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Anchoring the masts and vertical antennas - 2

Martin Huml, OL5Y/OK1FUA, JLIB_HTML_CLOAKING

In the first part we talked about forces and the issues regarding anchoring in general; today we will talk about the mast itself. Before I begin I would like to thank for all your feedback, questions and other topics. I am glad that you were interested in the previous article and I will try to keep it that way.

In this sequel we will focus on the most basic version – the tube mast anchored in one level below the antenna. This situation is illustrated under figure 1. To simplify the calculations, we assume that the entire mast is the same tube diameter and has the same properties throughout its length. We will also assume that the wind velocity along the length of the mast is the same (in reality it is lower just above the ground).

mastr sily en

  When analyzing quantities and properties that affect the behavior of the system we get to this list:

  • the total height of the mast, height of the attached rope, distance of the anchor from the mast bottom (to determine forces affecting the system)
  • external and internal diameters of the tube (to determine the strength and the weight of the mast)
  • physical properties of the material from which the tube is made from: density, elastic modulus, strength limit, proportional limit (to determine the strength and weight of the mast)
  • area and weight of the antenna (to determine the wind resistance force)
  • coefficient of the resistance of the mast and the antenna (to determine the wind resistance force)
  • properties of the environment (air): kinetic viscosity, gravitation acceleration, air density
  • wind velocity

Outputs of the calculations we wish to obtain:

  • force in the axis of the mast bottom (action on the point of placement of the mast bottom)
  • force in the axis of the rope (for the selection of the suitable rope)

However, we will be interested particularly in safety - if the mast will survive and to what degree of safety.

But how to assess and compare safety if it has no unit and its expression in words is quite difficult and above all subjective? We will be probably unable to measure it. Construction sectors use a unit called safety coefficient. It is calculated differently for each type of structure, but its interpretation (sense) is always the same: If it is greater than 1, “there is a theoretical guarantee that the structure will survive”. The recommended minimum value is 1.4. If the safety of the structure involves several factors, the coefficient is calculated for each factor separately and the total safety of the structure is the smallest one of them. In our case, there are two critical factors: the strength of the material of which the mast is made (i.e. the tension in it), and the mast buckling (so the mast will not bend). Our considerations will result in the assessment of the total safety of the system.

From the foregoing, it is clear that there are a large number of quantities that are different for specific situations. Everybody has a different antenna, different mast, different mast height ... For illustration I have chosen several situations, that I find appropriate for demonstration and for which I calculated different outputs. In each case I chose the height of the rope attachment so that the total safety is the greatest. Individual variations are as follows:

  • The mast height of 13 m, on which an ECO antenna is placed (3el. tribander for 10/15/20m). This version is calculated for 3 different masts: tube diameter 80 mm with 3 mm thick wall from an average quality duralumin (ver. A), tube from the same material 100/4 mm (B) and steel tube 60/3 mm (C).
  • The mast height of 13 m with 11el. antenna for a 2 m band in two versions: average duralumin 60 mm in diameter with a 2 mm thick wall (D) and fiberglass 60 mm in diameter with a 5 mm thick wall (E).
  • The last version is a 23 m mast with a bulky antenna TH7DX (7el. tribander for 10/15/20m) again in 2 versions: high quality duralumin 100 mm in diameter with a 10 mm thick wall (F) and steel 100 mm in diameter with a 5 mm thick wall (G).

Other parameters used for calculations are: air density = 1.2 kg/m3, gravity acceleration = 9.82 m/s2, wind velocity = 36 m/s = 130 km/h, coefficient of mast and antenna resistance C = 1.2. The results are shown in table no. 1.

