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1、Chapter3Compositefloorwithsteelprofiled压型钢板压型钢板-混凝土组合楼板混凝土组合楼板ByProfessorShimingChenLectureNotesforPresentation2013OBJECTIVE/SCOPETo describe the design of one-way spanning composite slabs, formed using profiled steel sheeting and a concrete topping, including consideration of ultimate and serviceab
2、ility limit state design for building structures.压型钢板、压型钢板分类压型钢板-混凝土组合楼板应用范围设计方法构造3.1Introduction压型钢板-混凝土组合楼板是指将压型钢板与混凝土通过某种构造措施组合成整体而共同工作的受力构件。Composite flooring system consists of a cold-formed, profiledsteelsheetwhich acts, not only as the permanent formwork for an in-situ cast concrete slab, but
3、 also as the tensile reinforcementThe essential composite action between the steel deck and the concrete slab is provided by some form of interlocking device, capable of resisting horizontal shear and preventing vertical separation at the steel/concrete interface. Composite slab with profiled steel
4、sheetit provides a working platform for construction.it acts as formwork for the concrete slab.it constitutes bottom reinforcement for the slab.Profiled Steel sheeting(a pattern of embossments) 板面的齿槽与压痕可提供界面粘结力；界面的摩擦粘结等 Construction stage: place the profiled steel sheeting over the support beams Con
5、struction stage: weld studs through the steel sheeting with portable welding gunConstruction stage: place the light steel reinforcement/ steel meshConstruction stage: cast concreteTypesofProfiledSheet压型钢板类型压型钢板类型Re-entranttypes闭口型压型钢板闭口型压型钢板Trapezoidaltypes开口型压型钢板开口型压型钢板Advantagesidentifiedasthefoll
6、ows:Thesteeldeckacts as permanent shuttering for the in-situ cast concrete slab, with a consequent saving in time and labor.It once in position, immediately provides a platform to support construction loads and a safe, sturdy working surface. It acts as the tensile reinforcement.The steel deck geome
7、try can result in a reduction of labor about 30% in the amount of concrete fill required for the floor, significant reduction in dead weight loads .3.2. DESIGNPRINCIPLES设计验算设计验算 DesignSituations（设计工况）（设计工况） Two distinct structural states must be checked: firstly, the temporary state of execution, wh
8、en only the sheeting resists the applied loads（construction stage 施工阶段）; secondly, the permanent state, after the concrete is bonded to the steel giving composite action（composite stage 正常使用阶段）.Relevant limitstatesand loadcasesare considered for both designsituations.a)Steeldeckshuttering（施工阶段） Veri
9、fications at the ultimate limit and serviceability limit states are required, with respect to the safety and serviceability of the steeldeckacting as formwork for the wet concrete. The effects of any temporary props used during execution, must be taken into account in this design situation.b)Composi
10、teslabs（正常使用阶段） Verifications at the ultimate limit and serviceability limit states are required, with respect to the safety and the serviceability of the compositeslabafter composite behaviour has commenced and any props have been removed.设设计计考考虑虑因因素素：Three major aspects identified forconsideration
11、 during the design of a compositeflooringdeck:oThe steel deck itself must be sufficiently strong and rigid to support the weight to wet concrete during casting-construction stage behavior.oThe steel deck acting compositely with the hardened concrete, and spanning between the supporting steel beams,
12、must support the imposed live loading-composite slab action.oThe steel beams, acting compositely with the hardened concrete through the stud shear connectors must support the imposed live loading-composite beam action.3.2Criteriaforthedesignofcompositefloors设计准则设计准则In design, it is necessary to ensu
13、re that the strength and deflections both during construction (when the concrete is still green) and in service (when composite action has been achieved) are satisfactory. Constructionstage: the profiled steel deck alone withstands the weight of wet concrete, workman and equipment. Compositeslabstag
14、e:the hardened concrete slab, acting compositely with the profiled steel sheet, spans between the supporting beams and carries the imposed live loadsKeypointsforConstructionstage-Profiled steel as shutteringInstallation of the sheeting is carried out by laying one or more span lengths over the suppo
15、rting beams. The sheeting behaves as a folded plate structure and, for low load levels, the behavior is similar to simple beam behavior.At higher load levels, buckling of the component plates may occur. The prediction of buckling stresses on the component plates can be achieved using classical or en
16、ergy methods. The sheeting has to have adequate bending strength and stiffness.The section properties of profiled sheets can be computed based on the analytical methods provided by design codes. Manufacturers prefer to carry out load tests on their products to assess full capacity and provide load-s
17、pan tables appropriate to each profile.Propping can dramatically reduce deflections.KeypointsforcompositestageThe steel deck acts as tensile reinforcement to the slab and the development of composite action depends entirely upon adequate transference of horizontal shear forces at the steel/concrete
18、interface. To evaluate the shear bond resistance at the interface between the concrete and the profiled deck, Porter and Ekberg (1976) proposed a testing program (shear-bond test) now worldwide adopted in determination of the shear bond resistance for composite slabs. 3.3BEHAVIORANDANALYSIS Steel de
