2. Background Art Main cable is the most important and characteristic part on a suspension bridge. Main cables are tremendously difficult to be replaced and normally govern the useful life of suspension bridges. Therefore, corrosion protecting system for a main cable should be treated as perfect as possible. A dehumidification protecting system for main cable has been developed and applied on more and more suspension bridges, because of its advantages of reliability. The following papers introduce its application aspect: [Ito M., Saeki, S. and Tatsumi, M. , Corrosion protection of bridge cables : from Japanese experiences, Proceedings of the International<BR> Seminar on new Technologies for Bridge Management, IABSE, Seoul, 1996. p. 24-28, Fig. 5-8. ] [Wai-Fah<BR> Chen and Lian Duan, Bridge Engineering Handbook chap. 18. 5. 4, CRC Press LLC, U. S. , 2000. p. 18-34- 18-36, Fig. 18.34.], [Satosi Kashima, Yukikazu Yanaka, Shuichi Suzuki and Kunihisa Mori, Monitoring the Akashi Kaikyo Bridge : First Experiences, Structural Engineering International, Journal of the IABSE, Zurich, May 2001. p. 120-121, Fig. 2-5.], [Makoto Kitagawa, Maintenance of the Honshu-Shikoku Bridges, Proceedings of the IABSE Conference, Seoul, 2001. ch. 3.2*.] and [Matthew L. Bloomstine, Martin Justesen, Jens Sandager Jensen and Frank Rubin, Operation Management and Systems for Cable-Supported Bridges, Proceedings of the IABSE Conference, Seoul, 2001. ch. 7*. ]. (* The full papers are saved in a disk attched in the abstract proceedings of the conference).

However, there are some problems in this current system. When an ordinary dehumidification protection system used for a closed room, for example a bridge box-girder or a storehouse, the system can directly touch the better part of the room, therefore moisture hiding in some corners can be gradually exhausted to the dehumidification plant by humidity gradient and no need to change the general atmospheric pressure in the room. Unfortunately, this kind of dehumidification operation is not enough for the current main cable protection. The reason is that, according to the above papers, only the cable surface at the area of air injection cover and the exhaust cover can directly touch the dehumidification system. Length of an air injection cover and an exhaust cover is usually less than 1.5 m, while their distance is 140-150 m approximately i. e. only 1% of the cable surface can directly touch the dehumidification system. This implies that moisture somewhere in main cable has to travel a 140-150 m long way along the void between compacted wires with large friction resistance then arrive to the exhaust cover. This movement can't be supplied only by humidity gradient, so that an air blower with 300mmAq air overpressure has to be added. All the cable covers and exclusive air injection pipes have to suffer from this inner air overpressure and a layer of rubber sheet, elastic durability of which becomes an uncertain problem, between wrapping wire and coating has to be therefore added. Considering all the above problems together, the key weakness of the current system is its low efficient i. e. its large electric power consumption and higher requirement of cable covers. The aim of this invention is to create a new dehumidification protecting system for main cable with much higher efficient.

3. Disclosure of Invention and Brief Description of Drawings On some suspension bridges, each main cable consists of two cable-elements, such as George Washington Bridge and Verrazano-Narrows Bridge in USA, Aquitaine Bridge and Chavanon Viaduct in France, Musa River Bridge in Latvia, Mosel Wehlen Bridge in Germany as well designed Messina Strait Bridge in Italy etc.

The two cable-elements are wrapped individually and their minimum spacing is governed by the size of wrapping machine. For example on designed Messina Strait Bridge, the diameter of one cable-element is 1.24 m while the spacing of the two cable-elements is up to 1.75 m [http://www. strettodimessina. it/immag- pagine/cavol6-5. gifl. If the two cable-elements are wrapped together and an oval shaped main cable is formed, the spacing of the two cable-elements can, be reduced. As a result of this kind of wrapping, the quantity of wrapping wires and coatings, the size of Pylon saddles, splay saddles, cable clamps and central nodes are possible to be reduced, furthermore important, a passageway simultaneously a cover for dry air injection and moisture exhaustion is automatically formed between the two cable-elements and the wrapping wires, consequently, a high percentage of cable surface available for direct dehumidification touching is also automatically obtained. This is the starting point of the invention.

