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Ensure legs are vertical; feet are level & cannot slide. Ensure that both feet & guys are secured to something that cannot move**. Guy must be anchored out a distance 2/3 the leg height. Tighten guy lines to about 400 lbf & ratchet ropes to 120 lbf.
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Installing Tentnology Marquee tents is fun & easy when done right. Most of the Tentnology Marquee tents are free standing, needing no anchorage to stand inside a building. However, placed outside, they must be held down properly so you can sleep at night.
**Something that cannot move…meaning here, an anchor. One of the perennial mysteries of tenting seems to be anchoring them. I will try to demystify it here, mindful that whatever lies below the ground surface is usually unknown to the installer.
Wind acts on surfaces, either pushing or pulling it. Wind increases with height above the ground. The higher the tent, the more the tent is exposed to higher wind speeds. Since most Tentnology Marquees are similar height, let’s set aside the height question for now.
The greater the surface exposed to the wind, the higher the forces on the tent. Although experts may engage in obscure debates on whether it is better to have an open or closed tent in high wind, we’ll leave the debate in the conference room & deal with the reality of Tentnology Marquees. More surface => higher force. So, this means an open tent on level ground far away from a cliff’s edge will attract less wind force than the same tent with walls on.
However, do not think for a minute fewer walls will lower the force. It won’t. Simply put, since the area potentially exposed to the wind will be bigger. So, expect the force to be greater than if the tent were fully enclosed. Our computer modelling & years of field trials of the Marquee tents confirms:
If you expect high winds:
- Re-tension all lines, check all anchors, ensure feet cannot move
& legs are plumb vertical
- Close all walls or Remove all walls
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As my grandfather would say, “Batten down the hatches”. Of course if you can, orient any openings to the lee of prevailing winds or gusts.
The installation is only as good as the weakest link. If the sub-soil is loose sand or top soil, when that 45 knot gust hits you may see your tent click its heels crying “Auntie Emma, Auntie Emma” as it sails off into the Land of Oz. So, what you anchor into or tie off to is quite important.
Asphalted or un-surfaced unconsolidated earth & compact clays
This represents perhaps 85% of the typical situation to date. The 22” x ¾” (560 x 18 mm) galvanized steel stake issued with the Marquee is usually adequate for these soils.
Sand
Sand is really variable. There are small to large augers available in hardware stores or hydro hardware suppliers that can do. However, limestone deposits can also be hidden under Florida soil. This means an anchor might go in 12" then encounter an obstacle. Someone knowledgeable should test the site soil conditions & report back so we can supply the most appropriate anchor or assortment of anchors. It may consist of a variety of duck-bills, augers, spikes, etc.
No staking allowed?
Ballast
The best arrangement for ballast anchoring in my opinion was client designed (see below). Please note the clever & almost invisible rubber under the foot. This rubber pad is there to resist sliding. The rubber pad increases friction & is glued/riveted to the metal ballast bar. Furthermore, the barrel holder has rubber attached to its bottom to resist its sliding or swivelling about under high wind. The web strap that retains the barrel would be more effective if attached to the same hook as the guy line, but in general, the arrangement is excellent.
Other useful information for the professional engineer:
1. Water as ballast....See attachment. Water is about 10 lb/gallon. A 45 Imp Gallon drum can contain 450 lb water. You need to develop pretension of 200 lbf per guy & resist a total force each guy of so many lbf tension (see table attached). Technically, weight required to anchor safely depends upon friction which depends upon what the barrels are made of & what the surface is made of that the barrels sit upon. As well, the installer must be mindful that whatever he ties the guy line to might tip over, spoiling his erstwhile cunning plan. Furthermore, water evaporates or may be sucked up by thirsty horses at a polo match. Surfaces change with temperature, ie ice forms changing friction
coefficients from 10 to .1, etc.
Beware of walking feet. If the tent feet are allowed to move, the legs go out of vertical & may destroy the water shedding slopes critical to a good stable installation. In such cases, water pools weighing hundreds of pounds might form, causing the eventual collapse (usually not catastrophic, but nonetheless, damaging & disturbing) of the party tent & the party. In short, as popular as water barrels & other ballasting is amongst tent people, it really is an unreliable, tricky method & in windy regions should be practiced only by those who have a good understanding of the physical world & the mechanics that keep it together. The pictured arrangement makes ballasting easy & we recommend it.
2. MQ10 = 10 ft x 10 ft square plan view tent, 100 sq ft
MQ5M = 5 m x 5 m = 16.4' x 16.4' square plan view tent, area 269 sq ft or 25 m2.
Hex10M = MQ10MHex = Hexagonal plan view tent 10 meters across corner to diagonally opposing corner, area 700 sq ft.
Analysis of the MQ 10m Hex tent with walls, 2 sides open emulates a worst case scenario. Maximum shear force*** = 825lbs. Maximum down-force at a leg = 1089lb; Minimum down-force at a leg = 213 lbs. The tent did not incur a lifting force under any of the conditions tested by our analysis.
