Fatigue Life Evaluation of Changeable Message Sign Structures. Volume 2.211 Retrofitted Specimens

摘要

This report outlines the research program undertaken at the Earthquake211u001eEngineering Research Center (EERC) to investigate the fatigue life of retrofitted 211u001eChangeable Message Sign (CMS) structure posts. Following the failure of one CMS 211u001estructure in Southern California, field studies were undertaken that indicated 211u001ethat the groove-welded post-to-base plate connections were susceptible to wind-211u001einduced fatigue cracking. Laboratory studies on CMS posts indicated that the post 211u001ecross-section adjacent to the electrical conduit hole was also susceptible to 211u001efatigue-induced cracking. To increased the fatigue life of CMS structures, 211u001eCaltrans engineers identified the following retrofit strategies: (1) increase the 211u001esection modulus of the post near the post-to-base plate connection and the 211u001econduit hole to reduce the cyclic stress ranges at the critical cross-sections; 211u001eand (2) increase the mechanical damping of the sign structure. Two retrofit 211u001eschemes corresponding to the first retrofit strategy were developed and tested: a 211u001esteel gusset-retrofit (GR1), and a cast-in-place concrete-jacket retrofit (CIP1). 211u001eSpecimen GR1 was tested to approximately one million cycles before significant 211u001ecracking developed. Specimen CIP1 was subjected to 4,500,000 cycles of loading 211u001ewithout failing.