· LRFD or LFD specifications
· AASHTO or State (CA, PA,…) Default Settings
· US or SI units
Superstructure Support Conditions
· Integral Bent
· Simply Supported
· Simple Dead Load, Continuous Live Load
· Wall Piers
· Hammerhead Piers
· Single Column Bents
· Multi Column Bents
· Multi Column Bents on part height Pier Walls
· Non-prismatic, stepped, and mid-height offsets
· And More
· Spread Footings
· Pile Footings
· Columns on Drilled Shafts
· Combined Footings
· Cap / Column / Footing
· Cap and Footing shear stirrups
· Copy reinforcement patterns to other columns or
footings in pier
Modeling and Analysis
· Moment magnification
· Finite element model generation and solution
· Fix or pin columns at bottom or top
· Unlimited structure size and loads
· Exhaustive search for critical load conditions and
· Footing stability checks
· Intuitive user interface – no need for a wizard
· LRFD limit states / LFD load groups
· Modifiable load factors
· Comprehensive program generated load cases /
· Default and user defined load combinations
· Advanced live load algorithm to determine critical
· Longitudinal live load force generator for simply
· Default Design Vehicles (HL93, HS20, etc.)
· Default Permit Vehicles (CA & PA)
· Default Fatigue Vehicle
· User defined live load vehicles
· User can limit number of loaded lanes
· Vehicle loads represented by uniform distribution or
· Service checks (crack control, fatigue)
· Pile and spread footing checks
· Prismatic or tapered
· Rectangular, T-Beam, or Flanged
· Dead Load (superstructure, substructure)
· Additional Dead Load (wearing surface, utilities)
· Vehicular Live Load (design, permit, fatigue)
· Water and Ice
· Wind (on structure, on live load, overturning)
· Prestress (from superstructure post tensioning)
· Earth Vertical
· Differential Settlement
· User Loads (on cap, column, footing, bearings) can
be point, distributed, or moments
· Tabular results (user selected)
· Standard and detailed reports
· Easy to navigate Table of Contents
· User controlled output locations
· Modify face-of-support locations
· Windows XP, 2000, ME, 98, NT 4.0
· PC with Pentium Processor
· 256 MB RAM
· 30 MB free space on hard drive
Program Description Summary
VBent's advantages and capabilities.
Key Program Algorithms A sample of VBent’s key algorithms.
Summary of Program Features A bullet list of specific VBent features.
Pier analysis is a complex, rigorous process. Designers often simplify the process by making general assumptions and taking shortcuts. VBent removes these shortcuts and the resulting uncertainties in pier/bent design by internally handling the computational complexities, while at the same time providing the user a simple tool to use.
The new AASHTO LRFD specifications add even more complexities by requiring load combinations to consider maximum and minimum load factors and eta factors; separating the live load into design truck (with impact) and lane load (without impact) components; and introducing modified compression field theory to shear analysis, among other changes.
These are in addition to complex pier issues such as determining transverse live load placement in multiple column piers, load combination routines certain to maximize response, moment magnification (slenderness) effects on columns, footing stability checks, and calculation of spread footing capacity from soil parameters.
Integral/monolithic bents (where the bent is monolithic with the superstructure) further complicate the pier design due to the longitudinal moment interaction at the top of the bent. In order to accurately distribute forces throughout the pier, this interaction must be accounted for during the structural (finite element model) solution. Our developers have been designing integral bent bridges for over 18 years and understand the complexities which must be addressed to accurately model and design this bent type.
VBent performs all these functions for the designer in one analysis. All the components (cap, column, & footing) in a pier/bent are analyzed in one computer run: there is no need to break the pier/bent into individual components for analysis with separate computer programs. This saves the designer time and eliminates potential errors due to data transfer between computer programs. VBent also allows the user to analyze any desired point along the cap or column.
In VBent, defining the pier geometry, reinforcement, and loading, is a very straight-forward, easy to follow process. Unlike other programs in which a user can get lost moving from tab to tab, all tool bar buttons required to define the pier and view results can be seen and accessed immediately upon opening the program, as shown below.
The VBent environment upon opening the program. All tool
bars for describing the input,
navigating the output, and manipulating the model are immediately available.
Defining a new pier is easily accomplished by moving from
left to right along the description tool bars. Tabs are not used to
separate input, output, model, and component dialogs in
However, multiple windows can be open within the program for the model view,
output reports, and graphic displays. Additional examples of
dialogs are available on our
Sample Screens page.
