Steel prices have increased globally by 30% causing a spike in construction costs in the real estate industry. This has consequently affected the prevailing housing prices making home ownership an increasingly costly endeavor for new homeowners. In time there is a significant reduction in the uptake of housing as mortgage financing rates go beyond the reach of the middle class. Developers will have to contend with a shrinking target market and must be innovative in their construction methods to remain cost-effective and profitable.
Post-tensioning is an innovative way to reinforce suspended slabs with a lower quantity of steel per unit volume of concrete. In traditional reinforced concrete the steel reinforcement remains inactive until the formwork is removed. In post-tensioned concrete high-tensile steel, tendons are placed and stressed making the reinforcing steel active. It utilizes high-tension steel tendons four times the tensile strength of standard steel bars with a value of 1860N/mm2 compared to 460N/mm2 for the steel bars. This allows the use of less steel per unit weight to obtain the same required tensile reinforcement of suspended slabs.
Additional benefits of utilizing this technology include thinner concrete members spanning longer between supports. Reduced building and floor-to-floor height from the elimination of down-stand beams with post-tensioned flat slabs, in effect, reducing building loading to foundation hence a more economical column and footing design. This results in a lighter structure that requires a lighter lateral load-resisting system; hence the building is more resistant to earthquake and wind loading.
There is a need to raise awareness of this technology which is relatively new to the Kenyan market but has been used extensively in overseas construction markets since the early 20th century. Developers and consultants are advised to lean towards this technology to address the arising challenges of traditional construction methods. The recent spike in steel prices calls for a paradigm shift in our methods of reinforcing suspended slabs for our industry to stay competitive.