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1、外文翻译原文China-Japan Joint Seminar on Steel and Composite BridgesDesign of Steel Plate-Truss Composite Girder ofCable Stayed Minpu Bridge IIJ. Peng, W.L. Deng, L. Zhou, Y.C. Lu, M. ZhuShanghai Urban Construction Design & Research Institute, Shanghai 200011, ChinaAbstract : Minpu Bridge II is a super la
2、rge bridge with the integrated double decks for highway and railway traffic. The main part is cable-stayed through a single pylon and double cable sectors, with the span largest in China. Described hereby is how to select the main girder of the main span cable-stayed bridge from multiple options. Th
3、e steel plate-truss composite girder is finally adopted, which is structurally reliable, with appropriate functions and simple construction.Key words : highway-railway double-deck bridge; cable-stayed bridge; steel plate-truss composite girder; bridge design1 .DESCRIPTION OF WORKSAcross the Huangpu
4、River in Shanghai at the upper stream of Minhang and Fengxian, and 1.7km from Fengpu Bridge down, Minpu Bridge II is a super large bridge with integrated double decks for highway and railway traffic. The main part is formed by a double-deck cable-stayed bridge with a single pylon and double cable se
5、ctors, and the main span is 251m wide. The upper deck is 18m in width, used for a two-way four lane highway (Class II); the lower deck is for two light rails, i.e. Shanghai Rail Transit Line 5 in Min-Feng Section, with the minimum functional width of 10m.Figure 1 The layer of the main bridge2 .COMPA
6、RISON OF OPTIONS FOR MAIN GIRDERWith only a few exceptions, the large span double-deck bridges built usually use the steel truss girder for the main girder, which is no doubt more appropriate in terms of structural performance and construction applicability. The effect of the trussed girder is diffe
7、rent, subject to the arrangement of members, so it is critical to select an optimal design adaptable to the type of bridge. In the design of the main trussed girder on the main span of Minpu BridgeII, comparisons and studies are carried out on three aspects, i.e. the shape of truss, the cros section
8、 of the truss and the deck.2.1 Shape of Truss The shape of truss currently prevailing is mainly of the pure warren truss (triangular truss), warren truss and Pratt truss (N-formed truss), the difference of which lies only in the arrangement of the web members while no great difference is found in th
9、e structural performance, all applicable technically. With more succinct lines and contour, the triangular and N-formed trusses are widely used on modern trussed girder bridges. Besides, the number of members connected to the truss nodes is minimum, i.e. only 4, which is beneficial to simplify the f
10、abrication of trusses. For the triangular truss, which is widely used in a truss of a rectangular section, it is more complicated to provide the transverse knee-brace for lack of the vertical post. On the other hand, the shape of truss shall also match the cable arrangement of the cable-stayed bridg
11、e to keep a proper relationship with the force thereon. For an N-formed truss to the harp-shaped cable sector, the best matched shape is that the diagonal web and cables are close to a straight line. In that case, the fabrication of nodes is almost standardi like Oresund Bridge in Sweden. It must be
12、 quite careful, however, to use this type as the length between the trusses is greater than normal, causing greater force on the web. There is no substantial difference in the shape and the complexity at the node between the triangular truss and the normal N-formed truss with the fan-shaped or harp-
13、shaped cable sector, but the triangular truss is a trend of development of the steel truss. 2.2 The Cross Section of TrussThe cross section of the truss is mainly arranged in two shapes, rectangular and inverted trapezoid, and the former is the most popular in truss bridges, with no exception of the
14、 double-deck type. In normal cases, the upper deck for the highway in the double-deck bridge is usually wider than the lower deck for the railway or light rail so it is most appropriate to adopt the shape of an inverted trapezoid only in terms of matching the cross arrangement of the bridge and econ
15、omic benefit. However, the composition of the truss section and the type of bridge, the advantage and disadvantage are more apparent. For arch and suspension bridges, the inverted trapezoidal cross section is most suitable as there is no horizontal component of force along the bridge due to the vert
16、ical hanging members and as no extra complexity may arise in the force sustained and the structure. If the rectangular cross section is adopted for cable-stayed bridge, the cables and the main truss are generally on the same plane, and the horizontal component of the cable force is transferred direc
