- Enter the method of performing moving load analysis and the location of output for element results.
From main menu, select [Analysis] tab > [Analysis Control] group > [Moving Load]
Moving Load Analysis Control Data dialog box
Option for Dynamic factor (SK, Subway Trains, Tramcars)
Select the material and the bridge type for the calculation of Dynamic factor as per the Russian Moving Load Code. Dynamic Factor can be defined in the Vehicles dialog box.
Select the material type as RC, Steel and SRC.
Rail Road Bridge, Subway, Tram or Rail Road Bridge, Subway, Tram ( Main Truss Only) or Rail Road Bridge, Subway, Tram ( Combined Bridge) for Steel and SRC type of material and Rail Road Bridge, Subway, Tram or Rail Road Bridge , Subway, Tram for RC
Truck/Train Load Control Option
Set the method of performing moving load analysis using vehicular loads and the method of applying loads.
Set the moving load analysis method.
For detailed information on each method, please refer to the "Moving Load Analysis for Bridge Structures" section in the manual "Analysis for Civil Structures" under the Structural Analysis Features.
Load Point Selection
Set the selection method for application location of vehicular loads.
Influence Line Dependent Point
This is a method which controls the vehicular loads in a moving load analysis according to the influence values.
Maximum value(+) : From the locations of the applied loads only the loads that result in positive influence values are used in the computation.
Minimum value(-) : From the locations of the applied loads, only the loads that result in negative(-) influence values are used in the computation.
This method is used for general vehicular loading and yields results larger than that from the All Points method because the loads are controlled according to the influence values.
This is a method which analyzes the structure for applied vehicular loads in the moving load analysis at all locations without controlling the influence values.
The method is used for train loading and yields results smaller than that from the Influence Dependent Point method because the loads are not controlled according to the influence values.
Influence Generating Points
Number / Line Element
Assign the number of reference points on a line element for moving loads and drawing influence line in an influence line analysis. The accuracy of results increases with the increase in the number, but the analysis time may be excessive. If the length of beam element assigned with traffic line lane or plate elements assigned with traffic surface lane is large, then the "Influence Generating Point No. / Line Element" should be increased for more accurate analysis.
Distance between Points
Assign the distance between the consecutive reference points on a line element for moving loads. The accuracy of results will increase if the distance between the points decreases, but the analysis time will increase. The user can manage the time and accuracy by choosing the appropriate distance.
Set the position of the elements for which the moving load analysis results are calculated.
For plate elements, member forces per unit length are calculated as a result of moving load analysis. The form of member force results is selected from below.
Center : Calculate the member forces per unit length with respect to the centers of the elements and the output results are produced for the entire elements.
Center + Nodal : Calculate the member forces per unit length with respect to the element centers and the nodes constituting the elements and produce the results accordingly.
Stress Calculation : Assign whether or not to calculate the stresses of plate elements.
The moving load analysis results for Frame elements are produced in the form of member forces pertaining to 5 Points of each member. The form of member forces is selected from below.
Normal : It outputs the member forces for each component (axial force, shear force, moment, torsional force) at the reference point of the beam element. Each component is outputted as the maximum and minimum values.
Normal + Concurrent Force/Stress : In addition to the Normal format, it outputs the remaining member forces/stresses at the same load combination where a specific force/stress component is maximum or minimum. For example, when the axial force is maximum, it can output the moment, shear force, and torsional force.
The results are displayed in the Result Tables > Beam > Force/Stress section. After generating the table, right-click and select "View by Max Value Item" to display the table.
If Normal + Concurrent is not checked, i.e., if concurrent forces are not calculated, during PSC design, the maximum and minimum values are used for all 12 sets of concurrent forces. In other words, if the maximum value is selected, all six sets will have the same values, and if the minimum value is selected, all six sets will have the same values for design purposes.
Combined Stress Calculation : Assign whether or not calculate the combined stresses of frame.
Select the nodes or elements to be included in the moving load analysis.
Select and enter the supports where the moving load analysis results related to reactions are to be obtained.
All : Select all supports.
Group : Use the Group identified in the model, and enter the supports in the Group.
Select and enter the nodes where the moving load analysis results related to displacements are to be obtained.
All : Select all supports.
Group : Use Group to enter nodes.
Select and enter the elements where the moving load analysis results related to member forces are to be obtained.
All : Select all elements.
Group : Use Group to enter elements.
Bridge Type for Impact/CDA Calculation (India code only)
Select the bridge type for the automatic calculation of the impact factor. When the user defines a Traffic Line Lane with an Impact Factor, midas Civil will ignore this option.
Impact (Clause 211 of IRC: 6-2000)
Impact factor fraction for the RC bridge type
Impact factor fraction for the Steel bridge type
where L is length in metres of the span as specified in Clause 211.5 of IRC: 6-2000
• For Class AA, Class 70R, Class 40R or user-defined wheeled/tracked/bogie vehicle loading
(Spans less than 9m)
Impact percentage of tracked vehicles: 25% for spans up to 5m linearly reducing to 10% for spans of 9m.
Impact percentage of wheeled vehicles: 25%
(Spans of 9m or more)
- Impact percentage of tracked vehicles: 10% up to a span of 40m and in accordance with the curve in Fig.5 of IRC: 6-2000 for spans in excess of 40m.
Impact percentage of wheeled vehicles: 25% for spans up to 12m and in accordance with the curve in Fig.5 of IRC: 6-2000 for spans in excess of 12m.
- Impact percentage of tracked vehicles : 10% for all spans
Impact percentage of wheeled vehicles : 25% for spans up to 23m and in accordance with the curve indicated in Fig.5 of IRC: 6-2000 for spans in excess of 23m
Railway Bridge Information (India coed only)
Track : Select whether the bridge will carry single, double or multiple tracks. This detail is used in calculation of Coefficient of Dynamic Augmentation (CDA) as per IRS Bridge rules under clause 2.4.
Longitudinal Load Dispersion
Type1 : Classification as per IRS Bridge rules clause 22.214.171.124. Single sleeper under both rails at a location
Type2 : Classification as per IRS Bridge rules clause 126.96.36.199. Single sleeper sear under each individual rail at a location
Depth of Fill (d)
To modify CDA as per IRS Bridge rules clause 188.8.131.52.
Maximum Successive Vehicles (India code only)
Select the maximum number of successive vehicles considered for moving load analysis. A low number is suggested to decrease the Moving Load Analysis time.