COMMITTEE MANDATE Concern for crack initiation and growth under cyclic loading as well as unstable crack propagation and tearing in ship and offshore structures. Due attention shall be paid to practical application and statistical description of fracture control methods in design, fabrication and service. Consideration is to be given to the suitability and uncertainty of physical models. The work shall be coordinated with that of Committee V.2.

Fatigue and Fracture

The 1985 AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals (referred to here as the current Supports Specifications) has been revised in its entirety with significant additions to its content and scope. This work is the result of an extensive research study performed under NCHRP project 17-10. The main objective of the study was to update the previous edition of the Supports Specifications based on the most recent state-of-the-art information for the design and use of structural supports. Considerable effort was made to specify the best practice, realizing the characteristics and limitations of each material. From a design safety standpoint, all materials for structural supports were treated equitably. Safety, aesthetics, and economy were three main guidelines in developing the provisions of the Supports Specifications, but manufacturing practices and experiences were also considered. The proposed specification is presented in a specification/comment...

Proposed Revisions to AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals

Exploiting wind energy in complex sites like mountain terrains implies the necessity for remote structural health monitoring of the wind towers. In fact, such slender vertical structures exposed to wind may experience large vibrations and repeated stress cycles leading to fatigue cracking. Possible strategies for remote fatigue damage detection are investigated. Specifically, this paper is focused on the use of suitable strain sensors for crack detection in critical sites of the structure, suggesting several strategies taking into account the possibility of wind direction changes and/or wind calm phases. They are based on a radial arrangement of strain sensors around the tower periphery in the vicinity of the base weld joint. The most promising strategy uses the strain difference between adjacent strain sensors as an index of the presence of a crack. The number of sensors to be installed is dictated by the minimum crack size to be detected, which in turn depends on the expected extreme wind conditions and programmed inspection/repair schedule for the structure.

Structural health monitoring of wind towers: remote damage detection using strain sensors

Target-less computer vision for traffic signal structure vibration studies

Wind-induced vibration of a traffic-signal-support structure with cantilevered tapered circular mast arm

This report contains the findings of a study on fatigue resistance of cantilevered signal, sign, and light supports. Recommended specifications for the fatigue-resistant design of these structures are included. The contents of this report will be of immediate interest to bridge and structural engineers, traffic engineers, and manufacturers. The research determined that, for a typical sign or signal support structure, galloping is the primary cause of vibrations that may result in fatigue damage. It was also determined that the number of structures observed to be galloping in field applications is low. Much variation in the detailing of connections was found, and several details of low fatigue resistance are in use. The research suggests that, through changes in the recommended design wind loads used for design of these structures and avoidance of fatigue-susceptible details, the probability of failure of these structures may be reduced. In addition, the research suggests that mitigation of wind-induced vibrations of structures, once they are observed in the field, may also be a desirable action. The report recommends additional research in this area and provides guidance that designers may consider pending any formal changes to design specifications by the American Association of State Highway and Transportation Officials.

J P Van Dien

Papers

Fatigue-resistant design of cantilevered signal, sign, and light supports