Design of reinforced concrete subjected to restraining forces

Transkript

1 Thesis Projects at Reinertsen 2013, Göteborg 1(12) General information of Thesis projects at Reinertsen in Göteborg Since its introduction in Sweden in 1990, there has been a cooperative scheme between Reinertsen and Chalmers University of Technology in Göteborg. Among other things Reinertsen is a frequent supervisor of Thesis projects in the field of Civil Engineering for the last twenty years. Supervision of Master and Bachelor Thesis projects is an important part of Reinertsen s marketing towards the future engineers currently being students. The Thesis work is usually carried out at the Reinertsen office, in close contact with the supervisor, and the subjects studied are usually related to past or coming projects. In order to apply for doing your Thesis project at Reinertsen, follow the instructions shown below. Reinertsen usually get approximately 5-15 applications each year regarding Thesis work at the company. Previously, our resources have been limited to about 2-3 theses/year in the field of Structural Engineering. This year, though, we hope to increase the number of Thesis projects carried out at Reinertsen. Hence, we will consider all applicants and then determine who/whom we will accept. To do this we will need the following information: Description of the applicants with CV (personal letter, no more than one A4-page). Copy of grades from the University. Information of which Thesis project(s) is/(are) of interest. When during the year you would prefer to do your Thesis at Reinertsen and how flexible you are in this. Even though it is not a strict demand, Reinertsen do recommend that the projects are carried out by a group of two persons rather than alone. If you are a pair of two persons applying together make sure that your applications clearly state this and that your information is sent in together. Deadline for applying to do your Thesis at Reinertsen during 2013 is set to 22 October, Send in your application to Morgan Johansson by . Note that the Thesis projects described in this documented will be carried out at the Reinertsen office in Göteborg; they do not apply for Thesis projects at other offices. Morgan Johansson Lilla Bommen 5 Phone: Mail: morgan.johansson@reinertsen.com

2 Thesis Projects at Reinertsen 2013, Göteborg 2(12) Design of reinforced concrete subjected to restraining forces If a structure needs to elongate in any way and it is hindered to do so, restraining forces will appear. In a concrete structure such restraining forces may occur due to for example temperature and shrinkage. Both can be regarded as deformation induced loads acting on a structure, and hence, differ from those loads one usually regard as the main loads acting on a structure; e.g. dead weight, load from traffic, wind or snow etc. However, those restrained forces may often be the cause of considerable problems in the design process, especially in the Serviceability State. This is partly due to the engineer not being used to think in terms of restrained forces, and thus, does not realise how to make a proper design in order to take their effects into consideration. This Master Thesis will be a continuation from four previous projects carried out at Reinertsen in 2006, 2007, 2009 and In these Theses unreinforced, reinforced and fibre reinforced structures have been studied. Restraints due to connection with ground and/or connecting structural members are considered. Special interest will be put on: the cracking process in fibre reinforced concrete structures, interaction of restraining forces and load induced forces, investigate the effect of crack widths and crack patterns of edge beams and retaining walls of different parameters, the development of a simple method and/or design tool that can be used when dealing with restraining forces in the preliminary and final design stages, The aim of the master s project is to increase the knowledge of how to design reinforced concrete structures with regard to the restraining forces that are obtained due to deformation induced loading. The work consists of literature studies in combination with linear and nonlinear finite element analyses used to study different load cases. The Master Thesis project is carried out as a co-operation between Reinertsen, Thomas Concrete Group and the Division of Structural Engineering, Chalmers. The work is mainly carried out at Reinertsen s office in Göteborg. Supervisors are Morgan Johansson (Reinertsen), Ingemar Löfgren (Thomas Concrete Group) and Björn Engström (Chalmers).

