Steel bar

Abstract

Longitudinal steel bars for reinforcement elements in column reinforcements and other applications are disclosed. The bars are made from at least 600 MPa yield strength steel and have non-round cores, such as at least generally square cores, and 5 transverse ribs on outer surfaces of the cores. The bars have proportionally larger amounts of steel in the cores than in the ribs than is the case in longitudinal bars made from lower yield stress steels known to the applicant. The invention provides an opportunity to manufacture longitudinal bars with smaller equivalent diameters and at least the same load capacities as those of known longitudinal bars and with adequate 10 buckling resistance and bond strength. 34 21015269_1 (GHMatters) P121266.AU.1 20 24 20 50 24 22 J ul 2 02 4 A B S T R A C T 2 0 2 4 2 0 5 0 2 4 2 2 J u l 2 0 2 4 5 3 4 Figure 1 t( ii , i , Hf:11 r,11 l f • Figure 1 Diagram showing Core and Rib Figure 3 1 / 151 / 15 Figure 1 3 9 5 5 7 5 is 9 SCALE 11 SECTION 11F11 SCALE 2 0:8 BPASS D18 PASS 9 Figure 1 Diagram showing Core and Rib 9 3Figure 2 3 Figure 3 5 9 5 11 5 7 13 9 7 7 5 Figure 4 5 7 9 3 3 INCEL heart - NIC > 9 5 20 24 20 50 24 22 J ul 2 02 4 3 2 0 2 4 2 0 5 0 2 4 2 2 J u l 2 0 2 4 9 5 5 9 D 1 8 P A S S 9 3 3 1 1 5 > L 9 7 0 7 5 7 9 7 7 5 5 7 9 3 1 3 9 > 5

