Probabilistische Bemessung von geklebten Anschlüssen im Holzbau

Kleben von tragenden Bauteilen ist im Holzbau auf wenige Anwendungsgebiete beschränkt. Es wird hauptsächlich zur Herstellung von Brettschichtholz oder zur Ertüchtigung bestehender Strukturen eingesetzt. Um Kleben als Alternative zu stiftförmigen mechanischen Verbindungsmitteln einzusetzen, muss die Bemessung geklebter Anschlüsse ermöglicht werden. Holzspezifische Faktoren wie Anisotropie, Streuung der mechanischen Eigenschaften und sprödes Versagen erschweren eine genaue Vorhersage. Aufgrund der auftretenden Spannungsspitzen ist ein deterministischer Spannungsnachweis nicht geeignet. Eine Alternative zur Bestimmung der Tragfähigkeit geklebter Anschlüsse bietet die in diesem Beitrag vorgestellte probabilis tische Methode, die es erlaubt, die Spannungsverteilungen in geklebten Verbindungen mit ihren Spannungsspitzen und die Streuungen der Festigkeitswerte des Werkstoffes zu erfassen. Im Rahmen der vorgestellten Arbeit wurden geklebte Doppel‐Laschenanschlüsse sowohl experimentell als auch numerisch betrachtet, wobei der Einfluss der überlappungslänge, der Klebschichtdicke und des Klebstoff‐E‐Moduls betrachtet wurde. Im Anschluss wurde ein probabilistisches Bemessungsverfahren angewendet und eine gute übereinstimmung zwischen experimentellen und theoretischen Traglasten erreicht. Das Verfahren kann unmittelbar für die Bemessung geklebter Anschlüsse angewandt werden. Probabilistic design of adhesively bonded timber joints. The use of adhesive bonding in structural timber engineering is limited to the production of laminated wood and the toughening of existing structures. To use adhesives as an alternative to mechanical fasteners, an accurate and reliable design method has to be developed. Characteristic material properties of wood such as anisotropy, large scattering of mechanical values and brittle failure complicate the capacity prediction of bonded joints. A deterministic approach is not able to deal with the stress peaks inside the joints. With the probabilistic concept, an alter native solution is presented, which allows for a strength prediction under consideration of the complex stress distributions and the stress peaks in the joint, as well as the scatterings of the mechanical properties of the material. Adhesively bonded double lap joints were investigated both experimentally and numerically under consideration of various parameters such as overlap length, adhesive layer thickness and type of adhesive. The probabilistic design method was applied and good agreement between experimental and theoretical failure loads was obtained. The proposed method has immediate actionable application for the dimensioning of adhesively bonded timber joints.     

Optimisation of the shear stress transfer in structural bonded assemblies using a curved bonded joint geometry

Structural adhesive bonding is coming into increasing use in civil engineering either for strengthening operations involving the adhesive bonding of external reinforcements or to replace traditional assembly techniques in new structures. However adhesive bonding induces stress concentrations at the edges of the joint, which have been studied by a large number of researchers in order to reduce these phenomena and increase the capacity and service life of the assembly. These studies are all, therefore, concerned with optimizing shear stress transfer in adhesively bonded joints. This paper investigates the role of the hydrostatic pressure on the ultimate capacities of common civil engineering adhesives. This led us to investigate a new joint geometry, the “curved” bonded joint that naturally creates compressive stresses on the edge of the joint. Initially, classical modelling is conducted to determine how the geometry affects the stresses in the joint. Then, fracture mechanics is used to investigate crack propagation. After this theoretical modelling, several experimental investigations are presented. These are quasi-static tests which compare classical shear lap joints to curved joints. The experimental results are then exploited using the modelling described before. Additional testing is currently in progress, but the curved bonded joint seems to hold good prospects and a patent has been filed.     

Ganzglastreppe mit transparenten SGP‐Klebeverbindungen – Konstruktion und statische Berechnung

Glass staircase with transparent SGP bonding foils – structural details and analysis. At the Glasstec 2006 in Düsseldorf, the worlds largest fair for the glass‐producing and trading industry, a glass staircase with a free span of 7,0 m was erected by the company Seele. Each of the supporting walls of the staircase consists of one laminated float glass pane without any joints. In addition to the large span of the glass panes an innovative aspect is the new adhesive joining technique using the highly transparent SGP (SentryGlas^® Plus) foils. This report focuses on the structural layout of the staircase as well as on the application of the new bonding technique and the structural analysis of the adhesive joints.     

