土木工程專業(yè)英語(yǔ) 教學(xué)課件 陳瑛 1.1 Classification and Behavior of Structural Systems and Elements

1、在線教務(wù)輔導(dǎo)網(wǎng)： :/教材其余課件及動(dòng)畫素材請(qǐng)查閱在線教務(wù)輔導(dǎo)網(wǎng)QQ:349134187 或者直接輸入下面地址：1.1 Classification and Behavior of Structural Systems and ElementsPrimary Structural Elements (Based on Stiffness) Rigid element beam, column or strut, arch, flat plate, singly-curved plate, and shellFlexible elements cable (straight or draped)

2、 and membraneDerived elements frame, truss, geodesic dome, netFrames The frame has rigid joints that are made between vertical and horizontal members. This joint rigidity imparts (給予) a measure of stability against lateral forces. In a framed system both beams and columns are bent or bowed（彎如弓的）as a

3、 consequence of the action of the load on the structure. AnimatebentbowedTrusses 桁架Trusses are structural members made by assembling short, straight members into triangulated patterns. The resultant （組合的, 合成的）structure is rigid as a result of the exact （精確的) way the individual line elements are posi

4、tioned relative to one another. gusset 5Qsit角撐板Chord kC:d鉉Trusses 桁架Some patterns (e.g. a pattern of squares rather than triangles) do not necessarily yield a structure that is rigid (unless joints are treated in the same way as in framed structures). Square truss is unstable Square frameA truss is

5、a structure made by assembling individual linear elements arranged in a triangle or combined triangles to form a framework.Pinned connection at intersections.Members are in compression or tension.CTCCTForces in Truss MembersTrusschordchordwebA truss composed of discrete elements is bent in an overal

6、l way under the action of an applied transverse loading in much the same way that a beam is bent. Individual truss members, however, are not subject to bending but are only either compressed or pulled upon. Arches An arch is a curved, line-forming structural member that spans between two points.bloc

7、k arch (塊拱）rigid arch （剛性拱）fixedtwo-hinged,three-hingedspanBlock arch(塊拱）The common image of an arch is that of a structure composed of separate wedge-shaped pieces that retain their position by mutual pressure induced by the load . mutual 5mju:tFuEl adj. 相互的, 共有的spanBlock archeswedge-shaped piecesT

8、he exact shape of the curve and the nature of the loading are critical determinants as to whether the resultant assembly is stable. When shapes are formed by simply stacking rigid block elements, the resultant structure is functional and stable only when the action of the load is to induce in-plane

9、forces that cause the structure to compress uniformly. Structures of this type cannot carry loads that induce elongations or any pronounced type of bowing in the member (the blocks simply pull apart and failure occurs). ArchPure compressionpull apartBlock archesThe strength of a block structure is d

10、ue exclusively to the positioning of individual elements, since blocks are typically either simply rested one on another or mortared together (the mortar does not appreciably increase the strengthen of the structure). The positioning is, in turn, dependent on the exact type of loading involved. The

11、resultant structure is thus rigid only under very particular circumstances.Blocks are mortared togetherBlocks simply rested one on anotherThe rigid arch is frequently used in modern building. It is curved similarly to block arches but is made of one continuous piece of deformed rigid material.Concre

12、te archSteel archThe rigid archIf rigid arches are properly shaped, they can carry a load to supports（支座） while being subject only to axial compression, and no bending occurs. The rigid arch is better able to carry variations in the design loading than is its block counterpart made of individual pie

13、ces. The rigid archMany types of rigid arches exist and are often characterized by their support conditions (fixed, two-hinged, three-hinged).Three-pin arch hinged at the crown (頂) and at each support point. allows for movementadjusts to different temperature changes,allows for expansion and contrac

14、tion. Three-hinged arch 三鉸拱 Two-pin arch pin joints at the abutments only. bending moments are distributed more evenly than in the 3-pin archdifferential settlement at the abutments can result in damage to the arch.Fixed arch:no pin joints or any connections between the supports foundation (supports

15、) are rigid. abutmentsFixed archTwo-pin archWalls and Plates. Walls and flat plates are rigid surface-forming structures. A load-bearing wall can typically carry both vertical loads and lateral loads (wind, earthquake) along its length. Resistance to out-of-plane forces in block walls is marginal. w

16、allload-bearing wall承重墻out-of-plane forcesvertical loadslateral loadsWalls and Plates A flat plate is typically used horizontally and carries loads by bending to its supports. Plate structures are normally made of reinforced concrete (鋼筋混凝土）or steel.Walls and Plates墻和板Horizontal plates can also be m

