david ojala, s.e., leed ap, cwi eeri annual meeting 3 ... · david ojala, s.e., leed ap, cwi. eeri...

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ATC-20-1:

A Rough Guide to Using Your Trusty Field Manual for Safety Assessment and Reconnaissance

David Ojala, S.E., LEED AP, CWIEERI Annual Meeting3 April 2015

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Outline Reconnaissance vs. Safety Assessment Overview of ATC-20 Concepts Review of ATC-20-1 Resources Guidelines for Inspection Case Study!

Presenter

Presentation Notes

ATC-20 is intended for safety assessment, not for recon. It is a great resource for recon, but the distinction needs to be understood before we “misuse” the document.

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Reconnaissance vs. Safety Assessment Similar Methodologies, Different Judgment, Different

Timelines Reconnaissance: Subjectively document building

performance for future action or academic research. Identify both damaged and undamaged structures and

components to verify successful practices and identify areas for future improvement (research, codes, optimization)

Safety Assessment: Identify damage that renders a building unsafe for immediate, continued use. Get people back into safe buildings and out of unsafe

buildings as soon as possible.

Presenter

Presentation Notes

ATC-20 is intended for safety assessment, not for recon. It is a great resource for recon, but the distinction needs to be understood before we “misuse” the document. In both cases we are looking at the condition of buildings after earthquakes, but the difference comes in what we do with that information. Recon: Document everything, the good and the bad, analyze and study back home, sleep on it, sleep on it again, review information with peers and experts, write code change proposals/grants. Safety Assessment: A poor family of 6 is staying in a small house with cracks in the walls and a precarious-looking front porch. Do you tell them they need to leave?

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Seismic Performance Assessment Common task for both recon and safety assessment Steps:

1. Look for damaged components. Look for structural and nonstructural vulnerabilities. Track load paths from roof to foundation (or foundation to roof)

2. Assess severity of damage. Compare to published data/studies/research. Use judgment. Both? (See ATC-20-1, Page 11)

3. Determine next steps. Code change? Tag? More research?

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ATC-20 A tool for rapid seismic performance assessment. The purpose of safety assessment, or “tagging” is built

into the methodology. Judgements (bias?) are built into the methodology.

Can be used as a resource for generic reconnaissance with care. Advises whether or not building is safe for occupancy, not

cause, failure mechanism, design intent, code compliance, etc.

Presenter

Presentation Notes

Usability/occupancy

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ATC-20 Purpose and Scope GOAL: Disaster Recovery. Get people back into safe

structures and out of unsafe ones. Evaluate BUILDING safety, not just structural safety. Geotechnical Hazards Nonstructural/Falling Hazards Hazardous Materials/Utilities Hazards

Needs to be usable by both engineers (of varying abilities) and non-engineers. Simple, conservative directions for non-technical users. Allows engineers to utilize their “better” judgment.

Presenter

Presentation Notes

ATC-20 is much maligned in the structural engineering community, mostly for being over-simplistic and over-conservative. I think the critics miss the point of the document, which is to provide a guideline for evaluating building safety that can be effectively and safely used by non-engineers, while not cramping your proverbial engineering style. I think it does this very well.

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Conservatism… Don’t be overconservative, but when in doubt, follow

the manual. Still in doubt? Yellow Tag and request a Detailed or

Engineering Evaluation.

Source: Applied Technology Council. ATC-20-1 Field Manual: Postearthquake Safety Evaluation of Buildings, Second Edition. Page 13.

Presenter

Presentation Notes

The document actually talks about conservativism too. If you feel a recommendation is overconservative or inappropriate, it probably wasn’t intended for you, but for someone who didn’t have the expertise to make that assessment on their own (architects, contractors, building inspectors). But if you don’t know, you are out of your comfort zone, or the stress of the situation clouds your thinking, follow the manual. It provides a prescriptive procedure to guide you to an acceptable answer. Maybe not the BEST answer, but a valid one. I have yet to find a situation that this manual did not provide at least a related piece of advice for.