Quantity Symbol A B C D E F G Unit
11m duralumin ECO 11m duralumin ECO

11m

steel ECO

11m duralumin 11el. 2m 11m fibreglass11el. 2m 23m duralumin TH7DX

23m

steelTH7DX

mast - tube                  
total height h 13 13 13 13 13 23 23 m
height of rope attachment h_ki 12 12 12 11 9 17 20 m
anchor distance r_ki 10 10 10 10 10 15 15 m
external diameter D_o 80 100 60 60 60 100 100 mm
internal diameter D_i 74 92 54 56 50 80 90 mm
mast density ro_s 2700 2700 7850 2800 1200 2800 7850 kg/m3
elastic modulus E_s 60000 60000 200000 60000 18000 60000 200000 MPa
strength limit sigma_t 300 300 320 300 220 350 320 MPa
proportional limit sigma_tu 200 200 120 200 200 200 120 MPa
rope reaction F_ropex 1355 1486 1223 629 768 2446 2079 N
reaction in mast bottom F_forces in the axis of the mast 2023 2346 2153 856 858 4951 5808 N
reaction in mast bottom perpendicular F_axis -381 -492 -270 -267 -128 -376 -743 N
force in rope axis F_rope 2116 2321 1911 934 1034 3697 3466 N
antenna                  
area of antenna S_ant 0,82 0,82 0,82 0,18 0,18 0,9 0,9 m2
weight of antenna m_ant 15 15 15 3,5 3,5 40 40 kg
assesing the safety                
tension in the mast k_t 4,01 6,21 2,86 2,37 2,14 3,16 3,34  
buckling k_b 2,47 5,84 3,62 2,01 1,89 3,27 4,75  
total safety k 2,47 5,84 2,86 2,01 1,89 3,16 3,34  

In version (A) I wanted to show that although a relatively thick tube is used the total safety is not as perfect as some might expect based on their experience. This is because the arrangement of the system with a single anchor height is definitely not optimal and places high demands on the strength of the mast material. We will talk about other versions next time, but I can disclose that the strength of the system in dual anchoring is four times greater and even nine times greater in triple anchoring levels (of course, if they are placed in optimal heights). I have also included version (E) because I have seen similar masts being used by several radio amateurs.

material density elastic modulus strength limit proportional limit
  kg/m3 MPa MPa MPa
duralumin 2800 60000 180-450 x
aluminum 2700 60000 60-150 x
steel 7850 200000 320-835 120-290
fiberglass 1200 18000 220 x

Table no. 2: physical properties of the materials

In addition to its own safety system, it is also interesting to look at the distribution of some quantities along the length of the mast. This is shown in figure 2 (for version C) and 3 (E). If the anchoring height is chosen at a height to maximize safety, then the curve shapes are very similar - that is why I show only 2 typical examples.

dopl01

dopl02

Anchoring the masts and vertical antennas - 1

Martin Huml, OL5Y/OK1FUA, JLIB_HTML_CLOAKING

(note: all tables are available in Excel format)

During my radio amateur activities, I dedicate most of my time (probably like any one of us) to the question of antennas. And one of the most important and maybe the most challenging task is to get the antenna “into the air” and keep it there. Apparently this applies to all antennas, perhaps with the exception of beverage antennas... I wrote about this subject in the article “How to build and anchor simple antenna masts” (magazine “Radioamatér” 2 & 3/2004). At that time, I already felt that this issue is so interesting, complicated and extensive that it would be appropriate to return to it.

Another motive for writing the following article was to include the questions asked either by my friends or emerging on their own, e.g. “Why are you anchoring the vertical so low down?”, “Will this rope be strong enough?”, “Will this mast be able to carry the antenna?” and so forth. Most of the time I couldn't find a better answer than “because I think it's enough” or “because I saw it somewhere like that”. This doesn't sound very scientific.  Practice and experience are great and irreplaceable, but too much of it is guesswork, so when my activities brought me to “anchoring” I decided to look into it from the theoretical perspective as well. First, I would like to state that I am not an engineer; so, after studying some time, I consulted Engineer Richard Beber, who, unlike me, has studied this issue. Here, I would like to thank him - the article wouldn't have been written if it weren't for him.

Hence, as indicated by the name of this article, its main subject is focused on how to anchor antennas. This doesn't mean that owners of the non-anchored masts won't find something interesting. For instance, calculations of forces acting on the antenna in the wind or other matters might be useful.

Used terms and simplification

I ask the experts and linguists for leniency - I use these terms as I know them from amateur practice:

  • Place (point) of mounting = the place where the anchor rope is mounted on the mast
  • Height of mounting = the distance between the point of mounting and the mast bottom
  • Anchoring place (point) = the place where the anchor rope is attached to the ground (or other fixed point)
  • Distance of anchoring = the distance between the point of anchoring and the mast bottom
  • The system = the mast with antenna

 mastr sily en

A vertical antenna is actually a mast without the antenna. Therefore, where it is not appropriate in the following text, I will not distinguish between these two types of antennas. In other words, e.g. the phrase “anchoring in the middle of the mast” will have to be understood as “anchoring in the middle of the vertical”.

