Lateral Loads

Lateral Load sources

WindTornado, hurricane, explosion

Seismic Flood or Tsunami Earth pressure

Basement or retaining walls

Probability

Code specified maximum wind velocities have a frequency of once per 50 years.

Code specified seismic loads have a frequency of once per 500 years.

Hurricanes Floyd 1999 Andrew 1992

Tornado Spawned by Katrina

Wind Damage (Hurricane Andrew)

Hurricane Storm Surge

Camille (1969) storm surge damage

Surf City, New Jersey 1944

BEAUFORT SCALE  Original scale developed in 1805 by British naval officer Sir Francis Beaufort.

Beaufort

Number

International

Description

Miles per

Hour

Description

0 Calm Less than 1 Calm; smoke rises vertically.

1 Light Air 1-3 Direction of wind shown by smoke but not by wind vanes.2 Light Breeze 4-7 Wind on felt on face; leaves rustle; vanes move.

3 Gentle Breeze 8-12 Leaves and small twigs in constant motion.

4 Moderate Breeze 13-18 Raises dust and loose paper

5 Fresh Breeze 19-24 Small trees in leaf begin to sway.6 Strong Breeze 25-31 Large branches in motion; whistling heard in telegraph

wires; umbrellas used with difficulty.Moderate

(or near) gale

Gale(or fresh gale)

9 Strong Gale 47-54 Slight structural damage occurs.

Storm

(or whole gale)

11 Violent Storm 64-72 Accompanied by widespread damage.

12 Hurricane 73*-136 Devastation occurs.

*The U.S. uses 74 statute mph as the speed criterion for hurricanes.

10 55-63 Trees uprooted; considerable damage occurs.

8 39-46 Breaks twigs off trees; generally impedes progress.

Beaufort Scale

7 32-38 Whole trees in motion; inconvenience in waling.

Wind Scale

Saffir-Simpson Hurricane ScaleSustained Wind Velocities

Category One Hurricane: Winds 74-95 mph , Storm Surge 4 ~ 5 feet

Category Two Hurricane: Winds 96-110 mph, Storm Surge 6 ~ 8 feet

Category Three Hurricane: Winds 111-130 mph, Storm Surge 9 ~ 12 feet

Category Four Hurricane: Ex. Andrew 1992 Winds 131-155 mph, Storm Surge 13 ~ 18 feet

Category Five Hurricane: Ex. Camille 1969 Winds greater than 155 mph, Storm Surge >18

feet

F-0 Gale Tornado 40 - 72 MPH Chimneys damaged; branches broken off trees; shallow-rooted trees uprooted

F-1 Moderate Tornado 73 - 112 MPH Roof surfaces peeled off; mobile homes pushed off foundations or overturned; moving autos pushed off roads.

F-2 Significant Tornado 113 - 157 MPH Roofs torn off frame houses; mobile homes demolished; box cars pushed over; large trees snapped or uprooted; light-object projectiles generated.

F-3 Severe Tornado 158 - 206 MPH Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown.

F-4 Devastating Tornado 158 – 206 MPHWell-constructed houses leveled; structures with weak foundations relocated; cars thrown and large projectiles generated.

F-5 Incredible Tornado 261 - 318 MPH Strong frame houses lifted off foundations and carried considerable distance to disintegrate; automobile-sized projectiles hurtle through the air in excess of 100 yards; trees debarked; other incredible phenomena expected.

Tornado Classifications

Hurricane Frequency

0

2

4

6

8

10

12

14

1945 1955 1965 1975 1985 1995 2005

Year

Number of Hurricanes

Global WarmingGlobal Average Temperature vs. Number of

Pirates

13

13.5

14

14.5

15

15.5

16

16.5

35000 45000 20000 15000 5000 400 17

Number of Pirates

Global Avg. Temperature (C)

18201860

1880

1920

1940

1980

2000

Wind Flow across a Low Rise Building

Positive pressure area

Negative pressure areas

Wind flow across a low rise building

Wind Effect on Roofs

Windward roof steep enough to feel pressure. Leeward roof subjected to suction.

Leeward Roof

Windward roof shallow enough to feel suction. Breakpoint approx 20°.

