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Case studies of the investigations and repairs of façades of three buildings in the Midwestern United States are discussed. Strength and water penetration issues were identified. The years of initial investigation of the deficient façades range from 1992 to 2000. Building characteristics include: 1) 45+ stories; mid-1980s; glass and aluminum curtainwall on upper portion of building; steel framing. 2) 30 stories; mid-1980s; brick veneer on shelf angles, individual windows; primarily reinforced and post-tensioned concrete framing. 3) 22 stories; 1930; limestone panels on shelf angles; steel framing. Deficiencies and repairs included:
Building One: Substantial leaking occurred at many locations in the glass-and-aluminum curtainwall. Initial repair attempts disclosed the existence of some cracked screws, which secured the glass retainers. Repairs included additional sealing, installation of missing end dams, and installation of a different type of screw to avoid hydrogen-assisted stress-corrosion cracking of screws.
Building Two: Extensive leaking occurred, and cracked mortar joints existed at a recurring architectural feature. These items led to extensive investigation (by two firms) and repair. Other significant deficiencies were uncovered as veneer was removed and analyses were made, including errors regarding torsional stiffness and attachment of the shelf angles. Construction errors had been made in field-modifying the angles. Field changes, to permit erection, were needed because of a shop drawing error in the connection detail. Repairs included installation of new flashings (EPDM in lieu of stainless steel) and angle reinforcing.
Building Three: Several limestone panels (units) fell to the sidewalk from the tenth story. Investigation revealed cracks in some of the limestone units, severe rusting of some shelf angles and the lack of a functioning soft joint below some angles. Repairs included installation of repair anchors and soft joints.
façade, hydrogen-assisted stress-corrosion cracking, limestone panel, shelf angle, water penetration
Associate, Computerized Structural Design, S.C., Milwaukee, WI