Civil Engineering Reference
In-Depth Information
the additional prestressing effects are included, that deficient member becomes satisfactory.
In the full-size experiment of the original structure, resistance strain gauges are arranged
on the upper and lower chords, diagonal tensile members, additional prestressing tendons
and tensile reinforced bars to test its load situation. The result reports that the internal
forces in those tested members become different to some larger or small extent as the roof
loads change, which proves the effectiveness of the second retrofit design since the original
and additional members are able to work together compatibly.
(3) Retrofit program
On the basis of computation, analysis and test, the method of binding steel roof truss
dual structure is chosen, considering the high temperature of electric furnace smelting in the
eastern part. For the western part, reinforcement on the original retrofit follows these three
points:
a. Adding sway rods and altering the load path can solve the problem of insucient
bearing capacity of the upper chords in both end bays, such as setting up joists with angles
and stay bars in that area (see Fig. 3.48) and strengthening vertical bars in the bottom
with a formed steel jacket.
b. Although the lower chords crack seriously, the bearing capacity is adequate and the
additional prestressing tendons in sunk style method can work together well with the original
members despite the inappropriately designed detailing. Therefore, blocking some concrete
of C30 grade into the steel channel anchorage at the prestressing tendons and then tightening
the anchoring caps on them are enough to prevent deformation in anchoring plate from
having negative effects on the load state, with no retrofit in the middles of lower chords.
c. It is found that the upper chords in the second bay are unsafe because of the additional
diagonal stay bars in the first bay, which require the jacketing formed steel to strengthen
them.
d. For other tensile web bars, the screw caps on the original prestressing bars should
merely be tightened.
After the retrofit construction mentioned above, the roof truss system performed well.
