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STRUCTURE ASSESSMENT

STRUCTURE ASSESSMENT. INTRODUCTION. RELIABILITY STRUCTURE

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STRUCTURE ASSESSMENT

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  1. STRUCTURE ASSESSMENT

  2. INTRODUCTION RELIABILITY STRUCTURE The probabilistic measure of assurance of performance with respect to some prescribed conditions. A condition can refer to an ultimate limit state (such as collapse) or serviceability limit state (such as excessive deflection and/or vibration)

  3. INTRODUCTION STRUCTURE ASSESSMENT • purpose of assessment is to know the condition and ability of the structure • the results of assessment may be used to determine necessary action to be taken, (prioritize inspection, inspection methods, repair or retrovit) • assessment involving code driven inspection, experience and field survey

  4. PHILOSOPHY OF RISK BASED INSPECTION IN STRUCTURE ASSESSMENT • Risk is a function of both probability of failure and consequences of failure. • Risk based strategies use the concept of risk to focus inspection and maintenance resources to the parts of the plant where they have the greatest benefit in reducing risk. • Risk based strategies only work when a feedback process is used on a regular basis to keep the risk assessment and strategy up to date.

  5. RISK MATRIXRisk = Probability of Failure X Consequences of Failure

  6. PURPOSES OF STRUCTURE ASSESSMENT • Inventory the structure facilities and equipment condition • Overall reduction in risk for the facilities and equipment assessed • Acceptance/understanding of the current risk • Predictive maintenance

  7. ASSESSMENT METHOD • COLLECTING DATA • QUALITATIVE ASSESSMENT (VISUAL INSPECTION + NDE IF NECESSARY) • PROBABILITY AND CONSEQUENCES OF STRUCTURE FAILURE • STRUCTURE RISK (CRITICALLITY RANKING) • QUANTITATIVE ASSESSMENT (NDT/NDE PERFORMANCE) • STRUCTURE ANALYSIS/ENGINEERING ANALYSIS • RECOMMENDATION

  8. ASSESSMENT METHOD • Structure classification • Primary • Secondary • Tertiary • Visual inspection (qualitative) • Member condition • Deformation • Connection member • Environment and safety hazards • NDT inspection (quantitative) • MT/PT • UT (thickness and or scanning) • Eddy current • Load test (if applicable)

  9. ASSESSMENT METHOD • Define Probability of Failure • Service condition • Environment • Construction quality record • Define Consequences of Failure • Standby • Finance • Location • Structure analysis (applicable code) • Actual load • Deflection limit and Stress analysis

  10. REFERENCE • STANDARD CODE ACI (AMERICAN CONCRETE INSTITUTE) • ACI 318 • ACI 117 AISC (AMERICAN INSTITUTE of STELL CONSTRUCTION) • ASD (ALLOWABLE STRESS DESIGN) • LRFD (LOAD RESISTANCE FACTOR DESIGN) • CLIENT SPESIFICATION ENGINEERING & CONSTRUCTION DATA

  11. PERSONNEL & EQUIPMENT Personnel in Each Plant • Structure Engineer (1 person) • Structure Inspector (2 person) • NDT/NDE Inspector (2 person) • Helper (3 person) Inspection Equipment • Welding Gage • Measurement Gage (caliper, roll meter, etc) • Binocular and inspection mirror • Scraper, hammer & wire brush • UT – Thickness • Safety Equipment • Camera with high resolution (optional)

  12. Steel Member Structural deficiencies affecting steel member : • Corrosion - Minor/Light A surface corrosion with no apparent loss of section - Moderate Corrosion that is loose and flaking with some pitting. The scale or exfoliation can be removed with some effort by use of a scrapper or chipping hammer. The element exhibits measurable but not significant loss of section - Severe Heavy, stratified corrosion or corrosion scales with extensive pitting. Removal requires exerted effort and may require mechanical means. Significant loss of section

  13. Steel Member • Impacted Corrosion Corrosion collected between two interfacing surfaces, usually two steel plates. Impacted corrosion can be minor, moderate, or severe as described above. Impacted corrosion can severely deform the steel member due to expansive nature of the corrosion product. • Pitting Formation of cavities due to corrosion

  14. CONCRETE MEMBER Structural deficiencies affecting steel member : • Cracking (overstress, corrosion & general) A separation into two or more parts as identified by the space between fracture surfaces in the concrete - Hairline - crack width less than 1/32 in - Fine – crack width between 1/32 in and 1/16 in - Medium – crack width between 1/16 in and 1/18 in - Wide – crack width greater than 1/8 in • Efflorescence A white deposit caused by crystallization of soluble salts brought to the surface by moisture leaching through the concrete • Delamination A layered separation of the concrete. When a delaminated area of concrete is struck (sounded) with a hammer, ahollow sound will be emitted • Leaching The dissolution and washing away of the calcium hydroxide in concrete. Moisture enters the through cracks open to the surface.

  15. CONCRETE MEMBER • Spall A roughly circular, oval, or elongated depression in the surface of a concrete element caused by separation of a portion of the surface concrete. - Small (pop-out) – less than 6 in in diameter and 1 in deep - Medium – between 6 in and 12 in in diameter and up to 2 in deep - Large – over 12 in in diameter and any depth • Scaling (Erosion) The gradual loss of surface mortar and aggregates - Light – loss of surface mortar up to ¼ in deep - Medium – loss of surface mortar between ¼ in and ½ in deep, including loss between large agregate - Heavy – loss of mortar greater than ½ in deep significantly exposing large agregate

  16. CONCRETE MEMBER • Hollow Area An area of concrete that emits a hollow sound when struck with a hammer, indicating the existence of a fracture plane beneath the surface • Honeycomb Typically small pocket voids formed by the entrapment of air during the placement of the concrete

  17. END PRESENTATION

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