A time-domain model for predicting aerodynamic loads on a slender support structure for fatigue design

Cantilevered signal, sign, and light support structures are used nationwide on major interstates, national highways, local highways, and at local intersections for traffic control purposes. Recently, there have been a number of failures of these structures that can likely be attributed to fatigue. In light of the fact that there is considerable uncertainty in the calculation of vortex shedding loads in both the American Association of State Highway and Transportation (AASHTO) and the Canadian Highway Bridge Design Code (CAN/CSA) code provisions, the current equations used for vortex shedding fatigue design need to be reevaluated and likely re-formulated or modified.;A luminary support structure or High Mast Light Pole (HMLP) is generally susceptible to two primary types of wind loading induced by natural wind gusts or buffeting and vortex shedding, both of which excite the structure dynamically and can cause fatigue damage. Vortex shedding is a unique type of wind load that alternatively creates areas of negative pressures on either side of a structure normal to the wind direction. This causes the structure to oscillate transverse to the wind direction.;The primary objective of this study was to develop a procedure for predicting wind loads in the time domain for the fatigue design of slender, tapered luminary support structures. To accomplish this, monitoring of long-term response behavior of a HMLP subjected to wind-induced vibration was needed. This was accomplished by full-scale measurement of the response of a HMLP located near Mason City next to I-35 in Iowa. Wind tunnel testing was also conducted to determine the required aerodynamic parameters of the pole cross section. Further, these aerodynamic parameters were cast into a coupled dynamic model for predicting the response of any HMLP in the time. Finally, the model was validated by comparing its results with the data collected from field monitoring.;Fatigue life of the given HMLP was estimated with further modeling of the wind speed distribution and stress amplitudes predicted by the time-domain model. The predicted fatigue life was compared with those calculated with the full-scale data

Performance Study on Evacuated Tubular Collector Coupled Solar Still in West Texas Climate

Experimental study was performed on a single basin active solar distillation system augmented with a solar collector using evacuated solar tubes. Field tests were conducted over several days under the climatic conditions of West Texas to evaluate the effect evacuated solar tubes have on the daily distillate yield rate. To investigate the feasibility of the solar tubes, active and passive solar stills with and without exterior insulation were examined. The maximum daily production rate for the active distillation system using evacuated solar tubes and the passive distillation system was 3.6 and 1.4 kg/m2day, respectively. The results showed the augmentation of the still with evacuated solar tubes increased its production capacity by a factor of 2.63. It also increased the maximum temperature of the water in the still basin by at least 20 °C. Economic analysis shows that it is feasible to use evacuated tubular collector coupled solar still as an alternative means for reclaiming water in farmlands with a payback period of approximately 6 years

Evaluation of Wind and Solar Energy Investments in Texas

The primary objective of the project is to evaluate the benefits of wind and solar energy and determine economical investment sites for wind and solar energy in Texas with economic parameters including payback periods. A 50 kW wind turbine system and a 42 kW PV system were used to collect field data. Data analysis enabled yearly energy production and payback period of the two systems. The average payback period of a solar PV system was found to be within a range of 2-20 years because the large range of the payback period for PV systems were heavily influenced by incentives. This is in contrast to wind energy, where the most important factor was found to be wind resources of a region. Payback period for the installed wind system in Texas with federal tax credits was determined to be approximately 13 years

Experimental Heat Transfer Study on Green Roofs in a Semiarid Climate During Summer

An experimental study was conducted on green roofs under the semiarid summer climatic conditions of West Texas to investigate the effect of soil type, moisture content, and the presence of a top soil grass layer on the conductive heat transfer through the roof. Two soil types were investigated: uniform sand and local silt clay. Tests were also conducted on a control roof. A dual-needle heat-pulse sensor was used to conduct thermal property tests on the soils. The tests reveal that unlike sand, the thermal conductivity of silt clay did not increase continuously with soil moisture. Better heat transfer conditions were achieved when the sand and silt clay roofs were watered to a water depth of 10 mm per day rather than double the amount of 20 mm per day. The roof with silt clay soil had the lowest fluctuation in inner temperature between daytime and nighttime. Green roofs with silt clay soil required more than twice the amount of soil moisture than green roofs with sand to achieve similar roof heat transfer rates. The best net heat flux gains for vegetated green roofs were 4.7 W/m2 for the sand roof and 7.8 W/m2 for the silt clay roof

Structural Behavior and Design of Barrier-Overhang Connection in Concrete Bridge Superstructures Using AASHTO LRFD Method

