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Research on spatiotemporal characteristics of urban crowd gathering based on Baidu heatmap

Meng Yunwei, Li Shibao, Chen Kang, Li Binbin, Zang Ji'en, Qing Guangyang

Archives of Transport

2023

Vol. 68, iss. 4

41--54

With the rapid development of urban transportation and the increase in per capita car ownership, the problem of urban traffic congestion is becoming increasingly prominent. Due to the uneven distribution of crowd in different regions of the city, it is difficult to determine and solve the traffic dynamics congestion. In order to solve the problem that it is difficult to determine the dynamics of traffic congestion areas caused by uneven distribution of vitality in different regions of mountainous cities, a crowded mega mountainous city is selected as research object and it proposes a model to calculate the change characteristics of regional crowd gathering. Baidu Heatmap is used as it could distinguish crowd gathering in certain urban core area. The heat map pictures in dozens of consecutive days is extracted and researchers conducted pixel statistical classification on thermal map images. Based on the pixel data of different levels of the pictures, the calculation model is established and an algorithm based on particle swarm optimization is proposed. The calibration of the relative active population equivalent density is conducted, and the distribution characteristics of crowd gathering in time and space are analyzed. The results show that there are obvious spatiotemporal characteristics for this selected city. In time, holidays have an important impact on crowd gathering. The peak time of crowd gathering on weekdays is different from that on rest days. The research in this paper has a direct practical value for the identification of traffic congestion areas and the corresponding governance measures. The dynamic identification of population gathering areas in mountainous mega cities, demand prediction for various transportation regions, and future population OD(Origin-Destination) planning are of great significance.

Shear force distribution law of inclined webs box girder under live load

Cui Yujun, Wu Longqing, Wang Weiqi, Cao Wei, Xue Xingwei

Archives of Civil Engineering

2022

Vol. 68, nr 2

593--610

Inclined web box girders are widely used in urban areas because of their attractive appearance. However, there are few studies on the vehicle shear force distribution of this type of bridge. In this study, we established 62 three-dimensional finite element models in which the shear force of each web of the box girder can be extracted; furthermore, we investigated the shear force distribution law in webs of the box girder under live loads, including single-chamber and multichamber inclined web box girders. The main parameters studied include the number of vehicle lanes and chambers, slope of the inclined webs, and support conditions. The results reveal that an uneven distribution of web shear force exists in both the single-chamber box girder and multichamber girder under live loads, and the maximum value of the vehicle shear force distribution factor is greater than the average shear value shared by all webs. Therefore, the uneven distribution of shear force in the webs of the box girder cannot be ignored under eccentric vehicle loads. These values greatly exceed the safety factor of 1.15 that is used in conventional calculations.

Destrukcyjny wpływ temperatury na eksploatację przekryć stalowych dużych rozpiętości

Lytvyn Oleksandr, Sakharov Volodymyr, Marcinowski Jakub, Sakharov Volodymyr

Builder

2020

R.24, nr 4

111--113

Przedmiotem rozważań zaprezentowanych w pracy są przemieszczenia i naprężenia w elementach stalowych dźwigarów kratowych, spowodowane zmianami temperatury zewnętrznej i nierównomiernym rozkładem temperatur wewnątrz hali. Wielodniowe pomiary przemieszczeń stalowych, kratowych dźwigarów dachowych dużej rozpiętości połączone z pomiarami temperatury w przestrzeni hali i w różnych punktach dźwigarów wykazały znaczący wpływ nierównomiernego rozkładu temperatur na przemieszczenia. Zmierzone wartości przemieszczeń zostały porównane z przemieszczeniami otrzymanymi drogą symulacji numerycznych, w których danymi wejściowymi były pomierzone temperatury. Poza przemieszczeniami w pracy przeanalizowano także wzrost naprężeń w wybranych elementach dźwigara kratowego, spowodowany nierównomiernym rozkładem temperatur. Oceniono destrukcyjny wpływ temperatury na stan wytężenia analizowanych stalowych dźwigarów kratowych.

The subject of considerations presented in the work are displacements and stresses in steel elements of truss girders, caused by changes in the external temperature and uneven distribution of temperatures inside the hall. Multi-day measurements of displacement of steel, large-span truss roof girders combined with temperature measurements in the hall space and at various points of the girders showed a significant influence of uneven temperature distribution on the displacements. The measured displacement values were compared with the displacements obtained by numerical simulations, in which the input data were measured temperatures. In addition to displacements, the increase of stress in selected elements of the truss girder, caused by uneven temperature distribution, was also analyzed in the paper. The destructive effect of temperature on the strain and stress state of the analyzed steel truss girders was assessed.