SEANep Abstracts

New Generation FRP Re-bars

For last decade, the concept of non-metallic reinforcement compatible to concrete structures is emerging at a tremendous pace. Its merit includes: non-corrosiveness, magnetic transparency, high strength-to-weight ratio, better creep resistance, excellent fatigue resistance, good impact resistance, impervious and low water absorption, non-conductive (thermal and electric), light weight etc. Fiber Reinforced Polymer/Plastic (FRP) is the combination of a polymer matrix like epoxy and a reinforcing material like carbon. The combination offers some of the strongest material to their weight that technology has ever developed. In this paper, general introduction of FRP rebar and its usage in the world is noted. A new concept has been demonstrated with carbon fiber composites as continuous fiber flexible shear reinforcement. It is shown that it can do what steel reinforcement is doing till date. It is also demonstrated how FRP reinforcement fails at the ultimate state.

New Generation FRP Re-bars

In all the structural elements different grade of materials are needed. Higher grade materials are needed in columns and beams. Lower grade of materials can be used in slabs and foundations. Design of some elements like slab in a structure is governed by serviceability criterion as in slab demanding greater depth than required by state of collapse. This leads to the use of lower grade of concrete and steel. It has been shown that use of mild steel bars are preferred in slab design.

We need different grades of steel which are needed in different situations. Sometimes use of the higher grade of steel may lead to a technically faulty situation becoming the section over reinforced. Normally, heavy reinforcements are needed in columns, moderate reinforcements in beams and least reinforcements are needed in slabs and membrane structures. In the same way the various grades of concrete and reinforcement are needed for lesser quantities with appreciable level of quality.

The use of scarce materials should be technically and economically effective. We should not limit the flexibility in choice of various grades of materials, which would not be technically appropriate and economically cost effective.

We find slow development in concrete grades and fast development in reinforcement side. Development of both materials will be sustainable. We should have an effort equally to produce higher grade of concrete along with the higher grade of steel.

High Strength Bars and Design Considerations

Fe500 Quenched and self-Tempered (QT) reinforcing steel bar has been gradually replacing the cold-twisted bars from the market. There are obvious benefits of this high strength bar such as economy in the reinforcement cost and low susceptibility to rusting due to the manufacturing process. However, manufacturing process introduces some inherent deficiencies such as reduction in ductility and increase in low-cyclic fatigue, which affects seismic behavior of the structure. Further, it will have other design/ detailing implications; such as, ratio between bar diameter and depth of column or beam, mandrel diameter that should be considered in the design. In addition to it, the high-strength bars require special handling in site processing. This paper will try to elaborate on basic mechanical properties required, precautions in design and handling of the bar.

Structural Requirements of High Yield Strength Deformed Bars

Reinforcement steel, integral part of concrete structures, accounts for 30 to 40% of the cost of reinforced concrete. The development of high yield strength deformed bars with necessary properties, and its use may reduce the cost of construction. The properties of rebars produced by the prevalent in-line heat treatment are discussed. Provisions on rebars of high strength in various codes and standards are evaluated, with a special emphasis on the components of recently introduced AS/NZS 4671-2001.   Yield strength, ultimate strength to yield strength ratio and uniform elongation are the main parameters to be considered in specifying the requirements. The development of the set of structural requirements for rebars considering the seismicity and other local conditions of Nepal has become necessary. A credible agency for implementation and monitoring of such standards is important for the efficient use of the rebars. A need for exercising the norms on quality control and assurance is emphasized.

Codal Requirements and Testing of Rebars

Code of practice is a basic guideline for design of structures. It restricts the minimum strength and other properties of construction materials. It also specifies the conditions and process of testing of materials. In case of dispute, only codes of practice give the way for solving dispute, based on specifications of the signed agreement. The properties of reinforcing bars required as per code of practice and their testing methods are discussed in this paper.