Amir Gheitasi

Overload Flexural Distribution Behavior of Composite Steel Girder Bridges

AbstractUsing equations proposed by the AASHTO LRFD specifications, live-load distribution factors in bridge superstructures were calculated based on the linear-elastic behavior of the system. In this study, the applicability of these equations in predicting girder distribution behavior in the presence of high material nonlinearity and oversized loading scenarios was investigated. Two representative composite steel girder bridge superstructures, which are in service in the state of Michigan and had been previously subjected to a live-load testing program, were selected for this study. Sixteen cases were analyzed to study the effect of boundary conditions, loading position, and load configuration on the girder distribution behavior of the selected bridges as they approach their ultimate capacities. Comparing the results obtained from nonlinear finite-element analysis with those proposed by the AASHTO LRFD specifications demonstrated that the code-specified values for the distribution factors are overly con...

Failure Characteristics and Ultimate Load-Carrying Capacity of Redundant Composite Steel Girder Bridges: Case Study

AbstractWith the existence of aging highway bridges within the U.S. transportation network, federal and local agencies typically encounter a wide assortment of maintenance issues ranging from cracking, spalls, delaminations, and corrosion to high load hits and fire damage. This paper presents an approach for capturing the full system-based behavior and stages of failure in the composite bridge superstructures as they approach ultimate capacity. This step is instrumental to understanding how redundant bridges behave in the presence of coupled and uncoupled damage and deteriorations. The investigation included 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. Results demonstrate the high degree of additional reserve capacity, inherent to redundant superstructures, over the theoretical nominal design capacity. A rational approach was established to describe the actual ...

Effect of Deck Deterioration on Overall System Behavior, Resilience and Remaining Life of Composite Steel Girder Bridges

During the past few decades, several studies have been conducted to characterize the performance of in-service, girder-type bridge superstructures under operating conditions. Few of these efforts have focused on evaluating the actual response of the bridge systems, especially beyond the elastic limit of their behavior, and correlating the impact of damage to the overall system behavior. In practice, most of the in-service bridge superstructures behave elastically under the routine daily traffic. However, existing damage and deteriorating conditions would significantly influence different aspects of the structural performance, including reserve capacity, resilience and remaining service-life. The main purpose of this study is to evaluate the response of composite steel girder bridges under the effect of subsurface delamination in the reinforced concrete deck. Commercial finite element computer software, ANSYS, was implemented to perform a nonlinear analysis on a representative single-span, simply-supported bridge superstructure. The system failure characteristics were captured in the numerical models by incorporating different sources of material non-linearities, including cracking/crushing in the concrete and plasticity in steel components. Upon validation, non-linear behavior of the system, with both intact and degraded configurations, was used to evaluate the impact of integrated damage mechanism on the overall system performance. Reserve capacity of this bridge superstructure was also determined with respect to the nominal element-level design capacity. As vision to the future path, this framework can be implemented to evaluate the performance of other in-service bridges degraded under the effect of different damage scenarios, thus providing a mechanism to determine a measure of capacity, resilience and remaining service-life.

The Challenges Related to Interface Bond Characterization of Ultra-High-Performance Concrete With Implications for Bridge Rehabilitation Practices

Over 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 paper 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.

Redundancy and Operational Safety of Composite Stringer Bridges with Deteriorated Girders

AbstractAs a critical component of the national transportation network, bridges have received a lot of attention regarding their safety and condition state. Bridge superstructures begin to degrade after they are placed in service; to combat this issue, owners have begun to utilize a variety of technologies to monitor the behavior and detect different sources of damage in these structures and generate higher fidelity condition metrics. However, an appropriate maintenance decision-making process requires knowledge of the influence of detected damage and deterioration mechanisms on the overall system behavior. This paper presents a performance measurement and evaluation framework that can be used to characterize the impact of deteriorating conditions on the performance of in-service bridge superstructures. The framework was established based on a numerical modeling approach and was validated through a sensitivity analysis of two representative in-service composite steel girder bridges under the impact of cor...

Performance and Behavior of Hybrid Composite Beam Bridge in Virginia: Live Load Testing

AbstractThe hybrid composite beam (HCB) system is an innovative structural technology that has been recently used in bridge construction within the U.S. transportation network. This investigation focused on evaluating the in-service performance of a newly constructed HCB bridge superstructure located on Route 205 in Colonial Beach, Virginia. In the live-load-testing program, the bridge superstructure was instrumented with a series of internal and external strain gauges to evaluate the structural response. The test was conducted using tandem axle dump trucks under both quasi-static and dynamic conditions, and results obtained from the experimental investigation were used to determine three key behavior characteristics: lateral load distribution, internal load-sharing behavior, and dynamic load allowance (DLA). With respect to the live load performance, the HCB system relatively conformed to the provisions of the AASHTO specifications for beam-type bridges but did exhibit some characteristics of a flexible ...

