• Concrete Cover Requirements: Rebar must be embedded a specific depth within the concrete to protect it from corrosion and fire. E.g., 75mm minimum when cast against permanently exposed earth; 40mm to 50mm for beams and columns exposed to weather; 20mm for interior slabs.
• Bar Splicing: Since standard rebar lengths are typically 6m or 9m, continuous bars must be joined. Methods include Lap Splices (overlapping two bars by a calculated development length, usually 40 times the bar diameter), Mechanical Splices (using threaded couplers), and Welded Splices.

Beams experience both bending (flexure) and shear forces.

• Top Bars (Continuous & Extra): Placed near the top face of the beam. They resist negative bending moments (tension at the top) that occur primarily over the column supports. Extra top bars are often added specifically at the supports and terminated shortly after.
• Bottom Bars (Continuous & Extra): Placed near the bottom face of the beam. They resist positive bending moments (tension at the bottom) that peak at the midspan of the beam.
• Stirrups (Ties/Hoops): Closed rectangular loops of smaller diameter rebar (e.g., 10mm or 12mm) that wrap around the main longitudinal bars. They resist shear forces (diagonal tension) and prevent the main bars from buckling outward. Because shear forces are highest near the columns, stirrups are spaced very closely together near the supports (e.g., @ 50mm or 100mm) and spaced further apart at midspan (e.g., @ 200mm).
• Concrete Cover: The specified distance between the outermost surface of the concrete and the outermost edge of the rebar (usually the stirrup). This is not arbitrary; it is the primary defense against fire (which softens steel) and corrosion (rust expansion). Common standards: 40mm for indoor beams/columns, 75mm for concrete cast directly against earth (footings).

Columns primarily carry massive axial compressive loads, but during an earthquake, they experience severe bending moments and shear forces.

• Vertical (Main) Bars: The heavy longitudinal bars that carry the load. They must be evenly distributed around the perimeter of the column core.
• Transverse Ties (Hoops): Similar to beam stirrups, these confine the concrete core (increasing its compressive strength dramatically) and prevent the vertical bars from buckling outward like dry spaghetti under immense pressure.
• Seismic Hooks: In high seismic zones (like the Philippines or California), it is absolutely mandatory that the ends of column ties and beam stirrups are bent into a 135° hook that extends deep into the confined concrete core. Standard 90° hooks will simply pop open and fail during the violent shaking of a major earthquake, leading to catastrophic column failure.

If there isn't enough physical space to provide a straight development length (e.g., at the end of a beam framing into an exterior column), the bar must be hooked to provide mechanical anchorage.

• 90° Hook: A right-angle bend. The standard tail extension must be at least 12 times the bar diameter ($12 d_b$).
• 180° Hook: A U-shaped bend. The standard tail extension must be at least 4 times the bar diameter ($4 d_b$), but not less than 65mm.
• 135° Seismic Hook: Essential for ties and stirrups. The tail extension must be at least 6 times the bar diameter ($6 d_b$) or 75mm, whichever is greater, projecting directly into the confined concrete core.

The strength of a steel frame lies entirely in its connections. Detailing specifies exactly how the beams attach to the columns.

• Bolted Connections: The most common field connection method. Requires precise detailing of bolt hole patterns, edge distances, and the use of high-strength structural bolts (e.g., ASTM A325 or A490) tightened to specific torques (slip-critical connections).
• Welded Connections: Often done in the fabrication shop for higher quality control, though field welding is common for moment connections.
• Gusset Plates: Thick steel plates used to connect multiple intersecting members, especially diagonal bracing or truss webs, to a central node.
• Base Plates: Heavy, thick steel plates welded to the bottom of steel columns. They distribute the massive concentrated column load over a wider area of the concrete pedestal or footing, secured by embedded anchor bolts.

A specialized shorthand language used on drawings to dictate exact welding instructions without cluttering the plan with text notes.

• The Reference Line: A horizontal line where all symbols are attached. An arrow connects one end of the line to the joint to be welded.
• Symbol Placement (Crucial):
  • If the weld symbol is placed BELOW the reference line, the weld is to be made on the Arrow Side (the side the arrow is pointing to).
  • If the weld symbol is placed ABOVE the reference line, the weld is to be made on the Other Side (the side opposite the arrow).
• Common Symbols: A Right Triangle (Fillet Weld), a "V" shape (V-Groove Weld), two parallel lines (Square Groove Weld). A circle at the intersection of the arrow and reference line means "Weld All Around."

• Member / Location: e.g., "Beam B-1 (2nd Floor)".
• Bar Mark: A unique identifier (e.g., "MK-01") cross-referenced on the detailing plans.
• Shape Code: A standardized graphical symbol or code (e.g., straight, L-bend, U-bend, rectangular tie) indicating how the bar must be bent.
• Diameter ($d_b$): The physical size of the bar (e.g., 10mm, 16mm, 20mm, 25mm).
• Dimensions (A, B, C, D): The exact cut lengths for every straight segment and bent leg of that specific shape code.
• Total Cut Length: The overall length of straight rebar required before bending, including the allowances for standard hooks.
• Quantity: The number of identical bars required.
• Total Weight: Calculated as: Total Length * Quantity * Unit Weight (kg/m). The total tonnage dictates the material cost of the project.