This study provides new insights into the comparison of cable-stayed and extradosed bridges based on the safety assessment of their stay cables.These bridges are often regarded as identical structures owing to the use...This study provides new insights into the comparison of cable-stayed and extradosed bridges based on the safety assessment of their stay cables.These bridges are often regarded as identical structures owing to the use of inclined cables;however,the international standards for bridge design stipulate different safety factors for stay cables of both types of bridges.To address this misconception,a comparative study was carried out on the safety factors of stay cables under fatigue and ultimate limit states by considering the effects of various untoward and damaging factors,such as overloading,cable loss,and corrosion.The primary goal of this study is to describe the structural disparities between both types of bridges and evaluate their structural redundancies by employing deterministic and nondeterministic methods.To achieve this goal,three-dimensional finite-element models of both bridges were developed based on the current design guidelines for stay cables in Japan.After the balanced states of the bridge models were achieved,static analyses were performed for different safety factors of stay cables in a parametric manner.Finally,the first-order reliability method and Monte Carlo method were applied to determine the reliability index of stay cables.The analysis results show that cable-stayed and extradosed bridges exhibit different structural redundancies for different safety factors under the same loading conditions.Moreover,a significant increase in structural redundancy occurs with an incremental increase in the safety factors of stay cables.展开更多
In order to analyze the possibility of detecting defects in bend pipe using low-frequency ultrasonic guided wave, the propagation of T(0,1) mode and L(0,2) mode through straight-curved-straight pipe sections was studi...In order to analyze the possibility of detecting defects in bend pipe using low-frequency ultrasonic guided wave, the propagation of T(0,1) mode and L(0,2) mode through straight-curved-straight pipe sections was studied. FE(finite element) models of bend pipe without defects and those with defects were introduced to analyze energy distribution, mode transition and defect detection of ultrasonic guided wave. FE simulation results were validated by experiments of four different bend pipes with circumferential defects in different positions. It is shown that most energy of T(0,1) mode or L(0,2) mode focuses on extrados of bend but little passes through intrados of bend, and T(0,1) mode or L(0,2) mode is converted to other possible non-axisymmetric modes when propagating through the bend and the defect after bend respectively. Furthermore, L(0,2) mode is more sensitive to circumferential notch than T(0,1) mode. The results of this work are beneficial for practical testing of pipes.展开更多
In this paper, the behavior of barrel-vaulted structures undergoing rocking of the abutments and the effectiveness of a few retrofit solutions are discussed. The comprehension of the structural performance of vault-ab...In this paper, the behavior of barrel-vaulted structures undergoing rocking of the abutments and the effectiveness of a few retrofit solutions are discussed. The comprehension of the structural performance of vault-abutment systems is fundamental for their seismic vulnerability assessment, and for the design of efficient strengthening techniques. In the paper, traditional techniques such as extrados thin concrete slab or masonry spandrel walls as well as an innovative solution with an extrados thin improved lime mortar slab reinforced by means of glass fiber mesh are considered. The different strengthening solutions are studied and compared on the basis of the results of non linear numerical analyses and by reference to a simplified analytical approach. Numerical and analytical models are validated through comparison with the results of a recent experimental study focusing on the behavior of vaulted masonry structures subjected to rocking of the abutments. The validated models can be used by engineers for the seismic vulnerability assessment of masonry vaulted structures as well as for the proportioning of possible extrados strengthening solutions, and will be used in the future to explore different structural system configurations.展开更多
While a small-radius induction bend is manufactured,various cross-section distortions may occur,such as its cross section tending to be elliptic,and wall thickness reduction or increase.These defects may deteriorate t...While a small-radius induction bend is manufactured,various cross-section distortions may occur,such as its cross section tending to be elliptic,and wall thickness reduction or increase.These defects may deteriorate the bearing capacity of pipelines.In order to study the effect of cross-section distortion on the performance of small-radius induction bends,3D(D refers to pipe diameter)induction bends were manufactured based on different combinations of process parameters.Then,the cross-section distortion,structure properties and their correlation of 3D bends and conventional 5D bends were analyzed comprehensively by means of cross-section geometry analysis,distortion analysis,physical and chemical property test,micro-structural analysis and so on.The following results were obtained.First,the wall thickening/thinning rate of 3D bends is about 2 times that of 5D bends,and the roundness of 3D bends is about 2e4 times that of 5D bends.Second,the cross-section distortion of 3D bends is obvious,so its heating temperature varies greatly in different parts,leading to different structure morphologies and contents.As a result,the numerical distribution of mechanical properties of each part of 3D bends(e.g.intrados,extrados and neutral zone)is discrete.Third,the strength at the intrados of most bends doesn't meet the standard,and it is sorted form the higher to the lower as extrados,neutral zone and intrados while the sequence of Charpy impact toughness is right contrary to the strength.Fourth,the strength at intrados and extrados decreases with the increase of roundness.The strength at intrados decreases with the increase of thickening rates.And the strength at extrados increases with the increase of thinning rates.展开更多
The Dongshuimen Bridge over the Yangtze River and the Qiansimen Bridge over the Jialing River in Chongqing,China are located at the tip of the Yuzhong Peninsula.Together,they are called the Twin River Bridges.Both are...The Dongshuimen Bridge over the Yangtze River and the Qiansimen Bridge over the Jialing River in Chongqing,China are located at the tip of the Yuzhong Peninsula.Together,they are called the Twin River Bridges.Both are double deck structures carrying four lanes of traffic on their upper decks and two transit tracks on their lower decks.The girders are steel truss structures with orthotropic plates and the towers are made of concrete.Aesthetics were carefully considered for the design of these bridges because of their visibility in the city and their neighboring landmarks.展开更多
文摘This study provides new insights into the comparison of cable-stayed and extradosed bridges based on the safety assessment of their stay cables.These bridges are often regarded as identical structures owing to the use of inclined cables;however,the international standards for bridge design stipulate different safety factors for stay cables of both types of bridges.To address this misconception,a comparative study was carried out on the safety factors of stay cables under fatigue and ultimate limit states by considering the effects of various untoward and damaging factors,such as overloading,cable loss,and corrosion.The primary goal of this study is to describe the structural disparities between both types of bridges and evaluate their structural redundancies by employing deterministic and nondeterministic methods.To achieve this goal,three-dimensional finite-element models of both bridges were developed based on the current design guidelines for stay cables in Japan.After the balanced states of the bridge models were achieved,static analyses were performed for different safety factors of stay cables in a parametric manner.Finally,the first-order reliability method and Monte Carlo method were applied to determine the reliability index of stay cables.The analysis results show that cable-stayed and extradosed bridges exhibit different structural redundancies for different safety factors under the same loading conditions.Moreover,a significant increase in structural redundancy occurs with an incremental increase in the safety factors of stay cables.