Description

TECHNICAL FIELD The present disclosure relates to a longitudinal steel bar for use as a 5   reinforcement element, such as in a column reinforcement of a reinforced concrete column or a reinforced concrete beam or any other suitable reinforcement applications. The present disclosure also relates to a column reinforcement of a reinforced concrete column or any other suitable application. The present disclosure also relates to a reinforced concrete column that 10 comprises (a) concrete and (b) a column reinforcement embedded in the concrete. BACKGROUND ART The following description focuses on a longitudinal steel bar for use as a reinforcement element in a column reinforcement of a reinforced concrete column. 15           It is noted that the disclosure is not confined to this application for the longitudinal steel bar. Other applications comprise, by way of example, beam and wall reinforcement applications. The term “reinforced concrete column” is understood herein to mean a structural 20 member designed to resist compressive and bending loads, comprising (a) concrete and (b) a column reinforcement embedded in the concrete. The reinforced concrete column may be, by way of example, square, rectangular, T-shaped, L-shaped or circular in transverse cross-section. The term “column reinforcement” is understood herein to mean a framework of 25   (a) longitudinal steel reinforcing bars, described herein as “longitudinal bars”, that provide the principal reinforcement in reinforced concrete columns and other applications and (b) transverse steel reinforcing bars that provide lateral restraint to the longitudinal bars, confinement of a core of a column, and shear reinforcement, described herein as “fitments”, “ligatures” and “ties” in the construction industry. 30          It can be appreciated that the term “column reinforcement” applies to reinforced concrete columns, reinforced concrete beams and other applications. Basically, there is vertical column reinforcement, horizontal beam reinforcement, with a column and a 2024205024  16 Jun 2026 beam being similar except that but one is essentially vertical and the other is essentially horizontal. In walls the reinforcement is both vertical and horizontal. Australian Standard AS 3600: 2018 - Concrete structures - specifies minimum requirements for the design and construction of concrete building elements that are 5 made from concrete and steel reinforcing bars, such as longitudinal bars and fitments for use in column reinforcements. Longitudinal bars and fitments have particular functions in column reinforcements and require particular properties to carry out those functions. Important properties for longitudinal bars are the design load capacity in tension 10 of the longitudinal bars and the moment of inertia (I) of the longitudinal bars. Design load capacity is a property of a steel and is independent of the shape of a steel product. Moment of Inertia is a measure of the buckling resistance and is independent of the design load capacity of the longitudinal bar. Clause 1.6.3.42 of Australian Standard AS 3600 - defines the required 15   properties of fitments as being to “... restrain from buckling the longitudinal reinforcing bars in beams, columns and piles; carry shear, torsion and diagonal tension; act as hangers for longitudinal reinforcement; or provide confinement to the core concrete.” The term “design load capacity” of a steel bar, for example a longitudinal steel bar, is understood herein to mean the specified yield stress of the bar as manufactured 20 by a steelmaker. The references herein to “yield stress” are understood herein to be references to “design yield stress” and bars are manufactured by steelmakers to have a specified lower characteristic design yield stress which corresponds to the design yield stress in any given situation. 25           The term “moment of inertia”, i.e., I, of a steel bar is understood herein to be a measure of the capacity of the steel bar to resist bending, i.e., buckling resistance. It can be seen as advantageous to provide an alternative column reinforcement to known column reinforcements. It can also be seen as advantageous to provide an alternative longitudinal steel 30 bar for a column reinforcement to the known longitudinal steel bars that are used in column reinforcements. 2024205024  16 Jun 2026 Further, it can be seen as advantageous to provide an alternative reinforced concrete column that comprises (a) concrete and (b) a column reinforcement embedded in the concrete. The above description is not to be taken as an admission of the common general 5 knowledge in Australia or elsewhere. SUMMARY OF THE DISCLOSURE The disclosure is based on a realisation that making longitudinal steel bars for use as a reinforcement element in column reinforcements or any other suitable 10 applications from at least 600 MPa yield strength, typically high strength low alloy (“HSLA”), steel with (a) non-round cores, such as at least generally square cores, and (b) transverse ribs on outer surfaces of the cores with proportionally larger amounts of steel in the cores than in the transverse ribs than is the case in longitudinal round bars made from lower yield stress steels known to the applicant (or the same or higher yield 15 stress steels known to the applicant) creates an opportunity to provide longitudinal bars with smaller equivalent diameters and at least the same load capacities as those of known longitudinal bars made from lower yield stress steels and with adequate buckling resistance and bond strength (where “bond strength” is understood herein to mean a property that builds a mechanical bond between concrete and its reinforcement 20   bars). The applicant is not aware of any longitudinal steel bars that are used in, for example, column reinforcements of reinforced concrete columns that have the abovedescribed combination of features, namely: - non-round cores, such as at least generally square cores, 25           - proportionally larger amounts of steel in the cores than in the transverse ribs, i.e., proportionally lower rib volumes, than is the case in longitudinal round bars made from lower or higher yield stress steels. Other applications comprise, by way of example, reinforced concrete beams and reinforced concrete walls. 30           The disclosure is also based on a realisation that it is possible to make embodiments of the above-described longitudinal steel bars by forming the bars with 2024205024  16 Jun 2026 four longitudinal ribs that form the four corners of the non-round core of the bars and with transverse ribs that extend between and merge with the longitudinal ribs. In broad terms, the disclosure provides a longitudinal steel bar for use as a reinforcement element in a column reinforcement and other applications. The 5 longitudinal steel bar can be an at least 600 MPa yield stress steel bar comprising (a) a non-round core, such as a generally square core, (b) four longitudinal ribs that form the four corners of the non-round core, and (c) transverse ribs that extend between and merge with the longitudinal ribs. The longitudinal steel bar can have at least the same design load capacity as that of a known generally round cross section 500 MPa yield 10 stress bar (the “round 500 MPa bar”) and can have a smaller equivalent diameter than that of the round 500 MPa bar. Also, in broad terms, the disclosure provides a longitudinal steel bar for use as a reinforcement element in a column reinforcement and other applications. The longitudinal steel bar can be an at least 600 MPa yield stress bar that comprises a non-15 round core, such as a generally square core, and four longitudinal ribs. The four longitudinal ribs can be arranged to form four comers of the non-round core such that the 600 MPa yield stress bar has increased buckling resistance compared to a 600MPa round bar of equivalent diameter. In further broad terms, the disclosure provides a longitudinal steel bar for use as 20 a reinforcement element in a column reinforcement and other applications, the bar being an at least 600 MPa yield stress steel bar of at least the same design load capacity to that of a generally round cross section and lower yield stress bar (the “lower YS bar”), with the bar having a different shape to a generally round bar of equivalent cross sectional area and at least the same yield stress as the bar (the “equivalent round bar”), 25 the bar comprising (a) a non-round core, such as a generally square core, and (b) transverse ribs having a rib volume proportionally lower than that of the equivalent round bar, with a result that there is proportionally more steel in the core than is in the core of the equivalent round bar or the lower YS bar, with a result that there is proportionally more steel in the equivalent round bar or the lower YS bar. 30          The moment of inertia of the bar may be at least 3%, typically at least 4%, higher than that of the equivalent round bar. In the case of a non-round bar that is a 2024205024  16 Jun 2026 square cross-section bar, the moment of inertia of the bar is 4.72% higher than that of the equivalent cross-sectional area round bar. In one embodiment, the disclosure provides a longitudinal steel bar for use as a reinforcement element in a column reinforcement and other applications, the bar being 5 a 600 MPa yield stress steel bar of at least the same design load capacity to that of a generally round cross section 500 MPa yield stress bar (the “round 500 MPa bar”), with the bar having a different shape to a generally round 600 MPa yield stress bar of equivalent cross sectional area (the “round 600 MPa bar”), the bar including (a) a nonround core, such as a generally square