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Identification of the most critical element of a truss member: stress time histories of all the elements located on one weld line (top) and stress time histories of eight elements adjacent to the hole (bottom) (1 ksi = 6.895 MPa).
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Dynamic Message Signs (DMSs) are increasingly used in highways as an effective means to communicate time-sensitive information with motorists. To ensure the long-term performance of DMSs, it is critical to ensure that the truss structures that hold them can resist not only extreme loading events, but also fatigue induced by service loads. The exist...
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... to select the most critical element for each truss member. Following is the procedure used for this purpose: All the elements lo- cated on one weld line are selected. The stress time histories are then obtained for the selected elements and comparisons are made to identify the elements that constantly experience the highest stress values. Fig. 10 shows the elements selected for deriving the stress time histories, as well as the stress time histories derived from the numerical ...
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... outcome of this investigation highlights that the elements with the highest stress are those closest to the hole of the truss members. This criterion leads to four elements at each end of the truss member. There are eight elements in each tubular member adjacent to the hole, which directly experience the welding effects. Fig. 10 depicts four of those eight elements at one end of a member. The stress time histories for the eight elements are illustrated in Fig. 10. The element with the highest value of stress in this figure is the most critical element of the member. For example, Element 322 is the most critical element in the member that carries Sensor S1. The ...
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... of the truss members. This criterion leads to four elements at each end of the truss member. There are eight elements in each tubular member adjacent to the hole, which directly experience the welding effects. Fig. 10 depicts four of those eight elements at one end of a member. The stress time histories for the eight elements are illustrated in Fig. 10. The element with the highest value of stress in this figure is the most critical element of the member. For example, Element 322 is the most critical element in the member that carries Sensor S1. The next step is to examine the stress time history at the middle of the member. In reality, a sensor can be mounted anywhere on the ...
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... outcome of this investigation highlights that the elements with the highest stress are those closest to the hole of the truss members. This criterion leads to four elements at each end of the truss member. There are eight elements in each tubular member adjacent to the hole, which directly experience the welding effects. Fig. 10 depicts four of those eight elements at one end of a member. The stress time histories for the eight elements are illustrated in Fig. 10. The element with the highest value of stress in this figure is the most critical element of the member. For example, Element 322 is the most critical element in the member that carries Sensor S1. The next step is to examine the stress time history at the middle of the member. In reality, a sensor can be mounted anywhere on the perimeter of the truss member. Thus, the ef- fect of the sensor's mounting location must be considered as well. To address this aspect, all the elements at the middle of the truss member are selected in one cross section for deriving the averaged stress time histories. Since the truss members normally experience pure compres- sion or tension, averaging the stress in the cross section is expected not to introduce a major approximation. Fig. 11 shows how the stress time histories obtained for the middle of the member are compared with the one recorded at the most critical element at the end of the same mem- ...
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... outcome of this investigation highlights that the elements with the highest stress are those closest to the hole of the truss members. This criterion leads to four elements at each end of the truss member. There are eight elements in each tubular member adjacent to the hole, which directly experience the welding effects. Fig. 10 depicts four of those eight elements at one end of a member. The stress time histories for the eight elements are illustrated in Fig. 10. The element with the highest value of stress in this figure is the most critical element of the member. For example, Element 322 is the most critical element in the member that carries Sensor S1. The next step is to examine the stress time history at the middle of the member. In reality, a sensor can be mounted anywhere on the perimeter of the truss member. Thus, the ef- fect of the sensor's mounting location must be considered as well. To address this aspect, all the elements at the middle of the truss member are selected in one cross section for deriving the averaged stress time histories. Since the truss members normally experience pure compres- sion or tension, averaging the stress in the cross section is expected not to introduce a major approximation. Fig. 11 shows how the stress time histories obtained for the middle of the member are compared with the one recorded at the most critical element at the end of the same mem- ...
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... on the AASHTO Specifications [20], the stress time history in- tended to be used for fatigue analysis must be derived from the areas adjacent to the welded parts. Therefore, a comprehensive procedure is implemented to select the most critical element for each truss member. Following is the procedure used for this purpose: All the elements lo- cated on one weld line are selected. The stress time histories are then obtained for the selected elements and comparisons are made to identify the elements that constantly experience the highest stress values. Fig. 10 shows the elements selected for deriving the stress time histories, as well as the stress time histories derived from the numerical ...
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The paper deals with the modal analysis and frequency response analysis of a bucket wheel excavator (BWE) boom, obtained by simulation, based on a virtual model of an existing BWE boom. The boom, which generally is realized as a spatial truss, is the most vulnerable subsystem of the BWE, being submitted to severe operational loads characterized by...
