1、Composite Structures of Steel and Concrete 钢钢-混凝土组合结构混凝土组合结构 Todays Lecture:Part 1 what are composite structures Part 2 About the course&assessment Part 3 Introduction to composite structures Basic structural components:composite beams composite slabs composite columns What are composite structures?
2、The structures consist of members of combining structural steel and concrete effectively.Composite construction Structural systems in which there is interaction between concrete and structural steel Why is composite construction?Example 1Composite beamNon composite beam67in-situ concrete on shutteri
3、ngpartially prefabricated slabsfully prefabricated slabs89 Composite construction is a product of recent design and construction practice,began just prior to the start of the twentieth century.Many countries have their own stories to tell about composite construction.The first composite construction
4、 with design approval appeared in the year of 1894 when a bridge and a building were constructed in the USA,namely,the Rock Rapids Bridge in Rock Rapids,Iowa,and the Methodist Building in Pittsburgh.Many novel advantages:combining concrete and steel in the design of the primary structure for a high-
5、rise building.Using the best properties of both materials to solve the design challenge can result in a cost-effective solution that best meets a projects architectural and functional requirements.Strictly composite:interaction of two materials within one construction element(e.g.a concrete-filled t
6、ubular steel column)the philosophy of mixed building technology includes the combination of construction elements or members built up with different construction methods(e.g.concrete column in combination with a composite beam and a prefabricated slab).Introduction to Composite Constructionsome appl
7、icationsLatitude at World square-SydneyLatitude at World square-SydneyShanghai Tower in constructionBrief Introduction to Shanghai Tower Location:Lujiazui Finance and Trade Zone,Pudong district,Shanghai,China Owner/Developer:Shanghai Tower Construction and Development Co.,Ltd.Design Architect:Gensle
8、r Local Design Institute:The Architectural Design&Research Institute of Tongji University Structural Engineers:Thornton Tomasetti Mechanical,Electrical and Plumbing(MEP)Engineers:Cosentini Associates Date of Commence:Sep.18,2010 Date of Anticipated Completion:Dec.30,2014上海中心大厦结构体系特点上海中心大厦结构体系特点 地上12
9、4层,高632m,采用巨型框架-核心筒-伸臂桁架抗侧力结构体系,钢-混组合结构。巨型框架结构由8根巨型柱、4根角柱以及8道位于设备层箱形空间环带桁架组成 核心筒为钢筋混凝土结构,截面平面形式根据建筑功能布局由低区的方形逐渐过渡到高区的十字形；1 2区核心筒翼墙和腹墙中设置钢板,形成了钢板组合剪力墙结构,墙体中含钢率为115%410%Composite floor Aims of the course To gain knowledge of composite structures To master design principle of composite structures To kn
10、ow key research/application topics in composite structures To develop comprehensive understanding of steel and concrete composite construction via summarizing and reporting on the selected topics Reference books Composite Structures of steel and concrete:Beams,Slabs,Columns,Frames for Buildings by R
11、.P.Johnson Blackwell Publishing,2004 Composite Construction,by D.Nethercot,Pron Press,2004 Steel and Concrete Composite Structures,Lecture Notes by Shiming Chen,2010 钢-混凝土组合结构,by 陈世鸣，中国建筑工业出版社，2013年 ESDEP Course web-site Useful Link:http:/www.fgg.uni-lj.si/kmk/esdep/master/toc.htm Homework:review an
12、d preview;read reference books some design/calculation exercisesExamination:Quiz&Report Outcome and Assessment Students should develop good/excellent understanding of composite construction The assignment will allow students to get a feeling on how material and geometric parameters affect the struct
13、ural response Quiz：To test the ability in developing analytical tools which are required in design for strength and/or serviceability limit states Assessment will be formed as:60%-assignment;40%-quizChapter 1 Composite Construction-General OBJECTIVE/SCOPE To introduce steel-concrete composite member
14、s and construction;to explain the composite action of the two different materials and to show how the structural members are used,particularly in building construction.1.1 Why is composite construction Traditional Structures for buildings:Masonry structures Wood structures Steel structures Steel rei
15、nforced concrete structures Steel-concrete composite structures (composite structures as brief)Other composite materials(FRP)Comparison with other methodsAlternative Steel Beam TypesIn a composite floor system the concrete acts together with the steel to create a stiffer,lighter,less expensive struc
16、ture (Allen 1999)Metal DeckingSteel deck-concrete:composite construction Composite decking works together with the concrete fill to make a stiff,light-weight,economical floor system Composite decking is available in various profiles and thicknessesFeatures:Shear connector installation The additional
17、 subcontractor needed for shear connector installation will increase field costsInstallation of shear connectors is another operation to be included in the scheduleA concrete flatwork contractor who has experience with elevated composite slabs should be secured for the job A typical composite multi-
