Rissbreitenberechnung bei “Kombibewehrung”

Crack Width Limitation for Combined Reinforcement In recent years, steel fibre concrete has more and more found a wide spread application in structural engineering. This applies to building members made from steel fibre concrete or in combination with normal re‐bar reinforcement (combined reinforcement). In this context the question of crack width limitation very often has to be answered, and the interaction of the steel fibres with the rebars has to be observed. Some design rules are available in the relevant literature, whereas the design rules for a combined reinforcement use the basics of DIN 1045‐1. This paper deals with the applicability of these design proposals for a combined reinforcement, based on research results and some characteristics in the design consideration of the post‐cracking tensile strength of steel fibre concrete will be given.     

Bemessung von Fundamentplatten aus Stahlfaserbeton gemäß ÖVBB Richtlinie Faserbeton und DBV Merkblatt Stahlfaserbeton

Static Analysis and Verification of Steel Fibre Reinforced Concrete Foundation Slabs according to the Austrian Guideline “Fibre reinforced concrete” and DBV (German Concrete Association) Recommendations “Steel fibre reinforced concrete” Steel fibre reinforced concrete is used for foundation slabs of housing structures since many years. The Austrian guideline [1] and the DBV recommendations [2] provide material properties and design values for calculation and verification of steel fibre reinforced concrete structural members. This paper provides a comparative study on foundation slabs taking both guidelines into account. A nonlinear finite element parameter study has been performed in order to verify a simplified static calculation and verification method. This calculation method is based on the yield line theory. This paper concludes with a sample calculation for steel fibre reinforced foundation slabs according to the Austrian and German design recommendations.     

Torsional response of fibrous reinforced concrete members: Effect of single type of reinforcement

Studies on the torsional behaviour of reinforced concrete members in general and fiber reinforced members in particular are of interest to several researchers as torsional rigidity, torsional stiffness and torsional toughness of the members play a vital role in the analysis of structures subjected to Seismic loads and Wind loads. In the present paper an investigation of the behaviour of steel fiber reinforced concrete members having single type of reinforcement, viz., longitudinal reinforcement or transverse reinforcement, has been presented. Torsion tests on 10 reinforced SFRC members revealed that single type of reinforcement, either longitudinal or hoop reinforcement, can not improve the torsional strength of the member beyond the torsional strength of the plain member without any reinforcement. However, single type reinforcement improved the ductility of the member. Steel fibers improved the cracking torque of the members noticeably.     

高强钢筋混凝土复合受扭构件的延性分析

对压弯剪扭复合受力下,23根高强钢筋混凝土柱模型进行了试验研究,并结合9根普通强度钢筋混凝土柱的复合受扭试验数据,对压弯剪复合受扭构件的延性性能进行了综合分析。探讨了轴压比、相对偏心距、混凝土强度、加载方式及纵筋与箍筋配筋强度比等参数对复合受扭构件延性的影响。分析了以上各参数对构件的初始刚度、开裂刚度和极限刚度的影响及其变化规律。为钢筋混凝土柱的抗震设计提供了理论依据。     

Analytical model and evaluation of maximum crack width for unbonded PSRC frame beam under short‐term service load

Prestressed steel reinforced concrete (PSRC) beam members have the advantages of both ordinary prestressed concrete and SRC members and are usually applied to the structures with large span or heavy load. They are often designed to crack under service load. In this paper, the service‐load behavior is studied based on the experimental results of four unbonded PSRC frame beam specimens. The cracking behavior, deflection, and strains in tensile reinforcement during service‐load stage are described in detail. A computer program for a simple macroelement analysis approach, based on conventional matrix‐displacement method, is written to predict the response of unbonded PSRC frame beam members under service load. The calculation results by this method agree well with the observed experimental results. Moreover, an approach based on two enacted Chinese codes, one for ordinary concrete members (GB50010‐2010) and another for steel‐concrete composite members (JGJ138‐2001), is provided to calculate the short‐term maximum crack width of PSRC beam members. By comparing with the test results, it implies that this approach can be applied to the evaluation of short‐term maximum crack width.     

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.     

