SHIOSAI BRIDGE IN JAPAN

The Shiosai Bridge in Shizuoka, Japan, is a prestressed concrete four-span stress-ribbon bridge with roadwayslab decks, which forms a so-called inverted suspension bridge. The bridge, for cyclists and pedestrians, was completed in 1995. The superstructure consists of roadway slab decks, columns which support the slab decks, and stress ribbons forming the lower cord. The bridge length is 232 m, the clear width is 3.0 m, and the span lengths are 55, 61, 61 and 55 m.

In this structure, loads are transferred via the slab decks into the columns, which are supported by the stress ribbons that in turn are supported by the piers and abutments. Overall stiffness was increased using elastic connections with horizontal neoprene bearings, which were installed between the ends of the roadway slabs and the abutments. Most of the superstructures were precast using lightweight concrete, in order to minimize the horizontal forces acting on the abutments, thus making the structure more economical. To ensure corrosion protection, epoxy-coated prestressing strands were used for bearing cables and prestressing cables for the stress ribbon. 

Forces and stresses to be considered in designing Road Bridges?

Forces and stresses to be considered in designing Road Bridges?

IRC:6 gives procedure for design and construction of road bridges in India. It gives information about load, forces and stresses to be considered in designing Road Bridges:

• Dead load due to 

1. Footway and kerb
2. Self weight of parapet
3. Deck Slab

• Live Load
• Snow Load
• Impact caused due to:

1. Floating bodies or vesssels as the case may be
2. Vehicles

• Wind load
• Water current
• Longitudinal forces caused by:

1. Tractive effort caused through acceleration of the driving wheels.
2. Bracking effort resulting from the application of brakes to braked wheels.
3. Frictional resistance offered to the movement or free bearings due to change of temperature or any other cause.

• Centrifugal forces (in case a road bridge situated on a curve).
• Secondary stresses due to:

1. Movement of supports.
2. To the deformations in geometrical shape of structure.
3. Members resulting from causes such as rigidity of end connection.
4. Loads applied at intermediate points of trusses.
5. Restrictive shrinkage of concrete floor beams.

• Buoyancy
• Earth pressure including live load surcharge if any
• Seismic forces.
• Temperature effects
• Deformation stresses 
• Secondary stresses
• Erection stresses
• Permissible increase in stresses in various members due to combination of load.

CASTING OF SEGMENT

CASTING METHODOLOGY OF SEGMENT

MOULDS:-

There are three types of inner mould for casting of segments.

(a) Pier Segment Mould

(b) Intermediate Segment Mould for segment S2

(c) Intermediate Segment Mould for remaining segments

Each mould comprises 3 major components – Outer Shutter, Bottom shutter and Inner shutters. Bottom Shuttering is supported on casting bed pedestals. Outer shutters are supported on a Movable Trolley.

     BOTTOM SHUTTERING

Bottom Shuttering is supported on 3 rows of concrete pedestals. Bottom shuttering is fabricated in the form of panels of 7.8m x 1.25m sizes.

Bottom Shutters shall be fixed for all segments on the Long Line casting bed.

    SIDE SHUTTERS

Side shutters are mounted on a movable trolley. Each Long Line casting bed shall have two such moulds so that two intermediate segments are cast simultaneously, one from either side.

SEQUENCE OF CASTING

A long line bed shall be provided wherein width of bed shall be 7800mm. In a typical casting sequence two pier segments (which shall be cast separately on pier segment bed) shall be brought and placed on bottom shutter on either side of long line bed. Two intermediate segments are match cast simultaneously, starting from either end. Subsequent to casting of S2, S3 is match cast. This procedure is continued till 2 segments are balance. The last segment of the span is match cast between 2 segments. The other shutter is used to start the next span from the pier segment.

      REBAR JIG

Three Rebar jigs for intermediate segments and one Rebar Jig for pier segments shall be fabricated to meet the requirement of 40mm clear cover from all sides of concrete surface.

 REBAR CAGE

The rebar cage shall be cut & bent by using cutting & bending machine at the centralized reinforcement yard adjacent to the casting yard.

The cage shall be lifted with a structural frame holding the cage in a manner to prevent any distortion while lifting and placing in position inside the casting mould.

The cage shall be lifted and placed in the casting mould by the 20T capacity Goliath Crane

  

     CONCRETING

The sequences of concrete shall be as follows:-

1)    Soffit Slab

2)    Half height of Web – 1

3)    Half height of Web – 2

4)    Half height of Web – 3

5)    Remaining Portion of Web – 1

6)    Remaining Portion of Web – 2

7)    Remaining Portion of Web - 3

8)    Deck Slab including Cantilevers on both sides

The concrete of M-45 grade with a slump of 80mm to 120mm shall be produced at the centralized Batching plant, and transported to location by transit mixers. The concrete shall be placed in sequence mentioned above by concrete pump. The concrete shall be vibrate by both shutter vibrators fitted to the web shutter as well as needle vibrators (60mm dia needles). Cubes in required number shall be cast from respective concrete pours. Roughing of deck slab of the segment shall be done in required locations were secondary pour is to be carried out.

