The increased amount of traffic combined with higher traffic loads leads to many existing bridges needing strengthening in the future to ensure their expected lifespan. This means the bridge owners will be focusing more on strengthening projects and smart solutions will be crucial for preserving a healthy bridge stock. When strengthening existing non-composite bridges (with steel girder and concrete deck) one potential method is to achieve composite action by installing shear connectors. The post-installed shear connectors prevent slip between the steel girders and the concrete. The composite action will reduce bending stresses and deflection of the bridge, due to the increase in moment of inertia and relocation of the neutral axis. Different types of shear connectors can be used for achieving composite action and each type of connector has its own installation method. The biggest distinction between the methods is how the connectors gain access to the steel girder for installation and what technique is used when installing them. This thesis presents the theory behind composite action, the current methods used for achieving composite action on existing bridges and to what extent a bridge can be strengthened by composite action. The thesis also provides a status of the existing road bridge stock around the world. The four case studies examined in this thesis have used different post-installed shear connectors to manage different strengthening problems like weight restriction, fatigue life of shear connectors and a unique problem on the Pitsund Bridge where loud bangs appeared from the bridge when truck passed in the morning. For the case study on the Pitsund Bridge an interview was conducted that explains the entire procedure of the project, from the noise problem to how the installation of coiled spring pins was performed. The bridge over Lule River at Akkatsfallen consists of two steel girders and a concrete deck. This bridge is chosen as a real case study to determine to what extent a bridge can increase its capacity by achieving composite action. The calculations are performed in accordance with the Eurocodes on both non- and full-composite action and the result is compared to the other case studies.

Today in most design offices the practice when designing infrastructure is to adopt a trial-and-error based approach. This means that one solution to the problem is evaluated and based on the results the design is altered. This process is then repeated until satisfactory results have been achieved. This is an iterative process and in this project, a software has been developed as a tool for the practicing engineer to use for preliminary design. The software carries out this iterative process and optimizes the solution using algorithms. The software is developed to evaluate road traffic composite bridges according to the Eurocodes. The bridges are made up from two main steel beams with a concrete deck on top. The software has then been used in a number of different studies in order to evaluate its potential as a preliminary design method. The results show that this is a viable tool for preliminary designs, with the drawback that, each iteration is computationally expensive and therefore, optimization of a real-case problem takes a lot of time in order to find the optimal design. / I dagsläget använder de flesta konstruktionsföretagen sig av en iterativ process när de konstruerar infrastruktur. Man utvärderar en lösning och beroende av resultatet så justeras lösningen och utvärderas på nytt, detta återupprepas tills en tillfredsställande lösning har erhållits. Detta är en iterativ process och i samband med detta arbete så har en mjukvara utvecklats som ett verktyg till konstruktören. Mjukvaran utför det iterativa arbetet och optimerar konstruktionen med hjälp av optimeringsalgoritmer. Programmet utvärderar vägbroar av en samverkanskonstruktion i form av två stålbalkar med en betongplatta ovanpå, beräkningarna sker enligt Eurokoderna. Programmet har använts för att utvärdera det här arbetssättets potential vid anbudsskede i projekt. Resultaten visar att det finns potential för detta med nackdelen att varje iteration är tidskrävande vilket gör att optimering av ett realistiskt projekt tar lång tid.

In the year 2006, only 10 years after the steel- concrete composite bridge, Vårby bridge was built, fatigue cracks were found during an inspection. To further investigate the reasons and the potential danger of the cracks, an investigation under the commission of the Swedish Transport Administration was issued in 2009. After the detection of fatigue cracks, several measurements were carried out in order to monitor the static behavior by the use of strain gauges at selected positions along the bridge. The measurements from the strain gauges monitoring the global behavior were then used to calibrate an finite element model.   The present report is part of the research of understanding the behavior of steel-concrete composite bridges. Numerical analysis and model updating have been used in order to understand and determine how different parameters affects the strain range and the global behavior. The numerical analysis and parameter study were performed in the Finite Element software Abaqus and programming language Python. The outcome of the parameter study was then used to perform the model updating by the method of falsification in MATLAB.   The results from the parameter study and the model updating showed that the measured strains could be reached with a wide range of parameter combinations. Even with unreasonable parameter values, the measured strains were obtained. To investigate the reason for this, a multiple linear regression analysis was performed which showed that the strain range is strongly correlated to the Young’s modulus of steel and concrete and also to the connector elasticity, which resembles the studs in the real bridge.   Two different finite element models, with two completely different input parameter values, obtain the same strain range for the global behavior. It is therefore not certain to assume that a model is accurate and valid based on the fact that the predicted strain range from the finite element model is close to the measured strain range since the global behavior of a steel- concrete composite bridge can be modeled by many different sets of parameters.

