Building Expansion Joint for Steel Frame Structures

Steel frame buildings have larger thermal movements than concrete frame buildings due to the higher coefficient of thermal expansion of steel (12 x 10^-6 per degree C vs 10 x 10^-6 per degree C for concrete) and the lower thermal mass of steel, which causes larger temperature changes. Expansion joints in steel frame buildings must accommodate these larger movements. Thermal movement in steel frame buildings depends on the building length, the temperature range, and the restraint provided by the foundation and cladding. For a 60-meter steel frame building with a temperature range of 50 degrees C, the thermal movement is approximately 36 mm. This is significantly larger than for a concrete building of the same length. Joint spacing in steel frame buildings is typically 30-50 meters, depending on the building configuration and the allowable stress in the steel frame. Buildings with moment-resisting frames can tolerate larger thermal movements without joint than buildings with braced frames, because the moment frame can deform without cracking. Sliding connections at expansion joints in steel frame buildings allow the two building sections to move independently while maintaining structural stability. The sliding connection typically consists of a slotted hole in one member and a bolt that can slide within the slot. The slot length must be sufficient to accommodate the full movement range. Cladding at expansion joints must accommodate the movement of the steel frame without damage. Metal cladding panels can be detailed with sliding connections that allow movement. Glass curtain wall systems require flexible sealant joints between the glass panels at the expansion joint location. The sealant joint must be wide enough to accommodate the full movement range. Roof expansion joints in steel frame buildings must maintain weatherproofing while accommodating the movement. Standing seam metal roofing can accommodate movement through the flexibility of the seam. Built-up roofing requires a flexible flashing at the joint location. The flashing must be bonded to both sides of the joint and must be flexible enough to accommodate the full movement range.