Prestressed Precast Concrete

Property

Prestressed concrete is concrete subjected to compressive stresses by inducing tensile stresses in the reinforcement. The purpose of prestressing is to counteract tensile stresses in the concrete caused by external loads before the external loads are applied. Prestressing is achieved by either pre-tensioning or post-tensioning.

The major advantage of prestressed concrete is its ability to span longer distances with much thinner sections while carrying heavier loads. Span and load requirements determine the member thickness and the amount of prestressing force.

Beside columns and beams, prestressed precast slab are used as floors, roof decks, includes solid planks and hollow planks.

The design procedures and components for prestressed concrete mixture are the same as those for conventional reinforced concrete members, except that they are extended to provide for the effects of prestressing.

Types of Reinforcement

Effective prestressing requires high-strength steel for tensile reinforcement. Prestressing reinforcement can be in the form of single wires (cold-drawn, hot-rolled), strands (low-relaxation) composed of several wires twisted to form a single element (standard or compacted), and high-strength alloy steel bars (plain or deformed). These shall comply with SS 475 Part 1:2000.

System and prestressing/ post tensioning material: [5]

Note: Strand wire comes in 9.6mm and 12.9mm diameter. Modulus Elasticity ranges from 185-205 kN/mm².

Source: Underwood, Red & Michele Chiuini; Architectural Design- A Practical Guide for Architects; John Wiley & Sons; New York; 1998. [5]

Tensile Strength

Allowable concrete tensile stresses (N/ mm²): [6]

Source: Hurst, MK; Prestressed Concrete Design (2nd edition); E&FN Spon; New York; 1998 [6]

Modulus Elasticity

Source: Hurst, MK; Prestressed Concrete Design (2nd edition); E&FN Spon; New York; 1998 [6]

Other Property

Refer to property of Reinforce Dense Concrete