Research

In-service Performance Evaluation of Hybrid Composite Beam (HCB) Bridge System

HCB PerformanceA relatively new technology, Hybrid Composite Beams (HCB), are being deployed in bridges throughout North America as an alternative to traditional materials. A HCB is comprised of a glass-fiber reinforced polymer (FRP) box shell containing a tied parabolic concrete arch. In a girder-type bridge superstructure, these beams can support a conventional reinforced concrete deck, while the inclined stirrups provide shear integrity and enforce composite action between the HCBs and the concrete deck. The HCB system offers an efficient use of materials, ease of construction, and resistance to corrosion, making the system ideal for sustainable bridge design. This research study focuses on evaluating the in-service performance of a new HCB bridge in Virginia. In the corresponding evaluation program, the bridge was tested under live-load conditions and monitored using a suite of sensors. Results from the experimental program were used to better understand the bridge behavior including how the loads are transmitted, both at the system and element levels. Moreover, the test results provided validity to the rational design approach employed for this system, but also highlighted some of the key non-composite system behavior that warrant further consideration in future design. In addition to the testing program, a detailed finite element model was generated to support the experimental data and provide additional insight into the system behavior characteristics.

 

Bond Characteristics of UHPC with Implications for Bridge Deck Rehabilitation

UHPC BondOver the past decade there has been a significant increase in the number of concrete transportation structures reaching the end of their service lives, typically as a result of age and severe degradation. This deterioration is often the result of exposure to aggressive environments and substantial increases in vehicle loading. Rehabilitation is typically the most appropriate solution for these structures because of the high cost of full replacement, resulting in the need for cost-effective and suitable solutions for rehabilitation. Ultra-high performance concrete (UHPC), one of the more recent advances in construction materials, appears to be a promising material for the repair of concrete structures. The potential benefit of UHPC is primarily derived from its negligible permeability, which prevents water or chemical penetration, and its high mechanical properties, which serve to increase the bearing capacity of the structure. Some of the primary challenges associated with the use of UHPC as a repair material are uncertainty in the bond performance and interaction with the existing substrate material. This study focuses on the characterization of the interface bond and compatibility between UHPC and normal concrete. The testing program was conducted in the spirit of ASTM because no standard test  methods currently exist for UHPC. In addition, a series of numerical models were developed to support the results obtained in the experimental investigations. The results highlight the exceptional performance of the bond, but they also demonstrate a number of challenges with respect to characterizing the bond. Specific challenges included characterization of surface roughness, premature specimen failure, material strength mismatch, and the quality and consistency of the testing methods used.

 

Operational Safety of In-Service Stringer Bridges with Corroded Girders

Amir GheitasiIn composite stringer bridges, degradation often manifests as corrosion, section loss, and fatigue cracking in steel girders. Steel corrosion is an electro-chemical reaction which results in deterioration and eventual destruction of the metallic material. The rate and progress of the corrosion are affected by several factors including type of steel, surface protection, state of stress, and the environmental conditions (i.e. presence of chemicals, temperature, humidity, and airborne pollution). Corrosion in steel bridge superstructures is classified in many forms such as uniform corrosion, crevice corrosion, and deposit attack. However, it is well recognized in transportation community that girder corrosion is most likely to occur at end span locations due to chemicals such as deiceners and water leaking from the deck joints or from salt spray caused by passing vehicles. These deteriorating conditions may significantly reduce the load-carrying capacity of the degraded member and eventually the bridge system, due to localized failure mechanisms such as local buckling, web crippling or crushing of the end stiffeners. The main objective of this study was to characterize the influence of corrosion in steel girders on the system safety, redundancy, and performance of in-service bridge superstructures. Using non-linear finite element analysis, a sensitivity study was performed on representative in-service bridges to assess their performance and functionality under a variety of damage scenarios.

