INTRODUCTION
SNAPBoxBeam™ is a family member of SNAPBridge™: Bridge Analysis and Design Suite, which is used for Steel Box Girder Bridge Analysis and Design.
This chapter describes the features of SNAPBoxBeam program.
SNAPBoxBeam Features
Structural Analysis
Structural Model
Material Properties
Girder Section Properties
Typical Bridge Section
Loads
Structural Design and Code Check
General Code Check
Fexural Capacity Check
Shear Capacity Check
Fatigue Stress/Strength Check
Constructability Check
Serviceability Check
Shear Connector Design
About This Manual
SNAPBoxBeam Features
SNAPBoxBeam is a user-friendly powerful tool for steel box girder bridge analysis and design, which offers the following features:
- Most-friendly user interface makes users to build structural models visually.
- Complete linear static analysis of simply-supported and continuous spans of straight steel box girder bridges for various types of loads.
- Complete code checks for flexural, shear capacity, fatigue, and longitudinal stiffeners etc..
- Support the Allowable Stress Design (ASD), Load Factor Design (LFD) or Load and Resistance Factor Design (LRFD) criteria of the latest AASHTO Standard Specifications for Highway Bridges or AASHTO LRFD Bridge Design Specifications.
- Design shear connector etc. according to codes.
- Graphic output of the analysis and design results to create design sketches.
Structural Analysis
2D finite element model is used for the structural analysis. Only vertical translation (y-direction) and rotation freedoms are considered. Linear elastic material and small strain/displacement are assumed.
Structural Model
Coordinate System: x-y rectangular coordinate system is used. x-axis coincides with the longitudinal direction of the bridge.
2D beam elements, each of which has two nodes. Each node has two degrees of freedom: y-translation and z-rotation.
Supports are assumed as vertical restraints.
Element ID and Node ID are generated automatically.
There is no limit in terms of number of elements and/or nodes.
Material Properties
Materials are assumed to be linear elastic.
Concrete is transformed to steel through the modular ratio between the two materials. The ratio is different for different construction stages.
Girder Section Properties
Girder types could be box girder with either vertical or inclined webs.
Users define the dimensions of the girder sections in the girder section definition dialog box.
The program automatically calculates the non-composite section properties, 1N and 3N transformed section properties of the girders. The effective width of deck slab is determined by the program in accordance with the requirements of codes.
There is no limit in terms of the number of girder sections.
Typical Bridge Section
Users define the typical bridge section dimensions in the typical section definition dialog box. The dimensions include the beam spacing, overhang width, roadway width, structural depth of deck slab etc.
The typical bridge section dimensions are used to determine the load distribution factor, effective concrete slab width etc.
Only one type of bridge section can be defined.
Loads
Loads are classified into four categories: (1) Dead Loads of self-weight of steel girders and deck slabs, which are applied on the non-composite sections. (2) 3N Superimposed Dead Loads, which are on the 3N-transformed sections. Wearing surface, barriers etc. could be assumed to be in this category. The loads could be either distributed or concentrated. (3) 1N Superimposed Dead Loads, which are on 1N-transformed sections. The loads could be either distributed or concentrated. (4) Live Loads, which are applied on 1N transformed sections and include vehicle live loads and impact and sidewalk live load.
The current version of SNAPBoxBeam supports the following types of vehicle live loads:
- Standard H xx-44 Truck
- Alternate Military Loading
- Standard HS xx-44 Truck
- Standard Lane Loading
- HL93 Loading
There is no limit on the number of load cases for 3N and 1N Superimposed Dead Loads.
Only one type of vehicle live loads can be defined for each run.
Notes: If LRFD is used for the design, only HL93 is supported as the vehicle live load. The program will set the vehicle live load to HL93 when you select LRFD design code in the Settings dialog box.
Structural Design and Code Check
Users can specify one of the three design methods: Allowable Stress Method (ASD), Load Factor Design Method (LFD) of AASHTO Standard Specifications for Highway Bridges or Load and Resistance Factor Design Method (LRFD) of AASHTO LRFD Bridge Design Specifications.
General Code Check
The program automatically checks the live load deflection requirements of codes.
Uplift forces at supports are checked in accordance with codes.
Girder depth is checked.
Section Ductility requirement is checked for composite girders.
Overload stress is checked for ASD and LFD Design.
Flexural Capacity Check
Flexural capacity of girder sections is checked in accordance code requirements.
For ASD and LRFD, the non-composite section capacity in construction stage and the maximum DL plus Live Load flexural capacity of composite sections are checked.
For LRFD, flexural capacity is checked for Strength Limit State of maximum DL and Live Load. It is also checked for constructability.
Shear Capacity Check
Web transverse stiffener information is defined by users in Details Definition dialog box, which is related to the shear capacity of the sections.
The program supports three types of transverse stiffeners: Single Plates, Plate Pairs and Angles.
In accordance with the code requirements, unstiffened web and stiffened web shear capacity are calculated and the transverse stiffener section defined by users are checked.
For ASD and LFD design, shear capacity is only checked for maximum DL plus LL+I load case.
For LRFD, shear capacity is checked for constructability and Strength Limit State.
Fatigue Stress/Strength Check
Users shall specify the type of road or ADTT in General Information dialog box, which are used to determine the allowable fatigue stress range.
The program checks the fatigue stress range due to truck loading, lane loading and single truck loading in ASD and LFD and determines the allowable weld details.
The program checks the fatigue stress range due HL93 truck loading in LRFD and determines the allowable weld details.
For LRFD design, web fatigue requirements for flexure and shear are also checked accordance with the code.
Constructability Check
Minimum plate thickness for constructability is checked for LRFD design.
For LRFD, the program checks the constructability for flexure and shear capacity of the girders.
Serviceability Limit State Check
Serviceability Limit State control for Permanent deflection requirements of LRFD is checked.
Shear Connector Design
The program supports three kinds of shear connectors: (1) Shear Studs, (2) Channels, and (3) Others. In reality, all types of shear connectors are covered in the program.
For shear connector design, the basic information for shear connectors is required to be defined in the Details Definition dialog box.
The spacing of shear connector is designed by the program in accordance with the Fatigue Criteria of codes, and checked with the ultimate strength.
About This Manual
This manual describes features, commands and functions and how-to's about the modeling, analysis and design offered by SNAPBoxBeam. The analysis and design theory is briefly discussed in Chapter 2. The menu commands and their functions are introduced in Chapter 3. Chapter 4 provides two step-by-step examples..
- The information provided in Chapter 2 covers the basic assumptions of the program. It is also the basics for straight composite steel box girder bridge analysis and design. Users are recommended to read this chapter to refresh your concepts and understand the restrictions and conditions of the program before using the program
- Users can skip Chapter 3 if you are familiar with other Windows application software because SNAPBoxBeam is totally Windows-based system with user-friendly GUI. You can also directly play around the program to make you familiar with it.
- Users are strongly recommended to read through Chapter 4, which can make you more quickly get into the program. When you are familiar with SNAPBoxBeam, you will find the software is so easy to use.
- Engineers are not "computer operators". Users of the program should have some experience and training for steel box girder bridge design. Please remember users are recommended to verify the program output and your input carefully to make sure the design correct, practical and feasible.
Notes: SNAPBoxBeam not only provides a menu bar, which contains all the commands, but also provides a shortcut menu containing some of the frequently-used commands. You can click the right button of your mouse to initiate the shortcut menu.