LARSA 4D Introductory Training Manual for Bridge ... - LARSA, Inc.

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LARSA 4D Introductory Training Manual for Bridge Projects Vehicle and UDL Setup The influence analysis in LARSA 4D was developed with AASHTO LRFD and AASHTO LFD in mind, although the influence solver can be used for many design specifications. We will use AASHTO LRFD in this example. In the AASHTO LRFD code, a lane is loaded with combinations of a Design Tandem, Design Truck, and a Design Lane Load. LARSA 4D’s standard load pattern database consists of the following two load patterns suitable for this code: • HL-93 Design Truck in conformance with AASHTO LRFD 3.6.1.2.2. This truck has three axles of 8, 32, and 32 kips spaced (a minimum of) 14 ft. apart. The spacing between the two 32 kip axles may vary between 14 ft. and 30 ft. to produce extreme force effects. (Loads are lumped on the centerline of the lane, so no transverse effects are considered. • HL-93 Design Tandem in conformance with AASHTO LRFD 3.6.1.2.3. The design tandem consists of a pair of 25 kip axles spaced 4 ft. apart. The uniform load (UDL) is specified separately from the vehicle type. We first must load into the project the vehicle definitions from a database of vehicles provided with LARSA 4D. Go to Input Data → Connect Databases and choose Connect Standard Database . Open the file “AASHTO Vehicle Patterns.dml”. Then click OK . Connecting the AASHTO LRFD Load Patterns Database Each lane will be configured separately. For each lane, we will create an Influence Line result case which specifies how to perform AASHTO LRFD live load. Click Results → Influence Line/Surface Case to start configuring a new influence-based result case. Make sure that “Influence Line Coefficients Right Lane” is chosen at the top. All of the default options on the first tab are correct. Note that Load for Extreme Force Effects is turned on. Click Vehicular Loading . Click Add Lane Type . Then click the Select Vehicle Pattern entry in the list on the left. On the right, where it reads (Select Pattern) , click it and choose HL-93/HS20-44 Design Truck. 26
LARSA 4D Introductory Training Manual for Bridge Projects Next we will enter the specification for the tandem condition. Click Add Lane Type . Set the vehicle for this lane to HL-93 Design Tandem. A Lane Type refers to the way a design lane may be loaded. The influence line solver will choose the lane type that produces the most extreme effects. Click Add Lane Type a third time. Set the (first) vehicle for this lane to HL-93/HS20-44 Design Truck. Set the factor (to the right of the vehicle type selection) to 0.9. Click Add Vehicle . A second HL-93/HS20-44 Design Truck with the same factor is added into this lane type. Set the UDL Factor to 0.9. This applies to the current lane type. (We have not yet set the UDL magnitude.) Set the minimum back-to-front spacing to 50 feet. And turn on the option One Load Pattern Per Span . The One Load Pattern Per Span option pertains to the two-trucks lane type, in which the two trucks must be placed on different spans. The span break markers inserted into the lane path definition control what LARSA 4D knows to be the spans. Verify that your screen looks like the following figure: Influence-Based Results Setup Change to the Uniform/Patch Loading tab, and enter a UDL magnitude of 0.64 kip/ft. At the top of the window, set the result case name to Right Lane. Click OK to finish creating this case. Then repeat this process for the left lane. The Analysis Results Explorer will show a new group called Influence-Based with two new result cases inside. Influence Analysis Result Cases in the Analysis Results Explorer 27
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LARSA 4D Introductory Training Manual for Bridge ... - LARSA, Inc.

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