3.1 Normal structure of the novel main cable.

The normal structure of the novel main cable with oval shape is illustrated in Fig. 1. The following parts and procedures form the structure: 1) Two symmetrical cable-elements (1. 1) are erected with AS (aerial spinning) method or PS (prefabricated parallel wire strand) method.

2) When the two cable-elements (1. 1) are compacted by one compacting machine with a clearance c as small as possible, bands (1.2) are individually fastened for one cable-element with spacing a2 = d approximately.

3) Position holders (1.3) made of low-carbon steel or HDPE and fixed by their tie bolts are inserted with spacing a3, which depends on the d and the influence of wrapping force or wheel force of gantry crane for stiffening girder lifting.

4) Wrapping wires (1.4) are wrapped on the two cable-elements (1. 1) by a wrapping machine with working diameter of Dw = 2d + c.

5) Primer and outer coatings (1.5) are painted, so that an isolating cover consisted by (1.4) and (1.5) is formed and a vent-way simultaneously a working surface (1.6) for dry air injection and moisture exhaustion appears.

Comparing with the current technique, features of the novel system are: 1) By the corrosion protection point of view, cross-section of the novel main cable inside the isolated cover can be divided into two parts: the protected part (1.1) with area of d 2 it/2 and the protection supplying part (1.6) with area of (d+c-dn/4) d. The part (1.6) supplies a vent-way simultaneously a working surface for dry air injection and moisture exhaustion all the way to the part (1.1). Therefore, its dehumidification efficient is very high ; furthermore, the arrangement of dehumidification plants and transmission system can be simplified.

2) Percentage of cable surface available for direct dehumidification touching is almost 50%, which is much higher than the relative figure 1% of the current system. Moisture somewhere in the protected part needs to travel a quit short distance less than d, which is much smaller than the relative figure 140-150 m of the current system, along the void between compacted wires then arrive to the exhaust working surface.

Consequently, the function of humidity gradient is good enough for the operation of dehumidification and no need to change the inner general air pressure and structure for the cable covers, which can still be formed by conventional wrapping wires and coatings.

3) Cross-section area of the protection supplying part is (d + c-d s/4) d, which is more than 13.7 % of the protected part d27r/2, and much bigger than the relative section area of the exclusive air injection pipes used in the current system. Therefore, a much lower friction resistance in the vent-way is obtained.

4) All the isolating treatments are performed outside the wrapping wires; consequently, the exhausting friction resistance from the void between galvanised wires to the hollow part (1.6) can be reduced.

5) There is no need to use the rubber sheet with the problem of elastic durability.

6) A [2 (d + c) / (2 d + oc d + 2 c)] > 25.7 % part of the total wrapping wire surface inside the isolated cover can directly touch the dehumidification airflow, which protects the wrapping wires efficiently from corrosion.

7) Spacing of the two cable-elements can be reduced, for example on the designed Messina Strait Bridge the spacing of the two cable-elements is possible to be reduced from 1.75 m to 1.30 m.

3.2 Positioning of the oval main cable.

The invention at first hand will be used on new suspension bridges for both types of pin plate connection and bearing connection between main cable and hangers. According to the different arrangements of hangers and linking axis of the two cable-elements, the oval main cable can be positioned with four types, which are showed in Fig. 2: Type A-Horizontal linking axis with vertical hangers.

Type B-Vertical linking axis with vertical hangers.

Type C-Inclined linking axis with inclined hangers.

Type D-Horizontal linking axis with inclined hangers.

3.3 Arrangement of dehumidification plants.

Because the oval main cable itself contains a continuous dehumidification cover with almost 50% direct protected cable surface touching and also a vent-way with its quit big section area (d + c-d n/4) d (see Fig.

1), the arrangement of dehumidification plants becomes simple. Fig. 3 illustrates how the five plants are arranged:

I) A dry air injection plant (G) is assembled in the stiffening girder near the central nodes, which covers the dry air injection for the main cable of the centre span. A humidity meter is equipped in the central nodes (confer Fig. 6 and 7) to join the control of the plant (G).

