Dear COADE staff,

Hello, I have a question for Wind Load.

According to ASCE 7-02, Wind Force is calculated by the following formula:
F = qzGCfAf
where:
F: Wind Force.
qz: Velocity pressure evaluated at height z above ground (N/m2)
qz = 0.613 KzKztKdV2I
Kz: Velocity pressure exposure coefficient evaluated at height z. (taken from Table 6)
Kzt: Topographic factor = 1.0
V: Basic wind speed (m/s)
I: Importance factor (taken from Table 5)
G: Gust effect factor (0.85)
Cf: Force coefficient to be used in the determination of wind loads (Table 7)
Af: Area of building (m2)

G is 0.85 and Cf is 0.7(refer to figure 6-19 of ASCE 7-02)

According to CAESAR II manual, the G Factor is not shown like Follow formula:

F = PeqSA
Where:
F = the total wind force on the element
Peq = the equivalent wind pressure (dynamic pressure)
S = the pipe element wind shape factor
A = the pipe element exposed area as shown in the figure as follows

If formula of ASCE 7-02 is applied, wind shape factor shall be 0.595(G x Cf). However if CAESAR II is applied, wind shape factor shall be 0.7 only.

What's the difference between ASCE 7-02 and CAESAR II?

Please give me the solution if you know about that.

Best regards,

The shape factor (Cf) is an input value - you define this in the Piping Input.

The gust factor defaults to 0.85 unless you define the 1st natural frequency of the piping system. If this frequency is defined, the equations in ASCE#7 are used to compute the gust factor. At the moment (ASCE-2005), you can find this information (and the equations) in Section 6.5.8. (In ASCE-2002 this section was in the Commentary.)

Thanks for your information.

But now I'm still confusing. That's why we have 3 methods to evaluate wind load in CAESAR II as follows.

1. Use ASCE#7 Wind Load Parameters
2. Use User-Defined Wind Pressure vs Elevation
3. Use User- Defined Wind Velocity vs Elevation

If we choose 2 or 3 method, we don't need to concern about any factor.
However if we choose 1 method, all factor including G(gust factor) should be inputted. But I can't find to input G factor anywhere in CAESAR II.
What I guess is wrong? And also, where is G?
I really want to know what I missed, why the different formula for wind force between ASCE-7 and CAESAR II shall be used.

One more, I will follow that The shape factor (Cf) is an input value by 0.7.

Thanks,

Best regards.

If you select the ASCE7 method, CAESAR II implements the equations from ASCE7 - there is no difference. The gust factor "G" is either (a) assumed to be 0.85 if you don't specify the first natural period (as required by ASCE7), or (b) computed according to the ASCE7 equations in Section 6.5.8.

If you select either of the "user-defined profile" methods, your input is only multiplied by the "shape factor", which you define in the Piping Input.

One question:

Where you can check the values pressure Vs elevation ,if you select ASCE7 method?

I´d like to check my manual calculation with Caesar calculation according by ASCE.

Thanks

CAESAR II does not report the internally generated element wind loads. For verification, you can define a "wind only" load case and sum the restraint loads.

Good morning Richard,

We have one question. We have the following data:
Basic wind speed: 49 m/s
Exposure category: B

We are using Caesar2 2016 and ASCE7-10
Our piping system is bellow 3,5 m and we are considering pressure vs elevation in Caesar 2.

We understand that in the input in Caesar2, we have to consider the mínimum design wind loading as per paragraph 29.8, which is 0.77 KN/m2.

Our question is:

This mínimum design force, we enter this value 0.77 directly in the wind user profile and also the factor 0.65 (for piping)in the input of Caesar.

Are we doing right?

Or we must consider the cf factor(as per tables 29.5-1 to 29.5.3) is already considered in the mínimum design force. And we don´t have to multiplied by it again.

Thanks a lot in advance

A basic wind speed of 49 m/s correspond to a basic wind pressure of 0.625*49^2 [Pa], where 0.625 is half of "standard" air density, so the first question would be why you input there the mínimum design wind loading.

ASCE 7 just asks for a design wind not less than 16 lb/ft2 (0.77 kPa).

My question was,

which was the value to input in Caesar 2?