***Shear means the foot will want to slide. It must be prevented from sliding as sliding will loosen the fabric causing flutter, more drag, loosened guy lines, higher stress & rain water pooling. Legs must be vertical & feet secured against 1000 lbf shear.
The maximum tension in a guy line is 525lbs. The rope has a breaking strength of 2200 lbs yielding a safety factor of 4.2. Pretension the guy line to keep frame deflection to a minimum. If you are in a very wind-exposed area you might want to double up on guy lines or use cable guys to keep the frame from moving too much.
This analysis used the same velocity pressure with the same rationale as for the MQ5m. The only difference is the mean roof height is 14' which is still below 15' and therefore the same Kz.
The tent was tested with wind blowing into the two open sides, and against two closed walls. When the wind was blowing into the tent, we deemed it to be partially enclosed and used an internal pressure coefficient of ±0.55. When the wind loading was against the closed side of the tent, we deemed it enclosed and we used an internal pressure coefficient of ±0.18, in accordance with IBC-2003.
Our software program applied the 4.52 PSF velocity pressure to the tent and calculated the external pressure coefficient based on the tent's shape. * (to International Building Code 90 MPH Basic Wind Speed, factored for typical situations in suburban exposure yielding 4.52 psf)
Even more details:
Stress Analysis
Done to IBC-2003/ASCE 7-02 (Equivalent)
Velocity Pressure
qz=0.00256 Kz Kzt Kd V2 I ASCE Eqn 6-15
P= qzCpG ASCE Eqn. 6-17
Our program calculates as: P=qzCp
So by basic manipulation: qz=0.00256 Kz Kzt Kd V2 I G
To Find qz we need: Basic Wind Speed, v Importance, I Exposure Coefficient, Kz Topographical Factor, Kzt
Wind Directionality Factor, Kd Gust Effect Factor, G
Basic Wind Speed, v
V=90 MPH From IBC Fig 1609 Corresponds to Majority of USA
Wind speed can be reduced because the MRI (mean return interval) is <5 years.
From ASCE Table C6-3, V=85-100 Multiply basic wind speed by 0.78 V=0.78 (90) V=70.2 MPH
Importance, I
Building falls Category I, Certain Temporary Facilities
I=0.87 from IBC Table 1604.5
Exposure Coefficient, Kz
Exposure Category: B Urban/Suburban Area From IBC 1609.4 Mean Roof Height “The average of the roof eave height and the height to the highest point on the roof surface.”
Eave Height = 99.25” Max Roof Height = 236.25” Mean Roof Height = 167.75” =14’ With: Exposure B, Mean Roof Height =14’
Case 2 (This is for design of Main Force Resisting System) From ASCE Table 6-3 Kz = 0.57
Topographical Factor, Kzt
Assume area of tent is going to be set up in has no topographical effects.
Kzt = 1.00 From ASCE 6.5.7
Wind Directionality Factor, Kd
This structure is a building so:
Kd = 0.85 from Table 6-4
Gust Effect Factor, G
This structure is Rigid, so
G = 0.85 From ASCE 6.5.8
Velocity Pressure. qz
qz=0.00256 Kz Kzt Kd V2 I G
Kz = 0.57
Kzt = 1.00
Kd = 0.85
V = 70.2 MPH
I = 0.87
G = 0.85
qz= 0.00256 x 0.57 x 1.00 x 0.85 (70.2)2 x 0.87 x 0.85
qz= 4.52 PSF = 0.0314 PSI
Pressure Coefficients, Cp
External Pressure coefficient:
Cpexternal = -cos (theta)
For more explanation see the report
Internal Pressure Coefficient
Cpinternal is dependent on the enclosure classification The structure has 2 walls open. If the opening is facing the direction of wind, the structure is partially enclosed as the openings on open edge are greater than 20% of the area of the openings on the rest of the tent.
If a wall is facing the wind, the structure is enclosed as it doesn’t fall into the categories of Open or partially enclosed.
Cpi = +.- 0.55 @ 0 Deg
Cpi = +,- 0.18 @ 120 Deg
TentCAD XP version 0.8.54 used: Highlighted values were entered
Weight of Fabric: 0.0007475 PSI Weight of Cable: 0.0017 PLI
All 4 beams have same material constants?
NO
Beam 1: 2.5x0.100 Beam 2: 2.5x0.120 Beam 3: 2.5x0.120 Beam 4: 2.5x0.100
(For Beam groups and section properties see HERE.)
Wind Pressure Calculation:
Manual
P= -0.0314 PSI (DD said pressure must be entered negative to agree with Cosine Model)
Input Material Constants:
Wind
Type of Pressure coefficient:
Cosine Wind load model
Internal Pressure coefficient: 0.55, -0.55, 0.18, -0.18 (0.55 for 0 Deg, 0.18 for 120 Deg)
Direction: 0 , 120
Number of Steps: 10