Earthquake Resistant Structural Systems 土木工程外文翻译.docx

1、Earthquake Resistant Structural Systems 土木工程外文翻译Earthquake Resistant Structural Systems -土木工程外文翻译3Building Engineering : Building Structures and SeismicResistance3.1Text3.1.1PassageEarthquake Resistant Structural Systems1Rigid Frame StructuresRigid frame structures typically comprise floor diaphragm

2、s supported on beams which link to continuous columns (Figure 3-1). The joints between beam and columns are usually considered to be “rigid”. The frames are expected to carry the gravity loads through the flexural action of the beams and the prop ping action of the columns. Negative moments are indu

3、ced in the beam adjacent to the columns causing the mid-span positive moment to be significantly less than in a simply supported span. In structures in which gravity loads dictate the design, economies in member size that arise from this effect tend to be offset by the higher cost of the rigid joint

4、s.Figure 3-1 Rigid frame structureLateral loads, imposed within the plane of the frame, are resisted through the development of bending moments in the beams and columns. Framed buildings often employ moment resistant frames in two orthogonal directions, in which case the column elements are common t

5、o both frames.Rigid frame structures are well suited to accommodate high levels of inelastic deformation. When a capacity design approach is employed, it is usual to assign the end zones of the flexural beams to accept the post-elastic deformation expected, and to design the column members such that

6、 their dependable strength is in excess of the over-strength capacity of the beam hinges, thereby ensuring they remain within their elastic response range regardless of the intensity of ground shaking. Rigid frame structures are, however, often quite flexible. When they are designed to be fully duct

7、ile, special provisions are often needed to prevent the premature onset of damage to non-structural components.Rigid frame construction is ideally suited for reinforced concrete building because of the inherent rigidity of reinforced concrete joints. The rigid frame form is also used for steel frame

8、buildings. But moment resistant connections in steel tend to be costly. The sizes of the columns and girders at any level of a rigid-frame are directly influenced by the magnitude of the external shear at that level, and they therefore increase toward the base. Consequently, the design of the floor

9、framing can not be repetitive as it is in some braced frames. A further result is that sometimes it is not possible in the lowest storeys to accommodate the required depth of girder within the normal ceiling space.While rigid frames of a typical scale that serve alone to resist lateral loading have

10、an economic height limit of about 25 storeys, smaller scale rigid frames in the form of a perimeter tube, or typically scaled rigid frames in combination with shear walls or braced bents, can be economic up to much greater heights.2Infilled Frame StructuresInfilled frames (Figure 3-2) are the most u

11、sual form of construction for tall buildings of up to 30 storeys in height. Column and girder framing of reinforced concrete, or sometimes steel, is infilled by panels of brickwork, or cast-in-place concrete.Figure 3-2 Infilled frameWhen an infilled frame is subjected to lateral loading, the infill

12、behaves effectively as a strut along its compression diagonal to brace the frame. Because the infills serve also as external walls or internal partitions, the system is an economical way of stiffening and strengthening the structure.The complex interactive behavior of the infill in the frame, and th

13、e rather random quality of masonry, had made it difficult to predicate with accuracy the stiffness and strength of an infilled frame. For these reasons, the use of the infills for bracing buildings has mainly been supplementary to the rigid frame action of concrete frames.3Shear WallsA shear wall is

14、 a vertical structural element that resists lateral forces in the plane of the wall through shear and bending. The high in plan stiffness and strength of concrete and masonry walls make them ideally suitable for bracing building as shear walls.A shear wall acts as a beam cantilevered out of the grou

15、nd or foundation9 and, just as with a beam, part of its strength derives from its depth. Figure 3-3 shows two examples of a shear wall, one in a simple one-storey building and another in a multistorey building. In Figure 3-3a, the shear walls are oriented in one direction, so only lateral forces in

16、this direction can be resisted. The roof serves as the horizontal diaphragm and must also be designed to resist the lateral loads and transfer them to the shear walls.a) End shear walls and interior shear wall b) Interior shear walls for bracing in two direction Figure 3-3 Shear wallFigure 3-3a also

