fracturas, Apuntes de Ingeniería Infórmatica

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May 2006 AASHTO Bridge Subcommittee Meeting 1 Myint Lwin FHWA Office of Bridge Technology Ed Wasserman Tennessee Department of Transportation George Christian New York Department of Transportation Bill Wright FHWA Office of Research Update on Fracture Critical Bridge Member Design, Fabrication, and Inspection Issues May 2006 AASHTO Bridge Subcommittee Meeting 2 Outline • Recap of past events - Myint • Current status of… – Design initiatives – Ed – Fabrication initiatives – Bill – Inspection initiatives – George • Questions May 2006 AASHTO Bridge Subcommittee Meeting 5 Fracture Critical Workshops • Objective: Work towards developing a modern and cost- effective fracture control plan for new steel bridges and an inspection plan for existing steel bridges through integration of technologies. • Met twice: November 2004 & June 2005 May 2006 AASHTO Bridge Subcommittee Meeting 6 Workshops (continued) Design • Dennis Mertz (Lead) • Ed Wasserman • Michel Ghosn • Ray McCabe • John Kulicki • Ben Tang • Vasant Mistry • Tom Strock Materials and Fabrication • Bill Wright (Lead) • Bob Cisneros • Karl Frank • John Fisher • Krishna Verma • Alex Wilson • Stan Rolfe • Bill McEleney Inspection • Robert Connor (Lead) • Stanley Woods • William Nickas • Ralph Anderson • Robert Dexter • Tom Everett • Shay Burrows • George Christian May 2006 AASHTO Bridge Subcommittee Meeting 7 Design Group Action Plan • Use only fatigue detail categories with resistances greater C(in other words, A through Cdetails) • Design for infinite life only • For low ADTT (100 trucks per day) – – may go below C – may design for finite life • For non-redundant members – – apply the FCM Fracture-Control Plan • Schedule – AASHTO 2006/2007 May 2006 AASHTO Bridge Subcommittee Meeting 10 Fracture Control Plan Philosophy • AASHTO 1978 (Now AWS D1.5) • Controls welding & fabrication defects • Material toughness to prevent brittle fracture initiation from small fatigue cracks • Emphasis on fatigue design • No reserve capacity to resist “pop-in” fracture from unforeseen events. • New FCP • Retain a high emphasis on fabrication quality • Supplemental high toughness requirements to provide some fracture arrest capability (Reserve capacity) • Strict detailing rules for fatigue and constraint . l l i i i i l i l i i i i ll i i i i • reser e c cit t resist -i fr ct re fr f resee e e ts. t i i i i ti lit l t l i t i t t i t t ilit it t i t t ili l ti t i t May 2006 AASHTO Bridge Subcommittee Meeting 11 Stricter Controls on Design Detailing 1. Fatigue Detailing • Category C’ or higher? • Prevent distortion-induced fatigue issues 2. Avoid “high-constraint” details – Intersecting longitudinal and transverse attachments – Intersections of thick, primary plates 3. Possible controls on plate proportions and geometries when internal redundancy is needed – Limits on thickness matching tt t May 2006 AASHTO Bridge Subcommittee Meeting 12 Maintain FCM Controls for Quality Fabrication • Designers clearly designate FCM • Welding procedures to assure low H2 practice • High In-shop inspection requirements (UT preferred over RT) • Possible changes to PQR process and weld metal testing requirements. May 2006 AASHTO Bridge Subcommittee Meeting 15 Goal of new Fracture Control Plan • Provide a consistently high standard for fracture critical fabrication • Provide a higher reserve capacity to resist fractures from unforeseen conditions • Eliminate concerns for special in-service fracture critical inspection May 2006 AASHTO Bridge Subcommittee Meeting 16 Inspection Group Action Plan • Revisit definitions of “fracture critical,” redundancy and inspection types. May 2006 AASHTO Bridge Subcommittee Meeting 17 Definitions (continued) • Initial Inspection – The first inspection of a bridge as it becomes a part of the bridge file to provide all SI&A data and other relevant data and to determine baseline structural conditions. – To be completed with 90 days • Routine Inspection – Regularly scheduled inspection to ensure that the structure continues to satisfy present service requirements. This does not need to be hands-on. – Not to exceed 24 months • Hands-on Inspection – Inspection within arms length of the component. Inspection uses visual techniques that may be supplemented by nondestructive testing. – Frequencies in flowchart are maximums May 2006 AASHTO Bridge Subcommittee Meeting 20 Definitions (continued) • Fracture non-critical , or, fracture critical – low risk, or, fracture susceptible – low risk (under consideration): – A new classification for fracture critical bridges that have undergone an assessment as part of the decision process for establishing inspection intervals, and received other than a low score. May 2006 AASHTO Bridge Subcommittee Meeting 21 Inspection Group Action Plan • Revisit definitions of “fracture critical,” redundancy and inspection types. • Define a framework for a decision process, identify decision criteria, define relevant terms. May 2006 AASHTO Bridge Subcommittee Meeting 22 Proposed decision tree looks like this. Is Bridge New? Is member load path redundant? Want to perform a system analysis? Perform analysis Perform initial hands-on inspection w/i 3 mos. Want to perform an assessment? Perform hands- on inspection NTE 24 mo. Perform assessment Determine assessment score If score is medium (fair) Perform hands- on inspection NTE 48 mos. and routine NTE 24 mos. If score is low (poor) Perform hands- on inspection NTE 24 mos. If score is high (good) Perform hands- on inspection NTE 72 mos. and routine NTE 24 mos. No Yes No/ uncertain Follow inspection plan for redundant bridges (Routine inspection NTE 24 mo.) Yes No Yes No Yes Fracture Critical Inspection Interval Decision Process If score is very high (excellent) Perform routine inspection NTE 24 mo. Supplement w/ in-depth inspection at owner’s discretion Fracture Critical Fracture non-Critical Adjust assessment score and inspection plan as necessary based on most recent inspection findings Conduct hands- on inspection if none w/I past 24 mo. Conduct hands- on inspection if none w/I past 24 mo. May 2006 AASHTO Bridge Subcommittee Meeting 25 Inspection Group Action Plan • Define assessment criteria and develop a scoring system to be used as part of the decision process. • Fatigue resistant details • Vulnerability to distortion cracking • Fracture controls - fabrication • System redundancy – how long can other redundancy support the loads? • Stress cycles (fatigue life) • ADTT • Structure age • Structure condition and performance history; when would adjustment of frequency be appropriate? • Load rating • Material properties (toughness) • Frequency and degree of overloads and enforcement level •Impact (collision) vulnerability May 2006 AASHTO Bridge Subcommittee Meeting 26 Prepared a Statement of Work Significant Project Tasks • Perform a literature search of existing methodologies for assessing fatigue prone and fracture critical bridges (e.g., TX, OR, and NY). May 2006 AASHTO Bridge Subcommittee Meeting 27 Statement of Work Significant Project Tasks (continued) • Develop a rational engineering-based methodology for classifying bridges according to the results of a screening process. – Define the specific criteria – Define the relative importance of criteria – Identify a system for assigning bridges into various inspection frequency categories – Develop criteria for the baseline inspection performed to qualify a bridge for consideration under this process