BauBuche Fasteners and connections Beech laminated veneer lumber Chapter under revision 05
BauBuche Fasteners and connections 05 04-18 - EN Sheet 1 / 10 Fasteners and connections Sheet CONTENTS 2 3 4 9 5.1 Introduction 5.2 Mechanical fasteners 5.2.1 Screw connections 5.2.2 Predrilling of nail and screw connections 5.3 Connections 5.3.1 Connections with metal fasteners Fully threaded screws Hook-in fasteners Beam connectors Dowel-slotted plate connections Joist hangers Bracing connections 5.3.2 Joinery connections Step joints Dovetailed joints Scarf joints Pollmeier Massivholz GmbH & Co.KG Creuzburg sales office Advice on sawn timber, BauBuche Panel; dealer support Pferdsdorfer Weg 6 D-99831 Creuzburg P +49 (0)89 36926 945 5-0 F +49 (0)89 36926 945 5-91101 info@pollmeier.com Munich sales office Advice on BauBuche boards and beams for proprietors, architects, planners, engineers and builders Friedenheimer Brücke 29 80639 Munich P +49 (0)89 693 392 5-0 F +49 (0)89 693 392 5-99 baubuche@pollmeier.com Photo: Chris Kister, Rensteph Thompson, Eckhart Matthäus, Christian Grass
04-18 - EN Sheet 2 / 10 5.1 Introduction Fasteners and joints contribute to the appearance of a timber construction. The joints and fasteners to be used should therefore be considered and chosen at an early stage. Apart from the load-bearing capacity and the visual impact, fire safety requirements might also need to be taken into account. This brochure has been compiled to assist you in choosing suitable fasteners and connections for BauBuche constructions. Observe the approvals of the fastener manufacturers. For details regarding dimensions, please refer to the»baubuche beech laminated veneer lumber manual for structural calculations according to Eurocode 5«available from www.pollmeier.com 5.2 Mechanical fasteners At the moment, only mechanical fasteners are approved for use with BauBuche. There are no general approvals for use in construction projects for glued joints. Fasteners must be dimensioned with reference to section 4.2 of EN 1995-1-1 in conjunction with EN 1995-1-1/NA, using the equations for solid timber. For such fasteners, the specifications in the table below apply, subject to additional requirements stated in the above standards. All sides consisting primarily of end grain are considered face sides. All other sides are narrow sides. Calculation according to Coverage Narrow side Face side Bearing of hole Nails, screws Equat. 8.16, 100 % Option A: 100 % not permissible (predrilled) DIN EN 1995-1-1 Option B: 60 % Dowels and bolts Equat. 8.32, DIN EN 1995-1-1 100 % Load rel. to board plane parallel: 70 % 1) perpendicular: 80 % not permissible Load bearing capacity of fastening unit Ring dowels, plate dowels NCI NA 8.1, DIN EN 1995-1-1/NA 100 % 100 % 100 % Withdrawal capacity Timber screws (45 α 90 ) Equat. 8.38 (kd=1), DIN EN 1995-1-1 100 % 100 % 100 % Option A applies to BauBuche S and beams BauBuche GL70 (longitudinal-ply laminated veneer lumber). Option B applies to BauBuche Q (laminated veneer lumber with cross-plies) 1) for beams BauBuche GL70, the reduction factor for embedding strength for pin-shaped fasteners with a diameter d > 8 mm used in narrow sides is 80 % according to ETA-14/0354 For calculations, use the following densities: for Q and S boards: 730 kg/m³; for GL70: 680 kg/m³. Combined loads must be calculated according to section 8.3.3 of EN 1995-1-1. For the production of timber connections with BauBuche, use only steel dowels and bolts (including fitting bolts), nails, timber screws, ring dowels and plate dowels and adhere to the instructions and specifications below.
04-18 - EN Sheet 3 / 10 Also observe the instructions in the above table. The minimum distances between fasteners that are exposed to shearing-off and withdrawal stress correspond to those for solid timber and plywood. If there is shearing-off stress on the narrow sides of a BauBuche S board or GL70 beam, the nails must have a minimum diameter of 3.1 mm, and screws must have a minimum diameter of 6 mm. If there is withdrawal stress on the face and narrow sides of a BauBuche Q board, only use screws with a minimum diameter of 6 mm. 5.2.1 Screw connections For screw sizes for use in BauBuche, observe the approvals of the screw manufacturers. These approvals normally contain upper limits for the characteristic density of the material that might be used for the dimension calculations (maximum values). 5.2.2 Predrilling of nail and screw connections All holes for nails and screws in BauBuche must be predrilled, even if self-drilling screws are used. As is recommended for all hardwood products, BauBuche must be predrilled with a drill bit whose core diameter is larger than the screw diameter. For details, see screw approvals. For predrilling in BauBuche, follow the instructions for beech or oak timber. Excerpt of ETA 11/190, Würth screws: Diameter of the pre-drilled holes in softwood and in beech or oak Outer thread diameter [mm] Diameter of the pre-drilled hole with a tolerance of ± 0.1 mm Wood-based member made of softwood Wood-based member made of beech or oak 4.0 2.5 3.0 4.5 2.5 3.5 5.0 3.0 3.5 6.0 4.0 4.0 7.0 4.0 5.0 8.0 5.0 6.0 10.0 6.0 7.0 12.0 7.0 8.0 14.0 8.0 9.0
04-18 - EN Sheet 4 / 10 5.3 Connections 5.3.1 Connections with metal fasteners Fully threaded screws The use of fully threaded screws in timber constructions has become increasingly popular. Fully threaded screws are often preferred as they are easy to install in conventional constructions combined with a high shearing-off strength. Their main advantage is however their axial strength as regards tension and compression. These properties come primarily to the fore in connection with angled screw connections with large thread sections in both members. The load bearing capacity is only limited by the potential tensile failure of the screw. Fully threaded screws are an economical solution for transverse tensile reinforcement, transverse compression reinforcement and for auxiliary beams connections. Concealed installation has advantages as regards aesthetics and fire safety. The screw connection must be fully predrilled in both members. Fully threaded screws with cheese-heads can be fully embedded in the timber. Many screw manufacturers offer easy-to-used aids for fast installation and optimised screwing angle. Transverse compression reinforcement Transverse tensile reinforcement Transverse tensile reinforcement at recesses
04-18 - EN Sheet 5 / 10 Connection between girder and auxiliary beam Connection between post and beam Project euregon AG, Holzbau Gumpp & Maier GmbH, Installation of auxiliary beams The beams are connected with fully threaded screws (Würth Assy plus VG 8 x 330). In this project, pocket-shaped recesses for the beams were milled into the girder. This approach made installation easy, as the beams slotted perfectly into these recesses and were then secured with concealed fasteners. Brace connection Simple and cost-effective solution: The screws are inserted at an angle to the girder axis, so that they are exposed primarily to an axial load.
