Verbunddecken aus Stahlfaserbeton und Holz

Composite Floors made of Steel Fibre Reinforced Concrete and Timber For many years the timber‐concrete composite construction is known and approved particularly with regard to the revaluation and strengthening of timber beam ceilings. The benefits are an obvious increase of the load bearing capacity, a reduction of the deflection, a better vibration behaviour of the ceiling and an improvement of building physical properties like sound insulation and fire resistance. The reinforcement of the concrete slab is necessary, but leads to a large slab thickness in connection with the necessity of a sufficient concrete cover and to disadvantages during the execution of construction work. Therefore it is reasonable to replace the conventional reinforcement by steel fibres. This paper reports on two building projects and their associated experimental pre‐tests, in which steel fibre reinforced concrete was applied for the strengthening of timber beam ceilings.     

Ingenieurholzbau für mehrgeschossige Industriebauten – Konzept und Detaillösungen

Timber construction engineering for multiple storey buildings A multiple storey industrial building was erected in Berlin with timber and timber‐concrete‐composite technology. The load bearing system made of glued laminated timber has a height of four floors in visual quality and with a fire resistance level of R90. The design was done by Roswag architects, the load bearing system with timber and TCC ceilings was developed by Stephan Holzbau GmbH. A special challenge are the joints of the post and lintel construction. The high load impact from the posts had to be transfered by the continuing timber lintels. Therefore, a special solution was found in a polymer compound grout with a very high compression resistance. Drill holes, perpendicular to the grain, were filled with the grout to produce integrated columns. Hence, the impact to the cross section of the glulam lintel is low and the load bearing system transfer still works without limitations. Due to the pre‐fabrication and computer‐aided wood‐working in the workshops of Stephan Holzbau it was possible to meet the very high standards of visual appearance and precision of the construction. Furthermore, the cost of the joints could be reduced by about 30 % compared to usual steel details.     

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].     

Innovative Betone für Holz‐Beton‐Verbundkonstruktionen

Innovative concretes for timber‐concrete composite constructions. Timber‐concrete composite constructions are currently applied mainly for new buildings or when strengthening existing timber beam slabs. The load bearing capacity of timber‐concrete composite slabs is essentially affected by the material properties of the concrete slab and timber beam itself as well as the efficiency of bond between both parts. As nowadays a wide spectrum of different innovative concretes is available their applicability for timber‐concrete composite constructions has to be verified. In the following the focus is set for self‐consolidating concrete, steel fibre reinforced concrete, structural lightweight concrete, high‐strength and ultra high‐strength concrete. The advantages but also disadvantages of these concretes will be explained considering structural, economic and processing aspects and building physics.     

陶粒混凝土-开孔薄壁钢梁组合楼板的受力性能研究

由腹板开孔且翼缘卷边的H形薄壁钢梁和陶粒混凝土预制板经后浇砂浆和抗剪键组装而成的组合楼板,具有轻质、高强、无需支模、装配化程度高等优势。为研究该类组合楼板的受力性能,对6组不同构造的两边简支组合楼板试件开展静载试验,分析抗剪键分布及薄壁钢壁厚的变化对组合楼板整体受力性能的影响。结果表明：对应等效均布荷载2kN/m2的组合楼板,中心挠度远小于L/500,能够承担的最大荷载值为13.25kN/m2;当混凝土严重开裂且板跨中最大挠度达到L/45时,组合楼板试件并未出现整体塌落;主钢梁上抗剪栓钉的增加,对提高组合楼板的极限荷载和整体刚度均不明显;边梁增设抗剪栓钉对组合楼板的屈服荷载及整体刚度均产生显著影响,当边梁设置与主梁同样的抗剪栓钉时,屈服荷载和整体刚度增幅分别为82.1%和35.6%。     