Earthquakes

Niigata 1964

Tsunami 12/2004

http://www.ldeo.columbia.edu/news/2005/images/tsun_eq.mp3

Tsunami Effects

SOURCE: US NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION PACIFIC MARINE ENVIRONMENTAL LABORATORY, US NATIONAL DATA BUOY CENTER; © 2004 KRT

Scale for Measuring earthquakes was developed by seismologist Charles Richter Class Magnitude

Great 8 or more Major 7 - 7.9 Strong 6 - 6.9 Moderate 5 - 5.9 Light 4 - 4.9 Minor 3 -3.9

Types of Seismic Waves

http://www.analog.com/library/analogDialogue/archives/35-01/earthquake/index.html

Probability (statistics of chance)

http://www.barringer1.com/feb05prb.htm

Defining Lateral Loads Codes specify environmental and live loads

Local geography affects intensity of wind loads

Importance factors are used to adjust loads for more important buildings

Seismic loads are affected by building geometry, mass, structural system and local geological conditions

Soil lateral loads affect by soil type and groundwater level

Seimic Loads

SEI/ASCE 7-02

Total lateral force V in each principal direction should be computed as

V = CsW

Cs = seismic response coefficient

W = Total dead load and applicable portions of other loads

Applicable portions of other loads

Storage areas: minimum of 25% floor live load. Not needed for garages and open parking

When partition load is included in floor load design, actual partition weight or minimum of 10 psf whichever is greater

Total operating weight of permanent equipment Where flat roof snow load exceeds 30 psf, design snow

load should be included in W. When jurisdiction authority approves it, snow load contribution may be no less than 20% of design snow load.

For the given occupancy classification, the appropriate Seismic Use Group and corresponding Importance Factor Is is determine.

Building Classification for Lateral Loads: Category I Buildings and other structures that

represent a low hazard to human life in event of failure, such asAgricultural facilitiesCertain temporary structuresMinor storage facilities

Building Classification for Lateral Loads: Category II Every building or structure that is not listed

in Categories I, III, or IV

Building Classification for Lateral Loads: Category III Buildings with substantial

hazard to humans in case of failure, such as Where more than 300

people congregate Day care facilities greater

than 150 Schools greater than 250 Colleges greater than 500 Heath care greater than 50,

but no surgery or emergency

Jails and detention facilities Power generation facilities

no in Cat IV Buildings not in Cat IV that

mfg, process, handle, store, use or dispose of hazardous fuels, chemicals, waste, or explosives containing sufficient quantities to be dangerous if released

Building Classification for Lateral Loads: Category IV Essential facilities such

as Hospitals/health care Fire, rescue, ambulance Emergency shelter Emergency preparedness,

communication, operations Power generating

facilities/public utilities + ancillary facilities (towers, storage tanks, substations, etc.)

Aviation control towers Water storage facilities and

pump stations Critical national defense Hazardous materials

facilities where quantity

exceeds threshold quantity determined by the relevant authority

Seismic Use Group Designations

Seismic Use Group

I II III

Occupation Category I ✪II ✪III ✪IV ✪

Occupancy Importance Factors

Seismic Use Group Is

I 1.0

II 1.25

III 1.5

Site classification (A-F) must be determined, and then the site coefficients Fa and Fv can be found.

These are the maximum considered earthquake (MCE) spectral acceleration.

Fa is for short period and Fv for 1 second.

Ss and S1 values are taken from the maps

Seismic Site ClassificationSite Class vs N or Nch su

A: Hard Rock >5,000 ft/s NA NA

B: Rock 2,500 – 5,000 ft/s NA NA

C: Very dense soil and soft rock

1,200 – 2,500 ft/s >50 >2,000 psf

D: Stiff soil 600 – 1,200 ft/s 15-50 1,000 – 2,000 psf

E: Soil <600 ft/s <15 <1,000 psf

F: Soil requiring site-specific evaluation

1. Soils vulnerable to potential failure or collapse2. Peats and/or highly organic clays3. Very high plasticity clays4. Very thick soft/medium clays

Vs =measured shear wave velocityN = Standard penetration resistance (blows/ft)Nch = corrected N for cohesionless layers (blows/ft)

su = undrained shear strength

Value of Fa for short-period max spectral accelerationSite Class Ss ≤ 0.25 Ss = 0.5 Ss = 0.75 Ss = 1.0 Ss ≥ 1.25

A 0.8 0.8 0.8 0.8 0.8

B 1.0 1.0 1.0 1.0 1.0

C 1.2 1.2 1.1 1.0 1.0

D 1.6 1.4 1.2 1.1 1.0

E 2.5 1.7 1.2 0.9 0.9

F * * * * *

* Site specific response analysis shall be performed except for structures with periods of vibration less than 0.5 sec. Values of Fa for liquefiable soils may be assumed equal to the values for the site class determined without regard to liquefaction in Step 3.

