Function
Enter the traffic (line) lanes for moving load analysis.
Call
From the main menu, select [Load] tab > [Type: Moving Load] > [Moving Load Analysis Data] group > [Traffic Line Lanes]
Input
- To enter new or additional traffic line lanes, click the Add button.
- To modify previously entered traffic line lanes, select the traffic line lane to be modified in the dialog box and click the Modify button. When the Modify button is clicked, the selected lane elements will be displayed on the screen.
- To delete previously entered traffic line lanes, select the traffic line lanes to be deleted in the dialog box and click the Delete button.
Data entry method when the Add button is clicked.
Lane Name
Enter the name of a traffic line lane.
Traffic Lane Properties
Eccentricity
Enter the eccentricity of a traffic line lane relative to a traffic line lane element.
(-) Negative represents the left side of the traffic line element and vice versa.
Traffic line lane element is defined as the reference frame element from which the eccentricity is measured.
Wheel Spacing
Enter the spacing between the wheels. For influence line analysis, the program automatically applies a load equal to "Load ÷ no. of wheels" to each wheel.
Truck Load Lane Load
For influence line analysis, the Uniform Lane Load is loaded to each wheel as a uniform line load, which is the load per unit length divided by no. of wheels. For influence surface analysis, Uniform Lane Loads are applied as uniform area loads acting on the traffic lane surface.
For influence line analysis, Concentrated Lane Load divided by no. of wheels is applied to each wheel. Concentrated Lane Load needs to be applied as a uniform line load perpendicular to the traffic line lane, but this is not supported in influence line analysis using beam elements. For influence surface analysis using plate elements, Concentrated Lane Load divided by no. of wheels is applied to each wheel. Applying Concentrated Lane Load as a uniform line load is currently not available.
Lane Width
Enter the carriageway width. This value is used to consider a single lane bridge based on clause 207.4. of IRC: 6-2000. This clause states when the carriageway width of a bridge is less than 5.3 m, the number of lanes for design purposes is '1.' When the user defines a Sub-Load Case in Load > Moving Load Analysis Data > Moving Load Cases and the Number of Loaded Lanes is '1,' midas Civil automatically calculates the remaining width of the carriageway.
Impact Factor
Enter the impact factors for the entered traffic line lane elements.
Span Length
Enter the length of the span to calculate the Impact Factor automatically (Please refer to Analysis > Moving Load Analysis Control). The user is required to enter the span length for each element according to the span where the element is located.
Eccentricity of Vertical Load to consider Cant
The eccentricity of loading with respect to the center line of the track.
The effect of cant, the relative vertical distance between the uppermost surface of the two rails at a particular location along the track may be considered by taking the eccentricity of loading with respect to the center-line of the track, which will increase the wheel load on the inside of the curve and a concomitant decrease in the outside wheel load.
The wheel load reactions, RL and RR are calculated by summing moments about Point O and enforcing equilibrium.
If the slope is 5%, (s = 2.0m, h = 2.0m)
Figure 1. Effects of cant of the wheel load reactions
This can be simulated by applying the eccentricity of vertical loads. In the above case, the associated eccentricity can be calculated by summing moments about the center of gravity as follows:
Figure 2. Eccentricity of vertical loads
1
This function works with the Rail Traffic loads only. Road Bridge and Permit vehicle are not supported for this function. The supported trains are as follows:
Load Model 71, Load Model SW/0, Load Model SW/2, Unloaded Train, HSLM A1 ~ A10, HSLM B
2
Sign convention of eccentricity: The positive value means that the sum of vertical loads (W) is applied to the right side of the track by the amount of eccentricity with respect to the center line of the track. The green arrows represent the direction of the lane.
Centrifugal Force
Left Wheel of Vehicle Moving Forward
Enter the input value for the left wheel of vehicle moving in forward direction that need to be considered to simulate the overturning effect in terms of multiplication factor to the total load of the axle (W).
As per the entered value the program would automatically calculate the corresponding factor for the right wheel of forward direction and both wheels of backward direction. The results of vehicle application will be the combination of vertical effect and overturning effect of the vehicle. The overturning component causes the exterior wheel line to apply more than half the weight of the truck and the interior wheel line to apply less than half the weight of the truck by the same amount.
