Tension Members

There are four commonly occurring states of stress, shown in Fig. 3.2. The simplest is that of simple tension or compression (as in a tension member loaded by pin joints at its ends or in a pillar supporting a structure in compression). The stress is, of course, the force divided by the section area of the member or pillar. The second common state of stress is that of biaxial tension. If a spherical shell (like a balloon) contains an internal pressure, then the skin of the shell is loaded in two directions, not one, as shown in Fig. 3.2. This state of stress is called biaxial tension (unequal biaxial tension is obviously the state in which the two tensile stresses are unequal). The third common state of stress is that of hydrostatic pressure. This occurs deep in the earth s crust, or deep in the ocean, when a solid is subjected to equal compression on all sides. There is a convention that stresses are positive when they pull, as we have drawn them in earlier figures. Pressure,... 

Kelley spinners, when used as tension members An adapter between the swivel and the kelley that spins the kelley for rapid attachment and disattachment to joints of drill pipe. 

Tension members for sub sea handling equipment shouid be inspected according to the manufacturers recommendations. In general, tension members should be checked for wear, cracks, reduction of area and eiongation. 

Tension members in sub sea handiing equipment should be maintained in accordance with manufacturer s recommendations. 

Figure 4-35. Tension members of subsea handling equipment [10].

It is useful to get preliminary learning on the mechanical properties of materials under simple static tension. Members of engineering structures are often subjected to steady axial loads in tension. Moreover, the response of materials subjected to other types of loading also can often be explained or predicted on the basis of knowledge of their behaviour under simple tension. In addition, such behaviour is usually quite easy to study experimentally. 

Select low-temperature steels for fracture-critical structural members designed for tensile stress levels greater than a ksl (40 MPa) and specify a minimum Charpy V notch Impact energy absorption of 20 ft-lb (27 J) for base metal, heat-affected zones (HAZs), and welds when the structures are exposed to low-ambient temperatures. Fracture-critical members are those tension members whose failure would have a significant economic impact. 

For fracture-critical tension members, Charpy impact test may be required,... 

Most booms are also fitted with one or more tension members that run along the bottom of the boom and reinforce it against the horizontal load imposed by waves and currents. Tension members are usually made of steel cables or chains but sometimes consist of nylon or polyester ropes. The boom fabric itself is not strong enough to withstand the powerful forces to which booms are subjected, except in protected waters. For example, the force on a 100-m-long section of boom could be as much as 10,000 kg, depending on sea conditions and the construction of the boom. 

Booms are sometimes constructed with ballast or weights designed to maintain the boom in an upright position. Lead weights have been used for this, but steel chain in the bottom of the boom often serves as both ballast and tension member. A few booms also use a chamber filled with water as ballast. Many booms nowadays are constructed without ballast, however, and their position in the water is maintained by balancing the forces on the top and bottom of the boom. Another construction feature common in larger booms is the addition of stiffeners or rigid strips, often... 

The three basic types of booms are fence and curtain booms, which are common, and external tension member booms, which are relatively rare. Booms are also classified according to where they are used, i.e., offshore, inshore, harbour, and river booms, based on their size and ruggedness of construction. 

External tension member booms, which are constructed with a tension member outside the main structure, are used in strong currents and in water containing ice or debris. 

Planing — Planing occurs when the boom moves from its designed vertical position to almost a horizontal position on the water. Oil passes over or under a planing boom. Planing occurs if the tension members are poorly designed and do not hold the boom in a vertical position or if the boom is towed in currents far exceeding the critical velocity. 

Containment boom — A floating mechanical structure that extends above and below the water surface and is designed to stop or divert the spread or movement of an oil slick on the water. Booms consist of floats, a freeboard member to prevent oil from flowing over the top of the boom, a skirt below the water surface to prevent oil from being swept under the boom, and one or more tension members to support the entire boom. Booms are an integral part of virtually all cleanup programs after oil spills on water. (See also Boom failure, Critical velocity, Freeboard.)... 

Tension member — The part of a floating oil containment boom that carries the load placed on the barrier by wind, wave, and current forces. Tension members are commonly made of wire cable or chain due to their strength and stretch resistance. 

Generally a belt consists of a carcass made of rubberised fabric, steel cord and the rubber top. The carcass is the tension member. This is covered on the top, the edges and the bottom with different qualities of rubber compounds to protect the tension member from damage and the rubber acts as a binder in addition to its primary function of protecting the belt against the wear. 

AN EPOXY FIBERGLASS TENSION MEMBER SUPPORT FOR SUPERCONDUCTING MAGNETS ... 

The basic geometry selected was that of a tension member support, which would support the cold mass of a magnet relative to the structure of the insulating vacuum vessel. This geometry was selected, since it permits configurations that could resist dynamic loading and could result in a support system whose loading was independent of temperature. 

The basic member of the tension member support is considered to be the element that bridges the 300 to 4.2 K environments. Several types of basic members were evaluated. Two (i.e., a bar with pin connections at its ends and a rod with threaded connections at its ends) were determined to be unacceptable, since the members failed in the region of the end connections at a force that was significantly less than the force that could be withstood by the balance of the member. These premature failures were due to the stress concentration characteristic of the end connection method employed. The geometry eventually selected for the basic member was that of a link, in which the composite is wound in a continuous fashion around a mandrel. The result is a structure that uses the strength of the material fibers in their most advantageous way. The link ends are connected to circular pins. 

An Epoxy Fiberglass Tension Member Support for Superconducting Magnets... 

Table I. Parameters of U. S. SCMS Tension Member Support System...

Consider, for example, the assessment of a simple steel member in a lattice girder subject to uniform tension. It is first necessary to define a critical stress above which the tie would be considered to have failed. Using elastic theory this would be tlic yield stress of the steel, The permissible stress is then obtained by dividing the critical stress by a safety factor which is Judged to be appropriate. For oxiitnple in B.S. 449 Table 2, the permissible stress of tension members of steel to H.S. 4360 Grade 43 is 16.S and its yield stress is 247 The... 

P(2) For tension and bending at the serviceability limit state, the maximum combined tensile strain at any cross-section of the member shall not exceed the appropriate values for a tension member under similar environmental and service conditions. 

Walton J M and Yeung Y C T, Flexible tension members from composite materials. In Proc 6th Arctic Eng Symp, Vol III, American Soc of Mech Eng, 1987. 

Tension members are those structural elements which are subject to direct axial stress without significant bending. Examples are hangers, struts, ties and braces in frames. They are designed to have adequate resistance to the apphed loads, taking into account any reductions in the cross-sectional area and stress concentrations due to discontinuities. 

As glass fibre composites have a relatively low Young s modulus, axial strain can be significant. Hence it may be neccesary to apply a serviceability limit state to this criterion to ensure that if for instance the tension member is used as a brace, it adequately prevents excessive sway in the structure. In any event there is a hmiting allowable strain to ensure that the resin does not craze. 

Consider as an example a tension member manufactured from uni directional E glass fibres and polyester resin by the pultrusion process. The design criteria are hsted below ... 

Yeung, Y.C. and Parker, B.E., Composite tension members for structural applications. Composite Structures, 4, 1309-19. 

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