17、tly to the main chord member so the force is clear and definite and the structure of cable-truss connection is normal. While fo the inverted trapezoidal section, the extra secondary truss is required to transfer the cable force as the cable and the main truss is not on the same vertical plane, where
18、 it is difficult to handle the horizontal component of cable force. Beneficial attempts have been made in this aspect on Oresund Bridge and Wuhu Yangtze Bridge. It shows through comparisons that the economic advantage of the inverted trapezoid section is weakened as the material for the extra powerf
19、ul secondary truss almost offsets the quantity of material for the reduced lower deck, and the cost of its fabrication is higher due to the structural complexity of the cable-truss connection. So it is appropriate to use the truss with the rectangular section for the cable-stayed bridge.Table 2.1 A
20、Comparison of Truss SectionsRectangularInverted TrapezoidSchematicsAdvantages1.Adaptable to any type of truss,simple in handling the node, bearing the force direct and definite.1.The lower deck being less wide than the upper one enables a more compact structural layout and the lower transbeam bears
21、less force.Disadvantages1.The lower deck being less wide than the upper one means the structural layout is less economic and the lower transbeam bears greater force.1.For trusses of Pratt or Warren type,it is easier to handle the node as the subdiagonal rod and the vertical web are on the same verti
22、cal plane ,but it is difficult in case of the pure Warrant truss;2.Theres force between the trusses.Conditions Applicable1.It is structurally simple for any type of bridge, bearing the force clear,definite and reliable.1.For arch and suspension bridges,it is structurally simple,bearing force more de
23、finite,but for cable-stayed bridges,it is more complicated as extrasecondary trusses are required to bear the horizontal component force.2.3 The Deck(1) Upper DeckThe upper deck structure is of two types, i.e. the orthotropic steel plate and the concrete sla corresponding to two kinds of connection
24、with the truss, i.e. the system of the orthotropic steel plate and the truss composition and the system of the concrete slab and truss composition. The concrete deck may also be subdivided into two forms, the concrete deck slab is only connected with the upper chord (Form 1) and the concrete deck sl
25、ab is connected with both the upper chord and the transbeam (Form 2), whose advantages and disadvantages are shown in the following Table 2.2Table 2.2 A Comparison of Upper Deck FormsOrthotropic steel plateConcrete slab (Form 1)Concrete slab (Form 2)Features of force borneForce is borne by the whole
26、 plateForce is borne by the whole slabForce is borne by the whole slabAdvantages1.The plate and truss are of the same material without the material difference in connection;2.with less self-weight1.Force on slab-truss composition is clear and definite;2.The upper structure cost less;3.The main girde
27、r is of higher rigidity and lower flexibility1.A two-way deck, and the deck thickness may be reduced;2.The cost is lower for the superstructure;3.the main girder is of high rigidity and lower flexibility, especially with the structural weight rigidity increased, the non-linear deformation of dynamic
28、 loads is reduced.Disadvantages1.The superstructure costs more as more steel is required;2.Paving asphalt on the steel deck requires higher technique so the cost is higher.1.Greater selfweight requires more anchors and spans to keep balance;2.The internal force is redistributed due to contraction an
29、d creep of concrete;3.Requiring more steps of construction procedure1.Greater selfweight requires more anchors and spans to keep balance;2.The internal force is redistributed due to contraction and creep of concrete;3.The force on the slab is more complicated.ExamplesCaiyuanba BridgeOresund BridgeWu
30、hu Yangtze Bridge(2) Lower DeckTable2.3 A Comparision of Lower Deck FormsOpen DeckConcrete Rail GirderOrthotropic steel box girderOrthotropic steel plateFeatures of force borneSmall beams are provide under the sleepers which only bear the local force.The rail beam is placed on the upper transbeam fi
31、xed or connected with the bearingForce is borne by the whole girderForce may be borne by the whole plate or only by some local places.Advantages1.Structurally simple;2.With smaller selfweight;3.Force borne is clear and definite1.The rigidity of the main girder will be increased if it bears the force
32、 jointly.1.With smaller selfweight;2.The truss rigidity vertical and horizontal is increased1.The internal rigidity under the truss is increased.Disadvantages1.Rails generate greater noise during operation;2.Difficult in maintenance;3.Difficult in handling the stray current on the rail.1.With greate
33、r selfweight during operation;2.The lower transbeam is under greater and more complicate force,i.e.bending,shear and twisting;3.Special machinery is required to erect the rear frame beam1.For rail transit systems,ballast or concrete facing must be paved on the steel deck,making greater selfweight;2.
