Impact factors of an old bridge under moving vehicular loads

Liu, Yang,Yin, Xinfeng,Zhang, Jianren,Cai, C.S. Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.46 No.3

This paper presents a new method to study the impact factor of an old bridge based on the model updating technique. Using the genetic algorithm (GA) by minimizing an objective function of the residuals between the measured and predicted responses, the bridge and vehicle coupled vibration models were updated. Based on the displacement relationship and the interaction force relationship at the contact patches, the vehicle-bridge coupled system can be established by combining the equations of motion of both the bridge and vehicles. The simulated results show that the present method can simulate precisely the response of the tested bridge; compared with the other bridge codes, the impact factor specified by the bridge code of AASHTO (LRFD) is the most conservative one, and the value of Chinese highway bridge design code (CHBDC) is the lowest; for the large majority of old bridges whose road surface conditions have deteriorated, calculating the impact factor with the bridge codes cannot ensure the reliable results.

Impact factors of an old bridge under moving vehicular loads

Yang Liu,Xinfeng Yin,Jianren Zhang,C.S. Cai 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.46 No.3

This paper presents a new method to study the impact factor of an old bridge based on the model updating technique. Using the genetic algorithm (GA) by minimizing an objective function of the residuals between the measured and predicted responses, the bridge and vehicle coupled vibration models were updated. Based on the displacement relationship and the interaction force relationship at the contact patches, the vehicle-bridge coupled system can be established by combining the equations of motion of both the bridge and vehicles. The simulated results show that the present method can simulate precisely the response of the tested bridge; compared with the other bridge codes, the impact factor specified by the bridge code of AASHTO (LRFD) is the most conservative one, and the value of Chinese highway bridge design code (CHBDC) is the lowest; for the large majority of old bridges whose road surface conditions have deteriorated, calculating the impact factor with the bridge codes cannot ensure the reliable results.

The influence of vehicles on the flutter stability of a long-span suspension bridge

Yan Han,Shuqian Liu,C.S. Cai,Jianren Zhang,Suren Chen,Xuhui He 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.20 No.2

The presence of traffic on a slender long-span bridge deck will modify the cross-section profileof the bridge, which may influence the flutter derivatives and in turn, the critical flutter wind velocity of thebridge. Studies on the influence of vehicles on the flutter derivatives and the critical flutter wind velocity ofbridges are rather rare as compared to the investigations on the coupled buffeting vibration of thewind-vehicle-bridge system. A typical streamlined cross-section for long-span bridges is adopted for bothexperimental and analytical studies. The scaled bridge section model with vehicle models distributed on thebridge deck considering different traffic flow scenarios has been tested in the wind tunnel. The flutterderivatives of the modified bridge cross section have been identified using forced vibration method and theresults suggest that the influence of vehicles on the flutter derivatives of the typical streamlined cross-sectioncannot be ignored. Based on the identified flutter derivatives, the influence of vehicles on the flutter stabilityof the bridge is investigated. The results show that the effect of vehicles on the flutter wind velocity isobvious.

The influence of vehicles on the flutter stability of a long-span suspension bridge

Han, Yan,Liu, Shuqian,Cai, C.S.,Zhang, Jianren,Chen, Suren,He, Xuhui Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.20 No.2

The presence of traffic on a slender long-span bridge deck will modify the cross-section profile of the bridge, which may influence the flutter derivatives and in turn, the critical flutter wind velocity of the bridge. Studies on the influence of vehicles on the flutter derivatives and the critical flutter wind velocity of bridges are rather rare as compared to the investigations on the coupled buffeting vibration of the wind-vehicle-bridge system. A typical streamlined cross-section for long-span bridges is adopted for both experimental and analytical studies. The scaled bridge section model with vehicle models distributed on the bridge deck considering different traffic flow scenarios has been tested in the wind tunnel. The flutter derivatives of the modified bridge cross section have been identified using forced vibration method and the results suggest that the influence of vehicles on the flutter derivatives of the typical streamlined cross-section cannot be ignored. Based on the identified flutter derivatives, the influence of vehicles on the flutter stability of the bridge is investigated. The results show that the effect of vehicles on the flutter wind velocity is obvious.

LES of wind environments in urban residential areas based on an inflow turbulence generating approach

Shen, Lian,Han, Yan,Cai, C.S.,Dong, Guochao,Zhang, Jianren,Hu, Peng Techno-Press 2017 Wind and Structures, An International Journal (WAS Vol.24 No.1

Wind environment in urban residential areas is an important index to consider when evaluating the living environment. However, due to the complexity of the flow field in residential areas, it is difficult to specify the correct inflow boundary conditions in the large eddy simulation (LES). In this paper, the weighted amplitude wave superposition (WAWS) is adopted to simulate the fluctuating velocity data, which satisfies the desired target wind field. The fluctuating velocity data are given to the inlet boundary of the LES by developing an UDF script, which is implemented into the FLUENT. Then, two numerical models - the empty numerical wind tunnel model and the numerical wind tunnel model with spires and roughness elements are established based on the wind tunnel experiment to verify the present method. Finally, the turbulence generation approach presented in this paper is used to carry out a numerical simulation on the wind environment in an urban residential area in Lisbon. The computational results are compared with the wind tunnel experimental data, showing that the numerical results in the LES have a good agreement with the experimental results, and the simulated flow field with the inlet fluctuations can generate a reasonable turbulent wind field. It also shows that strong wind velocities and turbulent kinetic energy occur at the passageways, which may affect the comfort of people in the residential neighborhood, and the small wind velocities and vortexes appear at the leeward corners of buildings, which may affect the spreading of the pollutants.

