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Strengthening of existing structures with Carbon Fibre Reinforced Polymers (CFRP) is a method that has been more common in the building sector during the last decades. The materials strength in relation to its weight is a huge advantage but the lack of knowledge in the building sector results that professionals uses more proven materials such as steel to strength structures. In this report five minor projects in which steel was the strengthening material has been analysed to see if CFRP could be a competitive strengthening material considering mainly practical and economical aspects. The main purpose of this report was to evaluate when CFRP is the most suitable option for strengthening of concrete structures. The results showed that CFRP was applicable in every project but the total cost were higher comparing to the steel solution in four out of five projects. The results indicate that it is difficult to motivate CFRP regarding the economical aspect in relation to minor project that were evaluated in this report. Nevertheless, the tendency is that the advantages with CFRP is more useful when there are more comprehensive projects such as advanced steel works and when it is necessary to save room volumes.

i Abstract The Nockeby Bridge, in the western part of Stockholm, is a prestressed concrete bridge with an openable swing span of steel. The bridge was built during 1970 and should now be widened with 0.5 meters on each side. The concrete bridge deck is supported by two main-beams and cross-beams are located at the position of all supports. Previous studies of the bridge show that the torsional resistance is too low and the bridge needs strengthening while widened. The aim of this master thesis was to study and compare different strengthening methods for The Nockeby Bridge. Eight different bridges in Sweden and China were reviewed to find possible strengthening methods for The Nockeby Bridge. External prestressing tendons and additional cross-beams between the two main-beams were seen to have good influence on the resistance. The effect from strengthening with carbon-fiber reinforced polymer was questioned during small loads and was not seen as a suitable strengthening method for The Nockeby Bridge. Four different FE-models were generated to be able to compare two strengthening methods. The compared strengthening methods were a method with additional cross-beams between the main-beams and a method with external prestressing tendons. All FE-models were built up by solid- and truss elements where the concrete was modelled with solid elements and the prestressed reinforcement was modelled with truss elements. Only a few load-cases were included to limit the scope of the study. The included load-cases were deadweight, prestressing forces and vehicle load from standard vehicle F, G, H and I. Two influence lines were created to be able to place the vehicle loads in an unfavorable way. From the FE-models, shear stresses were extracted along two lines, one on each side of the main-beam. The torsional part of the shear stresses was calculated from these two results and compared with the torsional resistance of the bridge. While calculating the torsional resistance, the normal force in the cross-section from prestress was extracted with the function “free body cut”. The results showed that none of the tested strengthening methods were enough to strengthen The Nockeby Bridge. However, the method with additional cross-beams was seen as a better method than external prestressing tendons. A combination of the two methods might be suitable but was not tested. Adding four cross-beams in each span might also increase the resistance enough, but this was neither tested. It was also seen that a reduction of the torsional stiffness had a large influence on the result. Such a reduction is allowed in some cases and should be utilized if possible. Furthermore, it was seen that solid-models were extremely time consuming and there is not a good alternative to design a bridge with only a solid model. Nockebybron i västra Stockholm är en förspänd betongbro med ett öppningsbart svängspann av stål. Bron byggdes 1970 och ska nu breddas med 0.5 meter på varje sida. Betongplattan stöds upp av två huvudbalkar och tvärbalkar är placerade vid samtliga stöd. Tidigare studier av bron visar att brons vridstyvhet är låg och bron behöver förstärkas i samband med breddningen. Syftet med detta examensarbete är att undersöka och jämföra olika förstärkningsmetoder för Nockebybron. Åtta olika broar i Sverige och Kina undersöktes för att hitta möjliga förstärkningsåtgärder för Nockebybron. Extern spännarmering och extra tvärbalkar mellan de två huvudbalkarna hade en bra inverkan på kapaciteten. Kapacitetsökningen fån förstärkning med kolfiberförstärkt plast är ifrågasatt vid låga laster och uppfattas inte som en bra metod för att förstärka Nockebybron. Fyra olika FE-modeller skapades för att jämföra två förstärkningsmetoder. Förstärkningsmetoderna som jämfördes var metoden med extra tvärbalkar mellan huvudbalkarna samt en metod extern spännarmering. Alla FE-modeller byggdes upp med solid- och stångelement där betongen modellerades med solidelement och den förspända armeringen modellerades med stångelement. Enbart ett fåtal lastfall inkluderades i studien för att minska studiens omfattning. De inkluderade lastfallen var egenvikt, förspänningskrafter samt trafiklast från typfordon F, G, H och I. Två influenslinjer skapades för att placera trafiklasten på ett ogynnsamt sätt. Från FE-modellerna extraherades skjuvspänningar från bägge sidor av en av huduvbalkarna. Från dessa skjuvspänningar beräknades vrid-delen av skjuvspänningarna som jämfördes med brons vridkapacitet. När vridkapaciteten beräknades togs tryckkraften från tvärsnittet fram genom funktionen ”free body cut”. Resultatet visade att ingen av de testade förstärkningsmetoderna var tillräckliga för att förstärka Nockebybron. Hur som helst, metoden med extra tvärbalkar ansågs som en bättre metod än extern spännarmering. En kombination av de bägge förstärkningsmetoderna kan vara lämplig men detta testades inte. Att lägga in fyra tvärbalkar i varje spann kan också leda till en tillräcklig ökning av kapaciteten, men detta fall testades inte heller. En reduktion av vridstyvheten sågs ha en stor påverkan på resultatet. En sådan reduktion är tillåten i vissa fall och borde utnyttjas om möjligt. Vidare upptäcktes att en solidmodell är väldigt tidskrävande varför det inte är lämpligt att dimensionera en bro enbart med hjälp av en solidmodell.

