Download or read book Mitigating Fatigue of Cantilevered Overhead Sign Structures Due to Natural and Truck induced Wind Gusts written by Mohamed Salah Gallow and published by . This book was released on 2014 with total page 281 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cantilevered overhead sign structures (COSS) are widely used across highways in the U.S. Several cases of failures have been reported for such structures due to fatigue wind loads. The structure's dynamic characteristics such as natural frequency and critical damping are responsible for its behavior during those loads. When the frequency of wind gusts load matches the fundamental frequency of the OSS, resonance occurs, which causes excessive vibrations. Consequently, fatigue stresses in crease and may exceed the fatigue critical limit, resulting in failure. Vibrations and fatigue stresses amplitudes are dependent on the structure's natural frequency. The objective of this study is investigating natural frequencies of COSS in order to mitigate fatigue stresses due to natural and truck-induced wind gusts. Investigating damping and other fatiguee wind loads are out of the scope in this study. Alterations in factors such as the members' configuration, arrangement, sizes, and layout of the structure control its stiffness and mass distribution which controls its natural frequency and consequently, fatigue stresses. A parametric study was considered in order to investigate the effect of these factors and recommend the best layout between 4-chord, 2-chord, and monotube CSS in mitigating fatigue. Structures were designed according to the American Association of State Highway and Transportation Officials (AASHTO) 2013, Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals (mentioned hereafter as the AASHTO Support Specifications (2013)) and modeled using commercial finite element analysis software. Wind pressure power spectral density and time history loading functions were applied on these structures to simulate natural and truck-induced wind gusts, respectively. Eventally, on the contrary of the 2-chord structure, slanted monotube CSS with curved end post was found to have least mass, highest frequency and nearly smallest fatigue stresses.
Download or read book Fatigue resistant Design of Cantilevered Signal Sign and Light Supports written by Mark R. Kaczinski and published by Transportation Research Board. This book was released on 1998 with total page 268 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Fatigue resistant Design of Cantilevered Signal Sign and Light Supports written by Robert Joseph Dexter and published by Transportation Research Board. This book was released on 2002 with total page 111 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Fatigue Performance of Variable Message Sign Luminaire Support Structures written by Gary R. Consolazio and published by . This book was released on 1998 with total page 76 pages. Available in PDF, EPUB and Kindle. Book excerpt: In Order to determine equivalent static pressures for fatigue loads on cantilevered highway support structures a cantilevered Variable Message Sign(VMS) located along Interstate westbound at mile marker 48.5 in northern New Jersey was continuously monitored for three months. The structure was instrumented with strain gages, pressure transducers, and a wind sentry. All the data was collected with a Campbell Scientific CR9000 digital data acquisition system. A cellular phone transceiver enabled remote communication with the data logger. The system and instrumentation was powered with solar powers and marine batteries. Short-term testing was performed on the structure to determine the dynamic characteristics such as stiffness, natural frequency, and percent of critical damping. Results of the short-term test indicated that the stiffness was 0.24 kN/mm, the first and the second modes were 0.87 cycles/s and 1.22 cycles/s respectively, and the percent of critical damping for the first and second modes were 0.57 percent and 0.25 percent respectively. Long-Term monitoring was performed to capture the structures response to natural wind gusts, galloping, and truck-induced wind gusts. This data would then be used to determine appropriate fatigue design wind loads for future sign support structures. During the three months of monitoring the structure did not experience galloping, which is a phenomena highly dependent on location. A galloping design pressure of 1000 Pa was recommended based on previous research. The summer months, which is when the structure was monitored, were not conductive to the strongest natural winds patterns in Northern New Jersey. The highest natural wind speed that was recorded was 7.5m/s. It is believed that much stronger winds are present in winter and spring, therefore a natural wind gust design pressure of 250 Pa was recommended. Truck-induced gusts were measured and a linear gradient for the truckinduced gust design pressure was determined. The truck-induced gust design pressure ranged linearly from 1760 Pa at 0 to 6m above the surface of the road to 0 Pa at 10.1m and over.
