____________________________________________________
ARCH5023/ARCH4343 - ARCHITECTURAL
STRUCTURES II
CONCRETE
STRUCTURES
THE UNIVERSITY OF OKLAHOMA
- COLLEGE OF ARCHITECTURE
____________________________________________________
LATERAL
FORCES
CODES
CODES & REGULATIONS
Building Codes
control structural design
UBC - Uniform Building Code
West Coast
BOCA -Building Official Conference of America
Basic National Building Code
East and Midwest
SBC - Standard Building Code
Southeast
State Codes
New York State Code
Southern Florida Building Code
Wisconsin Administrative Code
BOCA
UBC NY,NJ,MA
SBC
South Florida Building code
Codes govern:
Minimum Required Live Loads
Use of occupancy
Wind Loads
wind speed
Snow Loads
geographic zones
Seismic (Earthquake)
Effects assumptions
Load Duration
fraction of a second - seismic
wind loads
Load Combinations
snow & wind
wind & seismic
Design Data for Type of Structures
material - load tables
specific structures - balconies
special problem - retaining wall
Fire Resistance
structural loss
control spread
Other Codes:
Plumbing
Electrical
Zoning
Ordinances
State
County
Town
Neighborhood Association
Regulations
ADA American Disability Act
Flood Plan
Military Construction
Army
Airforce
Corps of Engineer Manual
ASTM Specification
American Standard Testing Methods
AISC Specifications
American Institute of Steel Construction
LATERAL FORCES
WIND FORCES
P&A 565-569
Nature of Wind:
============
high wind
turbulent wind
open area
down-town (high-rise) construction
Wind Flow:
=========
stagnation point
at 60 - 70% of building height
wind splits into
upper
lower
left
right
separation flow
the flow separated from the building corners
is faster than other airflows nearby
descending flow
fast wind high above is
drawn to the ground level
to low pressure regions produced behind buildings
vortex flow
part of the wind sweeps down to the ground
and produces a reverse flow
the velocity of vortex flow is higher if there are
low buildings in front of a tall building
Monroe Effect
turbulence and up-lift created by
high-rise construction
Major Problems caused by Wind:
=========================
Buildings
difficulty opening and closing doors
imperfect ventilation
drafts
roof tiles blown away
secondary hazards of flying objects
broken windows
unpleasant whistling sound
rain blown into buildings
dust raised
building collapse
People
hair disarranged
clothing disordered
dificulty in walking
umbrellas break
Trafic
momentary loss of control
bicyclists fall over
Prediction of Wind Environment:
=========================
velocity and amplification ratios around various shape
Basic Wind Speed (Velocity)
======================
OKC is between the 70 mph and 80 mph zone
interpolate between 70 and 80
80 - 70 = 10
10 / 2 = 5
70 + 5 = 75
75 Mph Oklahoma
70 Mph accepted by most code
officials in southern part of Oklahoma
Exposure:
========
A, B, C, D
A = high-rise structures use wind tunnel test
B = irregularities 20 ft or more in height 1 mile
surrounding site Urban and suburban areas
C = open terrain with scattered obstructions less than
30 ft open country and grasslands
D = Coastal areas
see special regulations
UBC Code:
========
Wind Stagnation Pressure (qs)
qs = 0.00256 (V*V)
Example: 100 mph
qs = 0.00256 (100*100)
qs = 0.00256 (10,000)
qs = 25.6 psf
qs = 26 psf rounded
Design Wind Pressure (p)
p = Ce x Cq x qs x I
Ce = combined height, exposure and gust factor coefficient UBC 23-G
Cq = pressure coefficient for the structure or portion of structure under consideration UBC 23-H