core, and (b) transverse ribs having a rib volume 10 that is lower than the rib volumes of the round 600 MPa bar or the round 500 MPa bar, with a result that there is proportionally more steel in the core than is in the round 600 MPa bar or the round 500 MPa bar. The moment of inertia of the bar may be at least 3%, typically at least 4%, higher than that of the round 600 MPa bar. In the case of a non-round bar that is a 15 square bar, the moment of inertia of the bar is 4.72% higher than that of the equivalent cross-sectional area round bar. In broad terms, the disclosure also provides a longitudinal steel bar for use as a reinforcement element in a column reinforcement and other applications, the bar being an at least 600 MPa yield stress steel bar comprising (a) a non-round core, such as a 20 generally square core and (b) transverse ribs, with the core having at least four longitudinal ribs where a proportion of the volume of the transverse ribs has been transferred to the core in a manner which increases buckling resistance whilst maintaining adequate bond strength to the concrete. In broad terms, the disclosure also provides a longitudinal steel bar for use as a 25 reinforcement element in a column reinforcement and other applications, the bar being an at least 600 MPa yield stress steel bar comprising (a) a non-round core, such as a generally square core, (b) four longitudinal ribs that form the four corners of the nonround core, and (c) transverse ribs that extend between and merge with the longitudinal ribs. 30          In one embodiment the bar is a 600 MPa yield stress steel bar. 2024205024  16 Jun 2026 The applicant has found that this arrangement of a non-round core, four longitudinal ribs, and transverse ribs extending between and merging with the longitudinal ribs makes it possible to provide a longitudinal bar: (a) made from 600 MPa yield stress Class N (600N) steel that has the same 5              design load capacity as 500 MPa yield stress Class N (500N) steels in known longitudinal bars that have round transverse cross-sections (round “500 MPa” bars), and (b) having the same buckling resistance in a concrete column as the known 500 MPa yield stress Class N (500N) steel bars in a concrete column. 10          It is noted that “Class N” is terminology of the industry, with “N” describing that the steel in this class has “Normal” ductility as explained in Australian / NZ Standard AS / NZS 4671 - Steel for the reinforcement of concrete. It is noted that it is taken as read that all steels described below are “Class N”, noting that it is a requirement in Australia that all columns etc., be Class N. 15           Typically, the spacings of the ribs of the bar is greater than that of the ribs of known round 500 MPa and 600 MPa yield stress steel bars having round transverse cross-sections known to the applicant. As a consequence, the rib volumes of the bars are reduced proportionally. Typically, the nominal pitch of the transverse ribs is at least 12 mm, typically at 20 least 14 mm. Typically, the 600 MPa yield stress longitudinal bar has a smaller equivalent diameter than that of the round 500 MPa bar. Typically, the 600 MPa yield stress longitudinal bar has adequate buckling resistance and adequate bond strength. 25          Typically, the 600 MPa yield stress longitudinal bar has a proportionally smaller rib volume that that of the “round 500 MPa bar. The term “generally round cross section 500 MPa yield stress bar (the “round 500 MPa bar”)” is understood herein to mean for example the bar shown in Figure 8. The term “generally round 600 MPa yield stress bar of (the “round 600 MPa 30   bar”)” is understood herein to mean a bar that is the same cross-sectional profile as the bar shown in Figure 8 and for example the bar sold by NatSteel as “Grade 600N rebar”. 2024205024  16 Jun 2026 The term “generally square” is understood herein to mean a cross-sectional shape with four equal length sides, with each side being at least generally straight with at least generally square corners, such as shown for example in Figure 9. The term “generally square” is understood herein as a broad term and, for 5 example, may be influenced by the method of manufacturing a longitudinal bar. By way of explanation, typically, a longitudinal steel bar in accordance with the disclosure is formed by hot rolling a feed steel billet and, as a consequence of the rolling steps to form the bar, the core of the longitudinal bar may not be perfectly square with straight sides and may in some cases be described as being slightly more 10 hexagonal or octagonal or other higher polygonal in cross-section. It is noted that the applicant has found that a square cross-section, to the extent possible given manufacturing constraints, is an optimal shape compared to hexagonal or octagonal or other higher polygonal shapes in cross-section. Basically, in practice, a round steel reinforcing bar will not be truly round and a 15 square reinforcing steel bar not truly square. Assuming that steel bars are perfectly round and perfectly square, a square bar has a moment of inertia (I) that is 4.72% higher than that of a round bar of equal area. This is the same for all diameters. A better way of expressing it is the ratio of Isquare = Icircle X n / 3. 20         The steel may be a low C or a medium C or a HSLA steel. The steel may be a 600 MPa HSLA steel. The term “600 MPa yield stress HSLA steel” is understood herein to mean a steel having the following composition, in wt.%: - C: 0.08-0.20 25           - Si: 0.10-0.55 - Mn: 0.80-1.60 - Any one or more of the micro-alloying elements Ni, Cr, Mo, V, and Cu, in ranges of 0.05-0.50 - Iron, and unavoidable impurities from steelmaking. 30          The unavoidable impurities from steelmaking may include N and P. The combination of the use of the 600 MPa yield stress steel, typically a 600 MPa yield stress HSLA steel, and a change to a standard hot rolling process to form a 2024205024  16 Jun 2026 10 15 20 25 30 non-round core, such as a generally square core, from the steel makes it possible to produce a steel with the equivalent design load capacity, which consequently has a reduced cross sectional area, when compared to the diameter of the above-mentioned 500 MPa round bar, i.e., a longitudinal bar that has a round transverse cross-section and is made from a 500 MPa yield stress steel. Such a bar uses up to 16.7% less steel which is an advantage in terms of sustainability of steel manufacture in terms of material conservation and emissions reductions. In addition, the applicant has found that there are smaller variations in buckling resistance of a square cross-section bars with changes in orientation of the bars than is the case with changes in orientation of round bars. Typical features of the longitudinal bar in accordance with the disclosure for use for example as a column reinforcement are summarised below. 1.     As-manufactured bar lengths: 6 - 20 m (but could be any length). 2.     Bar diameter: 12 - 40 mm (but could be lower or higher). 3.     Bar lengths in manufactured column reinforcements: 4 - 8 m. 4.     Bar shape - non-round core, such as generally square core, and ribs extending from the core. 5.     Transverse cross-sectional area of bar 78.5 - 1256 mm2 (but could be lower or higher) - based on bar diameters. NB - the diameter of a bar is defined in AS / NZS 4671: 2019 - Steel for the reinforcement of concrete, as follows: “nominal equivalent diameter” means “the diameter in mm of an equivalent circular section of reinforcing steel having the same mass per meter of the deformed or indented bar.” 6.     Transverse cross-sectional area of core: 74.5 - 1193 mm2 - if it is assumed 5% of the steel is in the transverse ribs. 7.     Rib volume: up to 5 or 6% of the bar volume. 8.     Design load capacity: 47 - 755 kN. 9.     Yield stress: 600 MPa. 10. When the steel is a HSLA steel, a HSLA composition (in wt.%), typically as follows in Table 1: Table 1 - HSLA composition C P Mn Si S Ni Cr Mo Cu V N CEQ 2024205024  16 Jun 2026 0.10 0.30 0.050x 0.80 1.60 0.15 0.55 0.050x 0.35x 0.50x 0.10x 0.50x 0.050 0.150 0.015 0.040 0.49x 11.    Table 2 provides data on design load capacity, diameter, and cross sectional area of embodiments of the bars of the disclosure and examples of known 500 MPa round bars: Table 2 - design load capacity, diameter, and cross-sectional area of bars Designation Diameter (mm) Area (mm2) Known 500 MPa round bars Embodiment of Disclosure 600 MPa Design load capacity (kN) Known 500 MPa round bars Embodiment of Disclosure 600 MPa Known 500 MPa round bars Embodiment of Disclosure 600 MPa N12 S11 56.5 12.0 11.0 113 94.2 N16 S15 101 16.0 14.6 201 168 N20 S18 157 20.0 18.3 314 262 N24 S22 226 24.0 21.9 452 377 N28 S26 308 28.0 25.6 616 513 N32 S29 402 32.0 29.2 804 670 N36 S33 509 36.0 32.9 1020 848 N40 S37 628 40.0 36.5 1260 1050 Approx Reduction -known embodiment 0% 8.5% 16.7% 5 The 500 MPa bar may be made from a low C, a medium C or a HSLA steel. The 500 MPa bar may be made from 500 MPa yield stress steel. It is also noted that 500 MPa steel may be HSLA steel or a low carbon steel that has been quenched and tempered. 10          It is also noted that 600 MPa steel is predominantly steel that has a HSLA composition. The term “500 MPa yield stress steel” is understood herein to mean a steel having the following typical composition, in wt.%: - C: 0.10-0.30 15           - Si: 0.10-0.50 - Mn: 0.50-1.50 - Iron, and unavoidable impurities from steelmaking. 