19、ck（混凝土结硬前：压型钢板）During execution when the concrete is wet, the steel deck alone resists the exterior loads. Its behavior is then comparable to that of profiles used for roof decking.The steel deck is subjected mainly to bending and shear; compression due to bending may arise in either the flanges or
20、the web; shear occurs essentially near the supports. Once the concrete has hardened the steel deck and concrete combine to form a single structural unit, the composite slab.Behavior of a composite slab is analogous to that of a conventional reinforced concrete slab.The bond between the steel deck an
21、d concrete may not be fully effective and longitudinal slip may occur before the steel deck yields.CompositeslabfailuremodetypesFailure type I :弯曲破坏(flexural failure)：Failure type II :纵向剪切破坏(longitudinal shear failure, shear-bond failure.)：Failure type III :垂直剪切破坏(vertical shear failure)Loaddeflecti
22、onresponseofbrittleandductileslabsThe brittle or ductile mode of failure depends on the characteristics of the steel-concrete interface.ShearbondfailureBrittle behavior in which slip causes a sudden decrease in load carrying capacity as the surface bond is broken. The extent to which the load reduce
23、s is dependent on the effectiveness of the mechanical embossments. Ductile behavior in which case the mechanical shear connection is capable of transferring the shear force until failure occurs. This may be flexural or by longitudinal shear.Behavior of Composite Slabs Longitudinalshearincompositesla
24、bs Three types of shear connection between a profiled steel sheet and a concrete slab: (1) natural bond between the two, known as frictional interlock (2) mechanical interlock provided by pressing dimples or ribs into the sheet (3) end anchorage provided by means of shot-fired pins, or by welding st
25、uds through the sheeting to the steel flange.DeterminationofthelongitudinalshearstrengthThe m-k or shear-bond testMode 1 brittle (or non-ductile) behaviorMode 2 ductile behavior Empirical method for evaluating longitudinal shear resistanceThe merits of using profiled steel deck composite floors: its
26、 efficiencies in construction and its higher load carrying capacity over the traditional steel deck as shuttering. The shear-bond resistance is essential to the interaction between steel sheeting and concrete at the sheet-concrete interface, and governs the composite slab design. Shear-bond tests mu
27、st be carried out to calibrate different types of steel decks. Normally, slabs are tested with no shear connectors. Relationship between failure mode and span If longitudinal shear resistance of the slab is not sufficient, it can be increased by the use of some form of end anchorage.Partialconnectio
28、nmethodThe partial connection method can also be used for the verification of the resistance to longitudinal shear. (slabs with ductile behavior).The verification procedure is illustrated in the Figure above for two slabs with different types of loading and span. Resistant moment diagrams and design
29、 bending moment diagrams are plotted against Lx on the same axis system. For any cross-section of the span, the design bending moment MSd cannot be higher than the design resistance MRd.Partialconnectionmethod(another expression)The partial connection method can also be used for the verification of
30、the resistance to longitudinal shear. The partial-interaction design method requires that the mean ultimate shear stress is determined. Vl design longitudinal shear force of the composite slab Vu shear bond resistance determined by tests组合楼板前提：压型钢板与混凝土组合作用，要确保组合楼板前提：压型钢板与混凝土组合作用，要确保界面黏结强度：界面黏结强度：She
31、ar-bondstrengthrequirement纵向抗剪强度验算纵向抗剪强度验算AnalysisofCompositeSlabs（组合楼板（组合楼板受力分析）受力分析）linear elastic; linear elastic with moment redistribution（线弹性分析、考虑弯矩重分布的线弹性分析）.plastic according to the theory of plastic hinges（极限状态的塑性分析）.Higher order analysis taking into account non-linear behaviour and slip（考虑
32、非线性特性以及滑移的高阶分析）.VerificationofProfiledsteelsheetingasshutteringatultimatelimitstate(ULS)The sheeting should resist to construction and wet concrete loads. Bending moment resistance of the section is then given by:Verificationofprofiledsteelsheetingasshutteringatserviceabilitylimitstate(SLS)For the u
33、ltimate limit states (强度极限状态；uncracked section)For the serviceability limit states（使用极限状态）The slab is comparable to a continuous beam of constant inertia, equal in value to the average inertia of the cracked and uncracked section（均匀截面模量）.Long-term loading effects on the concrete are taken into accou
34、nt using a variation in the modular ratio Ea/Ec（考虑长期、短期效应时引入混凝土模量系数来简化）. For simplification.3.4RESISTANCESOFSECTIONSSection I: ultimate moment of resistance failure for positive bending.Section II: ultimate moment of resistance failure for negative bending.Section III-IV: ultimate resistance to vert
35、ical shear failure.Section V: ultimate resistance to longitudinal shear failure.Verificationofcompositeslabatultimatelimitstate(ULS)Sagging bending resistance. That failure mode is reached if the steel sheeting yields in tension or if concrete attains its resistance in positeslabatultimatelimitstate
36、Case 1 Plastic neutral axis above the sheetingCase 2 Plastic neutral axis in steel sheetingCase 1 Plastic neutral axis above the sheetingCase 2 Plastic neutral axis in steel sheetingVerification of the hogging bending resistanceBendingresistanceanddeflection Atconstructionstage: bending resistance o
