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Design, Fabrication and Erection of the “Pedestrian Bridge in the Road-Park of Ikei-Tairagawa” in Okinawa UNO Nayomon : KITAYAMA Nobuhiko :
Chief Engineer Chief Engineer,, Bridge Bridge & Road Construc Construction tion Divis Division, ion, Logistics Systems & Structures Planning Plan ning & Engin Engineeri eering ng Departm Department, ent, Bridg Bridgee & Road Road Construction Division, Logistics Systems & Structures
Okinawa is known it has severe environment that leads corrosion of steel fabricated products. How to cope with such corrosion or damage from salty breezes is one of important tasks. Use of FRP materials that are durable against such damages has been studied and was recently put into a practical use for the pedestrian bridge. There is a few structural example in civil engineering, and no design criteria is available, and design, fabrication and erection of an FRP pedestrian bridge conducted in Okinawa is described together with study items.
(a) Side view
1. Intr tro oductio ion n A road in Okinawa Prefecture —Ikei-Tairagawa-Line— is located in an important development area that is part of the Okinawa Tropical Resort Plan. In that plan the construction of a road park for beach recreation was needed, which required a pedestrian bridge to connect facilities planned on both sides of the road. IkeiTairagawa-Line is in a heavily corrosive environment surrounded by the ocean. In Okinawa Prefecture, it is reported that concrete bridges are damaged by salt, and how to cope with salt damage was an important issue when this pedestrian bridge was constructed. So the use of corrosion-resistant FRP (Fiber Reinforced Plastics) was investigated and FRP was adopted for the main material. This report describes the design, fabrication, and erection of the FRP Ikei-Tairagawa-Line Road Park Pedestrian Bridge.
Bridge length length 37 760 Girder length length 37 700
30
Span length length 19 677
400
17 223
400
V. C. L. 37 700 V. C. R. 600 m i = 3%
i
P1 MOV MO V
1.000%
P3 MOV
P2 FIX
2.000%
= 3%
2.000%
2.000%
(b) Cross section
4 300 400
3 500 Tile pavement t = 35
400
61 mm
FRP floor slab t = 60 mm CL
2. Ou Outli tline ne of of FRP FRP pede pedestr stria ian n brid bridge ge This bridge is a 2-main-girder bridge with the main girder section as “[” type and 2-span continuous girder bridge 37.760 m long and 3.5 m wide. Except for the joint portions for which ordinary steel is used, all the members of this bridge, including not only the main members but also the deck plates and handrails, are made of FRP. Fig. 1 shows a general view of the bridge, and the design specifications are described below. Type 2-span continuou s FRP girder bridge Bridge length 37 760 mm S p a n l e ng t h 1 9 6 77 m m + 1 7 2 23 m m E ff ffective wi width 3 50 500 mm mm A n g l e of sk e w 9 0° Slope L o n gi t u d i n al V. C .R . 6 0 0 m C r o ss sl o p e ± 1 . 5%
30
1.5%
5 3
1.5%
0 0 6
15
1
Fig. 1
General arrangement (unit : mm)
Applic App licabl ablee sta standa ndards rds Specification Specification for pedestrian crossing bridge (January 1979) Specifications for Highway Bridge (December 1996) Others separately specified D es i g n l oa d Live load 3 430 N/m2 {350 kgf/m2} (for main girder) 4 900 N/m2 {500 kgf/m2} (for 35
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deck plate and floor system) Wind load U d = 52.2 m/s Design horizontal seismic coefficient K h = 0.18
3. Design In designing this bridge, “Specifications for pedestrian crossing bridge” and “Specifications for Highway Bridge” were applied, but these standards do not include FRP. We therefore made separate specifications for FRP parts of the bridge, though we used the above standards as much as possible for applicable items such as design loads. However, for the wind load, we did not use the above standards in consideration of the peculiarity of the erection site and instead adopted a value 1.7 times the specified value of the “Specifications for Highway Bridge.” 3. 1 Outl ine of de si gn The main girder was made “[” type section because we used the hand lay-up process, and the girder height was made constant because changing it does not provide any cost advantage. The bridge length is about 38 m, but if we had adopted a single span, it would not have been economical and may have made to drivers feel uncomfortable. Therefore, this bridge was made 2-span continuous providing intermediate supports because it was possible to build the pier at the median. When the main girder section was decided, allowable stress has been set. Considering a maximum deflection of 1/600 of the span, the generated stress would become very small, about 1/7 against the separately specified design strength. We therefore considered there would be no problem with the material strength and did not investigate any further. The safety factor against the breaking strength was evaluated. The transportation and erection was planned to carry out in one operation, but since the manufacturing and assembling factories were separately located and thus required transportation by truck, the bridge was divided into 3 parts axially and joints were provided to the main girder. 3.2 Design of deck plate Considering to use a ready-made section for the deck plate from the viewpoint of cost, a hollow pultrusion FRP panel was selected (Fig. 2). Since the main girder width is 3.5 m, the axial direction of the bridge was made the direction of the deck plate span, and floor systems were provided at intervals of 1.5 m. Thus the design was made as the simple beam of the span. The