 

Effect of Deck Delamination on the Performance of In-Service Bridges

Reinforced concrete decks suffer from a variety of deteriorating conditions associated with cracking due to the low tensile resistance of the concrete material. These cracks would provide direct pathway for chloride and moisture penetration and allow for accelerated exposure, which eventually leads to corrosion in the reinforcement. Once initiated, the corrosion by-products can occupy up to 10 times the volume that it replaces, and create internal pressures resulting in longitudinal surface cracks, delaminations, and spalls. Delamination usually occurs as a result of separation in the concrete layers parallel and close to the surface at or near the outermost layer of rebars. Separation of the concrete layers occurs when corrosion induced cracks join together to form a fracture plane. With a random and irregular pattern, delamination is historically considered one of the most complicated issues associated with in-service concrete structures. This study aimed to provide a fundamental understanding on the impact of subsurface deck delamination on the system behavior including both the ultimate load-carrying capacity and serviceability of composite steel girder bridge superstructures. Using this numerical analysis framework, an efficient and practical modeling approach is presented in this study, which is expected to help the preservation community evaluate the condition of in-service structures with deteriorated deck systems.

 

Performance-Based Evaluation Framework for Bridge Preservation 

Amir GheitasiThe safety and condition of transportation infrastructure has been at the forefront of national debates in recent times due to catastrophic bridge failures, but the issue has been a longstanding challenge for transportation agencies for many years as resources continue to diminish. The performance of this infrastructure has a direct influence on the lives of most of citizens in developed regions by providing a critical lifeline between communities and the transportation of goods and services, and as a critical component of the transportation network, bridges have received a lot of attention regarding condition assessment and maintenance practices. Despite successful implementation of advanced evaluation techniques, what is still lacking is a fundamental understanding of the system behavior in the presence of deteriorating conditions that can be used for preservation decision-making. This study aims to present a performance-based framework that can be used to characterize the behavior of in-service bridge superstructures. In order to measure the bridge system performance with deteriorating conditions, system-level behavior of a representative composite steel girder bridge, degraded with different ideal damage scenarios, was investigated in this study. It is expected that the proposed framework for evaluating system behavior will provide a first step for establishing a critical linkage between design, maintenance, and rehabilitation of highway bridges, which are uncoupled in current infrastructure decision-making processes.

 

Performance and Rating of In-Service Bridges Subjected to Overloads

Amir GheitasiWith the ever-increasing demands for transporting goods and services, transportation officials are facing a growing challenge with the safety of in-service bridges under the passage of over-sized and/or over-weight vehicles. Current load rating practices provide the basis for evaluating the operational safety of the in-service structures using engineering judgments and simplifying assumptions. However, a true measure of the system performance under the impact of irregular loading scenarios requires knowledge of different aspects of the system-level characteristics including the lateral load distribution behavior. In this study, non-linear FE analysis has been implemented to evaluate the evolution of load distributing mechanism in two representative in-service structures in the state of Michigan subjected to overloads. In addition, rating factors were defined for the selected structures based on the LRFR methodology, to assess the safety of the selected in-service structures under the effect of irregular loading conditions. This investigation highlighted the importance of implementing a refined method of analysis which can help bridge engineers to support their permit and posting decisions.

 

Failure Characteristics of Composite Stringer Bridges

Amir GheitasiThe main focus of this study was to present an analytical approach for capturing the full system-level response and behavioral characteristics of the composite bridge superstructures as they approach ultimate capacity. This study is instrumental to the understanding of how redundant bridges behave in the presence of coupled and uncoupled damage and deteriorations. The investigation includes a comprehensive nonlinear finite element analysis of two representative intact composite steel girder bridges that were tested to failure and provided sufficient details for model validation. Novel to this investigation is the classification of system response into different behavioral stages and the development of a generic failure criterion to predict the overall system capacity of the composite steel girder bridges irrespective of local failure effects. The proposed generic failure criterion not only provides a mechanism to describe system-based structural capacity, but also a rational foundation for understanding the impact of damage and deteriorating conditions on the system-based behavior.  In addition, a limited sensitivity study was performed on one of the selected representative bridges to investigate the sensitivity of the characterized failure stages to variations in the geometrical parameters and material properties of the bridge system.