04-18 - EN Sheet 6 / 10 Hook-in fasteners Hook-in fasteners are approved two-piece system fasteners. The metal system elements are secured with fully threaded or system screws to the timber elements. The system elements can be attached to the surface or installed in recesses. The second option allows for connections with concealed fasteners and offers additional advantages as regards fire safety. The system elements slot together, similar to dovetailed joints, and the connection can be secured with screws, if necessary. Such systems are not only suitable timber-to-timber connections but also for connections between timber and steel or concrete elements. Observe the approvals of the fastener manufacturers. In BauBuche, all screw holes must be predrilled. Beam connectors Beam connector are single-piece system connectors suitable for load-bearing, non-visible timber-to-timber connections, for instance between beams and girders or beams and columns. Beam connectors are screwed to one of the timber members and then attached to the second member by means of a dowel-slotted plate connection. Such connections can be established at various angles. For easy installation of the beams, a split dowel driven into the beam engages in the slot in the connector bracket, holding the beam in place. Observe the approvals of the fastener manufacturers. In BauBuche, all screw holes must be predrilled.
04-18 - EN Sheet 7 / 10 Dowel-slotted plate connections In timber constructions, multi-slit steel-timber connections with joist brackets have proven most successful. The steel parts are thereby recessed into the timber. Apart from the elegant look, such connections offer also greater safety in the event of a fire, as exposed steel parts quickly lose their strength when becoming hot. As all parts must be prepared and assembled with extreme accuracy, such constructions are only possible with the help of CNC machining. SFS-Intec offers a system with self-drilling dowels that are driven through both the timber and the metal plates in a single process. Dowel connections are also widely used for trusses (see chapter 8) and are equally recommended for the attachment of timber beams to steel and concrete structures. Detail view of dowel-slotted plate connection Project Zukunftspavillon Frankfurt Joinery Hess Timber GmbH Photos Rensteph Thompson, Chris Kister
04-18 - EN Sheet 8 / 10 Column base with dowel-slotted plate connection Dowel-slotted plate connectors for cross-struts Joist hangers Joist hangers are simple formed metal components for the fixture of timber beams or joist to timber, steel or concrete elements. In most cases, the timber is secured to the hanger by means of threaded nails, but screws are equally suitable. In BauBuche, all screw and nail holes must be predrilled. Observe the approvals of the fastener manufacturers. Joint hangers are primarily used where they are not visible.
04-18 - EN Sheet 9 / 10 5.3.2 Joinery connections Step joints Step joints are most common types of connection for struts and other connections exposed to compression. Due to their high transverse compression and shear strength, step joints are particularly suitable for use with BauBuche. The main criteria for proper force transfer with low deformation is accurate machining and installation. Step joints must be secured with bolts or screws. The special properties of BauBuche allow for more advanced and even stronger joinery connections. The multiple step joint is characterised by an optimised contact connection and a high load bearing capacity. At the moment, there is however no recognised standard for such joints. For calculation instructions, see: Enders-Comberg, M., Treppenversatz Leistungsfähiger Kontaktanschluss für Druckstäbe. Bauingenieur Band Blaß, H.J. 89, 04/2014, Springer-VDI-Verlag, Düsseldorf Treppenversatz Leistungsfähiger Kontaktanschluss für Druckstäbe. Single step joint Heel notch joint Double step joint Multiple step joint BauBuche GL70, strut connection with single step joint Project Tischlerei Mohr Joinery Kaufmann Zimmerei
04-18 - EN Sheet 10 / 10 Dovetailed joints Using modern trimming machines, dovetailed joints can be produced relatively cheaply and are therefore becoming increasingly popular. As BauBuche is a new material, it has not yet been approved for dovetailed joints in load-bearing constructions. The application for approval is currently pending. For aesthetic reasons, dovetailed joints might however still be an option, for instance in combination with fully threaded screws that bear the load. Scarf joints In a scarf joint, two timber members are jointed together in longitudinal direction. They are particularly suitable for long, unsupported structures, especially for cantilever girders or articulated beams. The scarf joint must thereby be positioned at the zero point of moment. Scarf joints must be secured with bolts or screws.