Fundamentplatten aus Stahlbeton und Stahlfaserbeton. Experimentelle Untersuchungen zur Gebrauchstauglichkeit und Tragfähigkeit

Reinforced Concrete and Steel Fibre Reinforced Concrete Rafts Experimental tests on serviceability and ultimate loading performance Houses and residential buildings are increasingly built on rafts instead of strip foundations. The main advantages of rafts are more efficient excavation works and easy concreting of the rafts itself. The use of steel fibre reinforced concrete slabs offers economic advantages if there are no special requirements on service ability such as water tightness or crack limitations. At Aachen University of Applied Sciences a comparative experimental study on the load carrying behaviour of rafts made of concrete, reinforced concrete and steel fibre reinforced concrete was carried out. The tests have proven steel fibre concrete as suitable material for rafts in case of sufficient stiffness of the subbase. In case of special requirements on service ability, reinforced concrete or combined fibre and bar reinforced concrete should be used. In that case stresses should be calculated based on the elastic theory.     

Neue Konstruktionsprinzipien bei Tunnelinnenschalen

New Design Philosophy of Inner Tunnel Linings Examinations are presented aiming at the optimisation of reinforcement and thickness of an inner tunnel lining in order to improve the behaviour at serviceability (SLS) and ultimate limit state (ULS). It is expected that especially an acceleration of the construction progress leads to advantages in competition compared with conventionally reinforced linings. A reduced thickness of a lining out of steel fibre concrete (SFB) or a combination of reinforced concrete and steel fibres (SFvSTB) came out best when being experimentally and theoretically examined. Particularly with regard to the cracking formation at SLS, that rules the design of watertight linings, the slender lining is advantageous compared to a conventionally reinforced one (STB).     

Berechnung einer Kombinierten Pfahl‐Plattengründung am Beispiel des Hochhauses “Skyper” in Frankfurt/Main

Am Bespiel des Hochhauses “Skyper” wurden durch den Unterausschuss “Kombinierte Pfahl‐Platten‐ und Pfahlgruppengründungen” des DIN verschiedene Berechnungsverfahren zur Berechnung einer Kombinierten Pfahl‐Plattengründung angewendet. Die Ergebnisse werden verglichen und diskutiert, wobei sich für den vorliegenden Fall herausstellte, dass sowohl numerische Verfahren als auch vereinfachte Verfahren, die auf der Halbraumtheorie basieren, akzeptable Ergebnisse liefern. Für eine Auswahl der geotechnischen Berechnungsverfahren wurden Federmodelle für die Abbildung der Reaktion der Baugrundoberfläche und der Pfähle abgeleitet und mit Ansatz dieser Federmodelle die Fundamentplatte bemessen. Auf dieser Grundlage gibt der Unterausschuss eine Empfehlung zur Anwendung von Berechnungsverfahren. Calculation of a piled raft foundation as a case study for the high rise building “Skyper” in Frankfurt/Main. Various calculation methods were applied on the piled raft foundation of the high rise building ”Skyper“. The results are compared and discussed. Numerical methods as well as simplified methods based on the elastic half space theory lead in the actual case to reasonable results. With the derived subgrade reaction modulus and pile stiffness the raft reinforcement was computed. A recommendation for the application of numerical and simplified methods is given.     

Zum Einfluß der Temperatur auf die Bemessung von Kühlturmschalen aus Stahlbeton

Temperature effects on the design of cooling tower shells. Bending moments caused by temperature constraints substantially influence required reinforcement quantities in cooling tower shells. Important parameters in linear structural analyses are the extents of characteristic thermal actions and their combinations as well as global reduction factors that account for the loss of stiffness by cracking. The sensitivity to variations in temperature scenarios is presented using numerical simulations of a representative cooling tower shell and the design specifications of “BTR‐Kühltürme (2005)”. The characteristic design‐scenarios are simulated in geometrically and materially nonlinear computations to realistically estimate the loss of stiffness by cracking, the influence of temperature effects on the ultimate load bearing capacity as well as actual extents of steel and concrete stresses.     

Torsion und Querbiegung in Plattenbrücken,gegebenenfalls mit einbetonierten Stahlträgern (WIB‐Bauweise)

Torsion und transverse bending in plate bridges, also those containing cast‐in steel beams (WIB‐construction). In usual reinforced‐concrete plate bridges, torsion and transverse bending are superfluous for equilibrium. These secondary moments depend on the assumed stiffness and will be unnecessarily overestimated in a homogeneous elastic analysis without consideration of cracking. This results in excessive transvers reinforcement, particularly for railroad bridges containing cast‐in steel beams. Apparently paradoxical aspects of the plate twisting moment are clarified. This facilitates insight into modeling plates by gridworks. Procedures to determine the strain‐induced stress in the transverse reinforcement are described.     

