Practice Periodical on Structural Design and Construction

Located near downtown Milwaukee, the Marquette Interchange reconstruction project is the largest and most complex highway project ever undertaken by the Wisconsin Department of Transportation. The construction staging on this project is very complex and it is critical that the Department meet the project’s December 2008 completion date. The reconstruction involves a significant amount of structural steel for rebuilding plate I-girder, prestressed concrete of girder and concrete box girder bridges. Throughout the design process the Department had identified steel delivery as a potential risk item for the project and monitored delivery times as the design proceeded. To expedite the schedule, the Department has selectively procured preliminary shop drawings for critical structures and provided those to all prospective bidders prior to the bid opening.

Integral-abutment bridges have many advantages over full-height-abutment or stub-abutment bridges. Integral abutments eliminate or reduce the number of expansion joints in bridge superstructures and simplify design, detailing, and construction. In this paper, foundation design concepts, such as fixed-head pile, pinned-head pile, hinged abutment, fixed-base pile, prebored hole, sleeved pile, and asymmetry are reviewed. The typical foundation type for support of integral abutments is the steel H pile. Depending on bridge length, skew, and site conditions, other types of foundations, such as precast prestressed-concrete pile, pipe pile (steel encased concrete pile or metal shell pile), timber pile, combined H pile (or W section) and drilled shaft, caisson wall, drilled shaft, sheet pile, and spread footing can be used to support integral abutments. Several design methods and proposed limits for typical integral abutment bridges are reviewed.

Turbo generator pedestals are one of the critical structures in any power plant complex. Stringent vibration requirements particularly at the bearing locations have been stipulated for proper functioning of turbo generator installations. Normally the dynamic analysis is carried out using a deterministic approach with constant material properties. The effect of variability of modulus of elasticity of concrete, and operating speed of the turbo generator can lead to increased amplitudes of vibration. The designer always looks for conservative estimates of the expected responses and is interested in keeping them within allowable limits. This paper provides a methodology for computing peak dynamic response at bearing locations once the results of the dynamic analysis with a given input stiffness is available. The approach is essentially based on modal synthesis of responses, namely contribution of individual modes to amplitude of vibration at a particular location. The frequency range of interest is divided into three regions, namely, nonresonant region where undertuned conditions exist, nonresonant region where overtuned conditions exist, and the resonant region. Simple analytical formulation has been developed to compute the peak dynamic response and is illustrated with an example. The suggested method can be programmed for effective use through spread sheet and MS EXCEL software.

Structural designers use parametric equations to convert results of simple beam models to detailed hot spot stress distributions. Knowledge of hot spot stresses improves fatigue performance predictions. This paper extends the use of the parametric equation approach to joints with extra stiffening such as doubler plates. Doubler plates are commonly used on tubular structural joints against actual or anticipated punching shear failure. Reinforced tubular T, Y, K, X, and DT joints with and without doubler plates are considered. Results without doubler plates are compared against past studies and also the recommended design formulas used in international codes. Finally, a sensitivity analysis is performed describing the effect of joint geometry variations on the stress concentration factor values.

The objectives of the research reported in this paper were to monitor and document the rapid bridge deck replacement work of the Georgia Department of Transportation (GDOT) on two bridges in Gainesville, Ga., and two bridges in Atlanta. Documentation of the GDOT work included a time sequence, deck replacement square footage per work period, total construction time, typical work period construction tasks, and photographic display/discussion of the deck replacement work. The precast exodermic deck panel system used by the GDOT provided an excellent means for rapid bridge deck replacement while under staged construction/concurrent traffic conditions. The GDOT work was completed within the imposed time limits while maintaining minimum traffic interruption.