2024205024  16 Jun 2026 Typically, 500 MPa yield stress steel is manufactured by a quench and temper route, which avoids the need to the use of micro alloying elements. The term “diameter” is understood herein to mean the diameter of a transverse cross-section of the core of ma longitudinal bar having a round core, noting that the 5 diameter of a bar is defined in AS / NZS 4671: 2019. The “equivalent” diameter of a longitudinal bar having a non-round core, such as generally square transverse cross-section core, is calculated by converting the crosssectional area of the non-round core, such as square core, into a round cross-sectional area and then determining the diameter of the round cross-sectional area. 10          Table 4 below provides examples of diameters of longitudinal bars that have round transverse cross-sections and are made from 500 MPa yield stress steel and equivalent diameters of embodiments of longitudinal bars of the disclosure with nonround cores, such as at least generally square cores, that are made from a 600 MPa yield stress HSLA steel that has the same design load capacity as that of the 500 MPa yield 15 stress steel. Table 4 - diameters and equivalent diameters Known round 500 MPa bars -Diameter (mm) Embodiments of 600 MPa bars of the disclosure - Diameter (mm) 12 11.0 16 14.6 20 18.3 24 21.9 32 29.2 36 32.9 40 36.5 The smaller equivalent diameters of the non-round cores, such as generally square cores, of the longitudinal bars of embodiments of the disclosure that are made 20 from 600 MPa yield stress HSLA steel in Table 4 mean that, all other things being equal, the moments of inertia, i.e., buckling resistance, of these longitudinal bars are lower than the moments of inertia of the longitudinal bars that have round transverse cross-sections that are made from 500 MPa yield stress steel. This is a disadvantage. 2024205024  16 Jun 2026 However, to compensate for this, the longitudinal bars of the disclosure have proportionally lower rib volumes than the rib volumes of at least round cross sectional 600 MPa yield stress longitudinal bars. The result is that there is a larger amount of steel in the cores of the disclosure in proportional terms to the amounts of steel in cores 5 of round 500 MPa and 600 MPa yield stress bars. This proportionally larger amount of steel in the cores of the disclosure at least in part compensates for the loss of buckling resistance caused by moving to smaller equivalent diameter longitudinal bars of the disclosure. One option for further compensating for any loss of buckling resistance, should 10 compensation be necessary at all, is to reduce the spacings of fitments in column reinforcements More particularly, the applicant has found that when the above proportional reduction in rib volumes does not completely compensate for the loss of buckling resistance of the longitudinal bars, it is not always necessary to change the fitment 15   spacings in column reinforcements made from the longitudinal bars to accommodate loss of buckling resistance. For example, AS 3600 provides that there should be a maximum 15 bar diameter spacings of fitments in column reinforcements i.e. fitment spacing < 15 x D b where Db is the diameter of the longitudinal bars. An equivalent design load capacity 20 for a 16 mm 500N longitudinal bar made from 600 MPa yield stress HSLA steel with a generally square core in accordance with the disclosure has an equivalent diameter of 14.6 mm (see Table 4). Testing of scaled down columns reinforcements made from longitudinal bars with embodiments of the disclosure and a maximum of 240 mm (16.4 bar diameters) fitment spacing found had the same buckling resistance performance to 25 that of the 16 mm round transverse cross-section longitudinal bar. Therefore, the smaller diameter of these embodiments of longitudinal bars of the disclosure could be included in a column reinforcement without requiring a reduction in the fitment spacing from that required by AS 3600 for round transverse cross-section longitudinal bars made from existing 500 MPa yield stress steel. 30          The term “rib volume” is understood herein to mean the volume of the transverse ribs of a bar. 2024205024  16 Jun 2026 The volume of continuous longitudinal ribs is not within the definition of “rib volume”. The term “transverse rib” is understood to be a rib that is inclined at any angle to a longitudinal axis of the longitudinal bar. 5           The term “transverse rib” does not include a longitudinal rib. The rib volume may be less than 10% of the volume of the bar. The rib volume may be less than 8% of the volume of the longitudinal bar. The rib volume may be less than 6% of the volume of the longitudinal bar. The rib volume may be 4-6% or less by volume of the volume of the 10 longitudinal bar. The rib volume may be at least 3% of the volume of the longitudinal bar. The transverse ribs may be in a pattern that is configured to contribute to bond strength of the longitudinal bar in concrete in use in a column. The minimum bond strength required in any given situation is the design load 15 capacity of a longitudinal bar calculated from bar diameter and yield strength. It becomes more complicated if the bar does not meet the physical requirements of the Standard (AS / NZS 4671). To determine the bond effectiveness the bar is cast in concrete and subjected to a specified load, which is a function of the diameter and the design yield stress of the bar. At that load the slip of the bar is measured. The slip 20 must be <0.2 mm. The transverse ribs may be in any suitable rib pattern. The transverse ribs may be any shape that provides an appropriate bond provided they do not exceed the rib volume specified. The transverse ribs may have: 25           (a) transverse grooves or indents at rib crests, noting that the grooves or indents may also increase bond strength in concrete, and noting that material that is not in grooves or indents can be in the core, (b) longitudinal grooves or indents at rib noting that the grooves or indents may also increase bond strength in concrete, and noting that material that is not 30              in grooves or indents can be in the core; and (c) small indents on one face, or possibly both faces, of the ribs, and noting that material that is not in indents can be in the core. 2024205024  16 Jun 2026 In each of items (a) to (c), the material that would otherwise fill the grooves and indents may form part of the core of the longitudinal bar. Typically, the longitudinal bar is hot rolled from a square cross-section billet. The disclosure also provides a method of forming the above-described 5   longitudinal steel bars that comprises rolling the longitudinal bars from a square cross section billet. The disclosure also provides a column reinforcement comprising a framework comprising parallel longitudinal bars and fitments interconnecting the longitudinal bars and positioned at spaced intervals along the length of the column reinforcement, with 10 the longitudinal bars comprising the above-described longitudinal bar. The applicant has found that reducing fitment spacing compared to fitment spacings in column reinforcements known to the applicant with longitudinal bars having round transverse cross-sections and made from steel that has equivalent load capacity reduces the impact of loss of moment of inertia, i.e., buckling resistance, by 15 moving to smaller equivalent diameter longitudinal bars in the column reinforcement. Specifically, reducing the spacing of fitments improves the, buckling resistance, of the longitudinal bars. As noted above, the applicant has also found in test work that a reduction in fitment spacing is not always necessary. This is a further advantage of the disclosure in 20 terms of minimising the amount of steel that is required in a column reinforcement and therefore in terms of sustainability of steel manufacture and construction. The column reinforcement may comprise any suitable number of longitudinal bars and fitments depending on the end-use application. The column reinforcement may be any suitable “diameter” as this term is 25 described herein depending on the end-use application. The column reinforcement may comprise any suitable length depending on the end-use application. The disclosure also provides a reinforced concrete column comprising (a) concrete and (b) the above-described column reinforcement embedded in the concrete. 30 DESCRIPTION OF THE DRAWINGS 2024205024  16 Jun 2026 The disclosure is described further by way of example only with reference to the accompanying drawings of which: Figure 1 is a series of diagrams of one embodiment of a longitudinal bar in accordance with the disclosure for use in a column reinforcement; 5          Figure 2 shows a standard longitudinal bar with mark-ups on the Figure that indicate modifications to the rib pattern in accordance with an embodiment of a longitudinal bar in accordance with the disclosure for use in column reinforcements; Figure 3 shows a standard longitudinal bar with mark-ups on the Figure that indicate modifications to the rib pattern in accordance with an embodiment of a 10 longitudinal bar in accordance with the disclosure for use in column reinforcements; Figure 4 shows a rib pattern of a longitudinal bar in accordance with another, although not the only other, embodiment of the disclosure for use in a column reinforcement; Figure 5 are section drawings that show a rib pattern of a longitudinal bar in 15 accordance with another, although not the only other, embodiment of the disclosure for use in a column reinforcement; Figure 6 are section drawings that show a rib pattern of a longitudinal bar in accordance with another, although not the only other, embodiment of the disclosure for use in a column reinforcement; 20          Figure 7 are section drawings that show a rib pattern of a longitudinal bar in accordance with another, although not the only other, embodiment