LES of wind environments in urban residential areas based on an inflow turbulence generating approach

Lian Shen,Yan Han,C.S. Cai,Guochao Dong,Jianren Zhang,Peng Hu 한국풍공학회 2017 Wind and Structures, An International Journal (WAS Vol.24 No.1

Wind environment in urban residential areas is an important index to consider when evaluating the living environment. However, due to the complexity of the flow field in residential areas, it is difficult to specify the correct inflow boundary conditions in the large eddy simulation (LES). In this paper, the weighted amplitude wave superposition (WAWS) is adopted to simulate the fluctuating velocity data, which satisfies the desired target wind field. The fluctuating velocity data are given to the inlet boundary of the LES by developing an UDF script, which is implemented into the FLUENT. Then, two numerical models - the empty numerical wind tunnel model and the numerical wind tunnel model with spires and roughness elements are established based on the wind tunnel experiment to verify the present method. Finally, the turbulence generation approach presented in this paper is used to carry out a numerical simulation on the wind environment in an urban residential area in Lisbon. The computational results are compared with the wind tunnel experimental data, showing that the numerical results in the LES have a good agreement with the experimental results, and the simulated flow field with the inlet fluctuations can generate a reasonable turbulent wind field. It also shows that strong wind velocities and turbulent kinetic energy occur at the passageways, which may affect the comfort of people in the residential neighborhood, and the small wind velocities and vortexes appear at the leeward corners of buildings, which may affect the spreading of the pollutants.

Fatigue Behavior of High-Performance Steel Beams Subjected to Different Corrosion Conditions

Ying Chai,Jianxin Peng,Linfa Xiao,Xinhua Liu,Jianren Zhang 한국강구조학회 2023 International Journal of Steel Structures Vol.23 No.4

The existing research mainly considers the fatigue properties of steel structures under the influence of the environment, corrosion rate, and load conditions without considering the effect of corrosion locations and areas. However, corrosion can happen to a steel structure in a practical engineering setting at any position. This paper investigates the fatigue behavior of high-performance steel beams (Q550E) subjected to different corrosion conditions through various tests. Results show that the fatigue life of the wholly corroded steel beams decreases as the frequency increases and increases as the stress ratio increases. Additionally, local corrosion has a greater impact on flexural stiffness than whole corrosion, and the lower half area has a greater impact than the right half area. Other corroded steel beams, with the exception of SCU-10, have fracture positions that are within the corrosion area. Because, despite the corrosion in the bending shear section, the fatigue strength of the corrosion area is higher than that of the fracture location. In addition, the degradation curves of the mid-span flexural stiffness of other steel beams under cyclic loading have not observed S-shaped curve characteristics, with the exception of GC-10B and SCU-20.

Single-cell sequencing reveals that endothelial cells, EndMT cells and mural cells contribute to the pathogenesis of cavernous malformations

Jian Ren,Xiao Xiao,Li Ruofei,Lv Cheng,Zhang Yu,Leiming Wang,Tao Hong,Hongqi Zhang,Wang Yibo 생화학분자생물학회 2023 Experimental and molecular medicine Vol.55 No.-

Cavernous malformations (CMs) invading the central nervous system occur in ~0.16–0.4% of the general population, often resulting in hemorrhages and focal neurological deficits. Further understanding of disease mechanisms and therapeutic strategies requires a deeper knowledge of CMs in humans. Herein, we performed single-cell RNA sequencing (scRNA-seq) analysis on unselected viable cells from twelve human CM samples and three control samples. A total of 112,670 high-quality cells were clustered into 11 major cell types, which shared a number of common features in CMs harboring different genetic mutations. A new EC subpopulation marked with PLVAP was uniquely identified in lesions. The cellular ligand‒receptor network revealed that the PLVAP-positive EC subcluster was the strongest contributor to the ANGPT and VEGF signaling pathways in all cell types. The PI3K/AKT/mTOR pathway was strongly activated in the PLVAP-positive subcluster even in non-PIK3CA mutation carriers. Moreover, endothelial-to-mesenchymal transition (EndMT) cells were identified for the first time in CMs at the single-cell level, which was accompanied by strong immune activation. The transcription factor SPI1 was predicted to be a novel key driver of EndMT, which was confirmed by in vitro and in vivo studies. A specific fibroblast-like phenotype was more prevalent in lesion smooth muscle cells, hinting at the role of vessel reconstructions and repairs in CMs, and we also confirmed that TWIST1 could induce SMC phenotypic switching in vitro and in vivo. Our results provide novel insights into the pathomechanism decryption and further precise therapy of CMs.