SPACE TRUSS SYSTEMS TECHNICAL RULES :
The rules that used during analyzing, manufacturing and assembling are below :
• TS 648 RULES FOR CALCULATION AND MAKE OF STEEL STRUCTURES
• TS 3357 CALCULATION AND MAKING RULES OF WELDING CONNECTIONS IN STEEL CONSTRUCTIONS
• TS 498 LOADS FOR THE CALCULATION OF THE SIZE OF STRUCTURAL MEMBERS
These systems have high hyper static degree. Therefore they solved by using computer without making any simplification. We use SAP 90 program which analyze with matrix method. All the live loads act to the spheres at nodes. With the help of spheres at nodes the loads transfer to tubes as linear forces. By the tubes, loads transfer to the supports.
Loading which can make moment in tubes is not acceptable for tubes of Space Truss Systems if otherwise is wanted. These elements are designed by using elastic theory under the loads getting from static analyze
Uzay kafes sistemin statik analizinde göz önüne alınacak yük kriterleri;
3.1 Dead Loads
The loads of the system members (nodes, tubes, Purlins, roof cladding
3.2 Live Loads
If the system is used as slab you must noticed the live loads.
3.3 Service Loads
Climate channels, electricity lines and apparatuses, suspended ceilings, etc.
3.4 Snow Load
3.5 Wind Load
3.6 Earthquake Load
3.7 The Effect of Temperature
PARTS THAT MAKE THE SYSTEM
System consists of tubes, conical ends, screws and spheres. The force of pressure in tubes is transferring to the spheres with the help of conical ends; the tension force on the other hand is transferring with the help of screws. The norms of quality and safety tension values of these materials are listed below.
4.1 Tubes
These elements are designed by using elastic theory under the loads getting from static analyze. They have a high capability to be welded with less carbon according to DIN 17100. They are ST 37.2 or ST 52.3 types pipes.
|
St 37.2
|
3,700 - 4,500 kg/cm 2 |
2,400 kg/cm 2 |
St 52.3 |
5,200 - 6,200 kg/cm 2 |
3,600 kg/cm 2 |
According to the project ,they can be selected from the pipes that are produced by TS 301/3 and DIN 2440.
|
|
26.9 mm |
2.65 mm |
2.02 cm2 |
|
33.7 mm |
3.25 mm |
3.11 cm2 |
1 ¼" |
42.4 mm |
3.25 mm |
4.00 cm2 |
1 ½" |
48.3 mm |
3.25 mm |
4.60 cm2 |
2" |
60.3 mm |
3.65 mm |
6.50 cm2 |
2 ½" |
76.1 mm |
3.65 mm |
8.31 cm2 |
3" |
88.9 mm |
4.05 mm |
10.80 cm2 |
4" |
114.3 mm |
4.50 mm |
15.52 cm2 |
4" |
114.3 mm |
5.40 mm |
18.47 cm2 |
|
5"
|
139.7 mm |
4.85 mm |
20.55 cm2 |
5" |
139.7 mm |
5.40 mm |
22.78 cm2 |
6" |
165.1 mm |
4.85 mm |
24.42 cm2 |
6" |
165.1 mm |
5.40 mm |
27.09 cm2 |
The conical ends are made from cylindrical materials by the help of CNC machines. In order to satisfy the connection of sphere and the tube a hole is opened in the conical ends according to the screw to be used. The quality or conical ends must be the same with the pipes. The screw diameter and length are computed according to the forces acting on it. The conical ends are welded to both ends of the pipe with special welding process.
While the computation of pipe diameter, the forces that can be carried by pipes in safe , is computed as shown below :
| Pipe outer diameter |
D |
| Wall thickness |
t |
| Pipe inner diameter |
d=D-2t |
| Section area |
F=3.14*(D2-d2)/4 |
| Moment of inertia |
I=3.14*(D4-d4)/64 |
| Inertia radius |
i=(I/F)½ |
Tube length |
s |
Stiffness degree |
s/i |
Torque constant |
w |
Tension tubes |
Pmax=σcm*F |
Compression tubes |
Pmax=σcm*F/w |
4.2 Screws
The screws are used to connect the tubes to the spheres. They getting from inside the sphere to the conical end of the tube. They are chosen according to the loads that transfer by the tubes they screwed. Screws can be used according to their diameters and quality. They can be six corners, imbus or conical head . In Space Truss Systems 8,8 or 10,9 quality metric screws can be used. The classification table about screws is given below
M12 |
12mm |
10.25mm |
M14 |
14mm |
12.15mm |
M16 |
16mm |
14.00mm |
M20 |
20mm |
17.50mm |
M24 |
24mm |
21.00mm |
M30 |
30mm |
26.50mm |
safe tension values of screws, according to their quality
8.8 |
8,000 kg/cm2 |
6.400 kg/cm2 |
5,800 kg/cm2 |
10.9 |
10,000 kg/cm2 |
9.000 kg/cm2 |
8,800 kg/cm2 |
4.3 Spheres :
At the nodes of Space truss Systems usually eight tubes become together on a sphere . These spheres must be in the range of 60mm - 150 mm by diameter, We used sfero spheres. The reason of using sfero spheres is: under the effect of huge forces they can continue on load bearing with small shape changes without cracking or breaking. The compression test of these spheres is made by Dokuz Eylül University Civil Engineering Department Laborites. Here the breaking values of spheres under compression:
Sphere Diameter Breaking Load
| Sphere Diameter |
Breaking Load |
| 150 mm |
46.000 kgf. |
| 120 mm |
20000 Kgf |
| 75 mm |
10200 Kgf |
5. Purlins
5.1 Purlin Holders :
Purlin holders are connected to the upper part spheres in order to give slope to roof cladding. The length of them are changing related with the slope of roof cladding. There is a conical end at one end of these element in order to connect it with the upper parts spheres. At the other end there is a ''U'' shaped steel in order to hold the Purlin. Between the ends there is a pipe that length changes related with the slope of roof cladding.
5.2 Purlins
Usually box profiles are used with minimum 2,50mm thickness according to the kind of cladding material. They are connected to the Purlin holders (upper) U parts by screws. When the distance between two spheres are too large for the roof cladding material, secondary Purlins with useful distances between each other are used on the primary Purlins.
6. PROTECT AGAINST CORRUSION
6.1 All screws are Electro-galvanized by 25 micron thickness.
6.2 Spheres can be hot boiled galvanized by average 80 micron. They also can be Electro-galvanized by average 25 micron and painted by Electro-static paint in average 70 micron thickness.
6.3 Tubes and Purlins can be painted by Electro-static paint in average 70 micron thickness after all their surfaces cleaned form dust, oil, etc. If it is wanted they can also be galvanized before paint.
7. TRANSPORT
Each element of space truss system is packed with nylon alone in order to prevent damages during transportation to the construction site. By this kind of packing we don't need a large storage area at workshop or site. The elements don't effected from the weather conditions.
8. ASSEMBLING
At the beginning of assembling the supports position and distance of axes are controlled. After all of them is OK the assembling can be done.
All the system members are connected each other by screws. During the assembling according to the mind of site chief temporary supporting or vice curving can be applicable. The most used types of assembling:
• All system established at ground level then hold by a machine
• By using single or tripod elements assembling the system at final level
• Combination of (a) and (b)
• Establish the system at the final level and move it to the final position over the rails.
Generally welding on site don't wanted. But especially supports or gutters or Purlins can be welded. These welds are protected against corrosion.
