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1、Chapter 3 Composite floor with steel profiled压型钢板-混凝土组合楼板,By Professor Shiming Chen Lecture Notes for Presentation2013,OBJECTIVE/SCOPETo describe the design of one-way spanning composite slabs,formed using profiled steel sheeting and a concrete topping,including consideration of ultimate and service
2、ability 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,3.1 Introduction,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,profiled steel sheet which acts,not only as the permanent formwork for an in-situ cast concrete sla
3、b,but 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 st
4、eel sheet,it 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
5、,Construction stage:weld studs through the steel sheeting with portable welding gun,Construction stage:place the light steel reinforcement/steel mesh,Construction stage:cast concrete,Types of Profiled Sheet压型钢板类型,Re-entrant types闭口型压型钢板,Trapezoidal types开口型压型钢板,Advantages identified as the follows:T
6、he steel deck acts 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 geometry ca
7、n 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.DESIGN PRINCIPLES 设计验算,Design Situations（设计工况）Two distinct structural states must be checked:firstly,the temporary state of execution,when only the sheeting
8、 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 limit states and load cases are considered for both design situations.,a)Steel deck shuttering（施工阶段）Verifications at th
9、e ultimate limit and serviceability limit states are required,with respect to the safety and serviceability of the steel deck acting 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)Composite slabs（正常使用阶段）
10、Verifications at the ultimate limit and serviceability limit states are required,with respect to the safety and the serviceability of the composite slab after composite behaviour has commenced and any props have been removed.,设计考虑因素：Three major aspects identified for consideration during the design
11、of a composite flooring deck:The steel deck itself must be sufficiently strong and rigid to support the weight to wet concrete during casting-construction stage behavior.The steel deck acting compositely with the hardened concrete,and spanning between the supporting steel beams,must support the impo
12、sed live loading-composite slab action.The steel beams,acting compositely with the hardened concrete through the stud shear connectors must support the imposed live loading-composite beam action.,3.2 Criteria for the design of composite floors 设计准则,In design,it is necessary to ensure that the streng
13、th and deflections both during construction(when the concrete is still green)and in service(when composite action has been achieved)are satisfactory.Construction stage:the profiled steel deck alone withstands the weight of wet concrete,workman and equipment.Composite slab stage:the hardened concrete
14、 slab,acting compositely with the profiled steel sheet,spans between the supporting beams and carries the imposed live loads,Key points for Construction stage-Profiled steel as shuttering,Installation of the sheeting is carried out by laying one or more span lengths over the supporting beams.The she
15、eting 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 energy methods.,The sheeti
16、ng 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-span tables appropriate to
17、 each profile.Propping can dramatically reduce deflections.,Key points for composite stage,The 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 interface.To evalua
18、te 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.,3.3 BEHAVIOR AND ANALYSIS,Steel deck（混凝土结硬前：压型钢板）During
19、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 the web;shear occurs esse
20、ntially 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 and concrete may not be fully
21、 effective and longitudinal slip may occur before the steel deck yields.,Composite slab failure mode types,Failure 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),Load deflection response of brittle
22、and ductile slabs,The brittle or ductile mode of failure depends on the characteristics of the steel-concrete interface.,Shear bond failure,Brittle behavior in which slip causes a sudden decrease in load carrying capacity as the surface bond is broken.The extent to which the load reduces is dependen
23、t 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,Longitudinal shear in composite slabs Three t
24、ypes 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 studs through the sh
25、eeting to the steel flange.Determination of the longitudinal shear strength The m-k or shear-bond test,Mode 1 brittle(or non-ductile)behaviorMode 2 ductile behavior,Empirical method for evaluating longitudinal shear resistance,The merits of using profiled steel deck composite floors:its efficiencies
26、 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 must be carried ou
