Background of knowledge

 This method is similar to a developed steel box rahmen overhead bridge. The steel box beam is placed in a simple beam system on the columns, and connected both ends of simple beam by PSC steel bars. Oil jacks are placed between the center of the beam and the PSC steel bars. After being manufactured by this method, The beam is loaded by oil jacks. This beam is continuous columns and PSC bars are eliminated. Results of this method rise to positive moments to parts of negative moments and  negative moments to parts of positive moments. These moments resist moments which are occurred by dead and live load.  A newly developed method, the prestressed steel box rahmen overhead bridge using vertical load, decreases above 50% to sections of columns and foundations when loaded a lower load, but disadvantages to parts of positive moments and has difficulty in working for loading a vertical load.

 However the steel box whose parts of center and ends are able to make variable sections which have straight or curved, the former method is slenderer than the latter for appearance of the beam and decreases about 30% than a simple beam system for quantity of steel.

The method of construction

Manufacture and construction of the prestressed steel box rahmen overhead bridge using PSC steel bar

 

 The construction program for this method is described as follows

 

  STEP1 : The steel box beam is placed in a simple beam system on the column

 

This method is similar to a developed steel box rahmen overhead bridge. The steel box beam is placed in a simple beam system on the column.

(Fig. 1)

  STEP 2 : After being installed PSC bars and oil jacks to both ends of the beam, the beam is prestressed.

 

When loaded with oil jacks, tendon force occurred in PSC bars. This force rise to negative moments to parts of positive moments and positive moments to parts of negative moments for the steel box beam. The number of oil jacks is 1 when the length of beam is about 50m, and 2 when  the length of beam is longer than 50m.

(Fig. 2)

(Fig. 3)

  STEP 3 : The steel box beam is continuous columns and tendon forces is eliminated

 

(Fig. 4)

  STEP 4 : The overhead bridge is completed

 

When the overhead bridge is completed, the figure 5 is the moment diagram by dead and live load. However negative moments rise to both ends of the beam and positive moments rise to center of the beam, these moments is equal to moments of (4).

(Fig. 5)