qs = wind stagnation pressure
at 30 ft given in UBC Table 23-F
I = Importance Factor
BOCA:
======
Pd = Pe x I x I x Cp
Pd = Design pressure
Pe = effective velocity pressure
including gust effect
For Buildings & Structures
Exposure B
(Table 1112.3.3a)
lower 9
Exposure C
(Table 1112.3.3b)
higher 15
I = Importance Factor
Classification of Buildings
(Table 1112.2b)
Nature of Occupancy Category
Single Family I
with more than 300 people II
Essential Facilities (Hospitals) III
low hazard to humans (Storage) IV
Importance Factor
(Table 1112
Category 100 miles f. Ocean Ocean
I 1.00 1.05
II 1.07 1.11
III 1.07 1.11
IV 0.95 1.00
Cp = external pressure coefficient
Wall Pressure
Windward Wall 0.8
Leeward Wall - 0.5
Side Walls - 0.7
Roof Pressure
Wind Direction Angle
Normal to ridge
Parallel to ridge
Arched Roofs
Tanks
Solid Signs
Trussed Towers
Monosloped roofs over
unenclosed buildings
Open Signs & Lattice Framework
Design Methods:
============
Method 1 = Normal Force Method
simultaneous pressure
on all surfaces
Method 2 = Projected Area Method
single pressure
used for structures < 200 ft
Uplift:
=====
entire roof (stick-built construction)
entire structure (carports, decks)
local phenomenon (balconies)
Overturning Moment:
================
dead load resisting moment
= restoring moment
= stabilizing moment
overturning moment = dead load resisting moment x 1.5
if not fullfilled
provide anchorage to prevent overturning
entire structure turns over
tall and slender buildings = critical
individual elements may turn over
shear walls
trusses
frames
Drift:
====
= horizontal deflection of the structure due to lateral loads
max. story drift = 0.005 x story height
for masonry construction
max. story drift = 0.0025 x story height
affects
curtain walls
interior partitions
Special Problems:
=============
Tall Buildings
height
foot print
upper elevations
surrounding
Flexible Structures
vibration
flutter
movement
Unusual Shapes
open structures
structures with large overhangs
structures with projections
complex shape
(floorplan)
(elevation)
Combined Loads:
=============
wind effects are investigated as isolated phenomena
critical load combinations
required load combinations UBC Sect. 2303
UBC:
1. dead plus floor live plus roof life (or snow)
2. dead plus floor live plus wind (or seismic)
3. dead plus floor live plus wind plus snow/2
4. dead plus floor live plus snow plus wind/2
5. dead plus floor live plus snow plus seismic
Example Problem UBC Wind Loads:
Calculate the Design Wind Pressure (p)
under UBC 1997 edition
for a Hotel
100' long x 120' wide rectangular shape
10 floors
9' story height finished floor to fin. floor
flat roof
to be built in Downtown
Dallas, Texas
using concrete construction
A. Given:
UBC 1997 edition
Hotel
100' long x 120' wide
rectangular shape
10 floors
9' story height finished floor to fin. floor
flat roof
Downtown Location
Dallas, Texas
concrete construction
B. Asked:
Calculate the Design Wind Pressure (p)
under UBC 1997 edition
C. Graph:
10 floor
9' fl height
100' long
120' wide
Hotel
Concrete
Structure
Downtown
Dallas, Texas
D. Calculations:
1. Location
Dallas Texas
2. Obtain Basic Wind Speed
Basic Wind Speed Map
from UBC code
or
(Page 3/3 Report No 2093P in handout)
or use
(Fig. 1112.3.2 BOCA map)
3. Locate Dallas/Fort Worth Metro Plex
in hatched area
70 mph
4. Wind Stagnation Pressure (qs)
qs = 0.00256 (V*V)
qs = 0.00256 (70*70)
qs = 0.00256 (4,900)
qs = 12.544 psf
qs = 13 psf rounded
5. Design Wind Pressure (p)
p = Ce Cq qs I
Ce = combined height, exposure and gust