27、t 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.,Partial connection method,The part
28、ial 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 bending moment
29、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.,Partial connection method(another expression),The partial connection method can also be used for the verification of the resistance
30、 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，要确保界面黏结强度：Shear-bond strength requirement纵向抗剪强度验算,Analys
31、is of Composite Slabs（组合楼板受力分析）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（考虑非线性特性以及滑移的高阶分析）.,Verification of Profiled steel sheeting
32、 as shuttering at ultimate limit state(ULS),The sheeting should resist to construction and wet concrete loads.Bending moment resistance of the section is then given by:,Verification of profiled steel sheeting as shuttering at serviceability limit state(SLS),For the ultimate limit states(强度极限状态；uncra
33、cked 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 account using a variation in the modular
34、 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.,3.4 RESISTANCES OF SECTIONS,Section 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 vertical shear failure.Section V:ultim
35、ate resistance to longitudinal shear failure.,Verification of composite slab at ultimate limit state(ULS),Sagging bending resistance.That failure mode is reached if the steel sheeting yields in tension or if concrete attains its resistance in compression.,composite slab at ultimate limit state,Case
36、1 Plastic neutral axis above the sheetingCase 2 Plastic neutral axis in steel sheeting,Case 1 Plastic neutral axis above the sheeting,Case 2 Plastic neutral axis in steel sheeting,Verification of the hogging bending resistance,Bending resistance and deflection,At construction stage:bending resistanc
37、e of the steel deck is checked as the following:Deflection of the steel deck must satisfy the deflection requirement as:,At composite slab stage,Bending resistance,diagonal shear resistance and shear bond resistance should be checkedIf sufficient shear bond is provided at the interface between concr
38、ete and 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 verification,Vertical and punch shear resistance（抗冲切承载力）,punch shear resistance is checked as,Longitudinal shear resistance(纵向抗剪承载力）,To enable a composite slab,the longitu
40、dinal shear bond resistance at the interface between the concrete and the profiled deck should be sufficient.Diagonal shear resistance（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 c);for deflection
41、 under long term load（荷载长期效应）,divided by 2a E.,3.5 Some detailing requirements（构造要求）,Detailing is 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 thicker sections,so the
42、 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.,The required bearing overlaps of composite s
43、labs over the different（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 6 m.Distributing steel mesh is suggested be used to compensate shrinkage and thermal stress in concrete.
44、The minimum steel reinforcement ratio in the two individual directions is 0.002(rs=As/bhc).,Negative steel reinforcement ratio not less than 0.002 for crack width control is required in the top layer of concrete slab at the supports of a simply supported slab,the distance from the edge of the suppor
45、t to the cutting point of the reinforcement should not be less than l/4,and 5 re-bars minimum per meter width.,3.6 Design example floor slab,A one way composite floor with profiled steel sheeting,the slab span is 2.2 m.Steel grade Q235,t=1mm,As=1700 m2/m(weight 0.149 kN/m2);I s=0.96106mm4/m.The dept
46、h of concrete above the top ribs is 80 mm,Concrete grade C20,dead load:g k1=0.29 kN/m2,live load:qk=2 kN/m2.Check bending strength,diagonal shear strength and deflection of the slab,Solution:Calculations of load and internal forces Take the unit width b=1m.Dead load(the mean depth of the concrete sl
47、ab 101 mm)gk=0.10125+0.149+0.29=2.964 kN/mg=1.22.964=3.56 kN/m Live load qk=21=2kN/m q=1.42=2.8 kN/m,M=(g+q)l02/8=(3.56+2.8)2.22/8=3.85 kNm V=(g+q)l0/2=(3.56+2.8)2.2/2=7.0 kNCalculation of moment resistance fsy=205 N/mm2,Es=2.06105 N/mm2fc=9.6 N/mm2,h0=150 70/2=115 mm mm=0.81700205(115 36.3/2)=27.0
48、kNm M,Diagonal shear strength,Take one wave length(200 mm)as a checking unit,subjected 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 Calculation of deflection Take one wave length(200 mm)as a checking unit.Elastic modulus of concre
49、te:Ec=2.55104 N/mm2 aE=E s/E c=2.06105/2.55104=8.08 Deflection 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
50、 mm 4 pk=gk+qk=2.954+2=4.964 kN/mDeflection under long term loading,Steel Deck P3623,3.7 Advanced composite floor systems,a number of trends in modern construction have led to the development of more advanced forms of composite construction Fabricated beams with tapped webs,Haunched beams,Composite
