Simplified mechanical loading paths, which represent more complex loading paths observed during penetration, were investigated using a triaxial chamber and a high-strength concrete. Objectives were to determine the effects that stress/strain (load) paths had on the material’s unconfined (UC) residual strength. The loading paths included hydrostatic compression (HC), uniaxial strain in compression (UX), and uniaxial strain load biaxial strain unload (UXBX). The experiments indicate that load paths associated with non-visible microstructural damage were HC and UX, which produced minimal impact on the residual UC strength (<30%), while the load paths associated with visible macro-structural damage were UXBX, which significantly reduced the UC strength (>90%). The simplified loading paths were also investigated using a material model driver code that was fit to a widely used Department of Defense material model. Virtual experiment data revealed that the material model investigated overestimated material damage and produced poor results when compared to experimental data.

In reinforced concrete (RC) structures, adequate bond between the reinforcement and concrete is required to achieve a true composite system, in which reinforcing steel carries tensile stress, once concrete cracks, and concrete and reinforcing steel carry compression. Determining bond strength and required development length for shear transfer between concrete and reinforcement is an ongoing research subject in the field of reinforced concrete with advances in the concrete and reinforcement materials requiring continuous experimental efforts. Finite element analysis (FEA) provides opportunities to explore structural behavior of RC structures beyond the limitations of experimental testing. However, there is a paucity of research studies employing FEA to investigate the reinforcement-concrete bond-zone behavior and related failure mechanism. Instead, most FEA-based research associated with RC bond has centered on developing a bond (or interface) constitutive model for use in FEA that, by itself, can characterize bond-zone behavior, typically represented by the bond stress-slip displacement relationship. This class of bond models is useful for simulating the global behavior of RC structures but is limited in its ability to simulate local bond resistance for geometries and material properties that differ substantially from those used to calibrate the model. To fill this gap in research, this study proposes a finite element (FE) modeling approach that can simulate local bond-zone behavior in reinforced concrete. The proposed FE model is developed in a physics-based way such that it represents the detailed geometry of the bond-zone, including ribs on the deformed reinforcement, and force transfer mechanisms at the concrete-reinforcement interface. The explicit representation of the bond-zone enables simulation of the local concrete compression due to bearing of ribs against concrete and subsequent hoop tension in the concrete. This causes bond failure either due to local concrete crushing (leading to reinforcement pullout) or global concrete splitting. Accordingly, special attention is given to the selection and calibration of a concrete model to reproduce robust nonlinear response. The power of the proposed modeling approach is its ability to predict bond failure and damage patterns, based only on the physical and material properties of the bond area. Thus, the successful implementation and application of this approach enables the use of FEA simulation to support the development of new design specifications for bond zones that include new and improved materials.

I detta examensarbete undersöks hur stödmurar av olika slag kan utföras på ett underhållsvänligare sätt. Med det menas att kostnaden för drift och underhåll ska hållas på en rimlig nivå med "normalt underhåll". Arbetet har genomförts på uppdrag av Nacka Kommun. Stödmurar har till uppgift att ta hand om jordtryck och även eventuella trafiklaster från vägar eller parkeringar. Detta ställer krav på att stödmuren är dimensionerad för de laster, och även för de olika typer av angrepp som kan förekomma med hänsyn till miljö. Stödmurar som är i stort behov av underhåll är idag ett problem för Nacka kommun som beställare. I dagens läge får kommunen sina stödmurar levererade av i princip samma typ och företag, vilket gör att kostnaderna för drift och underhåll också ligger på samma nivå. För att undersöka vilka typer av stödmurar som finns på marknaden, har en kategorisering gjorts av de vanligast förekommande stödmurarna, deras fördelar och nackdelar, samt användningsområden för de olika typerna. En LCC beräkning har gjorts för att lättare kunna se skillnaden mellan de olika stödmurarna med avseende på initialkostnader för produkten samt drift och underhållskostnader under dess livslängd. Betong som är det klart dominerande materialet som stödmurarna byggs av idag, har förklarats lite mer ingående med hänsyn till vilka skador som kan förekomma och även hur dessa kan undvikas. Ett av resultaten som är framtaget genom livscykelkostnadsberäkning visar, att gabioner som stödkonstruktion har minsta totalkostnad under dess livslängd. En av slutsatsen som arbetet har mynnat i är att med ett högre krav under projekteringsskedet kan skador som är ofta förekommande undvikas, eller hållas på en acceptabel nivå under stödmurens livslängd. Skadorna kan vara sprickbildning, avspjälkning eller korrosion av armering. / In this thesis an literature study have been done to examines how the retaining walls of various kinds can be performed in a maintenance friendly way. This means that the cost of operation and maintenance must be kept at a reasonable level with "normal maintenance". The work has been carried out on behalf of and supervised by Nacka Municipality. Retaining walls have the task of caring for earth pressure and also possible traffic loads from roads or parking areas. This demands that the retaining wall is dimensioned for the loads, and also for the different types of attacks that can occur with regard to the environment. Retaining walls that are in great need of maintenance is now a problem for Nacka municipality. At present, the municipality is getting all its retaining walls supplied by basically the same type and company. This means that the costs of operation and maintenance are also located on the same level. To examine the types of support walls that are available in the market today a categorization have been made of the most common retaining walls, their advantages, disadvantages and uses of the different types. An LCC calculation has been done to help identify the difference between the different support walls with respect to the initial cost of the product, and operation and maintenance costs over its lifetime. Concrete which is the dominant material that retaining walls are built of today have been explained more thoroughly with regard to the damage that may occur and also how they can be avoided. One of the results of the work is that with higher requirements during the design stage can damages that are frequently be avoided, or kept at an acceptable level during retaining walls durability. Effects may be cracking, spalling and corrosion of reinforcement.