37、f the steel deck is checked as the following: Deflection of the steel deck must satisfy the deflection requirement as:Atcompositeslabstage Bending resistance, diagonal shear resistance and shear bond resistance should be checkedIf sufficient shear bond is provided at the interface between concrete a
38、nd steel sheeting, its bending resistance normal to strong bending direction as the following: Positive bending : When a composite slab spans continuously over supporting beams, with negative reinforcement over the internal support region, the negative moment resistance of the slab can be calculated
39、. Negative bending:The bending resistance normal to weak bending direction is treated as reinforced concrete slab. Vertical shear verificationVerticalandpunchshearresistance（抗冲切承（抗冲切承载载力）力）punch shear resistance is checked as Longitudinalshearresistance(纵纵向抗剪承向抗剪承载载力）力）To enable a composite slab, th
40、e longitudinal shear bond resistance at the interface between the concrete and the profiled deck should be sufficient.Diagonalshearresistance（斜截面抗剪）（斜截面抗剪）Deflections 组合板挠度，按荷载短期效应组合与荷载长期效应组合计算。 For deflection under short term load（荷载短期效应）, the area of concrete section is divided by a E (a E = E s/E
41、 c);for deflection under long term load（荷载长期效应）, divided by 2a E. 3.5Somedetailingrequirements （构造要求）（构造要求）Detailingis to ensure that the full strength of components can be developed under the most adverse conditionsThe effects of corrosion on steel sheets about 1 mm thick are more severe than on th
42、icker sections, so the materials are usually galvanized.The overall depth of a composite slab should not be less than 90 mm, while the distance between the top surface of concrete and the top of the steel ribs should not be less than 50 mm. The concrete grade is better over C20. Therequiredbearingov
43、erlapsofcompositeslabsoverthedifferent（构造要求）（构造要求）When shear studs are welded through steel profiles to the top flange of a steel beam, the diameter of the studs should be 13 to 16 mm if l3 m, and 16 to 19 mm if 3 m l M Diagonalshearstrength Take one wave length (200 mm) as a checking unit, subjecte
44、d to shear force as: V1 = V200/1000 = 7.0 200/1000 = 1.4 kNf t = 1.10 N/mm2 (C20)0.7 f t bbm h0 = 0.71.10(70+50)/2115 = 5.31 kN V1 Calculationofdeflection Take one wave length (200 mm) as a checking unit.Elastic modulus of concrete: Ec = 2.55104 N/mm2 aE = E s/E c = 2.06105/2.55104 = 8.08 Deflection
45、 under short term loading Equivalent width of concrete slab: Equivalent width of rib: second moment of area of the transformed section of one wave length of composite slab second moment of area per meter of slab: Isk = 5 Isk = 5475104 = 0.238 108 mm 4 pk = gk + qk = 2.954 +2 = 4.964 kN / mDeflection
46、 under long term loading SteelDeckP36233.7Advancedcompositefloorsystemsa number of trends in modern construction have led to the development of more advanced forms of composite construction Fabricated beams with tapped webs HaunchedbeamsCompositetrusses StubgirdersParallel beam grillage systemBeamwi
47、thsinglewebopeningsBeams with web openings Cellular and castellated beams Slimfloorsystem3.8CONCLUDINGSUMMARYThe design of a composite slab must consider the performance of the profiled steel sheeting, when it acts as shuttering for the wet concrete during execution, as well as the composite perform
48、ance of the steel and hardened concrete under the imposed floor loading.At the execution stage, the profiled steel sheeting acts as a thin-walled member. Its design must take into account the possibility of local buckling.The design of the composite slab must consider the resistance to positive and
49、negative moments and also to vertical and longitudinal shear.The resistance to longitudinal shear at the steel/concrete interface is largely derived from embossments in the steel sheet or from connectors placed at the ends of the spans. Empirical methods are used to ensure adequate shear resistance.
50、shallow floor systems, which combine the floor and slab in the same vertical space, offer a competitive alternative to concrete flat slab construction.In seeking an economic design, consideration should be given to overall project costs and flexibility for future changes in building use and services
51、.Reviewpoints:What is the longitudinal shear?Which are governing factors in design of a composite slab?Determination of the longitudinal shear by shear bond tests and defects of the m-k method.简述压型钢板-混凝土组合板在施工阶段和使用阶段有哪些破坏模式。Further reading of design methods for resistance to fireFireresistance （抗火性能
52、）The composite floor must provide satisfactory performance in terms of stability, integrity and insulation in the event of fire. The thickness of the slab is directly related to its insulation capacity. Integrity is ensured by the sheeting which acts as a shield to concrete and helps to contain spal
53、ling.Stability of the structure depends upon conventional reinforcement provided for the slab. A small amount of additional reinforcement may be needed depending upon the extent of fire resistance needed. Based on a large number of fire tests, many carried out in association with British SCI, a design guide has been published, which provides practical assistance in assessing fire resistance of composite slabs.抗火评定：fire-proof rating: 1 hr, 2 hr, etc.