3 Thesis Projects at Reinertsen 2013, Göteborg 3(12) Structural analysis of new openings in existing concrete structures Existing structures are subject to changes during its life time. One example is when new openings are made in walls or slabs. This affects the stress distribution of the structure and loads may have to transfer in a different way than originally designed for. Hence, a new way to carry the load might be needed for the structure to obtain an appropriate behaviour. Wall Slab Examples of questions to be examined in this Master Thesis are: How is the stress distribution influenced by new openings? How does the response from a linear analysis differ from non-linear finite element analysis? To what extent will the fact that the structure is loaded during the process of making the new opening influence its behaviour? What are the possibilities to reinforce the structures to achieve a better behaviour, and what methods are there to cause minimal damage during this construction phase? What calculation methods are suitable to study this problem? The aim of the master s thesis project is to increase the knowledge and give guidance in how to approach these problems. The work consists of literature studies in combination with hand calculation methods and linear and non-linear finite element analyses. Reinertsen s office in Göteborg. Supervisors are Morgan Johansson (Reinertsen) and Björn Engström (Chalmers).

4 Thesis Projects at Reinertsen 2013, Göteborg 4(12) Minimum and maximum reinforcement requirements in concrete structures In Eurocode 2 different requirements of the minimum and maximum amount of reinforcement and its configuration are described. In several cases the reason for these requirements are clear but in some cases it is not. Further, it is not always fully clear how to interpret the requirements given, which may result in significant diversity of what is an acceptable solution. F s A s F s configuration A s, A s,max A s,min The aim of this Master Thesis is to identify, interpret and describe the reasons for the reinforcement requirements set up in Eurocode for minimum and maximum reinforcement amounts, and reinforcement configurations, in concrete structures. Where applicable interpretations of different cases will be made and exemplified. Further, a survey to experienced designing engineers about their interpretation of some of the identified cases will be of interest. Examples of cases that will be treated: Minimum amount of reinforcement due to restraining forces. Maximum reinforcement amount for bending moment. Demand on stirrup reinforcement configurations for shear force and torsional moment. Demand on transverse reinforcement amount and configuration for spliced bars. Reinertsen s office in Göteborg. Supervisors are Morgan Johansson (Reinertsen) and Björn Engström (Chalmers).

5 Thesis Projects at Reinertsen 2013, Göteborg 5(12) Design with regard to explosions Explosions are accidental actions that need to be considered in the design of structures for various applications. Except from apparent cases, such as military installations and civil defence shelters, design with regard to explosions is required for instance in the processing industry and for tunnels. Pressure, p [kpa] 5 4 p Time [ms] The knowledge of how to design buildings to withstand the effect of explosions and other impact actions is limited. Hence, the aim of this master s project is to put together information about available design approaches for impulse loading on different types of structures. This project is a continuation of five previous Master Thesis carried out , 2009, 2010 and 2012, in which the behaviour of concrete beams and slabs were studied. Possible questions to examine are: Previous Master Theses have dealt with the response of impulse loaded beams and slabs. How should this knowledge be applied to analyse the response of a whole structural system? In static analyses the load intensity and distribution influence the reaction force in its supports. For an impulse loaded structure, though, time also becomes an important parameter. In what way is a structure s resulting reaction force-time relation affected by the stiffness of the impulse loaded structure? An impulse loaded structure will sway back and forth. What effect will it have on the response for a structure for which its mechanical properties and boundary conditions depend on which direction the structure deforms? Often the impulse load from an explosion load is regarded to act uniformly on a structure. In reality though, there will be a difference in both load intensity and arrival time due to different distances to the explosion centre. What effect would occur if a more detailed analysis was made, taking these differences into account? Reinertsen s office in Göteborg. Supervisor will be Morgan Johansson at Reinertsen.

