Lateral Loads
Lateral Load sources

Wind
 Tornado, 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
Wind Scale
BEAUFORT SCALE ÊOriginal scale developed in 1805 by British naval officer SirÊFrancisÊBeaufort.
Beaufort Scale
Beaufort
International
Miles per
Description
Number
Description
Hour
0
Calm
1
Light Air
1-3
2
Light Breeze
4-7
3
Gentle Breeze
8-12
4
Moderate Breeze
13-18
Raises dust and loose paper
5
6
Fresh Breeze
Strong Breeze
19-24
25-31
7
Moderate
(or near) gale
Gale
(or fresh gale)
32-38
Small trees in leaf begin to sway.
Large branches in motion; whistling heard in telegraph
wires; umbrellas used with difficulty.
Whole trees in motion; inconvenience in waling.
39-46
Breaks twigs off trees; generally impedes progress.
9
Strong Gale
47-54
Slight structural damage occurs.
10
55-63
Trees uprooted; considerable damage occurs.
11
Storm
(or whole gale)
Violent Storm
64-72
Accompanied by widespread damage.
12
Hurricane
73*-136
8
Less than 1 Calm; smoke rises vertically.
Direction of wind shown by smoke but not by wind
vanes.
Wind on felt on face; leaves rustle; vanes move.
Leaves and small twigs in constant motion.
Devastation occurs.
*The U.S. uses 74 statute mph as the speed criterion for hurricanes.
Saffir-Simpson Hurricane Scale
Sustained 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
Tornado Classifications

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 MPH
Well-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.
Hurricane Frequency
14
Number of Hurricanes
12
10
8
6
4
2
0
1945
1955
1965
1975
Year
1985
1995
2005
Global Warming
Global Average Temperature vs. Number of
Pirates
16.5
2000
1980
Global Avg. Temperature (C)
16
1940
15.5
1920
15
1880
14.5
1860
1820
14
13.5
13
35000
45000
20000
15000
5000
Number of Pirates
400
17
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.
Windward roof shallow
enough to feel suction.
Breakpoint approx 20°.
Leeward Roof
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 as
 Agricultural
facilities
 Certain temporary structures
 Minor 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
Occupation Category
I
✪
II
✪
III
IV
II
III
✪
✪
Occupancy Importance Factors
Seismic Use Group
I
II
III
Is
1.0
1.25
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 Classification
Site Class
vs
N or Nch
su
>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
600 – 1,200 ft/s
15-50
1,000 – 2,000 psf
<600 ft/s
<15
<1,000 psf
A: Hard Rock
D: Stiff soil
E: Soil
F: Soil requiring sitespecific evaluation
1.
2.
3.
4.
Soils vulnerable to potential failure or collapse
Peats and/or highly organic clays
Very high plasticity clays
Very thick soft/medium clays
Vs =measured shear wave velocity
N = 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 acceleration
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
*
*
*
*
*
* 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 acceleration
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
*
*
*
*
*
* 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
S DS
Cs 
R
Is
SDS = design spectral response in short period range (g)
R = response modification factor for structure
Is = occupancy importance factor for seismic use group
Cs 
However, Cs has a max value of

Use the smaller value
SDI
 
T R I 
 s 
SD1 = design spectral at 1 second

T = fundamental period of the structure (s)
Design spectral accelerations
SDS = (2/3) SMS
SD1 = (2/3) SM1
SMS = Fa Ss
SM1 = Fv S1
Fundamental period
Actual 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 forces
Lateral 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 V
where
Cvx 
w x hxk
n
k
w
h
 ii
i1
wi is the portion of total gravity load of W at level I
hi = height from base to level I
with T ≤ 0.5 s; 2 when T≥2.5 s (interp between)
k = 1 for building
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 Class
Site Class
vs
N or Nch
su
>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
600 – 1,200 ft/s
15-50
1,000 – 2,000 psf
<600 ft/s
<15
<1,000 psf
A: Hard Rock
D: Stiff soil
E: Soil
F: Soil requiring sitespecific evaluation
1.
2.
3.
4.
Soils vulnerable to potential failure or collapse
Peats and/or highly organic clays
Very high plasticity clays
Very thick soft/medium clays
Seismic Use Group

Seismic Use Group
First need occupancy
category
I
II
 Low
occupancy,
Occupation
Category
I

Category I
II
III
IV
III
industrial
building
✪
✪
✪
✪
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
Site Class
S ≤ 0.25
S = 0.5
S
Ss1 == 0.75
0.3
S1s == 0.4
1.0
S
SSs1 ≥≥ 1.25
0.5
A
A
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
B
B
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
C
C
1.2
1.7
1.2
1.6
1.1
1.5
1.0
1.4
1.0
1.3
D
D
1.6
2.4
1.4
2.0
1.2
1.8
1.1
1.6
1.0
1.5
E
E
2.5
3.5
1.7
3.2
1.2
2.8
0.9
2.4
0.9
2.4
FF
**
**
**
**
**
Site Class
Ss1 ≤ 0.1

Use the
tables!S1s = 0.2
For Fav, we have S1s = 1.5
0.6 so Fav =1.5
= 1.0
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 steel
 From

table, Ct = 0.028 and x = 0.8 and R = 5
E-W we have a braced frame system
 Thus
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
S DS
Cs 
R
Is
N-S: Cs = 1.0/(5/1.0) = 0.20

E-W: Cs = 1.0/(4.5/1.0) = 0.22
Seismic base shear coefficient
But, there are limits
Max value:

Cs 
SDI
 
T R I 
 s 
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 load
 69

+ 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
889 kips
1,102 kips
Seismic Weight
Shear force
V = Cs W
 N-S: V = 0.2 * 1,102 = 220.4 kips
 E-W: V = 0.22 * 889 = 195.6 kips