2) In each anchor block a dry air injection plant (B) is assembled, which covers the dry air injection for the main cable of one side span and in one anchor block. A humidity meter is equipped in each of the anchor block to join the control of the plant (B).

3) On the top of each pylon a moisture exhaustion plant (P) is assembled, which covers the moisture exhaustion for the main cables of half centre span as well as one side span and in one anchor block. A humidity meter is equipped at each of the pylon saddles (confer Fig. 8) to join the control of the plant (P).

3.4 Clamps and central nodes of oval main cable and their vent-ways.

Since the outer size of oval main cable should be reduced as much as possible to save the costs of wrapping wires (1.4), coatings (1.5) and position holders (1.3) (see Fig. 1), the two cable-elements must be clamped together at all the clamps and central nodes. Furthermore, special dehumidification vent-ways must be arranged at all clamps and central nodes to connect the normal dehumidification vent-ways from their both sides. A series of conceptual design are carried out for those requirements.

In this invention, structures of all the camps and central nodes are similar as those of the conventional except that the two cable-elements can be clamped at the same time, which are going to show in the schemed drawings of this chapter. Therefore, focal point of description in this chapter is how the special vent-ways for dehumidification airflow are arranged. In this and the following chapters the meaning of symbol Type A, B, C and D is the same as in the chapter 3.2.

3.4. 1 Structures for clamps of the positioning Type A, D and Type B, C.

Fig. 4a, 4b/Fig. 5a, 5b illustrate the structures and their assembling method of positioning Type A, D/Type B, C for pin plate and bearing connections respectively: 1) Two cover-plates (4.2), (4. 3)/ (5.2) made of HDPE or anti-corrosion metal are fasten on the clamp (4.1) / (5.1) by the screws (4.4)/ (5.4).

2) The cover-plates (4.2), (4.3)/ (5.2) are then fasten on the cable covers (4. 5c)/ (5. 5c) of the main cable (4.5)/ (5.5), which consists of (1.4), (1.5) (see Fig. 1), by the tight bands (4.6)/ (5.6), so that appear special dehumidification vent-ways (4.7), (4.8)/ (5.7), which make the dehumidification airflow to continuously pass through the clams (4.1)/ (5.1). It can be seen that the area of (4.7) + (4.8)/2 (5.7) is quit close to the area of (1.6) in Fig. 1, therefore, there is no sudden increasing of friction resistance at the clamps.

3) Vent-holes (4.9)/ (5.9) are arranged on the clamp (4.1)/ (5.1) at the area of vent-ways (4.7), (4.8)/ (5.7) to facilitate the moisture exhaustion for the main cable part inside the clamp (4.1)/ (5.1).

4) Isolating stuffmg is pasted in all the gaps between (4.1, 4.2, 4.3 and 4.5)/ (5.1, 5.2 and 5.5) before fasting and tightening to ensure reliable isolation and to avoid galvanic corrosion if anti-corrosion metal cover-plates are used.

3.4. 2 Structures for central nodes of the positioning Type A, D and Type B, C.

Fig. 6/Fig. 7 illustrate the structures and their assembling method of Type A, D/Type B, C respectively: 1) Two cover-plates (6.2), (6.3)/ (7.2) made of HDPE or anti-corrosion metal are fasten on the central node (6.1)/ (7.1) by the screws (6.4)/ (7.4).

2) The cover-plates (6.2), (6.3)/ (7.2) are then fasten on the cable covers (6. 5c)/ (7. 5c) of the main cable (6.5)/ (7.5), which consists of (1.4) and (1.5) (see Fig. 1), by the tight bands (6.6)/ (7.6), so that appear special dehumidification vent-ways (6.7), (6. 8)/ (7.7), which make the dehumidification airflow to continuously pass through the central nodes (6. 1)/ (7. 1). It can be seen that the area of (6.7) + (6.8)/2 (7.7) is quit close to the area of (1.6) in Figure 1, therefore, there is no sudden increasing of friction resistance at the central nodes.

