2. LVL STRUCTURES IN FLOORS, WALLS, ROOFS AND IN SPECIAL APPLICATIONS 2.2.5 Multiple-glued beams, GLVL For longer spans or higher loads on main beams, larger cross sections of multiple-glued GLVL can be used. Beam heights can be tailored for the projects case-specifically, but for optimized material efficiency, standard LVL beam heights or 5-10 mm smaller heights are recommended. The beam thicknesses are multiple thicknesses of sanded LVL laminas (e.g. 2 x 42 mm = 84 mm). Massive multiple-glued GLVL cross sections have the advantage that they are not sensitive to cracking in dry conditions. However, when they are used in visible applications, the sanding and face veneer specifications must be separately agreed with the supplier to achieve clean veneer surfaces. • Recommended beam thicknesses: 84, 96, 90, 108, 120, 133 and 144 mm • Recommended beam heights: 200, 225, 240, 260, 300, 360, 450 and 600 mm 2.2.6 Stressed-skin panels: rib panels, box panels or open box panels Rib panels are efficient structures for long span floors or for cases where the floor height is limited. They utilize the composite action of the panels and the ribs achieve by mechanical connections or glued joints. Glue joints are recommended as they are much stiffer and more efficient but, as they constitute structural gluing, their manufacturing requirements are higher. The simplest alternative is a T-cross section where a 25-37 mm thick LVL-C panel is structurally glued onto 200-400 mm Figure 2.18. Multiple-glued GLVL beams. high LVL-P ribs. Compared to typical LVL joist floor dimensions this can save ~100 mm in floor height or enable ~1 metre longer spans. Other alternatives include a box slab where another LVL-C panel is glued to the bottom of the element, or an open box element where LVL-P flanges are glued in the flatwise direction under the ribs. With typical dimensions these options can save another 100 mm in floor height or add an extra metre to the maximum span length compared to T-sections, see Figure 2.23. However, due to the high stiffness of box slabs the bottom panel emits sounds easier through the structure, making it difficult to fulfil the acoustic requirements of compartment floors between apartments. Therefore, an open box structure is recommended for compartment floors. Rib slab (T- section) Box slab Open box slab Figure 2.19. LVL rib slab, box slab and open box slab for floor constructions. LVL Handbook Europe 61
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