Masonry spires are a typical part of church architecture. Since it is rare that masonry is used as a load-bearing material in the western world today, it is important to maintain and increase the knowledge of modelling masonry structures both from a maintenance point of view and to build new masonry structures. The purpose of this master thesis is to look at and evaluate some different methods to model masonry spires exposed to common loads such as gravity, settlement and wind. The spire of the Salisbury Cathedral is used as a template regarding geometry and mechanical properties for the modelling methods. Two modelling methods are used in the master’s thesis. The first one is the limit analysis method applied to masonry. It is used to calculate a critical thickness for the masonry of the spire for a severe wind load. The second method is the Finite Element Method (FEM). The commercial finite element software Abaqus is used to create the model and the discretization used with the FE modelling is the macro-modelling approach. Concrete Damage Plasticity (CDP) in Abaqus is used as the material model and adapted to masonry. The finite element model consists of the spire itself along with the supporting structure beneath it down to the piers. Four different simulations (jobs) are run with varying wind direction and two of them have settling piers. The results from the finite element simulations indicate that the membrane stresses in the spire faces for the various jobs were not significantly different from one another. One of the jobs with settling piers could not be completed because the tensile stresses in the arches reached the tensile strength capacity of the material. The other simulation with a settlement that did complete did not have any significant difference in stress compared with the simulations without settlements. While the arches and the piers underwent plastic straining the spire itself did not. The stress levels there remained in the linear range for all the completed simulations. The finite element results also agree with the limit analysis. These findings call into question some of the modelling choices. The inclusion of the structure beneath the spire in the finite element model, as a way to study the effect of settlements, did not give more insight into the spire’s behaviour. Furthermore, the method to implement settlements was too inaccurate and another approach should be used to study the effect of settlements on the state of spires. Further work needs to be done on that topic. Improvements can also be made regarding how CDP was adapted for masonry. / Murade tornspiror är en vanlig takkonstruktion inom kyrkoarkitekturen. Eftersom det numera är sällsynt att murverk fungerar som lastbärande material i västvärlden, är det viktigt att upprätthålla och utöka kunskapen om murverkskonstruktioner för både underhåll och nybyggnation. Syftet med denna masteruppsats är att betrakta och utvärdera några olika modelleringsmetoder för murade tornspiror som är utsatta för några typiska laster såsom egentyngd, sättningar och vind. Katedralen i Salisbury används som en modelleringsmall i uppsatsen med avseende på katedralens geometri och materialegenskaper. Två modelleringsmetoder används i uppsatsen. Den första är gränsanalys tillämpad på murverkskonstruktioner. Den används för att beräkna en kritisk tjocklek för tornspiran under en stor vindlast. Den andra metoden är Finita Elementmetoden (FEM). Den kommersiella finita elementprogramvaran Abaqus används för finita elementanalysen och diskretiseringen som används för murverket i finita elementmodellen är makromodellering. Concrete Damage Plasticity (CDP) i Abaqus används som materialmodell och anpassas för murverk. Finita elementmodellen består utav själva tornspiran inklusive de bärande delarna under spiran och ned till pelarna. Fyra olika simuleringar ("jobb") körs med vindlast som angriper från olika riktningar och två av simuleringarna har pelare som sätter sig. Resultaten från simuleringarna visar att membranspänningarna i tornspirans väggar, för de olika jobben, inte skilde sig i någon betydelig grad från varandra. Ett av jobben med pelare som satte sig kunde inte köras klart eftersom dragspänningarna i valvbågarna överskred draghållfastheten på murverket i modellen. Den andra simuleringen med sättningar som kördes klart uppvisade inte några avsevärda skillnader i spänningar i tornspiran jämfört med simuleringarna utan sättningar. Medan plastiska töjningar uppkom i både valvbågarna och pelarna i modellen, uppkom de inte i tornspiran. Spänningsnivåerna i tornspiran var inom det linjära intervallet för alla simuleringar. Resultaten från finita elementanalysen stämde överens med resultaten från gränsanalysen. Analysresultaten ifrågasätter vissa av modelleringsvalen. Att inkludera de bärande delarna under tornspiran i finita elementmodellen, för att undersöka effekten av sättningar, gav inte en större insikt i hur sättningar påverkar tornspiran. Dessutom, var metoden för att tillämpa sättningar för oprecis och en annan metod borde användas. Mer arbete måste utföras vad gäller det ämnet. Sättet att tillämpa CDP för murverk kan också förbättras.