500
shear key was provided in the axial direction of the bridge. 3.3 Design of main girder For designing the main girder, the analysis model was made 1-beam, and the analysis was made with the load as 1/2 without considering distribution, though there were 2 main girders. The physical properties (Table 1), including material strength, were decided basically by conducting material tests. The design strength was calculated using m (average value) – 4 s (standard deviation) from the results of the material tests, and the bearing strength was made 1.5 times the compressive strength. The section was decided using these factors, and as a result, the stress was very small, as aforementioned, and the section was decided based on the necessary rigidity from the deflection limit. With FRP, it is known that the flexural modulus is smaller than the tensile modulus, (1) and so the shearing strain is big when compared with the bending strain, but we secured the shearing rigidity by using bias cloth with a fiber arrangement of 45° for the web. In this connection, the loading tests for actual bridge was carried out after the factory assembly was completed and the strain and deflection were measured, thus confirming that the specified rigidity was obtained. For the longitudinal slope, the camber was made the arc of r = 600 m to reduce the manufacturing cost. The main girder was divided into 3 parts in consideration of transportation, and the joint was provided at a point where the bending moment becomes 0 in dead load. For the joint structure, we adopted a tensile-type bolted joint by constructing a frame using a stainless steel plate inside and tightening it with a PC steel bar to hide the joint. Fig. 3 shows the joint structure. As to this structure, loading tests were performed using a full-size sample and its results were compared to the FEM analysis. To improve the appearance of the bridge, following method was considered. The web was provided with a horizontal square timber, thus shading it and making the beam height look lower. The upper flange also serving as the felloe guard was inclined toward the bridge deck so that no trace of water droplets will remain on the web. Some irregularity is produced on
Table 1 Item
Unit MPa
130
200
Bending strength
MPa
130
200
―
MPa
130
200
240
50
50
50
MPa
195
300
450
Tensile modulus
GPa
12
12
20
Flexural modulus
GPa
Coefficient of linear expansion / C °
36
FRP deck plate panel (unit : mm)
300
MPa
Bearing strength
Fig. 2
Hand lay-up formed material Drawn formed material Main girder Stiffener
Tensile strength Design Compressive strength strength Shear strength
0 6
4
Materials’ physical properties
Density
t/m3
12
12
20
2.0 × 10-5
2.0 × 10-5
2.0 × 10-5
1.7
1.7
1.9
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500 80 80 80
15
140 7050
3
16
317
16
0 7 5 3
3
4 8 1
6 1 6 0 2
Overlay 10-ply
1 1 2
Overlay 4-ply 5 0 4
4 6 1
Resin mortar filling
1 4 2
100
0 0 6 1
16
168
Fig. 3
100 100
34
20
59
16
39 59
Detail of joint (unit : mm)
the main girder due to resin shrinkage. To make this less conspicuous, the web was warped a little on purpose. 3.4 Design of sway bracing Since the deck plate span was made 1.5 m, the sway bracings were installed at that interval. As to the section of the sway bracing, the live load for the upper chord member was considered. For the other members, the sway bracing on the support was decided using wind load that would give the largest horizontal load. Using pultrusion material for the sway bracing as in the case of the deck plate, existing materials were selected. As a result, only the sections of the sway bracing on the intermediate support became larger, and other intermediate sway bracings were made the same section as the sway bracing on the end support. 3 .5 D esi gn o f bea ri ng Rubber bearings were used to cope with the horizontal movement due to vertical load and temperature. To fix the bridge in longitudinal direction and restrict up lift, the lower flange was held by anchor plates. And to fix the bridge in transverse direction, the concrete key raised from the substructure was used. 3.6 Design of expansion joint, handrail, and lighting equipment Temperature changes in the range of ±30°C were considered, but the movement of the main girder — in the range of ±12 mm — was small. Therefore, a simple stainless steel plate was adopted to put over the expansion spacing, and a sliding movement occurs on the deck surface on the installation side. The handrails were manufactured by combining pultruded and hand lay-up FRP and installed to the upper flange of the main girder
using stainless steel anchor plates. Lighting equipment was buried in the strut. For the lighting equipment, 20 lx was secured as the average illuminance. 3.7 Pavement and painting Porcelain tiles were used for the surface of the deck. We initially considered asphalt pavement but gave it up due to anxiety about the adverse effect of heat during rolling compaction. Hand lay-up members are normally covered with a protective layer called a gel coat, which is considered sufficient to prevent corrosion. (2) But for this bridge, a fluorine top coat 3 × 25 µm was performed because the area has strong ultraviolet rays and sand blown by the wind.
