WJE performed a structural analysis and designed repairs for an unusual steel-framed parking garage in Connecticut. The garage consists of steel moment frames with unshored, composite concrete slabs designed in 1974 by Engineer #1. The girder end plates were originally bolted to the column flanges causing immediate column flange bending and web buckling after placement of the concrete. Over the next 44-years, non-trivial lessons were learned by all six engineering firms involved in this saga that we now wish to share with you. In 1985, Engineer #2 found and fixed two cracked welds at these ill-conceived girder to column moment connections. In 1988, Engineer #3 found and an additional cracked end plate and indications of cracking at 23 additional connections. Engineer #3 contemplated the merits of “cutting the moment connections loose” and fortunately lost the debate to Engineer #4 who recognized the need for overall stability of the frame and wisely added stiffened seats beneath all of the girders, instead. In 2002, Engineer #5 decided to add some ineffective stiffeners to the columns’ panel zones, ignore the water leakage noted by Engineer #4 and call it a day. During a routine assessment in 2012, Engineer #6 (WJE) observed deformation of the column webs and flanges at the moment connections, uncontrolled water leakage through the expansion joints, and moderate corrosion of several steel members. Knowing that something was not quite right, we recommended repairs to address the water leakage and further analysis of the beleaguered structure. The owner disregarded our recommendations, choosing instead to perform limited patching of the concrete slab. When we returned in 2017, structurally significant corrosion was found on several of the columns and connections. After showing photos of the holes in several of the column webs and flanges to the Owner, we had their attention.
WJE completed an assessment of the garage structure, including section loss measurements at the corroded columns and girders. To better understand the behavior of the structure, representative areas of the garage were modeled in CSI SAP2000 and Autodesk Simulation Mechanical finite element analysis software. The finite element model permitted examination of the ill-conceived moment connection including the effects of supplemental stiffeners and the seated connections. In combination with the finite element analysis, the SAP model provided better understanding of the behavior of the moment frame, including composite action of the girders and slabs. Columns with critical utilization ratios (demand/capacity) and severe section loss were recommended for repairs. WJE’s repair design accounted for significant axial loads in the columns and moment transfer at the existing girder to column connections. Based upon collaboration with the project team, we developed a practical and efficient design that limits the need for temporary shoring of the structure and permits continued use of the parking garage during repairs. Close coordination with the project team also provides the flexibility needed to customize repair designs just in time for shop fabrication to begin, thereby transforming an unfeasible project into merely an expensive repair.