Because of an eventual ban of creosote-impregnated products, alternative materials for poles used in the electrical grid are needed. Concrete is one alternative and spun concrete poles have been manufactured for the Swedish grid before. These poles are still in use since the high strength and good functioning. However, they weigh too much in terms of the way that poles are assembled on the grid today. Therefore, a study comparing the capacity of different geometries, resulting in lower weight, is of interest.  In this Master’s Thesis, crack initiation and compressive failure in concrete poles are examined by creating FE-models in the software BRIGADE/Plus, using concrete damage plasticity. Thus, guidance is provided about how thin the concrete walls can be made without risking failure – which also means how low the weight of such a pole can be. The failure most likely to occur is a compressive failure in the concrete with a ductile behavior. The result shows that a geometry change, which implies a thinner concrete wall, is possible. This means a weight reduction between 30-75 % or even more, depending on which network the poles are designed for.

In Sweden, there are about 64,000 shelters in different places in the country. There is a shortage of shelters, and they arenot enough for the entire country's population, but only about 7 million civilians can be accommodated. Shelters havebecome a highly topical topic lately, but the maintenance of these shelters is still neglected. Many of the existing sheltersneed to be renovated or modernized. This thesis has been carried out in collaboration with Ramboll AB in Uppsala withthe aim of developing possible proposals for future upgrades of a population shelter in Katarinaberget in Stockholm andstudying the construction and its associated problems. The work was based on the following questions; what damage isthere in the concrete structures? and what technical solutions are required to ensure the strength of the concrete structures?  The result of the work was based on the empirical material consisting of previously completed concrete inspections andtechnical documentations, as well as interviews with some experts in the subject. The results showed that there are severaldifferent types of concrete damage in Katarinaberget's population shelter. It also showed several repair methods to ensurethe construction, the method that is most suitable to use to fix the established concrete damage is the dry spraying method. / I Sverige finns cirka 64 000 skyddsrum på olika platser i landet. Det råder brist på skyddsrum och de räcker ej till hela landets befolkning, utan endast cirka 7 miljoner civila får plats. Skyddsrum har blivit ett högst aktuellt ämne på senaste, men underhållet av dessa skyddsrum är fortfarande eftersatt.  Många av de befintliga skyddsrummen behöver renoveras eller moderniseras. Detta examensarbete har utförts i samarbete med Ramboll AB i Uppsala med syftet att ta fram möjliga förslag för framtida uppgraderingar av ett befolkningsskyddsrum insprängt i Katarinaberget i Stockholm och studera konstruktionen samt dess tillhörande problem. Arbetet utgick från följande frågor; vilka skador finns det i betongkonstruktionerna? och vilka tekniska lösningar krävs för att säkerställa hållfastheten hos betongkonstruktionerna?  Resultatet av arbetet baserades på det empiriska materialet som utgörs av tidigare genomförda betongbesiktningar och tekniska dokumentationer, samt intervjuer med några experter inom ämnet. Resultatet visade att det finns flera olika typer av betongskador i Katarinabergets befolkningsskyddsrum. Det visade även flera reparationsmetoder för att säkerställa konstruktionen, den metoden som mest lämplig att använda för att åtgärda de fastställde betongskadorna är torrsprutnings metod.