Citations
... In the second step, a rainflow-counting technique was used on a 10-min nominal stress history to accumulate the number of different types of stress cycles [4,6,20], as shown in Fig. 11a. The rainflow-counting technique is used in the analysis of fatigue data in order to reduce a spectrum of varying stress into an equivalent set of simple stress reversals. ...
Many failures of cantilever traffic signal structures have been reported in the USA in the past two decades, which have revealed the vulnerability of such structures to wind force and created a need to study their wind-induced behavior and fatigue performance. Previous studies have provided a thorough understanding on the wind-induced behavior of traffic signal structures in regular wind conditions. However, the wind-induced behavior of such structures in the extreme wind conditions has never been studied before. In this study, a cantilever traffic signal structure was selected for long-term monitoring. It was the first time that a traffic signal structure was monitored during a derecho, which has a wind speeds of more than 240 miles and wind gust at least 58 mph. In the first part of the study, the monitoring data during the August 2020 Iowa Derecho were analyzed to understand its wind-induced behavior in extreme wind conditions and the monitoring stress data were used to evaluate the wind speeds could possibly create fatigue damage on the structure. In the second part of the study, to more accurately quantify the fatigue damage on the structure, a data-driven algorithm for estimating fatigue life and reliability of wind-excited structures was proposed. The monitoring stress data in both regular and extreme wind conditions were used to develop fatigue damage model, which addressed the issue of insufficient monitoring data at high wind speeds from previous studies. Fatigue life was then estimated by combining the fatigue damage model and the local wind speed probability. In reliability analysis, uncertainties were considered as the wind speed probability, the fatigue resistance of the mast arm base, and Miner’s sum, and Monte Carlo simulations were conducted to generate a probability-of-failure curve. Finally, to demonstrate the algorithm, wind speed probability data from three cities in Iowa were used to estimate the fatigue life and reliability. The proposed data-driven algorithm could be widely used on other wind-excited structures, and the results from reliability analysis can serve as a reference in determining the period of regular maintenance for such structures.
... In addition, monitoring the stresses induced in a structure not only during lifting but also throughout the delivery process is critical to obtain information about the extent of damage to a structure. Arabi et al. observed and monitored the transportation of sign-support (truss) structures and performed fatigue analysis to predict the damage caused by road-induced excitations [16]. Moreover, to ensure human and asset safety, adequate planning before commencement of the delivery process is crucial for avoiding failure [17]. ...
During the delivery process, precast concrete structures (PCS) undergo drastic changes in strain response that could induce damage resulting from the lifting process or shocks during delivery. However, the continuous logging of vibration and strain measurement during the delivery of a PCS remains limited because of difficulties related to sensor installation and condition assessment. This paper presents (1) a multimetric portable sensing system that simultaneously measures strain and acceleration, and (2) a safety assessment strategy that adjusts the offset of the initial strain measurement and calculates the absolute strain response for assessing the safety of PCS during the delivery process. The experimental validation was performed during the 80-min delivery process of a 12-m-long PCS. The acceleration, tilts and strain of the structure were measured during its delivery, and the measured data were processed and analyzed to conduct a safety assessment.
... However, the low inherent frequency and small 2 damping ratio [2][3] of the flexible cantilevered structure induce it susceptible to the wind-induced vibration and fatigue damage. As for the bridge-type truss structures, the fatigue damages caused by temperature changes [4] and road-induced excitations [5] are also pronounced. ...
Sign and traffic signal structures are susceptible to fatigue damages caused by wind, temperature change, and road-induced excitation. This study focuses on the stress intensity factor (SIF) ranges for octagonal tube-to-transverse plate joints widely used in sign and traffic signal structures. The finite element (FE) models were established and calibrated by using Newman and Bowness equations. The SIF ranges of the joints with fillet weld and full-penetration groove weld were compared. The effects of initial crack location, transverse plate thickness, tube diameter and thickness, taper ratio of tube, weld size, and number of bolts, on the SIF ranges of tube-to-transverse plate joint with fillet weld were intensively investigated. The suggestions for improving the remaining fatigue life of the joint were offered.
... Compared to bolted connections, the gusset plate of this connection is welded on a slotted CHS tube which has the advantage of reducing the production costs together with an easy fabrication. Therefore, in recent years, this type of connection has been increasingly used in bridges [1][2][3][4], towers [5] and sign-support structures [6,7]. ...
Slotted circular hollow section (CHS) tube-to-gusset plate connections are frequently used in structures such as bridges, towers, etc., However the fatigue strength of this type of connections needs to be characterized. In the present study, the fatigue performance of the slit end area of this connection is investigated. Four sets of large-scale fatigue tests on the connection with coped hole at the slit end are carried out. Additionally, fatigue tests on CHS connections, available in the literature, are re-analyzed by means of effective notch stress (ENS) approach. Subsequently, parametric studies are carried out to analyze the influence of different geometrical and welding strategies on the notch stress concentration factor. The shortcomings of the ENS approach applied to this type connection are pointed out, proposing possible alternative solutions. Lastly, the optimal design for improving the fatigue strength of this slotted CHS tube-to-gusset plate connection is recommended.