6 Thesis Projects at Reinertsen 2013, Göteborg 6(12) Dynamic response of concrete structures subjected to earthquake loading There are a significant numbers of dynamic loads that civil structures are analysed for; e.g. wind, road and railway traffic, explosions and earthquake. In order to perform the dynamic analysis correct, the stiffness of the analyzed structure has to be represented in a realistic way. However, it is often difficult to establish the correct stiffness for a concrete structure, since it may consist of both cracked and uncracked regions. Furthermore, the cracking occurring during the dynamic loading itself is a phenomenon that essentially influences the structural response and the loading on the structure Time history, Horisontal X response spectra, probability level 10-7 measured from SKI Technical Report 92:3 SSE X E-7 Acceleration [m/s 2 ] Horisontal ground response spectra, probability level 10-7 measured from SKI Technical Report 92:3 0.5 % Damping 2 % Damping 5 % Damping 7 % Damping Frequency [Hz] A common approach in the context of dynamic analysis of concrete structures is to assume that the whole structure is either uncracked or with reduced stiffness due to cracking, in which the uncracked Young s modulus is multiplied by a reduction factor. It is of interest to further investigate the effects of these assumptions on a typical structure, subjected to a dynamic load. The cracked regions in the structure will be predetermined from the permanent and quasi-permanent loads and the secondary response in different sections of the structure will be studied. A method which can take into consideration the potential cracking under the dynamic loading is also of interest. This Master Thesis project will include an information gathering part in which common analysis approaches are presented and discussed. These methods will then be further analysed using linear and non-linear finite element analyses. The focus is meant to be on the numerical modelling and analysis of the structures, and not on the consequent detail design. Reinertsen s office in Göteborg. Supervisor at Reinertsen will be Ginko Georgiev.

7 Thesis Projects at Reinertsen 2013, Göteborg 7(12) Redistribution of force concentrations in 3D finite element analyses In the bridge design community the usage of 3D finite element analyses (FE analyses) have increased substantially in the last few years. Such analyses provide the possibility for a more accurate study of the structure than what is possible by using more traditional design tools. In liaison with the increased usage of three-dimensional FE analyses, though, there have appeared some special problems that were not present when using simplified 2D analyses. One such problem is how to interpret local force concentrations that arise in linear elastic analyses; concentrations that are not as critical in reality. In a concrete structure such force concentrations lead to cracking and yielding of the reinforcement, resulting in redistribution of forces. Hence, in a real structure there will be a considerably more favourable force distribution than what is the case in a finite element analysis assuming linear elastic response. An important problem to deal with is how such force concentrations should be distributed over a larger region in the design process. Recently guidelines have been presented of how to do this. The aim of this master s project is to examine how the force concentrations in linear elastic finite element analyses can be redistributed to better imitate the real behaviour of a structure. Tools for this will be a combination of literature studies, linear and non-linear finite element analyses in which the present guidelines will be compared. Reinertsen s office in Göteborg. Supervisors will be Morgan Johansson (Reinertsen) and Mario Plos (Chalmers).

8 Thesis Projects at Reinertsen 2013, Göteborg 8(12) Dynamic analyses of pedestrian bridges Pedestrian bridges are generally lightweight structures which may be extremely sensitive to loads that have oscillating character, such as wind and walking or running groups of people. In Eurocode comfort levels for bridge structures are stipulated as maximum vertical and lateral accelerations. However, it does not present the loads nor the methodology for performing the analysis that provides these accelerations. In the literature several methods are proposed of how to model the loading for a pedestrian bridge. The methods present possibilities for both simple and more advanced numerical models. However, there is need for increased understanding where the respective method is applicable, how much conservatism is included in the simplified methods, and whether the methods can be classified in term of time consumptions vs. improved quality of the obtained results. This Master Thesis will aim at presenting basic understanding of modelling pedestrian bridges for the purpose of dynamic analysis where the evaluation is made on a typical bridge structure. Examples of questions that are of interest to study are: What type of loads is applicable in the analysis? What influence does the mass have on the obtained accelerations? How relevant is the problem for bridges made of concrete, steel or timber? Is there a possibility to show the relevance of the check using simple methods? What is the conservatism in the simple methods? How does the accelerations response obtained in a 3D analysis compare to a simplified 2D analysis? Can rules be established for when 2D analysis are sufficiently accurate? Reinertsen s office in Göteborg. Supervisors will be Emanuel Trolin (Reinertsen), Ginko Georgiev (Reinertsen) and Mario Plos (Chalmers).

