Process, operational, and electrical restrictions inherent in the design of a regulatory compliance upgrade for an industrial plant, and overburdened existing structure, required an unusual structural retrofit. There were multiple restrictions on placement of structural members and multiple needs for additional strength in the existing members. To manage the constraints, the load path was reformulated to bypass problem areas and focus upgrade work on just a few locations. The key in selecting upgrade locations was determining where there was reserve capacity in the existing foundation. Two such locations were identified and super-bents were formed there using existing moment frames. Horizontal trusses were built to bridge between the super-bents. A super-bent included a new grade beam, with end bulbs surrounding existing column pedestals, column section augmentation, new heavy anchor bolts and new diagonals to convert two parallel beams into a deep truss. Embedded structural steel was utilized in the grade beam end bulbs to distribute anchorage forces and develop reliable load paths around obstructed columns. Unusual uses of structural steel, work in obscured areas, unconventional structural systems and construction schedule interruptions led to an increase in construction management and inspection scope and complexity. CM lessons learned from the project involved better interaction of disciplines during design and greater input from engineering just prior to and during construction.
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