Prestressing

Post-tensioning

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VSL live end anchorage VSL stressing jack Menara Peninsula, Jakarta, with post-tensioned transfer slab VSL CT Stressbar VSL HR Stressbar VSL Threadlok Bar VSL MT600 Bar Temporary Post-tensioning with VSL bars for precast segmental bridge erection. Pasupati project, Bandung, Indonesia Circular PT in Silos Indocement, Indonesia Vertical tendons in Silo RAPP Riau, Indonesia Our aim is always to offer not only the best post-tensioning solutions but also innovative construction techniques, designed to increase site safety, save time, improve durability, and reduce costs. Post-tensioning in Building Post-tensioning allows the floor framing to be more slender, solving the problem of the conflicting needs for long spans and small structural depth, and that it replaces a significant amount of reinforcement, thus reducing steel quantities and allowing standarization and simplification of the reinforcement. Further reasons why posttensioning helps to improve the structure are that usually the concrete quantities are reduced and that the formwork can be stripped earlier than for non-prestressed floors. Also, the often required strict limitation of deflections and crack widths can be effectively achieved by post- tensioning. Unbonded monostrand tendons with colored sheath in speed cycle flat slab construction. CityLofts Project, Jakarta, Indonesia Since the draped prestressing tendons typically balance a significant part of the permanent floor loading, deflections and cracking are substantially reduced compared to a reinforced floor. In addition, the in-plane compression forces from the prestressed tendons neutralize tensile stresses in the concrete to a degree, delaying the formation of cracks. Transfer Beam/ Slab In many high-rise hotel and office buildings large column-free lobbies are required at ground level, often extending over several floors, while the hotel or office floors above have columns and walls at much closer spacing. The transition from the small support grid to the large column spacing in the lobby is either by means of transfer beams or a transfer plate. In order to transfer the high concentrated forces from the columns and walls of the upper levels to the lower supports these beams and plates usually require considerable depths and large reinforcement quantities. Post-tensioning is a very effective way to reduce both the depth and the reinforcement content The prestressing force enables an arch system to form within the beam, transferring the column forces from the upper floors to the supports. Part of the loads, including the self weight of the beam, is balanced by the upward acting deviation forces from the parabolic tendons. The deflection is thus reduced considerably. The in-plane compression stress provided by the posttensioning tendons improves the cracking behaviour of the beam. The same principle applies to transfer plates Post-tensioning in Bridge VSL post-tensioning systems have been utilized for many bridge projects in Indonesia and other countries in Asia, Australia, Europe, America and Africa. Post-tensioned bridge, Barelang, Indonesia The finished product has several advantages over conventionally reinforced concrete. Dead loads are balanced by the use of longitudinal post- tensioning reducing the sustained loading and associated creep. Corrosion resistance is increased due to the duct and grouting protection of the prestressing steel. Through the use of transverse post-tensioning, added compression improves the longevity of the structure by adding resistance to environment. Post-tensioned haunched slab bridges allow for a larger span to depth ratio than that of conventionally reinforced haunched slab bridges. The labor and material savings on mild reinforcement is another clear advantage to using post-tensioning for this application. Post-tensioned bridges are not only a superior economic solution, but they are also aesthetically pleasing. Stressbar VSL have been manufacturing and designing bar systems in Australia for use by the construction industry since 1971. These have proven to be one of the most popular tools of Engineers wishing to induce and control loads and forces in structures. The systems range from High Tensile Cold Worked Stressbar to Low Tensile Architectural Tendons, all with compact and easy to assemble fittings. A range of diameters is available to give a wide selection of tendon forces. The prestressing force is anchored at the end of the bar by a rolled thread, nut, washer and bearing plate. Where necessary bars can be joined with threaded couplers, and clevis fittings may be used where pin connections are required. The VSL bar system complies with the requirements of AS1313 and AS1314. VSL bar systems are ideal for the economic