Unless stated otherwise, we assume that the mast is built on a horizontal surface; therefore, the anchoring points and the mast bottom are at the same level, perpendicular to the axis of the mast. This is for simplicity - the reality definitely tends to be different. Therefore, the following text will indicate how to deal with the reality.

In our considerations, we also do not deal with the behaviour of the antenna itself - we assume that the antenna on the mast does not change.

And, finally, for those who are not friends with physics - we will talk a lot about force, whose unit is 1 N (Newton). For instance, if you lift a weight of 1 kg, the acting force on you is approximately 10N.

The Antenna and the Mast

If we look at the simplified model of the anchored mast and the antenna at its top (fig. 1), the following forces will affect the system:

  • gravity force (mass of the mast, ropes and antennas)
  • resistant wind force,
  • Tension force of the anchored ropes.

This set of forces will produce a reaction so that the resulting forces will be balanced. The reaction will appear in the gripping of the mast bottom and in the places of mounting of the anchoring ropes. There will also be a flexible deformation of the mast and the ropes. In this respect, we do not consider the irreversible deformation or destruction of the material - it is these cases that we want to avoid and therefore we will focus on the identification of all acting forces.

But forces do not represent all factors that will influence the behaviour of the system. We must not forget about the structure of the mast (tube, lattice structure etc.) and the material of which it is made, especially its physical properties such as density (specific gravity), flexibility and strength. Similarly, we need to know the properties of the anchoring ropes - their strength and elongation. Let's summarise what we need to know: 

  • antenna - mass
  • antenna - shape (number, length and diameter elements)
  • mast - structure, material
  • anchoring rope - elongation (stretch at working load), strength

And the parameters with which we will be dealing are as follows:

  • total height (the height of the antenna above ground = the height of the mast)
  • the number of the anchoring directions (3 or 4)
  • the number of anchoring levels (at how many levels will the mast be anchored)
  • the height of the anchor mounting(s)
  • the distance of the anchoring from the base

The distance of the anchoring

The first question that we will address is the influence of the distance of anchoring on the size of the forces (acting on the mast and the anchoring ropes). We will divide this task into the following marginal situations - in the first case, the wind is blowing from the anchoring direction; in the second case, the wind is blowing “in between the anchors”. (fig. 2)

If the wind is blowing from the point of anchoring direction, it is a simple composition of forces - the case of a right triangle where one of the legs is the mast (h), the second one the distance between the mast bottom and the point of anchoring (r), where the anchoring rope is the hypotenuse (l). The proportion in which the individual legs of this triangle are is the proportion of forces acting in individual directions. We know (can calculate) the force Fant caused by the wind acting on the antenna. (Its specific value is not important at this moment; we will deal with it later - as we are now assessing the influence of the distance of the point of anchoring.) So the force on the mast (in its axis) is Fst = Fant * h / r, and the force acting on the anchoring rope is Fko = Fant * l / r. We will calculate the length of the rope by the Pythagorean Theorem: l = √(h2 + r2).

When the wind is blowing from the direction of the axis between the anchors the situation is somewhat more complicated, because we have to bear in mind the angle between the anchors - in other words, to how many directions the mast is anchored.

Anchoring directions

For this purpose we look at the mast from the top and introduce a total of 3 points - the mast and 2 anchoring points. Further we will introduce the direction from which the wind is blowing - it is the axis between the anchoring points going through the mast. The place where this axis intersects the connecting line between both of our anchoring points is a point that represents the virtual anchoring point for the calculation of acting forces. We see that it is much closer to the mast bottom than the anchoring distance - the closer it is, the larger the angle between the anchors.

This is again a case of triangles, but not necessarily right angle triangles. If we apply the basic goniometric functions we get to these relations:

For 4 anchors in 90°:

 

Fst = Fant * (h / r) * √2 = Fst = Fant * (h / r) * 1,414

Fko = Fant * (l / r) * (√2) / 2 = Fant * (l / )r * 0,707

for 3 anchors 120° each:

Fst = Fant * (h / r) / cos(60/180π) = Fant * (h / r) / 0,5

Fko = Fant * (l / r) / cos(60/180π) = Fant * (l / )r .

