle materials. It is an attractive method since it avoids the well known convergence and bifurcation problems that are often encountered when using incrementaliterative schemes such as NewtonRaphson. SLA uses a series of linear analyses to model the nonlinear behavior of the structure. By directly specifying a damage increment in each linear analysis, extensive iterations within the load or displacement increment can be avoided.
The main objective of this research was to see how the Sequentially Linear Analysis approach could be extended to solid elements, so that it could be used for threedimensional fracture problems as well. Although threedimensional geometries such as masonry structures have been analyzed before using SLA, it was always restricted to twodimensional finite elements only (shell elements). Therefore, first a theoretical constitutive model for threedimensional stressstrain states has been developed that served as the starting point. Implementation in DIANA was the major second step from which the third and last step could be started: the verification on various fictive and real cases. A single element pull test was used to solve programming errors, whereas the notched beam offered the possibility to check how the newly developed SLAcode would perform for larger models. Both cases showed excellent agreement with the experiment. However, most attention was dedicated to the verification and physical interpretation of a real reinforced concrete slab. The results were critically evaluated, interpreted and compared to results from the experiment and the incrementaliterative NewtonRaphson method. It was concluded that the Sequentially Linear Analysis is able to properly capture the quasibrittle behavior of the reinforced concrete slab. Especially in comparison to the threedimensional NewtonRaphson results, SLA turned out to be more robust and accurate.

[PDF]
[Abstract]

15 

2D Numerical Analysis of Settlement Damage to Buildings: Including a nonlinear Masonry Model and Soilstructure Interface
The increased number of underground infrastructure projects asks for a reliable and efficient assessment of settlement damages to buildings. Currently a threestage method is in use: the first stage looks into the greenfield deformations, the second stage is a linear elastic 2D method in which greenfield deformations are applied onto a building and the third stage uses finite element methods and 3D models. The goal of this thesis was to improve the second stage by incorporating a nonlinear masonry model and a soilstructure interface.
A 2D parametric analysis has been performed in which various material and geometrical parameters were varied. The soil model was simplified to a linearelastic model. The results of the research are twofold. On the one hand there are the results of the parametric analysis showing the effect of incorporating the nonlinear masonry model and the soilstructure interface. On the other hand incorporating these two aspects a number of issues came up: the influence of the crack model and convergence criterion, the influence of the building location, the influence of the initial stress and the influence of the participating soil width. For each issue an explanation was sought and the consequences were determined.
The results of the parametric analysis showed that including a nonlinear material model and a soilstructure interface leads to lower acceptable volume losses. In practice it is generally believed that the current models are already too conservative. The difference between reality and the models must be sought in components that are still missing in the current model.

[PDF]
[Abstract]

16 

Threedimensional numerical analysis of tunnelling induced damage: the influence of masonry building geometry and location
Recent tunnelling projects have received a great amount of media attention due to settlement induced damage. Due to the simplified approach of existing risk assessment methods, a new assessment system is in development, which can account for threedimensional structural aspects of buildings. The aim of this study is to investigate the influence of the position and geometry of masonry buildings on the development of damage, while undergoing tunnelling induced settlements. In line with previous research, threedimensional finite element analyses are used as a tool to perform a parametric study. A parametric study consists of an evaluation of the parameters position, aspectratio, grouping and orientation. The position parameter is divided into three characteristics: the sagging zone, a combined settlement profile and the hogging zone. The aspectratio parameter is also divided into three characteristics: shallow buildings, square buildings and deep buildings. The grouping effect parameter also distinguishes three characteristics: small and large isolated buildings and grouped buildings. The orientation parameter includes seven different increasing angles of the building main axis with respect to the tunnelling axis. The maximum measured crack width in the buildings gives input for a classification of damage, according the system of Burland et al. (1977). An average trend in the damage classification indicates the sensitivity to tunnelling induced settlements of the parameters. Both during and after tunnelling, a position of the building in the combined settlement profile appears to be the most sensitive to differential settlements. Buildings far away from the tunnelling axis generally obtain no more than slight damage. Structures with a low aspectratio seem on average to obtain equal amounts of damage as buildings with an aspectratio of 1. Structures with a higher aspectratio are less affected, both during and after tunnelling. Grouping of the buildings seems to be an influential parameter. Small isolated buildings obtain far less damage than large or grouped buildings. In relation to the numerical analyses, the empirical Limiting Tensile Strain Method (LTSM) seems to overestimate the damage for an isolated small building, but underestimate the damage in large or grouped buildings. For buildings in the sagging zone, a building with a low orientation angle is the least sensitive to differential settlement, while the maximum measured crack width increases by increasing the angle. The difference in maximum crack width can grow to a factor 3. A building in the combined settlement profile or in the hogging zone displays opposite behaviour. Cases with low orientation angles are the most susceptible to damage, while increasing the angle to 90 degrees lowers the maximum measured crack width. The difference in results can grow up to a factor 2.