The purpose of this report is to simplify the process of designing carbon fiber strengthening for existing concrete constructions, specifically beams. The intention has been to establish a flow chart containing information on the necessary testing and calculations for the design, to as far degree it is possible satisfy the requirements stipulated by Swedish and by extension, European authorities.To do this the report will examine a parking garage situated underground by Akademiska Sjukhuset, Uppsala. The parking garage was built in the mid-seventies, and has in recent years been subjected to a greater load than designed for by the construction of a road on top of it. FEM-Design has been used to obtain the internalforces of the beams and thereby determine whether they are in need of strengthening or not and thereafter design the strengthening according to Täljsten (2006) with some corrections from Täljsten (2011) due to new regulations.The result of this report is that the flow chart used is viable to design carbon fiber strengthening, atleast with the conditions met in our reference project.The conclusion drawn after working with this report is that there is a need for a clear standard for carbon fiber strengthening , preferably a standard that can be used throughout Europe.

Henningsvär is an island to the east of Lofoten, in northern part of Norway. The traffic to the island is increasing, especially during summer. Since the bridge to the island only has room for traffic in one direction at the time, the transport department in Norway wants to broaden the bridge to make room for two traffic lines. They want to investigate the possibility to strengthening the supporting structure with composite material to manage the increasing loads. This thesis will investigate how the composite material will work as reinforcing material to the supporting structure. The structure is formed as a concrete box girder with both normal and pretension reinforcement. The aim is to present strengthening methods for both shear and bending moment. To gain knowledge and understanding about the problem a research is made about prestressed concrete, composite material and strengthening methods. The loads from two traffic lines are used to get the new forces in the bridge. The new forces are then compared with the old capacity in both shear and bending moment to see where and how much strengthening the bridge needs to carry the new loads. Spännd To strengthening the bridge the use of carbon-fiber plates seems to be the best method. With this method all sections but one was able to carry the load in bending moment. In this study carbon-fiber sheets had to be used for shear force to gain required strengthening, but that is a very expensive method for this bridge. Because of conservative assumptions and boundaries the method with carbon-fiber plates seems to be the best strengthening solution for the bridge, in both shear and bending moment. Validerat; 20130319 (global_studentproject_submitter)

Validerat; 20101217 (root)