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Hello all,

I am a student in my 4th year of civil undergrad. With a group, we have to work on the structural design ofa multistorey building. We have created a mock-up company and have received an architectural drawing forthe building. Right now we are doing preliminary report, and for that we need to present different design

alternatives. I have been assigned the task of calculating wind loads, snow loads already done!, dead" liveand their distributions #oading cases I guess$!.

I have all the data resources available to me for the location of the building.

I have been trying to figure this one out for a while and I can%t. &ational 'uilding (ode of (anada does notmake it clear what I am supposed to do. I need help with figuring out what to do with Wind #oads.

'uilding #ocation) *aughan Woodbridge!. It has two roofs, a main one and then a mechanical penthouse

that also houses the elevator shaft in one of its corners. We are thinking of making shear walls around theelevator shaft. +r steel bracing.

he building is surrounded by rough terrain on north and east. West side - highway and then rough terrain.outh side - small warehouses located about /00 m away and that%s it, the rest is open terrain.

+ do I design for open terrain$

I have to follow 1igure I-2/ for the case of my building, it%s a high-rise.

I am having a hard time figuring out coefficients.

3o we calculate wind load at different heights$ like at every floor$ 3o we take each face and calculate thewindward pressure$ 3o we calculate wind pressure for the whole building, and then for main structuralelements$ What is the difference in calculation$

he gust factor (g is .0 for the whole building, "-./ for small cladding and small elements. he internalgust factor, (gi, is .0. Where and how do I make use of this internal factor$

1or the pressure coefficient, (p, I can make an assumption and get the coefficient for the windward andleeward sides. How does the I&R&5# pressure coefficient fit into this$ 6y building falls into category 2.

(pi7 -0.2/ to 0. Why is it a range$

3o I take each building face and calculate the windward, leeward and sideface pressures$ hen do I design

for the ma8imum$ What about the leeward face$ when I take that face as a windward, what do I do in thevery end$ subtract leeward from windward to get overall effect on that face$ How does internal pressure fitinto all this$

he code gives specific gust factors and pressure coefficients for small elements or cladding. Isn%t the whole

building cover cladding$ 9lass and concrete:aluminum cladding$ Why then am I given the ;other;coefficients for whole building and main structural members$ How do they relate, interact$

If the roof has a parapet, with cladding, the (p is higher on roof and building corners. 3o I calculate windpressure on cladding and then see how this transfers over to the concrete parapet underneath the cover$How do I do this$

I have many more <uestions. I am really lost. What do i do with wind load$ If I have a steel framed roof, I

know I take into account wind uplift. What if I have concrete roof$ 3o I use only 2./ dead load " 2./ nowload$ How do I know if I should design for wind or seismic load$ How do wind lateral loads transfer into the

interior members$ a8ially on beams all the way to the shear wall inside$

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Here is the e8cerpt on Wind loading from +ntario 'uilding (ode 00=)

4.2.>.2. pecified Wind #oad

(1) he specified e8ternal pressure or suction due to wind on part or all of a surface of a building shall becalculated using the following formula)

p 7 Iw<(e(g(p

where,

p 7 the specified e8ternal pressure acting statically and in a direction normal to the surface, either as apressure directed towards the surface or as a suction directed away from the surface,

Iw 7 importance factor for wind load, as provided in able 4.2.>.2.

< 7 the reference velocity pressure as provided for in entence 4!,

(e 7 the e8posure factor as provided for in entence /!,

(g 7 the gust effect factor, as provided for in entence =!, and

(p 7 the e8ternal pressure coefficient averaged over the area of the surface considered.

Table 4.1.7.1.

Importance 1actor for Wind #oad, #W

1orming ?art of entence 4.2.>.2.2! and @!

Column 1 2 3

Importance (ategory

Importance 1actor, I

W

A# #

#ow 0.B 0.>/

&ormal 2.0 0.>/

High 2.2/ 0.>/

?ost-disaster 2./ 0.>/

(2) he net wind load for the building as a whole shall be the algebraic difference of the loads on thewindward and the leeward surfaces, and in some cases may be calculated as the sum of the products of thee8ternal pressures or suctions and the areas of the surfaces over which they are averaged as provided inentence 2!.

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(3) he net specified pressure due to wind on part or all of a surface of a building shall be the algebraicdifference of the e8ternal pressure or suction as provided for in entence 2! and the specified internal

pressure or suction due to wind calculated from,

pi 7 Iw<(e(gi(pi

where,

pi 7 specified internal pressure acting statically and in a direction normal to the surface, either as a pressure

directed toward the surface or as a suction directed away from the surface,

Iw 7 importance factor for wind load, as provided in able 4.2.>.2.

< 7 the reference velocity pressure, as provided for in entence 4!,

(e 7 the e8posure factor, as provided for in entence /!,

(gi 7 internal gust effect factor, as provided for in entence =!, and

(pi 7 the internal pressure coefficient.

(4) he reference velocity pressure, <, shall be the appropriate value determined in conformance withubsection 2.2.. based on a probability of being e8ceeded in any one year of 2-in-/0.

(5) he e8posure factor (e, shall be,

a! h:20!0. but not less than 0.C for open terrain, where open terrain is level terrain with only

scatteredbuildings, trees or other obstructions, open water or shorelines, h being the reference heightabove grade in metres for the surface or part of the surface,

b! 0.>h:2!0.@ but not less than 0.> for rough terrain, where rough terrain is suburban, urban or woodedterrain e8tending upwind from the buildinguninterrupted for at least 2 km or 20 times the building height ,

whichever is greater, h being the reference height above grade in metres for the surface or part of thesurface,

c! an intermediate value between the two e8posures defined in (lauses a! and b! in cases where the siteis less than 2 km or 20 times the building height  from a change in terrain conditions, whichever is greater,provided an appropriate interpolation method is used, or

d! if a dynamic approach to the action of wind gusts is used, an appropriate value depending on both height

and shielding.