A sample of features and algorithms within VBent that assist the bridge engineer with simplifying the design process include:
· AASHTO Specifications – Either AASHTO Load Resistance Factor Design (LRFD) or the Standard Specifications for Highway Bridges (LFD) can be selected for analysis. In addition, since many states customize their approach to pier design, a Locality setting has been built into the program. This allows users to customize program behavior to match local practice. For example, spread footings set on soil foundations can be analyzed by checking average bearing pressures or peak bearing pressures. The Locality option (i.e., choosing US, CA, or PA) provides the user an option to easily set all VBent behavior to match local practice.
· Pier Model Generation – In VBent the user describes the pier using bridge terminology. A graphic window exists within each geometric component dialog to provide real time feedback of the data being entered in three dimensions; there is no need for a graphic “generate” or “update” button. This process quickly and accurately guides the user through the model generation.
When load types are defined or requested, these are automatically placed on the pier. For example, if wind load is to be applied, VBent will determine the load magnitude, direction and location utilizing the AASHTO LRFD or LFD specifications. However, in order to maintain full control of the model, the user has the option of overriding the AASHTO default specifications.
· Create and Solve Finite Element Model (FEM) – After the model has been described, VBent automatically generates the FEM. The user never needs to see (unless you want to) or manipulate the creation of nodes, elements, loads, or the FEM results.
· Integral (Monolithic) Bents –The longitudinal moment connection between the superstructure and substructure complicates the analysis of integral bent bridges, such as the California box girder bridge. No longer can the substructure be completely isolated from the superstructure. For example, longitudinal braking forces will not be resisted by the bent alone; the moment connection at the top of the bent will cause the entire bridge frame to resist the load. VBent is the first and only program to address and analyze this unique bent type for both AASHTO LRFD and LFD specifications.
· Live Load – Maximizing transverse live load response is a critical step in pier analysis. For single column piers, transverse live load calculations could be performed by hand calculations (although it can be time consuming), but multiple column piers can be a computational challenge. VBent performs an exhaustive search for the controlling live load condition (vehicle location and number). Design, fatigue and permit (permit trucks with and without design trucks concurrently applied) vehicles are analyzed. VBent has extensive vehicle libraries as well as the ability for the user to define vehicles. As part of the live load analysis during load combinations, the appropriate number of vehicles and force direction for centrifugal and braking forces are combined with the forces induced from vertical live load.
· Load Combinations – To ensure critical load conditions are found for the cap, column, and footing components, VBent employs an extensive load combination routine. First, VBent internally determines which Group Load or Limit State combinations need to be investigated based on load types applied to the pier, such as wind, temperature and stream flow. The user does not need to build the load combinations because VBent does so automatically. (Note: The user can remove load combinations, if desired.) Second, multiple load cases within each combination are automatically investigated. In the column, for example, the combination that produces maximum and minimum moments along each principal axis is determined. This is taken one step further by also checking that the concurrent forces have also been maximized. This ultimately results in seven load cases for the cap and 28 for the columns and footings, within each load combination.
· Moment Magnification – Approximation methods outlined in both the LFD and LRFD specifications are used by most programs to determine moment magnification (slenderness) effects in column members. These methods assume the column is prismatic and the column axial load is constant over its entire length. VBent improves on the moment magnification method in two manners. First, for non-prismatic columns, an equivalent column stiffness is computed that accurately reflects the variable column stiffness for use in the Euler buckling equation. Second, the user can control the axial load, which is especially useful for tall columns in which the self weight is a significant portion of the total axial load.
· Output Reports – VBent output is very flexible and extremely easy to navigate. Upon analysis, VBent automatically opens a standard set of reports summarizing input data and specification results for all components in the pier. Then, at the user’s option, detailed reports can be requested for nearly every computational result, along with intermediate values computed by VBent. This provides an exceptional insight into the computations performed by VBent. For example, live load influence lines, unfactored load results, and individual loads that make up each of the load cases and load combinations described above, can be requested. Output navigation is made simple by finding the desired output report in the Table of Contents and clicking on the report name.
· Execution Time – All the above computations, and more, are performed in an extremely efficient and fast manner. A typical single column pier takes less than 5 seconds to analyze with a P5 3.0 GHz processor. A three column pier takes approximately 10 seconds to analyze.