4. Fabrication 4.1 Fabrication of main girder The hand lay-up members used for the main girder were manufactured at Miyagi Factory and the pultrusion members at Sagamihara Factory. As to the hand layup members, the manufacturing accuracy of the form greatly affects the finished size, but since hand lay-up members had never been used for large civil engineering structures and we had no experience laminating thick plates, it was difficult to estimate resin shrinkage. We therefore experimentally carried out the laminating in advance and checked the shrinkage before manufacturing. The laminating work was done indoors, and since it was February, we controlled the temperature in the room with jet heaters, etc. Fig. 4 shows the laminating work. The blocks, each measuring 10 m to 15 m in length in the bridge axial direction, were laminated by about 10 workers. Fiber glass called knitted fabric was used in 37
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Fig. 4
Laminating work
place of the conventional roving cloth. The knitted fabric has fibers arranged longitudinally and laterally and an intercrossed portion bound with fibers and is not woven in a lattice structure as is the conventional cloth, allowing the initial strength to appear early. Since the fibers are not bulky, impregnating with resin is smoothly done during laminating, and the work can be done easily. For the vertical stiffener, pressed FRP material was used as the core, which was overlaid on the main body, and the cores were laminated almost in the same way as for the main body. For bolting, the bearing-type connection was adopted, and drilling was done as follows. In the main body, prepared holes with smaller diameters were made in accordance with the dimensional positions of the drawing, the fitting members were normally drilled, the members were installed during the trial assembly and the drilling was done with the holes of the fitting members applied as the template after the dimensions were measured. A stainless steel plate was to be buried in the joint portion of the main girder, and this burying work was done with the main girder adjusted during trial assembling, thus improving the assembling accuracy. 4.2 Assembly The members manufactured at the Miyagi and Sagamihara factories, were transported to the Sunamachi Factory of Ishikawajima Zosen Kakoki Co., Ltd. and assembled on the ground. Fig. 5 shows the shop assembly. For the batch transportation, all members, except the pavement, were almost completely finished on the ground. As to the assembling sequence on the ground, the main girder on one side was installed first and the sway bracing was fit. Then, the main girder on the other side was installed, and the sway bracing was opened and fit to the vertical stiffener, and finally the adjustment was made. This work was repeated on the 3 blocks in the bridge axial direction and the bolts of the sway bracings were tightened after dimensional measuring and the dimensional shape was adjusted with the blocks placed in the bridge axial direction. Then 38
Fig. 5
Assemble in shop
the blocks in the bridge axial direction were joined. The joint in the bridge axial direction has such a structure that the PC steel bar was tightened, and after the blocks were installed, dimensional adjustment was made and then PC tensioning was done. The tension control was made using a jack reaction meter because the tightening force was small at less than 10 tf. After the tightening was completed, pulling was done again with the jack, and it was confirmed that the specified axial force was installed. The deck plates were placed and bolted to the upper chord members and the surface boards were laid. The handrails were then installed, and at the same time, the lighting equipment was assembled and the wiring of the beam was done. The handrails were finally painted before installation, and the stainless steel base plates were painted in advance with epoxy primer. Then the main girders were painted. After the final painting was completed, the underside plates painted in advance were installed.
5. Transportation and erection To minimize the site work, the method of assembling at factory/batch field erection was adopted taking advantage of the light weight of FRP. After the assembling on the factory was completed, the members were transported to Okinawa on a 499-ton ship. A lifting frame was used to lift the members, and the main body was turned with nylon slings. We planned to unload the members at a fishing port near the site, but the port was too shallow for the ship. Instead, we transferred the members onto a barge, transported them to the fishing port and then used a pole trailer for land transportation because the bridge length was about 38 m. The bridge was erected at night. As we controlled traffic, we completed the transportation to the site in about one hour and a half. For lifting, we used the same 160 tf truck crane that was used for landing and completed the erection in about 4 hours. Fig. 6 shows the site erection.
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Pedestrian Bridge Technical Committee (chairman: Michio Okahara, manager of Bridge Structural Department, Public Works Research Institute, Construction Ministry) was set up, and we received valuable opinions from the committee members. We also received cooperation on tests from the staff of the Chemical Research Room of Public Works Research Institute, including Mr. Meiarashi, manager. Furthermore, we received generous help from the staff of Public Works Research Center, including Mr. Saeki, director, that was in charge of designing this bridge. We express our heartfelt thanks to them all. REFERENCES Fig. 6
Erection in one operation
– Acknowledgment – In constructing this pedestrian bridge, we received generous cooperation from the staff of the Okinawa Department of Infrastructure. To study the construction of this bridge, the Ikei-Tairagawa-Line Road Park
(1) The Japan Reinforced Plastic Society : Manual for FRP Structural Design, September 1992 (2) The Japan Reinforced Plastic Society : Handbook for FRP, October 1996 (3) Okinawa Department of Infrastructure, Middle Branch and Public Works Research Center : The Report of Pedestrian Bridge in the Road-Park of Ikei-Tairagawa in Okinawa, March 2000
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