9 Thesis Projects at Reinertsen 2013, Göteborg 9(12) Structural analyses of a trough bridge using FEM In the bridge design community the usage of three dimensional finite element analyses (FE analyses) have increased substantially in the last few years. Such analyses provide the possibility for a more accurate study of the structure than what is possible by using more traditional design tools. In liaison with the increased usage of three-dimensional FE analyses, though, there have appeared some special problems that were not previously taken into account. The typical cross section of a concrete railway bridge is a plate-girder section. The praxis for modelling this types of structures has until recently been using simple 2D models, while the needs and requirements of the current standards are for a proper 3D modelling. However, there are a number of modelling-to-design related issues that have to be resolved in order to present a satisfactory workflow procedure for this type of structures: In a previous thesis different model approaches were studied: 3D beam grillage, shell model and combined shell-beam model. A comparison of obtained results with results from a corresponding model using only 3D solid elements is of interest. Which type of model is best suited to deal with the effects from loads that introduce secondary static forces such as pre-stressing and temperature? Redistribution of applied loads takes place by means of the track ballast and the concrete material itself. How should this load distribution load be taken into account: directly in the model or in the post processing of the results? The torsion section forces are extremely sensitive to the stiffness and eccentricities presented by the boundary conditions in the model. The effects of the end wall and different choices for the supports in the middle are of interest in this study. Reinertsen s office in Göteborg. Supervisors will be Ginko Georgiev (Reinertsen), Morgan Johansson (Reinertsen) and Mario Plos (Chalmers).

10 Thesis Projects at Reinertsen 2013, Göteborg 10(12) Vippning och vridning av öppna ståltvärsnitt För att dimensionera en stålbalk enligt dagens gällande standarder såsom Eurokod 3 krävs en stor mängd beräkningar som är mycket tidskrävande. Detta har medfört att konstruktören till större mån använder sig av färdiga program, såsom Colbeam och SAP2000, för att utföra dimensioneringen. Nackdelen med att använda färdiga beräkningsprogram är att användaren tappar kontrollen över viktiga antaganden, något som kan medföra ofullständiga eller felaktiga beräkningar. Risken för detta är större vid problem med komplexa analytiska lösningar, som till exempel vippning eller vridning av öppna tvärsnitt. Detta förslag till examensarbete syftar till att fördjupa sig i bakgrunden och teorierna för kontroll av öppna ståltvärsnitt. Målet är att jämföra resultat från analytiska formler med resultat från beräkningsmodeller skapade i beräkningsprogram som Colbeam, SAP2000 och ADINA. Exempel på frågeställningar som är av intresse i detta examensarbete är: Vilken analytisk formel för beräkning av kritiskt vippningsmoment stämmer bäst överrens med resultat från dimensioneringsprogram? Hur väl stämmer dessa formler med en beräkningsmodell skapad i SAP2000/ADINA? Vilka påkänningar får man i en vertikalt belastad UPE-profil? Vilka tillskottsspänningar får man av den vridning som uppstår i tvärsnittet? Hur behandlas dessa tillskottsspänningar av program som Colbeam och SAP2000? Introduktioner och kontinuerlig handledning kommer ges för användningen av samtliga aktuella program. Examensarbetet är således en bra förberedelse, och ett försprång in i arbetslivet eller fortsatta studier. Examensarbetet utförs i samarbete mellan Reinertsen och Byggingenjörsprogrammet på Chalmers. Handledare på Reinertsen kommer vara Martin Gustafsson och Emanuel Trolin.