 

At a first glance, an interesting feature might not be seen - when anchoring in 3 directions the force acting on the anchoring rope is the same as with wind “from the anchor” as well as “in between the anchors”.

vitr

  

How does this look in practice

From the theoretical perspective, which is probably boring for most of us, we move on to practical effects. (I promise that the following text will be without formulas - they would be much more complicated ...)

For illustration, I chose a simple example - a mast 10 m high with a tribander (10/15/20m) on top. I repeat again – it is an example to show the impact of anchoring distance and the number of directions to which the mast is anchored.

Therefore we are not interested in the mast or rope properties. So - we let the wind blow on the tribander at 130 km/h. It can be approximately calculated that the wind's acting force is approximately 775N. How I got to this result will be explained in the next chapter; for now this result will do.

I will however mention a very important fact, i.e. that the force is proportional to square (squared) velocity (e.g. half velocity = quarter force; the force in the case of 80 km/hour will thus be approx. 290 N). However, the force grows at a similar pace – so you can then understand what a tornado with its wind velocity reaching over 300 km/h in its centre can do, so please do not think that cars flying the air are a mere invention of the American filmmakers.

But now back to anchoring. In the following tables you will see the force calculated for both versions of anchoring (3 and 4 directions) and for the anchoring of 10 and 5 m. I think it is obvious that bringing the anchoring points closer to the mast results in unnecessary increase of the acting forces. This is similar in case of anchoring into 3 directions, which increases the load on the mast.

High of the fixation 10 m
Distance of anchoring points 10 m
Speed of the wind 130 km/h
Direction of the wind number of directions Force [N] effecting:
guy-wire mast
from direction of the guy-wire 4 1 095    775   
between of the guy-wire 4 775    1 095   
from direction of the guy-wire 3 1 095    775   
between of the guy-wire 3 1 095    1 245   
High of the fixation 10 m
Distance of anchoring points 5 m
Speed of the wind 130 km/h
Direction of the wind number of directions Force [N] effecting:
guy-wire mast
from direction of the guy-wire 4 1 732    1 549   
between of the guy-wire 4 1 224    2 191   
from direction of the guy-wire 3 1 732    1 549   
between of the guy-wire 3 1 732    3 098   

 

As you can see, given a sensible layout, forces caused by such high wind are not so huge.  In other words - we do not need any extreme ropes for anchoring such an antenna. As can be found in a lot of places, even a relatively weak rope will endure if it’s designated for this purpose. The weakest places are all joints ... And in our conditions, we must not forget situations where the antenna is encased with frost... But this is really a distraction here and we will return to it.

Just to complete, one more paragraph - observant readers have definitely noticed that it is not about absolute height and distance - we will get the same results with mast of 20m and the distance of 20 and 10m. It is the angle formed between the anchoring rope and the mast. This should be acknowledged especially in situations where the anchoring point cannot be placed at a level perpendicular to the mast (it is on a slope). In such case, for example, if you had to place the anchoring point 3m lower than the mast bottom and you want to keep the angle between the rope and the mast 45° you have to place the anchoring point 13m from the axis of the mast (be careful, not from the mast bottom!). This can be hardly calculated at times, that is why it is possible to calculate and measure the length of the anchoring rope - in this case being 13*1,41 = 18.3m (1,41 = √2).

Wind force

If we place an object in the fluid stream, in our case the air, it will cause resistance by the friction and pressure elements. This resistance is determined experimentally in aerodynamic wind tunnels and is expressed in relation to the resistance force:

anchoring 1 formula ,

where FO is the resistance force [N], C is the resistance coefficient of the object (-), A is the area of the object perpendicular to the wind direction [m2], ρvz is the air density [kg/m3], &vvz is the wind velocity [m/s].

The value of the resistance coefficient is not constant, but depends on the so-called Reynold's number - non-dimensional criterion, expressing the ratio of inertial and viscous

Re = vvz * d / v ,

where d is the characteristic dimension [m] a v is the kinematic viscosity  of the air.

