Moving Load : All You Need to Know

December 10, 2020

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This webinar is the follow-up session for "Traffic Load Consideration to Different Types of Bridges: Case Study by Vishal Prasad"


When we consider Moving Load (Live Load) Analysis in midas Civil it is important to use various options properly for the purpose. In this session, we took a look at each function and option deeply in midas Civil. We highly recommend this session to all bridge designers who have to deal with vehicle loads on a daily basis around the world.



This project tutorial highlights


1. Traffic Line/Surface Lanes & Vehicles 


Midas Civil has 2 types of traffic lanes. The one is the line type and the other is the surface type. The line type of traffic lane is defined along the frame elements and the surface type of traffic lane is defined along the nodes of planar elements. Those traffic lane types have Moving Load (Live Load) Optimization function. In order to check critical results from the moving load analysis, we need to define various load cases. Moving Load Optimization helps the user to find the results with a few load cases.

Vehicles function suggests 2 types of vehicles according to the selected design code to cover various vehicle loading. The user is able to select a vehicle loading that is provided by SW directly or user-defined vehicles that have editable values.


2. Moving Load Cases & Moving Load Analysis Control


The user can define moving load cases with traffic lanes and vehicles in Moving Load Cases function. Depending on the selected design code, Moving Load Cases function provides different options such as Lane Scale Factor, Combination methods, Fatigue, and etc.

Moving Load Analysis Control provides some optional selection. The user can see results on certain elements group or get certain results types among Concurrent Forces/Stresses, Reaction, Displacement, Forces/Moments, and Elastic/General Links. And also, there are some options regarding the influence line/surface analysis.



3. Post-processing


Midas Civil results about forces, stresses, displacement and etc.. after the moving load (live load) analysis. Results are shown on the model view or on the table. For the moving load analysis, SW shows the influence line/surface diagram with the critical location of vehicles for each element and load cases.



1. Traffic Line/Surface Lanes & Vehicles 


Traffic Line/Surface Lanes have several options to cover the information of a traffic lane. Here are some details as shown on the figure for the options.



A. Traffic Lane Properties


Lane Width, Eccentricity for Line type / Offset Distance to Lane Center for Surface type, and Wheel Spacing. These options are regarding the information of a notional lane and vehicle loading.

Cross Section View



B. Transverse Lane Optimization


This option is used for checking additional cases.







C. Vehicular Load Distribution for Traffic Line Lane


There are two types to consider wheel loads of a vehicle. These have a different concept.

Therefore, select a suitable one for your design. 

Vehicular Load Distribution for Traffic Line Lane





D. Skew


This option is used to consider skew angle of a lane and it is available for Cross Beam type in Vehicular Load Distribution.






E. Moving Direction


When the moving load analysis is performed, the vehicle will be moving along the lane path. The direction of movement depends on the direction of the lane. Through this option, we can select a certain direction or consider both directions.

Moving Direction




F. Select by


This option provides 3 methods for defining the path of the lane.


a) 2 Points method

2 Points method

b) Picking method

Picking method

c) Number method

Number method


Moving Load (Live Load) Optimization function has similar options as Traffic Line/Surface Lanes. However, there is a special option to consider lanes automatically instead of defining the location of lanes. It is called Generate Analysis Lanes.


1. Traffic Lane Optimization Properties

Traffic Lane Optimization Properties

2. Generate Analysis Lanes


a) Number of Lane: This option creates lanes in the middle of a carriageway and both ends of the carriageway(When N=1). If N is more than 1, additional lanes are created between the middle lane and both end lane. Available value is 1 to 5.


Generate Analysis Lanes


b) Offset from centerline: This option creates lanes in the offset line of the center line. 


Offset from centerline


Vehicles function provides two types. midas Civil has various vehicle types in each design code. And also vehicle types are updated continuously.

Vehicles function



2. Moving Load Cases & Moving Load Analysis Control


Moving Load (Live Load) Cases function is used for defining a moving load case with vehicles and traffic lanes. Some details of options such as Fatigue, Lane Factor, and etc.  Sub Load Cases option is a common option that you can see under various design code. Through this option, we can consider combination cases for vehicles and lanes. Here shows the comparison between Combined and Independent option.

Moving Load Cases & Moving Load Analysis Control

Moving Load Cases & Moving Load Analysis Control 1

Moving Load Cases & Moving Load Analysis Control 2

After finishing works for the moving load analysis, we need the additional function for more effective analysis. Moving Load Analysis Control function helps you to control result types and the moving load analysis.




Moving Load Cases & Moving Load Analysis Control




3. Post-processing


Moving Load (Live Load) is one of variable load type. Therefore, midas Civil shows critical results for the moving load as the maximum or minimum results basically. And there is All case. It shows result values of max. and min. together.


Bending moment diagramsFig. Bending moment diagrams



In Moving Load Tracer function, we can see the influence line/surface diagrams and the location of a vehicle according to selected load case, element number, and force/moment component. 




Fig. Influence line/surface diagram with the vehicle


This function has an additional option called Write Min/Max Load to File. This option converts the selected moving load to the static load case. We can consider the vertical load as well as centrifugal forces and braking forces.



Fig. The dialogue of Write Min/Max Load to File


When we select a design code, we can see additional functions next to Moving Load Cases function. Those depends on selected design code. To get more details, please take a look at the document attached.


design code


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About the Author
TaeYong Yu | Technical Engineer | MIDASIT

Tae Yong is a bridge engineer within MIDASIT Technical Planning Team in South Korea. He has over 3 years of experience in the design of bridges and civil structures in Korea. He is familiar with international codes of practice including AASHTO, Eurocode and BS code. He has experience in discussing technical issues with engineers in Singapore, Malaysia, and Romania. From this webinar, he will share one of his experiences in Cable-stayed bridge design.

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