Download or read book Fatigue Loading of Cantilever Sign Structures from Truck Wind Gusts written by Bruce Montel Creamer and published by . This book was released on 1979 with total page 208 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Fatigue Related Wind Loads on Highway Support Structures written by Kevin W. Johns and published by . This book was released on 1998 with total page 93 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Dynamic Performance of Cantilevered Sign Trusses for Fatigue written by Hunter Senior and published by . This book was released on 2020 with total page 161 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cantilevered overhead sign structures (COSS) experience cyclic loading due to stochastic loads such as natural wind gusts (NWG). Wind loading can produce large deflections in the cantilever and large-magnitude stresses can develop at the box-type connection between the cantilevered arm and mast where fatigue performance is a concern. Modifications to the sign structures pose further concerns as changes to the aerodynamic properties could have unintended consequences. A design consideration of COSS is serviceability of the sign through use of a steel grate walkway that workers can use for maintenance on the sign. The steel grate walkways on COSS are rarely used for maintenance, and thus are being removed by multiple state DOTs to prevent vandalism. However, the impact on COSS with the removal of the walkways is unknown. This report describes an investigation in which the dynamic and aerodynamic properties of COSS were studied, and the effect of the walkway presence on structural response was explored. Computer simulations of 32 different COSS configurations were carried out to see the effect of the grate removal on the natural frequency and the mass of the overall structural system. Aerodynamic performance was considered through the use of computational fluid dynamics (CFD) and experimental testing, where wind pressure on the sign in both axial directions and effects of vortex shedding were examined. Findings include: 1) the walkway had a minimal effect on the system’s mass and natural frequencies, 2) the walkway had a minimal influence on the wind-induced force on the sign, 3) vortex shedding was not exacerbated with removal of a walkway attachment, and 4) walkway removal did not significantly change stress magnitudes at the connection between the cantilever and mast. Based on these findings, the removal of walkways from KDOT’s COSS was not found to be problematic.
Download or read book Fatigue Loading and Design Methodology for High Mast Lighting Towers written by Robert J. Connor and published by Transportation Research Board. This book was released on 2012 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt: TRB’s National Cooperative Highway Research Program (NCHRP) Report 718: Fatigue Loading and Design Methodology for High-Mast Lighting Towers provides criteria for the fatigue design of high-mast lighting towers.
Download or read book Mitigating Wind Induced Fatigue in Steel Traffic Signal Support Structures written by Kyle Thomas Wieghaus and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Traffic signal structures undergo wind-induced vibrations that result in fatigue damage accumulation and reduced service life. Mast arms have failed and required removal while in service. A dual experimental and analytical modeling approach is taken to mitigate fatigue and fracture in steel traffic supporting structures. A full-scale prototype structure is instrumented to study natural wind response. Excitation mechanisms are identified, and response is characterized statistically by a lognormal distribution. Helical strakes are found to reduce the vortex-induced vibration of cantilevered traffic signal structures, however are not a panacea for fatigue mitigation as marginal service life gains occur in severe wind environments. A probabilistic framework is extended to assess the risk of wind-induced fatigue and estimate service life while considering uncertainties in fatigue demand and capacity. The framework is successfully demonstrated against compiled inspection records. Locations with higher prevailing winds are susceptible to wind-induced fatigue, but the prevalence of low-speed vortex-induced response is primarily responsible for the early fatigue failures in more mild environments. A low-cost damage avoidance system is proposed to mitigate fatigue and fracture in steel traffic supporting structures. Applied prestress introduces a fail-safe, supplementary load path to balance dead load moment, eradicating the detrimental tensile mean stress found in traffic signal structure connections. Field observations are made without and with the proposed system installed. The benefit of applied prestress is quantified by determining service life without and with the system based on changes in response and fatigue resistance using: (i) a code-based technique; and (ii) the proposed probabilistic framework. Fatigue performance is modeled as mean stress-dependent by modifying nominal stress-life relationships. Service life is shown to increase by an order of magnitude, regardless of wind environment. The concept shows potential to reduce the detrimental effects of non-redundancy for a variety of similar, fatigue-critical infrastructure components. The validity of simplified mean stress-dependent connection modeling is explored. A fracture mechanics-based, total life (initiation-propagation) model is used to demonstrate the detrimental effect mean stress has on tube-to-transverse base plate fatigue resistance. Using fatigue strength curves derived from total life analyses, probabilistic analyses are repeated to justify the use of simplified models. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/155395