If we simplify the antenna (in our case a tribander) to several cylinders, then the characteristic dimension is the diameter and Re equals roughly 104 in normal conditions while the resistance coefficient of the object C is approximately 1.2. By the resistance force acting on the antenna (tube diameter d = 35 mm, length l = 23.6 m, wind velocity vvz = 36 m/s = 130 km/h; air density 1.2 kg/m3) we can determine:

anchoring 1 formula 2.

This force acts as a continuous load on the whole antenna (if we simplify the actual situation on the same velocity profile for the whole surface of the antenna). We can determine the resistance force acting on the mast in a similar way.

The following table illustrates forces calculated for several typical antennas (I apologize to those who can’t find their exact antenna in the table, please just extrapolate).

Antenna Wind area [m2] Force of the wind [N] at speed as [km/h]
50 130 180
HF - 3el. tribander ECO 0,82 116 765 1476
HF - 3el. tribander A3S 0,40 56 373 720
HF - 3el. tribander TH3JRS 0,32 45 299 576
HF - 7el. tribander TH7DX 0,88 124 821 1584
HF - 11el. 5-bander TH11DX 1,17 165 1092 2106
HF - 10el. LP 10-30m LP1010 1,49 210 1390 2682
HF - 5el. for 6m F9FT 0,13 18 121 234
HF - 5el. for 10m LJ105CA 0,37 52 345 666
HF - 5el. for 15m LJ155CA 0,49 69 457 882
HF - 5el. for 20m LJ205CA 0,84 119 784 1512
HF - 6el. for 20m HD OWA 1,80 254 1680 3240
HF - vertical 6-20m R6000 0,14 20 131 252
HF - vertical 6-40m R8 0,24 34 224 432
HF - Inv.V full-size 20-160m 0,90 127 840 1620
2m - 9el. 2M9 0,12 17 112 216
2m - 11el. F9FT 0,18 25 168 324
2m - 12el. 2M12 0,14 20 131 252
2m - 17el. F9FT 0,29 41 271 522
2m - 18el. 2M18XXX 0,30 42 280 540
70cm - 18el. 440-18 0,08 11 75 144
70cm - 21el. 440-21ATV 0,12 17 112 216
70cm - 38el. 432-13WLA 0,24 34 224 432
23cm - 35el. 23CM35EZ 0,06 8 56 108

  

What can be caused by frost?

The frost, which is a very important element in our calculations, affecting the function (as well as survival) of the antenna, causes

  • increase of the surface the wind effects and
  • mass gain.

Because I do not have any personal experience with the frost I have consulted this issue with a few friends who have their antennas on a variety of problematic places including those where the frost lasts several months. Their experience indicates that frost on the components adds up to 50-100 % and in extreme cases up to 200 % to their original diameter (the component then increases its diameter). Let’s see how much this increases wind loading.

The previous chapter shows that the resistance force of the wind is directly proportional to the surface of the antenna perpendicular to the wind direction and, therefore, to the diameter of its components. So if the diameter of the components increases 2x, it doubles the wind force. These are very easy calculations - if you wish to design an antenna system for extreme frost, multiply the forces by 3. 

The mass issue is more complicated. For its calculation, we need to know not only the thickness of the frost but also its density. Although the density of ice is 917 kg/m3, the density of frost stated in literature and standards is considered 400-500 kg/m3 - let 's calculate preferably 500 kg/m3. Since we are interested in the amount of increase of the mass of the standing antenna, we also need to know the density of the material, which it is made from. This is usually some aluminium alloy whose density is around 2800 kg/m3.

A brief remark about the calculation: for the sake of simplicity, we would again consider an antenna consisting of tubes or rods.  The mass of the object m = V * ρ, where V is the volume and ρ the density. The volume of the cylinder is V = π * r2 * l, where r is the radius and l the length. If we substitute the known values we will calculate the original mass and the mass of the frost. This is demonstrated below.

