Tutorial

The use of refined methods and the subsequent benefits are illustrated in the following presentation of an extension of Tutorial 4 (Continuous 3 Span Bridge in LRFD mode).

In the following tutorial, we will present the benefits of using refined methods of analysis over code specified equations for the computation of live load distribution factors. To highlight the difference, we will deal with an exterior beam, where the lever rule is used for computation of live load distribution factors for Moment in the code equation mode.

All of the steps up to Step 18 are the same as those given in Tutor 4 starting on page T4-1. However, in Step 18 of Tutor 4, instead of selecting Span 2 and Beam 2, make sure you select Span 1 and Beam 1 and follow these steps below. Also keep in mind that the default distribution factor computation method has been set to the "Use Code Equation" option and we will leave it as such.

Step 19

Click the Strand Pattern button to activate the Strand Pattern. Next, click on the Auto Design button and the program will generate a strand pattern with 34 strands as shown in the figure above. Click the OK button to close this screen.

Step 20

Now, come back to Analysis tab and select the Analysis Factors button. Select the option to Use Refined Methods of Analysis to compute the Live Load DF's.

Note: We are making this selection only for this span and this beam (i.e. Span 1 and Beam 1); however, you could chose to apply this methodology to all beams.

Click the OK button to close this dialog and then click on the Run Analysis button. You may notice that the analysis may take more time to complete than usual because of the more refined finite element methodology being applied.

step 21

After the analysis is completed, come back to the Distribution Factors tab and look at the values for the Live Load Distribution Factors for Span 1, Beam 1. You will see that the program has computed Distribution Factors for each of the tenth points along the beam for both single lane and multi-lane cases for each of the positive moment, negative moment and shear force effects. By clicking on the location drop down list box, you can select the different locations along the beam to see the individual values at each of the locations.

Click the OK button to close this dialog and then go to the Beam tab. By default Span 1 Beam 1 is already selected. Click on the Strand Pattern button to activate the Strand Pattern.

step 22

Click the Reset Button, followed by the Auto Design button. The program now generates a strand pattern with only 30 strands instead of 34 strands it generated when the Use Code Equations option was selected, thus showing us the direct benefits of using the refined methods of analysis to compute the Live Load Distribution factors more accurately.

Click the OK button to close the Strand Pattern and then click on the File menu and select the Print menu item. Select Beam Specific Results for Span 1 Beam 1 and check the Properties check box and click OK. You can scroll down the results shown on screen to view the Live Load Distribution Factors computed for this specific beam as shown below.