Pitting corrosion is harmful during bridge construction,which will lead to uneven roughness of steel surfaces and reduce the thickness of steel.Hence,the effect of pitting corrosion on the mechanical properties of col...Pitting corrosion is harmful during bridge construction,which will lead to uneven roughness of steel surfaces and reduce the thickness of steel.Hence,the effect of pitting corrosion on the mechanical properties of cold-formed thin-walled steel stub columns is studied,and the empirical formulas are established through regression fitting to predict the ultimate load of web and flange under pitting corrosion.In detail,the failure modes and load-displacement curves of specimens with different locations,area ratios,and depths are obtained through a large number of non-linear finite element analysis.As for the specimens with pitting corrosion on the web,all the specimens are subject to local buckling failure,and the failure mode will not change with pitting corrosion,but the failure location will change with pitting corrosion location;the size,location,and area ratio of pitting corrosion have little influence on the ultimate load of cold-formed thin-walled steel short columns,but the loss rate of pitting corrosion section area has a greater impact on the ultimate bearing capacity.As for the specimen with flange pitting corrosion,the location and area ratio of pitting corrosion have less influence on the ultimate load of cold-formed thin-walled steel short columns,and the section area loss rate has greater influence on the ultimate bearing capacity;the impact of web pitting corrosion on the ultimate load is greater than that of flange pitting corrosion under the same condition of pitting corrosion section area.The prediction formulas of limit load which are suitable for pitting corrosion of web and flange are established,which can provide a reference for performance evaluation of corroded cold-formed thin-walled steel.展开更多
Freeway work zone forms as a result of traffic crash or road rehabilitation.To ascertain the effects of work zone with lane II completely blocked on vehicular flow on ring freeways with a tunnel,a three-lane continuum...Freeway work zone forms as a result of traffic crash or road rehabilitation.To ascertain the effects of work zone with lane II completely blocked on vehicular flow on ring freeways with a tunnel,a three-lane continuum model is put forward.The mandatory net lanechanging rate from lane II to lane I or III just upstream of the work zone is described by a random number model,with the random number being produced within a small range around a median based on a golden section analysis.The net-changing rate between adjacent lanes is described using a lane-changing time on the basis of an assumption:the time ratio to relaxation time equals infinity when the absolute value of traffic densities between the two adjacent lanes is less than 1 veh/km,implying that the net-changing rate is zero;otherwise,the time ratio is inversely proportional to the vehicular spatial headway,which is equal to unity for traffic flow at saturation state,but infinity when the traffic flow is completely jammed.It is assumed that the freeway is a three lane ring with a total length of 100 km,and has a tunnel with a speed limit of 60 km/h and a length of 1.6 km located downstream the work zone with a length of 0.16 km.The free flow speeds on lanes I,II,and III are 120 km/h,100 km/h,and 85 km/h,respectively.For the vehicular flow on the ring freeway with a tunnel,numerical simulations based on the three-lane continuum model are carried out with a reliable numerical method of high accuracy.It is found that the vehicular flow has two thresholds of traffic jam formation,one depending upon the tunnel and the other upon the work zone.The tunnel triggers a traffic jam when the initial density normalized by jam density is equal to the first threshold 0.15,and the work zone originates another traffic jam when the normalized initial density equals the second threshold 0.19.The freeway tunnel plays a dominant role in the prediction of mean travel time as soon as the tunnel has generated a traffic jam at the tunnel entrance.For the vehicular flow at unsaturated state,the average speed through the tunnel is about 26.67 km/h.When the normalized initial density exceeds the second threshold 0.19,the mean travel time through every lane increases with the initial density linearly.Vehicle fuel consumption can be estimated by interpolation with the time averaged grid traffic speed and an assumed vehicle performance curve.It is found that the vehicle fuel consumption is lane number dependent,and distributes with the initial density concavely,as well as has a value in the range of 6.5 to 8.3 l.展开更多
基金funded by the‘Research Project of the Sucheng to Sihong Section of the Yanluo Expressway-Measurement Technology and Application of Bridge Quality Project Based on UAV Binocular Imaging(No.00-00-JSFW-20230203-029)’,received by H.Z.Wang.