... Attributable to their functionality, highway sign structures must support large truss spans to provide the needed information for the passengers without disturbing their way and introducing any possible hazard that may result from any intermediate supports. Due to their long spans and the use of hollow circular tubes with a relatively small mass, these structures are considered semi-rigid with a low natural frequency and damping ratio [1][2][3]. As a result, they experience fatigue failure due to various fatigue loading scenarios, which include natural wind gust, galloping, vortex shedding, and truckinduced vibrations [4]. ...
Full-span overhead sign support structures can be found along any major highway across the US. Such structures experience different wind loading scenarios varying with time. As a result, these structures start to build up fatigue cracks within their members near the end of their fatigue life. Due to economic realities, the needed routine fatigue inspections on such highway structures can not be performed regularly. This paper is intended to present a comprehensive tool to accurately predict the remaining fatigue life of full-span overhead highway sign support structures subjected to a long and sustained wind fluctuation. Synthetic wind time histories were developed by superimposing cosine waves over a range of frequencies of 3–300 Hz and randomly generated phase angles. Kaimal spectrum was utilized to build a database of wind time histories for each daily mean wind speed along a period of 45 years in the State of Kansas. Moreover, each wind time history was modified to capture both the mean speed and high speed in each given day. After that, the wind speed vs. the number of cycle relationship, for a given time span, was extracted from the synthetic wind time history using the Rain Flow counting technique. Fatigue evaluations were conducted using axial truss member stresses extracted from a finite element solution corresponding to each wind speed in any given time range. Potential fatigue failure was assessed for each structural member after amplifying the stress range using an average dynamic amplification factor generated by integrating the frequency-response curve of harmonic excitations. These assessments evaluate the ratio of consumed fatigue cycles to ultimate fatigue cycles using Miner’s rule to estimate the fatigue life. A computationally affordable simulation package was developed to carry out the generation of wind time histories, cycle counting, structural modeling, and fatigue life calculations. This package was used to evaluate the fatigue life of a non-cantilever sign structure in Wichita, Kansas. The software predicted the end-of fatigue life of two members in this structure. Accordingly, inspections of these two members revealed the existence of unnoticed severe fatigue cracks while other members did not show any sign of distress.
... The fatigue damage due to wind-induced vibration on slender structures such as high mast luminaire structures, sign-support structures, or traffic signal structures has been numerically studied in previous research [3,[4][5]23,25]. In this study, the fatigue damage due to wind-induced vibration was evaluated through the monitoring stress range at the mast-arm base. ...
Recent failures of traffic signal structures have showcased the vulnerability of such structures to wind loading. During the wind-induced vibration of the mast arm, the large mass of the mast arm creates high-level stress at the pole-to-arm connection. Additionally the low mechanical damping results in accumulationof stress cycles ewhich could cause fatigue damage at the pole-to-arm connection. In this study, a traffic signal structure with three vertical traffic lights was selected for long-term health monitoring. The monitored acceleration data at the mast arm tip was used to study the wind-induced behavior and was compared with the theoretical analysis results. The monitored strain data at the pole-to-arm connection was used to evaluate the fatigue damage. Low stress ranges were recorded most of the time, which indicates that the wind-induced fatigue damage might not be a significant concern for the monitored traffic signal structure. However, high stress ranges have been recorded at high wind speeds, indicating fatigue damage can still be an issue at higher wind speed regions. The performance of monitored traffic signal structure was compared with those in the literature. An apparent discrepancy was noticed between their wind-induced behaviors, and the orientation of the attached traffic lights was identified as a key parameter to influence the wind-induced behavior. It was found that at low wind speed, attached vertical traffic lights can reduce the likelihood of vortex-induced vibration and, as a result, lower the stress range at the pole-to-arm connection.
... The stress-life method was employed in the current study to predict the fatigue life (a.k.a., S-N curve). This method was deemed appropriate, as the bulk material's response was elastic, emphasizing on overall stresses, rather than local ones [14][15][16][17]. To determine the S-N curve for ASTM A709 Grade 50CR steel, the stresses recorded in each fatigue test were plotted versus the number of cycles to failure in a log-log format. ...