17、 shows an important aspect of shear walls in particular and vertical elements in general. This is the aspect of symmetry that has a bearing on whether torsional effects will be produced. The shear walls in Figure 3-3a show the shear walls symmetrical in the plane of loading.Figure 3-3b illustrates a

18、 common use of shear walls at the interior of a multi-storey building. Because walls enclosing stairways, elevator shafts, and mechanical chases are mostly solid and run the entire height of the building, they are often used for shear walls. Although not as efficient from a strictly structural point

19、 of view, interior shear walls do leave the exterior of the building open for windows.Notice that in Figure 3-3b there are shear walls in both directions, which is a more realistic situation because both wind and earthquake forces need to be resisted in both directions. In this diagram, the two shea

20、r walls are symmetrical in one direction, but the single shear wall produces a nonsymmetric condition in the other since it is off center. Shear walls do not need to be symmetrical in a building, but symmetry is preferred to avoid torsional effects.If, in low-to medium-rise building, shear walls are

21、 combined with frames, it is reasonable to assume that the shear wall attract all the lateral loading so that the frame may be designed for only gravity loading. It is essentially important in shear wall structures to try to plan the wall layout so that the lateral load tensile stresses are suppress

22、ed by the gravity load stresses. This allows them to be designed to have only the minimum reinforcement.Since shear walls are generally both stiff and can be inherently robust, it is practical to design them to remain nominally elastic under design intensity loadings, particularly in regions of low

23、or moderate seismicity. Under increased loading intensities, post-elastic deformations will develop within the lower portion of the wall (generally considered to extend over a height of twice the wall length above the foundation support system). Good post-elastic response can be readily achieved wit

24、hin this region of reinforced concrete or masonry shear walls through the provision of adequate confinement of the principal reinforcing steel and the prohibition of lap splices of reinforcing bars.Shear wall structures are generally quite stiff and, as such interstorey drift problems are rare and g

25、enerally easily contained. The shear wall tends to act as a rigid body rotating about a plastic hinge which forms at the base of the wall. Overall structural deformation is thus a function of the wall rotation. Inter-storey drift problems which do occur are limited to the lower few floors.A major sh

26、ortcoming with shear walls within buildings is that their size provides internal (or external) access barriers which may contravene the architectural requirements. This problem canbe alleviated by coupling adjacent more slender shear walls so a coupled shear wall structure is formed. The coupling be

27、ams then become shear links between the two walls and with careful detailing can provide a very effective, ductile control mechanism (Figure 3-4).Figure 3-4 Coupled shear wall structure4Braced FramesA braced frame is a truss system of the concentric or eccentric type in which the lateral forces are

28、resisted through axial stresses in the members. Just as with a truss, the braced frame depends on diagonal members to provide a load path for lateral forces from each building element to the foundation. Figure 3-5 shows a simple one-storey braced frame. At one end of the building two bays are braced

29、 and at the other end only one bay is braced. This building is only braced in one direction and the diagonal member may be either in tension or compression, depending on which way the force is applied.a)Single story braced building b) Multistory braced building Figure 3-5 Braced frameFigure 3-5b sho

30、ws two methods of bracing a multistorey building. A single diagonal compression member in one bay can be used to brace against lateral loads coming from either direction. Alternately, tension diagonals can be used to accomplish the same result, but they must be run both ways to account for the load

31、coming from either direction.Braced framing can be placed on the exterior or interior of a building, and may be placed in one structural bay or several. Obviously, a braced frame can present design problems for windows and doorways, but it is a very efficient and rigid lateral force resisting system

32、.Two major shortcomings of braced systems are that their inclined diagonal orientation oftenconflicts with conventional occupancy use patterns; and secondly they often require careful detailing to avoid large local torsional eccentricities being introduced at the connections with the diagonal brace being offset from the frame node.5Wall-frame StructuresWhen shear walls are combined with rigid frames (Figure 3-6), the walls, which tend to deflect in a flexural configuration, and the frames, which tend to deflect in a shear mode, are constrained to adopt a common shape by the horizontal rigi