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Evaluation ProcessStructure identified

for evaluation

Rapid Evaluation

PostINSPECTED

PostLIMITED ENTRY

RESTRICTED USE

PostUNSAFE

Apparently OKOnly building exterior may

have been inspectedQuestionable

Obviously unsafe

Detailed Evaluation

PostINSPECTED

PostLIMITED ENTRY

RESTRICTED USE

PostUNSAFE

Safe but may need repairs Questionable Unsafe, must be repairedor removed

Engineering Evaluation

PostINSPECTED

PostUNSAFE

At the discretion of the Building DepartmentAt the discretion of the Building Department

Source: Applied Technology Council. ATC-20-1 Field Manual: Postearthquake Safety Evaluation of Buildings, Second Edition.

Presenter

Presentation Notes

You’ve seen this chart before, describing the three levels of evaluation. This guide provides prescriptive procedures for two of them: rapid and detailed. Placard definitions and points of inspection are defined for each method.

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Chapter 3: Rapid Evaluation 10-30 Minutes Often the only evaluation

each building will get.

Typically Exterior Only Six key points of

inspection.

Source: Applied Technology Council. ATC-20-1 Field Manual: PostearthquakeSafety Evaluation of Buildings, Second Edition. Page 6.

Presenter

Presentation Notes

We will be doing rapid evaluations today. These take 10-30 minutes (usually closer to 10 in practice) and are often conducted from your car window. The objective is to rapidly weed out obvious green and red tags. These are often done by non-engineers and the criteria is simple and conservative. If time and expertise allow, you can use the criteria in the detailed evaluation section to render a better opinion or aid your inspection, but you can fall back to this criteria in a pinch.

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6 Points of Inspection for Rapid Evaluation

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Chapter 4: Detailed Evaluation 1-4 Hours Should be performed by a structural engineer with

knowledge of the specific structure type. Typically interior and exterior. Generally must be requested by rapid evaluators via

placement of a yellow tag.

Presenter

Presentation Notes

Detailed evaluations are typically done by engineers with a little more time, so the placard definitions and points of inspection are more complex. This is where the bulk of the technical content is contained. For Recon, you may want to start here to be more thorough; time may not be as much of a limiting factor.

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Detailed Evaluation: Placard Definitions

Source: Applied Technology Council. ATC-20-1 Field Manual: PostearthquakeSafety Evaluation of Buildings, Second Edition. Page 21-22.

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Vertical and Plan Irregularities

Source: Applied Technology Council. ATC-20-1 Field Manual: Postearthquake Safety Evaluation of Buildings, Second Edition. Page 23-24.

Presenter

Presentation Notes

General information regarding common places to look for damage.

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Chapter 5: Wood-Frame Structures

Presenter

Presentation Notes

Chapters 5-9 contain detailed information on different building types. Handy diagrams show points of inspection. Tables list possible observed conditions and suggested tags.

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Chapter 6: Masonry Structures

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Chapter 7: Tilt-Up Concrete

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Chapter 8: Concrete Shear Walls

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Chapter 8: Concrete Frame

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Chapter 9: Light/Pre-Engineered Steel

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Chapter 9: Steel Frame Buildings

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Chapter 9:Concealed Damage/Pre-Northridge MF Clause

Presenter

Presentation Notes

Advice on when to ask for a more detailed, engineering evaluation.

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Can’t Determine the Structural System?

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Other Resources Chapter 10: Mobile Homes Chapter 11: Geotechnical Hazards Chapter 12: Non-Structural Hazards Appendices: Dealing with people Safety tips/Hazmat Building Entry Examples/Case Studies

Lots and lots of full-grayscale photos!

