Document Information

Document Type: FAQ

Product(s): LEAP CONBOX/CIP RC/PT Girder

Version(s): All

Original Author: Bentley Leap Bridge Technical Support Group – VM

QUESTION:  How the program is internally calculating the Live Load Forces and Moment for Service I Limit State ?

ANSWER:

1) A 1 span Box girder bridge was created in Leap Conbox. In the Load/Analysis TAB  I assigned HL-93 -Simple Span Truck..

2) The trucks Included Design Tandem ,Design Truck and Design lane then Ran the analysis and clicked on View Analysis Button.

3) In the Analysis Results window I selected these options Final --> Truck/Lane --> Design Tandem --> Min/Max Forces. The same procedure was followed for Design Truck as well.

4) At Mid span location of 30 ft I noted down the Max Moment of 700 K-ft and & 800 K-ft for Design Tandem and Design Truck respectively.

5) I followed the same procedure and for Design Lane I noted down the Max Moment as 288 k-ft.

6) In the Analysis Results window I selected these options Final --> Truck/Lane --> Design Truck --> Min/Max Forces.

7) After scrolling down halfway the user can see the Distribution Factors and Impact Factors for Service I, III and Strength I limit states at different POI.

8) Then in the Analysis Results window I selected Final --> Live Load  --> HL 93-Simple Span --> Min/Max Forces option.

9) At Mid Span Location of 30.00 ft I noted down the Total Max Moment as 6262 k-ft

10) Please follow the following procedure to calculate the Final Maximum Moment.

11)  Design  Truck + Design Lane = (800 x 4.63 x 1.33 ) + ( 288 x 4.63 x 1 ) = 4926.32 +  1333.44

12) The LRFD Live Load combination Factor is = 1 for Service I limit State.

13) Total Maximum Moment = 6260 k-ft

There is a minor difference between hand calculation and Conbox output results which can be ignored.

Please see the attached screen shot for more information.