A three dimensional nonlinear finite element model has been developed to study the behaviour of composite beams with profiled sheeting oriented perpendicular to its axis. The analysis of the push test was carried out using ABAQUS/Explicit with slow load application to ensure a quasi-static solution. Both material and geometric nonlinearities were taken into account. Elastic¿plastic material models were used for all steel components and the Concrete Damaged Plasticity model was used for the concrete slab. The post-failure behaviour of the push test was accurately predicted, which is crucial for realistic determination of shear capacity, slip and failure mode. The results obtained from finite element analysis were verified against the experimental push tests conducted in this research and also from other studies. After validation, the model was used to carry out an extensive parametric study to investigate the effect of transverse spacing in push tests with double studs placed in favourable and staggered positions with various concrete strengths. The results were also compared with the capacity of a single shear stud. It was found that shear connector resistance of pairs of shear connectors placed in favourable position was 94% of the strength of a single shear stud on average, when the transverse spacing between studs was 200 mm or more. For the same spacing, the resistance of staggered pairs of studs was only 86% of the strength of a single stud. The strength of double shear studs in favourable position was higher than that of the staggered pairs of shear connectors.

Ultra high performance fibre reinforced concrete (UHPFRC) is a relatively new fibre reinforced cementitious composite and has become very popular in construction applications. Extensive experimental studies have been conducted, demonstrating its superior properties such as much higher strength, ductility and durability than conventional fibre reinforced concrete (FRC) and high performance concrete. However, the material's damage and fracture mechanisms at meso/micro scales are not well understood, limiting its wider applications considerably. This study aims at an in-depth understanding of the damage and fracture mechanisms of UHPFRC, combining microscale in-situ X-ray computed tomography (µXCT) experiments and mesoscale image-based numerical modelling. Firstly, in-situ µXCT tests of small-sized UHPFRC specimens under wedge splitting loading were carried out, probably for the first time in the world, using an in-house designed loading rig. With a voxel resolution of 16.9µm, the complicated fracture mechanisms are clearly visualised and characterised using both 2D images and 3D volumes at progressive loading stages, such as initiating of micro-cracks, arresting of cracks by fibres, bending and pulling out of fibres and spalling of mortar at the exit points of inclined fibres. Secondly, based on the statistics of pores in the µXCT images obtained for a 20mm cube specimen, an efficient two-scale analytical-numerical homogenisation method was developed to predict the effective elastic properties of the UHPFRC. The large number of small pores were first homogenised at microscale with sand and cement paste, using elastic moduli from micro-indentation tests. 3D mesoscale finite element models were built at the second scale by direct conversion of the µXCT images, with fibres and large pores were faithfully represented. The effects of the volume fraction and the orientation of steel fibres on the elastic modulus were investigated, indicating that this method can be used to optimise the material micro-structure. Thirdly, 3D mesoscale finite element models were built for the specimen used in the in-situ µXCT wedge splitting test, with embedded fibre elements directly converted from the µXCT images. The fracture behaviour in the mortar was simulated by the damage plasticity model available in ABAQUS. Finally, 2D mesoscale finite element models were developed to simulate the fracture behaviour of UHPFRC using cohesive interface elements to simulate cracks in the mortar, and randomly distributed two-noded 1D fibres and connector elements to simulate the pull-out behaviour of fibres. This approach offers a link between the fibres pull-out behaviour and the response of the whole composite at the macroscale, thus it can be used to conduct parametric studies to optimise the material properties.