17、ade by assembling patterns of short, rigid line elements. Three-dimensional triangulation schemes （設(shè)計(jì)） are used to impart stiffness to the resultant assembly.Truss space frameFolded plates 折板Long, narrow rigid plates can also be joined along their long edges and used to span horizontally in beam-lik

18、e fashion. These structures, called folded plates, have the potential for spanning fairly large distances.beam-likespanCylindrical Shells and Vaults 柱形殼和拱頂Cylindrical （sI5lIndrIk(E)l圓柱的）barrel shells and vaults (vC:lt ) are examples of singly curved-plate structureCylindrical barrel shells（柱筒形殼）vaul

19、tsCylindrical Shells and Vaults 柱形殼和拱頂A barrel shell spans longitudinally such that the curve is perpendicular to the direction of the span. When fairly long, a barrel shell behaves much like a beam with a curved cross section. Barrel shells are invariably made of rigid materials (e.g., reinforced c

20、oncrete or steel). direction of the spanspans longitudinallycurved cross sectionSpherical Shells and Domes spherical 5sferikEl adj. 球的, 球形的, Having the shape of a sphere A wide variety of doubly curved surface structures are in use .These include structures that are portions of spheres and those tha

21、t form warped surface ( , the hyperbolic paraboloid ). hyperbolic 7haipE:5bClik adj. 雙曲線的 paraboloidpE5rAbElCid n.拋物面 portions of sphereshyperbolic paraboloidSpherical Shells（球殼） and Domes（穹頂）Probably the most common doubly curved structures is the spherical shell. It is convenient to think of this

22、structure as a rotated arch. This analogy, however, is actually misleading with respect to how the structure actually carries loads because of the fact that loadings include circumferential forces （切線力） in spherical shells which do not exist in arches. Domed structures can be made of stacked blocks

23、or a continuous rigid material (reinforced concrete). St Jacobs CathedralStone dome Stone dome concrete domeRoof of Panthenon （concrete dome) 米蘭大教堂Shells and domes are very efficient structures capable of spanning large distances using a minimum of material.Cables（索）Cables are flexible structural el

24、ements. The shape they assume （呈現(xiàn)，take on ）under a loading depends on the nature and magnitude of the load. When a cable is simple pulled on at either end, it assumes a straight shape. This type of cable is often called a tie-rod （拉桿）.tie-rodCables When a cable is used to span between two points and

25、 carry an external point load or series of point loads, it deforms into a shape made up of a series of straight-line segments. When a continuous load （distributed load, 分布荷載）is carried, the cable deforms into a continuously curving shape. straight-line segmentsCablesThe self weight of the cable itse

26、lf produces such a catenary curve （懸鏈線）the equation for this catenary in rectangular coordinates, with a as the y-intercept is: y = ( a/2 ) (ex/a+ e-x/a)Suspension cables 懸纜, 吊索 can be used to span extremely large distances. They are often used for bridges, where they support a road deck, which in t

27、urn carries the traffic loading. Suspension cables 懸纜, 吊索Suspension structure: Since moving traffic loads would ordinarily cause the primary support cable (主纜main cable) to undergo shape changes as load positions changed, and with this changes the shape of the road surface would occur, the horizonta

28、l bridge deck (橋板）is made into a continuous rigid structures so that the road surface remains essentially flat and the load transferred to the primary support cables remains essentially constant. Cable-stayed structures （斜拉結(jié)構(gòu)） are used to support roof surfaces buildings, particularly in long-span si

29、tuations.Membranes, Tents, and Nets 膜、 帳篷、網(wǎng)A membrane is a thin, flexible sheet. Tent structureCable membrane structure索膜結(jié)構(gòu) Pneumatic （nju(:)5mAtik裝滿空氣的）membrane structure 充氣膜結(jié)構(gòu)Stress-skin membrane structure 應(yīng)力蒙皮膜結(jié)構(gòu)帳篷膜結(jié)構(gòu) Tent structureA common tent is made of membranes surfaces. Both simple and comp

30、lex forms can be created using membranes. For surfaces of double curvature, such as a spherical surface, however, the actual surface would have to be made as an assembly of much smaller segments, since most membranes are typically available only in flat sheets. 斜拉式索膜cable-suspended membrane structur

31、eA further implication of using a flexible membrane to create the surface is that it either has to be suspended with the convex side pointing downward or, if used with the convex 5kCn5veksside （凸側(cè)）pointing upward, ( it has to be )supplemented(5sQplimEnt )by some mechanism to its shape. Radial pleate