深圳大中华国际交易广场中央交易大厅巨型框架预应力楼盖结构设计

深圳大中华国际交易广场中央大厅柱网尺寸达34m×42.5m,共3层,只在四角设有柱子。楼层活荷载为5kN/m2,建筑面层及管道吊顶荷载为3kN/m2。若采用现浇钢筋混凝土框架结构方案,边框架梁的扭矩和柱子双向大偏压问题十分严重。本工程主要采取了以下技术措施解决了结构设计上的技术难题:将楼盖设计为密肋梁体系,并沿42.5m方向设置,34m跨向设计为主框架梁;42.5m向密肋梁与34m向主框架梁之间的连接设计为铰接,不传递端弯矩,从而解决边梁扭矩与柱子大偏压问题;将34m跨一、二层框架梁合并为一拱架,承受一、二层楼盖的荷载,拱架上、下弦截面高度仅为0.8m;楼盖、大梁、拱架上、下弦及柱子均设计为预应力混凝土。经采取上述结构措施后,结构设计变得容易,且有利于设计与施工。     

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.     

Rissbreitenberechnung für Elementwände und ‐decken aus Stahlbeton für Zwangbeanspruchungen rechtwinklig zu den Elementfugen

Calculation of crack widths of element ceilings and walls made of reinforced concrete due to imposed deformation perpendicular to the assembly joints. Prefabricated walls and floors have load bearing properties similar to geometrically identical monolithic members. This also applies to the effects of restraint strain caused by constrained shortening of members, if it occurs in the main bearing direction. In contrast to that load‐bearing structures of half‐prefabricated elements differ from monolithic structures in their behaviour at restraint strain orthogonal to the direction of span. The element joints form notches, in which tensile cracking already occurs at low strains. Crack spacing is determined by the modular grid. A phase of developing cracks, as it can be seen at monolithic components, does basically not occur. After a very short period, in which single cracks develop and which is finished when a crack occurs in the last joint, only small restraint strain is needed to reach a fully developed crack pattern. Due to larger crack spacing (element width) the concrete strain between the cracks is more significant than it is in monolithic members. Broader elements require more reinforcement across the joints to ensure the same crack widths. A method is suggested to calculate crack width and minimum reinforcement of notched cross‐sections. Minimum reinforcement orthogonal to the joint is higher than it is in comparable monolithic components.     

Einfluß des Kriechens und des Betonschwindens auf das Tragverhalten von Holz‐Beton‐Verbundbalken – Ein erweiterter Bemessungsvorschlag und dessen Anwendungsgrenzen

Effects of creep and concrete shrinkage on the load‐carrying behaviour of timber/concrete composite beams – an extended design proposal and its limitations. In this paper, the effects of creep and shrinkage with respect to the load‐carrying behaviour are studied. In particular, the behaviour of green concrete causes significant changes compared to structures with the simplified assumption of constant elastic material properties. Furthermore, the influence of the duration and the procedure of unloading of a temporary assembly support are investigated to obtain practicable advices. The design proposal, which is extended to take the decrease of load‐carrying capacity due to concrete shrinkage into account, permits an economical design and guarantees a constant safety zone to the ultimate state.     

Effects of various admixtures and shear keys in wood–concrete composite beams

Wood–concrete composite beams are a layered system, which essentially utilize a concrete layer in compression and a wood layer in tension. This layered system offers a way to construct or rehabilitate wood floors in historic timber structures while increasing the floors’ stiffness and load carrying capacity. This research paper investigates past problems with poor consolidation of the concrete, transverse shrinkage cracks in the concrete, swelling of the wood, moisture loss from the concrete, and the resulting reduced composite efficiency. The research presented herein describes how these problems can be mitigated and thereby increase the composite efficiency of the wood–concrete composite system. By painting the specimens with a water proofing paint, the swelling of the wood can be reduced, which helps to maintain a tight interface between the wood and concrete. To improve consolidation, a self-leveling concrete was designed with a 28-day compressive strength of 34.5 MPa and a slump of 279.4 mm. Nylon fibers and Type I steel fibers were used as admixtures to the fresh concrete to determine their effect on the composite efficiency and the reduction of shrinkage cracks. Twelve full size specimens were constructed and tested to failure. It was found that the most common mode of failure was combined bending and tension at mid span in the wood. An average composite efficiency of 83.4% was reached in the full size test specimens when placed in four point bending.     