34、More steel is used.1.Composition of concrete and steel is structurally complicated.Conditions applicableRailway bridgeApproach of Oresund BridgeExt.main bridge of Oresund BridgeAs the main piers in water are confined by the navigation course, the dead load of the superstructure is reduced to the min
35、imum so that a smaller pier base is possible. After comparison of multiple options, a full steel structure is adopted, with the upper and lower decks both of the orthotropic plate.2.4 Result from Comparison“simple Appearance and Endurable Structure”is one of the trends of steel truss development in
36、current world, which is displayed mainly in such features as 1) the triangular truss, 2) box member, 3) large space between nodes, 4) an integrated node plate and 5) an all-welded structure. The transition from a bolted and welded connection to an all-welded connection is based on the structural dur
37、ability, and an all-welded structure can avoid corrosion caused by electroplating and gaps. To sum up, the steel plate truss composite structure is finally adopted for the main girder, with the triangular truss, rectangular cross section and orthotropic steel plates for the upper and lower decks wit
38、h the longitudinal and transverse beam system.3 .TRUSS3.1 Main TrussThe main truss is a composite structure of the steel plate truss, with the triangular truss, rectangular cross section. The truss is 9.5m high and 19.4m wide, with the standard panel length of 14.7m. All chords and webs of the main
39、truss are of the box section, with the size1000mm(W) 1200mm(H) for the chord and 1000mm(W) 700mm(H) for the webFigure 3.1 The standard section of the girder3.2 DeckThe upper and lower decks are of the orthotropic steel plate and longitudinal and transverse beam system. The cover plate on the upper d
40、eck is 14mm thick, with U-formed reinforcement. To simplify fabrication and raise precision, large U-formed reinforcing ribs are adopted with the prerequisite that the local rigidity of the deck is satisfied. The rib is 300mm high, with upper opening 360mm wide, the lower bottom 200mm wide and the w
41、all 8mm thick, at the interval of 700mm. The cover plate on the lower deck is 12mm thick. Four jack stringers are provided on the upper deck and six on the lower deck. A main transbeam is provided at the truss node, which is an I beam in variable depth. The beam in the middle of the span is 1.8m dee
42、p, with four secondary transbeams between the nodes, 800mm deep and spaced at 3.675m.3.3 Anchor BoxAs the cable and the main truss is of the same vertical plane and the upper chord is a box member, it is most appropriate to use the steel anchor box for the cable-truss connection. The two webs of the
43、 chord extend out of the top at the anchor cable, with the cable anchor plate and bearing plate set in the middle. The cable force is transferred to the web through the bearing plate and the weld seams of the web on both sides and finally to the truss. This construction is more reliable than the con
44、ventional connection of the anchor box to one side of the steel box girder.3.4 Nodes of Truss The nodes of truss are in the form of an integrated node plate, an all-welded structure. As the rib reinforced box member makes great intervals between nodes, and as the all-welded steel truss connected thr
45、ough integrated nodes is of greater rigidity and higher restraint degree, deflection from welding may be restrained, causing greater restraint stress. Together with the residual stress from welding, it is likely to have cracks if the welded piece is of poor yielding or tenacity, weak in redistributi
46、on of stress and improper treatment of details. So steel plate with higher durability is used at the node through the large arc transition to reduce stress concentration.Figure 3.2 The layer of the anchor box Figure 3.3 The integra joint of the lower chord member4 .CONCLUSIONDifferent from highway b
47、ridges in features like the load, traffic safety and comfort, the integrated highway-railway bridge faces greater and more challenges in its development to larger spans and the designers encounter various engineering problems. According to the site conditions, a single pylon cable-stayed bridge of c
48、ontinuous steel plate truss composite girder is adopted, with the main span 251m in length, which is the longest of its kind in China. Construction of Minpu Bridge II is a new starting point of developing this type of bridge.5 REFERENCES1 The Fabrication Techique of Steel Girders for Wuhu Changjiang River Bridge. Science Publishing Company, 2001.2 Detailed Design Of The Cable-Stayed Bridge, LARS HAUGE DEPARTMENT HEAD MAJO BRIDGES COWI. - 12 -