Design of element /boom Multiplication of weight with icing:
50% 100% 200%
Spar (all diameters) 1,2 1,5 2,4
Pipe ø 8 mm, wall 1 mm 1,5 2,2 4,3
Pipe ø 10 mm, wall 1 mm 1,6 2,5 5,0
Pipe ø 14 mm, wall 1 mm 1,8 3,0 6,4
Pipe ø 24 mm, wall 1 mm 2,4 4,4 9,9
Pipe ø 24 mm, wall 2 mm 1,7 2,8 5,7
Pipe ø 30 mm, wall 1 mm 2,7 5,2 12,1
Pipe ø 30 mm, wall 2 mm 1,9 3,2 6,7
Pipe ø 50 mm, wall 1 mm 3,8 7,8 19,2
Pipe ø 50 mm, wall 2 mm 2,5 4,5 10,3

 

The facts shown in the table may be shocking for some people. It is not easy to admit that the antenna consisting, for example, of tubes with 24mm in diameter with 1mm wall increases its mass in a 100% frost by 4.4 times! On the other hand, it is necessary to consider that the conditions for creating continuous frost on the entire perimeter of the tube, especially on those with larger diameters, are relatively rare in ordinary QTHs.

As a matter of interest, Wikipedia states the following about frost:

The frost is an atmospheric phenomenon that develops by creating ice crystals on the surface of the object by inflicting the following effects:

• freezing tiny droplets of the air's humidity (clouds, fog etc.) in it's contact with the surface of the ground, object or other subjects at the temperature of  0°C and below;

• precipitation (sublimation) of air's humidity on a sufficiently cold surface of the ground or subjects and that even without the presence of fog or clouds.

The highest probability of frost creation is with contact at a temperature (0 to -4 °C) between the surface of the object and the moist airflow. With temperature below -4 °C the possibility of frost creation decreases and at temperatures below -12 °C frost does not occur or is very weak.

The above data is interesting especially in the consideration of structure & design of the antenna - to what extent the components and the boom should be dimensioned and reinforced to avoid bending. That is again a completely different topic.

Next time, we will focus on anchoring a real mast, including considerations about its strength and other influencing elements. 

Guying ROHN Towers with MASTRANT Ropes

rohn with mastrant

Montageanleitung für Halteseile

  1. Berechnen oder messe sie die benötigte Länge der Abspannseile.
  2. Addieren sie dazu die Länge welche für eine sichere Befestigung (Seilkausche, Seilklemme, Knoten) benö-tigt wird. Die Länge ist ungefähr der 60-fache Durchmesser des Seiles.
  3. Schneiden sie das benötigte Seil mit einem heißen Messer ab. Alternativ kann das Seil auch mit einem scharfen Messer abgeschnitten werden. Nach dem Schneiden muss das Ende auf jeden Fall mit einer Flamme oder einem heißen Lötkolben verschmolzen werden. Der Kunststoff schmilzt bei 150°C (Dyneema) bis 260°C (Polyester).
  4. Legen sie die Seilkausche bereit. Sollte es notwendig sein, kann die Seilkausche mit einer Zange etwas auf-gebogen werden um sie über den Haltepunkt zu bekommen. Sie sollte dann aber auch wieder zugebo-gen werden. Kleine Unebenheiten oder Fehlstellungen (nach dem Zubiegen) haben keinen Einfluss auf die Zugfestigkeit.
  5. Legen sie die Seilklemme bereit und zerlegen sie wie auf dem Bild zu sehen.
  6. Legen sie das Seil um die Seilkausche und in die Seil-klemme (wie im Bild zu sehen). Dann schrauben sie die Seilklemme wieder zusammen. Das offene Ende des Seiles muss jetzt noch eine Länge von dem 35-fachen des Seiles haben (für die Sicherheitsknoten).
    recommended installation procedure 1
  7. Befestigen sie die Seilklemme so nah als möglich an der Seilkausche.
  8. Jetzt sind die Schrauben der Seilklemme anzuziehen. Mit Gefühl!!!!! Nun sind mit dem restlichen Seilende zwei Knoten zu machen. Das Seilende ist mit einem Kabelbinder zu sichern.
    recommended installation procedure 2
  9. Bedingt durch die Spannung des Seiles ist es notwen-dig die Seilklemmen immer wieder nachzuziehen (Seil wird unter Spannung dünner!).Sollten Sie den Ab-spannpunkt nach dem Aufbau des Mastes nicht mehr erreichen, dann müssen Sie die Muttern vorher schon kräftig anziehen.
  10. Bringen sie das Seil an der geplanten Stelle an und ziehen sie die Schrauben der Seilklemme vorsichtig etwas an.
  11. Überprüfe sie ob das Seil in den Seilklemmen ge-rutscht ist. Wenn dem so ist, muss das Seil nachgespannt werden.
  12. Ein Vorteil ist, wenn an den Abspannpunkten Seil-spannschlösser eingesetzt werden. Ausfahrbare Masten können auch ohne Seilspannschlösser abge-spannt werden. In diesem Fall sollten die Seile schon gespannt werden, wenn der Mast noch nicht ganz ausgefahren ist. Erst dann ist der Mast ganz auszufah-ren. Diese Prozedur ist aber von Mast zu Mast unterschiedlich.
  13. Die optimale Vorspannung der Seile hängt von ver-schiedenen Faktoren ab: Die Art des Mastes, Typ und Dicke des Seiles, Abstand zwischen Abspannpunkt und Maststandort. In den meisten Anwendungen sollte die benötigte Haltekraft des Seiles bei 5-20% der Fes-tigkeit des Seiles betragen. Und nicht vergessen!! Bitte für jeden Mast extra berechnen!
  14. Nachdem der Mast steht und die Seile auch richtig gespannt sind, sollte man auf jeden Fall die Spannung der Seite am nächsten Tag und dann im Abstand von einer Woche für einige Wochen kontrollieren.

