The grid of ribbed steel bars buried inside every reinforced-concrete slab, beam, column, foundation, bridge deck, sidewalk, retaining wall, and tilt-up panel. Concrete is strong in compression but weak in tension; rebar carries the tension load that concrete can't. The ribs (the 'deformations' rolled onto the bar at the mill) are how the steel grips the surrounding concrete — pull the bar without ribs and it slips out; pull the bar with ribs and the bond carries the load to the bar's full yield strength. Common sizes run from #3 (10 mm) through #11 (36 mm) in the US, with metric sizes from 10 mm through 50 mm internationally. Painted epoxy coating goes on bridge decks and marine work where rust would crack the cover concrete; uncoated black bar is the global default everywhere else.
Hot-rolled low-carbon to low-alloy steel reinforcement bar with rolled-on transverse rib deformations for mechanical bond to surrounding concrete. The principal North American specifications are ASTM A615 (carbon-steel rebar, the dominant grade) and ASTM A706 (low-alloy weldable rebar, ductility-controlled, used in seismic regions and welded reinforcement); the international counterpart is EN 10080 (with national grades B500A, B500B, B500C). ASTM A615 grades by yield strength: Grade 40 (280 MPa, legacy), Grade 60 (420 MPa, the modern dominant grade), Grade 80 (550 MPa, high-strength), Grade 100 (690 MPa, specialty seismic). Tensile strength is 1.25–1.5× the yield. Bar size designations: US #3 to #18 (3/8 inch to 2-1/4 inch nominal diameter, in 1/8-inch increments by number); European 6, 8, 10, 12, 14, 16, 20, 25, 32, 40, 50 mm. Carbon content 0.30–0.45% for A615 Grade 60, with manganese 0.5–1.5% — a steel composition tuned for hot-rolling consistency and adequate weldability without alloying cost. Density 7860 kg/m³, modulus 200 GPa, all the same as any low-carbon steel. Surface options: bare hot-rolled black bar (the default); fusion-bonded epoxy coating per ASTM A775 (green or purple, the bridge-deck and marine standard); galvanized per ASTM A767; stainless rebar per ASTM A955 (Type 2304, 304 SS, 316 SS, dual-phase 2205) for highest-corrosion-service applications such as coastal piers and aggressive-deicing environments. Bond mechanics are standardized: each rib's height, spacing, and angle is specified by ASTM A615 to ensure development length predictability — the rebar's 'grip' on concrete is a designed property, not an emergent one. Welding is restricted: A615 carbon rebar is not metallurgically tuned for weldability, and field-welded rebar splices are restricted to A706 grade, with mechanical couplers (Lenton, Bartec, Erico) the preferred non-welded alternative for splicing #11 and larger. Production is dominated by electric-arc-furnace mini-mills using scrap-steel feedstock — rebar is among the most-recycled-content steel products in industrial use, often 90+ percent recycled.
It was out of the relatively small-scale, craft-based operation of concrete construction that the next significant development, steel reinforcement, emerged. The story here was marked by an almost total absence of theory, and was conducted by inserting pieces of iron and steel into the concrete and hoping for the best. Architects and engineers showed no interest in these developments at all, remaining largely aloof and indifferent to them long after they had become accepted within the building trade.
Steel, lightweight, wholly reliant upon specialists from outside the traditional building trades, had many advantages in the modernity stakes over reinforced concrete — heavy, reliant upon carpenters to make the formwork, and with a need for much unskilled labour to realize it.
Principled BSDF defaults derived from the sphere metallic finish. Reasonable seed for Blender, Substance, Keyshot, Rhino — tune per material. Or grab the whole library at once: ForMaterials library →
# finish: metallic albedo #403832 metallic 1.00 roughness 0.25 ior 1.45 transmission 0.00 clearcoat 0.00 sheen 0.00 anisotropic 0.00
{
"albedo": "#403832",
"metallic": 1.0,
"roughness": 0.25,
"ior": 1.45,
"transmission": 0.0,
"clearcoat": 0.0,
"sheen": 0.0,
"anisotropic": 0.0
}
# Blender 4.x — Principled BSDF
# Steel Reinforcing Bar (Deformed Rebar, ASTM A615 / EN 10080) · finish: metallic
import bpy
mat = bpy.data.materials.new(name="mat_steel_rebar_deformed")
mat.use_nodes = True
bsdf = mat.node_tree.nodes["Principled BSDF"]
bsdf.inputs["Base Color"].default_value = (0.0513, 0.0395, 0.0319, 1.0)
bsdf.inputs["Metallic"].default_value = 1.000
bsdf.inputs["Roughness"].default_value = 0.250
bsdf.inputs["IOR"].default_value = 1.450
bsdf.inputs["Transmission Weight"].default_value = 0.000
bsdf.inputs["Coat Weight"].default_value = 0.000
bsdf.inputs["Sheen Weight"].default_value = 0.000
bsdf.inputs["Anisotropic"].default_value = 0.000
# KeyShot 11+ — lux Python API, Generic material
# Steel Reinforcing Bar (Deformed Rebar, ASTM A615 / EN 10080) · finish: metallic
# Run from Window → Scripting Console
import lux
mat = lux.createMaterial(name="mat_steel_rebar_deformed", materialType="Generic")
mat.setProperty("diffuse", (64, 56, 50)) # 8-bit sRGB
mat.setProperty("metallic", 1.000)
mat.setProperty("roughness", 0.250)
mat.setProperty("indexOfRefraction", 1.450)
mat.setProperty("transparency", 0.000)
mat.setProperty("coatingWeight", 0.000)
{
"_format": "Substance Designer / Painter \u2014 pbrMetalRough constants",
"_about": "Steel Reinforcing Bar (Deformed Rebar, ASTM A615 / EN 10080) \u00b7 finish: metallic",
"baseColor": {
"r": 0.0513,
"g": 0.0395,
"b": 0.0319
},
"metallic": 1.0,
"roughness": 0.25,
"ior": 1.45,
"opacity": 1.0,
"anisotropyLevel": 0.0,
"_notes": "Channels listed are the standard Substance pbrMetalRough output. Drop into a Uniform Color node per channel, or as the constant input on a layered stack."