A great deal of the design of bridges today is carried out using finite element models and analyses. These models are usually generalized versions of the actual bridge, as these kinds of models often is able to produce results similar to reality. In this thesis, a study regarding how the considerations of some of the details of a bridge affect the results using a FE analysis is performed. The analyses are focused on the change of transverse load distribution in the bridge slab. The thesis also addresses the use of a parametric design approach in FE modeling and analyses. The models are created using Python code with the possibility of choosing which properties that will be active or not before each analysis. The study is focused on the modeling of composite bridges with parallel box-girders. The bridge Kollektivtrafikbron, which is a new bridge currently in design as part of the Hisingsbridge project in Gothenburg, is used as a case study. The study has shown that a great deal of simplifications is reasonable to carry out in the modeling of a composite bridge, as long as the designer is aware of how these simplifications affect the results obtained. For the type of bridge investigated, the study has shown that the presence of transverse stiffening beams in the model as well as how the material properties of the edge beams are specified have a large impact on the transverse bending moment. The study has also shown that the use of shell or beam elements in the modeling of the main beams have a large impact on the shear force in the slab. Furthermore, the choice of element types and how constraints are specified have been shown to entail greater differences in the results than the detailing level of the model. These aspects should therefore be thoroughly considered in all modeling work. Additional aspects treated in the study is the impact of radius, the recess in the slab for the track as well as the size of the surface specified when applying traffic loads. The parametric design approach implemented in this study have provided the possibility of carrying out more analyses and investigating more details than what would have been possible if each model had been created manually. The greatest benefit of using a parametric design approach have been the possibility of carrying out analyzes automatically without monitoring or adjusting, which has made it possible to utilize the time provided for the study in a highly effective way. The design approach has been shown to be most effective when using simplified FE models, as these can be generated automatically fairly quickly. Therefore, it could be very beneficial to implement this kind of design approach in the early stages of design. / Idag utförs ofta dimensioneringen av broar med hjälp av finita elementmodeller och analyser. Dessa modeller utgörs i regel av generaliserade versioner av den verkliga bron då en kraftigt förenklad beräkningsmodell antas generera resultat som är väldigt nära verkligheten. I detta examensarbete undersöks hur vissa utvalda detaljer i brons utformning påverkar de resultat en finita elementanalys ger utifrån hur de beaktas vid modellering. Analyserna är inriktade på förändring av lastfördelning i tvärled hos brons farbana. Vidare undersöks möjligheten att använda ett parametriserat arbetssätt vid modellering och analys. Modellerna som analyseras formuleras i kod med möjlighet att välja vilka egenskaper som ska vara aktiva inför varje analys. Arbetet är koncentrerat på modellering av samverkansbroar med parallella lådbalkar som huvudbalkar. Som fallstudie används Kollektivtrafikbron. En ny plankrökt bro med denna utformning under pågående projektering inom projektet med den nya Hisingsbron i Göteborg. Arbetet har visat att det finns många förenklingar som är rimliga att genomföra vid modellering, så länge det finns en medvetenhet kring hur dessa påverkar resultaten. För den undersökta typen av bro har arbetet visat att förekomsten av tvärbalkar i modellen samt hur materialegenskaperna definieras för kantbalkar har stor inverkan på tvärledsmomentet. Utöver detta har arbetet visat att tvärkraften påverkas kraftigt utifrån om huvudbalkarna modelleras med skalelement respektive balkelement. Genomgående resultat är att modellering av huvudbalkarna med balkelement medför mycket högre max värden för tvärkraft. Vidare har arbetet visat att val av elementtyp och definiering av kopplingar kan ge större differenser än detaljrikedom och att dessa delar bör beaktas med stor noggrannhet vid all modellering. Ytterligare aspekter som behandlats är inverkan av radie, rälursparingar i farbanan samt definiering av lastytans storlek vid applicering av trafiklast. Det parametriserade arbetssättet som implementerats i detta arbete har gjort det möjligt att utföra fler analyser och undersöka fler faktorers inverkan än vad som hade varit möjligt om varje modell hade byggts upp manuellt. Den största vinsten med detta arbetssätt har varit att tiden som avsatts för arbetet kunnat utnyttjas mycket effektivt då analyser har kunnat utföras automatiskt utan krav på övervakning eller manuella korrigeringar. Mest effektivt har arbetssättet visats vara med modeller med lägre detaljrikedom då dessa förhållandevis snabbt kan genereras automatiserat. Detta kan framförallt vara väldigt effektivt att implementera i inledande projekteringsskeden.