The invention relates to structural member for the manufacture of towers such as microwave towers, antenna towers for TV and Radio, transmission line towers and the like.
Towers such as mentioned above are generally fabricated using structural steel angles and connections between angles ars bolted. If the tower is fabricated out of tubes, there will be a substantial reduction in the wind load acting on the structure because tubes offer less resistance to wind than angles with flat surfaces. Though the weight of tubular tower works out to be much less than structural steel towers with angles, the latter is preferred because of the following reasons.
1. Structural steel angles cost less per ton than tubes.
2. Fabrication of structural steel towers is very simple
because the operation involved are cutting the angles to correct
length and drilling/punching the holes in the angles whereas in
tubular towers the fabrication is complex involving welding of
thin tubes in addition to providing bolted connections.
3. Quality control is simpler in structural steel
fabrication than in tube fabrication.

4. Structural steel towers have greater thickness of the material and offer better resistance to corrosion than tubular towers.
The object of the invention is to provide a structural member for such application which has the advantages of both angles and tube as structural member for the manufacture of towers and which is very economical and easy to manufacture and erect. Another object of the invention is to reduce the cost of the foundation of the tower.
From the basic principles of fluid mechanics as well as from Indian Standard specification IS:875 part (3) 1987, it can be shown that the force acting on an angle when the wind blows is very significantly more than the force that acts when the same angle is covered with a circular sleeve even though the diameter of the circular sleeve is more than the width of the angle. By using structural members according to the invention, the total force acting on the tower due to wind will be significantly less when compared to a state-of-art angle tower and therefore the angle sizes can be significantly reduced to achieve economy. The foundation of the tower made with such structural members according to the invention will also be subjected to less downward, up lift and lateral forces when compared to conventional towers.

Thus the invention provides a structural member for the manufacture of towers such as microwave towers, antenna towers for TV and radio, transmission line towers and the like comprising a metal angle with at least a portion of the metal angle encased in a cylindrical enclosure and plurality of fixing holes being provided along the length of the metal angle for fixing each of the structural member with other structural members.
With reference to the accompanying drawings i
Fig. 1 ; shows a structural member according to the invention.
Fig. 2 shows another embodiment of a structural member according to the invention.
Figs. 3(a), 3(b) and 3(c) are the cross-sectional views of the structural member along A-A showing three embodiments of the structural member with a metalic angle having perpendicularly angled surfaces.
Fig. 4(a), 4(b) and 4(c) are the cross-sectional views of the structural member along A-A showing three different embodiments of the structural member with metalic starred angle.

Figs. 5(a), 5(b) and 5(c) are the cross-sectional views of
the structural member along A-A showing three different
embodiments of the structural member with metalic angle having an
acute angle between the angled surfaces.
Fig. 6 shows a typical joint for construction of a tower using the structural members according to the invention.
The structural member according to the invention comprises a metalic angle (1) with holes (2) for fixing the structural member to other structural members. Portion of the metalic angle is encased in a cylindrical enclosure (3, 4). The cylindrical enclosure may be tightly fitting to the metalic angle (1).
The cylindrical enclosure may be provided by means of a tightly fitting sleeve (3).The sleeve (3) with the metalic angle (1) inside may be preferably filled with grout (4). The grout (4) may be preferably made from one or more materials selected from cement mortor, concrete, re-inforced concrete, epoxy, plaster of paris etc. The sleeve (3) may be made of metal, plastic, fibre glass etc. In a prefered embodiment, the metalic angle may be enclosed in the grout (4) with a circular external surface to the enclosure. In this embodiment the sleeve (3) is not provided.

Preferably the structural member is provided with circular enclosure at all places except at the locations where the connections are made with other structural members as shown in fig. 6. Te location where connections are made can also be enclosed in a circular enclosure (5) after the connections are made and before the tower is completed. This will reduce the wind force at these locations as well. In a prefered embodiment, dimples, are provided on the outer surface of the sleeve which reduce the wind force on the structure made. The use of structural members according to the invention for the manufacture of towers such as microwave towers, antenna towers for TV and radio and transmission line towers reduce the weight of material substantially and therefore the cost as well.
By using the structural members according to the invention for manufacturing towers the following advantages are obtained :
1. Leads to reduction in the weight and cost of the tower.
2. Has all the advantages of using structural steel angles regarding fabrication, quality control and erection.
3. Providing the sleeve and grout is a very simple
operation and this also gives enormous protection to the tower
against corrosion.

4. The sleeve and grout also act as a structural member and help in reducing the deflection of the tower during wind. This aspect is particularly desirable because of the strict limiting deflection requirement of microwave towers supporting dish antennas.
5. The foundation cost is greatly reduced because of the reduction in the magnitude of the forces acting on the foundation.
6. Speeds up the construction of foundation.
The structural member according to the invention can be used in various other applications which are not specifically refered in the specification.

WE CLAIM :
1. A structural member for the manufacture of towers such as microwave towers, antenna towers for TV and radio, transmission line towers and the like comprising a metal angle (1) with at least a portion of the metal angle encased in a cylindrical enclosure (3, 4) and plurality of fixing holes (2) being provided along the length of the metal angle for fixing each of the structural member with other structural members.
2. The structural member as claimed in claim 1, wherein the metal angle has two mutually perpendicular angled surfaces of equal width.
3. The structural member as claimed in claim 1, wherein the metal angle has two mutually perpendicular angled surfaces with unequal widths.
4. The structural member as claimed in claim 1, wherein the metal angle is a starred angle.
5. The structural member as claimed in claim 1, wherein the metal angle has two angled surfaces subtending at an acute angle.

6. The structural member as claimed in anyone of the previous
claims, wherein the cylindrical enclosure is a sleeve encasing
the metal angle.
7. The structural member as claimed in anyone of the claims 1
to 5, wherein the cylindrical enclosure is formed with grout.
8. The structural member as claimed in anyone of the claims 1
to 5, wherein the cylindrical enclosure is a sleeve filled with
grout.
9. A structural member for the manufacture of towers,
substantially as hereinabove described and illustrated with
reference to the accompanying drawings.