The U.S. Departments of Transportation adopted the AASHTO LRFD Bridge Design Specifications during the year 2007, which is mandated by AASHTO and FHWA. The application of LRFD specification initiated numerous research works in this field. This investigation addresses the LRFD and Standard design methodologies of concrete deck slab, deck overhang, barrier and combined barrier-bridge overhang. The purpose of this study is to propose a simplified manual design approach for the barrier-deck overhang in concrete bridges. For concrete deck slab overhang and barrier, application of National Cooperative Highway Research Program crash test is reviewed. The failure mechanism, design philosophy and load cases including extreme event limit states for barrier and overhang are discussed. The overhang design for the combined effect of bending moment and axial tension is probably the most important part of the design process. The overhang might be a critical design point of the deck with significantly higher amount of reinforcement. The design process becomes complicated due to combined force effect, LRFD crash test level requirement and the existence of several load combinations. Using this program, different LRFD load combinations are plotted together with the interaction diagram and the design is validated

Analysis of Internet Visitors on Educational Websites

This study examines usage patterns of educational websites that employ databases, wikis, and general resources for information sharing and dissemination. To gather data about website usage, a quantitative survey was sent out to students and to the users of an existing educational website. Additionally, participants provided data on learning preferences and practices. Findings from the survey show that users visit an education website for finding information and getting connected to a community. The survey results also show that while communicating information should remain a top priority, educational web sites will need to adapt to an increasing desire for interpersonal communication within their own online communities

Optimization of Post-Tensioned Box Girder Bridges with Special Reference to Use of High-Strength Concrete Using AASHTO LRFD Method

With the Federal Highway Administration-mandated implementation of the LRFD specifications, many state departments of transportation (DOTs) have already started implementing LRFD specifications as developed by the AASHTO. Many aspects of the LRFD specifications are being investigated by DOTs and researchers in order for seamless implementation for design and analysis purposes. This paper presents the investigation on several design aspects of post-tensioned box girder bridges designed by LRFD Specifications using conventional or High-Strength Concrete (HSC). A computer spreadsheet application was specifically developed for this investigation. It is capable of analysis, design, and cost evaluation of the superstructure for a cast-in-place post-tensioned box girder bridge. Optimal design of a post-tensioned box girder is achievable by correct selection of design variables. Cost evaluation of superstructures with different geometrical and material configurations has led to the development of optimum design charts for these types of superstructures. Variables used to develop these charts include, among others, span length, section depth, web spacing, tendon profile, and concrete strength. It was observed that HSC enables the achievement of significantly longer span lengths and/or longer web spacing that is not achievable when using normal strength concrete

Review of Computer-Aided Numerical Simulation in Wind Energy

Many advances have been made during the last decade in the development and application of computational fluid dynamics (CFD), finite element analysis (FEA), numerical weather modeling, and other numerical methods as applied to the wind energy industry. The current information about this area of study may help researchers gage research efforts. Specifically, micro-siting, wind modeling and prediction, blade optimization and modeling, high resolution turbine flow modeling, support structure analysis, and noise prediction have been the main focuses of recent research. The advances in this area of research are enabling better designs and greater efficiencies than were possible previously. The trends toward system coupling, parallel computing, and replacing experiments are discussed. The shortcomings of recent research and areas of possible future research are also presented

Economic Feasibility of Campus-Wide Photovoltaic Systems in New England

Compared to the national average residential retail electricity price, Connecticut (CT) had the 4th 26 highest electricity price in the country with 19.23 cents/kWh in September 2015, nearly 50% 27 higher than the national average for price of electricity. This study aims to assess the economic 28 feasibility of the solar PV systems at the campus under realistic constraints, by analyzing actual 29 data from the solar array on campus. The project focused on the economic feasibility of solar PV 30 systems on campus with physical, spatial, and practical constraints that result in a project to 31 deviate from theoretical (estimated) values. To achieve that, the prediction of the PV power 32 generation from the building was developed and compared with the actual (measured) data. 33 The average payback period of a campus-wide PV system was calculated as primarily 11 34 years, within a range of 8-12 years, and was estimated to reduce overall building operating 35 expenses by $250,000, or 8%. The economic parameters such as NPV and IRR also validated the 36 investment worthiness. The results of the study could be used to analyze or further develop 37 feasibility studies of PV systems at other universities in Connecticut and neighboring states that 38 share similar climatic characteristics and economic factors