Download or read book Vehicle induced Gust Loads on Aluminum Overhead Sign Structures written by Joseph B. Zell and published by . This book was released on 1977 with total page 40 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Fatigue Performance of Full span Sign Support Structures Considering Truck induced Gust and Natural Wind Pressures written by Scott Ginal and published by . This book was released on 2003 with total page 756 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Structural Supports for Highway Signs Luminaires and Traffic Signals written by Fouad Hilmy Fouad and published by . This book was released on 1998 with total page 124 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Design of Structures 2004 written by National Research Council (U.S.). Transportation Research Board and published by . This book was released on 2004 with total page 278 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Calibration of Fatigue Design Wind Pressure for Sign Luminaire and Traffic Signal Support written by Guigui Zu and published by . This book was released on 2013 with total page 144 pages. Available in PDF, EPUB and Kindle. Book excerpt: The study is focused on calibration of fatigue design wind pressure for sign, luminaire and traffic signal support under natural and truck-induced wind gusts. The design of the support structures in Canada is governed by the current Canadian Highway Bridge Design Code (CHBDC). However, the code is not specific on the fatigue design wind pressure (natural or truck-induced) for these structures. Although there are equivalent static natural and truck-induced wind pressures for fatigue design recommended in the provisions of the American Association of State Highway and Transportation Officials (AASHTO), none of relevant studies discussed the implied reliability by using these design pressures based on Canadian practice. Code calibration analyses of the sign, luminaire and traffic signal support under natural and truck-induced wind gusts were carried out in the study. For the calibration, the support structures were approximated by a linear elastic single-degree-of-freedom (SDOF) system, structural response with selected natural frequencies, damping ratios under natural and truck-induced wind gusts was estimated. A target reliability index of 4.25 for a service period of 75 years was adopted for the calibration. The calibration results were used to recommend fatigue design wind pressure for sign, luminaire and traffic signal support under both natural and truck-induced wind gusts. The recommended values could be directly adopted by the CHBDC.
Download or read book Structural Supports for Highway Signs Luminaires and Traffic Signals written by Fouad H. Fouad and published by Transportation Research Board. This book was released on 2003 with total page 59 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Wind Loads on Dynamic Message Cabinets and Behavior of Supporting Trusses written by George Constantinescu and published by . This book was released on 2013 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt: Large Dynamic Message Signs (DMSs) have been increasingly used on freeways, expressways and major arterials to better manage the traffic flow by providing accurate and timely information to drivers. Overhead truss structures are typically employed to support those DMSs allowing them to provide wider display to more lanes. In recent years, there is increasing evidence that the truss structures supporting these large and heavy signs are subjected to much more complex loadings than are typically accounted for in the codified design procedures. Consequently, some of these structures have required frequent inspections, retrofitting, and even premature replacement. Two manufacturing processes are primarily utilized on truss structures - welding and bolting. Recently, cracks at welding toes were reported for the structures employed in some states. Extremely large loads (e.g., due to high winds) could cause brittle fractures, and cyclic vibration (e.g., due to diurnal variation in temperature or due to oscillations in the wind force induced by vortex shedding behind the DMS) may lead to fatigue damage, as these are two major failures for the metallic material. Wind and strain resulting from temperature changes are the main loads that affect the structures during their lifetime. The American Association of State Highway and Transportation Officials (AASHTO) Specification defines the limit loads in dead load, wind load, ice load, and fatigue design for natural wind gust and truck-induced gust. The objectives of this study are to investigate wind and thermal effects in the bridge type overhead DMS truss structures and improve the current design specifications (e.g., for thermal design). In order to accomplish the objective, it is necessary to study structural behavior and detailed strain-stress of the truss structures caused by wind load on the DMS cabinet and thermal load on the truss supporting the DMS cabinet. The study is divided into two parts. The Computational Fluid Dynamics (CFD) component and part of the structural analysis component of the study were conducted at the University of Iowa while the field study and related structural analysis computations were conducted at the Iowa State University. The CFD simulations were used to determine the air-induced forces (wind loads) on the DMS cabinets and the finite element analysis was used to determine the response of the supporting trusses to these pressure forces. The field observation portion consisted of short-term monitoring of several DMS Cabinet/Trusses and long-term monitoring of one DMS Cabinet/Truss. The short-term monitoring was a single (or two) day event in which several message sign panel/trusses were tested. The long-term monitoring field study extended over several months. Analysis of the data focused on trying to identify