Steel Plate Girder AASHTO LRFD Design Module

Overview

The Steel Plate Girder Bridge Module is a tool for AASHTO LRFD analysis and design of steel girder bridges. The tool integrates model generation based on a series of component based questions, influence line and surface live load analysis on construction stages, and full code check reports.

Model Generation

The module creates curved, straight and skewed 3D finite element models from basic parameters, such as span lengths, number of girders, transverse stiffener locations, and deck dimensions with no limitation on the number of spans and girders. Four girder types are supported:

Steel Plate I-Girder modeled as a single beam element. The beam element represents the web and flanges.
Steel Plate I-Girder modeled as a composition of plate elements for the web and beam elements for the flanges.
Steel Plate Box (Closed Top) Girder modeled as a single beam element.
Steel Plate Tub (Open Top) Girder modeled as a single beam element.

The deck is modeled using plate elements.

Steel Girder Module

LARSA 4D’s advanced bridge path coordinate systems simplify the geometry of curved bridge models. Horizontal and vertical alignments of curved bridges are used both for creating and editing the model. Geometry and results can be edited in “stationelevation- offset” coordinates that follow the curved path of the bridge, instead of straight “x-y-z”.

Bridge Path Coordinate Systems

Bridge Construction

The module generates roadway (lane) definitions, load cases for dead, live, and wind loading, staged construction analysis stages and steps, result combinations and envelopes according to AASHTO LRFD.

The staged construction analysis models the construction of the bridge in a sequence of steps:

DC1: Construct girders/cross-frames, apply self-weight, then deck weight. Apply temporary construction loads.
WS: Apply wind loads first in the positive direction, then in the negative direction.
DC2: Construct the deck and apply additional load.
DW: Apply additional loads.

Code Check

While the model generation component of the Steel Plate Girder Bridge Module can be used to rapidly create a LARSA 4D model, the module can also code check a model created independently. Elements such as girders and stiffeners are automatically located in the existing model.

Code checking is based on AASHTO LRFD 2006 (with 2007 additions) with detailed reports covering the following components of the code:

Cross-section proportion limits
Constructability
Service limit state
Strength limit state
Stiffeners

Members checked include tension, compression and flexural members with symmetrical or unsymmetrical section profiles made of plates as I-girders, box girders and rolled I shapes.

The V-Load or M/R methods are used when the girder is modeled as a single linear element.

Quick Code Check

This option performs code check on a particular cross-section along a girder. During the step by step procedure, the user provides the sectional and material properties along with the forces and stresses acting on the section. This eliminates the need for a LARSA model to run the code check. This option is ideal for examining the code-check procedure of this module. This process yields a detailed (formula by formula) report on how the code-check is carried out on the cross-section.

AASHTO LRFD Code Check Reports

Reports include overall structure status and detailed member reports at stations along the bridge for factored combinations for static, live load, and staged construction analysis results.

All equations and values used in the code check are reported. When a member fails the code check, the exact section of the code in which the failure occurred is reported. The report simulates a full manual computation.

Code Check Report

“4D” Analysis

All of this is integrated within the LARSA 4D Bridge application, taking advantage of its “4D” analysis engine, optimized sparse solver, and powerful user interface. Bridge models are analyzed using the LARSA 4D analysis engine, meaning all 3D and torsional effects as well as the locked-in forces of the construction sequence are fully considered. The combination of model generation, code check, and 3D analysis with “4D” time effects in a single application is unique and is what makes the Steel Plate Girder Bridge Module the most appropriate tool for any advanced AASHTO LRFD project.

An Integrated Tool

Through its integration with LARSA 4D, the user is free to inspect all input and result data and can modify the model prior to code check, going beyond code-check requirements as needed. Models created can include superstructure and substructure including foundation elements, such as modeled with LARSA 4D’s nonlinear grounded spring elements.

Models can take advantage of LARSA 4D’s full analysis capabilities, including response spectra, eigenvalue, and time history analysis, and LARSA’s other bridge design tools, such as post-tensioning, ultimate strength check, and macros for program extensibility.