Review of Design Practice and Performance of Finger Joints

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Title: Review of Design Practice and Performance of Finger Joints

Author(s): G. Busch

Publication: Special Publication

Volume: 94

Issue:

Appears on pages(s): 955-966

Keywords: bridges (structures); control joints; deterioration; maintenance; performance; serviceability; structural design; Design

Date: 7/1/1987

Abstract:
Through the course of history, bridge engineers have been plagued with problems resulting from kinematic dilations and displacements, particularly on longer spans, and curved and skewed structures. Numerous variations of expansion joint devices have been utilized, but the earliest and most popular large movement system has been the finger or tooth joint. This paper explores the origins of the finger-type expansion dam and traces the evolution of this system to its current state-of-the-art designs for bridges in North America in an effort to determine the adequacy of finger joints. The cost effectiveness of these devices is equated in terms of ridability, drainage, durability, protection of the span ends and substructure, and ability or inability to transmit rotation and abnormal movements. Customary problems such as repair of exposed and fatigued finger plates and removal of impacted debris from drainage pipes and troughs are illustrated. Numerous other types of large movement expansion devices such as slider plates, rubber cushions, and modular systems have been installed on structures with various degrees of success. A comparison of these types of mechanisms to that of the finger dam is portrayed to equate performance of both. Some design authorities have begun to require more advanced types of expansion devices while others have continued to utilize finger joints. This paper also attempts to determine the reasons for these decisions as they apply to contemporary structures. Finger joints have undergone a multiplicity of variations in design throughout the course of their history on bridges. However, the fundamentals and performance shortcomings have remained the same on all of these devices. It is the intent of this document to inform the design engineer in this field of expertise.