0.77 Kn /m2 and in the input of Caesar2 a cf=0.65
or the mínimum design force 0,77Kn/m2 in the wind user profile, and cf=1,in the input

because we already considered cf with the force (F=qz*G*cf*Af) and as per paragraph 29.8:

MINIMUM DESIGN WIND LOADING
The design wind force for other structures shall be
not less than 16 lb/ft2 (0.77 kN/m2) multiplied by the
area Af.

What I tried to say is that your approach based on "0,77Kn/m2" seems to ignore the data you have, i.e. Basic wind speed: 49 m/s, Exposure category: B. So the answer to your question is neither of your alternatives, except when your calculation shows values less than 0.77 kPa.
BTW, for the formula I've written, ASCE 7 considers the coefficient of 0.617 instead my 0.625- which is by EuroCode.

You can input data in Caesar under ASCE 7 template and give credit to software. It is expected that, based on your input, Caesar shall calculate qz as per 29.3-1, G as explained Mr.Ay- see above, Cf may be as per Figure 29.5-1 and is actually as per your input. The calculated qz*G*Cf, as per ASCE 29.5-1 requirements cannot be less than 16 lb/ft2 (0.77 kPa), you can check software considered ASCE 7/ 29.8.

In case you prefer to input an "user-defined profile", your have to calculate yourself max(qz*G*cf; 0.77kPa) on vertical axis and input it in software. Indeed, in this case does not make sense to input again Cf value in software (you can force it as 1 value in Caesar) because your inputted profile will be (probably unconservative) multiplied by the Cf when calculate the force acting on members.

Thanks a lot Mario

ok, I understood the answer, we don´t have to input cf again.
But,Could someone else confirm this issue?

Because in the paragraph 29.8 it´s said:

The design wind force for other structures shall be
not less than 16 lb/ft2 (0.77 kN/m2) multiplied by the
area Af.

But also in the definition of Af,

Af = projected area normal to the wind except where Cf
is specified for the actual surface area,in ft2 (m2)

"Cf" is typically about 0.6 for pipes. The equation CAESAR II uses to determine the force on each element is:

F = Cf * Af * pressure

You state above that you're defining the pressure in the "wind input". You need to define "Cf" in the piping input, otherwise CAESAR II won't know there is wind on the elements.

You can verify your understanding of the input and operation of the software by running a two or three element cantilever and verifying the load (reaction) manually.

But, in my case, I consider cf=0.65 in the input and

In the "wind user profile" pressure vs elevation 0.77 Kn/m2 (which is the mínimum)

Is it right?

The load on your elements is therefore:

Load = 0.65 * 0.77 * "projected area in M2".

The AISC Standard defines a minimum pressure, not a minimum element load.

I don't think so, because 29.8 refers to "design wind force", even refers to 16 lb/ft2 (0.77 kN/m2) as pressure units. That's I still think that the unit force on member is max(qz*G*Cf; 0.77kPa)*Af

ASCE 7-10, 29.8 MINIMUM DESIGN WIND LOADING
The design wind force for other structures shall be not less than 16 lb/ft2 (0.77 kN/m2) multiplied by the area Af.

I'll have to check the Standard again, I don't have it here with me.

In any event, "qz*G*Cf" is how CAESAR II computes the element load. You need a non-zero value for "Cf" to tell the software that the elements have wind. You can adjust "Cf" or use a multiplier on the "WIND" primitive in the load case editor.

But where to input Elevation in CII when we are using ASCE#7 for wind calculations.

In the piping editor, you specify the elevation of the first node with Alt+G. You can also access this function under the "Edit" menu, and in the toolbar.

You may alternatively also specify wind vs elevation in the wind load editor in a few different ways.

Edit to add:

By default the first element is 0,0,0. When you specify wind loads in the input editor the first time, it asks you where you want the origin to be.

if you use ASCE#7 for wind calculations you must go to global coordinates and insert elevation from ground.

correct but what Elevations to be used for ground to be 0.000 ?

as when we use Elevation V/s pressure or velocity profile, there we correlate the elevation coordinates with input coordinates, but when we are using ASCE#7 we are not know what is base/grade elevation taken in to calculations.

We can't tell you what the reference point is for your project. Your project lead has to direct you to that information, or you have to field verify.

Being the distance from ground to your element, I guess you can enter the 3D model and measure. For example a pump suction would be at around 500 mm ...800mm above earth.

If on iso the elevation is something 100.500 you can imagine that 100.000 is reference elevation so in global coordinate you will not insert 100.500 but 500 (if in mm)