32、d （褶皺） suspended tensile structureconvex side Cable-suspended membrane Pneumatic, or air-inflated, structures充氣式膜結(jié)構(gòu) The shape of the membrane is maintained by the internal air pressure inside the structure. Stressed-skin structures 應(yīng)力蒙皮結(jié)構(gòu)Another mechanism is to apply external jacking （抬升）forces that

33、 stretch the membrane into the desired shape. Various stressed-skin structures are of this general type. The need to pretension the skin, however, imposes various limitations on the shape that can be formed. Spherical surfaces, for example, are very difficult to pretension by external jacking forces

34、, while others, such as the hyperbolic paraboloid, can be handled with comparative ease. Nets three-dimensional surfaces made up of a series of crossed cables. Nets are very analogous to membrane skins. By allowing the mesh opening to vary as needed, a wide variety of surface shapes can be formed. A

35、n advantage of using crossed cables is that the positioning of the cables mitigates （減輕 5mitieit ）fluttering （飄動(dòng)）due to wind suctions and pressures. In addition, tension forces are typically induced into the cables by jacking devices, so that the whole surface is turned into a type of stretched skin

36、. This also gives the roof stability and resistance to flutter. 2.Basic Issues in the Analysis and Design of Structures 2.1 Fundamental Structural PhenomenaThere are several fundamental ways in which failure can occur.Loss of Overall /Global stability (整體穩(wěn)定）Loss of Internal stabilityLoss of Strength

37、 and stiffness of constituent elementsOverall Instability (Global )Overturn (lateral force, self-weight)Slide (lateral force, self-weight)Twist (lateral force, self-weight)Solution for overall instability Deep foundation Wide foundationInternal Instability CollapseSolution for internal instability d

38、iagonal bracing shear wall rigid jointStrength and Stiffness LossExcessive internal forceExcessive deformationSolution: carefully designing of componentsStructure components could break apart or deform badly. The forces causing overturning（傾覆） or collapse come from the specific environmental (e.g.,

39、wind, earthquakes, occupancies (5CkjupEnsi占有) or from the self-weight of the form itself. These same applied loadings produce internal force in a structure that stress the material used and may cause it to fail or deform. Global stabilityA first set of concerns deals with the overall stability of a

40、work. As a whole unit, a structure might overturn, slide, or twist about its base, particularly when subjected to horizontally acting wind or earthquake forces.Global Instability Sliding under its own weight. Overturning or twisting need not be caused only by horizontally acting forces. A work might

41、 simply be out of balance under its own self-weight and overturn.This can also occur where the soil adhering to the foundations slides over an adjoining layer, especially if the top layer of soil has a high moisture content.Global stability: solutionThe use of wide, rigid foundations helps prevent o

42、verturning, as does the use of special foundation elements such as piles capable of carrying tension forces.Internal Stability-Collapse of structureA second set of concerns deals with internal, or relational, stability. If the parts of a structure are not properly arranged in space or interconnected

43、 appropriately, an entire assembly(組裝)can collapse internally. Collapses of this type invariably involve large relative movements within the structure itself. Assemblies may be internally stable under one loading condition and unstable under another. Horizontally acting wind or earthquake forces, in

44、 particular, cause collapses of this kind. Internal Stability-solutionThere are several basic mechanisms-walls, frame action, cross bracing for making an assembly internally stable.Strength and StiffnessMember under Internal Forces - the action of an external force on a structure produces internal f

45、orces within a structure :TensionCompressionBendingTorsionBearing Internal forces stress and strainDeflection (excessive deformation)Strength and Stiffness A third set of concerns deals with the strength and stiffness of constituent elements.There are many structure issues that revolve around the st

46、rength of component parts of a structure. These failures, which may or may not lead to total collapse, may be caused by excessive tension, compression, bending, shear, torsional, bearing forces, or deformations that are developed internally in the structure as a consequence of the applied loadings.

47、Associated with each force state are internal stresses that actually exist within the fabric of the material itself. Strength and Stiffness Loss-solutionBy carefully designing components in response to the force state present, the actual stresses developed in the components can be controlled to safe

48、 levels.2.2 Structural StabilityFundamental consideration in designing a structureassuring structural stability under any type of possible loading condition. All structures undergo some shape changes under load. In a stable structure deformations are small internal forces tend to restore the structu

49、re to its original shape after the load has been removed. Structural StabilityIn an unstable structure, deformations are massive deformations tend to continue increase as long as the load is applied. An unstable structure does not generate internal forces that tend to restore the structure to its original configuration.often collapse completely and instantaneously as a load is applied to them. structural designers responsibility: to assure that a structure form a stable configurationStability is a crucial issue in the design of structures post-and-beam structure no capacity to resist ho