Lecture 2 ACES Wind Load Lect

7/29/2019 Lecture 2 ACES Wind Load Lect

1/41

ASCE 7 Wind Loading Provisions

CE 6999c

Lecture 2


2/41

Wind Loads

When structures block the flow of wind,the winds kinetic energy is convertedinto potential energy of pressure.


3/41

Wind Loads

The effect of wind on structuredepends:

Density of the air

Velocity of the air

Angle of incidence of the wind

Shape and stiffness of the structure

Roughness of its surface.


4/41

Wind Loads

For design purposes, wind loading canbe treated using:

Static Approach: Most common

approach.

Dynamic Approach: Building or other

structures not meeting requirements ofsection 6.5.1 (ASCE 7-05), or havingunusual shapes or response characteristic .


5/41

Wind Loads: Static Approach

The fluctuating pressure of constantlyblowing wind is approximated by amean velocity pressure:

is air density

- V is air velocity

2V

2

1 =q


6/41

Wind load: Static Approach

Previous equation is modified toaccount for:

Structure Importance (I)

Structure Height (Kz) Structure Location (terrain)

Considering the factors previously

mentioned, the mean velocity pressurebecomes:

)lb/ft(V00256.022IKKKq dztzz =


7/41

Wind load: ASCE 7-05 (cont.) Where:

V= Velocity in mi/h of a 3-second gust of wind measured

at 33 ft above the ground during a 50-year recurrenceperiod.

I = The importance factor that depends upon the natureof the building occupancy.

Buildings with low hazard to human life, in a non-hurricaneprone region:

Agriculture facilities have I = 0.87 Hospital facilities have I = 1.15

Kz = The velocity pressure exposure coefficient, which isa function of height and depends upon the groundterrain.

Kzt = A factor that accounts for wind speed increases dueto hills and escarpments. Flat ground Kzt = 1.

Kd = factor that accounts for the direction of the wind. Itis used only when the structure is subjected tocombinations of loads. If wind alone is to be consider, Kd= 1


8/41

Figures and images


9/41

Table for KD and I

Table 6-1: ITable 6-4: KD


10/41

Table 1-1: Occupancy Category of building and other structures


11/41

Table 1-1: Occupancy Category of building and other structures(cont.)


12/41

Topographic Factor, Kzt


13/41

Exposure B: Example


14/41

Exposure B: Example


15/41

Exposure B and C: Example

ExposureC


16/41

Exposure C: Example


17/41

Exposure C: Example


18/41

Exposure D: Example


19/41

ASCE/SEI 7-05 Method 1 Simplified Procedure (permitted

for regular shaped low-rise buildings) Method 2 Analytical Procedure (permitted

for re ular sha ed buildin s and structures

not susceptible to across wind loading orother special considerations due to location)

Method 3 Wind Tunnel Procedure (for all

structures)


20/41

Method 1 Simplified Procedure

Main Wind-Force Resisting System(MWFRS): An assemblage of structuralelements assigned to provide support

and stability for the overall structure.The system generally receives windloading from more than one surface.

Components and Cladding: Elements ofthe building envelope that do not

qualify as part of the MWFRS.


21/41


22/41


23/41


24/41


25/41

Mean Roof Height

h2

1

21

then,10If

2

then,10If

hh

hhh

o

o

=

+=>


26/41

Example


27/41


28/41


29/41


30/41


31/41

Method 2 Analytical Procedure


32/41


33/41


34/41

Example


35/41


36/41


37/41


38/41


39/41


40/41


41/41

Lecture 2 ACES Wind Load Lect

Documents

Transcript of Lecture 2 ACES Wind Load Lect