Dünnwandige,mikrobewehrte Betonbauteile unter Querkraftbeanspruchung

Shear strength of thin‐walled, micro‐reinforced concrete members Within the second funding period of the DFG Priority Programme 1542 ”Concrete Light“ investigations on the load‐bearing behavior of ”Ultra‐lightweight, Thin‐walled Tubular Concrete Members“ are carried out at the IBMB, division of concrete construction of the TU Braunschweig. Due to the currently insufficient amount of investigations dealing with the shear strength of micro‐reinforced concrete (ferrocement) members, fundamental studies had to be performed. These include experimental and theoretical investigations on the shear strength of profiled, thin‐walled concrete beams with micro‐reinforced webs. The performed tests showed the improved cracking behavior and failure notice of micro‐reinforced specimens, when compared to conventionally reinforced specimens. Furthermore, the conservative and thus secure estimation of the shear strength of micro‐reinforced beams using the design approaches provided by EC2+NA or ACI 318 is proven.     

Rissbildung und Zugtragverhalten von mit Fasern verstärktem Stahlbeton am Beispiel ultrahochfesten Betons

Crack Formation and Tensile Behaviour of Concrete Members Reinforced with Rebars and Fibres exemplified by Ultra‐High‐Performance Concrete Part 1: Crack Mechanical Relationships When combining conventional non‐pre‐stressed or pre‐stressed reinforcement with fibres, differences in the load‐carrying and deformation behaviour arise in comparison to the well‐known reinforced and pre‐stressed concrete. This fact holds true comparably for all concrete classes. However, it is of special interest for ultra‐high‐performance concretes (UHPC), because fibres are added to these concretes generally to improve ductility. With regard to durability, the positive influence of the fibres on the crack formation process and the crack widths in the serviceability range is significant. Especially for enhanced requirements concerning the crack width (order of magnitude: 0.1 mm) with combined reinforcement of rebars and fibres an essential improve compared to reinforced concrete can be achieved. The analysis of the crack formation process presumes the understanding of the different behaviours of the two reinforcing elements ”rebars” and ”fibres”. In part 1 of this contribution, the therefore required mechanical relationships are presented and linked with each other considering equilibrium and compatibility. In part 2 the derived relationships are validated on the basis of experimental investigations on tensile members with combined reinforcement made of UHPC. The application is furthermore illustrated by means of two examples. Because of its universal formulation, the presented proposal is generally applicable to all types of concrete reinforced with rebars and fibres, i.e. it is not limited to ultra‐high‐performance concrete.     

钢桁架混凝土组合剪力墙抗震性能试验研究

采用型钢桁架代替钢筋配置在剪力墙中形成钢桁架混凝土组合剪力墙（以下简称“桁架剪力墙”）,该剪力墙兼具钢结构延性好和混凝土结构受剪承载力高的优点,且能够克服钢结构耐腐蚀、耐火性能较差的缺点,其通过钢桁架替代钢筋更有利于装配化施工。对4个剪跨比为1.65的钢桁架剪力墙进行拟静力试验,通过试验得到的滞回曲线、骨架曲线和刚度退化曲线等,研究了不同轴压比（0.21和0.26）和不同抗剪键（短钢筋抗剪、短钢筋和栓钉共同抗剪）对剪力墙抗震性能的影响。采用有限元软件ABAQUS对钢桁架剪力墙进行参数分析,进一步考察了轴压比（0.2、0.3和0.4）、桁架竖杆含钢率（1.43％、2.09％和2.71％）和腹杆含钢率（1.37％、2.02％和2.64％）对其受剪性能的影响,并提出剪力墙受剪承载力计算公式。研究结果表明：当轴压比大于0.3时,随着轴压比的提升,剪力墙的受剪承载力有下降的趋势;钢桁架设置抗剪键对于剪力墙的受剪承载力影响不大,但能提高剪力墙的刚度和耗能能力;钢桁架竖杆含钢率对剪力墙受剪承载力有较大提升作用,而桁架腹杆含钢率对剪力墙受剪承载力的提升作用较小。计算钢桁架-混凝土剪力墙的受剪承载力时,可不考虑腹杆受压时平面外的失稳问题。     

