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ANALYSIS, DESIGN & CONSTRUCTION OF CABLE SUSPENDED ROOF STRUCTURES

contents ANALYSIS OF CABLE SUSPENDED ROOF STRUCTURE

CONSTRUCTION ASPECTS OF CABLE SUSPENDED ROOFS

DESIGN OF CABLE ROOFS

CONSTRUCTION ASPECTS OF CABLE SUSPENDED ROOFS1. STRUCTURAL STRND AND ROPE

2. CABLE FITTINGS

3. PLACEMENT AND TENSIONING OF CABLES

STRUCTURAL STRND AND ROPE

Structural strand and ropes are most Commonly utilized as cable.Strand is an assembly of steel wires wrapped helically around a central wireIn one or more symmetrical layers andhas cross section shown in fig.1.

A rope is composed of plurality of strands wrapped helically around a coreAs shown in fig.2.

STRUCTURAL STRND AND ROPEThe cables are invariably of high strength tensile steel, and they are normally steel wire ropes up to 100 mm dia.Typical minimum breaking loads are 240t for 50mm dia. and 530t for 75mm dia. ropes.Working loads of up to 45% of minimum breaking strength are commonly used.In shell system roofs ,concrete prestressing cables and anchorages are frequently used in place of conventional wire ropes.

CABLE FITTINGS

There are two types of terminal fittings:- Swaged- Zinc poured sockets

Swaged Fittings

Swaging is aforgingprocess in which the dimensions of an item are altered using dies into which the item is forced. In this type, the cleanly cut cable end is inserted into a close tolerance hole in the end of steel fitting which is then placed in a die block of a hydraulic press.The fitting is of softer steel then steel wires so that when the die block is under controlled pressure, the softer steel of fitting flows plastically around the wires.After initial squeezing ,the fitting may be squeezed several times with the fiting rotated in the die between squeezings.

Swaged fittings

Zinc poured socketsPoured sockets are used to make a high strength, permanent termination. They are created by inserting the wire rope into the narrow end of a conical cavity which is oriented in-line with the intended direction of strain.The individual wires are splayed out inside the cone, and the cone is then filled with moltenzinc.

zinc poured socket process

Zinc poured sockets

Placement and tensioning of cables

Prior to shipment of cables, they are prestretched. Cable is usually marked with a longitudinal line to indicate its untwisted position when subjected to dead load tension. When cables are ready for stringing ,they are unreeled to their final position. One end is attached to its anchor and the other end, with adjustable fitting is brought to its anchor. An adjustment is then made to bring cable to a predetermined position.