This option is only available if AASHTO LRFD is selected as Moving Load Code.
Traffic Lane Properties (France code only)
· Load System (A or B)
Loadable Width : Enter the carriageway width.
Load System A
Load System Bc
Load System Bt
Number of Lanes
Enter the maximum number of lanes. When the maximum numbers of lanes are different between Load System A and B, create the lanes for Load System A and B separately. The program will generate the individual lanes within the loadable width based on the lane width of Load System A and B specified by the French code. The lanes will be placed to find the most critical effects for each component of forces of the elements. The loads will be applied only in the unfavorable parts of the influence line, longitudinally and transversally.
Eccentricity
Enter the eccentricity of a traffic line lane relative to a traffic line lane element.
(-) Negative represents the left side of the traffic line element and vice versa.
Traffic line lane element is defined as the reference frame element from which the eccentricity is measured.
Dynamic Factor
Enter the span length, L and the span weight, G to determine dynamic factors for the traffic line lane elements. For the continuous bridges, when the span length and weight are different between spans, enter the values of L and G for each span separately. The value of S, the maximum total weight of the axles of system B that can be placed on the deck of the span, will be determined by the program. The option for the application of the dynamic factor can be selected from the definition of vehicles. The dynamic factors calculated by the program can be viewed from the Detail Result in the Moving Load Tracer.
Centrifugal Force
Left Wheel of Vehicle Moving Forward
Enter the input value for the left wheel of vehicle moving in forward direction that need to be considered to simulate the overturning effect caused by centrifugal forces in terms of multiplication factor to the total load of the axle (W).
As per the entered value the program would automatically calculate the corresponding factor for the right wheel of forward direction and both wheels of backward direction. The results of vehicle application will be the combination of vertical effect and overturning effect of the vehicle. The overturning component causes the exterior wheel line to apply more than half the weight of the truck and the interior wheel line to apply less than half by the same amount.
The bridge class can be defined from the Analysis>Moving Load Analysis Control Data dialog box.
· Military / Sidewalk / Pedestrian
Loadable Width
Enter the width of an individual lane, which should be larger than the width of the military vehicles. Number of lanes is fixed as one. These load types can only be applied to one lane.
The minimum loadable width for each vehicle:
Convoy Mc 80: 3.65m, Convoy Mc 120: 4.30m,
Convoy Me 80: 3.50m, Convoy Me 120: 4.00m,
Convoy Type D: 3.30m, Convoy Type E: 3.30m
Convoy Mc 80
Convoy Me 80
Eccentricity
Enter the eccentricity of a traffic line lane relative to a traffic line lane element.
(-) Negative represents the left side of the traffic line element and vice versa.
Traffic line lane element is defined as the reference frame element from which the eccentricity is measured.
Dynamic Factor
Enter the span length, L and the span weight, G to determine dynamic factors for the traffic line lane elements. For the continuous bridges, when the span length and weight are different between spans, enter the values of L and G for each span separately. The value of S, the maximum total weight of the axles of the vehicle that can be placed on the deck of the span, will be determined by the program. The option for the application of the dynamic factor can be selected from the definition of vehicles. The dynamic factors calculated by the program can be viewed from the Detail Result in the Moving Load Tracer.
The bridge class can be defined from the Analysis>Moving Load Analysis Control Data dialog box.
Traffic Lane Optimization (Transverse Lane Optimization)
In the previous versions (up to midas Civil 2015 V1.2)
When a traffic lane (line lane or surface lane) is defined, the moving load is applied with the vehicle loads located in the center of the lane only. In other words, the transverse floating of vehicle loading within a lane is not available.
However, the most critical member forces, stresses or reactions at each location may not always result with the vehicle loads placed in the middle of traffic lanes. In other words, the worst effect of vehicle placement is not guaranteed by placing the vehicle loads in the middle of the lane only.
(Users need to manually define additional lanes in order to obtain the worst effect of vehicle placement in the transverse direction.)
