SIMPLE/RAPID SEISMIC EVALUATION METHODS Advanced ...€¦ · Advanced Earthquake Engineering CIVIL-706 Rapid Visual Screening FEMA 154/155 • FEMA 154 = Rapid Visual Screening (RVS)

SIMPLE/RAPID SEISMIC

EVALUATION METHODS

Advanced Earthquake Engineering

CIVIL-706

Instructor:

Lorenzo DIANA, PhD

Why evaluation of existing buildings?

Rapid Visual Screening Advanced Earthquake Engineering CIVIL-706 -1-

Why evaluation of existing buildings?

Rapid Visual Screening Advanced Earthquake Engineering CIVIL-706 -2-

• Regeneration of existing cities implies the assessment of existing cities

• The assessment of existing cities implies the assessment of different aspects

• Assessment of seismic behaviour becomes and important central aspect

Strategy: Selection by steps

Rapid Visual Screening Advanced Earthquake Engineering CIVIL-706

Rapid evaluation

Vulnerability score

Sophisticated modeling

Retrofitting

e.g., FEMA or OFEG

STOP If OK?

STOP If OK?

-1-

By the end of today’s course…

Advanced Earthquake Engineering CIVIL-706

You will be able to answer:

• Why we do a rapid visual screening?

• What are the examples for conducting such a seismic assessment? (in US and CH)

• What are the particular means for that?

Ph

oto

: EE

RI

Rapid Visual Screening -2-

Why to do rapid screening?

Example of a building group

Advanced Earthquake Engineering CIVIL-706 Rapid Visual Screening -3-

Prioritizing the building group

Red: imminent collapse

Yellow: on the edge

Green: Safe

Why to do rapid screening?

Example of a building group


Main Steps…

1. Identify the building class

2. Detect structural irregularities

3. Estimate the height

4. Determine the soil

5. Estimate the construction year

6. Take photo for later references

Photo source: www.eagle-wi.gov


1. Building classification:

• Constructional material

• Structural properties

2. Basic score:

Probability of collapse

3. Score modifiers

Masonry, concrete with in-fills, steel structures, and etc.

Advanced Earthquake Engineering CIVIL-706 Rapid Visual Screening

Main Steps…


FEMA 154/155 • FEMA 154 = Rapid Visual Screening

(RVS) of buildings for potential seismic hazard

• One of the US seismic evaluation methods

• RVS – Rapid Visual Screening

• Identifying seismically hazardous buildings that need further analysis

• Level 1 and Level 2

Acknowledgment for the contribution to create the slides

Final Score = BS + ∑ SM


FEMA 154/155

Probability of collapse for the maximum

considered earthquake

Final Score >= Cut-off score

BS = - log10(P[collapse|MCER])

Basic Score

Score modifiers


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L, M, M-H, H, V-H 5 different seismicity Regions


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Building identification portion of Data Collection Form


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Photo and sketch


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Pre-field building data Land Register Cadastre

Sanborn maps Design drawings


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Pre-field building data

General Information - Number of stories. - Floor Area. - Year of construction - Determination of the Key Code Adoption Dates: • Seismic Code Adopted (Code year) • Improvements adopted (Benchmark year) In Basic Score determination a post Code year is assumed. Score modifiers are applied if the building is constructed before Code Year or after Benchmark year.

- Addition - Occupancy


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SOIL TYPE A predefined soil class C-D is assumed. Score modifiers are applied for soil class A, B or E. Soil class F implies a soil-evaluation needed.


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GEOLOGIC HAZARD • Liquefaction • Landslide • Surface fault rupture


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GEOLOGIC HAZARD • Liquefaction SOFT SOILS, SANDS and LOAMS Increase of pore pressure soil from solid to fluid state. Seismic event can augment pore pressure till the equivalence with the pressure above.

Nigata (Japon), Kawagishi-cho Apartment Complex 1964


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GEOLOGIC HAZARD • Liquefaction SOFT SOILS, SANDS and LOAMS Shear resistance of soil is negligible. The building undergoes rocking or sinking due to the incapacity of soil to resist vertical or lateral load.

Nigata (Japon), Kawagishi-cho Apartment Complex 1964


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GEOLOGIC HAZARD • Landslide Movement of the soil due to loss of slope stability. Landslide may occur if height of the slope is bigger than the distance to the slope. Pre-field information should be verified during the on-site survey.


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GEOLOGIC HAZARD • Surface fault rupture Due to shallow earthquake (<20km distance) Significant displacement of the earth’s surface

Canterbury earthquake in New Zealand, 2010


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GEOLOGIC HAZARD • Liquefaction • Landslide • Surface fault rupture

If one of the 3 geologic hazard is identified, a detailed structural evaluation is needed.


