We provide Unbonded Post-Tensioning System which is a means of complementing strength of the concrete in compression and overcoming its weakness in resisting tension. Post-Tensioning System applies compressive force to the structure through stressing of high strength steel strand with specialized anchorage assemblies. Flexibility of the strand is a major advantage, allowing it to be profiled through the concrete element, counteracting a portion of the applied loads to provide an exceptionally efficient structure.
When a narrow strip element needs to be designed to take care of heavy loadings, stresses govern the design than the deflections in such case. P-T cable might not generate enough force due to shorter length as anchor seating loss would govern the net overall receivable force of prestressing. This can be resolved to a manageable extent by providing the cable in looped profile. This is how the overall length of cable can be extended in best possible way. The loop configuration also helps to develop better integrity aspects in the member.
- Stress & lock the cable-1 at construction joint or pour strip face. Do not cut excess length of cable-1.
- Lock the end of excess length in fixture. Using stressing jack on site.
- Lock the end of cable-2 to be placed in next pour on other end of fixture using jack, either at site or at workshop.
- Attach both ends of fixture.
Generally pour-strips are provided for two purposes. One of them is to minimize effects of shrinkage of concrete. Second is to divide the portions based on the pouring capacity at a time. If pour-strip is to be provided for the second case, this can be resolved by making it as a construction joint with the prestressed and non-prestressed elements and reinforcement runs continuous through multiple pours. This is achieved using Fixture or Smart coupler. Here, its schematic figure is shown which provides its working methodology.
- Cover-to-reinforcement can be enhanced from 25 mm to 35 mm or more based on the severity aspects. There is an insignificant increase in the P-T requirement i.e. around 0.03 —0.05 kg/sq.ft. to accommodate such requirement of providing more cover.
- UBC criteria shall be utilized by providing passive reinforcement for 1 DL + 0.25 LL Load case. This would make sure that the pre-stressed slab performs as desired in case the fire damages all P-T cables. This provides required residual capacity in absence of P-T force. Opting UBC criteria should not increase the reinforcement to much extent, in many of the cases, the additional passive reinforcement required to satisfy 1.5 DL + 1.5 LL case corresponding to limit state of collapse condition would be sufficient enough to satisfy UBC criteria.