There are a huge number of uses: • Railway Sleepers; • Communications poles; • Pre-tensioned precast “hollowcore” slabs; • Pre-tensioned Precast Double T units – for very long spans (e.g., 16 m span for car parks); • Pre-tensioned precast inverted T beam for short-span bridges; • Pre-tensioned precast PSC piles; • Pre-tensioned precast portal frame … Read more
There are two methods of prestressing: • Pre-tensioning: Apply prestress to steel strands before casting concrete; • Post-tensioning: Apply prestress to steel tendons after casting concrete. Pre-tensioning This is the most common form for precast sections. In Stage 1 the wires or strands are stressed; in Stage 2 the concrete is cast around the stressed … Read more
Concrete The main factors for concrete used in PSC are: • Ordinary portland cement-based concrete is used but strength usually greater than 50 N/mm2; • A high early strength is required to enable quicker application of prestress; • A larger elastic modulus is needed to reduce the shortening of the member; • A mix that … Read more
The classic everyday example of prestressing is this: A row of books can be lifted by squeezing the ends together: The structural explanation is that the row of books has zero tensile capacity. Therefore the ‘beam’ of books cannot even carry its self weight. To overcome this we provide an external initial stress (the prestress) which compresses the books together. Now they can only separate if the tensile stress induced by the self weight … Read more