FEMA 154/155

Side-walk survey

ADJANCENCY Adjacent buildings may lead to several types of damage during earthquakes: • Pounding • Falling hazards from adjacent buildings


FEMA 154/155

Side-walk survey

ADJANCENCY Adjacent buildings may lead to several types of damage during earthquakes: • Pounding • Falling hazards from adjacent buildings

GAPS VH seismicity region = 2 inches (5.08 cm) per storey H seismicity region = 1.5 inches (3.81 cm) per storey MH seismicity region = 1 inches (2.54 cm) per storey M seismicity region = 0.5 inches (1.27 cm) per storey L seismicity region = 0.5 inches (1.27 cm) per storey


FEMA 154/155

Side-walk survey

ADJANCENCY • Pounding

IF a) Minimum gap not respected

+ b) Floors are separated vertically by more than 2 ft (60.69 cm) OR b) One building is two or more stories taller than the adjacent OR b) The building is at the end of a row of 3 or more buildings


FEMA 154/155

Side-walk survey



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Side-walk survey



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Side-walk survey

IRREGULARITIES • Vertical Irregularities

• Severe vertical irregularities • Moderate vertical irregularities

• Plan Irregularities


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Side-walk survey


1. Sloping site 2. Weak and/or soft story 3. Out-of-plane setback 4. In plane setback 5. Short column/pier 6. Split levels


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Side-walk survey


1. Sloping site


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Side-walk survey


1. Sloping site - Foundations at different levels - Irregularities and non-symmetry in both horizontal and

vertical directions - Irregularity in stiffness and mass - Centre of mass and centre of stiffness of a storey do not

coincide with each other and are not in a vertical line for different floors

- Lateral load leads to torsional response - Different column heights at the same storey level

Drastic variation in stiffness of columns of the same storey

Short stiff columns uphill attract higher lateral forces and are prone to damage


FEMA 154/155

Side-walk survey


1. Sloping site


FEMA 154/155 IRREGULARITIES • Vertical Irregularities

1. Sloping site

2 cases: 1) Along slope NO TORSIONAL EFFECTS but shear damages to shorter

columns uphill 2) Across slope TORSIONAL EFFECTS

CM

CS

ACROSS SLOPE ACTION

ALONG SLOPE ACTION

Side-walk survey


FEMA 154/155

Side-walk survey


1. Sloping site If at least 1 storey slope from one side to the other

= MODERATE VERTICAL IRREGULARITY

(for W1 typology = SEVERE) W1 typology = LIGHT WOOD FRAME SINGLE or MULTIPLE FAMILY DWELLINGS of ONE or MORE STORIES


FEMA 154/155

Side-walk survey


2. Weak and/or soft storey - Weak Storey = when a story has less strength (fewer

walls and columns) than the storey above or below - Soft Storey = when the stiffness of one storey is

dramatically less than that of most others


FEMA 154/155

Side-walk + internal survey


2. Weak and/or soft storey

CRIPPLE WALLS (for W1) =

MODERATE VERTICAL IRREGULARITY (SEVERE if crawl space is occupied)


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Side-walk survey



OCCUPIED SPECE OVER a garage (for W1) =

SEVERE VERTICAL IRREGULARITY



SOFT STORY =



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Side-walk survey



ONE STORY PARTICULARLY TALL =



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Side-walk survey


FEMA 154/155 IRREGULARITIES • Vertical Irregularities

3. Out-of-plane setback - When the seismic-resisting system at one story is not

aligned vertically with the seismic-resisting system of the storey above or below

- An outside survey may not indicate set-backs in the interior walls and the seismic-resisting system of the building

Side-walk survey


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Side-walk survey


3. Out-of-plane setback


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Side-walk survey




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Side-walk survey



If the setback is greater than 2 ft (60.96 cm) =



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Side-walk survey


4. In plane setback - When elements of the seismic force-resisting system at

upper levels are offset from elements at the lower level - Damage can be concentrated in horizontal elements that

connect the offset lateral elements and in vertical elements at the upper level


FEMA 154/155

Side-walk survey


4. In plane setback

MODERATE VERTICAL IRREGULARITY


FEMA 154/155

Side-walk survey


5. Short column/Pier - When columns (or piers) are shorter than typical

columns, these shorter and stiffer columns attract greater lateral load significant damage

- 3 main cases: a) Some columns/piers are much shorter than the

typical columns/piers in the same line

If at least 20% of the columns in line are short = SEVERE VERTICAL IRREGUALRITY

Le misure preventive (di cui il daspo fa parte) sono provvedimenti gravissimi, eredità del fascismo, che minano le libertà degli individui senza alcun processo e senza il diritto a una difesa Note this deficiency is typically seen in older concrete and steel building types.