[PDF]
[Abstract]

17 

Tunnel induced settlement damage: A case study to improve damage prediction for facades
The tunnel boring process introduces soil settlements. Damage to nearby building could occur if settlements become too large. A reliable damage prediction model is necessary too asses the risks of damage to tunnel induced settlements. A widely used method for damage prediction is the Limiting Tensile Strain Method (LTSM). The LTSM models a masonry building as a weightless, isotropic, linearelastic, rectangular beam on 2 supports. Although the LTSM is an easy method to use, it has its limitations. For facades for instance the perforation of the wall, which introduces weak spots in the wall and reduces the stiffness, is neglected. In this project the applicability of the LTSM in the case of facades is studied to improve damage predictions in the case of facades.
A case study is performed to examine the response of facades in the Daniel Stalpertstraat due to settlements caused by the tunnelling process of the North/Southline. This field data is used to find a calibrated 2D numerical model of the facades.
The calibrated numerical model is then subjected to larger settlements to obtain the behaviour of the facades at large settlements. Using linear and nonlinear analyses of the numerical model it is evaluated how accurate and how conservative 4 damage prediction models are.
The first two LTSM models were examined: the standard LTSM model with E/G=2.6 and one with E/G=12.5. Based on the findings in the linear analyses also two models based on conventional beam theory were examined for their applicability: portal frame model and ForgetMeNot model.
With linear analyses it is checked how reliable the methods are in terms of strains and deformation under the imposed settlements. With nonlinear analyses the conservativeness of each method in terms of damage is evaluated by comparing the crack with found I the numerical model to the crack width calculated with the damage prediction models.
The LTSM with E/G=12.5 gives the best results according to linear numerical analyses results. The LTSM with E/G provided the same curvature and shear distortion as found din the numerical analyses, the strains were approximated with 90%.
The ForgetMeNot model shows the best results according to the nonlinear analyses results. At large settlements this model provides the same results as found in the nonlinear numerical analysis results.

[PDF]
[PDF]
[Abstract]

18 

Progressive Collapse Indicator: A tool to indicate a structure's collapse resistance
Progressive collapse is a collapse where a local failure leads to a disproportionate collapse. Different terms like initial failure, propagation of failures and disproportionate damage are important aspects of such collapses. In current design practice, a method to measure a structures’ progressive collapse sensitivity in its early design phase and taking into account all aspects of a structures collapse resistance does not exist. The objective of this research is to develop a tool that takes into account all aspects of a progressive collapse and can aid the engineer in assessing a design, in its early design stage, on progressive collapse. At first, the initial failure is elaborated. Different events can cause the failure of elements. The probability an initiating event occurs at a certain element is different for each element. Mitigating measures can limit the chance of occurring for certain events. The initial events are applied on the model in 2 steps. First the location (or: element) of the event is chosen by a random selection method and a distribution of failure chances on the model. Second, the size of the damage is determined by applying a Gaussian curve over the model, both in x and zdirection. This determines if adjacent elements, related to the removed element in step 1, are removed. The model is calculated by FEAsoftware. Only linear and first order calculations are considered. These limitations lead to inaccuracies of the results compared with reality. A stability analysis has been performed to determine the buckling lengths of columns with more accuracy. Catenary action is one of the main modelling methods in designing against progressive collapse. This method is implemented into the tool. Iteratively, the forces and deformations are calculated which develop during the occurrence of catenary action.

[PDF]
[PDF]
[Abstract]

