Allen C. Estes

Updating Reliability of Steel Miter Gates on Locks and Dams Using Visual Inspection Results

Allen C. Estes — Wed, 13 Aug 2008 16:45:41 PDT

As both reliability analyses and systematic inspection programs for the world's infrastructure gain increased usage and prominence, it becomes more important to use the information from routine visual inspections to update lifetime reliability assessments and resulting life-cycle inspection/repair strategies. The Army Corps of Engineers currently uses reliability analyses to economically justify the major rehabilitation of navigation structures. This paper illustrates how the Condition Index visual inspections for locks and dams can be modified and used to update the reliability analysis of a steel miter gate. The miter gates on two existing locks and dams along the Mississippi River are used as examples for corrosion and fatigue deterioration. The approach used is applicable to any structure where the inspection condition states are quantitative and a model exists to relate visual inspection results to the actual deterioration state of the structure.

Load Rating versus Reliability Analysis

Allen C. Estes — Wed, 13 Aug 2008 16:45:38 PDT

The most common approach to assess the safety of a bridge is load rating. However, this approach cannot quantify the bridge safety in probabilistic terms or fully quantify the structural risk to the bridge. Reliability methods have become an increasingly popular and gradually accepted approach to assess the safety of structures. These methods account for the randomness and correlation of all relevant variables and failure modes in the analysis. This study performs both a load rating analysis and a reliability analysis on the same highway bridge, compares the results, and discusses the strengths and limitations of each approach.

Updating Bridge Reliability Based on Bridge Management Systems Visual Inspection Results

Allen C. Estes — Wed, 13 Aug 2008 16:39:52 PDT

Bridge management systems have become increasingly sophisticated over the past decade and provide valuable information about the structural condition of all bridges in the national database. At the same time, reliability methods have gained increasing prominence and are used to forecast life-cycle performance over many decades of structural life. Such reliability analyses need to be updated based on the results of inspections. Specifically targeted nondestructive evaluations are the preferred solution, but are not always available for every bridge. This paper examines how the visual inspection data provided from bridge management systems already in place can be used to update the reliability of a bridge. The limitations and necessary modifications to current practice are discussed. The superstructure of a Colorado highway bridge deteriorating due to corrosion is used as an example.

Repair Optimization of Highway Bridges Using System Reliability Approach

Allen C. Estes — Wed, 13 Aug 2008 16:39:32 PDT

As reliability based methods gain increased acceptance, there is greater opportunity to use scarce resources more efficiently while maintaining a prescribed level of reliability of a structure throughout its service life. The goal is to provide management decisions that will balance lifetime system reliability and expected life-cycle cost in an optimal manner. This study proposes a system reliability approach for optimizing the lifetime repair strategy for highway bridges. The approach is demonstrated using an existing Colorado State highway bridge. The bridge is modeled as a series-parallel combination of failure modes, and the reliability of the overall bridge system is computed using time-dependent deterioration models and live load models. Based on an established repair criterion, available repair options, repair costs, and updating, the optimum lifetime repair strategy is developed. The sensitivity of the optimum strategy to changes in various problem parameters including the prescribed service life, system failure criterion, and net discount rate is studied. Finally, the conclusions reveal that the proposed approach demonstrates real potential for practical applications, needs frequent updates through inspection, and requires considerable research effort to develop accurate input data.