3) Vent-holes (6.9)/ (7.9) are arranged on the central node (6.1)/ (7.1) at the area of vent-ways (6.7), (6.8) / (7.7) to facilitate the moisture exhaustion for the main cable part inside the clamp (6.1)/ (7.1).

4) Isolating stuffing is pasted in all the gaps between (6.1, 6.2, 6.3 and 6.5)/ (7.1, 7.2, and 6.5) before fasting and tightening to ensure reliable isolation and to avoid galvanic corrosion if anti-corrosion metal cover-plates are used.

5) At the lowest point of main cable, the middle area of central node, a drainage valve (6.10)/ (7.10) is arranged for eventually water pumping out as well as two dry air entrances (6.11)/ (7.11) and a humidity

meter (6.12)/ (7.12) are arranged to connect and join the control of the dry air injection plant (G) (confer Fig. 3).

3.5 Pylon and splay saddles of oval main cable and their dehumidification facilitate.

In this invention, structures of all the pylon and splay saddles are similar as those of the conventional, except the following feathers as shown in Fig. 8 with the centre cross-section of the saddles: 1. The two cable-elements (8.1) are erected in one saddle (8.2).

2. For positioning Type A and D, a longitudinal diaphragm (8.3) is arranged to separate the two cable- elements.

3. For positioning Type B and C, a group of curved steel bearing beams (8.8) with hollow section are arranged between the two cable-elements to form the lower part of the dehumidification vent-way (8.6).

4. On the top of any kind of saddle, an isolating plate (8.4) and its rubber belts (8.5) are arranged to form the upper part of dehumidification vent-way (8.6).

5. For each pylon saddle, two moisture-exhausted exits (8.7) and a humidity meter (8.9) are arranged at the isolating plate (8.4) to connect and join the control of the moisture exhaustion plant (P) (confer Fig. 3).

3.6 Special reforming of machines and equipments for the construction of oval main cables.

In this invention, most of the conventional machines and equipments can directly be used except that some of them are necessary to be specially reformed.

3.6. 1 Special compacting machine.

Fig. 9 illustrates the structure of special compacting machine, which comprises a conventional part and a special part. The conventional part consists of a steel frame (9.1) with ten sides, ten groups of compacting shoes (9.2) and ten groups of hydraulic jacks (9.3) to compact most of the wires, while the special part consists of two reinforcing beams (9.4) and two tie plates (9.5) to withstand the outward component of the frame (9. 1) during compacting as well as two groups of compacting wedges (9.6) and their hydraulic jacks (9.7) to compact the wires between the two cable-elements.

3.6. 2 Wrapping machine Structure of wrapping machine is similar as the conventional except that working diameter Dw of the machine becomes bigger i. e. Dw = 2d + c (see Fig. 1).

3.6. 3 Wheels of gantry crane.

For the positioning Type A and D, in order to avoid the injury on the isolating cover (10.4) and (10.5) when a gantry crane drives on the oval main cable (10.1), two solutions are created as shown in Fig. 10 respectively: If a gantry crane lifts the stiffening girder elements after/before the construction of wire wrapping (10.4), the gantry crane is equipped with wheel type (10.6)/ (10.7).

3.7 Extension of the efficient dehumidification protecting system to retrofitting on existing suspension bridges.

The dehumidification protecting system is not only created for new suspension bridges but also for existing suspension bridges. Since hanger connection type on most of the old suspension bridges is the bearing type, in this chapter, structures for the bearing connection type will be expressed by description and drawings first, and then structures for the pin plate connection will be expressed by description only. The subordinate details, for example the materials and the fixing screws, for the similar elements will not repeat in this chapter.

3.7. 1 The efficient dehumidification system for improvement of main cable protection on existing suspension bridges.

