BSI Newsletter - Summer 2004

Welcome to the first BSI Newsletter!

The Florida Bridge Software Institute (BSI) is starting its sixth year of providing software and support to the bridge industry. BSI was started through a grant from the Florida Department of Transportation (FDOT). As part of our commitment to service and quality, we are starting this newsletter in order to improve communications to our customers.

Our flagship product, FB-Pier, continues to be improved and have increased functionality. We have a demo version of FB-MultiPier available on the web. It is expected to be released this fall (Q4). It includes new features such as modeling multiple piers connected by a bridge superstructure. This can be very helpful for modeling ship impact effects. Dynamics are available including time domain and Response Spectrum analysis.

Our newest product, FB-Deep, is a Geotechnical Design program for piles and shafts. It is a combination of the Shaft and SPT-97 programs previously distributed by the Florida Department of Transportation.

We hope you find these newsletters helpful. Please share them with others and do not hesitate to let us know about how we can improve our products to meet your needs.

Marc Hoit - Director

FB-MulitiPier is a new program under development by BSI. This new program will be an upgrade from FB-Pier v3 adding several new features and changes. The user will now be able to model multiple piers with connecting bridge spans to have a more complete picture of the overall structure. Combined with the full bridge option, dynamic analysis modes have been added that will allow the user to view structure reaction over time. The dynamic loads can simulate the effects of earthquakes or vessel impacts!

FB-MultiPier test release is currently available. All features are available but users are advised against using it for production work until the final release update as possible bugs remain.

Download the test release of FB-MultiPier today!

When we refer to linear analysis of structural systems we generally refer to systems where the principle of superposition is applicable. Linear analyses assume that the displacements of the structural systems are infinitesimally small, the material behavior is linearly elastic and the boundary conditions remain unchanged. Clearly this means that the system can not crack or allow slip of components for this to be true. The response can be obtained using the methods like Moment Distribution, Virtual Work and Method of Redundants.

However, there are situations in which the structure is subjected to large magnitude excitations (earthquakes, blast loads, etc) and the linear assumptions are not valid. It is apparent that there are many physical systems for which the linear analysis is inadequate and a nonlinear analysis is required. The execution of a nonlinear analysis is computationally more demanding since it requires many re-analyses of the structure. However, the speed of modern desktop computers makes this complexity easy to do. In recent years there is an increasing demand for nonlinear analyses. Nonlinear phenomena are manifested in different forms in physical systems. For convenience, nonlinear analyses are categorized in the following basic classifications:

Material Nonlinearity
Geometric Nonlinearity
1. Large Displacements and Small Strains Nonlinearity
2. Large Displacements and Large Strains Nonlinearity

Material Nonlinearity

In this type of analyses only the nonlinear effects of the material stress strain relation are considered. As an example, Figure 1 shows a bilinear model often used in describing the elastoplastic behavior of steel. In such cases the principle of superposition is not applicable; that is if the magnitude of the strain is doubled the resulting stress is not necessarily doubled. Stress - strain curves describing the behavior of different materials are found in published literature!

Geometric Nonlinearity

In this type of analysis the structural system undergoes large displacements. The equilibrium equations must be written with respect to the deformed geometry which is not known in advance! The displacements may include rigid body motions and deformations which depending on their magnitude may cause linear (Figure 2) or nonlinear (Figure 3) response of the material!

FB-Pier

FB-Pier performs nonlinear analysis incorporating material nonlinearity for the soil elements. In addition, FB-Pier allows the user to choose linear or nonlinear material behavior for the piles, the pier columns, as well as the pier cap. The nonlinear behavior is described through user chosen nonlinear stress-strain curves. The curves can be defaulted based on the yield or specified by user defined curves. The pile cap in FB-Pier can only have linear behavior!

FB-Pier uses a fiber model based discrete element to model the pile behavior, pier columns and the pier cap. The discrete element is implemented to include P-Delta effects (P-Δ) and material nonlinearity.

It all started thirteen years ago with what was a mere dream at that time: one computer program capable of analyzing, in 3-dimensions, the elasto-plastic behavior of a bridge substructure subject to vessel impact loading.

The bridge design codes allow concrete cracking and significant displacements to occur at extreme event loading. Studying various alternative designs while allowing for such phenomenon as plastic moment redistribution, accounting for slenderness, and nonlinear soil response was a daunting challenge. Even through the utilization of multiple computer programs, one could only arrive at an approximate solution after days and weeks of effort. For this reason conservatism was the rule, because there was always sufficient doubt as to the actual structural behavior and also because the analysis was so time consuming that one did not have time to study many alternatives.

Thanks to professors and graduate students at the University of Florida working in the areas of soil mechanics, structural analysis and applied computer programming we, design engineers now have the software with the capabilities we were looking for.

The FB-PIER computer software has been used to design every major bridge crossing a waterway in Florida and in many other States for the past 10 years! Engineers working in the highly competitive design-build arena were the very first to use FB-PIER because there simply was (and is) no substitute.

FB-PIER has come a long way in thirteen years and now allows for seismic analysis and other general bridge LRFD design loading. The software has saved tax payers millions of dollars. The dollar saving on one bridge alone has offset all the costs expended on the program to date.

The very capable and professional engineers at the University of Florida Bridge Software Institute (BSI) continue to support and develop FB-PIER to meet the specific needs of the engineer practitioner.

Released: August 15, 2004 - Continuing Development - Technical Support Available

FB-Pier is 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. FB Pier 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.

Estimated Release: Fall, 2004 - Final Testing - Beta Release Available

FB-MultiPier is a nonlinear finite element analysis program capable of analyzing multiple bridge pier structures interconnected by bridge spans. The full structure can be subjected to a full array of AASHTO load types in a static analysis or time varying load functions in a dynamic analysis. Each pier structure is composed of pier columns and a cap supported on a pile cap and piles/shafts with nonlinear soil. This analysis program 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. FB-MultiPier 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-MultiPier, click here.