Visko‐elastisches Verhalten von Holz‐Klebstoff‐Verbindungen unter zyklischer Zug‐Druck‐Belastung

Visco‐elastic behavior of bonded wood under cyclic tensile and compression loading In the present contribution, a test method is used to simulate the static, cyclic loading of adhesive joints due to swelling and shrinking of the wood and to demonstrate the plastic deformation in the low load range. For tensile shear specimens prepared from beech wood and bonded with three different adhesives (MUF, PRF, PUR), the elastic behavior under cyclic tensile and compression loading was investigated and the loss and storage of energy was determined. All tested adhesives showed viscose parts even at a very low load level of 3 MPa. At a load level of 7 MPa, the PRF joints revealed a more elastic behavior than the other. The increased loss energy determined for the PUR bonding indicates a softening of the adhesive joint.     

一种测试胶体与钢质基体间粘结剪切性能的新方法

中国现行国家标准试验方法中的单层金属片搭接接头拉伸剪切试件,由于粘结区剪应力分布极不均匀,并在粘结面上产生很高的拉应力,试验结果不能真实反映胶体与金属基体之间的粘结强度,只能作为胶体质量的检验指标,不能作为强度条件使用.该文采用的组合圆盘粘结试件用于胶层粘结剪切性能测试时,胶层及结合面剪应力分布很均匀,均匀系数可达0....     

Water effects on the bond strength of concrete/concrete adhesive joints

The paper discusses the experimental work by the authors investigating bond strength of epoxy adhesives and their efficiency when joining to concrete elements; the epoxies studied were those currently used in the construction industry. Flexural tests were undertaken to determine the mechanical properties of the exposed and the control specimens of three different epoxy adhesives. In addition, the water resistance of concrete/concrete epoxy joints was investigated by comparing bond strength with those of control samples; the maximum period of immersion was one month. A reduction in the glass transition temperature and the stiffness at short immersion time was found for all the adhesives employed, with a subsequent slight increase for prolonged immersion, while the effects on the strengths resulted almost proportional to their initial values. The effect of water on the adhesion of the joints was found to be significant, especially at longer immersion times; the bond strength of concrete–adhesive specimens reduced by 30% after one month of immersion in water.     

Structural performance of the finger-jointed strength of some wood species with different joint configurations

This study was conducted to evaluate the effects of adhesive type, wood species, and finger joint configurations on structural performance of the finger joint. The wood species studied were oriental beech (Fagus orientalis lipsky.), oak (Quercus robur), Scots pine (Pinus sylvestris lipsky.), poplar (Populus tremula lipsk.) and Uludağ fir (Abies bormülleriana Matff.) and adhesives were poly(vinyl acetate) (PVAc), Desmodur-VTKA (D-VTKA). However, there is little information available concerning the bending strength and modulus of elasticity for finger joints in these field. In this study, it was aimed to determine the bending strength and modulus of elasticity for finger joints. For this purpose, samples were tested according to the TS EN 310 standard. It was observed that the highest bending strength and modulus of elasticity were obtained in beech control (solid wood) samples. As for the finger joints, after the control samples, the highest bending strength value (57.4 N/mm²) was obtained from Oriental beech wood samples having a 21 mm finger length and bonded with PVAc adhesive, the highest modulus of elasticity (8885.3 N/mm²) was obtained from beech wood samples having a 21 mm finger length and bonded with PVAc adhesive. As a result of the effects of finger joints on bending strength and modulus elasticity test, if the length of finger joints increases up to 21 mm, the properties of bending strength increase.     

