A common steel bar, and is commonly used as a tensioning device in reinforced concrete and reinforced masonry structures holding the concrete in compression. Deformed bar is usually formed from carbon steel, and is given ridges for better mechanical anchoring reinforced concrete.
Steel construction has so many advantages: the strength to weight ratio is excellent, metals join easily, efficient shapes are available, etc. With those advantages, though, come some challenges that are best solved by a good understanding of how the metals actually perform in a structure.
For most larger buildings, metals are a key element of the structural system. Steel beams and columns, steel joists, steel studs, aluminum framing are a few examples of metal construction.
A wise Superintendent understands not only how to erect the structure, but also the basics of how the structural system works and the ways in which it fails. Engineers, Architects and contractors here in the Philippines mainly uses deformed bars as a basic construction materials for their project. However, this bars have different sizes and specifications for residential use and large projects such as condo units and commercial buildings.
Specification and Grading
The three grades under this specification - namely, Grades PNS 230, 275 and 415 trace their roots to ASTM specifications and the terms 'Structural', 'Intermediate' and 'High-tensile' originated from earlier version of ATSM-A615 but remained unchanged in difference to custom and familiarity among users.
The table provides a handy reference as to the common understanding in the market regarding these grades.
|ASTM vs PNS Codes||Popular Nomenclature||Typical Application|
|Grade 33 / PNS 230||Structural Grade||Low-rise Building and Low Loading Conditions|
|Grade 40 / PNS 275||Intermediate Grade||Medium-rise Structures / Infrastructure Work|
|Grade 60 / PNS 415||High-Tensile Grade||Medium & High-rise Structures / Infrastructure|
The three grades are distinguished by different color markings painted at the ends of each bar, as shown in the following table.
|Class||PNS Grade||ASTM Grade||Color Grade|
|non-weldable Deformed Bars (same color on both ends)||230||33||White|
|Weldable Deformed Bars (different colors on each end)||230||33||white / Red|
|275||40||Yellow / Red|
|415||60||Green / Red|
The cut length of a rebar varies as well because of shrinkage as it cools down. The standard however limits this shrinkage and the minimum length of the finished rebar as shown below.
|Std. Length (m)||Min. Acceptable Length (m)|
Our rebar comes in these commercial lengths: 6.0, 7.5, 9.0, 10.5 and 12 meters. Special lengths of 13.5 and 15 meters are subject to special orders and negotiations.
It must be noted that, in the current PNS 49, rebars are further categorized into 'weldable' and 'non-weldable' grades. The difference between the two categories is primarily rooted in their different chemical compositions and carbon equivalents (CEQ). Despite the different nomenclatures and their connotations, both 'weldable' and 'Non-weldable grades can actually be welded. However, the relatively lower carbon content and CEQ of ther so called 'weldable' grades does make it easier to weld without having to worry about pre-heating and post-heating requirements and procedures, that is a concern highlighted especially in temperate situations.
MECHANICAL PROPERTY SPECIFICATIONS
|Class||Grade||Yield Strength, MPa min.||Tensile Srength, MPa min.||Specimen||Elongation in 200 mm, % min.||Bending Angle||Diameter of Pin (d= nominal diameter of specimen)|
|Hot-Rolled Non-Weldable Deformed Steel Bar||230||230||390||D<25mm|
|Hot-Rolled Weldable Deformed Steel Bar||230||230||390||D<25mm|
* Maximum yield strength of weldable steel bars shall not exceed 540 MPa
** Tensile strength not be less than 1.25 times the actual yield strength