18、storey steel-framed building during construction-a commercial building in London A typical composite multi-storey steel-framed building during execution-a factory building for the car industry in Germany The combination of concrete cores,steel frame and composite floor construction has become the st
19、andard method for multi-storey constructionBasic forms of composite constructionConventional and innovative composite beamsComposite beams1.2 Composite action in beams Consisting of a steel section acting compositely with concrete slab.The two materials are interconnected by means of mechanical shea
20、r connectors.A simply supported beams:under vertical loads,正（下垂）sagging bending moments cause tensile force in the steel section and compression in the concrete deck,optimum use of each material.At the steel/concrete interface,mechanical shear connectors are provided to resist the horizontal shear.I
21、f slip is free to occur,each component will act independently.If slip is eliminated,the slab and the steel member will act together as a composite unit.Definitions for strength and stiffness properties Complete and partial shear connection is regard to the design bending strength of the beam other t
22、han the horizontal shear resistance Complete or incomplete interaction results in a more or less stiff composite beam Composite beams are designed using plastic design methods and partial interaction theory,combing steel and concrete to great effectShear connectors are commonly referred to as“studs”
23、or“shear studs”in the tradeThey are available in a range of sizes,materials,and gradesHeaded studs(as shown)are most commonly usedShear ConnectorsTypes of shear connectorsShear connectionsDepending on the welding process used,the tip of the shear connector may be placed in a ceramic ferrule(arc shie
24、ld)during welding to retain the weldShear connectors create a strong bond between the steel beam and the concrete floor slab which is poured on top of the metal decking This bond allows the concrete slab to work with the steel beams to reduce live load deflectionShear Connectors Composite beams,subj
25、ect mainly to bending,consist of a steel section acting compositely with one(or two)flanges of reinforced concrete1.3 Composite floors or slabs Composite floor:steel deck with additional indentations or embossments acts as both permanent formwork during concreting and tension reinforcement after the
26、 concrete has hardened.Main advantages to the designer and client speed and simplicity of construction lighter construction than a traditional concrete less on-site construction high tolerances/under controlled factory conditions/quality procedures.Rquired composite action can be achieved if:a.Mecha
27、nical interlock be provided by deformations in the steel profile b.Frictional interlock for profiles shaped c.End anchorageMetal decking ready to be laid by handEdge trims for metal deck floor constructionFloors using metal decking which is embossed to provide composite action.Composite slabAs an al
28、ternative to welding,powder actuated tools may be used to attach metal decking to structural steel Powder actuated tools use the expanding gases from a powder load,or booster,to drive a fastenerA nail-like fastener is driven through the metal deck into the steel beamThe powder actuated tool,powder l
29、oad,and fastener must be matched to the thickness of the structural steel beam flangesInstallation of DeckingShear connectors are installed after the decking is in placeShear connectors may be installed by the steel erection contractor or a specialty shear connector installerThe welding equipment re
30、quired for installation is provided by the shear connector installerDaily output for shear connector installation averages about 1000 per day depending on the size of the connectors(Means 2004)Installation of Shear ConnectorsThe electrical arc process is commonly used for stud weldingAn arc is drawn
31、 between the stud and the base metalThe stud is plunged into the molten steel which is contained by the ceramic ferrule 环箍The metal solidifies and the weld is completeThe ferrules are removed before the concrete is poured(ASCE 2002,AWS 2004)Installation of Shear ConnectorsConcrete is installed by a
32、concrete contractor on top of the composite metal decking,shear connectors,and welded wire fabric or rebar grid(crack control reinforcing)Pumping is a typical installation method for concrete being placed on metal decking10,000 to 15,000 sq.ft.of concrete slab may be installed per day depending on s
33、lab thickness and crew size(Ruddy 1986)Installation of ConcreteThere is an art to the placement of concrete on metal deck and structural steelThe work,unless shoring is used,must be executed on a deflecting surfaceAn experienced concrete contractor should be employed for this workConcrete should be
