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Structural adhesive bonded steel-to-steel connections PDF

369 Pages·2014·26.45 MB·English
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Structural Adhesive Bonded Steel-to-Steel Connections An Introduction for Structural Engineering Master Thesis by J.H.J. Floor s e c n e ic os e G d n a g n ir ee n ig n E liv iC f o y t lu c a F Cover This picture was taken during the tensile test of one of the five tested stepped double strap connections at the Stevin II laboratory. During this test, besides two LVDT’s (linear variable differential transformer) also DIC (digital image correlation) is used for measurements. One of the two DIC camera’s, mounted on a Boikon profile, can be seen in the right front. In between the lamps connection 4, mounted in the tensile test machine, is visible. Master Thesis Structural Adhesive Bonded Steel-to-Steel Connections An Introduction for Structural Engineering in partial fulfilment to the requirements for the degree of Master of Science in Civil Engineering at the Delft University of Technology, to be defended publicly on Friday June 13, 2014 at 16h00 by ing. Jurriaan Hildebrand Jacobus Floor born in Maarssen, the Netherlands Structural adhesive bonded steel-to-steel connections Date May, 2014 University Delft University of Technology Faculty of Civil Engineering and Geosciences Department of Structural Engineering Section of Structural and Building Engineering Author J.H.J. Floor 4050614 (student number) [email protected] Master program Civil Engineering Structural Engineering Steel and Timber Construction Graduation committee prof. ir. R. Nijsse (Chairman) Delft University of Technology prof. ir. F.S.K. Bijlaard Delft University of Technology ir. J. Sinke Delft University of Technology dr. M.H. Kolstein Delft University of Technology ir. L.J.M. Houben (Graduation coordinator) Delft University of Technology 2 I Summary I Summary Today, there are only a few types of structural engineering applications where structural adhesives play a role, in contrast to other engineering sectors. The possibilities and difficulties of structural adhesive bonding in structural engineering, especially for steel-to-steel connections, are investigated. Practically all structural adhesives are polymers. The cohesive properties mainly depend on their polymer structure and eventual additives. Specific adhesion covers all adhesion types through intermolecular forces (chemical, adsorptive, diffusive and electrostatic). For specific adhesion, good wetting is important. Mechanical adhesion is characterised by interlocking. The mechanical behaviour of most structural adhesives is best described by the Drucker Prager (or related) model. Therefore the tension strength is limited, hence connections should be designed for shear and compression. Lap connections are prone to shear lag which causes a low effectiveness of long laps. Shear lag is mainly influenced by the axial stiffness of the adherents, and shear stiffness and thickness of the adhesive. Lap connections are also prone to peel, due to eccentricity of the lines of action (externally and/or internally). Peel is mainly influenced by adhesive and adherent thicknesses, bending stiffness of the adherents and axial stiffness of the adhesive. The material properties of adhesive are strongly influenced by time-and-environmental effects, especially temperature, moister and creep are important. The mechanical properties of adhesive bonds provide potential for lengthening of steel beams, structures with thin elements, small tolerances or HSS, and fatigue sensitive, composite, hybrid and laminated structures. Due to the relative low weight, adhesive bonds have potential for light weight structures. Due to the appearance, aesthetics may allow the choice for adhesive bonding. For structural engineering there are four specific points of attention. Firstly, the strength of adhesive bonds depend on the adhesive thickness. An optimal thickness exists which is relatively small. The tolerances used in structural engineering make the application of a thin bondline difficult. Secondly, the service life of structural engineering applications is usually 50 years. At such time spans the time-and-environmental effect may lower the design strength drastically. Thirdly, for adhesive bonding a clean working environment is needed, which is difficult to achieve on a construction site. Finally, there is a lack in knowledge, products and code/directives for structural engineering. For adhesive bonded beam-to-column connections a continuous beam instead of a continuous column is beneficial with respect to tension. Nevertheless, tension is hard