### THE BUILDING ENVELOPE: Lecture 4

```THE BUILDING ENVELOPE: Lecture 4
Designing the Building Envelope
Design Responsibility: Fee Structure
• Architect: building function and aesthetics
• Engineer: principal structural frame
Design Responsibility: Building Type
• High-rise and commercial - Architect
• Industrial (metal) buildings- Engineer
• Residential buildings - Builder/A/E
Criteria for Design
• Meeting Building Code Minimums
• Risk Analysis Approach
Criteria for Design: Code Minimums
ASCE 7-02 outlines three methods for
computing wind pressures
• Method 1: Simplified Method
• Method 2: Analytical Method
• Method 3: Wind Tunnel Analysis
ASCE 7-02 Method 1: Simplified Method
Nine criteria must be met:
(1) a simple diaphragm building
(2) a low-rise building
(3) an "enclosed" building
(4) of regular shape
(5) not flexible
(6) have no special wind sensitivities
(7) have no expansion joints
(8) sited with no topographic effects, and
(9) approximately symmetrical with roof slope < 45o
ASCE 7-02 Method 2: Analytical Method
p = q(GCp) – qi(GCpi)
q = 0.00256 Kz Kzt Kd V2 I
(ASCE 7-02, Equation 6-23)
(ASCE 7-02, Equation 6-15)
q is the "dynamic pressure" induced by the wind
G addresses wind gusts and gust-structure interactions
C (Cp and Cpi) is a factor reflecting building geometry
Kz addresses terrain; varies with height above ground
Kzt addresses topographic effects (hills, escarpments)
Kd addresses directionality of the wind
V is the design wind speed
I is the importance factor for the building
ASCE 7-02 Method 3: Wind Tunnel Method
[ Note: Leighton Cochran will provide an
determined from wind tunnel tests]
Criteria for Design: Risk Analysis Approach
• The Risk Model
• Precedent and Cost
• Appropriate Level of Risk
The Risk Model: Hurricane Occurrence
The Risk Model: V vs MRI
250
W in d S p e e d (m p h )
200
150
M e a n H o urly
100
O ne M inute
F a ste st M ile
50
P e a k G ust
0
10
100
1000
R e turn P e rio d (Ye a rs)
10000
The Risk Model: Precedent and Cost
Risks associated with building function
– Mass hurricane shelters - 500 yr MRI
– Health care facilities - 300 yr MRI
– Facilities with nuclear materials - 1M yr MRI
Cost considerations
– Costs are developed for several risk levels
– Trade-off between cost and MRI
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