Teaching Lessons Learned: Shock and Awe in the Civil Engineering Classroom

Allen C. Estes — Wed, 13 Aug 2008 16:39:17 PDT

Teaching Pedagogy 101

Ronald W. Welch — Wed, 13 Aug 2008 16:39:01 PDT

What are the basics to consider in becoming an effective teacher? So you are a new faculty member just assigned a course and a textbook. Your only teaching experience is as a TA filling in for your traveling professor while teaching directly from your personal course notes taken when you took the course. Sound familiar? Where do you go? Who do you call? How do you quickly prepare yourself to be an effective teacher? Or maybe you have a few years of teaching experience and want to improve your performance as a teacher. Where do you start in preparing the course and the individual lessons such that the students are engaged in learning, and maybe entertained as well?This paper will try to answer these questions by offering helpful hints from a team of participants who recently completed the ExCEEd Teaching workshop and applied its lessons at their home institutions. The ExcEEd (Excellence in Engineering Education) Teaching Workshop sponsored by the American Society of Civil Engineers (ASCE) provides the content and structure for presenting the pedagogical basics that every teacher should know. The workshop consists of 12 seminars covering how people learn, what constitutes good teaching, and how to prepare a good class. We will focus on the key points necessary to kick-start a teaching career or to begin to immediately improve a career. Over 300 workshop participants from over 170 CE programs have been touched by the ExCEEd (Excellence in Civil Engineering Education) Teaching Workshops 1999-2003, the ExcEEd 2004 (Excellence in Engineering Education) Teaching Workshop, and the NSF funded predecessor "Teaching Teachers To Teach Engineering" (T⁴E) Teaching Workshops 1996-1998. This does not include the Mechanical, Electrical, and Chemical faculty members who have participated in T⁴E and ExcEEd. Five years of long term assessment data will be summarized to demonstrate the effectiveness and benefit of these pedagogical basics to the participants.

Teaching Lessons Learned: Questioning: Bring Your Students Along on the Journey

Allen C. Estes — Wed, 13 Aug 2008 16:38:29 PDT

Reliability of Reinforced Concrete Girders Under Corrosion Attack

Dan M. Frangopol — Wed, 13 Aug 2008 16:38:10 PDT

Corrosion of reinforcement is a major problem affecting a large number of reinforced concrete structures. At present, most reliability-based design studies of reinforced concrete structures do not consider the effects of corrosion. In this paper, we present a reliability-based approach to the design of reinforced concrete bridge girders that are under corrosion attack. Both reserve and residual reliability constraints are satisfied. The approach is based on the American Association of State Highway and Transportation Officials (AASHTO) standard specifications for highway bridges and on data of chloride corrosion of steel in concrete. First, the effects of corrosion on both moment and shear reliabilities are investigated. Second, a reliability-based time-dependent design approach based on minimization of total material cost is proposed. This approach is demonstrated on several design examples. Finally, we suggest and illustrate a reliability-based design approach based on minimization of expected lifetime cost including corrosion effects and cost of failure consequences.

Bridge Deck Replacement for Minimum Expected Cost Under Multiple Reliability Constraints

Mark G. Stewart — Wed, 13 Aug 2008 15:32:04 PDT

The present paper investigates the effect of limit state selection (strength versus serviceability) on bridge deck life-cycle costs and thus on optimal repair strategies. Such a comparison may then help determine whether safety or functionality (or both) are important criteria when optimizing bridge life-cycle performance and costs. The structural element under consideration is a reinforced concrete bridge deck; namely, a State Highway Bridge in Colorado. Two limit states are considered: ultimate strength and serviceability. The exceedence of either of the limit states considered herein will result in deck replacement; namely, if the reliability index falls below a target reliability index or if widespread cracking and spalling occurs. The life-cycle cost analysis includes expected replacement costs as well as the random variability of material properties, loads, section dimensions, model errors, chloride penetration, and corrosion rates. Life-cycle costs can then be compared for strength and serviceability limit state violations. Life-cycle costs for deck replacement based on a serviceability limit state were generally larger than those obtained for the strength limit states. Hence, an unrealistically optimistic life-cycle cost will result when serviceability is not included in the analysis.

Life-Cycle Cost Design of Deteriorating Structure

Dan M. Frangopol — Wed, 13 Aug 2008 15:32:01 PDT

A lifetime optimization methodology for planning the inspection and repair of structures that deteriorate over time is introduced and illustrated through numerical examples. The optimization is based on minimizing the expected total life-cycle cost while maintaining an allowable lifetime reliability for the structure. This method incorporates: (a) the quality of inspection techniques with different detection capabilities; (b) all repair possibilities based on an event tree; (c) the effects of aging, deterioration, and subsequent repair on structural reliability; and (d) the time value of money. The overall cost to be minimized includes the initial cost and the costs of preventive maintenance, inspection, repair, and failure. The methodology is illustrated using the reinforced concrete T-girders from a highway bridge. An optimum inspection/repair strategy is developed for these girders that are deteriorating due to corrosion in an aggressive environment. The effect of critical parameters such as rate of corrosion, quality of the inspection technique, and the expected cost of structural failure are all investigated, along with the effects of both uniform and nonuniform inspection intervals. Ultimately, the reliability-based lifetime approach to developing an optimum inspection/repair strategy demonstrates the potential for cost savings and improved efficiency.