Fig. 11 illustrates the retrofitted normal cross-section and the added structure at existing cable clamp with bearing connection type. In order to avoid the obstacle to eventual hanger (11.3) replacement, a vent-pipe (11. 5), on which some vent holes are drilled and position holders (11.6) are welded with certain spacing, is erected underneath the existing main cable (11. 1). New wrapping wires (11.7) is wrapped the (11. 1) and (11.5) together then new primer and outer coatings (11.8) are painted, so appears a retrofitted egg-shaped main cable with a vent-way simultaneously a working surface (11. 9) for dry air injection and moisture exhaustion. On the dehumidification direct attached surface of existing main cable (11. 1), the old coatings (11.4) are taken out to get better condition for moisture exhaustion. Two vent-clamps (11. 11) are erected on

both sides of an existing clamp (11. 2) to fix a short vent-pipe (11.10), which connects the vent-pipes (11. 5) from both sides. Since the cross-section of the short vent-pipe (11. 10) is smaller than that of vent-way (11. 9), there is certain sudden increasing of friction resistance at the clamps. Therefore, the power of dehumidification plants in retrofitted main cable should be lager than that in similar new built main cable.

On most of the old suspension bridges, there is no central node. Fig. 12 illustrates the structure at the lowest point of the egg-shaped main cable (12.1) without central node. There, a vent-clamp (12. 2) is erected, on which a drainage valve (12.3) is arranged for eventually water pumping out as well as a dry air entrances (12.4) and a humidity meter (12. 5) are arranged to connect and join the control of the dry air injection plant (G) (confer Figure 3).

Fig. 13 illustrates the vent structure at the pylon and splay saddles. Two vent-clamps (13.3) are erected on both sides of an existing saddle (13. 2) to connect the vent-ways of the egg-shaped main cable (13. 1). In order to get a bigger vent cross-section (13.5) in the saddle, a new isolating plate (13.4) with trough shape replaces the old one. For each pylon saddle, two moisture-exhausted exits (13.6) and a humidity meter (13.7) are arranged at the isolating plate (13.4) to connect and join the control of the moisture exhaustion plant (P) (confer Fig. 3).

As for the pin plate connection type, the vent-pipe (11.5) is erected above the existing main cable (11. 1) and cross-section of the short vent-pipe (11.10) becomes closer or similar to that of vent-way (11. 9) therefore there is no sudden increasing of friction resistance at the clamps.

3.7. 2 The efficient dehumidification system and auxiliary cable-element for strengthening and protecting improvement of main cable on existing suspension bridges.

If capacity of an existing main cable loses apparently by serious corrosion and needs to get compensation, or, even to get increasing of the capacity; besides, the corrosion protecting system needs to be improved, the vent- pipe (11.5) in Fig. 11 can conceptually be replaced by an auxiliary cable-element, which is showed in Fig. 14a and 14b. For facilitating the arrangement of the auxiliary cable-element on saddles and the eventual hanger (14.3) replacement, the auxiliary cable-element (14.7) is arranged above the existing cable-element (14.1) with a clearance of S Ds, here the D, is the diameter of anchorage socket (14.4) of the bearing connected hanger (14,3). Position holders (14.8) are arranged between the (14.1) and (14.7) with certain spacing, after that, new wrapping wires (14.9) wraps the (14.1) and (14.7) together, then new primer and outer coatings (14.10) are painted, so appears a retrofitted egg-shaped main cable with a vent-way simultaneously a working surface (14.17a) for dry air injection and moisture exhaustion. On the dehumidification direct attached surface of existing cable-element (14.1), the old primer and outer coatings (14.6) are taken out to get better condition for moisture exhaustion. Two venting and force-transmitting clamps (14.11) are erected on both sides of an existing clamp (14.2) to fix the auxiliary cable-element (14.7) together with the existing cable-element (14.1).

On each piece of the venting and force-transmitting clamps (14.11) a bell-shaped trough is arranged, which will be able to form a vent-way (14. 17b) to connect the vent-way (14.17a) when the trapezoid cover plate (14.13) and the tight band (14.14) are erected. On one side of the venting and force-transmitting clamps (14.11) a trough-shaped shoulder (14. 12) is welded for fixing the auxiliary cable-element cover (14.15) with cross-section of trapezoid plus circle, which lies on the auxiliary cable-element (14.7) through some rubber plates (14. 16) and forms a vent-way (14. 17c) to connect the vent-ways (14.17b). Since the cross-section of the vent-ways (14.17b, c) are smaller than that of vent-way (14.17a), there is certain sudden increasing of friction resistance at the clamps. Therefore, the power of dehumidification plants in retrofitted main cable should be lager than that in similar new built main cable.

