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 < 45 o

ASCE 7-02 Method 2: Analytical Method p = q(GC p ) – q i (GC pi )(ASCE 7-02, Equation 6-23) q = K z K zt K d V 2 I(ASCE 7-02, Equation 6-15) q is the "dynamic pressure" induced by the wind G addresses wind gusts and gust-structure interactions C (C p and C pi ) is a factor reflecting building geometry K z addresses terrain; varies with height above ground K zt addresses topographic effects (hills, escarpments) K d 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 illustration of wind loads on cladding 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

The Risk Model: Precedent and Cost Risks associated with building function –Mass hurricane shelters yr MRI –Health care facilities yr MRI –Facilities with nuclear materials - 1M yr MRI Cost considerations –Costs are developed for several risk levels –Trade-off between cost and MRI