Minimum Shim Space Requirement for Safety under Lateral Loading

Shim space for a door is not only a construction tolerance requirement for installation but also essential for maintaining the proper function of the door as an emergency exit under extreme lateral loading. This study examines the minimum shim space required to prevent the door from jamming when the rough opening frame moves laterally. Typically, the rough opening frame moves with the primary structural elements and deforms into a parallelogram shape under lateral loading. To analyze the movement of the door within the rough opening frame, three unknown variables are introduced: the coordinates of one corner of the door frame and its tilt angle. It is assumed that the door frame is connected to the rough opening frame at four corners using linear-elastic fasteners. By considering the displacement of these fasteners, their total potential energy can be calculated. Using the principle of minimum potential energy, these variables are expressed as functions of the lateral drift ratio of the rough opening frame and the overall geometry of the door. The required minimum shim space can then be determined from the coordinates of the door frame and the rough opening frame. The results for the minimum shim space are presented as functions of the height-to-width aspect ratio of the door and the lateral drift ratio of the building. Calculations for three commonly used door sizes at a lateral drift ratio of 0.025 indicate that the conventionally used shim space may not be sufficient. These findings and the proposed procedure can serve as a benchmark for designing doors and similar building elements under extreme conditions.