Hybridbrücken mit blockverleimtem Brettschichtholz

Hybrid bridges with log‐glued‐laminated timber. In Germany, timber as load‐bearing element of bridges is only used for the construction of foot‐ and bicycle viaducts. The development of new timber‐based products and modern technologies gives interesting chances for timber bridge‐building in future. Main beams with high stiffness and stability of dimension can be produced by log‐glued lamination of timber. Efficient hybrid cross‐sections of superstructures as timber‐concrete‐composite constructions can be made by the combination of beams consisting of log‐glued‐laminated timber and concrete deck slab. For road bridges, these hybrid cross‐sections could be used alternatively to conventional methods of construction. The following paper gives a review of the development status of timber‐concrete‐composite construction in bridge building and shows static and constructive specifics.     

Berechnung von Holz‐Beton‐Verbunddecken

Evaluation of Timber Concrete Composite Slabs If timber and concrete acts together in a cross section, the carrying and deformation behaviour of this new composite section is affected by many influences e.g. geometry, material properties, connecting device, long‐term behaviour, etc. The advantages of this building method and an optimization of the cross sections only can be achieved, if these influences are known and can be taken into account in the structural design. For the proof of the short term behaviour different procedures, e. g. [1], are available. Regarding the long‐term behaviour of the timber concrete composite floors it becomes obvious that the rheological behaviour of timber concrete composite structures is not considered sufficiently by the design method in [1].     

Langzeitverhalten geklebter Bauteile aus Holz und hochfestem Beton bei natürlichem Klima

Longterm‐behavior of glued full‐scale specimens made from wood and high performance concrete at natural climate conditions The advantages of the construction materials wood and concrete could be used effectively in wood‐concrete‐composite constructions. The composite structure shows optimized load carrying capacity, a better vibrational behavior, higher noise protection and a higher thermally activatable mass in comparison to constructions that are entirely made from wood. Mechanical fasteners or form fitting connections are state‐of‐the‐art for connecting timber to concrete. This leads to more or less flexible bond. By using the adhesive technology a ”rigid bond“ can be achieved and it is possible to combine the advantages of a ”dry construction method“ with the advantages of the prefabrication. The questions of the production technology and the short‐term behavior of glued wood‐concrete composite constructions were answered yet at the department of timber structures at the University of Kassel. Knowledge of long‐term behavior was missing for an application in construction practice. This was studied in the last three years in detail. The experimental und numerical investigations on full‐scale specimens and the conclusions for a practical application are reported in the following article.     

Modelling criteria for r/c elements constructed with ultra‐high‐strength concrete and subjected to cyclic loading

High‐strength concrete (HSC) has several benefits in high‐rise concrete buildings; however, its structural use in active seismic regions may be questioned due to the lower ductility of such concretes. In addition, seismic macro‐models being used currently are based on R/C elements constructed with normal‐strength concretes (f ≤ 40 MPa (5.8 ksi)). In this paper, the performance of plastic hinges in flexural elements constructed with a concrete strength up to 175 MPa (25.4 ksi) is investigated. In addition, other variables were studied such as the sectional reinforcement asymmetry, hinge shear strength and hinge shear demand. The seismic performance is presented in terms of stiffness deterioration, strength degradation, pinching phenomenon and displacement ductility. The requirements to implement the use of HSC in current macro‐models are examined. Current hysteretic models may be used to evaluate structural components constructed with higher concrete strength; however, the influence of concrete strength is controlled by the other test variables. Copyright © 2009 John Wiley & Sons, Ltd.     

薄壁钢梁-陶粒混凝土装配式组合楼板受火后受力性能研究

由冷弯薄壁钢梁和陶粒混凝土预制板组成的装配式组合楼板具有轻质、高强和施工方便等优点。为研究该类组合楼板的抗火性能及高温后的受力性能,对6块遭受温度为700℃、持续90min烃类火灾升温作用的简支组合楼板试件进行受火后受力性能试验研究。结果表明：当施加的等效均布荷载达到2kN/m²时,受火作用后的组合楼板试件最大挠度小于跨度的1/400,且在加载过程中薄壁钢梁虽已明显扭曲、混凝土板多处开裂,但组合楼板试件未出现整体坍落现象;以普通栓钉为抗剪键的受火后组合楼板试件,其极限荷载比薄壁钢抗剪键组合楼板试件的提高14.2%;当用钢量相同时,主梁数量较多的组合楼板试件采用U形钢筋作为拉结件,其火灾后极限荷载比采用钢条拉结件的组合楼板试件的增加33%,且整体刚度也有所提高;该类组合楼板在受火后仍具有较高承载能力和整体刚度,且抗剪键类型、预制板之间设置的拉结件以及拉结件与抗剪键的连接方式均对其受火后的受力性能有较大的影响。引入组合效应系数可以较好地反映受火后组合楼板试件的组合效应及内部损伤程度。     