(6) he gust effect factor, (g, shall be one of the following values)

a! for the building as a whole and main structural members, (g 7 .0,

b! for e8ternal pressures and suctions on small elements including cladding, (g 7 ./,

c! for internal pressures, (gi 7 .0 or a value determined by detailed calculation that takes into account thesiDes of the openings in the buildingenvelope, the internal volume and the fle8ibility of the building envelope,or

d! if a dynamic approach to wind action is used, (g is a value that is appropriate for the turbulence of the

wind and the siDe and natural fre<uency of the structure.

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I have a physical copy of the Aser (ommentaries of &'( 020 so I cannot upload it here. 6y <uestion is ifthere is a guide on what to do.

(an someone e8plain to me 2!, ! and @! in relation to each other$ he algebraic difference to memeans) ?windward - ?leeward, but ?leeward is -ve, so we would end up actually adding the absolute value

of ?leeward to ?windward$ ?leeward is on the other side of the building, so how does that help me with thewindload on the windward face$ What if wind blows on the leeward face$

Aghhhh. I know this is not formatted nicely. I don%t know how to make you follow it logically because I don%teven understand the steps to windload calculations. I ask my technical advisor and he doesn%t help me. ells

me to figure it out myself and make assumptions. 'ut my level of understanding of windloads is so low thatI would be making too many assumptionsE omeone help me please$

hank you in advance

The building is surrounded by rough terrain on north and east. West side - highway and then rough terrain.

South side - 2 small warehouses located about 500 m away and that's it, the rest is open terrain.

SO do design !or open terrain" 

Here is where you find a difference between the academic solution and typical practice. echnically youshould design each of the four principal wind directions based on the upwind e8posure condition for each

direction. In practice you usually design all directions based on the most e8treme e8posure condition.

herefore, if one side faces open terrain I would use open terrain for design in all directions.

am ha#ing a hard time !iguring out coe!!icients.

$o we calculate wind load at di!!erent heights" li%e at e#ery !loor" $o we ta%e each !ace and calculate the

windward pressure" $o we calculate wind pressure !or the whole building, and then !or main structural

elements" What is the di!!erence in calculation" 

here are two parts to wind load design. Fou have to design the lateral load resisting system of the building

as a whole for strength and stability and you must also design the individual elements on the e8terior of the

building supporting the cladding to resist the wind pressures. he pressure on the leeward side is constant,

calculated with (e at mid-height. he windward pressure varies with height based on value of (e.

The gust !actor &g is 2.0 !or the whole building, -2.5 !or small cladding and small elements. The internal

gust !actor, &gi, is 2.0. Where and how do ma%e use o! this internal !actor" 

he internal wind pressures are only used for the design of the cladding and its supporting structural

members. Internal pressures cancel out when you look at the building as a whole.

(or the pressure coe!!icient, &p, can ma%e an assumption and get the coe!!icient !or the windward and

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leeward sides. )ow does the *T+* pressure coe!!icient !it into this" /y building !alls into category .

&pi1 -0.5 to 0. Why is it a range" 

Internal pressures can vary due to a number of factors. 5gain, they are only used to design the cladding and

its supports. Fou would use the highest positive number in combination with the leeward e8ternal pressure

and the highest negative number with the e8ternal windward pressure.

$o ta%e each building !ace and calculate the windward, leeward and side!ace pressures" Then do design

!or the maimum"

Fou design for one principal wind direction at a time. ideface pressures are only for cladding design.

What about the leeward !ace" when ta%e that !ace as a windward, what do do in the #ery end" subtract

leeward !rom windward to get o#erall e!!ect on that !ace" 

Fou are not calculating net pressures on a face when you are designing the building as a whole, Gust the net

force acting on the building. Fou have to check your building for four wind load cases, one positive and one

negative in each principal direction.

)ow does internal pressure !it into all this" The code gi#es speci!ic gust !actors and pressure coe!!icients !or small elements or cladding. sn't the whole

building co#er cladding" 3lass and concrete4aluminum cladding" Why then am gi#en the other

coe!!icients !or whole building and main structural members" )ow do they relate, interact" 

Whole building and main structural members refers to design of the building%s lateral load resisting system

such as the bracing or shear walls.

What i! ha#e concrete roo!" $o use only .25 dead load .5 Snow load"

Fou should check for 0.C3"2.4W but you will <uickly discover that it never governs in a concrete roof.

)ow do %now i! should design !or wind or seismic load"

Fou have to design for both.

)ow do wind lateral loads trans!er into the interior members" aially on beams all the way to the shear wall

inside" 

Fes, or through the floor and roof diaphragms. It depends on your layout and the magnitude of the loads.

ry to use the diaphragms first.

&an someone eplain to me 67, 627 and 687 in relation to each other"

2! is the formula for calculating e8ternal pressures

! tells you how to combine the e8ternal pressures to design the lateral load resisting system of the

building@! tells you how to calculate net pressures on cladding and its supporting members.

The algebraic di!!erence to me means9 :windward - :leeward, but :leeward is -#e, so we would end up

actually adding the absolute #alue o! :leeward to :windward" 

Fes. Wind pushes on the windward side and creates suction on the leeward side. herefore these two forces

are in the same direction and should add together.

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:leeward is on the other side o! the building, so how does that help me with the windload on the windward

!ace" What i! wind blows on the leeward !ace" 

Wind cannot blow on a leeward face. If it did then the wind would have changed direction. Remember your

are creating different load cases by looking at one wind direction at a time. Fou have to check your building

for four wind load cases, one positive and one negative in each principal direction.