Curtain Wall Embedded Parts | Cast-in Anchors & Brackets

What Were Curtain Walls Used For — From Medieval Defence to Modern Facades

The term "curtain wall" originates in medieval military architecture. A curtain wall was the section of outer defensive wall running between two fortified towers or bastions — a "curtain" hung between structural anchor points. It carried no roof or floor loads; its role was purely to enclose and defend. This defining characteristic — a wall that spans between structural supports without itself being structural — is carried directly into the modern architectural definition.

In contemporary construction, a curtain wall is a lightweight, non-structural cladding system that encloses a building's exterior but transfers none of the building's floor and roof loads. It was made practical in the early 20th century by the development of steel and reinforced concrete structural frames, which allowed buildings to stand entirely on their internal skeleton without requiring the outer wall to carry any structural load. The first fully glazed curtain wall facade in modern architecture appeared in the Hallidie Building, San Francisco (1918). By the 1950s, aluminium extrusion technology made the system universally adoptable, and today curtain wall systems clad the majority of commercial high-rise buildings globally.

The embedded parts that anchor these systems to the structural frame represent the technical continuity between the medieval principle — a spanning non-load-bearing skin held by anchor points in the structure — and its modern engineering expression.

Is Curtain Wall Metal — Materials, Components, and System Composition

A modern curtain wall system contains substantial metal content but is not a metal wall in the homogeneous sense. It is a composite assembly in which metal framing members carry structural load within the system, while various infill materials — glass, aluminium composite panels, stone, terracotta, or insulated spandrel panels — fill the voids between framing members to provide the weathering envelope.

The framing system — mullions and transoms — is almost universally aluminium in contemporary practice. Aluminium alloy 6063 extruded sections combine high strength-to-weight ratio, excellent corrosion resistance, and unlimited cross-sectional complexity from a single extrusion die. A standard curtain wall mullion for a 4-metre slab-to-slab span handles wind loads of 1.5–3.0 kPa in a section weighing approximately 3–5 kg/m — a structural efficiency that no other metallic extrusion material can match at comparable cost.

Is Curtain Wall Structural — Load Paths and Embedded Part Engineering

A curtain wall is non-structural in the precise engineering sense: it does not carry any floor loads, roof loads, or the weight of other building elements. The primary structural frame — concrete or steel — stands and functions entirely independently of the curtain wall. However, "non-structural" does not mean "unloaded" — a curtain wall system carries significant design loads that must be carefully engineered and transferred into the structure through the embedded part and bracket system.

Curtain Wall Embedded Parts — Types, Design, and Installation Requirements

Embedded parts for curtain walls are not a single product category but a family of anchor types selected based on the structural substrate, design load magnitude, required adjustability range, and construction programme constraints. The four principal types in current practice are:

• Cast-in channels (Halfen, Jordahl, or equivalent): A continuous hot-rolled steel channel with T-bolt slots, cast into the concrete slab or column face during the pour. The channel provides infinite positional adjustment along its length and a defined load capacity per unit length. Cast-in channels are the preferred embedded part for high-rise unitised curtain wall on new construction — they allow the bracket position to be fine-tuned after the frame has been surveyed, accommodating the as-built position of the structure. Load capacities range from 25 kN to 80 kN shear per anchor bolt depending on channel section and concrete strength.
• Welded plate embedded parts (steel face plate with shear studs or anchor bars): A flat steel plate with welded-on shear studs or deformed bar anchors, positioned in the formwork and cast into the structural element. The bracket is subsequently welded to the face plate on site. Welded plate systems are used where high point loads are concentrated — facade support at transfer beams, feature facades with large-format stone panels, or locations where the bracket geometry prevents use of channel systems. They require the highest positional accuracy at installation because post-cast adjustment is not possible without structural modification.
• Post-installed anchors (chemical or mechanical expansion): Anchors installed by drilling into hardened concrete after the structural frame is complete. Chemical resin anchors and mechanical expansion anchors both achieve comparable loads to cast-in systems provided the concrete is of adequate strength and the edge distances are maintained per the manufacturer's ETA (European Technical Assessment) or ICC-ES approval. Post-installed anchors are used for refurbishment projects, design changes, missed cast-in positions, and structures where formwork access for cast-in parts was not feasible. They introduce a significant site quality control requirement — drill angle, hole cleanliness, and resin temperature all affect the achieved load capacity.
• Precast embedded inserts: Factory-cast steel inserts in precast concrete elements — used in precast frame buildings where the precast column or slab edge is manufactured in a controlled factory environment. Factory setting achieves positional tolerances of ±2 mm, significantly tighter than site-cast concrete at ±10 mm, and produces consistently reliable anchor geometry that simplifies bracket design. Inserts are typically proprietary products from the precast concrete manufacturer's standard range.

Installation Tolerances and Structural Coordination for Embedded Parts

Positional accuracy of embedded parts is critical to the cost and programme of curtain wall installation. The curtain wall bracket system provides a finite adjustment range — typically ±20 to ±30 mm in three axes — to accommodate construction tolerances in the structural frame. If embedded parts fall outside this range, remediation is required before facade installation can proceed, adding cost and delay.

The industry-standard approach to tolerance management for major curtain wall projects involves a three-stage survey programme: pre-pour survey (formwork checked before concrete is cast), post-strip survey (as-built positions recorded after formwork removed), and setting-out survey (facade contractor surveys before installation to identify any positions requiring remediation). On high-rise projects, the post-strip survey data is fed directly to the curtain wall fabricator — bracket offsets are adjusted in the fabrication programme to compensate for structural as-built positions, rather than attempting to move the embedded parts.

Material Specification and Corrosion Durability of Embedded Parts

Curtain wall embedded parts operate at the interface between the alkaline concrete environment (pH 12–13) and the external bracket zone exposed to moisture and atmospheric pollutants. Material selection must address both environments. The two principal material paths are hot-dip galvanised carbon steel and stainless steel, each with specific application conditions:

• Hot-dip galvanised carbon steel (HDG to ISO 1461): The standard specification for embedded plates, channels, and anchor bars in internal or moderate-exposure applications. The zinc coating (minimum 85 microns per ISO 1461 for sections above 6 mm) provides approximately 40–60 years of protection in a C3 corrosivity environment (urban/industrial atmosphere) through sacrificial cathodic protection. HDG embedded parts should not be used in direct contact with dissimilar metals (aluminium, copper) without isolation — the galvanic potential difference causes accelerated zinc dissolution.
• Stainless steel (Grade 316L / EN 1.4404): Required for coastal and marine-adjacent applications, chemical processing environments, swimming pool enclosures, and any application where chloride deposition on the embedded part surface is likely. The molybdenum content of 316L provides critical chloride pitting resistance absent in standard 304 grade. All exposed bracket components in marine-classified environments (within approximately 1 km of the coast in exposed locations) should be 316L as a minimum. Duplex stainless (Grade 2205) is specified for applications requiring both high strength and enhanced chloride resistance — subsea facade structures, tidal zone architecture.
• Bi-metallic isolation requirements: Where aluminium curtain wall brackets contact steel embedded parts, an isolating washer or pad of PTFE, neoprene, or anodised aluminium must be interposed to prevent galvanic corrosion. The galvanic potential difference between steel and aluminium in an electrolytic environment (moisture with dissolved salts) causes accelerated corrosion of the aluminium — the anodic material in this couple. This requirement is specified in BS EN 1999-1-1 (Eurocode 9) and AAMA guidelines for aluminium facade connections and is non-negotiable in coastal applications.