eyebar
A straight bar, usually of metal, with a hole or "eye" at each end to allow it to be fixed to other components.
eyebar: tensile rod with pinned ends for structural loads
An eyebar is a straight metal rod, typically steel, with a circular hole (the eye) forged or drilled at each end. These eyes allow the bar to be connected to other structural members via bolts, pins, or rivets, making it a fundamental tension member in bridge and building frameworks. The bar itself carries tensile forces while the eyes accommodate the connection hardware, keeping the load path direct and predictable.
Eyebars are commonly made from structural steel with cross sections ranging from simple rectangular or circular stock to more complex built-up shapes. The eyes are usually enlarged relative to the bar body, either by upsetting (thickening) the metal during forging or by welding on reinforcing plates. This enlargement distributes stress around the hole and reduces the risk of tearing at the connection point, a critical consideration since the hole itself creates a stress concentration.
They appear most visibly in suspension bridges and arch bridges, where they serve as vertical or diagonal suspender rods, and in pin-jointed truss systems common in both historic and modern structures. The use of eyebars declined after mid-20th century welding became standard, but they remain in service in thousands of existing bridges and are still specified where pin connections are preferred for movement accommodation or for matching heritage construction methods.
Failure modes and inspection
Eyebar fatigue is a well-documented problem. Corrosion pitting inside the eye, stress concentrations at the inner edge of the hole, and metallurgical defects can initiate cracks that propagate through the bar body. Many historic eyebar failures, particularly in bridges, have been traced to fatigue cracking originating at the pin contact surface. Modern inspection relies on close visual examination, ultrasonic testing, or magnetic particle inspection to catch subsurface flaws before catastrophic failure.
The name is direct and descriptive: the eye is simply the hole itself, and the bar is the structural member. The term has been in continuous use in structural engineering for over 150 years and remains precise enough that a drawing specification mentioning an eyebar needs little elaboration.