ASTM A709 Grade 50CR steel includes a range of 10.5% to 12.5% chromium, which greatly enhances the corrosion resistance of this type of steel in comparison to conventional steels widely used for structural applications. Despite the wealth of information on the durability of ASTM A709 Grade 50CR steel in corrosive environments, there was a gap in the literature concerning how this type of steel responds to the loads that the structures experience during their service life. To investigate this critical aspect and facilitate the future use of corrosion-resistant steel, the current study devised a holistic structural testing program with a focus on bridge applications. For this purpose, a full-scale girder was designed, fabricated, and tested under a four-point bending setup. The girder’s ability to meet the design expectations was assessed by comparing the results to the requirements of AASHTO Bridge Design Specifications. In addition, several tensile and fatigue tests were carried out to obtain an in-depth understanding of the performance of ASTM A709 Grade 50CR steel under both monotonic and cyclic loading scenarios. This led to the development of load–displacement, stress–strain, and S-N curves. The investigations were then expanded to quantify the remaining capacity of three different types of steel, i.e., corrosion-resistant steel, weathering steel, and carbon steel. For this purpose, a set of simulations were performed to estimate the corrosion rate and section loss of the girders under consideration over time. The outcome of this holistic study contributed to providing the insight necessary for the safe and efficient design of structural members made with corrosion-resistant steel.
... From there, depending on how the structure is handled and transported, other cracks can occur or existing ones propagate. When the structure is in service, the daily loads and environmental conditions can exacerbate current cracks or cause new cracks to form (Arabi et al. 2018). These common failure modes can lead to shorter life spans and early failure for structures. ...
Dynamic messaging signs (DMS) are found in operation over freeways, expressways, and other major intersections and provide information to travelers. If the DMS structure fails, then pedestrians and motorists can be harmed. An unstudied contributor to the reduced operation life of DMS structures is yearly thermal cycles. During the winter and summer times, the thermal variations tend to be large in range, in which daily and seasonal temperature variation can contribute to cyclic-caused fatigue. The objective of this study is to analyze thermal-induced fatigue life of highway overhead support structures. Field monitoring, mathematical analysis, and finite-element modeling were employed to perform the objective. The finite-element modeling extends to two different type of connection (slotted gusset welded joints and tube-to-tube welded joints) and two different materials (structural steel and aluminum alloy). Based on the estimated fatigue life for the overhead truss structures, the structural steel slotted gusset welded connection type provides larger fatigue life than other cases.
... Over the years, several methods have been developed by researchers and engineers to monitor civil infrastructure and evaluate its performance. Although conventional sensorbased methods are still popular and effective (Amezquita-Sanchez & Adeli, 2016;Amezquita-Sanchez, Valtierra-Rodriguez, & Adeli, 2018;Arabi, Shafei, & Phares, 2018, recently new computer-visionbased methods, such as deep-learning-based computer vision solutions, have caught the attention of researchers in different areas of civil and infrastructure engineering (LeCun, Bengio, & Hinton, 2015). Although the main building block of deep learning, that is, neural networks, has been utilized by researchers for decades (Adeli, 2001), only recently has detection (Xue & Li, 2018), and pavement crack detection (Zhang et al., 2017) have been investigated by researchers. ...
This paper aims at providing researchers and engineering professionals from the first step of solution development to the last step of solution deployment with a practical and comprehensive deep‐learning‐based solution for detecting construction vehicles. This paper places particular focus on the often‐ignored last step of deployment. Our first phase of solution development involved data preparation, model selection, model training, and model validation. Given the necessarily small‐scale nature of construction vehicle image datasets, we propose as detection model an improved version of the single shot detector MobileNet, which is suitable for embedded devices. Our study's second phase comprised model optimization, application‐specific embedded system selection, economic analysis, and field implementation. Several embedded devices were proposed and compared. Results including a consistent above 90% mean average precision confirm the superior real‐time performance of our proposed solutions. Finally, the practical field implementation of our proposed solutions was investigated. This study validates the practicality of deep‐learning‐based object detection solutions for construction scenarios. Moreover, the detailed information provided by the current study can be employed for several purposes such as safety monitoring, productivity assessments, and managerial decision making.
... Thus, researchers continually study structures to ensure their performance and reliability. For instance, Arabi et al. have investigate the fatigue behavior of dynamic sign support structures during transportation; [3], [4]; and during the service life of these structure under various environmental loads; [5], [6], [7]. ...
Materials used for structural members should achieve a quality approval from competent authorities under certain tests. Sometimes, in some projects, poor quality materials may be used due to poor supervision. When it comes to steel rebars, the lack of quality can be considered as higher resistance than nominal resistance, and the relative extension less than the minimum allowed. In this paper, the structural ductility has been evaluated in a way that structures have been designed based on standard material criteria, but in fact, inappropriate reinforcing steel rebars have been used in structure. In order to evaluate such circumstances, a typical material behavior is considered and numerical models analyzed in nonlinear static (with monotonic and cyclic loading) and dynamic (time-history) methods both for standard and non-standard rebars. It was observed that using the rebars with higher yield stress and the relative lengthening less than the standard value, despite the increase in the resistance of the overall structure, its ductility is reduced.
