711 Design of hubs with nailing plates and joints between the primary and secondary beams

Published: 8 October 2014

The project aims to: a) to provide a basis for dimensioning tools for hubs / joints, b) producing characteristic values ​​using tests for a number of different types of units. Förbandtyp selected in collaboration with industry and the results will form the basis for part a.

Area: Industrial wood construction
Budget: 600 000 SEK
Timetable: October - December 2014
Project leader: Mats Ekevad, LTU

Funding: This project is included in the project TräCentrum North in 2014 with funding from the County Administrative Board of Norrbotten, Västerbotten Region, Skellefteå, Piteå Municipality, Luleå University of Technology and TCNS industry partners .

Light

The introduction of Eurocode 5 has meant that a number of previous use hub solutions must be strengthened, and thus it has resulted in cost. Pressure perpendicular fiber direction and the risk of cross tensile cracks are examples of this. One possibility to increase the design load levels is to report calculations based on verified test values. Achieving genes all formulas that can later be incorporated into the Eurocodes is an extensive process, but with well-limited type solutions, solutions can be achieved within a reasonable time frame. Two different types of units have therefore been selected, nodes with nailing plates and joints at risk for spjälkningsbrott.

In first aid type has a feasibility study conducted in 2013 in the "Nodes with nailing plates." The project aimed to determine the importance of nailing plates contribution to improving the bearing capacity perpendicular fibers. The project has achieved the following results:

- Values ​​of pressure perpendicular to the fiber direction increased from fc, 90 = 4.7 to 5.2 MPa when the surface rose from 140x405 to 215x405 mm2 mm2 (Samples 1A-2A). This may indicate that edge effects / size effects.

- For units with dimensions 140x405 mm2 gives nailing plates and spikes when the number exceeds 20 + 20 pieces per plate, an increase in load capacity.

- Increased number of spikes gives higher overall carrying capacity, but the carrying capacity per spike subsides.

- For units with dimensions 215x405 mm2 obtained similar effect, however, requires the likely larger number of nails before clear effect is obtained.

- The benefit of nailing plates decreases for nailed joints where there is pressure parallel to the grain.

The pilot study was conducted four different test rounds and where the test round 1 and 2 showed clear increases in the carrying capacity of joints. Within each run, there is the test series that diverges without tangible explanations which may be due to the small statistical base. In order to fully use the results as support for the design of further studies should be done.

The pilot study was also a finite element simulations where theoretical tensions were determined at a specific node without nail plates and the pressure parallel and transverse to the fibers. The calculations showed that in this case without nail plates so does the friction between steel fittings and wood large role in the voltage across the fibers. This indicates that the nail plates in this case would be of great importance since it can be assumed that spikplåtars introduction corresponds to the friction between the steel and the wood increases.

In other dressings type with connections of type primary against second beam current design rules has brought greater dimensions because theoretically increased risk of spjälkningsbrott. With values ​​based on actual tests are expected to show higher design values.

Purpose and Goals

Project aimed at:

a) to provide a basis for dimensioning tools for hubs / joints,

b) identifying characteristic values ​​using tests for a number of different types of units. Förbandtyp selected in collaboration with industry and the results will form the basis for part a.

 

The project's main objectives are to:

1) Determine the characteristic values ​​for nodes with nailing plates for use in design.

2) Determine the characteristic values ​​of 1-2 types of units at risk of spjälkningsbrott and use in design.

 

 

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