钢筋混凝土剪力墙轴拉试验和轴拉刚度理论分析

文章完成截面纵筋率为17%、25%的钢筋混凝土剪力墙轴拉试验。试验结果表明：剪力墙轴拉刚度在混凝土开裂前由钢筋和混凝土共同提供,并随轴拉力的增加逐渐下降;在混凝土开裂时轴拉刚度迅速下降;在开裂后混凝土退出工作,轴拉刚度逐渐趋于截面纵筋刚度。基于试验结果,完成剪力墙的轴拉受力特性和刚度变化特征的理论分析,提出能够描述钢筋混凝土剪力墙轴拉刚度变化特征的二阶段计算方法：在混凝土开裂前及开裂时根据混凝土本构模型获得的受拉弹性模量进行计算,在开裂后则引入纵向受拉钢筋应变不均匀系数进行计算。由此得到的理论值与试验结果更为吻合,更能反映剪力墙在轴拉阶段的受力和刚度变化特征。     

Möglichkeiten zur Erhöhung der Festigkeit abrasionsbeanspruchter Betonoberflächen bei wasserbaulichen Anlagen

Possibilities for increasing the abrasion resistance of concrete surfaces in hydraulic structures. The results of abrasion test for textile reinforced concrete layers show that the abrasion resistance of the samples is dependent on the fineness of the reinforcement material as well as the fibre volume. High fibre volume can be achieved by a combination of textile reinforcement and short fibre reinforcement. These samples show reduced abrasion values of about 50% compared to the purely textile reinforced samples and likewise lower abrasion values to the non‐reinforced samples. Significant improvements concerning the abrasion behaviour are possible by further adjustment and optimisation of the used fine grade concrete matrices and the reinforcement materials. Beside a higher surface resistance of thin concrete layers against erosion and abrasion loads the use of near surface textile reinforcements leads to additional structural strength against other loads.     

基于STM理论钢纤维混凝土深受弯构件裂缝宽度试验研究

通过7根钢纤维混凝土深受弯构件的弯曲性能试验,分析了钢纤维掺量及配筋率对深受弯构件跨中截面混凝土应变、纵筋应变、破坏形态及裂缝宽度的影响。基于STM理论量化钢纤维、钢筋以及混凝土三者在受力过程中的组合作用,提出了适用于钢纤维混凝土深梁最大裂缝宽度的理论计算式,并与实测结果进行比对分析。研究结果表明:较普通深受弯构件而言,钢纤维混凝土深受弯梁的开裂荷载增幅11%~20%,极限荷载提高10%~16%,提高配筋率,开裂荷载提高约22%,极限荷载提高20%~31%;提高配筋率或钢纤维掺量,均可使试件破坏模式由正截面破坏向斜截面破坏转变;钢纤维掺加50、78 kg/m^3后,裂缝宽度可减少13%~29%;试件配筋率提高0.142%,裂缝宽度减少33%;推导出的理论计算式计算得到的最大裂缝宽度与实测值吻合。     

Zeitabhängiges Verhalten von Makrokunststofffaserbeton und dessen Einfluss auf die Bemessung von Industriefußböden

Time Dependent Behaviour of Macro Synthetic Fibre. Reinforced Concrete and its Influence on the Design of Industrial Slabs on Ground Material tests and tests on structural elements with synthetic macro fibre reinforced concrete are presented. The experimental program included the investigation of the load carrying capacity and the deformation behaviour under short‐term as well as under long‐term loading conditions. Long‐term load tests were carried out on pre‐cracked fibrereinforced concrete beams to measure the load level above which creep failure can occur. At service load level creep coefficients for a time period of up to three years were determined. Centre point load tests were carried out on concrete slabson‐ground. Two slabs were reinforced with steel mesh and two with synthetic macro fibres only. The tests were performed under short‐term and long‐term loading conditions over a period of 18 month. The current main application of synthetic macro fibre reinforced concrete is slab‐on‐ground. Slabs‐on‐ground can be designed under the assumption of elastic subgrade reaction. The concrete slab itself can be calculated either by elastic theory for uncracked concrete or by yield line theory taking fibre reinforcement into account. Based on the test results of the experimental programme, design recommendations for permanently loaded slabs‐on‐ground are presented.     

