In this issue's Technical Corner details regarding the use of the Wind Generator with the Bridge option. In our Discussions with.. Dr. Jae Chung talks about the "API Summary Report".

The articles 'Technical Corner' and 'Discussions with..' are open for input from all readers. If you have a topic that you think should be discussed, let us know. Did you create a great model with features that you want to share? Everyone is welcome to submit articles for possible inclusion in subsequent issues. Please contact BSI at BSI@ce.ufl.edu with your ideas.

We also introduce a number of short tutorials that are available on our website. The tutorials demonstrate the use of different features of the program including the new ones. The aim of these tutorials is to introduce the users of all levels to several features of the program. We will add new tutorials regularly to better communicate and explain the use of our program.

The newsletter is now also available in PDF format at View current newsletter (PDF).

Details regarding the use of the Wind Load Generator with the Bridge option.

The Wind Generator, which is available on the AASHTO page, provides a convenient and rapid generation of wind forces applied to the bridge superstructure and live load. These forces are displayed as vectors in the GUI and are applied to the bearing locations on the transfer beam. The values of the wind forces are best seen in the AASHTO load table, where they can also be modified. The wind forces generated are calculated based upon tributary superstructure areas and, as with self weight of superstructure, these forces are redistributed during the analysis if the superstructure is continuous. The wind forces generated can be manipulated in a number of ways including modifying the basic wind pressures from the defaulted Code values found in the Generator.

Some wind forces are not generated and must be manually added to the Wind on Structure (WS) load cases. These are wind on substructure and the upward wind force on superstructure. The wind on substructure is applied by the Engineer by applying calculated un-factored loads directly to the substructure nodes. The upward wind on superstructure should be applied as loads to the bearings. In previous versions of this program wind on substructure was also generated and applied at the bearings along with the wind on superstructure forces. Applying the wind directly to the substructure provides a more accurate solution than the previous methodology, where these forces were generated by the program and then concentrated at the bearing locations.

An often asked question: Does FB-Multipier consider non-linear behavior including P-Delta effects?

Yes, If the engineer supplies the full cross section details and material mechanical properties for pier caps, piles and columns and the program is run with the non-linear option selected both material and geometric nonlinearity is considered. In other words, what is known as P-Delta analysis is automatically computed by the software. This feature of the program may be its most powerful attribute. This also allows for the program to directly compute the demand / capacity ratio for concrete sections without any further manipulations such as moment magnification. Local buckling, as for non compact sections, is not computed by the software and the engineer must check this.

Details regarding the "Transfer Beam" which is used to connect the bridge superstructure (which is modeled using linear elastic beam elements) to the substructure via bearings.

The "Transfer Beam" is an elastic beam element that transfers superstructure loads to the bearings. Currently all loads from the superstructure are applied directly to the bearings on the transfer beam, and continuity effects due to a continuous superstructure are calculated as the analysis is conducted. The next version of this program will allow for loads to be applied directly to the superstructure.

It is imperative that neoprene bearings are modeled because their stiffness provides for the best and most realistic, distribution of forces between super and substructure. This is important for loads applied in both horizontal and vertical directions to the transfer beam. For example: in order to obtain an even distribution of Dead Load forces the vertical long term neoprene bearing stiffness should be included (use the custom bearing feature) otherwise the Dead Loads will "migrate" to the bearings that are closest to the stiffest parts of the pier cap (as a bearing located over a column). The custom bearing stiffnesses are very easy to input and typically require just 3 lines of data to describe the linear stiffness of these bearings.

A paper in the August 2000 Journal of Bridge Engineering, "Effect of Bearing Pads on Precast Prestressed Concrete Bridges" provides stiffness values for typical bridge neoprene pads. The publication "Construction and Design of Prestressed Concrete Segmental Bridges", by Jean Muller and Walter Podolny , page 245, provide an excellent reference for calculating neoprene bearing stiffness and also discusses the need to use the long term shear modulus for sustained loads.

Note in (Fig. 1) that the node on the Transfer Beam and the corresponding node on the pier cap are, so to speak, "master and slave nodes" that share the same coordinates in space but are linked by 6 springs that control the movement between super and substructure.

The stiffness of the Transfer Beam can be input by the Engineer or for preliminary design the Engineer may elect to use the stiff or soft Transfer Beam option provided by the program.

A future option we plan to develop at BSI is a preload option that would allow one to apply DL or other "built in" loads to the structure before the transfer beam is engaged. These built in loads, as is often the case with Segmental Bridges, would thus exist in addition to any other loads being applied.

There were errors found in the program's calculation of Buoyancy effects. (Only models that included buoyancy in the analysis could be affected. In non-AASHTO mode the "Buoyancy Factor" on the Load Page has a non-zero value or in AASHTO mode the box was checked "Include Buoyancy" on the AASHTO Page).

Version 4.12b corrects the errors in the program's calculation of buoyancy.

Engineers are advised to reanalyze foundations utilizing version 4.12b if uplift is a concern and if the automatic buoyancy calculation feature of the software was utilized.

Problems are encountered for the following:

    a) Situations where the pile head elevation is positive and water elevation is positive.
    b) Pile cap buoyancy was neglected if pile cap unit weight was specified as zero.
    c) Column buoyancy was neglected if column unit weight was specified as zero.
    d) In AASHTO mode the pile self weight was not calculated by the program.

This report summarizes six new soil models which have recently been incorporated into the FB-MultiPier computer program. The new soil models were developed by the Bridge Software Institute at the University of Florida according to the American Petroleum Institute Recommended Practice 2A LRFD (API RP 2A LRFD) in order to address specific needs of practicing design engineers. This report provides the basic input parameters for API Sand/Clay soil models, validation of the API soil curves, fundamental assumptions in the analysis, and case study for analysis/design of those types of soil-structure interaction models used herein. API Summary Report

FB-MultiPier is the successor to FB-Pier. In addition to all the capabilities of FB-Pier the FB-MultiPier program allows for the modeling of a whole bridge that consists of multiple piers that are connected with bridge spans. In addition to the multiple load cases and the AASHTO coefficients that are available in FB-Pier, the new program is capable of performing dynamic analysis for the whole bridge. For more information about FB-MultiPier, click here.

The FB-Deep computer program is a Windows based program used to estimate the static axial capacity of drilled shafts and driven piles. The methodology is based upon Federal Highway Administration (FHWA) reports. FB-Deep guides the user through pile and shaft materials data, shape and dimensional inputs, soil properties, and boring log info. FB-Deep presents the data analysis in both clear graphical and text form. For more information about FB-Deep, click here.

This program has been replaced by FB-MultiPier and all sales or renewals will be directed to the FB-MultiPier program. FB-Pier is still available for download by valid licensed holders.

FB-Pier was designed for the analysis of bridge pier structures composed of nonlinear pier columns and cap supported on a linear pile cap and nonlinear piles/shafts with nonlinear soil. FB-Pier couples nonlinear structural finite element analysis with nonlinear static soil models for axial, lateral and torsional soil behavior to provide a robust system of analysis for coupled bridge pier structures and foundation systems. The program performs the generation of the finite element model internally given the geometric definition of the structure and foundation system as input graphically by the designer. For more information about FB-Pier, click here.

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