Med teknikens utveckling kommer det en ny form av digital arbetsmarknad, även kallad för gig-ekonomi eller plattformsekonomi. Denna kvalitativa studie undersöker nio personers egna upplevelser om hur det är att besitta ett jobb inom gig-ekonomin som förare i serviceyrkena Foodora, Uber och Bolt. Studien inriktar sig på arbetsvillkor och välbefinnandet hos dessa taxiförare och matbud. Resultatet i undersökningen visar att dessa arbeten bidrar med en stor flexibilitet för utföraren där man är sin egen chef och har frihet att bestämma mycket själv. Däremot utmärker sig jobben med låg lön och därmed långa arbetsdagar som resulterar i olika former av otrygghet vilket leder till ohälsa.

The Accelerated bridge construction (ABC) techniques are gaining popularity among the departments of transportation (DOTs) due to their reductions of on-site construction time and traffic delays. One ABC technique that utilizes precast deck panels has demonstrated some advantages over normal cast-in-place construction, but has also demonstrated some serviceability issues such as cracks and water leakage to the transverse joints. Some of these problems are addressed by applying longitudinal prestressing. This thesis evaluates the service and ultimate capacities in both flexure and shear, of the finite element models of the post-tensioned system currently used by Utah Department of Transportation (UDOT) and a proposed curved-bolt system to confirm the experimental results. The panels were built and tested under negative moment in order to investigate a known problem, namely, tension in the deck concrete. Shear tests were performed on specimens with geometry designed to investigate the effects of high shear across the joint. The curved-bolt connection not only provides the necessary compressive stress across the transverse joint but also makes future replacement of a single deck panel possible without replacing the entire deck. Load-deflection, shear-deflection curves were obtained using the experimental tests and were used to compare with the values obtained from finite element analysis. In flexure, the ultimate load predicted by the finite element model was lower than the experimental ultimate load by 1% for the post-tensioned connection and 3% for the curved-bolt connection. The shear models predicted the ultimate shear reached, within 5% of the experimental values. The cracking pattern also matched closely. The yield and cracking moment of the curved-bolt connection predicted by the finite element model were lower by 13% and 2%, respectively, compared to the post-tensioned connection in flexure.

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Master of Science / Pallets are used all over the world in the field of distribution. The strength values associated with a pallet have been thoroughly investigated by many different researchers; however, the stiffness values associated with pallet joints have not. The goal of this work was to investigate the stiffnesses associated with pallets joints made with lag screws and carriage bolts. It is important to understand that different materials, fastening methods, and design considerations can have a huge impact on the stiffness of the joint. This paper will discuss the various tests that were used to measure the actual stiffness of pallet joints and the results of those tests. Afterwards, the researchers detail their attempt to predict the stiffness using an equation created from the actual test data. Finally, by understanding the effects of these various factors, better pallet designs can be created that are both safer and stronger using the investigated alternative fasteners.

