H. Fouad

Fatigue Design of Sign Support Structures for Loading Caused by Natural Wind Loads

A unified design method for fatigue loading caused by natural wind for highway overhead sign support structures is needed. Whereas the fatigue design provisions given in the 2001 AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals provide fatigue design criteria for natural wind, these provisions are applicable only within certain limitations. A comprehensive approach was developed for fatigue design for the treatment of sign support structures, considering the dynamic properties of the structures such as the natural frequency and damping characteristics. The approach is applicable for structures in which the dynamic response can be approximated by a single degree-of-freedom system. Typical examples include cantilever-and bridge-type overhead sign support structures. The proposed fatigue design approach incorporates these parameters in a simplified, systematic procedure that can be readily used by the engineer. The analytical work performed involved principles relating to random vibration in use of the vibration response spectrum (VRS). The fatigue load was selected from the VRS in terms of the natural frequency of the structure, the critical damping percentage (a.k.a., damping ratio), and the annual mean wind velocity of the intended site.

Design Fatigue Load of Sign Support Structures Due to Truck-Induced Wind Gust

This research presents a universal approach for determining the design fatigue load due to truck-induced wind gust for highway overhead sign support structures. The fatigue load is determined on the basis of the dynamic properties of the structure. It is applicable to structures in which the dynamic response can be approximated by a single-degree-of-freedom system. Typical examples include cantilever- and bridge-type overhead sign support structures. The developed approach incorporates these parameters in a simplified systematic procedure that can be readily used by engineers. Principles relating to mechanical vibration and utilization of the shock response spectrum were used to determine the load. The fatigue load is selected from the shock response spectrum in terms of the natural frequency of the structure and the speed of the truck. Comparisons were made with the current truck-induced gust fatigue design provisions given in the 2009 AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals. Additional comparisons were made with dynamic finite element analysis of a modeled support structure.

ESTIMATION OF SECOND-ORDER EFFECTS FOR POLE-TYPE STRUCTURES

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.

FRC POLES FOR DISTRIBUTION POWER LINES

Applications of fiber-reinforced composites (FRC) are expanding as the experience in using these materials increase. Although reinforced plastic composites have been successfully employed in major structural applications, the use of the material for poles supporting electric distribution lines is relatively new. The purpose of this paper is to present an overview on the general use of FRC poles for electric distribution lines. Information on manufacturing handling, installation and field considerations, testing, and design consideration is covered. MATERIALS AND MANUFACTURE FRC distribution poles are manufactured of two principal constituents, namely polyester resin and glass fiber reinforcement. Hence the material is sometimes referred to as fiberglass reinforced polyester composite or FRP. The FRP composite possesses superior properties not available to each constituent alone. The glass fiber reinforcement, which is significantly higher in strength than the polyester resin, constitutes the main load-carrying element of the composite. The polyester resin encapsulated the glass reinforcement providing thickness and rigidity to the FRP laminate. It also protects the underlying glass from the environment. Under the application of load, the polyester resin undergoes large deformations while the load is being transmitted to the glass fibers. From a practical standpoint, FRP may be considered an elastic material, which exhibits a stress-strain behavior that is fairly linear up to failure. The material does not yield nor exhibit a permanent set due to transient overloads. Various processes are employed for the manufacturing of FRP. Manufacturing processes that are commonly used for structural supports include filament winding, pultrusion, and centrifugal casting. From a structural standpoint, the manufacturing process can markedly influence the structural properties of the material. Other factors that affect the properties of the FRP laminate are the orientation of the glass fibers and the fiber content. Aligning fibers in a single direction provides high stiffness and strength parallel to the fibers, but properties in the perpendicular direction approach those of the plastic matrix.

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.

