Análise de estruturas de suporte para sinalizações viárias

El cálculo de las estructuras de soporte para señalizaciones viales se realiza mediante la norma AASHTO con la cual se realiza fundamentalmente el chequeo a Fatiga, pero con ella no se llegan a conocer las tensiones von Mises, las tensiones tangenciales ni los desplazamientos en cualquier punto de la estructura. En el presente trabajo se determinan las cargas actuantes, así como sus combinaciones más críticas para el análisis. Se realiza el cálculo analítico a través de los métodos y las normas establecidas para ello y se confecciona un modelo de elementos finitos cuya simulación numérica complementa los resultados obtenidos por las normas. The calculation of the support structures for highway signs is carried out by means of the AASHTO standard, with which the Fatigue check is fundamentally carried out, but with it the von Mises stress, the tangential stress and the displacements at any point of the structure are not known. In the present work, the acting loads are determined, as well as their most critical combinations for the analysis. The analytical calculation is performed through the methods and standards established for it and a finite element model is created whose numerical simulation complements the results obtained by the standards.

High visibility reflective sign sheeting materials: field and computational evaluations of visual performance

Highway signs provide important information to drivers to assist in navigation, to identify potentially hazardous roadway locations, and to remind drivers of safe operating practices. Ensuring that signs have sufficient visibility to the driving public is a key undertaking by transportation agencies. In order to assist in evaluating and comparing different materials for photometric and visual performance, the present study was undertaken to assess the utility of specifying sign sheeting performance in terms of visual performance. As part of this effort, a practical methodology for conducting field measurements of sign luminance along roadways was developed. In addition to describing the methods for an approach to visual performance based specifications, a spreadsheet tool for calculating minimum sign luminance and visibility from different sign sheeting materials was also developed.

Mitigating Fatigue in Cantilevered Overhead Sign Structures

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.

LEGIBILITY OF URBAN HIGHWAY TRAFFIC SIGNS USING NEW RETROREFLECTIVE MATERIALS

Unlighted highway signs, which use newly developed retroreflective materials, were installed along the major expressway in an urban area by the local department of transportation. Photometric measurements of the signs were used to assess their legibility applying the relative visual performance model, in comparison to lighted signs, con‐ forming to recommended illumination practices. The calculated visibility of the measured unlighted signs was similar to that of the signs equipped with exterior sign illumination. The practical significance and limitations of the relative visual performance approach are discussed.

Design of Cantilevered Overhead Sign Supports

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.

Wind Load Provisions in 2001 AASHTO Supports Specifications

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.