The properties of a high-strength concrete-mix with a compressive strength of more than 40 MPa is greatly influenced by the properties of aggregates in addition to that of the water-cement ratio. To achieve high strength, it is necessary to use lowest possible water-cement ratio, which invariably affects the workability of the mix and necessitates the(…)
Prestressed Concrete
PRESTRESSED CONCRETE POLES
In the past decades, prestressed concrete poles have become popular and have replaced the traditional poles made of timber, steel or reinforced concrete. The earliest prestressed concrete poles were designed in 1933 by Freyssinet. Prestressed concrete poles are commonly mass produced and are used in most countries for power transmission, antenna masts etc. The main(…)
PRESTRESSED CONCRETE PIPES
Prestressed concrete pipes are used for purposes like liquid retaining structures, such as circular pipes, tanks and pressure vessels etc. which are suited for circular prestressing. The circumferential hoop compression produced in concrete by prestressing counterbalances the hoop tension developed due to the internal fluid pressure. A reinforced concrete pressure pipe requires a large amount(…)
SPECIFICATIONS OF PRESTRESSING STEEL
Specification of Prestressing Steel For prestressed concrete members, the high-tensile steel, used generally, consists of wires, bars or strands. The high tensile strength of steel is generally achieved by marginally increasing the carbon content in steel in comparison to mild steel. High-tensile steel usually contains 0.6 to 0.85% carbon, 0.7 to 1 % manganese, 0.05%(…)
PRESTRESSED CONCRETE MIX DESIGN PROPORTIONS
Prestressed Concrete mix design proportions should be chosen in such a way that concrete of adequate workability is obtained. Workability of concrete mix should be such that it can be compacted well using the available means of compaction. The recommended values of workability of concrete can be taken from IS : 456-1978. Concrete should surround(…)
REQUIREMENTS OF PRESTRESSED CONCRETE
Requirements of prestressed concrete are mainly strength and durability of concrete. Properties of various materials used in prestressed concrete must suit the requirements which are connected with the performance of prestressed concrete. Prestressed concrete require a high strength – compressive as well as tensile component at an early age. It means that the rate of(…)
PRESTRESSING SYSTEMS AND ANCHORAGES
In concrete structures, prestress is introduced by stretching steel wire and anchoring them against concrete. Therefore, the prestressing systems should comprise essentially a method of stretching the steel and a method of anchoring it to the concrete. Different systems are adopted for pre-tensioning and post tensioning. PRE-TENSIONING SYSTEM: Hoyer system or long line method is(…)
PRE-TENSIONING AND POST-TENSIONING
PRE-TENSIONING AND POST-TENSIONING IN PRESTRESSED CONCRETE DESIGN The prestress in a structure is influenced by either of the two processes: Pre-tensioning, and Post-tensioning Pre-tensioning can be further classified into two categories: Linear pre-tensioning Circular pre-tensioning PRE-TENSIONING Pre-tensioning is accomplished by stressing wires or strands, called tendons, to predetermined amount by stretching them between two anchorages(…)
1 2