application of post tensioning forces on relatively short tendons. Through the use of threaded connections and anchorages they are simple to use and lend themselves to many applications in: Buildings: Pestressed Beams and Columns, Precast Connections, Roof Truss; Bridges: Stay Cables, Hangers, Prestressed Segments, Strengthening, Tension Piles and Caissons; Wharves & Jetties: Stressed Deck Planks, Tie Backs; Anchors: Permanent and Temporary Ground Anchors, Uplift Anchors (Dam & Foundation), Roof Bolting, Soil Nails (Slope Stabilisation), Crane Bases, Light Towers; Specialist Engineering: Heavy Lifting, Formwork Ties or Hangers, Frame Ties, Pile testing and Architectural Ties. Stressbar ties, Qantas Arrivals/Departure Hall, Sydney Airport Circular Structure Post-tensioning is used in circular structure construction for the following reasons: It provides the required resistance to the acting forces, it makes possible solutions more economic than those achievable with reinforced concrete or steel and it renders the concrete virtually free of cracks. The VSL Post-tensioning System with its wide variety of types of anchorage and cable units, is ideally suited for use in construction. The methods adopted for assembling the tendons are also of particular advantage in circular structure construc- tion, since they can be adapted to the particular circumstances encountered. The VSL Post-tensioning System uses, as tension elements, only 7-wire strands of 13 mm (0.5"), 15 mm (0.6") or 18 mm (0.7") nominal diameter, with ultimate tensile strengths of 1670 to 1860 N/mm2. In addition to the high strength and low relaxation, the great ease with which the strands may be grouted (due to the screw action) should be emphasized. The strands of the VSL cables are stressed simultaneously, but individually locked in the anchorage. Stressing can be carried out in as many steps as desired. In silo construction, the VSL Post-tensioning can provide the stressing anchorages types Sc, which are installed in buttresses. The special centre stressing anchorages types Z make the provision of buttresses unnecessary as these anchorages can be stressed in a block-out in the wall. Of the dead-end anchorages, apart from types H and U, special mention should be made of type L, in which the tendon can be returned through 180° in a small space. This type is especially suitable for vertical post-tensioning. External Post-tensioning External post-tensioning can be used for new structures as well as for existing structures needing strengthening. The application is by no means restricted to concrete structures. Any material with reasonable compression characteristics can be combined with external tendons. Thus, applications in structural steel, composite steel-concrete, timber and masonry structures are known. The technique has been used for various types of structures such as: - Bridge superstructures - Girders in buildings - Roof structures - Circular structures such as silos, reservoirs and large masonry chimneys - Buildings with masonry walls. Roof with external tendons, Belgrade Airport, Yugoslavia External tendons provide desirable features, such as the possibility of controlling and adjusting the tendon forces, inspecting the corrosion protection and replacing tendons, should this become necessary. This is, however, possible only if the tendon system together with its anchorages and saddles is designed accordingly. Advantages of external posttensioning include: - The absence of tendons inside a web means that pouring of concrete is made easier; there is no weakening of the compression area due to ducts. In this way a minimum web thickness is achievable. - A polygonal tendon layout allows angular deviations to be concentrated at carefully designed saddle locations, thus eliminating the influence of unintentional angular changes. Essentially, an external post-tensioning tendon consists of the following elements: - prestressing steel as tensile members, - mechanical end anchorage devices, - corrosion protection systems. In the case of deflected tendons: - saddles at points of deviation are also required. Most material standards for prestressing steel distinguish between smooth and ribbed bars, wires and strands. VSL scope of work in post-tensioning: Detail design of post-tensioning tendon, elongation and jacking force calculation report, construction stages analysis, method statement, shop drawing, supply and installation of strand, stressbar, duct, HDPE hose, casting, anchor block, wedges, bracket, saddle, bearing plate, nut, flat or spherical washer, operation of scanning, concrete coring, stressing with hydraulic jack and pump, patching, and grouting with grouting machine. Related pages: Building Projects Bridge Projects Circular Structure Projects Repair & Strengthening Projects Various Projects