Leistungsfähigkeit von Betonen mit Flugasche

Performance Capacity of Concrete containing Fly Ash The conception to take into account the addition of fly ash to structural concrete presented in the German Standard DIN 1045‐2 should guarantee a high resistance of concrete structures against corrosive attack. In this context, criteria such as compressive and flexural strength of concrete, modulus of elasticity, bond strength, shrinkage and creep as well as the pore structure are focused in this paper. The obtained results on concretes containing a maximum of fly ash according to DIN 1045‐2 compared with concretes produced only with ordinary Portland cement show similar strength values at the age of 28 days while the strength development is somewhat lower for the fly ash concretes. However, at the age of one year the strength of fly ash concretes in particular also the flexural strength is considerably higher. Shrinkage and creep of the fly ash concrete is lower resulting in an overall reduced risk of shrinkage and thermal cracking.     

Zur plastischen Bemessung hochfester kammerbetonierter Verbundträger

Plastic design method for high‐strength partially concrete encased composite beams. Partially concrete encased composite beams offer numerous advantages compared to conventional composite beams consisting of a steel beam and a concrete slab. In many cases these advantages are not used because of missing practicable design models. In the current paper the load bearing behaviour and the rotation capacity of partially concrete encased composite beams made of high strength steel and concrete is investigated using experimental tests and parametric studies. At first the influence of high strength concrete encasement and high strength structural steel on the cross section capacity is described. Taking into account the stress‐strain distribution of high strength concrete and steel a new plastic design method for partially concrete encased composite beams was affiliated. The experimental and theoretical results are documented in the research report [1] and the dissertation [2].     

Korrelation von Betondruck‐ und Zugfestigkeit historischer Betone

Correlation between the compressive and tensile strength of old concretes – Applicability of the relationship described by DIN EN 1992‐1‐1 In the design of a new structure, DIN EN 1992‐1‐1 [1] normatively regulates the correlation between the compressive strength and tensile strength of concrete, produced according to DIN EN 206‐1 [2]. However, as there are many different time‐ and load‐dependent impacts on existing structures, the relationship described by DIN EN 1992‐1‐1 [1] can't be assumed without any further observations for existing structures. At the moment, there is no comprehensive investigation on the influences of e.g. subsequent hardening and carbonation on the concrete compressive or tensile strength. The tensile strength of concrete defined in DIN EN 1992‐1‐1 [1] is based on a water storage and a testing age of 28 days. Furthermore, the in‐situ tensile strength is affected by micro‐crack formation cause of internal stresses due to outflow of hydration heat. Generally, there is a different influence of micro‐crack formation on the tensile strength of concrete than on the compressive strength of concrete. The real value of the in‐situ tensile strength of concrete affects the shear force resistance and the load‐bearing capacity of anchors with concrete cone failure as decisive failure mode. Within the framework of a research project, financed by ”Forschungsinitiative Zukunft Bau“, an initiative of the Federal Institute for Research on Building, Urban Affairs and Spatial Development (BBR) structural investigations on the correlation between the compressive and tensile strength of old concretes have been performed. Below, the results of the research project are presented.     

Stahlbeton‐Verbundkonstruktionen – Ein Bemessungskonzept für schubbeanspruchte Fugen. Teil 1: Korrelation zwischen Simulation und Bemessung

R/C Composite Constructions – A Design Concept for Shear Loaded Joints – Part 1: Correlation between Simulation and Design. In the modern engineering practice composite constructions are often used. This constructions consisting of prefabricated R/C components and in situ concrete are marked by the interaction of concrete interfaces with different age and different strength. With various examinations will be show, that the present designing practice and the distribution of reinforcement is not effective and leads to high reinforcement concentrations in uncritical joint sections and also to an unbalanced reinforcement along the joint. This paper is divided into 2 parts: Part 1 summarizes the state‐of‐the‐art, a special structural model and important results. A design concept, continued in part 2, will be presented for the practical use according to European standard EC 2, which enables the differentiation between narrow and broad bond surfaces for the first time. Additional, the new concept considers the non‐rigid bond and also decisive parameter in a subtly differentiated, nearly realistic and bearing structure referred way.     