Global Assessment of Hydrogen Technologies - Task 1 Report Technology Evaluation of Hydrogen Light Duty Vehicles

This task analyzes the candidate hydrogen-fueled vehicles for near-term use in the Southeastern U.S. The purpose of this work is to assess their potential in terms of efficiency and performance. This report compares conventional, hybrid electric vehicles (HEV) with gasoline and hydrogen-fueled internal combustion engines (ICEs) as well as fuel cell and fuel cell hybrids from a technology as well as fuel economy point of view. All the vehicles have been simulated using the Powertrain System Analysis Toolkit (PSAT). First, some background information is provided on recent American automotive market trends and consequences. Moreover, available options are presented for introducing cleaner and more economical vehicles in the market in the future. In this study, analysis of various candidate hydrogen-fueled vehicles is performed using PSAT and, thus, a brief description of PSAT features and capabilities are provided. Detailed information on the simulation analysis performed is also offered, including methodology assumptions, fuel economic results, and conclusions from the findings.

Global Assessment of Hydrogen Technologies – Tasks 3 & 4 Report Economic, Energy, and Environmental Analysis of Hydrogen Production and Delivery Options in Select Alabama Markets: Preliminary Case Studies

This report documents a set of case studies developed to estimate the cost of producing, storing, delivering, and dispensing hydrogen for light-duty vehicles for several scenarios involving metropolitan areas in Alabama. While the majority of the scenarios focused on centralized hydrogen production and pipeline delivery, alternative delivery modes were also examined. Although Alabama was used as the case study for this analysis, the results provide insights into the unique requirements for deploying hydrogen infrastructure in smaller urban and rural environments that lie outside the DOE’s high priority hydrogen deployment regions. Hydrogen production costs were estimated for three technologies – steam-methane reforming (SMR), coal gasification, and thermochemical water-splitting using advanced nuclear reactors. In all cases examined, SMR has the lowest production cost for the demands associated with metropolitan areas in Alabama. Although other production options may be less costly for larger hydrogen markets, these were not examined within the context of the case studies.

Global Assessment of Hydrogen Technologies – Task 6 Report Promoting a Southeast Hydrogen Consortium

The purpose of this project task was to establish a technical consortium to promote the deployment of hydrogen technologies and infrastructure in the Southeast. The goal was to partner with fuel cell manufacturers, hydrogen fuel infrastructure providers, electric utilities, energy service companies, research institutions, and user groups to improve education and awareness of hydrogen technologies in an area that is lagging behind other parts of the country in terms of vehicle and infrastructure demonstrations and deployments. This report documents that effort.

Global Assessment of Hydrogen Technologies - Task 2 Report Comparison of Performance and Emissions from Near-Term Hydrogen Fueled Light Duty Vehicles

An investigation was conducted on the emissions and efficiency from hydrogen blended compressed natural gas (CNG) in light duty vehicles. The different blends used in this investigation were 0%, 15%, 30%, 50%, 80%, 95%, and ~100% hydrogen, the remainder being compressed natural gas. The blends were tested using a Ford F-150 and a Chevrolet Silverado truck supplied by Arizona Public Services. Tests on emissions were performed using four different driving condition tests. Previous investigation by Don Karner and James Frankfort on a similar Ford F-150 using a 30% hydrogen blend showed that there was substantial reduction when compared to gasoline in carbon monoxide (CO), nitrogen oxide (NOx), and carbon dioxide (CO2) emissions while the reduction in hydrocarbon (HC) emissions was minimal. This investigation was performed using different blends of CNG and hydrogen to evaluate the emissions reducing capabilities associated with the use of the different fuel blends. The results were then tested statistically to confirm or reject the hypotheses on the emission reduction capabilities. Statistically analysis was performed on the test results to determine whether hydrogen concentration in the HCNG had any effect on the emissions and the fuel efficiency. It was found that emissions from hydrogen blended compressed natural gas were a function of driving condition employed. Emissions were found to be dependent on the concentration of hydrogen in the compressed natural gas fuel blend.

Finite Element Modeling of Wrap-Around Gusset Plates in Tension

Gusset plates are used in steel buildings to connect bracing members to other structural members in the lateral force resisting system. Horizontal bracing is commonly used to resist lateral loads in industrial structures and in commercial buildings where floor and roof diaphragms cannot carry the loads. Wrap-around gusset plates are L-shaped plates that are used where an opening is required at the corner of the plate. This typically occurs at horizontal bracing where the gusset plate is cut out around a column, as shown in Figure 1.