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10 Steps to A Successful (and Safe) Inspection…1. Prepare, if possible: Review your field manual Look at pre-earthquake photos (download Google Earth to

your smartphone, if you haven’t already) Determine PGA and intensities (USGS)

2. Look around you prior to approaching your subject: Evidence of geotechnical hazards Damage to/from surrounding buildings Environmental hazards Don’t die, it’s too early…

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10 Steps to A Successful (and Safe) Inspection…3. Look/listen/smell for non-structural hazards: Gas meters, power lines, storage sheds, strange liquids Look up for possible falling hazards Look for NFPA markings (commercial and industrial) Again, still to early to die…

4. Identify building occupancy: Layout of interior walls. Hazardous content. Benefits of bringing this building back into service.

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10 Steps to A Successful (and Safe) Inspection…5. Identify Structural System: Find appropriate chapter in Field Manual for points of

inspection. Check Figures 4-1 and 4-2 for vertical and plan

irregularities.6. Identify obvious damage/movement.7. If in doubt, track load path: Diaphragm to vertical elements (connections too!) Vertical elements to foundation (connections too!)

8. Enter if necessary and safe.

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10 Steps to A Successful (and Safe) Inspection…9. Ask yourself: Am I doing safety assessment or reconnaissance? Is the structure in significantly worse shape than it was

before the quake? Will any new damage increase the likelihood of collapse or

occupant harm in an aftershock or in service? Are there new dangers from hazmat, neighboring

buildings, landslides? Do people need to be in this building? Do I feel comfortable making this assessment?

10. Tag it, yo.

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Good Luck!

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CASE STUDY:

Pool and Recreation Center

David Ojala, S.E., LEED AP, CWIEERI Annual Meeting3 April 2015

Presenter

Presentation Notes

Thank you all for joining us. I’m going to present a case that I came across recently in that hotbed of seismic activity, Virginia. Before we get started, I’d like to encourage you all to actually fill out every last part of the Rapid Assessment Form to experience doing it under a time crunch. Lack of familiarity with the forms is a big piece of feedback we get from people who go out and tag. We’d also like to collect these to help us develop our trainings, so if you’d care to leave your name off, that’s fine.

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Background 3 days after Magnitude 5.8 quake. Minor aftershocks

daily, including 4.5 yesterday. Main Shock: PGA estimated at 10-15%g, MMI = VI. Most homes in area have little to no damage and have

green tags, moderate damage to buried utilities. Hot and muggy, major hurricane is inbound and heavy

wind and flooding rain are expected. Site is not coastal. About 200 local residents are seeking shelter, primarily

due to lack of electricity, running water, or fear.

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Aerial View

Presenter

Presentation Notes

You all downloaded google earth to your smartphone before the inspection, right?

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North Elevation

Slopes Down

PoolAdmin/

Classroom Wing

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East Elevation

Slopes Down

Pool

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South Elevation

Pool

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West Elevation

Pool

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Structure Phase 1 built around 1980, Phase 2 in 1983 Sloped site. Phase 1 Admin/Classroom Wing: CMU bearing/shear

walls with steel truss floors. Phase 2 Pool Area: Pre-engineered steel frame with CMU

infill walls. Designated as an emergency shelter site by county. Owners/users reported “significant movement” of pool

area. Spa losing water (2 inches/hour) since quake.

Presenter

Presentation Notes

Go into character: I’m Cletus, the building manager. You must be the evaluators they sent from the city, we’ve really glad you’re here. We’ve offered to host some displaced folks in the community for the weekend while this hurricane comes through, seeing as how we’re listed as a shelter site and the schools are busy getting ready to open up for the fall. Everything looks pretty good, we just need to finish cleaning up a bit and go through the formality of this “tagging” process. The center has been open for around 30 years now and I’ve lived here for most of that time. Tell you what, I’ve never experienced anything quite like this. I think this was built in a couple stages while they raised money for the pool. I was in the pool at the time getting ready for the tri-valley swim meet coming up this weekend when the building got to shaking. The roof of the pool got to leaning pretty good and the ducts and lights were swingin back and forth. A bunch of tiles and pieces of cinder block fell down off the end walls, but we cleaned all that up. Rest of the building looks pretty good, just some tiles falling and some books off shelves. No broken glass. Spa’s been losing water pretty steady, though… Anyway, let’s take a stroll.

