Improved design of highway bridge fingerplate expansion devices
Authors:   , Mutnbak Mohammed IBRAHIM 
Published: May 2022

Fingerplate expansion joints are used in highway bridges to account for large movements and rotations of two bridge deck slabs. These joints experience may premature failure that affects the structural integrity of the bridge superstructure. The main reason for early deterioration of fingerplates is the poor design of the joints combined with the lack of accessibility to inspect key components of the joint. Therefore, this research aims to investigate the behavior of the currently used designs and to develop new and improved designs. The investigation of the in-service designs was done experimentally and numerically. In addition, two new and designs were developed, and an optimization process was performed to improve the proposed designs. An experimental program was developed prepared to evaluate the static and fatigue performance of the fingerplate designs. The testing was performed on prototypes of the current fingerplate joint design used by the Missouri Department of Transportation. The tests were designed to study three joint key parameters which are the fingerplate thickness, stiffener locations, and anchoring system. The static tests show that the effect of the fingerplate thickness is minimal in the area between the stiffeners. The results show that support beam stiffeners are key component of the MoDOT fingerplate joint design. It was also found that welding lines that connect the fingerplate to the support beam are the first failure locations. Two more failure modes were observed, which are buckling of the front stiffener and weld rupture between the back stiffener and the support beam. Results of the static experimental program were used to validate the finite element (FE) models developed in this research. Finite element models were developed for the MoDOT design and were validated using the static experimental program results. Another validation process was performed against existing FE models that were verified using field test results. Excellent agreements were obtained between the FE models developed in this research and the experimental results and the existing FE model. Three parameters were investigated numerically, which are the stiffener size and location and the support beam size. Since MoDOT design is incorporating only welded connection, most of the failure points were at the weld lines. Increasing stiffener size was found to be the most important factor to significantly increases the joint strength and improve its performance. Stiffener locations, front side or back side of the support beam web, change the behavior of the fingerplate joint by reducing the fingerplate displacement and increasing load-carrying capacity. Additionally, the support beam size was found to be the least effective factor where stiffeners are present. The validated FE model was then used to study two additional in-service designs, which are current designs adopted by the Maryland and Illinois Departments of Transportation. MDDOT design incorporates bolted connection, and its failure was controlled by the excessive elongation in the bolts' bodies. ILDOT design is a completely welded design, and its failure mode is controlled by rupture of the weld lines. A design proposed to MoDOT by HDR company was also investigated, and the results show that its failure is controlled by the excessive elongation in the bolts. Two new, innovative, maintainable, and replaceable designs were developed to account for the various issues discovered in all the existing fingerplate designs investigated. The new designs resolve the issues observed with weld lines and the issues of bolts' bodies and weld lines being embedded in the concrete block of the bridge deck. In addition, the new designs have strengths greater than the existing designs investigated in this research. Step-by-step design guideline was developed for each of the proposed new designs by using AASHOT, FHWA, and AISC design specifications. A parametric study was performed on the proposed designs under design and service loads. In this parametric study, four different finger configurations along with two different bolting patterns were investigated to study the effect of different finger shapes on the joint behavior.