Entwicklung hybrider Stahl‐Glas‐Träger

Immer höhere Anforderungen an die Transparenz von Bauwerken führen zu einer stetigen Weiterentwicklung von tragenden Glaselementen, wobei dem Glas neben seiner ausfachenden Funktion mehr und mehr konstruktive Aufgaben zugedacht werden. Aktuelle Entwicklungen stellen die hybriden Stahl‐Glas‐Träger dar, bei denen schlanke Stahlflansche und Glasstege mittels geklebter Schubfugen zu einem “I”‐Träger zusammengesetzt werden [1]. Der Vorteil der linienförmigen Verklebung liegt hierbei in der gleichmäßigen Lasteinleitung in das Glasbauteil. Die Wahl des eingesetzten Klebstoffsystems trägt in Abhängigkeit seiner mechanischen Eigenschaften maßgeblich zum Tragverhalten des Verbundquerschnittes bei. Ebenso ist der Fugengeometrie eine große Bedeutung hinsichtlich der Tragfähigkeit und Herstellbarkeit zuzuordnen. Allerdings bestimmen Langzeiteffekte, wie Alterung des Klebstoffs und zeitabhängiges Tragverhalten, die Bemessung. Der Beitrag gibt einen Überblick über das systematische Vorgehen zur Untersuchung des Tragverhaltens und nennt wichtige Kriterien und Anforderungen beim Entwurf hybrider Stahl‐Glas‐Träger in Hin blick auf eine optimierte Ausnutzung der einzelnen Komponenten. Development of hybrid steel‐glass‐beams. Increasing higher requirements for transparent and filigree structures result in continuous development and improvement of load‐bearing glass elements, not only in a classic way being a space enclosing element but also increasingly offering load carrying functions. To realize architectural attractive transparent and lightweight constructions bonded hybrid steel‐glass beams have been developed, composed of slim steel flanges and glass webs which were assembled to ”I”‐beams using adhesives. The adhesive system significantly account for the structural behavior of the bonded composite section. Furthermore the joining geometry is of great importance concerning load carrying capacity and producibility but the design is governed by long‐term effects like ageing, creeping and time dependent load‐carrying behavior. This contribution shows the general systematic approach for the analysis of the load bearing behavior of hybrid steel‐glass beams and introduces important criteria and requirements for the design and its mechanical properties focused on an optimized exploitation of the components.     

Effects of scarf joints on bending strength and modulus of elasticity to laminated veneer lumber (LVL)

The role of geometry on the mechanical performance of scarf joints in laminated veneer lumber (LVL) bonded with phenol formaldehyde and melamine formaldehyde (MF) adhesives was investigated. Model joints consists of 3, 4 and 5 mm veneer thicknesses at 30°, 45° and 60° of varying scarf joints for LVL produced from brutia pine (Pinus brutia Ten) and elm (Ulmus compestris l.) woods. However, there is little information available concerning the bending strength and modulus of elasticity for LVL, and in particular, scarf joints in these field. In this study, it was aimed to determine the bending strength and modulus of elasticity for LVL. For this purpose, samples were tested according to TS EN 310 standard. It was observed that the highest bending strength (291.5 N/mm²) and modulus of elasticity (28 101 N/mm²) were obtained in control (solid wood) samples having three layered LVL, jointed with 30° angle and bonded with MF adhesive. As a result of the effects scarf joints on bending strength and modulus elasticity test, if the scarf angle decreases, the properties of LVL increase.     

对称和非对称粘合单盖板节点的变形和应力分析

采用粘合节点连接各种结构构件日益增多。只有充分了解粘合节点的性能,才能保证这种节点的功效、安全和可靠性。有些节点的构造,如单、双搭接接头受到了重视,但单盖板的构造并没有得到重视,部分原因是早期的研究显示这种节点效率低。本文的目的之一是论证只要经过合理设计,盖板节点与搭接接头同样有效。这项工作通过详细分析粘合剂中峰值应力的参数影响来完成。另一个目标是提出一个简单的方程,能够使盖板节点的设计便利及有效。为此,对解析表达式进行了简化并给出精确的结果,并对影响边缘力的参数有了进一步的理解。     

CFRP与钢材的粘结性能试验研究

与传统的钢结构加固方法相比,粘贴CFRP加固钢结构具有明显的优势。CFRP与钢结构之间的粘结性能直接影响加固效果,但是目前国内对这方面的研究还很少。从众多的粘结材料中优选出适合于粘贴CFRP加固钢结构的粘结剂,设计相应的试件,对CFRP与钢材之间的粘结强度和粘结耐久性进行试验。试验结果表明:选用的3种粘结剂可以作为粘贴CFRP加固钢结构的粘结材料,性能满足设计要求。对粘贴碳纤维布加固钢板进行静力拉伸试验,测量碳纤维布的应变分布,得到碳纤维布与钢板之间的粘结应力分布和碳纤维布的有效粘结长度。并与理论公式的计算结果进行了对比,二者吻合较好。     

Investigations on adhesively bonded curved CFRP panels with closed debonds subjected to compressive load

