Examining structural Failure Cases
Nghiên cứu các trường hợp bị sự cố kết cấu
By studying structural failures as a necessary part of civil engineering course, students can gain knowledge of the importance of design and detail. Designers, contractors and inspectors work hard to provide safe and economical structural and facilities for the public. Case studies of failures also help students understand the ethical and professional standards required of practicing engineers to prevent tragedies.
1. Formwork design must account for actual jobsite conditions:
Students should understand that formwork is a structure, and like any structure, must have sufficient strength and stability to support all loads.
Case 1: New York Coliseum 1955. Approximately 930m2 of the main exhibition hall collapsed during construction, killing one worker and injuring 50 others. The formwork was to stories high, supported by (90×90) mm timbers links together by a crossbeam at midheight; the crossbeam did not provide bracing against lateral instability. Buggies transported the concrete for the slab being cast; eight buggies were on the formwork at the time of collapse. According to the district attorney’s office, the cause of the failure was “inadequate provision in the formwork to resist lateral forces”. Without proper bracing, the structure became unstable under the dynamic loading of the buggies. Formwork designs that had been successful used before the use of the buggies proved unsafe under the new, heavier loads.
Case 2: Love Dam Cantilever form failure 1981
Concrete formwork at a dam construction site failed, killing two workers and injuring 13. The formwork was anchored into previously placed concrete using anchor bolts (“she bolts”) that were intended to be loaded in tension only. Because the existing of concrete dam face was slope and not vertical, the weight of concrete included force components into the anchor bolts that were both parallel and perpendicular to the face of the dam. The components produced a shear force and a bending moment in the anchor bolts, for which they were not designed. Examination of the failed anchor bolts indicated bending fracture.
Case 3: Bailey Crossroad 1973
Another tragedy was blamed on strip formwork below inadequately cured concrete. Fourteen workers were killed and 30 were injured. Shores were removed between the 22nd and 23rd floors of the building while concrete was being placed on the 24th floor. The collapse tore a 18m wide gap through the building all the way to the ground. The concrete, when tested, turned out to be well below its expected stripping strength. The floor slab failed in punching shear at the columns.
2. Cold weather affects concrete’s strength
(Continued soon in part II)
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