of the disclosure for use in a column reinforcement; Figure 8 are sections of a known round “N28” round cross section bar; Figure 9 are sections for an embodiment of a “S26” square cross section bar in 25 accordance with the disclosure; Figure 10 is a perspective view of one embodiment of a section of a column reinforcement in accordance with the disclosure; Figure 11 is a perspective view of another, but not the only possible, embodiment of a section of a column reinforcement in accordance with the disclosure; 30          Figure 12 is a series of side views and cross-sections that show the geometry and dimensions of three reinforced concrete (RC) columns tested by UNSW, with the RC columns being described as Types I, II, and III columns; 2024205024  16 Jun 2026 Figure 13 is a side view of one of the RC columns shown in Figure 12 and a perspective view of a middle section of the RC column that shows the location and number of 5 mm strain gauges attached to steel bars tested by UNSW; Figures 14-16 are graphs of load versus travel distance of actuators used in tests 5 on Types I, II, and III columns conducted by UNSW; Figures 17-19 are graphs of load-axial deformation / shortening over the gauge length of Types I, II, and III columns tested by UNSW; Figures 20-22 are graphs of load-average axial strain estimates over the gauge length of Types I, II, and III columns tested by UNSW Report; and 10           Figures 23-25 are graphs of load versus strain in the reinforcing steel bars of the RC columns (Types I, II, and III) tested by UNSW. DESCRIPTION OF EMBODIMENTS The following description focuses on longitudinal steel bars for use as 15 reinforcement elements of column reinforcements of reinforced concrete columns. As noted above, the disclosure is not confined to this application for the longitudinal steel bars of the disclosure. Other applications comprise, by way of example, beam reinforcement and wall reinforcement applications. 20 Longitudinal bars The embodiments of longitudinal bars 3 for column reinforcements shown in Figures 1-7 are made from a 600 MPa yield strength steel, typically a high strength low alloy (“HSLA”) steel, that is equivalent in design load capacity to a known 500 MPa 25 yield stress steel and the bars 3 have the same bucking resistance in concrete of the known 500 MPa yield stress steel bars. The disclosure is not confined to longitudinal bars 3 made from 600 MPa yield stress HSLA steel. The longitudinal bars may also be made from at least 600 MPa yield stress low 30 C or medium C steel. 2024205024  16 Jun 2026 The longitudinal bars 3 comprise non-round cores 5, such as at least generally square cores 5, in transverse cross-section and transverse ribs 7 extending outwardly from outer surfaces of the cores 5. The cores 5 have longitudinal ribs 9. The longitudinal bars 3 have a smaller equivalent diameter than the diameter of 5 longitudinal bars that have round transverse cross-sections and are made from 500 MPa yield stress steels known to the applicant. As noted above, all other things being equal, the smaller equivalent diameter means that the bars have a smaller buckling resistance and this is a disadvantage of moving to smaller diameters, noting that this move has advantages such as steel 10 sustainability in terms of material conservation and emissions reductions. In order to compensate for the smaller diameters (which are otherwise an advantage), the transverse ribs 7 of the bars 3 shown in Figures 1-7 are formed to have less than 10%, typically less than 8%, typically less than 6%, typically of the order of 45% or less, by volume of the total volume of the longitudinal bars 3, i.e., the volume of 15 the cores 5 (including the longitudinal ribs 9) and the volume of the transverse ribs 7. This is a smaller volume proportionally than the volume of transverse ribs 7 in relation to total volumes of longitudinal bars that have round transverse cross-sections and are made from 500 MPa yield stress steel and 600 MPa yield stress steel known to the applicant. 20          As a consequence, there is proportionally more steel in the cores 5 than is the case with longitudinal bars that have round transverse cross-sections and are made from 500 MPa yield stress steel and 600 MPa yield stress steel. In other words, the amount of steel in the cores 5 of the longitudinal bars 3 is a higher proportion of the total amount of steel in these bars than is the case with the 25 longitudinal bars that have round transverse cross-sections and are made from 500 MPa yield stress steel or 600 MPa yield stress steel. This proportional increase in steel in the cores 5 improves bucking resistance and compensates for the impact of smaller diameters on this parameter. The transverse ribs 7 are configured to contribute to the bond strength of the 30 longitudinal bars 3 in concrete in column reinforcements. Each of the embodiments of the longitudinal bar 3 shown in Figures 1 and 4-7 comprises: 2024205024  16 Jun 2026 (a) a non-round core 5 comprising four longitudinal ribs 9 that form the corners of a square core 5, and (b) transverse ribs 7 in the form of a series of parallel, spaced apart, ribs 7 that are at, for example, an angle of 60° to a longitudinal axis of the longitudinal 5              bar and extend between and merge with adjacent longitudinal ribs 5. The embodiment of the longitudinal bar 3 shown in Figure 2 comprises a nonround core 5, such as square core 5, comprising two longitudinal ribs 9 and a rib pattern in the form of transverse ribs 7 at 90° to a longitudinal axis of the longitudinal bar. The transverse ribs 7 are crescent shaped. The transverse ribs 7 have indents or grooves 11 10 that cut across the ribs 7 in the longitudinal axis of the longitudinal bar. The material that would have been in the indents or grooves 11 is in the core 5 and increases the area / equivalent diameter of the core. The embodiment of the longitudinal bar 3 shown in Figure 3 is the same as the embodiment shown in Figure 2, with the exception that the transverse ribs 7 are at an 15 angle of 60° to a longitudinal direction of the longitudinal bar 3 and the transverse ribs 7 extend to and merge with the longitudinal ribs 9. As is the case with Figure 2, the transverse ribs 7 shown in Figure 3 have indents or grooves 11 that cut across the ribs 7 in the longitudinal axis of the longitudinal bar. 20          As is the case with the Figure 2 embodiment, the material that would have been in the indents or grooves 11 is in the core 5 and increases the area / equivalent diameter of the core 5. It is noted that the indents or grooves 11 shown in Figures 2 and 3 may be at any angle in relation to the longitudinal axis of the bars 25          In any given situation, the number, size etc., of the indents and grooves 11 can be determined by modelling and / or testing. The material taken out of the transverse ribs 7 as a consequence of forming the indents and grooves 11 is part of the at least generally square cores 5 and contributes to the proportionally larger sizes of the cores. In the case of the Figure 4 embodiment, there are grooves 13 in the transverse 30 ribs 7 that extend along the length of the ribs 7. The material that was in the grooves 13 is in the core 5 and increases the area / equivalent diameter of the core. 2024205024  16 Jun 2026 The applicant has found that the Figures 1-7 embodiments are an effective structure of longitudinal ribs 9 and transverse ribs 7 for providing longitudinal bars: (a) made from 600 MPa yield stress steel that has the same design load capacity as 500 MPa yield stress steels in known longitudinal bars that have round 5               transverse cross-sections, and (b) having buckling resistance in concrete that complies with Australian Standards. It is noted that the main differences between the embodiments shown in Figures 5-7 is the spacing of the transverse ribs 7. 10          It is also noted that the spacings of the transverse ribs in the embodiments shown in Figures 1-7 are greater than that of the transverse ribs of known round 500 MPa yield stress steel bars and round 600MPa yield stress steel bars known to the applicant. This is one of the reasons it is possible to proportionally reduce the rib volumes of the bars shown in Figures 1-7. 15           Typically, the nominal pitches of the ribs shown in Figures 1-7 and generally in accordance with the disclosure is at least 12 mm, typically at least 14 mm. In another embodiment (not shown), there could be roll-formed dimples in a face of the ribs. The embodiments of the longitudinal bars shown in Figures 1-7 are typically 20 formed in a hot rolling mill, as described further below. An embodiment of a method of forming the longitudinal bars of the disclosure comprises hot rolling the longitudinal bars, typically from a billet of steel. In overall terms, the embodiment of the method is a standard hot rolling method for producing standard longitudinal bars for column reinforcement and other 25 applications, with modifications to roll-forming passes to form the non-round cores 5 and ribs 7, including ribs 7 with indents or grooves 11. In practice, the calculation of the new equivalent diameters (DYS) for longitudinal bars in accordance with the disclosure for use in column reinforcements is based on the design yield stress (YS) e.g. [D600 = SQRT(D5002 x 500 / 600)], such that, 30 for example, a 20 mm diameter longitudinal bar made from 500 MPa yield stress steel becomes an 18.3 mm diameter longitudinal bar made from 600 MPa yield steel. 