34、deposited over supporting members first,then spread toward the deck midspansThe accumulation of a deep pile of concrete must be avoided(AISC 2003,ASCE 2002)Installation of ConcreteThe contractor must be aware of camber in the beams and the expected deflectionsConsultation with the structural enginee
35、r may be necessaryAs the concrete cures it forms a connection with the composite metal decking and shear studsThe composite floor system is now complete(AISC 2003)Installation of ConcreteThe shear connectors used in composite construction require specific inspections and quality controlTesting proce
36、dures are specified in the contract documents or by a local building authorityAWS D1.1 Structural Welding Code Steel,Section 7:Stud Welding(AWS 2004)specifies the tests and inspections for shear studsQuality ControlAs described in the AWS code(AWS 2004),jobsite conditions may exist that prohibit or
37、delay the stud welding operation The primary issues affecting the installation of the shear connectors are:Moisture on the decking or ferrulesMoisture between the decking and the steel beam belowA steel temperature below 0 FIn the pictures above,a torch is being used to remove snow(left)from the are
38、as where shear studs are to be installed(right)Quality ControlRequired quality control procedures for shear connectors include pre-production tests and fabrication inspectionsPre-production testing is performed by the shear stud installer at the beginning of each work shift and includes the followin
39、g steps:The stud installer performs visual fabrication inspections as studs are installedOther testing may be specified or may be necessary if all visual inspections are not passed (SIN 1998)1.Weld two sample studs2.Inspect for flash 3.Perform bending test4.Equipment settings are recorded Quality Co
40、ntrolWhen used appropriately,typical overall building costs will be less for composite construction than non-composite constructionCost Impacts of Composite ConstructionThe duration for the installation of shear studs is project dependent and should be considered on a project by project basis Shear
41、stud installation usually has little or no impact on the overall project scheduleScheduling of Composite ConstructionIt may be possible,depending on the size of the structure and the sequencing of erection and decking,to install the shear studs as erection proceedsIt may also be possible to have a m
42、ajority of the shear connectors in place and begin placing concrete for the floor slabs while structural steel is being erected in another area of the buildingOn the structure shown above part of the composite first floor slab was placed while erection of the structural steel for the third floor pro
43、ceededScheduling of Composite Construction1.4 Composite columns Types of composite columns concrete encase steel columns/concrete filled steel tube columns/rolled section column partly encased in concrete Cross section of composite columnTubular column with shot fired nails as shear connectorsand re
44、inforcement on site Encased steel composite columns:Full composite interaction without any slip at the steel-concrete interface is assumed;The complete interaction must be ensured by means of mechanical connections.Concrete-filled composite columns Steel sections:rectangular and circular tubes Compl
45、ete interaction between the structural components of the column,through direct interface bondBeam-to-Column Connection:vertical shear transfer between beams and composite columns1.5 Composite bridges Medium-span composite bridges(from 35 m up to 60 or 70 m)are normally constructed from welded,built
46、up,steel plate girders and a wide reinforces concrete deck Smaller spans,from 20 up to 35 m,rolled steel sections are more popular Special considerations:during erection and concreting(usually without intermediate propping),during service life etc.1.6 Advantages over the traditional reinforced concr
47、ete or steel structures:high strength-to-weight ratios;structural integrity;durable finishes;dimensional stability;sound absorption and etc.One important argument:use of rolled steel sections,profiled metal decking and/or prefabricated composite members speeds up construction.Example:Steel framing s
48、upporting cast-in-place reinforced concrete slab construction was historically designed with no consideration given to the composite effect of the steel and concrete acting together.In composite construction,mechanical shear connectors to resist the horizontal shear which develops during bending are
49、 provided,so that the load carrying capacity of the structure is increased.Composite floor construction is highly competitive,if spans are increased to 12,15 and even 20 m.1.7 Development and applications Before 1950s:Individual case of using the forms of combination of steel/iron and concrete to pr
50、event metal from corrosion and fire attackRecognition beneficial effects on strength and stiffness in the structures with the combination:mainly:encased steel beams,encased steel columns,and concrete filled steel tubesApplication in reconstruction of bridges and building destroyed in the second Worl