This present work aims to investigate the effect of debonds on the structural performance of adhesively bonded curved carbon fiber reinforced plastic (CFRP) panels under compressive loading environment. Representative curved panels are fabricated with a quasi-isotropic lay-up. Two types of specimens are prepared for the studies, one without debonds and the other with debonds of specified size, artificially introduced within the lap region. Pulsed thermography non-destructive technique is employed for the detection of debonds on the specimens. A set of experiments are conducted with displacement, strain and acoustic emission sensors to ascertain the performance of adhesively bonded joints under compression loading. Computational analyses are carried out using commercial finite element code MSC/NASTRAN to reproduce the experimental behavior and to aid in understanding the effect of closed debonds on the bonded joints. The computational model predictions are in good agreement with experimental observations. The effects of location of debond and panel curvatures are studied computationally incorporating debonds of different sizes. It is observed that debond location along the specimen length has significant effect and the buckling load reduces when the panel curvature increases for the same debond size.     

Numerische Analyse geschweißter Verbindungen von Duplexstahl und Quarzglas

Numerical analysis of welded joints between duplex steel and quartz glass. Welded joints are a vital element in structural engineering. Originating from conventional carbon steel welding in construction, recent advancements in welding technology now allow the joint of modern high‐strength steel and glass materials. With today's methods, an analysis of the welded joints' structural behaviour can be conducted by experiment, as well as by numerical analysis. Particularly for the numeric analysis, capturing the non‐linear thermal and mechanical properties of the materials is important, in order to allow a realistic determination of temperature, microstructure and residual stresses for different types of joints. Simulations of multi‐layered weld joint on duplex steel show, that a targeted heat treatment during MAG‐welding by variation of the welding parameters achieves a beneficial ratio between ferrite and austenite which, for example, ensures a high resistance of the weld to corrosion. The material quartz glass can generally be welded as butt‐weld with a CO₂‐laser. The simulations of a welded joint of a plate and a pipe show, that an optimization of the welding technology of preheat laser beam and welding laser beam is necessary, in order to reduce the thermal impact during the welding process, as well as residual stress in the joint. At the Department of Steel Structures at the Bauhaus‐Universität Weimar, numerical simulations of welded joints between steel and glass materials are a current and topical research focus.     

钢-混凝土粘结组合结构的试验研究

针对粘结的钢-混凝土组合结构的机械性能进行试验分析。钢支架和混凝土楼板依靠粘合剂粘在一起,分析了主要参数如粘合剂性能、粘合节点的不规则厚度等对结构机械性能和极限荷载的影响。试验中采用了两种粘合剂,结果显示用环氧性粘合剂的连接性能很理想,并且在钢-混凝土结合面上没有任何滑移。用聚亚氨酯粘结剂的组合梁截面为柔性连接。粘结剂厚度的变化,横向为2mm,纵向为4mm,对机械性能和极限荷载影响并不大。混凝土楼板的第一条裂纹出现在横向。试验结果表明,依靠粘合剂连接的钢-混凝土组合结构有其实用价值。     

Influence of aggressive exposure conditions on the behaviour of adhesive bonded concrete–GFRP joints

This paper presents the interim results of an on-going study on the influence of aggressive exposure conditions on the behaviour of epoxy adhesive bonded concrete–glass fibre reinforced polymers (GFRP) joints. The type of specimen used in this study is a push-off double lap shear specimen. Twenty-four of these push-off specimens consisting of concrete prisms, 100×100×300-mm, bonded with 470-mm long, 90-mm wide, and 3.5-mm thick GFRP plates on two opposite faces were tested. The bond length of the plate over the concrete surface was 200 mm. Two different concrete strengths were used, and they were suitably air entrained. The specimens were subjected to three accelerated ageing regimes in the laboratory for approximately 9 months. The accelerated tests consisted of exposing the specimens to alternate wet–dry cycling in 5% sodium chloride solution, cyclic freeze–thaw in air with a temperature of 20°C and −17.8°C, and a combination of chloride immersion and freeze–thaw cycles. The specimens were comprehensively instrumented, and tested to failure after the exposure regime. The structural performance of the exposed specimens is then compared with that of similar control specimens kept in laboratory environment in terms of load carrying capacity, longitudinal force distribution, shear stress development in the plate, plate end slip, and differential movements between the plate and the concrete substrate. There was clear indication that all the exposure regimes increased the bond transfer length, the magnitude of the shear stress distribution and the plate slip. The combined chloride immersion/freeze–thaw cycles produced the largest differential movements between the plate and the concrete substrate. The duration of exposure, however, was not long enough to affect the strength of the joints. Overall, the results were very consistent, and showed that accelerated tests could inflict deterioration in the adhesive bonded concrete–GFRP joints.     

