Post Tensioning Benefits for Architects
Post-tensioning is an engineering solution that is flexible and offers many benefits over more common building structural solutions. It provides the Architect with a more flexible structural form that can increase columns spacing and reduce floor to floor heights whilst having inherent sustainable benefits:
- Post-tensioned slabs create the opportunity to reduce the number of columns within a building. PT slabs can span further than more traditional reinforced concrete slabs within the same structural zone therefore allowing the Architect to reduce the number of internal columns and give more flexibility for internal planning.
- Post-tensioned slabs give flexibility for the layout of a building and is commonly used in structures with irregular grids, unusual curves and complex geometry. The inherent structural benefits of post-tensioned structures provides the Architect the opportunity to cantilever structures that would not normally be possible with more traditional forms of construction. Post-tension systems help control the structures deflections that normally govern the design for this form of construction.
- Post-tensioned floors provide the most efficient solution for minimising floor thickness without the need for down stand beams in most instances. Keeping the structure to a minimum enables the floor to floor heights to be reduced which in turns minimises the height of the building, hence generating savings in cladding and on taller structures the possibility of introducing an additional storey.
- Post-tensioned slabs with flat soffits helps simplify the design for the distribution of horizontal services allowing tenants complete flexibility for future modifications. Data shows that MEP installation costs for horizontal services below a slab with down stand beams can be up to 15% more than a flat soffit slab. Adopting a post-tensioned flat slab reduces design team coordination effort, risk of errors and permits maximum off-site fabrication of services, higher quality of work and quicker installation.
- Post-tension slabs can accommodate openings without too much difficulty. Smaller holes provide little problems as these can be formed between the PT tendons which are typically spaced at 1.0-1.5m centres. The position of the tendons are normally marked on the soffit of a slab to allow for the formation of future openings a simple exercise.
- Many modern commercial buildings now utilise exposed soffits. Post-tensioned slabs have minimal cracking and therefore are ideal for a fair-faced finish. The exposing of the slabs soffit also presents the opportunity to utilise the thermal mass properties to help reduce temperature fluctuations of the working environment and therefore contribute to savings on heating and costly air-conditioning systems.
- The amount of concrete used in a post-tensioned concrete slab can be up to 30% less than that required in traditional reinforced concrete. This leads to a reduction in embodied energy and carbon emissions, a faster building program and fewer deliveries to site.
- The inherent mass of a post-tensioned concrete floor means any additional finishes to achieve acoustics requirements are either reduced or eliminated. Testing of a 250mm thick concrete slab within a student residential building provided results that exceeded the requirements of Approved Document E by 5 dB for both air borne and impact sound.
- A well detailed post-tensioned slab is expected to have a long life and require very little maintenance. They can easily achieve a 60-year design life and with careful attention to detail are able to achieve a 120-year life, even in aggressive environments.
- Post-tensioned concrete slabs can be specified with recycled aggregate plus have the benefit that at the end of its life both the concrete and steel tendons from demolished PT floors are 100% recyclable.
- Adopting a concrete slab simplifies the detailing at critical locations which can help reduce on site remedial work for compliance with Part L of the Building Regulations air tightness.