基金Project(51265044)supported by the National Natural Science Foundation of ChinaProject(2013TT2028)supported by the Science and Technology Project of Hunan Province of ChinaProject(2012QK162)supported by the Science and Technology Project of General Administration of Quality Supervision,Inspection and Quarantine of China
文摘In order to analyze the possibility of detecting defects in bend pipe using low-frequency ultrasonic guided wave, the propagation of T(0,1) mode and L(0,2) mode through straight-curved-straight pipe sections was studied. FE(finite element) models of bend pipe without defects and those with defects were introduced to analyze energy distribution, mode transition and defect detection of ultrasonic guided wave. FE simulation results were validated by experiments of four different bend pipes with circumferential defects in different positions. It is shown that most energy of T(0,1) mode or L(0,2) mode focuses on extrados of bend but little passes through intrados of bend, and T(0,1) mode or L(0,2) mode is converted to other possible non-axisymmetric modes when propagating through the bend and the defect after bend respectively. Furthermore, L(0,2) mode is more sensitive to circumferential notch than T(0,1) mode. The results of this work are beneficial for practical testing of pipes.
文摘In this paper, the behavior of barrel-vaulted structures undergoing rocking of the abutments and the effectiveness of a few retrofit solutions are discussed. The comprehension of the structural performance of vault-abutment systems is fundamental for their seismic vulnerability assessment, and for the design of efficient strengthening techniques. In the paper, traditional techniques such as extrados thin concrete slab or masonry spandrel walls as well as an innovative solution with an extrados thin improved lime mortar slab reinforced by means of glass fiber mesh are considered. The different strengthening solutions are studied and compared on the basis of the results of non linear numerical analyses and by reference to a simplified analytical approach. Numerical and analytical models are validated through comparison with the results of a recent experimental study focusing on the behavior of vaulted masonry structures subjected to rocking of the abutments. The validated models can be used by engineers for the seismic vulnerability assessment of masonry vaulted structures as well as for the proportioning of possible extrados strengthening solutions, and will be used in the future to explore different structural system configurations.
基金supported by the National Major Research and Development Project“Research on Disaster-caused Mechanism and Evolution Rules of Damages of Oil&Gas Pipelines and Storage&Transportation Facilities”(No.:2016YFC0802101)Scientific New Star Project of Shaanxi Province“Quality Forecast and Defect Control of Mold-free Hot-bending Cross Section with Small Radius of Pipe Material with Large Caliber”(No.:2015KJXX-73).
文摘While a small-radius induction bend is manufactured,various cross-section distortions may occur,such as its cross section tending to be elliptic,and wall thickness reduction or increase.These defects may deteriorate the bearing capacity of pipelines.In order to study the effect of cross-section distortion on the performance of small-radius induction bends,3D(D refers to pipe diameter)induction bends were manufactured based on different combinations of process parameters.Then,the cross-section distortion,structure properties and their correlation of 3D bends and conventional 5D bends were analyzed comprehensively by means of cross-section geometry analysis,distortion analysis,physical and chemical property test,micro-structural analysis and so on.The following results were obtained.First,the wall thickening/thinning rate of 3D bends is about 2 times that of 5D bends,and the roundness of 3D bends is about 2e4 times that of 5D bends.Second,the cross-section distortion of 3D bends is obvious,so its heating temperature varies greatly in different parts,leading to different structure morphologies and contents.As a result,the numerical distribution of mechanical properties of each part of 3D bends(e.g.intrados,extrados and neutral zone)is discrete.Third,the strength at the intrados of most bends doesn't meet the standard,and it is sorted form the higher to the lower as extrados,neutral zone and intrados while the sequence of Charpy impact toughness is right contrary to the strength.Fourth,the strength at intrados and extrados decreases with the increase of roundness.The strength at intrados decreases with the increase of thickening rates.And the strength at extrados increases with the increase of thinning rates.
文摘The Dongshuimen Bridge over the Yangtze River and the Qiansimen Bridge over the Jialing River in Chongqing,China are located at the tip of the Yuzhong Peninsula.Together,they are called the Twin River Bridges.Both are double deck structures carrying four lanes of traffic on their upper decks and two transit tracks on their lower decks.The girders are steel truss structures with orthotropic plates and the towers are made of concrete.Aesthetics were carefully considered for the design of these bridges because of their visibility in the city and their neighboring landmarks.
