The accurate assessment of fatigue damage is a crucial issue for the design of marine pipelines. In this study, we modified the approach of Zheng et al. (2007) to simulate the random wave elevations for the fatigue assessment of marine pipelines applied to intermediate seas, e.g., the Persian Gulf. The cumulative fatigue damage due to the bending stresses and the linear and nonlinear acting wave forces was estimated on the basis of the finite element program for free-spanning sections. The results showed that the fatigue damage is highly dependent on both the wave characteristics and the modeling approach for the irregular wave.
Traffic signals and information signs play a vivid role in maintaining safe travel by guiding drivers on highways and urban roads. Traffic mast arm structures are susceptible to vibrations induced by wind loads. Fatigue-induced failure is common in these structures. However, it is crucial to ascertain the functionality of signal support structures. This paper lays the foundation for a fully computational framework to model and mitigate wind-induced vibrations in traffic lighting support structures by conducting computational fluid dynamics (CFD) simulations, dynamic modeling, and damping enhancement. We validated the CFD simulations by aerodynamic testing. The dependence of flow pattern and aerodynamic loads on Reynolds number reveals the importance of full-scale CFD with large eddy simulation for wind load estimation on mast arm structures. Distributed tuned mass dampers were created by employing available weights of lighting boxes. The results show that distributed tuned lighting boxes are effective for vibration suppression. Besides, damping enhancement can significantly reduce vibration-induced stresses and hence extend the fatigue life. The proposed mitigation technique promises to save construction costs and improve the safety of the traveling public. The procedure followed for creating time histories of wind loads integrated with finite element modeling applies to other vibration lessening techniques for potential inclusion in the AASHTO standard.
Traffic signals and information signs play a vivid role in guiding drivers on highways and urban roads, to maintain safe travel. For this reason, it is crucial to ascertain the functionality of signal support structures. This paper lies the foundation for a fully computational framework to model and attenuate wind-induced vibrations in traffic lighting structures by using computational fluid dynamics (CFD) simulations & dynamic analysis. Dependence of flow pattern and aerodynamic loads on Reynolds number reveals the importance of full-scale CFD with Large Eddy Simulation for mast arm structures. By employing available weights of lighting boxes, distributed tuned mass dampers were created. The results obtained show that distributed tuned lighting boxes are effective devices for vibration suppression. In addition, damping enhancement can significantly reduce vibration-induced stresses, and hence extend the fatigue life with promises to reduce the cost of building new structures and improve the safety of the traveling public. The procedure followed for creating time histories of wind loads integrated with finite element modeling is useful for the investigation of other vibration lessening techniques.
Buildings are bluff bodies, compared to streamline objects, such as airfoil. Wind flow over buildings leads to separation and hence a complex spatial and temporal mechanism that governs the nature and intensity of aerodynamic forces. This complexity mainly comes from the transient nature of incident turbulent winds and the fluctuating flow pattern in the separation bubble. The study of building aerodynamics is vital for the evaluation of cladding pressures, drag, shear, and uplift forces that are essential for safe and economic design. Flow separation makes it challenging to estimate loads without referring to direct physical and/or computational simulation. For several decades, aerodynamic testing has been employed for the estimation of wind pressures and forces on buildings. However, for residential homes and low-rise buildings, it has been always a challenge to predict full-scale pressures by traditional wind tunnel testing, as per the lack of large turbulence and Reynolds number effects, among other factors. The mismatch in flow physics makes it difficult to scale up wind-induced loads as the process can be highly nonlinear, which is the case when full-scale pressure coefficients do not meet those from small-scale aerodynamic testing. This chapter presents the challenges in the modeling and evaluation of aerodynamic forces on low-rise buildings, along with recent advances in both experimental and computational methods.
The aerodynamic performance of a roof depends significantly on its shape and size, among other factors. For instance, large roofs of industrial low-rise buildings may behave differently compared to those of residential homes. The main objective of this study is to experimentally investigate how perimeter solid parapets can alter the flow pattern around a low-rise building with a large aspect ratio of width/height of about 7.6, the case of industrial buildings/shopping centers. Solid parapets of varied sizes are added to the roof and tested in an open-jet simulator in a comparative study to understand their impact on roof pressure coefficients. Roof pressures were measured in the laboratory for cases with and without parapets under different wind direction angles (representative of straight-line winds under open terrain conditions). The results show that using a parapet can alter wind pressures on large roofs. Parapets can modify the flow pattern around buildings and change the mean and peak pressures. The mean pressure pattern shows a reduction in the length of the separation bubble due to the parapet. The parapet of 14% of the building’s roof height is the most efficient at reducing mean and peak pressures compared to other parapet heights.
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