Development and Calibration of AASHTO LRFD Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals

2014 ◽  
Author(s):  
Jay A. Puckett ◽  
Michael G. Garlich ◽  
Andrzej (Andy) Nowak ◽  
Michael Barker ◽  
◽  
...  
Keyword(s):  
Traffic Signals ◽  
Aashto Lrfd ◽  
Highway Signs

Design of Cantilevered Overhead Sign Supports

2005 ◽  
Vol 1928 (1) ◽  
pp. 39-47
Author(s):  
Fouad H. Fouad ◽  
Elizabeth Calvert
Keyword(s):  
Traffic Signals ◽  
The United States ◽  
Support Structures ◽  
Fatigue Load ◽  
Fatigue Design ◽  
Previous Edition ◽  
Sign Support Structures ◽  
Design Calculations ◽  
Highway Signs ◽  
New Criteria

The AASHTO 2001 Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals include revised wind load provisions and new criteria for fatigue design. These provisions and criteria differ considerably from those in previous editions of the specifications, and their impact on the design of cantilevered overhead sign supports has not been fully studied. This study assesses the effect of these provisions and criteria on the design of cantilevered overhead sign support structures with the horizontal support composed of a four-chord truss. Wind and fatigue load design calculations of typical structures, located at sites across the United States, were performed with the design provisions of the 2001 supports specifications and compared with design in accordance with the previous edition of the specifications. The induced forces in the primary members of the cantilevered sign support structure were calculated, and corresponding member sizes and weights were estimated. The results of the study demonstrated the effect of the wind and fatigue load provisions on the design of cantilevered overhead sign support structures.

Estimation of Second-Order Effects for Pole-Type Structures

2000 ◽  
Vol 1740 (1) ◽  
pp. 151-156 ◽  
Author(s):  
Edgar Nunez ◽  
Fouad H. Fouad
Keyword(s):  
Nonlinear Analysis ◽  
Traffic Signals ◽  
Second Order ◽  
Order Effects ◽  
Simplified Approach ◽  
Bending Stresses ◽  
Pole Type ◽  
Second Order Effects ◽  
Factor C ◽  
Highway Signs

The design of pole-type structures for highway supports requires computation of second-order effects induced by the interaction of vertical gravitational and transverse wind loads. The 1994 Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals provides two methods to account for those second-order effects. The first method uses a simplified approach by introducing a factor, CA, into the combined stress ratio equation. The second method requires the computation of the exact bending stresses by means of a nonlinear analysis. Most structural design codes specify simplified methods for the evaluation of second-order effects to facilitate the design of structural members by using the forces obtained in a first-order static analysis. Therefore, simplified methods must be accurate to be considered an adequate alternative to a more sophisticated analysis. The purpose of this study was to determine the accuracy of the simplified method by using the CA factor to estimate the second-order effects for pole-type structures. An analytical study that included 241 pole configurations was conducted to evaluate the CA factor. Exact solutions were computed by using a computer program capable of performing second-order analysis. The study indicated that for typical pole-type structures, the results obtained with the CA factor were highly conservative. On the basis of the results, a modified expression for the CA factor is proposed. Results obtained by use of the modified expression for the CA factor were within 10 percent of those obtained by use of the “exact” nonlinear analysis.

Wind Load Provisions in 2001 AASHTO Supports Specifications

2003 ◽  
Vol 1845 (1) ◽  
pp. 10-18
Author(s):  
Fouad H. Fouad ◽  
Elizabeth Calvert
Keyword(s):  
Major Part ◽  
Traffic Signals ◽  
Structure Type ◽  
Wind Load ◽  
Wind Pressure ◽  
Major Research ◽  
National Cooperative ◽  
Departments Of Transportation ◽  
Highway Signs ◽  
Highway Research

The AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals (Supports Specifications) has been revised in its entirety through a major research project conducted under the auspices of the National Cooperative Highway Research Program (NCHRP Project 17-10). The new document was approved in 1999 by all state departments of transportation for adoption by AASHTO and was published in 2001. A major part of the revisions included new provisions and criteria for wind loads. These provisions differ considerably from those in previous editions of the specifications. A review of the changes in the wind load provisions of the 2001 Supports Specifications is presented. These changes, which are primarily due to the adoption of a new wind speed map based on a 3-s gust, could result in a significant increase in the magnitude of wind pressure in hurricane areas and a decrease in inland areas depending on location and structure type.

Mitigating Fatigue in Cantilevered Overhead Sign Structures

2015 ◽  
Vol 2522 (1) ◽  
pp. 18-26
Author(s):  
Mohamed S. Gallow ◽  
Fouad H. Fouad ◽  
Ian E. Hosch
Keyword(s):  
Structural Design ◽  
Endurance Limit ◽  
Time History ◽  
Traffic Signals ◽  
The United States ◽  
Wind Pressure ◽  
Wind Gusts ◽  
Power Spectral ◽  
Highway Signs ◽  
Fatigue Endurance

Cantilevered overhead sign structures (COSSs) are widely used across highways in the United States. Several cases of excessive vibrations and failures caused by fatigue wind loads from natural and truck-induced wind gusts have been reported. Not enough research has included the effect of making structural design modifications on the fatigue performance of COSSs. Under fatigue wind-induced loads, the dynamic characteristics (frequency and damping) of COSSs are important parameters affecting their structural behavior. When frequencies of wind load and the structure match, resonance may occur, causing excessive vibrations, depending on the frequency value. If accompanied fatigue stresses exceed the fatigue endurance limit, failure occurs after a certain number of loading cycles. The objective of this study was to investigate stiffness and mass distribution of COSSs to control the structural frequency, thus mitigating fatigue caused by wind-induced gusts. For this purpose, modifications in the members' shape, arrangement, size, and layout of structure were examined. Three layouts were compared: four-chord, two-chord, and monotube COSSs. These layouts were designed according to the 2013 AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals and modeled with SAP2000. Wind pressure power spectral density and time history loading functions were applied to these structures to simulate natural and truck-induced wind gusts, respectively. Results showed that the vertical mono-tube COSS design with curved end post had the least mass, but fatigue stresses were comparable with the four-chord COSS. The two-chord COSS design had the largest mass and exhibited the highest fatigue stresses.

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