The construction of the steel box girder by up-down support and casting concrete at the negative moment area

This method's purpose is improving stiffness necessary to negative moment area by shear connector installed and casting concrete on the bottom of the negative moment area of the steel box to steel box girder.
Otherwise, improving stiffness necessary for taking off tension force when design load applied by using the up-down method, compressive stress installed on the negative moment area of upside of deck plate concrete.

This method is more extend a span of bridge than existed steel box bridge and case of making nonprismatic section of the positive-negative moment area, most extend a span of bridge.
Otherwise prevent a decay in the steel box by being installed concrete at the bottom of the negative moment area and obtain effect that obsorbed noise or shake.
And reduce a fault of welding area by changing top and bottom flange thick into relatively simple.

The procedure of construction

(1) The manufacturing and construction of 2 span steel box girder bridge


  The drawing shows the procedure and details of construction.
1 is lifting-up support, 2 is lifting-down support, 3 points slab concrete and 4 indicates concrete that is cast in lower part of the steel box girder at the range of negative moment.

 

A. The state of lifting-up inner support after casting and curing concrete  in lower part of the steel box girders at the 50% range of negative moment in condition of setting steel box girder over 2 span

B. The state of setting in condition of lifting-down support after casting and curing concrete over full span in condition of lifting-up support

(2) The manufacturing and construction of 3 span steel box girder bridge

 The dynamic effects of 3 span is same as them of 2 span.

 

A. The state of lifting-up support after connecting 2 spans first among 3 spans and then casting and curing concrete in lower part of the steel box girder at the negative moment range of the first inner support

B. he state of lifting-down inner support that was lifted up after casting and curing concrete over full span except left-hand parts of the third support in condition of lifting-up the first inner support

C. The state of lifting-up support to induce compression stress to concrete in lower part of the steel box girder after casting and curing concrete in lower part of the steel box girder at the negative moment range of the right-hand support

D. The state of setting to support in condition of lifting-up  right-hand support after casting and curing concrete in remaining span

(3) The manufacturing and construction of steel box girder bridge more than 4 span


 The steel box girder bridge more than 4 span can be constructed by iterating above procedure and be applied to method of reinforcing rigidity.