Discussion of Tubular Steel Monopole Base Connections: The Base Weld Toe Crack Phenomenon; Crack Identification and a Proposed Severity Classification System

摘要

Tubular steel monopoles (poles) are popular support structures in many industries today and have been utilized as support structures in the communications, sports lighting, electric utility, and transportation industries for many decades. The number of poles in the communications industry has exploded in recent years caused by the ever-increasing demand for voice and data usage on wireless devices. Poles have a proven history of being reliable support structures, however, in the last decade there have been numerous failures of steel poles across the country in various industries that can be attributed to unmitigated cracks in welds ("toe cracks") at the pole to base plate connection. The property damage, in some cases, has been significant; and at the very least there are service interruption and repair/replacement costs associated with the subsequent loss of the structure. There are many contributing factors to this toe crack issue. Field inspections have shown the importance of understanding and reacting appropriately regarding this issue. Visual and NDE inspection techniques are critical and should be regularly scheduled. It is imperative that inspections are carried out by qualified personnel with specific pole experience, CWI credentials, and non-destructive ASNT credentials. If identified via timely inspection, these defects can be resolved via engineered weld repairs which restore the original integrity of the structure. Timetable for the required repairs is based on the severity of the weld cracking and age of the structure. As with America's other aging infrastructure, the cost of ignoring this issue can be significant to public safety and welfare. This paper presents a proposed monopole base crack classification system which is intended to standardize the way the industry deals with inspection, repair, and maintenance of pole base connections.