2024205024  16 Jun 2026 As noted above, buckling is not a function of strength but is a function of “I” (Moment of Inertia). For a circle, this is given by n D4 / 64, whereas for a square it is B4 / 12 (where B = dimension of the square of the same area as the circle). The ratio of the Moments of Inertia is therefore 5 Isquare = Icircle x n / 3 The Isquare is only 4.72% greater than that of Icircle. However, moving from a 20 mm longitudinal bar made from 500 MPa yield 10 stress steel known to the applicant to a non-round, such as an at least generally square, longitudinal bar made from 600 MPa yield stress steel which has the same design load capacity as the 500N steel results in a 600 MPa longitudinal bar having a smaller diameter of D = ~18.3mm. This is an important advantage from a perspective of steel sustainability in terms of material conservation and emissions reductions. A 15 disadvantage is a reduction in the Moment of Inertia by approximately 27% - which is substantial. As described above, the disclosure compensates for the reduction in the Moment of Inertia by proportionally increasing the amount of steel in the core of the longitudinal bar, i.e., proportionally reducing the rib volume. 20          The above numbers are constant no matter the bar diameter. It is evident from the above that the disclosure is a viable alternative to longitudinal bars having round transverse cross sections that are made from 500 MPa yield stress steel known to the applicant. An acceptable protocol for calculating rib volumes is an important 25 consideration. The calculation can be complicated given the usual rib patterns and changes in rib patterns along the length of bars. There are different approaches that can be taken to calculate rib volumes. As far as the applicant is aware, there are no Australian or other Standards that set out procedures for calculating rib volumes. 30         Table 5 provides calculated rib volumes for known round 500 MPa bars and generally square 600 MPa bars in accordance with embodiments of the disclosure. 2024205024  16 Jun 2026 The rib volumes were calculated in accordance with the protocol developed by the applicant that is set out in the following section of the specification. Table 5 - calculated rib volumes for known round 500 MPa bars and generally square 5 core 600 MPa bars in accordance with embodiments of the disclosure BAR DIAMETER (mm) MASS AREA DIAMETER MASS RIB VOLUME ACTUAL THEOR. A THEOR. ACTUAL A ACTUAL A (kg / m) (%) (mm2) (mm2) (%) (mm) (%) (kg / m) (kg / m) (%) N20 20 2.38 2.47 -3.53 314 285 -9.3 19.0 -4.8 2.24 0.142 5.75 S18 18.3 1.97 2.06 -4.56 263 239 -9.1 17.4 -4.7 1.88 0.094 4.57 N28 28 4.67 4.83 -3.41 616 560 -9.1 26.7 -4.6 4.40 0.27 5.65 S26 25.6 4.00 4.04 -1.05 515 495 -3.8 25.1 -1.9 3.89 0.112 2.78 N40 40 9.61 9.86 -2.57 1257 1146 -8.8 38.2 -4.5 9.00 0.615 6.23 S37 36.5 7.87 8.21 -4.23 1046 954 -8.8 34.9 -4.5 7.49 0.378 4.60 With reference to Table 5, the 500 MPa bars are referred to as N20, N28 and N40 and the 600 MPa bars in accordance with embodiments of the disclosure are referred to as S18, S26 and S37. 10          Figures 8 and 9 are sections of the N28 and S26 bars used for calculations of rib volumes. There are small scaling issues in the images in Figures 8 and 9 as they were taken from different images. The scaling issues are common to both Figures. Putting aside the scaling issues, it is clear from Figures 8 and 9 that the known 15   N28 bar has a round core and the N26 bar in accordance with an embodiment of the disclosure has a non-round, in this instance generally square core. With reference to Figures 8 and 9, it is clear that the S18, S26 and S37 bars had proportionally less rib volume than the equivalent N20, N30 and N40 round bars. The S26 bar which was comparatively “fatter” than the N30 bar as measured by the 20 deviation from the theoretical mass per meter i.e. -ve 1.05% compared to -ve 3.41%, had proportionally less steel in the transverse ribs.. This conclusion is based on an assumption that the ribs fill the cavity ground into the rolls to form the ribs, noting that this is not always the case in practice. There are several factors that influence rib fill / height, such as bar temperature, 25 bar speed through the roll pass, the amount of tension in the bar and the amount of reduction achieved in the finishing pass where the ribs are formed. For example, if 2024205024  16 Jun 2026 insufficient stock is presented to the final pass, there may not be enough metal flow into the full depth of the notch. Protocol for determining rib volumes 5          The applicant developed the following protocol for determining rib volumes of bars. 1. Determined the mass / m and its variation from nominal, by weighing and measuring the bar samples. In all cases they were -ve. Note - the maximum variation allowed is + / -4.5%. The -4.56% for the S18 is outside that limit but not consequential 10 for this exercise. 2. Sectioned the bars at an angle to avoid sectioning any transverse ribs. This isolated the core i.e. the critical part of the bar with respect to force capacity and buckling resistance. 3. Polished the bar faces to allow clear identification of the cores. The 15 colouring of the transverse ribs provided good contrast for the photograph (Figures 8b and 9b). 4.     Photographically isolated the core image (green area in Figures 8b and 9b). 5. Measured the distances across the longitudinal ribs of the actual bars to 20 provide a scale (see Figure 8c and 9c). 6.     With the core images and the scale computed the area of the cores. 7.     Determined the mass of the cores and referenced a standard density of 7850 kg / m3. 8. Knowing the actual mass of the bar (including ribs) and the mass of the 25 core, determined the mass of the ribs and their percentage of the overall mass. The references to “rib volumes” herein are understood to be determined by the above protocol. Column reinforcements 30          Figures 10 and 11 are perspective views of two embodiments of sections of column reinforcements 15 in accordance with the disclosure that are suitable for use in reinforced concrete columns in accordance with the disclosure. 2024205024  16 Jun 2026 Each column reinforcement 15 comprises a framework of parallel longitudinal bars 3 and fitments 17 interconnecting the longitudinal bars and positioned at spaced intervals along the length of the column reinforcement. The longitudinal bars 3 comprise any one of the embodiments of the 5 longitudinal bar shown in Figures 1-7. The column reinforcements shown in Figures 10 and 11 are suitable for use in the construction of reinforced concrete columns in accordance with the disclosure, with each reinforced concrete column comprising a column reinforcement embedded in concrete. 10 UNSW Report The applicant retained UNSW Sydney to conduct laboratory tests on three groups of reinforced concrete (RC) columns that include longitudinal steel bars in accordance with embodiments of the disclosure to investigate the failure mode and load 15 carrying capacity of the RC columns to investigate the effectiveness of the longitudinal bars and embodiments of RC columns in accordance with embodiments of the disclosure. A Report on the results of the tests prepared by Professors Hamid Vali Pour and Stephen Foster indicates that the buckling capacity of longitudinal steel bars in 20 accordance with embodiments of the disclosure is superior than that required by Australian Standard AS 3600. The Report also indicates that tests also showed that the longitudinal steel bars in accordance with embodiments of the disclosure could have the fitments, which provide resistance to buckling, spaced wider apart than that required by the Australian 25 Standard AS 3600 without impacting on the capacity of the column. The following sections of the specification are based on the Report. Figures 1225 are from the Report. 1. INTRODUCTION 30          The Report describes the results of laboratory tests performed on three groups of RC columns to investigate the failure mode and load carrying capacity of the RC columns when: 2024205024  16 Jun 2026 1- normal ductility (N500) longitudinal steel bars are replaced with embodiments of longitudinal steel bars (Grade S) that have higher yield strength, fsy= 600 MPa, but with a smaller diameter such that the total load causes yielding of the bars remains unchanged; and 5   2- the spacings of steel fitments (transverse reinforcing bars) are adjusted (increased) with respect to the spacings specified for N500 fitments (in AS 3600:2018). In the experimental program, special attention was paid to the buckling of the longitudinal steel bars (over the length) between the fitments and the impact of this 10 buckling on the failure mode and peak load-carrying capacity of the columns. 2. DETAILS OF MATERIALS AND FABRICATION OF SPECIMENS Fourteen RC column specimens were fabricated and tested. The specimens are denoted as Columns-1 to -14 in three types / groups, i.e., Type I, Type II, and Type III 15 (Figure 12). The columns were 350 mm x 275 mm in cross-section and 2,135 mm in total length (Figure 12). All columns were reinforced longitudinally with 6 S15 reinforcing bars; each S15 bar had a diameter of 14.6 mm, a cross-section of 167 mm2. and a nominal characteristic strength of 600 MPa. The geometry, dimensions, and details of the steel reinforcement for Type I, Type II and Type III columns are shown in 20 Figure 12. The three column types only differ in the spacing of the transverse reinforcing bars / fitments within the middle part of the specimens (Figure 12). In order to minimize the probability of failure outside of the gauged test zone (middle region) of the specimens, additional longitudinal steel bars were provided in each of the column’s end zones and the tie spacing was reduced (Figure 12 cross 25 sections S2 and S3). The added bars strengthen only that section of the column thereby ensure failure was at the mid-section of the column where all the strain gauges were located to monitor loads and deflections. This removed the impact of high local stresses where the column was loaded that would not normally happen in an actual column in a building. 