Concrete Destruction at Knife River
The hollow-core concrete beam spanned approximately 40 feet and was loaded with 24 tons before failure. Each concrete block placed on the beam by the forklift weighed 4 tons. Prior to failure, the beam deflected over 11 inches. Within the picture that shows the hollow-core end of the beam you can also see the minimal steel rebar reinforcement running along the bottom plane of the beam. There is one rebar piece in between each hollow-core. This image also shows a close-up of the crack, which developed along the central axis of the beam and likely led to the complete failure.
Below is the complete video of the loading and failure of the hollow-core beam. Throughout the video, you can track the growing deflection. Also, take note of the difficulty the forklift had in setting down the 4 ton weights without pressing on the beam. The intense failure is captured around the 9:00:00 mark.
The field trip to Knife River was excellent. Looking forward to the next adventure for the Ecology of Buildings Materials course. Thank you to Dusty for an informative tour.
