Abstract
Traffic signal and other ancillary structures have failed due to fatigue caused by wind. Such structures are typically lightly damped and have low natural frequencies. The fatigue cracks begin in the base metal near welds. Because of geometric and functional requirements, welds are often category E or lower. Additionally, transportation agencies use unique connection details for a variety of reasons including aesthetics and economy. Fatigue resistance is difficult to categorize because of the uniqueness of the geometries, member sizes, and manufacturing processes. A low-cost performance based procedure is needed in order to test joints as manufactured. Such a procedure would permit the many tests required to develop reliable fatigue performance of a connection. This research focuses on the development of an economical fatigue test procedure for mast arm connections and base plate connections. A full-scale cantilevered traffic signal structure was fitted with an eccentric-mass oscillator, and the oscillator was used to excite the structure near its natural frequency. Different stress ranges were achieved by controlling either the frequency of the motor or the mass-eccentricity of the oscillator in a reliable and repeatable manner. The observations indicate that near-constant amplitude and direction control are possible for in-plane, out-of-plane, and bi-directional load effects. The proposed test is conducted at a fraction of the cost of traditional actuator-controlled methods.