to avoid in T- or X-shaped beam-to-column connections. An L-shaped roof connection is the most suitable beam-to-column connection for adhesive bonding. The connection can be achieved by two adhesive bonded L- shape plates to the flanges of the beam and column at the inner and outer corner. Linear elastic FEM calculations with linear elements show that, due to shear lag, the effective length of these plates is limited. Due to the large differences of axial stiffness over the width of an H-shaped profile, load transfer mainly takes place near the web. Calculations with higher order element or non-linear material behaviour are not possible with commercial computers. To increase the efficiency of load transfer at the middle of a lap, stepped adherents can be used. The change of axial stiffness at the steps causes an uplift of the shear stress distribution. FEM and practice tests are executed for an adhesive bonded stepped double strap connection. The connection exists of two 15mm thick steel plates (S235) which are bonded (Sikadur®-30) by two bonded (Sikadur®-30) steel stepped straps. The straps exists of three 3mm thick, steel plates (S235) of 200mm, 400mm and 600mm length. FEM calculations predict a nearly linear load- displacement curve and a failure load of at least 400kN. The load-displacement curves of the practice tests are similar to the FEM curves up to ±300kN, afterwards the curve slowly flattens. A mean failure load of 561kN, a sample standard deviation of 12.85kN and a 5th percentile failure load of 549kN have been achieved. Failure was imposed by adhesion failure; all connections show delamination near nearly all lap ends. 3 Structural adhesive bonded steel-to-steel connections 4 II Samenvatting II Samenvatting Vandaag de dag zijn er slechts enkele constructieve bouwtechnische toepassingen waar constructieve lijmen gebruikt worden, in tegenstelling tot in andere technische sectoren. De mogelijk- en moeilijkheden voor constructieve lijmverbindingen in de bouw, in het bijzonder staal- op-staalverbindingen, zijn onderzocht. Praktisch alle constructieve lijmen zijn polymeren. De cohesieve eigenschappen hangen met name af van de polymeerstructuur en eventueel additieven. Specifieke adhesie omvat alle adhesie typen door inter-moleculaire krachten (chemische, adsorptie, diffusie en elektrostatische), hiervoor is goede bevochtiging van belang. Mechanische adhesie wordt gekenmerkt door interlocking. Het mechanische gedrag van de meeste constructieve lijmen wordt het best beschreven door het Drucker Prager (of gerelateerd) model. Derhalve is de treksterkte beperkt, dus kunnen verbindingen het best op schuif en druk worden ontworpen. Lapverbindingen zijn vatbaar voor shear lag, met een lage efficiëntie van lange lappen als gevolg. Shear lag wordt hoofdzakelijk beïnvloed door de axiale stijfheid van de adherent, en afschuifstijfheid en dikte van de lijm. Lapverbindingen zijn ook vatbaar voor afpellen, door excentriciteit van de werklijnen (uit- en/of inwendig). Afpellen wordt met name beïnvloed door lijm en adherent dikte, buigstijfheid van de adherenten en axiale stijfheid van de lijm. De materiaaleigenschappen van lijm worden sterk beïnvloed door tijds-en-omgevingseffecten, met name temperatuur, vocht en kruip zijn van belang. De mechanische eigenschappen van lijmen hebben potentie voor verlengen van stalen liggers, constructies met dunne elementen, kleine toleranties en HSS, en vermoeiingsgevoelige, composiet, hybride en gelamineerde constructies. Door het relatief lage gewicht hebben lijmen potentie voor lichtgewicht constructies. Door het uiterlijk, kan esthetica de keuze voor lijmverbindingen steunen. Voor de constructietechniek zijn er vijf aandachtspunten. Allereerst, de sterkte van de lijmverbinding is afhankelijk van de dikte. Er bestaat een optimale dikte die relatieve klein is. De toleranties die in de constructietechniek worden gebruikt maken het toepassen van een dunne lijmlaag moeilijk. Ten tweede, de levensduur van constructies is doorgaans 50 jaar. Op deze tijdschalen kunnen de tijds-en-omgevingseffecten de ontwerpsterkte drastisch verlagen. Ten derde, voor lijmverbindingen is een schone werkomgeving vereist, wat moeilijk te realiseren is op een bouwplaats. Tot slot, er is een gebrek aan kennis, producten en codes/richtlijnen voor de constructie techniek. Voor gelijmde ligger-kolomverbindingen is een doorgaande ligger in plaats van een doorgaande kolom voordelig met het oog op trek. Toch is trek moeilijk te verkomen in T- of X-vormige ligger- kolomverbindingen. Een L-vormige dakverbinding is de meest geschikte ligger-kolomverbinding voor lijm. De verbinding kan tot stand worden gebracht door twee L-vormige platen