文摘Pitting corrosion is harmful during bridge construction,which will lead to uneven roughness of steel surfaces and reduce the thickness of steel.Hence,the effect of pitting corrosion on the mechanical properties of cold-formed thin-walled steel stub columns is studied,and the empirical formulas are established through regression fitting to predict the ultimate load of web and flange under pitting corrosion.In detail,the failure modes and load-displacement curves of specimens with different locations,area ratios,and depths are obtained through a large number of non-linear finite element analysis.As for the specimens with pitting corrosion on the web,all the specimens are subject to local buckling failure,and the failure mode will not change with pitting corrosion,but the failure location will change with pitting corrosion location;the size,location,and area ratio of pitting corrosion have little influence on the ultimate load of cold-formed thin-walled steel short columns,but the loss rate of pitting corrosion section area has a greater impact on the ultimate bearing capacity.As for the specimen with flange pitting corrosion,the location and area ratio of pitting corrosion have less influence on the ultimate load of cold-formed thin-walled steel short columns,and the section area loss rate has greater influence on the ultimate bearing capacity;the impact of web pitting corrosion on the ultimate load is greater than that of flange pitting corrosion under the same condition of pitting corrosion section area.The prediction formulas of limit load which are suitable for pitting corrosion of web and flange are established,which can provide a reference for performance evaluation of corroded cold-formed thin-walled steel.
基金supported by the National Natural Science Foundation of China(No.11972341)the fundamental research project of Lomonosov Moscow State University‘Mathematical models for multi-phase media and wave processes in natural,technical and social systems’.
文摘Freeway work zone forms as a result of traffic crash or road rehabilitation.To ascertain the effects of work zone with lane II completely blocked on vehicular flow on ring freeways with a tunnel,a three-lane continuum model is put forward.The mandatory net lanechanging rate from lane II to lane I or III just upstream of the work zone is described by a random number model,with the random number being produced within a small range around a median based on a golden section analysis.The net-changing rate between adjacent lanes is described using a lane-changing time on the basis of an assumption:the time ratio to relaxation time equals infinity when the absolute value of traffic densities between the two adjacent lanes is less than 1 veh/km,implying that the net-changing rate is zero;otherwise,the time ratio is inversely proportional to the vehicular spatial headway,which is equal to unity for traffic flow at saturation state,but infinity when the traffic flow is completely jammed.It is assumed that the freeway is a three lane ring with a total length of 100 km,and has a tunnel with a speed limit of 60 km/h and a length of 1.6 km located downstream the work zone with a length of 0.16 km.The free flow speeds on lanes I,II,and III are 120 km/h,100 km/h,and 85 km/h,respectively.For the vehicular flow on the ring freeway with a tunnel,numerical simulations based on the three-lane continuum model are carried out with a reliable numerical method of high accuracy.It is found that the vehicular flow has two thresholds of traffic jam formation,one depending upon the tunnel and the other upon the work zone.The tunnel triggers a traffic jam when the initial density normalized by jam density is equal to the first threshold 0.15,and the work zone originates another traffic jam when the normalized initial density equals the second threshold 0.19.The freeway tunnel plays a dominant role in the prediction of mean travel time as soon as the tunnel has generated a traffic jam at the tunnel entrance.For the vehicular flow at unsaturated state,the average speed through the tunnel is about 26.67 km/h.When the normalized initial density exceeds the second threshold 0.19,the mean travel time through every lane increases with the initial density linearly.Vehicle fuel consumption can be estimated by interpolation with the time averaged grid traffic speed and an assumed vehicle performance curve.It is found that the vehicle fuel consumption is lane number dependent,and distributes with the initial density concavely,as well as has a value in the range of 6.5 to 8.3 l.
