Curtain walls are attached to buildings through an intricate system of components and mechanisms designed to safely transfer loads onto the building structure, accommodate building movements, withstand external forces such as wind pressure or thermal expansion, and ensure reliability and durability without altering its aesthetics. Here is an overview of how curtain walls typically are attached:
Anchors and Brackets
Curtain wall systems are attached to building structures by anchors and brackets made from strong materials like steel or aluminum, designed to attach curtain wall mullions (vertical framing members) directly to structural floors or columns in the building. Their design incorporates consideration of thermal expansion or building sway; enabling their curtain wall system to flex without jeopardizing its integrity of attachment or the system itself.
Types of Anchoring
Mechanical Anchors: Mechanical anchors include expansion anchors, undercut anchors or drilled-in anchors which expand or interlock mechanically into a building’s structure (be it concrete or steel), providing strong mechanical connections between curtain walls and structural frames.
Welded Connections: When connecting to steel structures, parts of an anchor assembly may need to be welded directly onto beams or columns of steel beams and columns for anchor assembly attachment. While welding is less often used directly for curtain wall attachment, it may still be used for setting up a primary attachment framework.
Bolted Connections: Bolted connections are popularly used when attaching curtain wall support structures to steel frames, as they enable prefabrication of connection points for easier on-site assembly.
Mullion Anchors
Mullion anchors attach either horizontally or vertically to various floor slabs on a building’s slabs and serve to support and transfer wind loads onto its structure, bearing its weight while accommodating differential movements due to thermal expansion/contraction between curtain wall systems and their frame structures.
Accommodating Movement
Since curtain walls serve primarily as the “skin” of a building rather than load-bearing components, their attachment system should accommodate building movements without stressing glass panels or framing elements and without creating stress points for stress or damage to occur in either case. This requires considering:
Thermal Expansion and Contraction: To accommodate expansion and contraction caused by temperature variations, sliding anchors provide flexibility to allow different parts of a curtain wall frame to respond without straining either glass or sealants.
Wind Sway and Differential Movement: Buildings, especially high-rises, tend to sway under wind load, requiring anchoring systems to allow a certain degree of relative movement between the curtain wall and structural frame to avoid damage and remain secure.
Sealants and Gaskets
Although sealants and gaskets do not directly connect a curtain wall back to its structure, they play an integral part in maintaining system integrity against water or air infiltration. Sealant selection must take into account movement while still providing an effective protective barrier.
Curtain wall anchoring systems will vary based on several factors, including building height, geographic location (and related environmental loads), curtain wall type (stick-built or unitized), architectural requirements, and engineering design specifications. Proper engineering and design to comply with local building codes and standards is vital to ensure successful and safe integration of curtain wall systems into building structures.