Rissbildung und Zugtragverhalten von mit Fasern verstärktem Stahlbeton am Beispiel ultrahochfesten Betons

Wegen des Problems möglicher Inhomogenitäten der Faserverteilung/‐ orientierung ist der Einsatz von Fasern als alleinige Bewehrung im konstruktiven Ingenieurbau auf wenige Anwendungsgebiete beschränkt (z. B. Aufnahme von Zwangbeanspruchungen). Unter Zugbeanspruchung lässt sich zudem mit den in der Praxis für normalfeste Betone gebräuchlichen Fasergehalten nach der Erstrissbildung kaum ein verfestigendes Verhalten erzielen. Kombiniert man jedoch Stabstahlbewehrung und Faserbewehrung zu einem stahlfaserverstärkten Stahlbeton, so addieren sich die Vorteile beider Verbundwerkstoffe gleichermaßen. Besonders bei erhöhten Anforderungen an die Rissbreite (Größenordnung: unter 0, 1 mm) kann durch gemischte Bewehrung aus Stabstahl und Fasern eine wesentliche Verbesserung gegenüber Stahlbeton erzielt werden. Im Teil 1 dieses Beitrags wurden die für das Verständnis der unterschiedlichen Wirkungsweisen der beiden Bewehrungselemente “Stabstahl” und “Fasern” erforderlichen mechanischen Zusammenhänge dargestellt. Im Teil 2 erfolgt eine Überprüfung der abgeleiteten Beziehungen anhand experimenteller Untersuchungen an gemischt bewehrten Zugelementen aus ultrahochfestem Beton (UHPC). Für UHPC erreicht die Thematik besondere Aktualität, da aus Gründen der Duktilität der Einsatz von Fasen bei diesen Betonen die Regel ist. Der Nachweis der Begrenzung der Rissbreite bei kombinierter Bewehrung wird zudem an zwei Rechenbeispielen veranschaulicht. Crack Formation and Tensile Behaviour of Concrete Members Reinforced with Rebars and Fibres exemplified by Ultra‐High‐Performance Concrete. Part 2: Experimental Investigations and Examples of Application Due to the problem of possible inhomogeneities of fibre distribution/orientation the use of fibres as sole reinforcement is limited in engineering practice to few applications (e. g. coverage of stresses due to constraints). In addition, it is hardly possible to obtain strain hardening after first crack formation with fibre contents commonly used for normal strength concretes. However, if steel fibre reinforcement is used in combination with bar reinforcement, the advantages of both components are additive in the composite material. Especially for enhanced requirements concerning the crack width (order of magnitude: 0.1 mm), with combined reinforcement of rebars and fibres an essential improvement compared to reinforced concrete can be achieved. In part 1 of this contribution the mechanical relationships required for the understanding of the different behaviours of the two reinforcing elements “rebars” and “fibres” have been presented. In part 2 the derived relationships are validated on the basis of experimental investigations on tensile members with combined reinforcement made of ultra‐high‐performance concrete (UHPC). For UHPC the topic is of special interest, because fibres are added to these concretes generally to improve ductility. The crack width control with combined reinforcement is furthermore illustrated by means of two examples.     

Tübbinge aus Stahlfaserbeton: Optimierung der Bewehrung durch experimentelle Untersuchungen

Steel Fibre Concrete for Precast Tunnel Segments The aim of these studies was to evaluate on precast tunnel segments the possibility of partially or totally replacing the usual steel reinforcing bars with steel fibres in a complex static system. In a first step, tests were carried out on connecting joints between precast segments and in a second step on whole tunnel segments coming from the precasting site of the Oenzberg tunnel (Swiss Railways, Berne–Zurich). They are 5.42 m long, have a width of 0.85 m and are 0.30 m thick. The segments were placed horizontally under a double hydraulic jack testing installation in the EIA‐FR structure laboratory. The double hydraulic jack introduced vertical forces while normal forces were produced by two metal pull‐rods simulating an arch‐effect. These experimental studies on connecting joints and on precast tunnel segments show good behaviour on the part of steel fibre reinforced concrete under such combined loads. This study highlights the major impact of compression forces in the bent section. Therefore, fibre reinforced concrete appears particularly well‐adapted for precast tunnel segments subjected to high compression loads. However, these studies also indicate the inadvisability of totally renouncing the use of conventional reinforcement in case of large tunnel segments.