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North Entrance

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Slope to right of north entrance (south face sim.)

Vertical Cracks through EFIS Panel Joints.

Presenter

Presentation Notes

This is the only significant cracking you notice on the exterior, safe to enter.

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Classroom/Admin Areas: Typical Damage

Trophies unharmed. Whew!

Presenter

Presentation Notes

Maintenance crews are currently fixing the ceilings and sweeping up debris, but there are still some spots they haven’t quite fixed.

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Pool: Looking West

Presenter

Presentation Notes

Things got swinging around a bit, but nothing fell down.

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Pool: Looking East

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Pool: Looking South

Bolted Splices, no other stiffeners.

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Pool: Looking South

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Pool: Typical Damage at Pilaster

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Pool: Typical Damage at Pilaster

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Pool: Looking North

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Pool: Typical Damage at Pilasters

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Pool: Spa Area (Southwest Corner)

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Pool: West Deck

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Pool: West Deck

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Pool: West Deck

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Pool: West Deck

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Pool: West Deck

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Pool: East Wall

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Pool: East Wall

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Pool: East Wall

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Damage Summary

Buckling of Bottom Flanges

of Girders

Spa Loosing Water

Damage to Infill Wall Connections

Hung Ceiling Disturbance, Minor Cracking of CMU Walls (Bed Joints,

Pilasters)Stairway with cracked pilaster

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“ANSWERS”

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Virginia Earthquake Low intensity shaking felt over long distances. Buildings not explicitly designed for earthquakes. Vulnerable, non-ductile building systems (URM, tilt-up,

infill walls), often 19th century vintage. Incomplete load paths. Poor foundation soils, expansive clays. Single family homes largely unaffected. Seemingly random buildings saw significant damage.

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Pre-Engineered Steel Frames Many different systems available. Typically used for warehouses, industrial facilities. Optimized for gravity loads for maximum spans. Two Different Lateral Systems: Moment Frame along girder lines Braced Frame or Shear Wall in opposite direction

Can perform very well in seismic and wind events IFdesigned appropriately.

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Example

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Example

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Critical Differences Long span required deeper beams (plate girders). Stiffening and bracing requirements were not

increased appropriately.

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Long, Inclined Span, Flexible Diaphragm

Compression Toward Lower End Under Gravity

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Few Stiffeners, No Cross Braces

Bolted Splices, no other stiffeners.

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Infill Wall Out of Plane Movement

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Tall, Torsionally Flexible

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Short, Restrained, Rigid

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Flange Local Buckling

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Global Lateral Torsional Buckling

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Lateral Torsional Buckling, Utica, NY

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ATC-20 Field Manual

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Considerations

Limited access/visibility of all moment frame connections. Full inspection is beyond your means. This may be a designated shelter but is not an

essential facility; don’t take unnecessary risks, especially if you are unsure of the consequences of the damage you’ve seen. Aftershocks are continuing, a hurricane is inbound. Pool area appears to be relatively isolated from

classroom/administration building to the east, which has little damage. Was the buckling actually caused by the earthquake?

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Rapid Assessment Form

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Rapid Assessment Form

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Things to Remember

Consider occupancy (do people need to be here?) Understand the limits of your expertise and call for

backup (in the form of a detailed evaluation) if needed. Don’t expect that damage will be textbook in nature;

not all buildings are designed to California “standards” If you identify some damage, trace the implied building

movement/load path back to the foundation and look for additional damage. You are evaluating BUILDING safety, not just structural

safety. Look out for Nonstructural/Falling Hazards, HazMat/Utilities, Geotechnical Hazards.

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QUESTIONS?COMMENTS?

david ojala, s.e., leed ap, cwi eeri annual meeting 3 ... · david ojala, s.e., leed ap, cwi. eeri...

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