Document Information

Document Type: FAQ

Product(s): LEAP CONSPAN/Precast/Prestressed Girder

Version(s): All

Original Author: Bentley Technical Support Group - VM

QUESTION: How can the user input new AASHTO live load HL93 which is a combination of truck load and lane load. The program would not allow the user to input lane loads on the design truck and vice versa (cannot input concentrated loads to lane loads) ?

ANSWER:

If the user has moved from LFD code to LRFD then according to LRFD there is no provision to add a concentrated load to the lane load as it is in LFD.  Live Loads can be input in accordance with AASHTO Standard (LFD) Art. 3.7.1 by selecting either the H/HS lane loads or H/HS truck loads. CONSPAN analyzes the H/HS lane and truck loads separately. Therefore, the user must select both the H/HS lane and truck loads for analysis. 

Moment and shear envelopes for live load are developed in two phases:

• Lane load analysis
• Truck + preceding/trailing uniform load analysis.

The truck load comprises the axle loads and preceding/trailing uniform loads acting together. When performing live load analysis, the program first considers the lane load (including associated concentrated loads) acting alone.  Then, it considers the truck load acting alone. At each section, the values of the live load envelopes are obtained by comparing these two envelopes and taking the critical value. This process is done for each of the trucks selected on the Loads screen; the final envelope covers each of these envelopes.

As per article 3.6.1.2  AASHTO LRFD 2007 code nothing has changed with respect to HL93 truck loading in the latest AASHTO 2010 code.

In Conspan if the LRFD option is selected in the loads tab then the user can see the Design lane and Design truck is preselected and are applied at the same time.