Page 7 - A4 Post tensioning bar 1030

Macalloy Post Tensioning System

Protection Against Corrosion Two or more of these systems and upon the friction within the
may be combined, to enhance the threads and between nut, washer
For normal prestressed concrete degree of protection. and end plate. Accuracy of the
construction, the alkaline tensile force cannot be expected to
environment, provided by a layer Particular care is always needed be more than ±25%.
of cement grout, injected into the at end connections and coupled
duct enclosing the bar gives good joints, to ensure continuity of The relationship, between the
protection. protection, over the whole tendon. torque applied to a nut bearing onto
a standard washer and the resultant
If bars are used in any exposed Advice is available from Macalloy’s load, is as shown in Table 4.
application, corrosion protection Technical department.
is essential for Macalloy 1030 and
can be advantageous for Macalloy Torque Loadings
S1030.
Macalloy 1030 bars are also used
The type of protection will be for non post tensioned concrete
governed by the conditions of applications, which require only a
exposure, appearance and cost. relatively small tensioning load.
Amongst the available options are:-
• paint systems (comprising For these applications, it is
of primer and one or more possible to develop a load in a
finishing coats) Macalloy bar up to 25% of the
• grease impregnated tape characteristic failure load, by
wrapping applying a predetermined torque to
• adhesive coated plastic tape the Macalloy nut. Torque wrenches
wrapping are available from Macalloy that
• shrink wrap have a dial, indicating the torque
• plastic tubing value exerted, or which can be
• ridged plastic tubing, with preset to slip at a specified torque
injected grease or grout. value.
• Thermal metal spray
The axial tension, induced by a
Macalloy 1030 should never be given torque, depends upon the
galvanised. diameter and pitch of the threads

Table 4: K Values for Macalloy Coarse Threads

Bar Diameter
mm K
Torque (Nm) = PxD
25 4.1
K
26.5 4.3
Where
32 4.7
P is desired axial load in kN
36 4.9
D is the nominal bar diameter in mm
40 4.5
K is a constant obtained by test measurements 50 4.1

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