Value of Fv for 1 second max spectral accelerationSite Class S1 ≤ 0.1 S1 = 0.2 S1 = 0.3 S1 = 0.4 S1 ≥ 0.5

A 0.8 0.8 0.8 0.8 0.8

B 1.0 1.0 1.0 1.0 1.0

C 1.7 1.6 1.5 1.4 1.3

D 2.4 2.0 1.8 1.6 1.5

E 3.5 3.2 2.8 2.4 2.4

F * * * * *

* Site specific response analysis shall be performed except for structures with periods of vibration less than 0.5 sec. Values of Fv for liquefiable soils may be assumed equal to the values for the site class determined without regard to liquefaction in Step 3.

Seismic design category (A-F) and response factor R for the basic seismic force-resisting structural system must then be identified (SEI/ASCE 7-02 or relevant building code)

R-factor value is proportional to the amount of ductility, overstrength, and energy dissipation the seismic force resisting structural system possess.

For more ductile systems with larger R, the lateral seismic design force will be lower than a more vulnerable system with a lower R.

R = 1.0 is the conservative lower-bound. This is pure linear response

Seismic Base Shear Coefficient

€

Cs =SDSRIs

SDS = design spectral response in short period range (g)R = response modification factor for structureIs = occupancy importance factor for seismic use group

However, Cs has a max value of

Use the smaller value

SD1 = design spectral at 1 secondT = fundamental period of the structure (s)

€

Cs =SDI

T RIs ⎛ ⎝ ⎜ ⎞

⎠ ⎟

Design spectral accelerations

SDS = (2/3) SMS

SD1 = (2/3) SM1

SMS = Fa Ss

SM1 = Fv S1

Fundamental periodActual determination is quite complex. Code allows the

following approximation

Ta = Ct hnx

Ta = approximate fundamental period

Ct = period parameter (table)

x = period parameter (table)

hn = height from base to highest level of bldg (ft)

Values of period parameters

Structure Type Ct x

Moment resisting frame systems of steel where frame resists 100% of the seismic force and not enclosed or adjoined by more rigid components preventing frame deflection

0.028 0.8

Moment resisting frames of reinforced concrete where frames resist 100% of seismic force and not enclosed or adjoined by more rigid components preventing frame deflection

0.016 0.9

Eccentrically braced steel frames 0.03 0.75

All other structural systems 0.02 0.75

Vertical distribution of seismic forcesLateral base shear V should be distributed over the height of the structure as

concentrated loads on each floor level.

At a given floor level

Fx = Cvx Vwhere

wi is the portion of total gravity load of W at level I

hi = height from base to level I

k = 1 for building with T ≤ 0.5 s; 2 when T≥2.5 s (interp between)

€

Cvx =wxhx

k

wihik

i=1

n

∑

Example

Industrial building 180’ x 90’, clear height approx 30’

Supported on spread footings on moderately deep alluvial deposits (medium dense sand)

Astoria, Oregon

Site ClassSite Class vs N or Nch su

A: Hard Rock >5,000 ft/s NA NA

B: Rock 2,500 – 5,000 ft/s NA NA

C: Very dense soil and soft rock

1,200 – 2,500 ft/s >50 >2,000 psf

D: Stiff soil 600 – 1,200 ft/s 15-50 1,000 – 2,000 psf

E: Soil <600 ft/s <15 <1,000 psf

F: Soil requiring site-specific evaluation

1. Soils vulnerable to potential failure or collapse2. Peats and/or highly organic clays3. Very high plasticity clays4. Very thick soft/medium clays

Seismic Use Group

First need occupancy categoryLow occupancy, industrial building

Category I

Seismic Use Group

I II III

Occupation Category I ✪II ✪III ✪IV ✪

Spectral Response Acceleration Ss and S1

Read from maps for short period and 1 second intervals for Oregon.

