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Assignment No.2 (Wind load analysis By ASCE 7-02)

Data on Design Problem (Wind load analysis)

My Serial No = 33

Nature of Building: Typical Office Building

Stories: 30 + 33 = 63 StoriesFirst floor height: 17ft

Typical storey height: 13 ft

Building height, h: 17 + (62x13) = 823 ft.

Location: Toronto, Ontario

Wind speed V: 110 mph

Terrain: Flat, open country with scattered obstructions having the size of single-family

dwellings, height generally less than 30 ft

Plan dimensions: 98.5 ft (B) x 164 ft (L)

Building lateral-load-resisting system: moment frame with shear walls.Fundamental period T= 3.12 sec.

The building is regular and it does not have unusual geometric irregularities. It does not have

response characteristics that would subject the building to across-wind loading, vortex

shedding, or instability due to galloping or flutter.

The building does not have a site location for which channelling effects or buffeting in the wake

of upwind obstructions warrant special consideration.

The building is sited on the upper half of a 2-D ridge and has the following topographic

conditions:

LH = 100 ft, H = 100 ft x = 50 ft (See Fig. 1.11)Damping factor: 1.5% of critical; the building is for typical office occupancy

Air density = 0.0024 slugs/ft3

Mode exponent = 1, KZT = 1

Coefficient Cfs = 1.3; Building density = 0.287 slugs/ft3

Requirements:

1. Determine the wind pressure on the windward and leeward sides as well as total windpressure on the building.

2. Total load/ft at each floor level and the Total base shear.

3. Overturning moment (OTM) at each floor level and total OTM.4. Calculate maximum along wind deflection and acceleration.5. Comment whether the building is safe based on drift index and comfort based

acceleration under dynamic wind gust effect.6. 30-Story Building on flat ground (computer program solution)

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DESIGN

Step 1: Building Classification

The building is for office occupancy with certain areas designated for the congregation of more

than 300 people. From Tables 1.7 and 1.7a, the classification of the building for wind loading:

Category: III Importance factor for wind Iw = 1.15.

Step 2: Building Exposure: Exposure category is B

Step 3. Basic Wind Speed V:

Basic wind speed V = 110 mph, as given in the statement of the problem.

Step 4. Determination of Gust Response Factor (G or G f)

Definitions according to which building may consider flexible

The building's height-to-least horizontal dimension is 823/98.5 = 8.4, greater than 4, So thebuilding is not flexible. It is rigid.

But according to the 2nd

definition natural frequency (1/T) = 1/3.12 = 0.32 less than 1Hz so, it is

flexible.

Therefore, gust effect factor G must be determined.

Determination of Gust Response Factor

V = wind speed in ft/sec

= Vmph x

= = 161.33 ft/sec= 0.6 x 823 = 493.8ft greater than zmin = 30ft (from Table 1.9) OK

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C =0.3 (Table 1.9) l = 320 (Table 1.9) and (Table 1.9) Q = the background response

=

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n1 = natural frequency = (1/T) = 0.321 Hz

=

=

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=

x ( 0.53 + 0.47

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G = 0.8378

Determination of along wind displacement

= 0.5013.909

Maximum along Wind displacement:

Air density = 0.0024 slugs/ft3; Mode exponent = 1, KZT = 1;

Coefficient Cfs = 1.3;

Building density = 0.287 slugs/ft3

Mass of the Building per unit height (z) = 0.467 x 98.5 x 164 = 7543.92 slugs / ft3

m1= z x (h/3) = 7543.92 x (823/3) = 2069548.72 slugs Xmax(z) is also commonly referred to as lateral drift, . Tall buildings are usually designed for a

drift index

. In our case,

, indicating that the building is

quite stiff.

=

Determination of along wind acceleration

= 3.909 x= 0.655 ft/s2= 0.655 x 31.11 = 20.38 milli-g

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Step 5. Directionality Factor Kd

Kd = 0.85 (Table 1.8)

Step 6: Combined Velocity Pressure, Exposure Coefficient Kz(windward) and Leeward (Kh)

Using Table 1.6 and formulas (vary with height)

Calculated in the table of calculations

Step 7: Determination of topographic factor, Kzt

The building is located on a 2-D ridge, may experience higher winds than buildings situated on

level ground and topographic effects should be considered.

For the given values of Lh, H, and x the multipliers K1, K2, and K3 are obtained from Fig. 1.11LH = 100 ft, H = 100 ft x = 50 ft (See Fig. 1.11) and substituting 2H for Lh for evaluating K2 and K3.

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Upwind of crest () = 1.5 ; = 3

Evaluating K2 and K3

( ) Calculated in the table of calculations

Calculated in the table of calculations

Step 8: Velocity Pressure qz (windward) or qh(leeward)

Step 9: External pressure coefficients, Cp (windward and leeward) Complete calculations are given in the table