The transmission line (TL) tower is an important component in electrical network system. These towers consist of members (angle sections) and connections (bolted connections) plus foundation, which act together to resist externally applied loads. The latticed towers are used to support conductors in transmission network for transmission and distribution of electricity. These towers are constructed in large numbers all over the world. The connections in electric TL classical latticed towers are peculiar compared to other types of bolted connections in buildings and bridges because (i) the angle members are connected directly or through gusset plates with bolts, (ii) the eccentric application of load due to the non-coincidence of centroid axes of angle members near the connection and (iii) members are designed as beam column element to sustain tensile or compressive forces. Bearing type bolts are used in TL towers in preference to friction type bolts, because they (i) connect thin walled angle members, (ii) are easy to use for erection at all heights, (iii) can be galvanized, (iv)erosion of galvanizing can be remedied and (v) do not require skilled personnel for installation. However, these connections are subjected to reversal of stresses due to wind load. Damage in the bolted connections generally occur due to loosening of bolts due to stress reversals (Feenstra et al. (2005) [23). The damage induced after extreme wind and earthquake may lead to collapse of the whole tower. The failure of a TL tower results in power shut down, which has huge impact on national economy. Hence, the structural safety and reliable performance of these towers are extremely important. The design of TL tower is based on minimum weight philosophy. The TL towers are highly repetitive and therefore, their designs need to be commercially competitive. The TL tower design has the following deficiencies such as misappropriate design assumptions, deficit detailing, defects in material, errors in fabrication, force fitting of members during erection, variation in grade of bolts, improper gusset plate detailing, notch cutting of member, vocalization of bolt holes, etc. Hence, to check the design and detailing aspects of members along with bolted connections and to study the behavior of tower under complex loading conditions, the prototype testing of tower is made mandatory requirement in many countries throughout the world. The structural behavior of TL tower is determined from its deflection response. Thus, the full scale testing of the towers is the only way that one can counteract the un conservatism due to structural analysis. The premature failure of TL towers occurs during prototype testing due to deficiencies in joint detailing, uncertainties in framing eccentricity, force fitting of members, unequal force distribution in bolts and gusset plate connections, etc. To have better structural response of TL tower to be tested, there is need to develop reliable model for bolted connections in TL towers. The bolted connection model plays an important role in determining the deflection response and predicting the premature member buckling failure of TL towers. The issues related to prototype testing of full scale TL towers such as fabrication errors, force fitting and notch cutting of members, application of loads, joint and crossarm detailing are discussed. The need to develop bolt slip model to simulate the actual behaviour of bolted connection in TL towers is also discussed. The bolted connections in TL towers play an important role in determining its structural behavior. The angle members used in TL towers are subjected to bi-axial bending in addition to axial load. The slip will occur in the bolted connections, due to the provision 1.5 mm bolt hole clearance. In the conventional Finite Element Analysis (FEA), the bolted connections are modeled as pin joint assuming the axial load transfer. The deflection predicted from pin joint analysis in TL towers generally does not match with experimental results. The analytical and experimental deflection value varies in the range of 30 to 50%. Hence, there is need to develop model to account bolt slip for accurate deflection and dynamic characteristic prediction of TL towers. Experimental and analytical investigations have been carried out to develop and validate bolt slip model for bolted connections in TL towers. All six degrees of freedom (both translational and rotational) have been considered to simulate the exact behaviour of bolted connections in TL towers. The model is developed based on experimental results of Ungkurapinan’s bolt slip model for axial stiffness. The rotational stiffness is formulated based on the component level experiment conducted on lap joint made of steel angle with single and double bolt subjected to tensile loading. The axial and rotational stiffness for different stages of bolt tightening is also formulated based on component level experimental investigation on lap joint. The proposed model is validated by comparing with experimental results at sub-structural level on full scale king post truss subjected to tensile loading. Further the bolt slip model is validated for different bolt tightening and failure prediction of TL tower sub panel subjected to tensile loading. Finally the proposed model is also validated for full scale TL tower for deflection prediction. NE NASTRAN, a nonlinear finite element analysis (FEA) software is used for analytical simulation and the load-deflection predictions, which are compared with the corresponding experimental results. The experimental and analytical results are in good agreement with each other. The steel pole structures are replacing the conventional lattice towers, because they