Zur Berechnung von Holz‐Beton‐Verbundträgern mit Methoden der mathematischen Optimierung

Holz‐Beton‐Verbundkonstruktionen weisen als hybride Tragwerke gegenüber reinen Holz‐ bzw. Stahlbetonkonstruktionen zahlreiche Vorteile auf. Wesentlich für die Effizienz der Hybridbauweise ist die Ausbildung der Verbundfuge. Der vorliegende Beitrag stellt ein neues Verbundelement für Straßenbrücken in Holz‐Beton‐Verbundbauweise vor, welches im Rahmen eines Forschungsprojekts an der Bauhaus‐Universität Weimar entwickelt wurde. Die rechnerische Analyse der Verbundkonstruktion erfolgt — abweichend von den im Hybridbau bisher üblichen Berechnungsmethoden — unter Anwendung von Energiemethoden und Nutzung von Algorithmen der mathematischen Optimierung. Calculation of timber‐concrete composite structures using mathematical optimization methods. Timber‐concrete composite structures have many advantages over conventional timber and re inforced concrete structures. The efficiency of such hybrid structures significantly depends on the properties of the com posite joint. This article presents a novel structural element for the joint of timber‐concrete composite bridges, which was developed as part of a research project at the Bauhaus‐Universität Weimar. In contrast to standard calculation methods, an energy method and the mathematical optimization is applied for the numerical analysis of the hybrid structure.     

Deformation capacity of ultra‐high strength concrete flexural elements subjected to inelastic load reversals

Ductility and plastic rotational capacity of flexural elements constructed with concrete strengths up to 175 MPa were investigated experimentally. Ten exterior beam–column sub‐assemblages were tested under cyclic displacements that represented a severe seismic event. The test variables included the concrete strength, the bottom/top reinforcement ratio, the transverse reinforcement ratio, and the shear‐span‐to‐depth ratio. The increase of concrete brittleness with the higher strength concretes did not inhibit the reinforced concrete flexural elements from attaining comparable ductility and deformation capacity with respect to counterpart elements constructed with normal strength concrete. However, the maximum concrete strength that could be used in achieving highly ductile elements depended on the other test variables of the beam element including the bottom/top reinforcement ratio, the transverse reinforcement ratio in the hinge region, and the shear‐span‐to‐depth ratio. Copyright © 2010 John Wiley & Sons, Ltd.     

Beschichtungen auf direkt befahrenen Tiefgaragenbodenflächen von Weißen Wannen. Physikalische Beanspruchungen – Planungsgrundlagen – alternative Beschichtungsvarianten

Coatings on directly vehicle‐carrying floor slabs of watertight concrete constructions in underground carparks physical stresses – design codes – alternative coating systems According to DIN 1045‐1 directly vehicle‐carrying park decks have to be realized with additional measures (crack‐bridging coating systems). At least surface protection system 11 (SPS 11) according to the Guidelines for the Protection and Repair of Concrete Components of the German Committee on Reinforced Concrete (DAfStb) are among others a possibility to meet this requirement. On the market available crack‐bridging coating systems with a general technical approval are not usefull on concrete surfaces with high water contents (water saturation values of 90 %) as they may occur in floor slabs of watertight concrete constructions. Experiences with practical damage cases show, that with approved SPS 11‐systems osmotic induced bubbles may occur preferably on backside saturated floor slabs of watertight concrete constructions. In consequence the physical stresses of a coating (osmotic processes, capillarity reactions, hydraulic pressures as well as gas pressures) will be quantitatively estimated and compared with the capability of market systems. Alternative coating systems are presented and practical recommendations in order to avoid damages are given.     

Stahlbeton‐Verbundkonstruktionen – Ein Bemessungskonzept für schubbeanspruchte Fugen. Teil 2: Normative Empfehlungen für Neubau und Revitalisierungsmaßnahmen

R/C Composite Constructions – A Design Concept for Shear Loaded Joints – Part 2: Normative Recommendations for New Building and Retrofit Measures In the modern engineering practice composite constructions are often used. This constructions consisting of prefabricated R/C components and in situ concrete are marked by the interaction of concrete interfaces with different age and different strength. With various examinations will be show, that the present designing practice and the distribution of reinforcement is not effective and leads to high reinforcement concentrations in uncritical joint sections and also to an unbalanced reinforcement along the joint. This paper is divided into 2 parts: Part 1 summarizes the state‐ofthe‐ art, a special structural model and important results. A design concept, continued in part 2, will be presented for the practical use according to European standard EC 2 which enables the differentiation between narrow and broad bond surfaces for the first time. Additional, the new concept considers the non‐rigid bond and also decisive parameter in a subtly differentiated, nearly realistic and bearing structure referred way.     