Häufig gemachte Fehler durch die Unfälle entste-hen:

  • Der Abspannpunkt ist zu nahe am Mast und dadurch ist der Abspannwinkel kleiner 45°.
  • Die Seilklemmen wurden nach dem Aufstellen des Mastes nicht nachgezogen!
  • Hinter den Seilklemmen wurde keine zweite Klemme zur Sicherheit angebracht.
  • Es wurde keine Seilkausche verwendet sondern das Seil wurde direkt am Mast angebunden.
  • Das Seil wurde durch ein Tier oder einen Menschen beschädigt (angeknabbert, bzw. durchgeschnitten).

Grundlegende Richtlinien zur Verankerung mit synthetischen Seilen

Beim Entwurf eines „Verankerungssystems“ (Verankerungsseil mit Endstücken, Kupplungen und Seilklemmen) müssen folgende Faktoren in Betracht gezogen werden:

  1. Die Stabilität des Systems hängt von der Stabilität seines schwächsten Gliedes ab. Aus diesem Grund ist es nicht effektiv, ein 50kN starkes Seil mit einem Spannhalter von 5kN zu verwenden.
  2. Sogar das beste synthetische Seil ist elastisch – beim Abspannen dehnt es sich aus. Bei der Planung des Masts und seiner Verankerung (ebenso bei der Befestigung der Antennenteile), muss man diese Eigenschaft in Betracht ziehen und stets berücksichtigen, wie die Dehnung des Verankerungssystems die gesamte Konstruktion beeinflusst. In Einzelfällen muss ein stärkeres Seil benutzt werden (mit geringerer absoluter Dehnbarkeit), im Gegensatz zu Konstruktionen, die durch eine Verlängerung der Verankerung nicht negativ beeinträchtigt werden. Probleme entstehen vor allem dann, wenn sich der Bodenverankerungspunkt zu nah an der Mastbasis befindet bzw. unter Einsatz eines Gittermasts mit geringer Flexibilität.
  3. Das Seil muss außer Reichweite von scharfen Kanten sein. Es muss also mit einer Kausche befestigt oder an eine Kupplung mit sehr glatter Oberfläche gebunden werden. Achtung: Ungeeignete Metallmaterialien können korrodieren und ihre Oberfläche raut auf. Sie sollten niemals Seile an Betonsäulen oder Steinelement festbinden! Wenn Sie Stein, Fels oder eine Betonsäule als Bodenverankerungspunkt verwenden wollen, empfehlen wir den Einsatz einer Stahlseilschlaufe, die mithilfe einer glatten Kupplung am Abspannseil befestigt werden kann.
  4. Die größte Gefahr für Seile besteht bei Reibung mit Objekten, die sich in seiner Bahn befinden (z.B. Äste, Steine, Gebäudeteile...). Sogar abgespannte Seile bewegen sich im Wind, was zur Abnutzung des Seils führen kann. Besonders gefährlich ist Reibung an Ästen (Seil–Ast–Reibung). Diese bewegen sich unter Windeinfluss oft relativ stark und wenn das Seil an Ästen scheuert, ist die Wahrscheinlichkeit ernsthafter Beschädigung innerhalb weniger Tage extrem hoch. Wenn Sie Bäume zur Befestigung von Antennen benutzten, empfehlen wir den Einsatz von Stahlseilen in Biegepositionen über Ästen und die Verankerung des Stahlseils mithilfe von Seilrollen.
  5. Der untere Teil des Verankerungssystems sollte aus 2–4 m langen Stahlseilen bestehen um sicher zu stellen, dass das synthetische Seil nicht von Tieren „angeknabbert“ oder (absichtlich oder unabsichtlich) von Menschen beschädigt wird.