have smaller plan dimension and occupy less space, when compared to lattice towers. The steel pole structures are dynamically sensitive structures and the determination of their natural frequency is extremely important. For the calculation of wind load through gust factor method, the preliminary estimation of natural frequency is required. Hence, the primary step involved in dynamic analysis is the evaluation of its natural frequency. Hence, a simplified model is proposed based on model order reduction technique for the evaluation of natural frequency of TL towers and steel pole structures. For the development of base line model to detect damage in TL towers, the natural frequency has to be updated. A semi empirical approach is proposed based on the deflection by using the proposed bolt slip model. The proposed approach of updating natural frequency is validated for different cases of member damage in TL tower sub panel, such as removal of tension, compression and hip bracing members. The transmission pole structures accumulate damage during their service life. Damage in these structures will cause a change in stiffness of the system and the physical properties of these structures, such as modal frequencies and mode shapes. Hence in the present study, the damage localization study based on modified modal strain energy approach is carried out for steel pole structures and the location of damage is identified correctly. To prevent premature failure of towers during its service life testing and failure analysis of TL towers is a mandatory requirement. In the present study, forensic failure investigation of a full scale TL tower due to deficient design of a redundant member is emphasized and the remedial measures are explained in detail. The stub failure of TL tower due to reduction in cross sectional area due to unfilled bolt hole is also discussed. To investigate the effect of unfilled bolt holes on the compression capacity of leg member, detailed FEA is carried out and compared with experimental results. The reason for failure of 9 m roof top communication tower due to redundant member deficiency is also discussed. The importance of guyed tower accessories in the guy rope design of 7 m roof top guyed pole structure is also investigated. Finally, failure investigation of compression bracing member, which has failed during testing of TL tower sub panel has been investigated. The failure load is predicted by using the proposed bolt slip model in the analysis. Thus the overall research contributions emerging from this thesis are, i) development of bolt slip model accounting for rotational stiffness, ii) development of direct method of damage detection for steel pole structures based on modified modal strain energy approach, iii) development of simplified model for prediction of natural frequency of TL tower and steel pole structures, iv) development of model updating technique through natural frequency based on semi-empirical approach and v) prediction of failure load for TL tower panel using the proposed bolt slip model.

A three-dimensional finite element model is constructed to predict the failure of a hybrid and thick laminate containing bolted joints. The results of the simulation are compared with test results. The simulation comprises two main challenging steps. Firstly, for a realistic model, a 3D model is established with geometric nonlinearities and contact is takeninto account. The laminated composite model is constructed by 3D layered elements. The effect of different number of elements through the thickness is investigated. The failure prediction is the second part of the simulation study. Solutions with and without progressive failure approach are obtained and the effect of progressive failure analysis for an optimum simulation of failure is discussed. The most appropriate failure criteria to predict the failure of a thick composite structure is also investigated by considering various failure criteria. By comparing the test results with the ones found from the finite element analyses, the validity of the developed model and the chosen failure criteria are discussed.

En aquest treball s'ha realitzat una anàlisi de la junta T-bolt aplicada a la unió de laminats gruixuts amb elements metàl·lics. Més concretament, l'estudi es centra en el tipus de juntes T-bolt emprades en la unió entre les pales i la boixa de grans aerogeneradors, que constitueix una de les principals aplicacions d'aquest tipus de junta.En primer lloc, s'ha realitzat una anàlisi simplificada dels factors que influeixen al comportament de la junta, a partir del qual es justifica la necessitat de realitzar un estudi en profunditat dels estats d'esforços presents al laminat a la proximitats de la junta, i d'estudiar la seva resistència enfront dels diversos modes de trencament possibles.El següent punt desenvolupat és l'anàlisi d'esforços al laminat, per la qual cosa s'ha emprat un model tridimensional d'elements finits de la junta. Primerament, s'han analitzat els esforços per una geometria típica sota tres situacions de càrrega diferents, i s'ha determinat l'evolució de l'àrea de contacte entre el buló i el laminat. A continuació s'ha realitzat una comparació entre la distribució d'esforços de la T-bolt i la que presenten les juntes amb encavalcament. Finalment, s'ha analitzat la influencia de la curvatura del laminat en els resultats.Per a la determinació de la resistència del laminat a la zona de la junta, un dels obstacles principals consisteix en que, als dissenys normals de la T-bolt, el pern trenca molt abans que s'assoleixi la càrrega de trencament del laminat en algun dels seus modes possibles. Per aquest motiu s'ha hagut de dissenyar un utillatge especial que permetés introduir