Anwendung von Hochleistungsbetonen bei der Bogenbrücke Wölkau im Zuge der BAB A17: Eine kritische Betrachtung

Application of high performance concretes for the arch bridge Wölkau in the course of motorway BAB A17 – a critical reflect For the arch structure Wölkau a self compacting concrete for the production of the arch and a high strength concrete for the superstructure were applied. The following paper summarizes the pointed demands on the concretes for this pretentious structure and which conclusions to future bridge constructions can drawn.     

Mechanische Hochtemperatureigenschaften von flugaschebasierten Geopolymerbetonen

Mechanical properties of fly ash‐based geopolymer concretes at high temperature At present, concretes based on alkali‐activated binders, so‐called geopolymer concretes, are investigated intensively in the building materials industry and by the research community as environmentally friendly alternative to Portland cement‐based concretes. These inorganic binders, which are based on industrial by‐products such as fly ash and ground granulated blast furnace slag, exhibit high resistance against corrosive acids and salts, if properly designed. The mechanical properties of fly ash‐based geopolymer concretes at high temperatures are subject of systematic investigations at the Bundesanstalt für Materialforschung und ‐prüfung (BAM) to create a basis for the structural design of fire exposed concrete members based on alkali‐activated binders. The concrete specimens, produced with quartz aggregates or lightweight aggregates and heated to a maximum temperature of 750 °C, exhibited a decrease of compressive strength up to temperatures of ca. 300 °C, attributed to formation of microcracks caused by dehydration. At higher temperatures the compressive strength of the investigated geopolymer concretes recovered partly, due to sintering processes starting from ca. 500 °C. Because of this beneficial property when compared to conventional concretes, geopolymer concretes can potentially be applied in infrastructure facilities where fire resistance is critical. From the results of the thermomechanical tests stress‐strain relationships are derived that can be used for the structural design of members made from geopolymer concretes.     

Bemessungsvorschlag für Holz/Beton‐Verbundbalken unter Beachtung abgestufter Verbindungsmittelabstände

Design proposal for timber/concrete composite beams with graded connnector distances. The distance of connections of timber/concrete composite beams is often graded for economical reasons according the shear force distribution. The load‐carrying capacity of composite beams according to DIN 1052 respectively E DIN 1052 with internal forces, which are linearly determined, (γ‐procedure) are clearly reduced compared to beams without graded distances of connectors. The actual load‐bearing behaviour distinctly shows non‐linearities. The influence of the gradations of the connectors on the load‐bearing behaviour of composite beams is investigated, because the influence of the stiffness of connections on the load‐bearing capacity of composite beams is small. The paper presents a comparison between failure loads determined by FE‐analysis and the working loads according to the current design rule. It is shown that the decrease of load‐bearing capacity is smaller than assumed by current code of practice. Structures with several different distances of connections have the largest safety‐factor. These systems can more economically be designed. As the result of the investigations, a new design proposal is presented, which takes non‐linearities into account and guarantees a constant safety‐zone between failure load and working load. These proposal permits an economic design of timber/concrete composite beams.     

Holz‐Beton‐Verbunddecken (HBV) – Neue Deckensanierungssysteme mit Vollgewindeschrauben,Stahlfaserbeton und Online‐Bemessungstools

Composite timber‐concrete structures – new floor renovation systems with fully threaded shear connectors, steel fibre concrete and online design tools. Composite timber‐concrete structures – efficiently static, oscillation‐technical and sound‐technical improvement of old timber joist floor systems. New products, design codes, approvals and investigation results are ready for online using in planning and structural design calculation.     

Stahl‐Beton‐Haftverbindungen für Verbundbrücken – Versuche und Bemessung

Connections by adherence for steel‐concrete composite bridges – tests and design. This paper presents experimental and analytical research that was conducted on new connections “by adherence” for steel‐concrete composite bridges. Their resistance is due to the frictional shear resistance of different interfaces positioned in a judicious manner. These connections makes it possible to erect the structure quickly with full‐depth precast concrete slabs, while the concreting works on site are as much as possible limited. Experimental results show that these connections exhibit a high resistance to horizontal shear forces and are very stiff compared to traditional connectors (headed studs). However, their ductility is limited. Based on the experimental results, a calculation model, taking into account the deformation observed during the tests and behavior laws for interfaces, was then developed and used in a parametric study. Some results are presented and discussed. A simplified method for determining the resistance of these connections, based on these results, some design rules as well as some recommendations for construction are finally proposed. The behavior of steel‐concrete composite beams with connections by adherence is also shortly discussed.