We get Ss = 1.5 and S1 = 0.6

MCE Spectral Acceleration

Use the tables!Site Class Ss ≤ 0.25 Ss = 0.5 Ss = 0.75 Ss = 1.0 Ss ≥ 1.25

A 0.8 0.8 0.8 0.8 0.8

B 1.0 1.0 1.0 1.0 1.0

C 1.2 1.2 1.1 1.0 1.0

D 1.6 1.4 1.2 1.1 1.0

E 2.5 1.7 1.2 0.9 0.9

F * * * * *

For Fa, we have Ss = 1.5 so Fa = 1.0

Site Class S1 ≤ 0.1 S1 = 0.2 S1 = 0.3 S1 = 0.4 S1 ≥ 0.5

A 0.8 0.8 0.8 0.8 0.8

B 1.0 1.0 1.0 1.0 1.0

C 1.7 1.6 1.5 1.4 1.3

D 2.4 2.0 1.8 1.6 1.5

E 3.5 3.2 2.8 2.4 2.4

F * * * * *

For Fv, we have S1 = 0.6 so Fv =1.5

SMS, SM1, SDS, SD1

SMS = Fa Ss = 1.0 * 1.5 = 1.5

SDS = (2/3) SMS = 1.0

SM1 = Fv S1 = 1.5 * 0.6 = 0.9

SD1 = (2/3) SDS = 0.6

Parameters

Site Class D

SS 1.5

S1 0.6

Fa 1.0

Fv 1.5

SMS 1.5

SM1 0.9

SDS 1.0

SD1 0.6

Seismic Use Group I

Period Parameters

N-S we have moment resisting frame system of steelFrom table, Ct = 0.028 and x = 0.8 and R = 5

E-W we have a braced frame systemThus Ct = 0.02 and x = 0.75 and R = 4.5

Seismic Base Shear Coefficient

Step 1 - Determine SS and S1 Step 2 - Determine site Soil Classification Step 3 - Calculate Response Accelerations Step 4 - Calculate the 5% Damped Design Spectral

Response Accelerations Step 5 - Determine the Seismic Design Category Step 6 - Determine the Fundamental Period Step 7 - Calculate Seismic Base Shear Coefficient

Seismic base shear coefficient

N-S: Cs = 1.0/(5/1.0) = 0.20

E-W: Cs = 1.0/(4.5/1.0) = 0.22€

Cs =SDSRIs

Seismic base shear coefficient

But, there are limits

Max value:

€

Cs =SDI

T RIs ⎛ ⎝ ⎜ ⎞

⎠ ⎟

We need the Period, T

Approx: Ta = Ct hnx

hn = 30.5

N-S: Ta = 0.028 (30.5).8 = 0.43 s

E-W: Ta = 0.02 (30.5).75 = 0.26 s

Maximum Cs values

N-S: Cs = SD1 I / (TR) = 0.6 * 1 /(0.43 * 5)

= 0.278

E-W: Cs = 0.514

Seismic Base Shear Coefficient

N-S: Cs = 0.20

E-W: Cs = 0.22

Vertical Distribution

We have just one story – mezzanine does not count because it is less than 1/3 of the footprint

F = Cv V = 1 V for single story building

V = Cs W

Loads

Snow load from map 25 psf Dead load on roof = 15 psf Mezzanine live load, storage = 125 psf Mezzanine slab/deck dead load = 69 psf Wall panels = 75 psf

Loads

On mezzanine, need 25% of storage load69 + 25%(125) = 100.25 = 100 psf

On roof, snow load is less than 30 psf, so not needed.

Roof

Projected roof area: 90 x 182 = 16,380 ft2

Inclined roof area: 90.32 x 182 = 16,438 ft2

Roof load: 15 * 16,438 = 246.5 kips

Mezzanine

Mezzanine area: 40 x 90 = 3,600 ft2

Mezzanine floor: 360 kips Mezzanine frames: 35 kips Main framing: 27 kips

Walls

Long walls: 2 x 32 x 180 x 75 / 2 = 437 Short walls: 2 x 35 x 90 x 75 / 2 = 224

Load by direction

Source E-W N-S

Roof D+L 243 243

Long walls -- 437

Short walls 224 --

Mezzanine slab 360 260

Mezzanine framing 35 35

Main framing 27 27

Seismic Weight 889 kips 1,102 kips

Shear force

V = Cs W N-S: V = 0.2 * 1,102 = 220.4 kips E-W: V = 0.22 * 889 = 195.6 kips