Thermal and structural behaviour of a full-scale composite building subject to a severe compartment fire

This paper presents a numerical investigation of the thermal and structural results from a compartment fire test, conducted in January 2003 on the full-scale multi-storey composite building constructed at Cardington, United Kingdom, in 1994 for an original series of six tests during 1995–1996. The fire compartment's overall dimensions were 11 m×7 m with one edge at the building's perimeter, using largely unprotected steel downstand beams, and including within the compartment four steel columns protected with cementitious spray. The compartment was subjected to a natural fire of fire load 40 kg/m² of timber, in common with the original test series, but the composite slab forming its ceiling was subjected to a uniform applied load of 3.19 kN/m², which is higher than the original.     

Flachdecken aus Stahlfaserbeton

Steel Fibre reinforced concrete Flat Slabs Steel fibre reinforced concrete is a proven and reliable material for slabs on grade of industrial floor systems. Since several years, steel fibre reinforced concrete with additional reinforcement bars is used for free suspended pile supported industrial floors. The load carrying behaviour under service loading conditions is similar to that of elevated flat slabs. Recently, concretes with high fluidity allow higher fibre dosages than before. A full scale loading test on a flat slab of 340 m² at TREFILARBED in Bissen, Luxemburg has proven that elevated slab structures made of steel fibre reinforced concrete with 100 kg/m³ fibre content can compete with traditional reinforced concrete slabs by means of load carrying capacity as well as concerning cost effectiveness. This paper deals with the development of free suspended SFRC slabs based on the performed full scale tests. Formulas for the ultimate limit state design according to the yield line theory are presented. Design criteria at serviceability limit state are provided.     

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.     

帽型薄壁钢梁-轻骨料混凝土组合楼板受力性能试验研究

由帽型冷弯薄壁钢梁作为组合楼板的承重骨架,与轻骨料混凝土预制板块经后浇水泥砂浆而形成轻质组合楼板。为研究其受力性能,设计并制作了5块具有不同构造特征的组合楼板试件,对其进行了简支条件下的静载试验。结果表明：该组合楼板具有较大的整体刚度和承载能力,当等效均布荷载达到正常使用状态的荷载标准值3.2kN/m2时,跨中挠度远小于L/500。当组合楼板的整体变形较大时,帽型钢梁内部的外伸腹板对提高组合楼板的整体刚度产生明显作用,极限状态下割线刚度是帽型钢梁内部无外伸腹板时的2.5倍;当次梁截面高度由20mm增至50mm时,组合板的极限荷载增幅为87.5%。     

Zur Berechnung von Holzstabtragwerken mit mehrlagigen nachgiebigen Verbundquerschnitten

Calculation of timber structures made of multilayered beam elements with flexible composite sections. The board rib construction technology offers owners, engineers, and architects the opportunity to realise efficient, economic and aesthetical shell‐like buildings. Board rib shells are relatively under‐utilized in spite of their advantages. The reason for this is the lack of a suitable computation method for these complex structural systems made of flexible composite cross‐sections. The solution methods used so far are restricted to just special cases or they represent only approximations. With an efficient, user‐friendly and reliable computation method, such structures will be realised more frequently than at present. Applicability and limitations of the derived method are given in order to avoid inexact solutions. This work presents a finite beam element with a quadratic formulation for the longitudinal displacements for almost any multilayered flexible composite cross‐sections with spatial structural behaviour at geometrical nonlinear theory of 2^nd order. The composite elements are verified with the help of analytical solutions depending on the ratio of the element length and of the joint stiffness. The element is also capable, for example, to calculate wood‐concrete‐composite floors including the effects of creep and shrinkage in sub‐sections.     

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.     

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.     