19 

Ant system based structural design of a roof in ultrahigh performance concrete
Objective
The recently developed material ultrahigh performance concrete (UHPC) has compressive strengths of over 150 MPa and a ductile behaviour. It has a higher stiffness and superior durability characteristics in comparison with ordinary concrete. The opportunity emerges to find new optimal structural topologies for this material.
The ant system is the first of a family of algorithms that are nowadays all referred to with the term ant colony optimisation (ACO). It is a computational algorithm that is able to solve combinatorial optimisation problems. Its optimisation process is based on the foraging behaviour of ants. ACO is not widely explored for structural design cases.
In the city of Apeldoorn a new sports centre called Omnisport is under construction. The centre consists of several halls, one of them containing a cycling and athletics track. The roof of this hall spans an elliptic area of about 120 by 100 metres.
This thesis focuses on the creation and evaluation of a structural topology design algorithm, based on the concept of the ant system, for ultrahigh performance concrete structures. The algorithm is applied to the design case of the Omnisport sports hall roof.
Algorithm
A new application for ant colony optimisation is developed in this thesis. Structures are mapped to a binary search space, which forms the link between the structure, ant colony optimisation and the finite element package DIANA. Structures are generated randomly in the first iteration of the routine by assigning material to some elements in a meshed space and leaving others empty. Elements that together form a wellperforming structure are more likely to be chosen again in a next iteration. The process is based on a performance that can be any function, and is not necessarily limited to structural information only. In the case considered in the thesis, the UHPC structure is optimised towards a combination of minimum volume, mould surface, prestress and the availability of holes for ducts and walking bridges. The algorithm’s multiobjective optimisation process results in a structural topology.
Design
The algorithm has been applied to the case of the Omnisport hall roof. Based on the results, a preliminary design for the loadbearing structure of the roof in UHPC has been made. A loadbearing structure in this material is found to be possible. The proposed design consists of trusslike supporting elements for the roof. A connection strategy is proposed, member sizes and necessary prestress are indicatively determined. Rough cost estimates show that the design is not necessarily more expensive than the current design in steel.

[PDF]
[Abstract]

20 

Beam or truss mechanism for shear in concrete: Problems converting a beam into a truss
An unpublished study by Prof. A.W. Beeby shows the differences in strength capacity between a reinforced concrete beam without shear reinforcement and the same beam with a cutout section at the middle of the span. The cutout section exists at the bottom part of the beam while the reinforcement still remains. It remarkably turns out that the strength capacity of the beam with the cutout section is 1.6 times larger compared to the reference beam.
The reference beam fails by a flexural shear crack which does not arise in the beam with the cutout section. On the occasion of Beeby’s experiments and the lack of a simple physical model for a flexural shear crack this thesis has the objective to clarify the difference between a beam and a truss mechanism and the failure due to flexural shear cracks. The study is based on a simple supported beam without shear reinforcement subjected to a oncentrated load with a three point bending test with a slendernessratio of 2.45 and a reinforcement ratio of 0.89%.
An analytical study describes the difference between the beam and a simplified truss mechanism. Linear analyses show the differences in stress distributions and deflections. The study shows the same
difference in strength capacity as the experiments of Beeby. In addition quite a difference is revealed in the displacements of both mechanism. The truss mechanism shows a larger deformation compared to the beam mechanism.
Finite element modelling with DIANA has been used to gain better insight in the difference of the strength capacity. The models use a total strain fixed crack model. The Hordijkcurve describes the tensile properties and an ideal relation describes the compressive properties. The decrease of the poisson ratio and the shear resistance around a crack have been taken into account by a damaged based shear retention model and a damaged based crack model.
The finite element models show differences of the strength capacity within the same level of Beeby’s experiments. The force mechanism in both systems is different before the flexural shear crack arises in
the beam. After a flexural shear crack occurs both mechanism seems to change into a similar truss mechanism, but detailed analyses show important deviations from this expectation.
Variation of the cutout dimensions shows that a too small gap results in a flexural shear crack and a too large gap in the failing of the cantilever part. Gaps between these limits all change into a truss
mechanism which reaches the same level of failure load as the basic truss. The decrease of stiffness of the beam results in more compressive stresses in the truss mechanism preventing the occurrence of the shear crack. If the shear crack does not occur in the beam it results in a higher strength capacity.
A dedicated shaped beam which has initially exactly the shape of a shear cracked beam without the concrete part below the crack, has a different strength capacity compared to a regular shear cracked
beam. The dedicated shaped beam proves that the crack shape itself has no influence on the ability of converting into a truss. It turns out that in the regular beam it is impossible to develop a perfect truss mechanism after a flexural shear crack due to the concrete that is still present beneath the crack. The concrete beneath the crack causes a different stress distribution in the top of the beam compared to the dedicated shaped beam without this concrete. A hypothesis is given for the failure of the shear crack.
The acquired knowledge of the influence of the concrete beneath the crack and the stiffness of the beam allows other design possibilities. It is possible to design a concrete truss, if among other, the yielding of steel, crushing of the concrete and the deformation capacity of the truss are taken into account. Further research is for instance possible for unbonded reinforcement and beams with a descending height.

[PDF]
[Abstract]