30         The transverse fitments were made of 4.75 mm wire of nominally 500 MPa yield stress. All the fitments (transverse reinforcing bars) and some of the steel cages were fabricated by the applicant and delivered to the Heavy Structures Laboratory of 2024205024  16 Jun 2026 the School of Civil and Environmental Engineering at UNSW Sydney. The S15 longitudinal steel bars were also supplied to the project by the applicant. The formwork for the specimens and the steel cages were fabricated in the CIES Heavy Structures Laboratory. After placing the steel cage in the formwork, a clear 5 cover on the closed fitment was measured again and it was between 20 and 25 mm. The specimens were cast. In addition to the fourteen RC columns, twelve 100 mmx200 mm cylinders were cast. The concrete cylinders were tested to determine the compressive strength of concrete at 29 days (3 cylinders), at 30 days (1 cylinder), at 36 days (2 cylinders), at 42 10 days (2 cylinders), at 50 days (1 cylinder) and at 56 days (1 cylinder). All columns and cylinders were cast with a nominal 20 MPa strength concrete, with maximum aggregate size of 10 mm and 90 mm slump (supplied by BORAL). Uniaxial compression tests (at a rate of 20 MPa / minute) were conducted on 200 mm high by 100 mm diameter concrete cylinders in accordance with AS1012.8. The 15 results of uniaxial compression tests performed on the cylinders and the numbers of cylinders tested are summarised in Table 6. Table 6 - summary of uniaxial compression tests performed on 100 mm*200 mm cylinders. Age No of cylinders Compressive strength (MPa) Mean compressive strength & CoV 29 days 3 21.1, 20.0, 21.1 Mean = 21.0 MPa, CoV= 3.5% 30 days 1 21.8 Ditto 36 days 2 25.7, 27.5 Mean = 6.5 MPa, CoV= 3.3% 42days 2 25.9, 27.0 Ditto 50 days 1 26.3 Mean= 27.2 MPa, CoV= 3.5% 56 days 1 28.2 Ditto 20 3. TEST SETUP, INSTRUMENTATION AND LOADING PROCEDURE The RC columns were tested under a 5 MN testing frame and actuator, under a ram displacement control. 2024205024  16 Jun 2026 In all the tests, except for the first (pilot) test, ram displacement-controlled load had an initial rate of 0.6 mm / minute up to a load of 1800 kN, then the displacement rate was reduced to 0.3 mm / minute up to a load of 2100 kN and in the final stage the displacement rate was reduced to 0.1 mm / minute until failure of the columns. Testing 5 was stopped when the load had reduced by approximately 10 to 15 per cent of the maximum load. The rate of loading used in each test and a short description of the loading protocol (including a loading to 1000 kN, unloading and reloading stage, to ensure the specimens were bedded in) are provided in Table 7. 10         A 5 mm thick Masonite board was placed between the concrete column specimen and the actuator to apply even pressure over the specimen’s loading surface. The axial deformation (shortening) of the column over a gauge length of 550 mm was measured by a pair of LVDTs (i.e., LVDT-1 and LVDT-2) placed on the opposite faces of the columns. The load applied on the columns was measured by the 15 built-in load cell of the 5 MN Instron actuator. In addition, eleven 5 mm long YEFLAB-5-3LJC-F steel strain gauges were attached to the surface of the reinforcing steel bars for the first three specimens of each group / type. The first nine strain gauges, i.e., Nos. 1-9, were attached to the surface of the longitudinal steel bars and the last two gauges were attached to the surface of the 20 closed ties. In the remaining two specimens of each group, only three steel strain gauges were installed on the longitudinal reinforcing bars. The location and strain gauge number attached to the surface of the longitudinal and transverse reinforcing steel bars are shown in Figure 13. 25 Table 7 - Summary of the test data, loading rate and loading protocol in the column tests. Test No. Column type Description of loading protocol Description of loading rate 1 I Monotonically increasing (No unloading / reloading) 0.1 mm / minute up to 200 kN 0.4 mm / minute up to 1200 kN 0.2 mm / minute up to 1900 kN 0.1 mm / minute up to failure 2024205024  16 Jun 2026 2 III Unloading / reloading between 1000 kN & 400 kN 0.6 mm / minute up to 1800 kN 0.3 mm / minute up to 2100 kN 0.1 mm / minute up to failure 3 II ditto ditto 4 III Unloading / reloading between 1000 kN & 200 kN ditto 5 I ditto ditto 6 II ditto ditto 7 I ditto ditto 8 II ditto ditto 9 III ditto ditto 10 III ditto ditto 4. TEST RESULTS The peak load and failure modes of the columns are summarised in Table 8. The load-vertical travel distance of the actuator and the load-axial shortening of 5 the columns are plotted in Figures 14-16 and Figures 17-19, respectively. Note the nonlinearity in the early stage (load to about 1000 kN due to bedding in phase). In Figures 12-14, two graphs corresponding to the axial deformation / shortening measured by the two displacement transducers (i.e., LVDTs / LSCTs on the West and East faces of the columns) are plotted. 10 Table 8 - Summary of the modes of failure, peak load, and coefficient of variation (CoV) of the peak loads of the columns. Column type Test No. Peak load (kN) Description of failure modes Mean peak load (kN) & CoV I 1 2445 Concrete crushing within the gauge length. Buckling of bars took place during the post-peak Mean= 2,381 kN CoV= 2.4% I 5 2339 Ditto Ditto 2024205024  16 Jun 2026 I 7 2358 Concrete crushing within the gauge length and some cracks at the end, but no buckling was observed Ditto II 3 2402 Concrete crushing within the gauge length. Buckling of bars took place during the post-peak Mean= 2,531 kN CoV= 5.4% II 6 2674 Concrete crushing within the gauge length, but no concrete spalling and buckling of bars were observed Ditto II 8 2517 Concrete crushing within the gauge length, minor concrete spalling and buckling of bars were observed Ditto IIII 2 2276 Concrete crushing within the gauge length and at the end of the column, but no evidence of bar Mean= 2,444 kN CoV= 6.1% IIII 4 2317 Concrete crushing and cracking at the end of the column, but no evidence of bar buckling Ditto IIII 9 2562 Concrete crushing within the gauge length and minor cracks at the end of the column, but no evidence of bar buckling Ditto 2024205024  16 Jun 2026 IIII 10 2620 Concrete crushing within the gauge length, minor concrete spalling and buckling of bars were observed Ditto The load-average strain in the concrete columns is plotted in Figures 20-22. The two strains for each column were determined over a gauge length of 550 mm. In all columns, at the peak load, the average longitudinal compressive strain over 5 the 550 mm gauge length was of the order of 2,000 to 2,500 ^e, which corresponds to the peak strain of the concrete. The load-strain in the longitudinal and transverse steel bars / fitments are plotted in Figures 23-25. The load-strain results show that the measured strains in the fitments (gauge SG-10 and SG-11) remained well below the nominal yield strain (ey= 0.0025). Except 10 for specimen no. 7 from Type I and specimen no. 2 from Type III, in all the columns, strain in at least one of the longitudinal steel bars reached and exceeded the mean yield strain (ey= 650 / 200,000= 0.0032) of the longitudinal S15 bars. Comparing average compressive strain (Figures 20-22) with the strain of longitudinal steel bars (Figures 23-25) shows a close correlation between the average 15 compressive strain (over 550 mm gauge length) and the average strain in the longitudinal bars (measured by SG-1 to SG-9). 5. SUMMARY AND DISCUSSION OF TEST RESULTS The visual observations made, and videos taken, during the column tests and 20   load-axial deformation diagrams (over the gauge length) of the columns showed that crushing of concrete took place before buckling of the longitudinal reinforcing bars and failure of the columns at peak load was always associated with onset of concrete crushing. Buckling of the longitudinal steel bars either did not occur or took place well 25 into the softening part of the response (after crushing of the concrete). The average peak loads of the three groups / types of the columns with fitment spacing of 15db, 16.5db and 20db (db being the diameter of the 14.6 mm diameter 2024205024  16 Jun 2026 longitudinal steel bars) were 2,381 kN, 2,531 kN and 2,444 kN, respectively. This shows that the spacing of the fitments (transverse reinforcing bars’ spacing) in the range of 15db to 20db has no, or negligible, impact on the capacity of concentrically loaded columns designed to AS 3600:2018. The small difference in the mean peak load of 5 three groups / types of columns is attributed to slightly increased concrete compressive strength with time, variability of the concrete compressive strength and variations in the accidental eccentricities, which are evaluated and discussed in the following paragraphs. The finding that fitment spacing up to 20db does not impact the buckling of 10 longitudinal bars and, thereby, not affecting a column’s axial strength, is in line with Eurocode 2 (EN 1992-1-1:2004) Clause 9.5.3(3), which specifies a maximum fitment spacing of 20db. By way of summary, the test work of UNSW showed that that the buckling capacity of longitudinal steel bars in accordance with embodiments of the disclosure is 15 superior to that required by Australian Standard AS 3600. Many modifications may be made to the disclosure as described above without departing from the spirit and scope of the disclosure.

