saikee119
Structural
- Mar 21, 2018
- 312
A two-direction bridge has four spans in one direction suddenly collapsed during construction. Each span appears to comprise of 6 precast RC I-beams likely to have been prestressed to be installed in simply supported condition. Apparently most of the beams were in place but a removable steel beam, used to lower the RC I-beam into position was still in place but remained somewhat in rotated condition after the collapse. Some unusual features can be seen in the news. Among them are:-
(1) During collapse the mid span deflected first so the the I-beams became V-shape. The two ends clear both end supports and dropped.
(2) From the footage taken from the rear of a car traveling away from the collapse it could be seen at least two spans failed simultaneously.
(3) The removable steel beam, temporary used for the installation of the prestressed RC I-beams was still left between the supports but its longitudinal axis seems rotated slightly.
For (1) to occur the six prestressed RC I-beams could have been temporarily restrained laterally by ties so that the whole deck dropped off instead of individual beams.
For (2) to occur the failed 4 spans would have been longitudinally restrained too. This is because the I-beams are simply supported during construction and therefore could have collapse in one span without affecting the adjacent span.