On most of the old suspension bridges, there is no central node. Figure 15 illustrates the structure at the lowest point of the egg-shaped main cable (15.1) without central node. There, a vent-clamp (15.2) is erected, on which a drainage valve (15.3) is arranged for eventually water pumping out as well as a dry air entrances (15.4) and a humidity meter (15.5) are arranged to connect and join the control of the dry air injection plant (G) (confer Fig. 3).

On all the existing pylon and splay saddles, an auxiliary saddle needs to be arranged for the auxiliary cable- element. Figurel6 shows the centre cross-section of the new saddles. In the existing saddle (16.2) on the existing cable-element (16.1), a bearing frame (16.3) is erected. The auxiliary saddle (16.4), in which some vent-holes (16.6) are arranged, stands on the bearing frame (16.3) and the existing saddle (16.2) so that forms the lower vent-way (16.5). An isolating plate (16.7) covers the auxiliary saddle (16.4) so that forms the upper vent-way (16.8), which is connected to the lower vent-way (16.5) by the vent-holes (16.6). For each pylon

saddle, two moisture-exhausted exits (16.9) and a humidity meter (16.19) are arranged at the isolating plate (16.7) to connect and join the control of the moisture exhaustion plant (P) (confer Fig. 3).

If new force of the retrofitted main cable is bigger than the existing and the existing saddle can't bear the new force, capacity of the existing saddle can be strengthened as showed also in Fig. 16. Strengthening procedure for pylon saddle is: 1) Several holes (16.10) are drilled through the web of the existing saddle (16.2). 2) Steel framed form (16.11) is erected around the existing saddle (16.2). 3) Post-tensioning tendons (16.12) with their sheath pipes are erected. 4) High strength concrete (16.13) is cast into form (16.11). 5) Post-tensioning tendons (16.12) are tensioned. Strengthening procedure for splay saddle is: 1) Beside the existing rollers or hinge (16.14), new rollers or hinges (16.15) are erected with coincidence of their axes. 2) Several holes (16.16) are drilled through the web of the existing saddle (16.2). 3) Steel framed form (16.17) is erected around the existing saddle (16.2) on the new rollers or hinges (16.15). 4) Post-tensioning tendons (16.18) with their sheath pipes are erected. 5) High strength concrete (16.19) is cast into form (16.17). 5) Post-tensioning tendons (16. 18) are tensioned.

Above or behind each anchor block an auxiliary anchor block is arranged to anchor the auxiliary cable element.

As for the pin plate connection type, all the structures and measures are similar, whoever, the following improvement will be able to get: 1) The requirement of S > Ds (confer Figure 14-A and 15-B) can be released i. e. spacing of (14.1) and (14.7) can be reduced, because the auxiliary cable-element (14.5) and its cover (14.15) don't obstruct the eventual hanger (14.3) replacement. 2) Cross-section of the vent-ways (14. 17b, c) becomes closer or similar to that of vent-way (14. 17a) therefore there is no sudden increasing of friction resistance at the clamps.

4. Industrial Applicability The invention will be able to be used on suspension bridge projects, an important part of civil engineering industry.

5. Modes for Carrying Out the Invention Suspension bridge is a bridge type with the longest spanning capacity and main cable is the most important and characteristic part on a suspension bridge. Main cables are tremendously difficult to be replaced and normally govern the useful life of suspension bridges. The invention creates a high efficient dehumidification corrosion protecting system for the main cables. Therefore, the invention is useful for a company, who intends to raise his competitive power in the field of long span bridge projects. Modes for carrying out the invention are possibly the follows: 1) A bridge construction company, who intends to award the contracts in tenders of suspension bridge projects both for new built or retrofitted, carries out the invention.

2) A post-tensioning technique company, who intends to build a professional team for main cable construction on suspension bridge projects, carries out the invention.

3) A bridge consulting engineers company, who intends to get good results in competitive designs on suspension bridges, carries out the invention.