Untersuchungen zur Dauerhaftigkeit von Verbindungen und Anschlüssen bei Luftdichtheitsschichten mittels Klebemassen und Klebebändern

Durability tests for airtight connections and joints based on adhesive compounds and adhesive tapes. To meet the basic requirements of structural stability, energy conservation and hygiene specified in the Construction Products Directive, components must be shown to be airtight, including proof of functionality at component, slabs or web joints, connections and terminations. Buildings are generally assumed to have a service life of around 50 years, construction elements, such as pitched roofs, for example, around 20 to 30 years. It is therefore necessary to demonstrate the suitability of the design and individual elements over the whole period. A task group of the German Association for Air‐tightness in Buildings (FLIB) prepared draft testing and labelling guidelines for adhesive tapes for internal application. A research project on testing adhesive compounds compared three artificial ageing techniques. As part of this project a new test procedure based on realistic loads was developed.     

建筑结构胶粘剂的发展和应用

建筑结构胶粘剂是一种具备承受较大载负能力的胶粘剂,性能要求较高。简述了该胶粘剂的发展历程,对比了国内外该胶粘剂的性能,指明了该胶粘剂的要求。     

Rehabilitation of timber structures – Preparation and environmental service condition effects on the bulk performance of epoxy adhesives

Epoxy adhesives have been used for many years in the rehabilitation of timber structures and are currently the most appropriate adhesive type for on-site operations. However, because they exhibit excellent initial joint strength when tested in standard climate conditions, there has not been a major concern about their service durability. In order to contribute to the ongoing discussion on the reliability of these adhesives, a study was conducted to evaluate the effect of environmental service conditions on the durability of four commercial two-component structural epoxy adhesives, as well as the effect that the type of mixing, curing and post-curing conditions, as well as the presence of moisture have on the adhesives viscoelastic properties. It was found that the preparation conditions, cure schedule and moisture have a significant effect on the performance of the bulk adhesives. Moreover, it was found that under ambient conditions there is potential for under-cure or slow progression of cure for the epoxy adhesive products typically employed in these applications, which in turn can compromise the durability of a bonded joint.     

用无机胶粘贴CFRP布加固混凝土板抗火性能试验研究

针对粘贴CFRP布用有机胶软化点过低的问题,研制出600℃时强度不低于常温强度的无机胶。为探索用无机胶代替有机胶粘贴CFRP布提高加固结构抗火性能的可行性,进行了5块用无机胶粘贴CFRP布加固混凝土板的抗火试验。考虑到高温时CFRP布在绝氧条件下强度降低较为缓慢的特点,试验前分别选用厚型隧道防火涂料和厚型钢结构防火涂料对其进行防火保护。试验板先按ISO 834标准升温曲线升温1.5h,再自然降温1.0h。各板底纵向CFRP布经历最高温度为90~300℃,火灾下跨中最大新增位移介于计算跨度的1/438~1/95。经历火灾后,CFRP布完好,无机胶与混凝土板可靠粘贴。试验结果表明:采用无机胶粘贴CFRP布加固混凝土板,厚型隧道防火涂料和厚型钢结构防火涂料均能达到对CFRP布进行控温和绝氧的目的,前者防火效果明显优于后者;用无机胶粘贴CFRP布加固混凝土板采用防火涂料保护后,火灾下和火灾后CFRP布与混凝土板均可有效共同工作。     

Strengthening of reinforced concrete beams in shear by the use of externally bonded steel plates: Part 2 – Design guidelines

Existing concrete structures may require strengthening or stiffening in order to increase their structural performance. One method for providing this enhanced capacity is to adhesively bond steel plates to the concrete surface. The results from experimental tests conducted to investigate the transfer of stress through a steel–concrete adhesive bond by Barnes and Mays [The transfer of stress through a steel to concrete adhesive bond. Int J Adhes Adhes 2001;21:495–502] combined with the shear strengthening and testing to failure of 30 reinforced concrete beams (Part 1 of this paper) was examined. By combining the results from each section of work, values for shear crack angle, effective anchorage length and mean shear stress levels in strengthened reinforced concrete beams were determined. These values were then used to develop a design method. This method can be used to determine the contribution to shear strength of continuous externally bonded steel plates in both rectangular and ‘T’ section reinforced concrete beams.