- What is a rebar / deformed bar / kabilya?
- What is PNS 49?
- What is ASTM A615? ASTM A706? How do they differ from PNS 49?
- How do I know if the deformed bars I bought conform to PNS 49?
- Where can I have my rebars tested?
- What is Tension Testing?
- What is Mass Variation Testing?
- Why is it important to have standard rebars?
- What are some practices that should concern a buyer?
- How do you measure the diameter of a rebar?
- What is rusting and how does it affect the performance of rebars?
- What is the smallest bend radius that we can bend a rebar?
- What are quenched and tempered (QT) rebars?
. . .
What is a rebar / deformed bar / kabilya?
Rebars (also known as reinforcing steel bars, deformed bars or debars, concrete reinforcement bars, or in the Filipino term kabilya) are round steels bar with protrusions called deformations (see DEFORMATION in our Technical Specifications) used as tension devices in reinforced concrete to strengthen and hold the concrete together.
. . .
What is PNS 49?
Rebars are covered by a mandatory standard called the Philippine National Standard 49 or PNS 49, as formulated by the Bureau of Philippine Standards (BPS) of the Department of Trade and Industry (DTI) with the help of the Steel Industry, the Association of Structural Engineers of the Philippines (ASEP), and the Philippine Construction Association (PCA).
. . .
What is ASTM A615? ASTM A706? How do they differ from PNS 49?
The American Society for Testing and Materials (ASTM) has developed various standards agreed upon and adopted internationally by a multitude of industries. For deformed bars, ASTM A615 (Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement) and ASTM A706 (Standard Specification for Deformed and Plain Low-Alloy Steel Bars for Concrete Reinforcement) are the prevailing standards. The Philippines’ national rebar standard, PNS 49, has been aligned to these standards as much as possible, however, the seismic conditions of our country as well as the requirements of the key stakeholders has introduced some distinctions between these rebar standards.
. . .
How do I know if the deformed bars I bought conform to PNS 49?
Check if the manufacturer is accredited by the Bureau of Philippine Standards (BPS). All manufacturers of deformed bars accredited by the BPS are required to place their distinguishing logo on every meter of their steel bars. The logo is registered with the BPS. However, a manufacturer can still attempt to circumvent PNS 49 despite its accreditation. Always have two or three steel bars tested in a reputable laboratory. The laboratories will measure, weigh and test the yield point, tensile strength, elongation, and bending of the deformed bars. One cannot ascertain the quality of a rebar simply through visual inspection.
. . .
Where can I have my rebars tested?
Your samples can be tested at ISO/IEC 17025 accredited laboratories such as the Metals Industry Research and Development Center (MIRDC) in Bicutan or the Philippine Geoanalytics Inc. (PGAI) in Quezon City to see if it conforms to PNS 49 specifications.
. . .
What is Tension Testing?
Tension testing, also called tensile testing, is material testing test performed to a rebar in which the rebar’s properties such as yield strength, ultimate tensile strength, fracture strength, elongation etc are measured directly. A tensile (stretching) force is applied to a rebar sample of certain area until it fractures.
The maximum pressure points wherein the rebar sample can withstand permanent uniform deformation (yield strength), permanent localized deformation (ultimate tensile strength), and inevitable fracture (fracture strength) are accounted for, usually with a graph that plots the pressure against the strain experienced by the sample.
The percent elongation and area reduction, both measures of a rebar sample’s ductility, can be calculated by comparing the dimensions of the rebar sample after the fracture from its original dimensions.
The fracture type of the rebar sample can also give indications of the ductility/brittleness of the rebar. Flat, grainy fracture surfaces imply a brittle rebar while cup-cone surfaces imply a ductile rebar. Deformed bars with irregular fractures fall in between ductile and brittle materials.
A typical rebar stress-strain diagram as well the different rebar fracture surfaces are depicted below.
. . .
What is Mass Variation Testing?
As the name implies, mass variation testing is a type of materials testing performed on a rebar wherein the unit weight (weight per length) of a rebar sample is compared with its theoretical unit weight. PNS 49 specifies the theoretical unit mass requirement of each rebar size. See WEIGHT TABLE our Technical Specifications. A rebar mass variation of ±6.0% is allowed by PNS 49, it can be computed by the following equation:
. . .
Why is it important to have standard rebars?
In an earthquake prone country like the Philippines, the use of substandard rebars can be life-threatening. The yield point and tensile strength ratio ensures that there is enough “reserve energy” for the steel you use to withstand the sustained swaying motions and the subsequent aftershocks of an earthquake.
. . .
What are some practices that should concern a buyer?
One common practice is to maximize the 6% weight tolerance allowed by PNS 49 for each rebar. Since weight deviations of 2% – 3% occur during the rolling process, undersized rebars are included in the production batch. Another practice is the use of unsuitable raw materials to produce rebars that are too brittle and cannot pass bending tests under laboratory conditions. Still another practice is passing a lower grade off as a higher grade by switching the color coding of the rebar. A rule of thumb is never to buy from a manufacturer whose selling price is more than 2% lower than other competitors. The savings involved are not commensurate to the risk.
. . .
How do you measure the diameter of a rebar?
The diameter of a rebar, say 16 mm, refers to the mean nominal diameter of the cross sectional area of the rebar, core and deformations included. It is a theoretical diameter which cannot be directly measured using a ruler, caliper or micrometer. This theoretical diameter is controlled by the mass variation and the height of lugs of a rebar. See MASS VARIATION and DEFORMATION in our Technical Specifications.
. . .
What is rusting and how does it affect the performance of rebars?
Due to the reactivity of iron with oxygen, mild steel products, including steel bars, are inherently sensitive to the atmosphere. The interaction between the iron in mild steel and the oxygen in atmospheric air causes the oxidation process more commonly referred to as rusting or atmospheric corrosion in the bars.
Superficial rusting of deformed bars does not affect its performance. In fact, surface rust can increase the bond of the rebar to the concrete. However, prolonged surface rusting can eventually lead to pitting of the steel bar and this may lead to a weakening of the steel section. Suspect steel bars can be checked by weighing a cleaned rebar sample to check that the section is not below the lower unit mass tolerance and tensile testing undertaken to ensure that the physical properties are still above the minimum requirements.
You can find more information about rusting and its effect on rebars here.
. . .
What is the smallest bend radius that we can bend a rebar?
PNS 49 specifies the minimum pin diameter for the inside bend diameters of the various rebar sizes and grades. See PIN DIAMETER in our Technical Specifications.
. . .
What are quenched and tempered (QT) rebars?
Quenched-tempered (generally known as quenched and tempered (QT) or quenched and self tempered (QST), but also sometimes mistakenly called as TEMPCORE™ in reference to one of the earliest trademarked QT process) rebars are manufactured through a thermomechanical process called quenching and tempering. This process involves the rapid, superficial cooling of a hot-rolled rebar (quenching) and then the subsequent reheating by the residual heat (tempering). Quenched-tempered steel bars have higher strength and toughness than simple hot-rolled deformed bars.
QUENCHING and TEMPERING
The higher strength is derived from the tempered martensite layer formed by the quenching and tempering process while the improved toughness is due to its bainite transition layer. The ductility of the bars is kept by its pearlite-ferrite core.
QUENCHING and TEMPERING
Structure of a Quenched & Tempered Rebar