Abstract

Curved composite I-girder bridges provide an excellent solution to problems of urban congestion, traffic and pollution, but their behavior is quite complex due to the coupled bending and torsion response of the bridges. Moreover, dynamic behavior of curved bridges further complicates the problem. The majority of curved bridges today are designed using complex analytical methods; therefore, a clear need exists for simplified design methods in the form of empirical equations for the structural design parameters. In this thesis paper, a sensitivity study is conducted to examine the effect of various design parameters on the free-vibration response of curved composite I-girder bridges. To determine their fundamental frequency and corresponding mode shape an extensive parametric study is conducted on 336 straight and curved bridges. From the results of the parametric study, simple-to-use equations are developed to predict the fundamental frequency of curved composite I-girder bridges. It is shown that the developed equations are equally applicable to curved simply supported and composite multi-span bridges with equal span lengths.

Highlights

  • It can be concluded that, for shorter bridges, the fundamental frequency decreases with an increase in spacing, but as the span length and curvature ratio increases, there comes a point where increasing the girder spacing results in very little change or even a slight increase in fundamental frequency

  • 2.) The girder spacing and the number of girders have a less pronounced effect on the fundamental frequency but in general the fundamental frequency decreases with an increase in spacing and number of girders

  • ; with an increase in span and curvature ratio a point is reached where an increase in number of girders results in an increase in fundamental frequency

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Summary

General

In the past, curved alignments in bridges were achieved using straight chord segments supported on a large number of piers. Open-sections of the !-girder offer very little torsional resistance thereby making cross-braces a primary design component which further complicates the overall design process for the engineer. This puts pressure on researchers to study the behaviour of these bridges in order to simplify the process. Erection of curved I-girder bridges is of great importance as the girders have a tendency to roll-over when lifted leading to combined bending and torsional stresses. To determine the stresses in the girder due to each lifting scheme a small finite elements study was conducted (Penrose and Davidson.).

The Problem
Objectives
Review of Linear Elastic Behaviour
Method of Analysis
Plane-Grid Method (Grillage)
Space-Frame Method
Finite-Element Method
Finite-Strip Method
Solutions to Differential Equations
Fundamentals of Dynamic Analysis
Single-degree-of-freedom systems (SDOF)
Overview of North American Bridge Design Codes
Canadian Highway Bridge Design
AASHTO Guide Specifications
AASHTO-LRFD Bridge Design Specifications
Historical Overview of Curved Bridge Design
Free-Vibration Studies
Forced-Vibration Studies
Parametric Studies
General Background
Finite Element Approach
Finite-Element Modeling of Curved Composite 1-Girder Bridges
Finite-Element Models - Calibration
Geometric and Material Modeling Using ABAQUS
CHAPTER IV SENSITIVITY STUDY
Effect of Boundary Conditions
Effect of Number of Cross-Braces
Effect of Span Length
Effect of Radius of Curvature
Effect of Girder Spacing
Effect of Number of Girders
Effect of Depth of Girders
Effect of Flange Thickness
Effect of Cross-Brace Stiffness
4.10 Effect of End Plate Diaphragms
4.11 Effect of Horizontal Bracing Systems
Outline of the Parametric Study
General Design Parameters
Key Parameters
Research Assumptions
Proposed Fundamental Frequency Equation For Simple Span Bridges
Proposed Fundamental Frequency Equation For Continuous Two-Span Bridges
Modification Factor for Span-to-Depth Ratio
Validity of the CHBDC L2/BR Curved Bridge Limit
Summary
Conclusions
Recommendations for Future Research
Method
Cir<le1· Spndng (1n)
Curved Bridge (L25S25N4R5)
Findings
Curved Two-Span Bridge (C2L25S25N3R5)

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