Reinforced concrete frames, infilled with brick/concrete block masonry, are the most common type of structures found in multi-storeyed constructions, especially in developing countries. Usually, the infill walls are considered as non-structural elements even though they alter the lateral stiffness and strength of the frame significantly. Approximately 80% of the structural cost from earthquakes is attributable to damage of infill walls and to consequent damages of doors, windows and other installations. Despite the broad application and economical significance, the infill walls are not included in the analysis because of the design complexity and lack of suitable theory. But in seismic areas, ignoring the infill-frame interaction is not safe because the change in the stiffness and the consequent change in seismic demand of the composite structural system is not negligible. The relevant experimental findings shows a considerable reduction in the response of infilled frames under reverse cyclic loading. This behaviour is caused by the rapid degradation of stiffness, strength, and low energy dissipation capacity resulting from the brittle and sudden damage of the unreinforced masonry infill walls. Though various national/international codes of practice have incorporated some of the research outcomes as design guidelines, there is a need and scope for further refinement. In the initial part of this work, a numerical modelling and linear elastic analysis of masonry infilled RC frames has been done. A multi-storey multi-bay frame infilled with masonry panels, is considered for the study. Both macro modelling and micro modelling strategies are adopted. Seismic loading is considered and an equivalent static analysis as suggested in IS 1893, 2002 is done. The results show that the stiffness of the composite structure is increased due to the obvious confinement effects of infill panels on the bounding frame. A parametric study is conducted to investigate the influence of size and location of openings, presence/absence of infill panels in a particular storey and elevation irregularity in terms of floor height. The results show that the interaction of infill panel changes the seismic response of the composite structure significantly. Presence of openings further changes the seismic behaviour. Increase in openings increases the natural period and introduce newer failure mechanisms. Absence of infill in a particular storey (an elevation irregularity) makes it drift more compared to adjacent storeys. Since the structural irregularities influence the seismic behaviour of a building considerably, we should be cautious while construction and renovation of such buildings in order to take the advantage of increased strength and stiffness obtained by the presence of infill walls. A nonlinear dynamic analysis of masonry infilled RC frames is presented next. Material non linearity is considered for the finite element modelling of both masonry and concrete. Concrete damage plasticity model is employed to capture the degradation in stiffness under reverse cyclic loading. A parametric study by varying the same parameters as considered in the linear analysis is conducted. It is seen that the fundamental period calculation of infilled frames by conventional empirical formulae needs to be revisited for a better understanding of the real seismic behaviour of the infilled frames. Enhancement in the lateral stiffness due to the presence of infill panel attracts larger force and causes damage to the composite system during seismic loading. Elevation irregularities included absence of infill panels in a particular storey. Soft storey shows a tendency for the adjacent columns to fail in shear, due to the large drift compared to other storeys. The interstorey drift ratios of soft storeys are found to be larger than the limiting values. However this model could not capture the separation at the interfaces and related failure mechanisms. To improve the nonlinear model, a contact surface at the interface is considered for a qualitative analysis. A one bay one storey infilled frame is selected. The material characteristics were kept the same as those used in the nonlinear model. Contact surface at the interface was given hard contact property with pressure-overclosure relations and suitable values of friction at the interface. This model could simulate the compressive diagonal strut formation and the switching of this compressive strut to the opposite diagonal under reverse cyclic loading. It showed an indication of corner crushing and diagonal cracking failure modes. The frame with central opening showed stress accumulation near the corners of opening. Next, the micro modelling strategy for masonry suggested by Lourenco is studied. This interface element can be used at the masonry panel-concrete frame interface as well as at the expanded masonry block to block interface. Cap plasticity model (modified Drucker – Prager model for geological materials) can be used to describe the behaviour of masonry (in terms of interface cracking, slipping, shearing) under earthquake loading. The blocks can be defined as elastic material with a potential crack at the centre. However, further experimental investigation is needed to calibrate this model. It is required to make use of the beneficial effects and improve upon the ill-effects of the presence of infills. To conclude, infill panels are inevitable for functional aspects such as division of space and envelope for the building. Using the lateral stiffness, strength contribution and energy dissipation capacity, use of infill panels is proposed to be a wiser solution for reducing the seismic vulnerability of multi-storey buildings.

Implementing pre-stressing cables is a viable option aiming at controlling deformation and cracking of concrete flat slabs in serviceability limit state. The pre-stressing cables also contribute to punching shear capacity of the slab when they are located in vicinity of the column. The positive influence of pre-stressing cables on punching capacity of the concrete slabs is mainly due to the vertical component of inclined cables, compressive in-plane stresses and counter acting bending moments near the support region. The method presented in Eurocode 2 to determine the punching capacity of the pre-stressed concrete flat slabs considers the in-plane compressive stresses but totally neglects the effect of counter acting moments. The effect of vertical forces introduced by inclined cables is only considered when they are within the distance 2d from the face of the column. This area is called basic control area in the Eurocode 2. In this master thesis nonlinear finite element analysis is carried out to study the effect of pre-stressing cables on punching shear capacity of concrete slabs respecting the distance of cables from the face of the column. To attain this objective, the concrete damage plasticity model is implemented to model the concrete. The results indicate that until the distance of 6d from the face of the column the contribution of pre-stressing cables in punching shear capacity of slabs is significant. Furthermore, comparing the numerical results with the punching shear capacity of slabs predicted by Eurocode 2 reveals that Eurocode tremendously underestimates the punching shear capacity when the cables are located outside the basic control area.