}{
"asset": {
"version": "2.0",
"generator": "ForMatter"
},
"materials": [
{
"name": "mat_steel_rebar_deformed",
"pbrMetallicRoughness": {
"baseColorFactor": [
0.0513,
0.0395,
0.0319,
1.0
],
"metallicFactor": 1.0,
"roughnessFactor": 0.25
},
"extensions": {
"KHR_materials_ior": {
"ior": 1.45
}
}
}
]
}# USD Preview Surface — UsdShade.MaterialLook prim attributes
# Steel Reinforcing Bar (Deformed Rebar, ASTM A615 / EN 10080) · finish: metallic
def Material "mat_steel_rebar_deformed" {
token outputs:surface.connect = </mat_steel_rebar_deformed/PreviewSurface.outputs:surface>
def Shader "PreviewSurface" {
uniform token info:id = "UsdPreviewSurface"
color3f inputs:diffuseColor = (0.0513, 0.0395, 0.0319)
float inputs:metallic = 1.000
float inputs:roughness = 0.250
float inputs:ior = 1.450
float inputs:opacity = 1.000
float inputs:clearcoat = 0.000
token outputs:surface
}
}
ASTM A615 deformed-bar standard; American Concrete Institute (ACI) corrosion-protection literature.
House vocabulary — terms ForMatter uses with intent.
Materials and processes for people who design and make things.
A local-first library of materials, processes, applications, and finishes — equal weight, citable everywhere, with cost-over-volume curves, trade-off profiles, equipment-tier filters, and second-life paths layered onto the data so a student can move from "what is this" toward "what's actually buildable here, now, by me." Part of the renato.design ecosystem — sibling of Plenum, Specimen, Ingenue, gesture, graf, and the Renato Rhino plug-ins. Form and matter, inseparable.
Half of teaching materials is teaching how the material is made into the thing. The standard subscription library was always light on that half. The wedge here isn't better samples or a prettier interface — it's treating Process as a peer entity, not a footnote.
Conway's Material World on raw materials, Lefteri's Making It on processes, Forty's Concrete and Culture, Sparke's Design in Context, Bürdek's Design: History, Theory and Practice of Product Design, Schröpfer's Material Design on materials in architecture, Winchester's The Perfectionists on tolerance, Minshall's Your Life Is Manufactured on the global supply chain, von Busch's Making Trouble on material activism, Were's How Materials Matter, Hegger / Drexler / Zeumer's Basics Materials, Untracht and McCreight on metalsmithing, USDA Forest Products Lab on woods, GIA on gemstones, Schott / CoorsTek / Toray / Owens Corning datasheets, MakeItFrom for verifiable property numbers, ASM Handbook, ISO standards. Museum holdings draw from the Met, MAD, V&A, Smithsonian American Art Museum, Newark Museum of Art, British Museum, Heard Museum, Smithsonian NMAI, Eiteljorg Museum, Philadelphia Museum of Art, Cranbrook Art Museum, and Grand Rapids Art Museum — collection-record permalinks only, designer overview pages and exhibition listings excluded. Voice blocks now ride on every entry kind — material, process, application, and finish — and include Ruskin on iron, Anni Albers on twining, Greg Lynn on the shred-and-teeth NURBS lineage, Pugin on the metal that won't be hammered, Barthes / Yanagi / Benjamin channeled within their philosophy; Sparke, Bürdek, Forty, Conway, Schröpfer, Minshall, von Busch, Lefteri, Pat Pruitt, Mary Lee Hu, Tom Joyce, Albert Paley, and the rest of the contemporary makers quoted verbatim with citation. All cited.
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