Deutsches Archäologisches Institut DAI in Rom

Die Bundesrepublik betreibt in Rom das Deutsche Archäologische Institut (DAI). Der achtstöckige Stahlbeton‐Skelettbau aus dem Baujahr 1963 mit ca. 8000 m² Geschossfläche als Rippendecken mit Ziegelhohlkörpern soll für Bibliothekslasten überprüft und erdbebensicher ertüchtigt werden. Rechnerische Nachweise und ein früherer Belastungsversuch mit Wasserballast ergaben keine ausreichende Tragsicherheit. Um einen sehr aufwendigen Dübelverbund der geplanten Aufbetonschicht zur Herstellung der erforderlichen Platten‐ und Scheibensteifigkeit zu vermeiden, ist im März 2009 an repräsentativen Testbereichen die Tragwirkung eines flächigen Haftverbunds in situ erprobt worden. Aus den Ergebnissen der zerstörungsfreien Ermittlung der Grenzschnittgrößen für das Verbundsystem Bestand — Verbundschicht — Aufbeton konnte anschließend in einem hybriden Verfahren die Tragsicherheit für Bibliothekslasten q = 6,0 kN/m² sowie die Erdbebensicherheit rechnerisch nachgewiesen werden. Die Belastungsversuche in situ erforderten regelbare Versuchslasten bis zu ΣF = 360 kN je Deckenfeld und haben eine Versuchsdauer von 2 Wochen in Anspruch genommen. Das gesamte Equipment wurde per LKW nach Rom transportiert und wog etwa 8 t. German Archaeologicial Institute in Rome — Structural safety for library loads and earthquake‐proof with hybrid statics. The Federal Republic of Germany supports the German Archaeological Institute in Rome. The 8‐storey steal concrete frame building from 1963 with 6000 m² storey area has ribbed slabs with hollow‐bricks should be enforced for library use and earthquake‐proof. From Numerical calculations and a former loading test with water ballast, no adequate structural safety results. In March 2009 at adequate test areas the bearing capacity of a mineral resin‐bonding was tested in situ to avoid a very expensive stud bond for the planned blinding concrete for the necessary slab stiffness. From the non‐destructive evaluation of the limit stress resultant for the composit system “actual slab — knitting layer — structural concrete topping” the structural safety for library loads q = 6,0 kN/m² and seismic design could be verified with hybrid statics. The loading tests in situ required controllable test loads up to ΣF = 360 kN for each ceiling panel have been accomplished during two weeks. The total equipment of about 8 tons was transported by truck to Rome.     

Seismic behavior of double steel concrete composite walls

An innovative double steel concrete (DSC) composite walls were developed to enhance constructability and lateral load resistance of buildings. In order to research the seismic behavior of DSC composite walls, experimental study was carried out. The high‐strength concrete and high axial load were considered. The failure mode, hysteresis behavior, lateral load‐carrying capacity, deformation, and energy dissipation of the composite walls under different testing parameters were observed. All specimens failed in a flexure behavior, with steel plate buckling and concrete compressive crushing in the bottom of composite walls. The pinching behavior was not significant for hysteresis loops of composite walls. Moreover, the lateral load‐carrying capacity and ductility coefficients increased significantly with spacing of constraining bolts and stiffeners decreased. In addition, the calculation method of the lateral load‐carrying capacity of DSC composite walls was proposed, with the consideration of force equilibrium and moment equilibrium. The finite element (FE) method was performed to analyze the failure process of the specimens with the cyclic load. The concrete damage plastic model was selected to simulate the damage progress of concrete. Validation of the FE models against the experimental results showed good agreement. The effect of different parameters was analyzed with FE models.     

Teilfertigdecken nach DIN 1045‐1. Wichtige Punkte der Bemessung und Konstruktion

Partly pre‐fabricated reinforced concrete Floors/Ceilings according to DIN 1045‐1. Important Points of Design and Construction There are invasive changes in design and construction of partly pre‐fabricated reinforced concrete floors/ceilings connected with the application of DIN 1045‐1, July 2001 issue. This applies specifically to the verification of acceptance of thrust force in the joint between pre‐cast slab and the on‐site concrete. The basic elements will be gathered for this extensive verification and an example is given. Regulations for the arrangement of lattice girders as bond/shear force reinforcement as well as concrete covers will be shown in detail. Structures of support are easier to implement in the future.