important behaviors under both ambient and truck induced winds and the effect of daily temperature changes. Results of the CFD investigation, field experiments and structural analysis of the wind induced forces on the DMS cabinets and their effect on the supporting trusses showed that the passage of trucks cannot be responsible for the problems observed to develop at trusses supporting DMS cabinets. Rather the data pointed toward the important effect of the thermal load induced by cyclic (diurnal) variations of the temperature. Thermal influence is not discussed in the specification, either in limit load or fatigue design. Although the frequency of the thermal load is low, results showed that when temperature range is large the restress range would be significant to the structure, especially near welding areas where stress concentrations may occur. Moreover stress amplitude and range are the primary parameters for brittle fracture and fatigue life estimation. Long-term field monitoring of one of the overhead truss structures in Iowa was used as the research baseline to estimate the effects of diurnal temperature changes to fatigue damage. The evaluation of the collected data is an important approach for understanding the structural behavior and for the advancement of future code provisions. Finite element modeling was developed to estimate the strain and stress magnitudes, which were compared with the field monitoring data. Fatigue life of the truss structures was also estimated based on AASHTO specifications and the numerical modeling. The main conclusion of the study is that thermal induced fatigue damage of the truss structures supporting DMS cabinets is likely a significant contributing cause for the cracks observed to develop at such structures. Other probable causes for fatigue damage not investigated in this study are the cyclic oscillations of the total wind load associated with the vortex shedding behind the DMS cabinet at high wind conditions and fabrication tolerances and induced stresses due to fitting of tube to tube connections.
Download or read book Analytical Investigation of Saddle Connections for Overhead Sign Trusses with Respect to Strength and Fatigue Performance written by Danqing Yu and published by . This book was released on 2021 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt: Bridge-type overhead truss sign structures (OHTSS) are widely used over active highways across the United States. An OHTSS is comprised of a 3D truss and two support frames at each end. The structures are usually made of steel or aluminum. Many state DOTs use their own types of connections that are not documented in specifications. Since 2015, the Kansas Department of Transportation (KDOT) has used a type of 'saddle connection' at the joints of truss chords and support frame pipes. Wind loads are the primary type of load a sign structure resists besides the gravity load. Since wind loads are periodic, fatigue properties are important in the design of OHTSS. As a newly developed connection, KDOT sought information regarding the mechanical performance of the saddle connection. Studies were needed to verify the safety of the connections, particularly regarding its fatigue susceptibility. This report presents a study mainly aimed at evaluating the fatigue susceptibility of the saddle connections using finite element analysis (FEA). The study consisted of the following four parts: Part 1: Global behavior analysis: an analysis aimed at determining the global behavior of the structures and the location of critical connections. Linear-elastic material properties were used. Part 2: Structural Hot Spot Stress analysis: an analysis was performed to determine structural Hot Spot Stresses along each weld in the critical connections identified in Part 1. Linear-elastic material properties were used. Part 3: Effective notch stress analysis: a linear-elastic analysis using the effective notch stress method to evaluate three welds identified to have larger stresses in Part 2. Linear-elastic material properties were used. Part 4: Extreme loading analysis: An analysis to evaluate the behavior of the saddle connections and the overall structures under extreme loading and provide comments regarding the strength-related safety of the saddle connections. Elastic-perfectly plastic material properties were used. Sign structures of four span lengths, including 60 ft, 83 ft, 110 ft, and 137 ft, were analyzed in Part 1 and Part 2. The 137-ft span structure was analyzed in Part 3 using the effective notch stress method. The 60-ft and 137-ft span structures were analyzed in Part 4. In Part 1 and Part 2, AASHTO fatigue loads, including natural wind gusts and truck-induced gusts, were applied in six load modes. They included: natural wind blowing from the back, front, and side of sign structures; and truck-induced gusts acting on the right, middle, and left 12 ft of sign trusses. In Part 3, the AASHTO fatigue load of the natural wind blowing from behind the sign structure was applied. In Part 4, the overall structures and the saddle connections were loaded until the analysis terminated. The termination of analysis was governed by loss of stiffness due to the yielding of material. The study resulted in conclusions that the natural wind in the direction facing the sign panel almost always governed the fatigue demand. The bottom saddle connections were more susceptible to fatigue damage than the top saddle connections, especially the stiffener-to-pipe weld in the bottom saddle connection. Fatigue failures of the saddle connections are not likely to occur in expected real use, but attention should be paid to the stiffener-to-pipe weld in the bottom saddle connection. The analysis of the structures under extreme loading suggests that the ultimate strength of saddle connections do not govern the strength of the overall structures.