les càrregues necessàries. S'han realitzat assaigs per dos materials diferents, forçant per cada un d'ells el trencament en tensió neta i compressió local.Finalment, s'ha demostrat que és possible realitzar una predicció força acurada de la càrrega de trencament del laminat de la T-bolt, emprant com a dades de partida, per una banda, les càrregues de trencament a tensió neta i compressió local del laminat i, per l'altra, les distribucions d'esforços de la junta que es vol analitzar i de la proveta emprada per estimar els paràmetres anteriors.S'observa que el marge de seguretat per al trencament del laminat a les juntes T-bolt emprades actualment a la indústria eòlica és molt elevat (entre 3.5 i 5), el que indica que hi ha un cert marge per a la optimització de l'espessor del laminat, sempre que es consideri admissible l'aparició d'esquerdes a la matriu. / En el presente trabajo, se ha realizado un análisis de la junta T-bolt aplicada a la unión de laminados gruesos con elementos metálicos. Más concretamente, el estudio se centra en el tipo de juntas T-bolt utilizadas en la unión entre las palas y el buje de aerogeneradores de gran tamaño, que constituyen una de las principales aplicaciones de este tipo de juntas.En primer lugar, se ha realizado un análisis paramétrico simplificado de los diferentes factores que influyen en el comportamiento de la junta, a partir del cual se justifica la necesidad de realizar un estudio en profundidad de los estados de esfuerzos presentes en el laminado en las proximidades de la junta, y de estudiar su resistencia frente a los distintos modos de fallo posibles.El siguiente punto desarrollado es el análisis de esfuerzos en el laminado, para lo cual se ha utilizado un modelo tridimensional de elementos finitos de la junta. En primer lugar se han analizado los esfuerzos para una geometría típica bajo tres situaciones de carga distintas, y se ha determinado la evolución del área de contacto entre el bulón y el laminado. A continuación se ha realizado una comparación entre la distribución de esfuerzos de la T-bolt y la que presentan las juntas a solape. Finalmente, se ha analizado la influencia de la curvatura del laminado en los resultados.Para la determinación de la resistencia del laminado en la zona de la junta, uno de los obstáculos principales consiste en que, en los diseños típicos de la T-bolt, el vástago rompe mucho antes de que se alcance la carga de rotura del laminado en alguno de sus distintos modos. Por este motivo, se ha tenido que diseñar un utillaje especial que permitiera la introducción de las cargas necesarias. Se han realizado ensayos para dos materiales distintos, forzando, para cada uno de ellos, el fallo en tensión neta y compresión local.Finalmente, se ha demostrado que es posible predecir, con una buena aproximación, la carga de rotura del laminado de la T-bolt, utilizando como datos de partida las cargas de rotura del laminado en tensión neta y compresión local, y las distribuciones de esfuerzos de la junta a analizar y de la probeta utilizada para estimar los parámetros anteriores.Se observa que los márgenes de seguridad respecto al fallo del laminado en las juntas T-bolt utilizadas actualmente en la industria eólica es muy elevado (entre 3.5 y 5), lo que indica que existe un cierto margen para la optimización del espesor del laminado, siempre que se considere admisible la aparición de grietas en la matriz. / An analysis of the T-bolt joint, applied to the joining of thick laminates with metallic parts, has been carried out. The study is particularly focused on the kind of T-bolt joints used in the blade root - hub attachments of large wind turbines, which is one of the major applications of these joints.First, a simplified analysis of the factors affecting the joint behavior has been performed. From this simple analysis, it has been shown the necessity of in-depth studies of both the stress states of the laminate in the vicinity of the joint, and the strength of the laminate for its different failure modes.The next point that has been developed is the stress analysis of the laminate, which has been performed by means of a three-dimensional finite element model of the joint. First of all, the stresses and strains of a typical joint geometry under three different load situations have been calculated, and the evolution of the contact area between the nut and the laminate has been estimated. Next, a comparison between the stress states of the T-bolt joint and those of a double-lap joint has been carried out. Finally, the influence of the laminate curvature on the stress distributions has been evaluated.One of the main obstacles to the determination of the strength of the laminate in the joint zone is that, in the usual T-bolt designs, the stud fails far before the laminate has reached any of its ultimate loads. Therefore, special fixtures have been designed that are able to transfer the necessary loads to the joint. Tests have been performed using specimens made of two different laminates which have been designed to fail either in the net tension or the bearing mode.Finally, it has been shown that it is possible to accurately predict the laminate failure load using as input data, on one hand, the net tension and bearing strengths of the laminate, and, on the other, the stress distributions of both the T-bolt and the test specimen used in the estimation of the laminate strengths. It has been also shown that the safety factors against the laminate failure in a typical T-bolt design used nowadays in the wind turbine industry is quite high (between 3.5 and 5), which shows that there is still some margin for the optimization of the laminate thickness, providing that the presence of some matrix cracks is allowed.

