An Investigation of Bridge Deck Overhang Falsework Systems Installed onto Modified Bulb Tee Girders

Abstract

Bulb Tee girders provide a practical, efficient means of spanning the large distances required in today's bridge designs by utilizing large moments of inertia to withstand the massive moments created in the spans. A bulb tee girder possesses a wider, thinner top flange than conventional precast concrete cross-sections. Previous research suggests the thin top flange of an exterior bulb tee girder in the bridge deck overhang falsework system to fail in punching shear and concrete bearing/spalling at premature loads.

Meadow Burke Products, Inc. has manufactured an innovative falsework hanger for use with thin flange girders such as the bulb tee. The hanger utilizes a bearing plate to distribute the vertical loads on the top flange. Experimental full scale testing of the innovative hanger on a bulb tee girder was completed as the first phase of this study. The hangers were installed onto a 63 in. North Carolina Department of Transportation (NCDOT) Modified Bulb Tee (MBT) girder and loaded by a hydraulic load cylinder at a 45 degree angle. The behavior and ultimate strength of the hanger and top flange of the girder were recorded.

Phase two of the experimental study consisted of testing the overhang falsework system with support brackets attached to the Meadow Burke hangers. The support brackets were loaded vertically utilizing hydraulic load cylinders. The load distribution behavior of the bracket and ultimate loading capacity of the system were recorded. Both phases of the experimental study concluded that a punching shear failure will occur in the top flange of the girder at a consistent loading.

Subsequent analytical studies were carried out in an attempt to predict and emulate the results seen in the experimental testing. The analytical study consisted of finite element models and ACI code provisional analysis for punching shear. The finite element models developed are able to accurately predict the behavior and ultimate strength of the system. ACI code for punching shear does not accurately predict the punching shear capacity of the MBT girder flange.