Claims

1. A longitudinal steel bar for use as a reinforcement element in a column reinforcement and other applications, the bar being an at least 600 MPa yield stress5 steel bar comprising (a) a non-round core, such as a generally square core, (b) four longitudinal ribs that form the four corners of the non-round core, and (c) transverse ribs that extend between and merge with the longitudinal ribs;wherein the longitudinal steel bar has at least the same design load capacity as that of a known generally round cross section 500 MPa yield stress bar (the “round 50010 MPa bar”) and has a smaller equivalent diameter than that of the round 500 MPa bar.

2. A longitudinal steel bar as defined in claim 1, the longitudinal steel bar having adequate buckling resistance and adequate bond strength.

3. A longitudinal steel bar as defined in claim 1 or claim 2, the longitudinal steel bar having a proportionally smaller rib volume that that of the round 500 MPa bar.15   4. A longitudinal steel bar as defined in claim 3, wherein the spacings of thetransverse ribs is greater than that of the ribs of the round 500 MPa bar thereby making it is possible to proportionally reduce the rib volume of the bar.

5. A longitudinal steel bar as defined in claim 4, wherein the nominal pitch of the transverse ribs is at least 12mm, such as at least 14mm.20   6. A longitudinal steel bar as defined in any one of the preceding claims, whereinthe rib volume is less than 10% of the volume of the bar, such as less than 8%, or less than 6%, or in the range 4-6% of the volume of the bar.

7. A longitudinal steel bar as defined in any one of the preceding claims, wherein each transverse rib comprises a spiral pattern along the length of the longitudinal bar.25   8. A longitudinal steel bar as defined in any one of the preceding claims, whereinthe transverse ribs comprise:(a) transverse grooves or indents at rib crests,(b) longitudinal grooves or indents at rib; and(c) small indents on one face or both faces of the ribs.30   9. A longitudinal steel bar as defined in any one of the preceding claims, whereinthe steel is any one of a low C or a medium C or a high strength low alloy (“HSLA”) steel.2024205024  16 Jun 202610. A longitudinal steel bar as defined in claim 9, wherein the HSLA steel comprises the following composition, in wt.%:-  C: 0.08-0.20-   Si: 0.10-0.555          - Mn: 0.80-1.60- any one or more of the micro-alloying elements Ni, Cr, Mo, V, and Cu, in ranges of 0.05-0.50- iron, and unavoidable impurities.

11. A longitudinal steel bar as defined in any one of the preceding claims, wherein a 10 moment of inertia of the bar is at least 3% higher than that of the 600 MPa round bar.

12. A longitudinal steel bar as defined in any one of the preceding claims, wherein the transverse ribs located on either side of a given longitudinal rib join the longitudinal rib at the same location along the longitudinal rib.

13. A longitudinal steel bar for use as a reinforcement element in a column15 reinforcement and other applications, the bar being an at least 600 MPa yield stress bar that comprises a non-round core, such as a generally square core, and four longitudinal ribs, wherein the four longitudinal ribs are arranged to form four comers of the nonround core such that the 600 MPa yield stress bar has increased buckling resistance compared to a 600MPa round bar of equivalent diameter.20    14. A longitudinal steel bar as defined in claim 13, the longitudinal steel bar beingotherwise as defined in any one of claims 1 to 12.

15. A column reinforcement comprising a framework comprising parallel longitudinal steel bars and fitments interconnecting the longitudinal steel bars and positioned at spaced intervals along the length of the column reinforcement, with the25 longitudinal steel bars comprising the longitudinal steel bar as defined in any one of the preceding claims.

16. A reinforced concrete column comprising (a) concrete and (b) the column reinforcement defined in claim 15 embedded in the concrete.

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