Precast Furnace Foundation
Here were the parameters, work in the center bay of the melt shop during production, and endure a 70% loss in construction production. Or work only on the mills down days which come once a week and last only six to eight hours, and try to stay on schedule.
The most labor intensive part of the project was the main furnace foundation. Estimated to take thirteen days at full production, we had only four weeks on the project schedule to complete it. The solution was to precast the entire foundation and set it as one unit. There was an area just large enough to precast the foundation in the bay north of the construction area. Utilizing the mills overhead cranes and a ladle transfer vehicle we were going to be able to move the foundation from the precast area to the permanent location without the costs of any rental equipment. So the decision was made to go with this solution.
A precast table was constructed using two inch square steel tube placed on two foot centers and shimmed to level and then decked with three quarter ply form. A lifting frame was installed in the base reinforcing steel before the forms were constructed. The frame was designed with arms that extended up into the foundation walls which were where the lifting points were located. After the foundation base was poured the remaining reinforcing steel was installed and the foundation walls were formed. The foundation walls would have transfer car rails embedded in there top surface when complete and because of the close tolerance of the rails it was decided to only pour the walls up to one foot below finish grade.
The entire foundation was constructed in eight days using 5000 psi concrete with high range water reducer. The precast structure was set on the thirteenth day after construction on it was started. The foundation weighed one hundred and sixty thousand pounds and was set in six hours on a scheduled down day. Nucor Steel suffered no loss in production during the construction of the foundation. Including demolition and excavation the foundation was in place on the seventeenth day of construction.