2. LVL STRUCTURES IN FLOORS, WALLS, ROOFS AND IN SPECIAL APPLICATIONS 2.2.3 Rim boards and rim beams Rim boards and rim beams are used in the walls around the timber frame floors and, depending on the structural system, they may have several different load-bearing functions. Rim boards work as edge binders preventing the joists from tilting, and as load transfer members for the timber floor assemblies by carrying the line loads from the walls above the floor level to the supporting walls below the floor level. Continuous rim beams are required for floor panel diaphragms to absorb the tensile forces from the floor planes. LVL-C products are supplied dry in long lengths and they have good resistance, stiffness and dimensional stability in the floor joist height direction, which makes them an ideal product for rim boards. LVL-C settlements are minimal, which prevents the risk of compression cracks in plasterboard walls or facade rendering and enhances building envelope airtightness. In partition walls between apartments rim boards must be designed for adequate resistance to fire to prevent fire spread in wall or floor cavities. A 30 mm rim board can serve as a fire separating component to meet the integrity E and insulation I performance criteria for 30 minutes for the structure. Rim beams may also be designed in more robust dimensions to act at the same time as lintels to carry loads, e.g., above door or window openings. In such cases, bending strength and stiffness are important. In some structural systems rim boards work as secondary load transfer routes to prevent disproportionate collapse if, e.g., a part of the wall structure is destroyed. A C E D B Figure 2.12. Rim boards and rim beams in different structural solutions of timer frame structures A) Rim board as egde binder and transferring loads from upper walls; B) Rim beams acting at the same time as a lintel over a window opening; C) Rim beam in compartment wall connection; D) Rim beam integrated in exterior wall element; E) Rim beam integrated to compartment wall element. 58 LVL Handbook Europe
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