 

A Stiffened Plate Model to Represent Lateral Distribution Behavior in Girder-Type Bridges

Amir GheitasiThis study sought to provide a basic methodology that can be applied to characterize lateral load distribution behavior using a classical plate approach. Presented in this study was a method applicable to slab-girder bridges, which simulates the deck system as a plate element stiffened by longitudinal and transverse members representative of the girders, diaphragms, and bracing, to characterize lateral load distribution behavior of a beam-type bridge. In addition, finite element simulations along with field investigation of three different bridges were implemented to examine the accuracy and validity of the proposed methodology. The proposed approach represents a departure from the norm, where traditionally the bridge system is simplified down to a single beam element; with this approach, the bridge is simplified into a plate system with stiffened regions representing the superstructure elements and lateral bracing. A primary advantage of this approach is that the lateral load distribution behavior of the bridge system is described with a mechanical-based formulation that accounts for the complex two-way behavior of the system and can be solved with relatively basic mathematical software or even a spreadsheet. Moreover, this approach allows for the evaluation of bridge systems outside of the current limits of applicability, such as new composite systems or non-conventional designs, without significant deviations from current practice.

 

Evaluation of Properties of Composite Steel Tubular Pilings

Amir GheitasiBridge foundations have significant contributions to serviceability and efficiency of in-service transportation networks. Their failure may lead to catastrophic failure of the entire structure, which in turn results in system failure, loss of life and detours. Closed-end, round, cast-in-place (CIP) tubular friction piles are deep foundations commonly used in bridge and retaining wall structures when competent bearing soil is not present near the ground surface. In steel tubular piles, the outer steel shell serves as formwork for the concrete core and also as both the longitudinal and spiral reinforcement. The presence of the concrete core also fills the space in the steel tube, enhancing the buckling capacity of the steel shell. In essence, these piles can take advantage of both component strengths and behave as a single unit, when designed correctly. Despite successful implementation, a challenge that often exists with these systems is the uncertainty surrounding in-service capacity as well as condition, which is difficult to determine from the surface. The main purpose of this investigation was to evaluate the behavior of this piling system, with a concentration on the compressive strength and composite behavior between concrete core and steel shell. In this regard, a series of experimental studies including: composite and non-composite compression loading, core samples, push-through, and flexural testing together with a compatible finite element analysis have been conducted on a series of field-cast piles with different geometrical properties. 

 

Shear Buckling Characteristics of Moderately Thick and Stocky Metal Panels

Plastic bucklingShear panels are widely used engineering structural members. Bridge and building plate girders, box girders, frame bracing systems, liquid and gas containment structures, shelters, offshore structures, ship structures, slabs, hot-rolled W-shape steel sections, steel plate shear wall buildings and many other naval and aeronautical structures are examples of engineering elements that according to their applications use various thickness plates. Shear buckling behavior of plates, which is an important characteristic in the design of plated structures, depends on boundary conditions, material characteristics, aspect ratio and slenderness parameter. In this study, buckling behavior of slender and compact carbon steel, stainless steel and aluminum plates under the action of in-plane shear was investigated via both numerical simulations and analytical methods. Unstiffened shear plates with respect to their slenderness parameter and buckling behavior were qualitatively and quantitatively divided into slender, moderate and stocky categories. Accordingly, slender plates have a low buckling capacity, followed by a large postbuckling reserve. Their ultimate load coincides with the formation of inclined yield bands. Stocky plates yield before buckling. They have some post-yield capacity, buckle plastically and their ultimate and critical loads are equivalent. Moderate plates have concurrent material yielding and geometrical buckling followed by a sudden loss of stiffness. They neither have post-yield nor postbuckling reserves. Results from this investigation also highlighted the facts that changes in the modulus of elasticity and shear modulus should be considered in the analysis and that the secondary bending stresses induced by initial out-of-plane curvature can cause significant reduction in the post-yield capacity and ultimate resistance of stocky plates.