The analysis presented in this thesis provides a methodology for grouted bolts design, based on empirical and analytical methods. Hence, the main objectives of this thesis are to offer practical means for better characterisation of poor to very poor rock masses, to better predict support pressure, and to develop an elasto-plastic analytical model for design of grouted bolts in tunnels excavated in such rock masses. To improve the applicability of the GSI (Geological Strength Index) in poor to very poor rock masses, using Broken Domain Structure (BSTR), Structure Rating (SR), and Intact Core Recovery (ICR), some modifications have been offered, resulting in the Modified-GSI. Applying rock-load height concept and Modified-GSI, an approach to estimate support pressure has been developed. The main advantage of this approach is its applicability in squeezing ground and anisotropic stress conditions. Numerical modelling was carried out in order to adjust the proposed support pressure equation. Considering convergence reduction approach, an elasto-plastic model based on the latest version of Hoek- Brown failure criterion has been developed for a more effective and practical grouted bolt design. The link between empirical approach and elasto-plastic solution makes it possible to reach more realistic and appropriate bolting pattern design. In this way, the need for the redesign procedure in the convergence reduction approach is eliminated. The results of the proposed elastic-plastic solution have been compared with a numerical model using FLAC2D, and a reasonable agreement was observed. The practical application of the developed methodology is depicted by an analysis of a case study in Turkey.

Recycling of plastics always plays an important role in keeping our environment better and safe. With the rise in usage of plastics and industrialization, the need for recycling the plastics has become a big business and is getting bigger. This thesis work was done for a company called Rapid Granulator AB, which works with the recycling of plastics as a big trade in Sweden. Like all the industries across the globe are trying to be economical in every way, Rapid Granulator AB wanted to develop an economical design of their high quality granulating knife. For achieving the economical design, they wanted to study the behaviour of the rotating knife during the process of producing plastic granules. The granulator cutting process was simulated and numerical analysis was done on the rotating knife of a plastic granulator machine by using the finite element code ABAQUS with 3D stress elements to find out the critical stresses and forces acting on the rotating knife. The bolt preload was applied by Abaqus/Standard, and the results of implicit analysis were imported to Abaqus/Explicit for the impact analysis where the flow of stresses on the rotating knife during the impact with materials were simulated and studied. The study was done on knife models of different thickness to see if the thickness of the current knife model can be reduced. Analysis were done also on a knife model assembly with a double sided cutting edge knife to see if the knife model can be used to its full extent. The simulation models and analysis results were given to the company to develop a more economical knife model.

Block shear is a limit state that should be accounted for during the design of the steel tension members. This failure mechanism combines a tension failure on one plane and a shear plane on a perpendicular plane. Although current design specifications present equations to predict block shear load capacities of the connections, they fail in predicting the failure modes. Block shear failure of a structural connection along a staggered path may be the governing failure mode. Code treatments for stagger in a block shear path are not exactly defined. A parametric study has been conducted and over a thousand finite element analyses were performed to identify the parameters affecting the block shear failure in connections with multiple bolt lines and staggered holes. The quality of the specification equations were assessed by comparing the code predictions with finite element results. In addition, based on the analytical findings new equations were developed and are presented herein.