Fatigue-life evaluation of steel post structures. II: Experimentation

Changeable message signs (CMS) are supported by cantilevered, inverted L-sh aped structural components composed of a vertical post and a horizontal mas t arm. The high-cycle fatigue failure of one CMS structure in southern Cali fornia led to a detailed analytical and experimental study of components of CMS structures. This paper reports the results of the experimental studies and presents recommendations for future CMS construction. A companion pape r documents the results of the field studies and finite-element analysis of components of CMS structures. Six cantilever specimens were tested to fail ure: one as-built post (AB1); two retrofitted posts (GR1 and CIP1); and thr ee mast arms (MAI, MA2, and MA3). The specimens were tested at a stress ran ge of 69+ MPa (10+ ksi). The fatigue life of all six specimens exceeded the AASHTO design fatigue life of 400,000 cycles for a stress range of 69 MPa. Alternate construction details; improved welding, fabrication, and quality assurance/quality control practices; additional field and wind-tunnel test ing; and further laboratory experimentation are recommended.