Elevated concrete slabs and concrete floor systems offer a myriad of choices for architects and engineers in the building construction markets. Resources, design examples, reference materials and design software products are available to facilitate incorporating concrete floors in achieving economy and durability in today’s buildings.
Concrete is reinforced to give it extra strength; without reinforcement, many concrete buildings wouldn’t be possible. Reinforced concrete can encompass many types of structures and components, including slabs, walls, beams, columns, mats, frames and more. There are multiple ways of reinforcing concrete; the two main methods are conventional reinforcement (nonprestressed) and prestressing.
Reinforced concrete is two materials merged together; plain concrete, which is characterized by having high compressive strength but low tensile strength, and steel bars embedded in concrete to provide the needed strength in tension.
In prestressed members, compressive stresses are introduced into the concrete to reduce tensile stresses resulting from applied loads including the self weight of the member (dead load). Prestressing steel, such as strands, bars or wires, is used to impart compressive stresses to the concrete. Pre-tensioning is a method of prestressing in which the tendons are tensioned before concrete is placed and the prestressing force is primarily transferred to the concrete through bond. Post-tensioning is a method of prestressing in which the tendons are tensioned after the concrete has hardened and the prestressing force is primarily transferred to the concrete through the end anchorages.
Much of the focus on reinforcing concrete is placed on floor systems. Designing and implementing the most efficient floor system is key to creating optimal structures. Small changes in the design of a floor system can have significant impact on material costs, construction schedule, ultimate strength, operating costs, occupancy levels and end use of a building.
The Concrete Reinforcing Steel Institute (CRSI)
offers many resources for engineers, architects, contractors—almost anyone who works with reinforced concrete. The CRSI Manual of Standard Practice
offers standards for estimates, detailing, fabrication and placement of reinforcing steel, and their Design Handbook
(based on ACI 318-98 Building Code Requirements for Structural Concrete)
is a valuable reference. The Precast/Prestressed Concrete Institute
(PCI) and the Post-Tensioning Institute
(PTI) both also offer resources for work with reinforced concrete.