STRUCTURE ASSESSMENT

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)

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

INTRODUCTION

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.

PROBABILITY OF FAILURE

CONSEQUENCES OF FAILURE

LOW MEDIUM HIGH

(3) (2) (1)

HIGH (1) 3 2 1

MEDIUM (2) 4 3 2

LOW (3) 5 4 3

RISK MATRIXRisk = Probability of Failure X Consequences of Failure

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

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

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)

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

ASSESSMENT METHOD

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

PERSONNEL & EQUIPMENTPersonnel 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)

Steel MemberStructural deficiencies affecting steel member : Corrosion

- Minor/LightA surface corrosion with no apparent loss of section

- ModerateCorrosion 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

- SevereHeavy, stratified corrosion or corrosion scales with extensive

pitting. Removal requires exerted effort and may require mechanical means. Significant loss of section

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.

PittingFormation of cavities due to corrosion

CONCRETE MEMBERStructural 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

EfflorescenceA white deposit caused by crystallization of soluble salts brought to the surface by moisture leaching through the concrete

DelaminationA layered separation of the concrete. When a delaminated area of concrete is struck (sounded) with a hammer, ahollow sound will be emitted

LeachingThe dissolution and washing away of the calcium hydroxide in concrete. Moisture enters the through cracks open to the surface.

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

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

HoneycombTypically small pocket voids formed by the entrapment of air during the placement of the concrete

END PRESENTATION