11 Thesis Projects at Reinertsen 2013, Göteborg 11(12) Kompatibilitet mellan ritning och beräkning för ökad effektivitet i projekt inom byggsektorn En viktig del med att arbeta som ingenjör inom byggsektorn är att effektivt kunna hantera olika program. Ofta används separata program för ritning och beräkning. Exempel på ritprogram är AutoCad, Revit samt Tekla och exempel på beräkningsprogram är SAP2000, FEM Design och ADINA. I många fall utförs även beräkningar med mer generella program såsom Excel eller Mathcad. Oftast kräver ett uppdrag kompetens inom både ritning/modellering och beräkning. I sådana projekt beror den övergripande effektiviteten, inte enbart på hur effektivt enskilda program hanteras, utan även på kompatibiliteten mellan program och kompetensen i att utnyttja denna. Detta förslag på examensarbete behandlar kopplingar mellan ritning/modellering och beräkning i kommersiella programvaror. Målet är att beskriva processen från bygginformationsmodell till beräkningsprogram med hjälp av en fallstudie. Arbetet är en fortsättning på ett examensarbete som tidigare utförts på Reinertsen. I detta examensarbete undersöktes kopplingen mellan programmen Tekla och SAP2000 där fokus låg på informationsöverföring av stålbalkprofiler. Exempel på frågeställningar som är av intresse i detta examensarbete är: Hur kan man effektivt överföra ytor mellan programmen Tekla och SAP2000? Hur bör en modell byggas i Tekla för att erhålla en bra uppdelning av ytor i SAP2000 där en FE-analys av strukturen ska utföras? Kan man integrera egna handberäkningar från Excel eller Mathcad i SAP2000? Är det möjligt att överföra en modell mellan programmen Tekla och ADINA? Introduktioner och kontinuerlig handledning kommer ges för användningen av samtliga aktuella program. Examensarbetet är således en bra förberedelse, och ett försprång in i arbetslivet eller fortsatta studier. Examensarbetet utförs i samarbete mellan Reinertsen och Byggingenjörsprogrammet på Chalmers. Handledare kommer vara Emanuel Trolin (Reinertsen), Keyvan Zeidi (Reinertsen) och Rasmus Rempling (Chalmers)

12 Thesis Projects at Reinertsen 2013, Göteborg 12(12) Effektivisering av modellering och redovisning av armering i BIM Att arbeta som ingenjör inom byggsektorn idag skiljer sig mycket jämfört med tidigt 80- tal när datorn precis börjat användas som hjälpmedel för att effektivisera ritandet i 2D. Idag projekterar de flesta ingenjörer i 3D på ett eller annat sätt. Dessa 3D-modeller fungerar ofta som en databas fylld med information om en hel byggnad och dess beståndsdelar och relateras i dagligt tal till beteckningen BIM (Building Information Modelling). Ett nytt spännande område inom denna utveckling är modellerering av armering i 3D. Fördelarna är många: att visuellt kunna visa komplicerade armeringsknutpunkter, generera ritningar, mängdning samt automatisk generering av armeringsspecifikationer. Detta förslag på examensarbete behandlar kopplingar mellan effektiv modellering och numrering för att generera armeringsspecifikationer enligt branschens standard. Målet är att beskriva processen från bygginformationsmodell till färdig armeringsspecifikation med hjälp av en fallstudie. Arbetet är en fortsättning på ett examensarbete som tidigare utförts på Reinertsen. Exempel på frågeställningar som är av intresse i detta examensarbete är: Armeringsspecifikation skapa mallfil för specning i Tekla Structures med den standard som används på Reinertsen. Effektiv armeringsredovisning i Tekla förbättra befintliga ritningsmallar. Metodik arbetsgång för effektiv modellering och numrering. Introduktioner och kontinuerlig handledning kommer ges för användningen av samtliga aktuella program. Examensarbetet är således en bra förberedelse, och ett försprång in i arbetslivet eller fortsatta studier. Examensarbetet utförs i samarbete mellan Reinertsen och Byggingenjörsprogrammet på Chalmers. Handledare på Reinertsen kommer vara Keyvan Zeidi och Jakob Andersson.