Der Abschluss des Seils ist eines der wichtigsten Sicherheitselemente.

  1. Abspannseile können am Ende mit einer Kausche zur dauer-haften Abspannung versehen werden. Oder sie werden direkt am Objekt angebunden.
  2. Wenn das Seil am Objekt angebunden wird, sollte sichergestellt sein, dass sich das Seil nicht bewegt oder scheuert. Besser ist es natürlich wenn das Seil zuerst an einem Schäkel oder Karabinerhaken befestigt wird. Und dieser wird dann im Befestigungspunkt des Mastes eingehängt.
  3. Auf jede Kausche muss natürlich eine Seilklemme folgen. Wir empfehlen Duplex-Seilklemmen oder einfache Seilklemmen mit Pressbacken. Hinter der Seilklemme sollte natürlich das offene Ende des Seiles durch ein weiteres Sicherungselement befestigt werden. Entweder durch eine weitere Klemme oder durch eine sogenannte Ankerbindung. Zu guter letzt sollte das offene Ende gegen Aufdrehen mit einem Kabelbinder gesichert werden.
     
     
  4. Other possibility is using crimped terminals (swaged “clips”). Those are only practical on one end of the rope – otherwise it is not possible to adjust the length.
     
  5. Abgespannte Seile verändern unter Last ihren Durchmesser, sie werden dünner. Deswegen sollten alle Klemmen nach einiger Zeit nachgezogen werden.
  6. Vorsicht vor den klassischen „bull-dog grips“. Diese Seilklemmen sind speziell für Stahlseile entwickelt worden. Wenn sie zu stark angezogen werden, können Sie das Kunststoffseil abschneiden. Wir empfehlen Ihnen unter keinen Umständen diese Seilklemmen als erste Klemme zu verwenden. Lediglich als zweite Sicher-heitsklemme könnten sie verwendet werden.
  7. Wir würden vorschlagen spezielle Abspannhalter zu verwenden. Leider sind sie relativ teuer. Aber sie bieten viele Vorteile und schonen das Seil. Durch spezielle Klemmbacken halten Sie das Seil, auch wenn es unter Zug dünner wird. Außerdem ist ein Nachspannen ohne weiteres möglich.
     

Häufig gemachte Fehler durch die Unfälle entste-hen:

  • Der Abspannpunkt ist zu nahe am Mast und dadurch ist der Abspannwinkel kleiner 45°.
  • Die Seilklemmen wurden nach dem Aufstellen des Mastes nicht nachgezogen!
  • Hinter den Seilklemmen wurde keine zweite Klemme zur Sicherheit angebracht.
  • Es wurde keine Seilkausche verwendet sondern das Seil wurde direkt am Mast angebunden.
  • Das Seil wurde durch ein Tier oder einen Menschen beschädigt (angeknabbert, bzw. durchgeschnitten).
  • Verwendung eines ungeeigneten Seil mit hoher Dehnung.
    guying with wrong rope

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  • 200m rolls of ropes 11. 9. 2016

    We extended our assortment by 200m (660 ft) rolls of all ropes and 500m (1650 ft) rolls of P 3, 4 and 5 mm.

     
  • Wir bieten neu 11. 12. 2015

    Safety harness LX4 - universal - M-XL

    Safety harness LX5 - profi with twist - M-XL

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  • Lengths by customer needs 29. 7. 2014

    Now you can order online ropes with different lengths than 100 m (1 reel). Check on-line shop!

     
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