L. Prieto-Portar - 2008EGN EGN- -5439 The Design of Tall
Buildings 5439 The Design of Tall BuildingsLecture 10 Lecture
10ASCE 7ASCE 7--02 Solved Problem #3:02 Solved Problem
#3:Analytical Method 2 for Tall BuildingsAnalytical Method 2 for
Tall BuildingsThe building for this third example is a 14-story
office building in Tampa. It is 100 feet wide and 200 feet long and
160 feet tall, including a 3 foot parapet. The structure is a
reinforced concrete rigid frame, with each floor and the roof
providing a diaphragm reaction to lateral loads. Each floor is 11
feet high, and is clad with two glazing panels 5 6 high and 5 feet
wide (aluminum mullions are spaced 5 feet on-center). The glazing
is resistant to wind-borne debris impact.For simplicity, the office
building is assumed to be in an Exposure B. It is not an essential
facility, nor will it be occupied by 300 people in a single area at
one time. Therefore, it is a Category II (see Table 1-1 on the next
slide).Example #3 will use the same location in downtown Tampa as
in Examples #1 and #2.For this Example #3 site, use V = 120 mph.( )
( )( )( )( )( ) ( )( )( )220 00256 0 00256 1 0 0 85 120 1350
3113157 31 3 1 12 (= = = == = = =z p pizz z zt d z zz hThe design
pressure p is,p q GC GCwhere the velocity pressure q is,q . K K K V
I . K . . . . KUsing ASCE-7-02, Table 6-3,at z feet . , q q . .
psfThe Gust Effect Factor, G.The building has a ratio of h / least
width = 160 ft / 100 ft = 1.6 < 4 which means that it can be
classified as a rigid structure. The gust G is given by Equation
6-4,( )( )( )( )( )( )( )( )( )( )min1 1.7 1 1.73.4 0.25 0.830.925
0.925 0.831 1.7 1 1.73.4 0.253.4 ( 6.5.8.1)0.6 157 94.2 (
6.5.8.1)30 ( 6 2)0.30 ( 6 2)33Q zv zQ vzg IQGgIwhere g g Sectionz
ft Sectionz z ft Tablec TableI cz + +( = = = ` `+ +( ) )= == == = =
|=\( )( )1 16 61 13 30.63 0.63330.30 0.25 ( 6 5)94.294.20.30 454 (
6 7)33 331 10.83100 1571 0.631 0.63454zzEquationzL c ft EquationQB
hL| | |= = ||. \ .| | | |= = = ||\ . \ .= = =+| | | |+++ | |\ .\
.The External Pressure Coefficients Cpfor walls.The external
pressure coefficients for the wall surfaces are taken from Table
6-6:Therefore, the wall Cp is,The Roof Pressure Coefficients Cpfor
winds normal to the 200-ft walls.For the first value and h/L =
157/100 ~ 1.6 > 1.0 and< 10 the roof pressure coefficients
are also given by Figure 6-6,Cpfor wind normal to the200 ft wall.C
Cp pfor wind normal to the 100 ft wall. for wind normal to the 100
ft wall.The second value of Cp= -0.18 is a small value and is not
used in this example.The roof Cpwith wind normal to the 100 ft
face, h/L = 157/200 ~ 0.8. Notice that interpolation is needed in
Figure 6-6.The external pressure at the roof at a distance from 0
to h/2 = 157 ft / 2 = 79 ft from the edge with the wind normal to
the 200 ft face.The external pressure at the roof at a distance
from 79 ft to 100 ft from the edge with the wind normal to the 200
ft face.( )( )( )35 1 0 83 1 04 30 3 = = = z pThe external design
pressure p is,p q GC . psf . . . psf( )( )( )35 1 0 83 0 70 20 4 =
= = z pThe external design pressure p is,p q GC . psf . . .
psfComparison of pressures between the two orthogonal faces.
Comparison of pressures between the two orthogonal faces.How do the
pressures change if some of the windows are breached?Internal
pressure coefficients GCpi.If the windows are breached by debris,
the building becomes a partially enclosedbuilding. In that case,
the internal pressure coefficient becomes,The negative internal
pressure piwill be evaluated using qi= qh= 35.1 psf,Negative
internal pressure = qh(GCpi) = (35.1 psf)(-0.55) = -19.3 psfThe
positive pressure is found at the height z = 90 ft and qzis found
through inter-polation,Positive internal pressure = (30.0
psf)(+0.55)= 16.5 psf( )z p i pip q GC q GC = 0.55piGC = Wind Force
on the Roof Parapet.The pressure on the parapet with MWFRS
ppis,Since the parapet is 3 feet high, the force on the parapet in
the MWFRS case is as follows,These forces are shown in the figures
of slides #14 and #16.( )( )( )( )35.4 1.835.4 1.1p p pnp p pnp qGC
psf for the windwardparapetp qGC psf for the leewardparapet= == = (
)( )( )( )( )( )35.4 1.8 3 191.235.4 1.1 3 116.8windward p pn
wallleeward p pn wallF qGC h psf feet plfF qGC h psf feet plf= = ==
= = References. References.1. American Society of Civil Engineers,
Publication ASCE 7-02, Minimum Design Loads for Buildings and Other
Structures, Washington DC, 2002;2. W. C. Bracken PE, Wind Load
Design, Florida Engineering Society, Tallahassee, 2007;3. K.C.
Mehta, J.M Delahey, Guide to the Use of the Wind Load Provisions of
ASCE 7-02 ASCE Press, Washington DC, 2003.Arizona cactus flower