Typologies: C1, C2, C3, PC1, PC2, RM1, RM2


FEMA 154/155

Side-walk survey



columns, these shorter and stiffer columns attract more of the lateral load significant damage

- 3 main cases: b) The columns/piers are narrow compared to the

depth of the spandrels

If the height is less then 50% of the depth of spandrels = SEVERE VERTICAL IRREGUALRITY

Apply if: Figure (a): Some columns/piers are much shorter than the typical columns/piers in the same line. Figure (b): The columns/piers are narrow compared to the depth of the beams. Figure (c): There are infill walls that shorten the clear height of the column. Note this deficiency is typically seen in older concrete and steel building types.



FEMA 154/155

Side-walk survey



columns, these shorter and stiffer columns attract more of the lateral load significant damage

- 3 main cases: c) There are infill walls that shorten the clear height

of the column

SEVERE VERTICAL IRREGUALRITY

Apply if: Figure (a): Some columns/piers are much shorter than the typical columns/piers in the same line. Figure (b): The columns/piers are narrow compared to the depth of the beams. Figure (c): There are infill walls that shorten the clear height of the column. Note this deficiency is typically seen in older concrete and steel building types.


Note this deficiency is typically seen in older concrete and steel building types.


6. Split levels - When floors or roof floors in one part are not aligned

with the floors or roof floors levels in other part - Damage is concentrated in the elements that connect

the offset floor level to the vertical framing

MODERATE VERTICAL IRREGULARITY


FEMA 154/155

Side-walk survey

IRREGULARITIES • Plan irregularities

1. Torsion 2. Non-parallel systems 3. Re-entrant corners 4. Diaphragm openings 5. Beams do not align with columns


FEMA 154/155

Side-walk survey


1. Torsion - When a building has a good lateral-load resistance in

only ONE DIRECTION

OR - When there are stiffness eccentricities in the seismic-

force-resisting systems which may cause twisting around vertical axis


FEMA 154/155

Side-walk survey


1. Torsion - Mainly in CORNER or FRONT buildings


FEMA 154/155

Side-walk survey




FEMA 154/155

Side-walk survey




FEMA 154/155

Side-walk survey


2. Non-parallel systems - Wedge-shaped buildings triangular in plan are

susceptible to torsion and collapse


FEMA 154/155

Side-walk survey


3. Re-entrant corners - Buildings with long wings. E,T,L,U,+ shaped with

projection of more than 20 ft (6.09 m) - STRESS CONCENTRATION at re-entrant corners could

lead to damage and collapse - In addition buildings are likely to experience torsion


FEMA 154/155

Side-walk survey


4. Diaphragm openings - Large openings in floors or roofs weaken the diaphragm

and reduce its ability to transfer seismic forces. - Floors and roofs have the role of distributing seismic

forces to vertical structures.

- IF large openings have a width > 50% of the width of diaphragm


FEMA 154/155



5. Beams do not align with columns - When exterior beams do not align with columns in plan - Mainly in concrete buildings


FEMA 154/155

Side-walk survey

Exterior falling hazards • Unbraced chimneys • Unbraced parapets • Cornices • Heavy veneers • Heavy claddings • Overhangs • Appendages • Canopies


FEMA 154/155

Side-walk survey

Damage and deterioration • Abandoned buildings • Beams, floors, roofs sagging • Beams or columns broken • Settlement occurred • Visible distressed from prior earthquake not repaired • Fire damage not repaired • For wood buildings: wood rotted • For unreinforced masonry buildings: mortar eroded

away • For concrete buildings: concrete damaged or eroded

such as the rebar is exposed • For steel buildings: elements are corroded • Foundations with cracks


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FEMA Typologies Every BUILDINGS TYPE has its own BASIC SCORE providing a measure of the expected seismic performance. 17 building types (steel plate shear walls buildings, earth buildings, native Americans buildings are excluded).


FEMA 154/155

Side-walk survey

FEMA Typologies


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FEMA Typologies


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FEMA Typologies


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FEMA Typologies


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FEMA Typologies


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FEMA Typologies


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FEMA Typologies


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FEMA Typologies


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FEMA Typologies


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FEMA Typologies


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Determination of the BASIC SCORE

1) Calculation of the peak response of the building for a given set of ground motions (MCER)

2) Calculation of the probability of complete damage given the peak response

3) Calculation of the probability of collapse given the probability of complete damage

4) Calculation of the BASIC SCORE


FEMA 154/155


1) Calculation of the peak response of the building for a given set of ground motion (MCER)

Peak response of the building is calculated as the intersection of the building CAPACITY CURVE and the DEMAND SPECTRUM of EARTHQUAKE GROUND MOTION .


