cables同济桥梁工程系

1、Cables吴 冲同济大学桥梁工程系Tel.02165981817 桥梁钢结构（硕士课程）1. Types of Cablesseven-wire strandnormally made from seven 5mmwires giving the strand a nominal diameter of 15mm (Figure 2.1).most common tensile strengths between 1770 and 1860MPa. typical modulus of elasticity of E=190 GPa (only 68% lower than for the

2、wires themselves).11. Types of CablesHelical bridge strands (spiral strands)Multi-wire helical strands are fabricated by successive spinning of layers generally with opposite direction of helix, starting out with a straight core(Figure2.2).typical nominal modulus of elasticity E=170GPa. 1525% below

3、the value for straight wiresTypically the strength of a helical strand is approximately 10% lower than the sum of the breaking strengths of the individual wires21. Types of CablesLocked-coil strandscomposed of two types of twisted wire: in the core, regular round wires arranged as in a normal helica

4、l strand, and in the outer layers, wires of a special Z-shape (Figure 2.3). Locked-coil strands are always manufactured in full length and full cross section, and delivered with sockets on large reels. The wires tensile strengths of 13701570 MPa generally nominal modulus of elasticity typically 180

5、GPa31. Types of CablesParallel-wire strands for suspension bridge main cablesall the wires were straight from one end to the otherthrough a local distortion of the wires inside the bundles, could actually be reeled and unreeled without creating unacceptable permanent distortionsgenerally fabricated

6、with the wires in a regular hexagonal pattern4Types of CablesParallel-wire stay cablescomposed of a larger number of wires, (19 Nos. 7mmwires up to 499 Nos. 7mm wires)corrosion protection the cable had to be surrounded by a tube made of polyethylene (PE) or stainless steel, use galvanized wires and

7、to have an inhibitor of a non-cracking, ductile material.51. Types of CablesNew PWS stay cablesthe wire bundle is slightly twisted with a long lay to ease reeling and unreeling and make the strand pacting when subjected to axial tension.the tensile strength and the axial stiffness arealmost unaffect

8、ed by twist angles up to 34.having the protecting polyethylene cover extruded directly onto the wire bundle61. Types of CablesParallel-strand stay cablesas parallel-wire cables, with the exception that the individual 7mm wires are replaced by seven-wire strands.7Types of CablesBar stay cablesStandar

9、d bar stay cables contained 710 round steel bars, each with a diameter of 26.5 mm, 32mmor 36 mm, made from steel with a yield stress of 1080 MPa and a tensile strength of 1230MPa. The bar bundle was placed inside a genuine steel tube that was finally filled with cement grout (Figure 2.13).relatively

10、 low fatigue81. Types of CablesMulti-strand stay cablescomposed of several multi-wire helical strands has been used both within cable stayed and suspension bridges91. Types of CablesMulti-strand stay cables101. Types of CablesParallel-wire suspension bridge main cablesmade either by the air-spinning

11、 method (AS method)or pre-fabricated parallel-wire strand method (PPWS method)111. Types of CablesParallel-wire suspension bridge main cables12Figure 2.23 PPWS supported on a roller at the catwalk when pulled across from anchor block to anchor block (Akashi Kaikyo Bridge)Types of CablesParallel-wire

12、 suspension bridge main cables131. Types of CablesComparison between different cable types142 Corrosion Protection2.1 Suspension bridge main cablesThe wrapping of suspension bridge main cables by a soft steel wire was replaced in some American bridges by a plastic cable covering in the mid-1960s. Th

13、is covering typically consisted of the following components:(1) a covering with polyester film;(2) an initial coating with acrylic resin;(3) a layer of non-woven glass mat pressed into place;(4) a second coating with acrylic resin;(5) a layer of woven 150mm wide glass cloth spiral wound on the cable

14、;(6) a third coating with acrylic resin;(7) a final coating with a mixture of acrylic resin and sand to give the surface a rough texture.152 Corrosion Protection2.1 Suspension bridge main cablesKurushima Kaikyo Bridges in Japan a new wire was used for the wrapping. In stead of the round wire a Z-sha

15、ped wire with a cross section as shown in Figure 2.27 was used. With this wire shape gaps will not occur and the exterior surface will be smoother and thereby make the paint more durable.162 Corrosion Protection2.1 Suspension bridge main cablessystem of dehumidification by dry air injection in Akash

16、i Kaikyu BridgeThe dehumidifiers are positioned in the deck at the pylons, at the anchor blocks and at midspan. From these locations the dry air is pumped through air supply pipes to special cable clamps with injection mouths (Figure 2.28). Halfway between the injection clamps exhaust clamps are pos

17、itioned so that the air flows from the air supply pipes through the voids between the wires to the exhaust openings (Figure 2.29).172 Corrosion Protection2.1 Suspension bridge main cables182 Corrosion Protection2.1 Suspension bridge main cables192 Corrosion Protection2.2 Stay cables202 Corrosion Pro

18、tection2.2 Stay cables21热挤双层HDPE护套拉索热挤单层HDPE护套拉索2 Corrosion Protection2.2 Stay cables22抗风雨振双螺旋线拉索3. Mechanical Properties3.1 Static strengthAtypical stressstrain relationship for a galvanized wire as used in cables is shown in Figure 2.36. Here the most important parameters for the designer are indi

19、cated:the modulus of elasticity: Ecthe 0.2% proof stress: fcb,0.2the limit of proportionality (0.01% stress): fcb,0.01the ultimate tensile strength: fcbuthe total elongation at rupture: ecbu23Figure 2.36 Typical stressstrain diagram for a wire used in cables (the dotted curve has a ten times larger

20、horizontal scale than the solid curve)3. Mechanical Properties3.2 Relaxationthe relaxation accelerates significantly when the permanent stress sg is chosen to take a value larger than 50% of the tensile strength. The stresses from permanent loads should therefore not exceed a value of 0.45 fcbu unle

21、ss a special low relaxation grade of steel is used.24Figure 2.37 Irreversible strain due to relaxation in a cable wire (normal relaxation grade) subjected to a constant stress sg for 1000 hours3. Mechanical Properties3.3 Fatigue strengthThe values of Table 2.3 and the plots in Figure 2.38 are valid for redundant load path structures For non-redundant load path structures, the allowable stress ranges shall be considerably smaller, typically only 6