In the previous versions (midas Civil 2015 V2.1 and midas Civil 2018 V2.1)
When the “Traffic Lane Optimization” option is checked on, midas Civil transversely floats the vehicle load within the lane and obtains the worst effect of the vehicle placement for each element.
Instead of every possible location, the middle (existing), left-end and right-end positions of the lane width are considered for the efficiency of analysis run time.
In other words, with this option, each vehicle has two additional positions, the left and right ends, within each lane.
Users can define vehicle loads and traffic lanes the same way as in the previous versions. With the “Traffic Lane Optimization” option checked, the worst transverse effect of the moving load analysis can be obtained for each element.
Existing vehicle locations (the middle)
Additional vehicle locations considered (left-end, right-end)
In the current version (midas Civil 2018 V2.1 and up)
Traffic Lane Optimization has been renamed to Transverse Lane Optimization. Previously, vehicle was positioned at the middle and both left and right ends within each traffic lane to find the worst transverse effect of the moving load. The vehicle will now be positioned at the middle and left and right ends within the allowable width specified below the Transverse Lane Optimization check box. Allowable width can be defined by checking on the Transverse Lane Optimization option and the default value of Allowable Width is taken from the Lane Width.
At the moment, this feature is not supported for India, Taiwan code.
Vehicular Load Distribution
Assign the means of distributing the vehicular load.
Lane Element : Apply loads to the traffic line lane elements reflecting the eccentricity.
When defining the lanes with lane element type, the vertical load components (vehicle loads) and the moment due to eccentricity is assigned only on the line lane element. Even though the lanes can be located on cross beam elements, if the lane element type is selected, then the distribution effect for the cross beam analysis will not be considered.
Cross Beam : Apply the traffic load to the cross beams.
When using Cross Beam type, the eccentricity is used only for locating the lanes from the line lane element. The vehicle loads are distributed to the girders by cross beam elements defined as a Cross Beam Group. If the user is modeling a bridge having multiple girders, the Cross Beam type is recommended for vehicular load distribution.
For example, an axle load of 100kN is located as shown below. Then, concentrated loads, 25kN and 75kN, are applied to point A and point B respectively. The cross beams themselves are loaded. The smaller spacing between cross beams gives the more correct results for the moving load analysis.
Cross Beam Group : Specify the name of the Structure Group to which Cross Beams are assigned. A wheel load is distributed to adjacent cross beams as shown below.
When Cross Beam option is selected in the curved bridge, the cross beam spacing must be dense enough (ex. 0.5m). If the cross beam spacing is large, the program can have a problem in detecting the adjacent cross beam elements. This problem can occur only when the radius of curve is relatively small comparing to the bridge length.
Skew : Specify the Skew Angles at the Start and End of the bridge.
Moving Direction
Assign the direction of traffic loads.
Forward : Consider the direction from the Start to End only.
Backward : Consider the direction from the End to Start only.
Both : Consider the both direction.
Selection by
2 Points : Beam elements in a line defined by 2 points are assigned as traffic line lane elements. The first point becomes the Start point.
Picking : Assign the traffic line lane elements with the mouse. The location of the first-assigned element becomes the Start point.
Number : Enter the element numbers pertaining to the traffic line lane elements. The location of the first-assigned elements becomes the start point.
Operations
The data entry is reflected when Selection by Number is selected.
Add : Add to the selected traffic lane elements with the specified eccentricity and impact factor.
Insert : Insert the selected traffic lane elements in between the previously entered traffic lane elements.
Delete : Select the traffic lane elements at the bottom of the dialog box and delete.
The traffic line lane must be consecutively entered in the direction of the moving path of the vehicles. When assigning elements with 2 points or Picking [Add] or [Insert] button need not be clicked.
Span Start
For multi-span bridges, select the starting element of each span to distinguish spans. This is used to calculate the maximum negative moment of a continuous bridge due to DL.
When Transverse Moving Load is selected in the Moving Load Code
Scale Factor
Enter the scale factor for the application of transverse moving loads.
Selected by
2 Points : Beam elements in a line defined by 2 points are assigned as traffic line lane elements. The first point becomes the Start point.
Picking : Assign the traffic line lane elements with the mouse. The location of the first-assigned element becomes the Start point.