factor coefficient UBC 23-G
Cq = pressure coefficient for the structure
or portion of structure under consideration UBC 23-H
qs = wind stagnation pressure
at 30 ft given in UBC Table 23-F
I = Importance Factor
6. Ce = combined height, exposure and gust
factor coefficient UBC 23-G
7. Cq = pressure coefficient for the structure
or portion of structure under consideration UBC 23-H
8. qs = wind stagnation pressure
at 30 ft given in UBC Table 23-F
9. I = Importance Factor
E. Answer:
Example Problem BOCA Wind Loads:
Calculate the Design Wind Pressure (p)
under BOCA
for a Hotel
100' long x 120' wide rectangular shape
10 floors
9' story height finished floor to fin. floor
flat roof
to be built in Downtown
Dallas, Texas
using concrete construction
A. Given:
BOCA
Hotel
100' long x 120' wide
rectangular shape
10 floors
9' story height finished floor to fin. floor
flat roof
Downtown Location
Dallas, Texas
concrete construction
B. Asked:
Calculate the Design Wind Pressure (p)
under BOCA
C. Graph:
10 floor
9' fl height
100' long
120' wide
Hotel
Concrete Structure
Downtown
Dallas, Texas
D. Calculations:
1. Location
Dallas Texas
2. Obtain Basic Wind Speed
Basic Wind Speed Map
(Fig. 1112.3.2 BOCA map)
3. Locate Dallas/Fort Worth Metro Plex
in hatched area
70 mph
4. Pd = Pe x I x I x Cp
Pd = Design pressure
Pe = effective velocity pressure
including gust effect
I = Importance Factor
Cp = external pressure coefficient
5. Pe = effective velocity pressure
including gust effect
Height:
9' finished floor to finished floor
10 floors
h = 10 x 9'
h = 90' above grade
Basic Wind Speed = 70 mph
Exposure B
irregularities 20 ft or more in height
1 miles surrounding site
urban and surburban areas
Table 1112.3.3a for BOCA
Only valid for exposure C
(Note: BOCA uses a table
UBC uses formula = 0.00256 V x V)
Basic Wind Speed mph
70 mph
Height 60'-100' 14 lb/sqft
Pe = 14 lb/sqft
6. Importance Factor Wind
Occupancy Hotel
occupancy over 300 people
Classification of Buildings
Nature of Occupancy Category
Single Family I
with more than 300 people II
Essential Facilities (Hospitals) III
low hazard to humans (Storage) IV
Hotel = Category II
Location = Dallas
more than 100 miles from Ocean
Table 1112.2a(1)
Importance Factor / WIND
Category 100 miles f. Ocean Ocean
I 1.00 1.05
II 1.07 1.11
III 1.07 1.11
IV 0.95 1.00
I = 1.07 for Hotel in Dallas
7. Cp = external pressure coefficient
L/B
length to width factor
120/100 1.2
Wall Pressure coefficients
(Table 1112.2a(2)
Surface L/B Cp
Windward Wall all values 0.8
Leeward Wall 0 - 1 - 0.5
2 - 0.3
>= 4 - 0.2
Side Walls all values - 0.7
Roof Pressure
Wind Direction Angle
Normal to ridge
Parallel to ridge
Load Combinations:
Wind from right
Wind from left
h/L
9'/100' = 0.09
Roof Pressure
(Table 1112.2a(3)
Wind Direction h/L Angle
Normal to ridge <0.3 0 - 0.7
0.5 - 0.7
1.0 - 0.7
> 1.5 - 0.7
Parallel to ridge < 2.5 - 0.7 > 2.5 - 0.8
8. Pd = Pe x I x I x Cp
Pe = 14 lb/sqft
I = 1.07
Cp
Wall
Windward 0.8
Leeward - 0.3
Sidewall - 0.7
Roof
Normal to Ridge - 0.7
Parallel toRidge - 0.8
Pd = Pe x I x I x Cp
Pd = 14 x 1.07 x Cp
Pd = 14.98 x CP
Wall
Windward 0.8 x 14.98= 11.98
Leeward - 0.3 x 14.98= - 4.494
Sidewall - 0.7 x 14.98= - 10.486
Roof
Normal to Ridge - 0.7 x 14.98= - 10.486
Parallel toRidge - 0.8 x 14.98= -11.984
E. Answer
Design Pressure
Wall
Windward 11.98 = 12 psf
Leeward - 4.494 - 4.5
Sidewall - 10.486 -10.5
Roof
Normal to Ridge - 10.486 = -10.5
Parallel toRidge - 11.984 -12 ps
WIND RELATED LINKSS
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©Dr. Gruenwald
1996, 1997, 1998
