We know that it is impossible to check what Caesar does as regards applying Wind Loading because there is no wind loading output from Caesar to do a "sanity" check. However I have just performed a test for ASCE 7-10 wind loading with strange results.
The "model" I created was four distinct horizontal sections of pipe not connected together and separated by 10000mm height difference. (So the first pipe was at 10m level - 2nd pipe at 20m level- 3rd pipe at 30m level and 4th pipe at 40m level.) The initial end of the pipes were anchored. I applied the wind loading perpendicular to these 4 pipes. I applied only wind loading. The results of the analysis showed that the reactions on all four anchors were the same. In practice this cannot be since the wind pressure must change with height. There is an error within Caesar for ASCE Wind Loading. I changed the wind loading Code and sure enough the reactions changed for each level. There should be output showing what wind loading is applied to each pipe so the USER can check that it has been applied correctly by Caesar internally.

Sounds like you're saying the wind loading code (ASCE 7-10) and whatever you changed it to the second time around are the real culprit? Because you're saying Caesar did what you expected when you changed codes.

I could be wrong but I don't think ASCE has any factor for multiplying the basic wind speed with changes in height. Maybe the second code you chose does change with elevation?

I would've thought the anchor forces would be different regardless due to extra leverage as the pipe got taller and more surface area for the force to apply pressure.

The wind load will change with height, assuming your above the minimum that ASCE sets. Note that wind loading increases in a parabolic shape, therefore the loading changes more a lower heights than at higher heights.

If you want us to look at the model, file a Support Request (SR) on Smart Support and send in your model.

Hi Richard,
I agree with what you say but try it yourself. Model say 4 pipes all the same diameter running horizontal as follows:-

Node X Y Z Node X Y Z
10 0 0 0 20 0 10m 6m
100 0 0 0 200 0 20m 6m
1000 0 0 0 2000 0 30m 6m
10000 0 0 0 20000 0 40m 6m

So we have four pipes above each other 6m long and 10m apart vertically.
Place anchors at Nodes 10,100,1000 and 10000

Now apply a ASCE wind to the model in the +x direction. Use a Cf of say 0.7 to all pipes.

Run the analysis and see what the loads are on the anchors. You will find that they are the same for each pipe. Which is fundamentally wrong. Wind pressure increases with height.
If you change the wind Code then the anchor loads are different as would be expected increasing with height.

I believe the ASCE Code has not been implemented correctly.

I've created three 10' sections of 4" sch 40 pipe at elevations of 10', 20', and 30', at 150 mph winds. Each pipe is anchored on one end, and and guided and supported on the other. No fluid, temperature, or pressure. A106 Gr B.

Lateral loads on the anchored ends are 109, 110, and 115, and the guided ends are 65, 66, and 69.

Rotational loads in the Y axis are 217.6, 220, and 225.4.

Rotational loads in the lateral axis are equal, because all pipes weigh the same.

In Caesar under aprox. 200 ft/sec (60m/s), the loads will be the same regardless the elevation. You can check in your model.
What speed did you used?
I need to check in ASCE for more info.

Hi danb,
If that is the case then Caesar must be wrong. The wind speed I used was 45m/s which is less than 60m/s which means that the loading does not change. You are correct when I changed the wind velocity to 70 m/s then the loads varied vs height. Strange how the wind loading changes for all of the rest of the Codes which can be chosen except for the ASCE Code. Thinking logically the wind loading is the wind loading and the wind pressure must change vs height no matter what the wind speed is - it is pure physics. The wind profile changes versus height.

About your remark about "pure physics": in engineering when working with SI units, the EuroCode basic wind pressure is 0.625*W^2 [Pa], where 0.625 is just half of "standard" air density. ASCE 7 considers the coefficient of 0.617 instead 0.625 because they have other "standard" conditions.

Considering the height of interest for structures under discussion here and the above equation, the only reason the wind pressure changes vs height is that the wind speed changes vs height.

In engineering, few decades ago a speed wind profile power law with exponent 1/7 was very popular. As a result, a power law with exponent 2/7=1/3.5 (or even 1/4 or " double square roots" rule, more friendly with an "ancient" hand- calculator) were applicable for wind pressure. ASCE Code and European Code just follow more sophisticated equations. But always a minimum pressure has been considered, otherwise near ground calculation will impose near-zero loads.

About your issue: by 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.
However, for ASCE the design pressure is- in their terminology- qz*G*Cf, so is not so simple to find out to which speed corresponds this minimum design pressure i.e. 16 lb/ft2 (0.77 kN/m2). As I know Caesar calculates "G" and consider it in calculation, however doesn't report it as value.

mariog And your point is???

If you computed (wind) load is less than the ASCE minimum, CAESAR II sets the load to the minimum. So it is possible that you end up with what looks like a constant load versus elevation.