aan de flensen van de ligger en kolom in de binnen- en buitenhoek te lijmen. Lineair elastische FEM berekeningen met kwadratische elementen laten zien dat, door shear lag, de effectieve lengte van deze platen beperkt is. Door het grote verschil in axiale stijfheid over de breedte van een H-vormig profiel, vindt de belastingafdracht hoofdzakelijk plaats ter plaatse van het lijf. Berekeningen met hogere orde elementen of niet-lineair materiaal gedrag zijn niet mogelijk met commerciële computers. Voor het verhogen van de belastingafdrachtefficiëntie in het midden van de lap, kunnen getrapte adherenten ingezet worden. Het verschil in axiale stijfheid bij de trap veroorzaakt een verheffing van de afschuifspanningsdistributie. Van een getrapte dubbele strapverbinding zijn FEM en praktijktesten uitgevoerd. De verbinding bestaat uit twee 15mm dikke staal platen (S235) welke verbonden (Sikadur®-30) zijn door twee gelijmde (Sikadur®-30) stalen getrapte straps. De straps bestaan uit drie 3mm dikke staal platen (S235) van 200, 400 and 600mm lengte. FEM voorspelt een bijna lineaire last-verplaatsingscurve en bezwijkbelasting van ten minste 400kN. De last- verplaastingscurve van de praktijktest is gelijk aan de FEM curve tot ±300kN, hierna vlakt deze af. Een gemiddelde bezwijkbelasting van 561kN, een steekproefstandaarddeviatie van 12.85kN en een 5 percentiel bezwijkbelasting van 549kN zijn behaald. Bezwijken is veroorzaakt door adhesie falen; alle verbindingen vertoonden delaminatie bij bijna alle lap einden. 5 Structural adhesive bonded steel-to-steel connections 6 III Preface III Preface This master thesis is the result of research carried out at the Structural and Building Engineering section of the Faculty of Civil Engineering and Geosciences at the Delft University of Technology. The research is an exploratory study on the applicability of structural adhesive bonding in the structural engineering. In search for a suitable thesis topic, I encountered a flyer about 'Glued connections in steel trusses'. None of the courses which I followed throughout my student career treated adhesive bonding. I could only enumerate two applications of structural adhesive bonding in structural engineering on the spot; laminated timber and adhesive bonded carbon fibre strips for reinforcement. I wondered a few things. Why aren't there more well-known applications of structural adhesive bonding in structural engineering? What are the mechanics behind adhesive bonding? How strong are adhesive bonds? Is a full strength structural steel-to-steel connection with adhesive bonds possible? What are the possibilities of adhesive bonds? Enough questions for a graduate research and that is why I started this research. Firstly, I would like to thank my graduation committee for giving me guidance, support and the opportunity to do this research. Also I would like to thank Bart Wiegant, Johan Boender and Fred Bosch of the Delft Aerospace Structures and Materials Laboratory. Without their help and advice during the fabrication of the double strap connections I certainly would not have been able to fabricate the connections with the achieved quality and strength. I am grateful to Berthil Grashof of the Delft Aerospace Structures and Materials Laboratory. Without his help and explanation with the DIC equipment, measuring with DIC was not possible. I am grateful to Fred Schilperoort and John Hermsen of the Construction Laboratory of the Macromechanic (Stevin II) laboratory at the Faculty of Civil Engineering and Geosciences. Their help and advice during the tensile tests of the adhesive bonded double lap connections was essential for reliable test data. I am thankful to Gérard Hagmolen of ten Have and Mark Nieuwpoort of Sika for sponsoring my research with two sets of 6kg of Sikadur®-30 and for the additional information about some of the adhesives of Sika. Last but not least, I would like to thank my girlfriend, Judith, for her moral support and for checking all the grammar and spelling. I hope that this thesis can take away some of the scepticism about structural adhesive bonded connections among structural engineers, architects and contractors. Hopefully this will result in an increase of adhesive bonded applications in the structural engineering. Jurriaan Floor Delft, May 2014 7 Structural adhesive bonded steel-to-steel connections 8

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section of the Faculty of Civil Engineering and Geosciences at the Delft Is a full strength structural steel-to-steel connection with adhesive bonds .. V shear force. N or kN. W section modulus. 3 mm prescribed displacement mm a.
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