Vibration Serviceability Assessment of an In-Service Pedestrian Bridge Under Human-Induced Excitations

Pedestrian bridges may experience significant vibrations under pedestrian traffic and wind loads. Design codes address the vibration limit state levels either by ensuring the frequency ranges associated with typical pedestrian passages are outside the lower fundamental frequencies of the structure or by restricting the maximum accelerations below the limits for pedestrian comfort. This paper discusses vibration serviceability assessment of a highly trafficked local pedestrian bridge based on the field dynamic tests. The selected bridge is a 60-m-long three-span steel structure with a continuous reinforced concrete slab supported on two longitudinal steel girders. First, a finite element model of the pedestrian bridge is developed to obtain the natural frequencies and mode shapes. Then, ambient vibration tests are conducted to validate the modal characteristics of the pedestrian bridge. Next, the dynamic response of the bridge in terms of peak accelerations is determined both experimentally and analytically under various pedestrian excitations. Finally, the implications of the results for the serviceability limit state assessment of the pedestrian bridge are discussed.

Implications of Overload Distribution Behavior on Load Rating Practices in Steel Stringer Bridges

With 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 oversized and overweight vehicles. Current load rating practices provide the basis for evaluating the operational safety of in-service structures by 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, nonlinear finite element analysis has been implemented to evaluate the evolution of load-distributing mechanisms in two representative in-service structures subjected to overloads in the state of Michigan. In addition, rating factors were defined for the selected structures on the basis of the load and resistance factor rating methodology. Results from this study demonstrated that current design and rating practices were overly conservative in predicting the actual distribution behavior and assessing the safety of the in-service structures under the effect of irregular loading conditions. This investigation also highlighted the importance and benefits of implementing a refined method of analysis that can help bridge engineers to support their permit and posting decisions.

Integration of Element Inspection Data in Model Updating and Performance Evaluation of In-Service Bridge Superstructures

With the volume of aging bridges approaching the end of their service lives nationwide, maintenance of these deteriorated structures is a growing challenge for transportation agencies. To manage this infrastructure, inspectors are tasked with providing an average rating based on element-level condition measurements. According to the National Bridge Inspection Standards (NBIS), many of the proposed inspection methods are visual and as a result, the evaluated condition states are generally qualitative and in most cases based on engineering judgments. To combat this issue, agencies have begun to utilize a variety of technologies to monitor the behavior and detect different sources of damage in the bridges and generate higher fidelity condition metrics. These condition metrics are used in the load rating process, which mainly focuses on the behavior of degraded elements to assess the remaining capacity of the bridge system. However in these practices, less attention is attributed to the overall system-level response under the reported condition states. An appropriate understanding of in-service performance requires knowledge of characterizing the influence of damage and deterioration on the overall system behavior. Today’s computational capabilities provide a tool to assess these characteristics using numerical and theoretical models representing the bridge structural system. Moreover, recent advances in monitoring and inspection techniques provide a mechanism to efficiently capture the damage data necessary for model updating. Using nonlinear finite element (FE) analysis, this paper presents a case study on evaluating the behavior of representative in-service bridges in the Commonwealth of Virginia, under the effect of deteriorating conditions. The geometrical characteristics of the selected structures represent common features of steel-concrete composite bridges serving within the state. The range of the corresponding damage characteristics was also selected through a questionnaire which collected inspection data from the Virginia Department of Transportation (VDOT) engineers in nine different districts across the state.

Influence of Internal Deterioration Mechanisms on the System Level Behavior of Composite Prestressed Concrete Girder Bridges

The ASCE’s 2013 Report Card for America’s Infrastructure assigned in-service bridges a score of C+. This rating reflects the extent of the deteriorating conditions and deficiency of the national aging infrastructure network. Currently, transportation agencies depend heavily on experiential-based practices to make decisions regarding maintenance and preservation. While practitioners and decision-makers already invest ample efforts towards this cause, the lack of a rational understanding of system-level behavior of in-service structures makes resolving the problem even more complicated. This constraint, coupled with limited resources and the vast network of existing structures in service, highlights the need to develop strategies to better understand the operational safety and remaining life of these structures. In pursuit of this objective, this study focuses on understanding the performance of deteriorated prestressed concrete bridges. A performance-based assessment framework was developed, which allows for the integration of the various sources of damage within the primary load carrying members. This framework is then used to quantify the implications of these mechanisms on the serviceability, capacity, and remaining service life of the structure. The investigation, conducted using a numerical analysis platform, is expected to help support the maintenance decision through rational and risk-based techniques, which will ultimately integrate condition-based system behavior.