Well if that is the case, which I believe is fundamentally wrong especially when considering other wind Codes, I believe the Caesar documentation should clearly indicate that this is the case. The User should be able to check what the software is doing in the background and what wind loads are applied on each element. This is a failing with Caesar as so much is done in the Black box but how can the analyst be sure of what Caesar is doing is correct???

Dear DBS1958,

Your posts are full of words like "wrong" and "fundamentally wrong".
I'll quote from Caesar Documentation and the capital letters are part of the original:
THE USER OF THE SOFTWARE IS EXPECTED TO MAKE THE FINAL EVALUATION AS TO THE USEFULNESS OF THE SOFTWARE IN HIS OWN ENVIRONMENT

In my opinion it is very useful to be aware of what a Code says, before having so strong opinions on forums.
ASCE 7 imposes a minimum load and explains in C29.7 MINIMUM DESIGN WIND LOADING
"This section specifies a minimum wind load to be applied horizontally [...]. This load case is to be applied as a separate load case in addition to the normal load cases specified in other portions of this chapter."

True, Caesar does not consider it as a separate case because does not implement the cases as shown "in other portions" of ASCE 7.

ASCE 7 loads are considered in piping analysis under provisions of other Codes, for example B31.3, 301.5.2 Wind. "The analysis considerations and loads may be as described in ASCE 7." You may see, as a detail, that the ASCE cases are not required or suggested to be implemented, just "analysis considerations and loads" may be as per ASCE.

"Thinking logically" (to quote you), in case the loads comply with the stuff "as described in ASCE 7", what exactly is "wrong" here?

mariog,
Comments taken on board and duly ignored!!!

Caesar is just a tool. If you don't understand the Code you're working with, you shouldn't be running the analysis. If you disagree with the Code, feel free to send them an email.

DBS1958, I hope your decision to duly ignore my comments just emphasize your determination to study the ASCE Code. Thinking logically, that's not wrong at all.

Anubis,
Strange you saying that Caesar is just a tool. You concur with the understanding of analysis software I have had for the last 45 years whilst working in engineering. I actually thought your statement enlightening.

mariog,
I do not need to study the ASCE Code. It would seem that the Code has some strange limitations which other Wind Codes do not. The possible limitations are probably due to the fact that the ASCE Code is basically for "Buildings" and we are dealing with "Pipes". To use the same "minimum" loading for a pipe as for a building is OTT from my point of view. Granted it is in accordance with the ASCE Code but it is for "Buildings" not "pipes". The problem is that the Caesar Documentation does not clarify what Caesar does in its "black box" so how can the User check what wind loading is being applied and why? That's the point!!!

Your point is valid, no doubt for me. Caesar may be improved in presenting the details of calculation. For example, the "G" factor is still within "the black box", as I know- and this really makes hard any checking.

Of course you are right about ASCE 7- it is just a building code, and the logic of implementing a minimum pressure was because there are surfaces where, under the prescriptive loads, you would have a pressure close to zero or negative that may not produce the worst case counting the total lateral force for stability analysis. That's why it is required a separate case considering the minimum design pressure.

But it is worst than you presumed and maybe you would find useful to study the ASCE Code.

Starting with ASCE7-10 the wind loads are ultimate loads, rather than service level loads. The value of minimum design pressure raised from 10 psf (pre ASCE 7-10) to 16 psf exactly for this reason.

Here B31.3 would be improved. Up to ASCE 7-10, things in B31.3 were clear.
For example, B31.3-1984 said "The method Of analysis may be as described in ANSI A58.1 or the Uniform Building Code", B31.3-2008 said "The method of analysis may be as described in ASCE 7".

But starting with B31.3-2010 the statement is "The analysis considerations and loads may be as described in ASCE 7".

In my opinion, when working with ASCE 7-10 or -16 as reference (where the loads are intended to be ultimate loads) , the solution would be to consider the combination loads according 2.4 Load Combinations for Allowable Stress Design, where you can see 0.6W as term. Does not make sense? May be a part of the "analysis consideration" under ASCE 7-10 or -16, why not?

As a detail, that would recover the same value as previously in ASCE 7 i.e. 10 psf as minimum design pressure. At this pressure level, for a rigid part of piping, wind speed must be about 36 m/sec which is about 80 mph and note that this is 3-sec gust basic wind speed (for other meteorological reference you must correlate the value, for example this is about 67 mph as fastest mile wind speed). Anyway, I find the value reasonable.

At least the "g" factor has pretty simple equations to check; I've made a quick Excel sheet that matches Caesar's output to confirm.

I think Caesar does a good job of being up front about what it does and how it does it. If you want to really peak behind the curtain you're essentially talking about seeing how the computer code goes through the steps for each load case. That's both likely proprietary and extremely time consuming.

The biggest issue (in this case) seems to be you expected the forces to do one thing and they didn't. That's not a knock on Caesar - As Richard Ay said, if loading is less than the ASCE minimum, they use the minimum to be conservative.