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Seismic demand (MCER)

Capacity Curve (buildings classification)

Performance Point




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FEMA 154/155

Fragility curves are lognormal cumulative distribution functions describing the structural behavior of building type




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Sd,c median value of spectral displacement for the complete structural damage state

Sd,c = ΔC HR(α2/ α3) ΔC story drift ratio

HR building height

α2 modal height factor

α3 modal shape factor

βS,C standard deviation

Sd,c


3) Calculation of the probability of collapse given the probability of complete damage


FEMA 154/155

P[collapse] = collapse factor x P[complete damage] Collapse factor are provided for each Model Building Type. The collapse factor is small for light wood frame single or multiple-family dwellings (W1) (3%) and larger for Model Building Types more prone to collapse, such as unreinforced masonry bearing-wall buildings (URM) (15%).


4) Calculation of the BASIC SCORE


FEMA 154/155

BS = -log10(P[collapse])


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Determining the final score:

SL1 = BS + ∑ SM SL1 >= SMIN

Cut-off score is mainly considered to be 2.0

!S cu t o ff b u ild in g is O K

S cu t o ff fu r th e r in ve s tig a tio n

BS

SM

Level 2 Level 2 analysis provides specific SCORE modifiers for every VERTICAL or PLAN irregularity.


FEMA 154/155


VL2

PL2

Level 2 There are specific SCORE modifiers also for: REDUNDANCY and POUNDING. Redundancy In rapid visual screening, redundancy observed due to multiple bays of lateral elements on each side of the building is beneficial to seismic performance.

Pounding There are a variety of pounding configurations, as discussed in for level 1.


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M

Level 2 Specific BUILDING TYPE score modifiers: 1. S2 buildings: K BRACING GEOMETRY

When braces intersect the column at the mid-height without horizontal connection to the diaphragm


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M

Level 2 Specific BUILDING TYPE score modifiers: 1. S2 buildings: K BRACING GEOMETRY 2. C1 buildings: FLAT PLATE MOMENT FRAME

When a concrete moment frame lacks a dropped beam running through the column, the risk of punching shear failure at the column increases.


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M

Level 2 Specific BUILDING TYPE score modifiers: 1. S2 buildings: K BRACING GEOMETRY 2. C1 buildings: FLAT PLATE MOMENT FRAME 3. PC1/RM1 building: with roof-to-wall ties

Do not combine with post-benchmark or retrofit modifier


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M

Level 2 In addition BUILDING TYPE SPECIFIC STATEMENTS: 1. S2 buildings: K BRACING GEOMETRY 2. C1 buildings: FLAT PLATE MOMENT FRAME 3. PC1/RM1 building: with roof-to-wall ties 4. PC1/RM1 building with closely spaced walls

When buildings are used as offices or for some other use, they may have relatively close spaced partitions that can provide some redundancy for carrying gravity loads and additional damping.


FEMA 154/155


M

Level 2 In addition BUILDING TYPE SPECIFIC STATEMENTS: 1. S2 buildings: K BRACING GEOMETRY 2. C1 buildings: FLAT PLATE MOMENT FRAME 3. PC1/RM1 building: with roof-to-wall ties 4. PC1/RM1 building with closely spaced walls 5. URM buildings: GRABLE WALLS are present

Out-of-plane wall failure might occur, compromising gravity support for the roof above.


FEMA 154/155


If multiple modifiers occur in the same section, the score modifier is the sum of the applicable modifiers, but is subject to a cap. The cap corresponds to the maximum value for the given seismicity range.

M

Level 2 Level 1 gives: SL1 = Final Level 1 score VL1 = Vertical Irregularity score PL1 = Plan irregularity score S’ (Adjusted baseline score) = (SL1 – VL1 – PL1) Level 2 gives: SL2 = Final Level 2 score VL2 = Vertical Irregularity sum score PL2 = Plan irregularity sum score M = Modifiers sum score SL2 = (S’+ VL2 + PL1 + M)


FEMA 154/155

If multiple modifiers occur in the same section, the score modifier is the sum of the applicable modifiers, but it is subject to a cap. The cap corresponds to the maximum value for the given seismicity range.


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SL1 or SL2>= SMIN

!S cu t o ff b u ild in g is O K

S cu t o ff fu r th e r in ve s tig a tio n

Cut-off score is mainly considered to be 2.0


FEMA 154/155

Exercise: • RVS of the building where you live

Documents

SIMPLE/RAPID SEISMIC EVALUATION METHODS Advanced ...€¦ · Advanced Earthquake Engineering CIVIL-706 Rapid Visual Screening FEMA 154/155 • FEMA 154 = Rapid Visual Screening (RVS)