For separation of match-cast segment a suitable bond breaking material (such as Concure WB from Forsroc) shall be used on the surface of previously cast segment.

FIXTURES IN SEGMENT

        All other fixtures such as drainage spout etc. shall be provided at specified            locations as detailed in the drawings.

 CURING OF SEGMENTS

Curing of concrete shall be complete and continuous with water. Curing will be done for 14 days from date of casting. As an alternative, the segments can also be cured by applying curing compound duly approved for use. After casting the segment curing compound shall be applied on all exposed surface after initial set is achieved and the surface is moist and free surface water has disappeared from concrete surface.

DESHUTTERING

The shuttering shall be removed after the concrete has attained 20 Mpa crushing strength.

The internal forms shall be collapsed using the turn buckles provided for movement of shutter.

WELL FOUNDATION

Well foundations:

It is the most common type of foundation in India for both road & railway bridges. Such foundation can be sunk to great depths and can carry very heavy vertical and lateral loads. Well foundations can also be installed in a boulder stratum. It is relatively rigid in its structural behavior.

Well Components :

well components

• Cutting Edge
• Well Curb
• Well steining
• Bottom Plug
• Sand Fill
• Top Plug
• Well cap

Cutting Edge:

cutting edge

It is lowermost part of well. It is the part which cuts through the earth. The mild steel cutting edge shall be made from structural steel sections.

Well Curb:

well curb

It is structure with outer wall of curb being straight and inner at appropriate angle which is fabricated over cutting edge. The well curb supports the steining. The curb should be slightly projected from the steining to reduce the skin friction during sinking of well .That's why thickness of well curb is kept 75 mm more than that of steining to prevent tilts. It is made of RCC with steel cutting edge. The inner portion of the steining should have a slope of 2:1 (V:H).

Well Steining:

well steining

It is longest part of well and it transfer load from well cap to the well curb. Steining is built in lifts of 2.15 m. It is designed such that it cam sunk under its own weight. The thickness should be sufficient so as to overcome skin friction developed during sinking by its own weight.   

Bottom Plug:

It transmits load to soil below. When sunk to its final depth bottom part is concreted to seal the bottom completely. The concreting should be done in one continuous operation. 

Sand filling:

After concreting the bottom plug the sand is filled above the bottom plug and below top plug. Sand filling provide stability of well, reduce tensile stress produced by bending moment and distributes the load of super structure on to the bottom plug.

Top Plug:
 
This is a plug at the top of the well below the well cap.

 Well Cap:

The well cap is RCC slab of sufficient strength to transmit the forces from pier to the body of well. it is generally kept at low water level. The dimension of the well cap should be sufficient to accommodate pier.

Bottom Plug concrete calculation

Bottom Plug concrete calculation

Download Excel sheet of Concrete Calculation in Bottom Plug

Excel sheet of Concrete Calculation in Bottom Plug

Download excel sheet containing Concrete Calculation in Bottom Plug


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Casting Yard

A casting yard  is a confined place where all the concrete structures like segments, I-griders/ beams etc are casted. The casting yard brings factory- controlled production techniques, efficiency, quality control, and time savings to bridge construction. Fabricating bridge segments in a separate area also removes casting operations from the construction critical path and reduces overall construction time.

 Regardless of the project location or size, a contractor's casting yard for bridge segments has several essential features. These include:

• delivery and storage areas, 
• a concrete batch plant, 
• a rebar cage assembly area, 
• one or more casting cells, 
• steam curing facilities,
• geometric control stations, and
• segment storage and handling facilities.

The size of yard depends upon the size of the job and required rate of segment production. A typical production rate is four or five segments per five - day work week.

Producing bridge segments in casting yard away from the bridge construction site is a major advantage of segmental concrete bridges.

(For more detail go to concreteconstruction.net)

EXTRADOSED PC BRIDGES

An extradosed prestressing concept, is a new type of structural system in which the tendons are installed outside and above the main girder and deviated by short towers located at supports. 

Extradosed PC bridges have several positive characteristics. The girder height may be lower than that of ordinary girder bridges, thus reducing self-weight of structures. The ratio of the girder height to the span length (H/L) in extradosed bridges ranges between 1/15 and 1/35, while it is approximately 1/15~1/17 for box-girder bridges. Comparing to cable-stayed bridges, the height of the main tower in extradosed bridges is lower; hence, a reduction in labor costs of construction can be achieved.