Hagastaden is a new district in Stockholm that is growing, and many structures are being built. Kv Forskaren, a funnel-like office building, will be built above the Haga tunnel in an ongoing project. During the design phase, where Bjerking AB carried out the construction design, it has been concluded that heavy concrete beams or steel trusses need to be placed over the tunnel that will lead the loads to the massive tunnel walls from the intended building above. In 2016, the Swedish construction and real estate sector released 21 million tonnes of greenhouse gases. This is an increase of 2 million tonnes in comparison from the previous year. Since the choice of construction material is strongly linked to the environmental impact, it is extremely important to choose the material that contributes to least emissions. In order to determine which construction material, concrete or steel, from an environmental perspective is the most suitable to use, a simplified LCA for each material was performed. The study was based on processes that are in the production phase. Environmental indicators that were studied and compared were carbon dioxide equivalents, CO2-e. Furthermore, the purpose was also to compare costs for the manufacturing of the materials. In addition to these factors, an overall assessment was also considered, such as maintenance and fire protection. To be able to make a simplified LCA, the program Construction's environmental calculation tool, BM, was used. Before using the tool, calculations of the material quantities were made based on given drawings on Forskaren from Bjerking. In order to determine which design type is preferable in a holistic perspective, a literature study was also done. The LCA study showed that the steel trusses contributed the least emissions of carbon dioxide equivalents during the production phase. Based on the work done, it has been established that there are both advantages and disadvantages to the construction materials. An active choice of one of these must be based on the specific conditions and requirements that exist in a project. / Hagastaden är en ny stadsdel i Stockholm som växer och många konstruktioner tillkommer. Kv Forskaren, en trattliknande kontorsbyggnad ska byggas ovanför Hagatunneln i ett pågående projekt. Under projekteringens förskede, där Bjerking AB utfört konstruktionsprojekteringen, har man dragit slutsatsen att kraftiga betongbalkar eller stålfackverk behöver placeras över tunneln som ska leda lasterna till de massiva tunnelväggarna från den tänkta byggnationen ovanför. Den svenska bygg- och fastighetssektorn släppte år 2016 ut 21 miljoner ton växthusgaser. Detta är en ökning med 2 miljoner ton jämfört med föregående år. Eftersom valet av konstruktionsmaterial är starkt kopplat till miljöpåverkan är det ytterst viktigt att välja det som bidrar med minst utsläpp. För att avgöra vilket konstruktionsmaterial, betong eller stål, ur ett miljöperspektiv är lämpligast att använda utfördes en förenklad LCA för respektive material. Studien utgick från processer som är i produktionsfasen. Miljöindikatorer som studerades och jämfördes var koldioxidekvivalenter, CO2-e. Vidare var syftet också att jämföra kostnader för tillverkning av materialen. Utöver dessa faktorer gjordes även en helhetsbedömning där aspekter som underhåll och brandskydd beaktades. För att kunna göra den förenklade LCA-studien har verktyget Byggsektorns miljöberäkningsverktyg, BM, använts. Innan verktyget användes gjordes en mängdberäkning utifrån givna ritningar på Kv Forskaren från Bjerking. För att kunna avgöra vilken konstruktionstyp som är att föredra i ett helhetsperspektiv gjordes även en litteraturstudie. LCA-studien visade att stålfackverken bidrog med minst utsläpp av koldioxidekvivalenter under produktionsfasen. Utifrån arbetet som gjorts har det kunnat fastställas att det finns både för- och nackdelar hos konstruktionsmaterialen. Vid ett aktivt val av något av dessa måste man utgå från de specifika förutsättningar och krav som förekommer i ett projekt.

[pt] O efeito da protensão pode ser introduzido sobre estruturas de aço em forma de arco, de tal modo que é adicionado um estado de tensões oposto ao estado proveniente da ação de sucção do vento. Dentro deste escopo, o presente trabalho de pesquisa visa apresentar os resultados obtidos com a modelagem numérica, através do Método dos Elementos Finitos (MEF), sobre o comportamento estrutural de treliças de aço utilizadas no projeto de coberturas protendidas. Para tal, a modelagem numérica é realizada com base em formulações não lineares, com o uso do programa computacional ANSYS, avaliando-se o comportamento estrutural de modelos de treliças de aço em forma de arco até o regime de ruptura. Considerando-se a complexidade do comportamento das treliças em estudo, foram feitas análises com inclusão do efeito da não linearidade física. Com base nos resultados obtidos por meio de uma análise paramétrica, no que tange a comparações entre os valores de resistência das treliças protendidas investigadas, são estabelecidas conclusões e recomendações de projeto. Cabe ressaltar que a economia de material obtida na solução estrutural com base no uso da protensão é resultante do aumento dos níveis de forças de tração nas barras da estrutura, diminuindo-se os de compressão que são menos eficientes. Assim, as soluções estruturais com protensão apresentam diversas vantagens que compensam o seu custo adicional. / [en] Prestressing forces can be introduced on arched steel structures in such a way that a state of tensile stresses is added which to the existing state counteract the state introduced by the wind negative pressures. Within this scope, the present research aims to present the results obtained with the numerical modeling through the Finite Element Method (FEM) on the structural behavior of steel trusses used in the design of prestressed roof structures. For this purpose, the numerical modeling is performed based on non-linear formulations using the ANSYS software in order to evaluate the structural behavior of arched steel trusses modelled up to failure. Considering the complexity of the behavior of the trusses studied, some structural analysis were carried out including the effects of physical nonlinearities. Based on the results obtained through an extensive parametric analysis, with respect to comparisons between the resistance values of the investigated prestressed trusses, conclusions and design recommendations are established. It should be noted that the material savings achieved by the use of prestressing is the resultant from the increase of tensile state of stresses in the bars of the structure, thus reducing the compression stresses, which are less efficient. In this sense, the structural solutions with prestressed trusses have several advantages that compensate for the additional cost of prestressing.