Timber construction has been popular for centuries as a versatile, sustainable, and beautiful building method. Recently, timber construction has seen major innovations, allowing for larger and taller timber buildings. The use of timber-to-timber bolted joints in cross-laminated timber (CLT) and other mass timber products. Bolted joints are taking timber construction to new heights.
Bolted joints offer many advantages over traditional timber joinery and connections. The precisely engineered bolted joints used in modern timber buildings provide superior strength, ductility, and performance compared to older methods. Bolted joints also enable quick and efficient on-site assembly of prefabricated timber elements. It allows for faster construction using fewer skilled craftspeople. Bolted joints have helped transform timber from a niche material to a competitive option for large-scale construction projects.
Advantages Of Bolted Joints In Timber Construction
Bolted joints provide many benefits that have elevated timber as a mainstream construction material:
- Superior Strength and Stiffness – Bolted joints achieve higher strength and stiffness than typical nailed joints. It allows larger panels and longer spans when using mass timber products like CLT, glue-laminated timber, and laminated veneer lumber. Timber buildings reach greater heights thanks to sturdy bolted joints.
- Reliable Seismic Performance – Bolted joints are highly resistant to seismic forces. Extensive research has proven the ductility and energy dissipation capacity of dowel-type and split ring connections under cyclic loading. Bolts firmly lock timber panels together to create rigid diaphragms that resist lateral loads. It makes timber suitable for earthquake-prone regions.
- Design Flexibility – Engineers optimize bolted joint configurations for any design scenario. Variables like bolt quantity, size, material, and layout are adjusted to achieve the required joint properties. Bolted connections accommodate diverse timber products, geometries, and loading conditions. The wide design envelope of bolted joints facilitates architectural freedom.
- Prefabrication and Ease of Assembly – Bolted joints enable modular offsite prefabrication using CNC machinery. Timber elements with pre-installed bolted joints are rapidly assembled on-site. This results in faster and less labor-intensive construction. Bolted joints eliminate complex timber joinery skills required for traditional construction.
- Fire Resistance – Timber structures must incorporate fire safety measures. Bolted joints maintain the integrity and load-bearing capacity longer during fire exposure than nails. Robust bolted joints prevent collapse and allow mass timber panels to self-char at predictable rates. It contributes to overall fire resilience.
Timber Beam To Column Bolted Joint Design
A critical aspect of tall timber buildings involves connections between beams and columns. These joints must transfer gravity, wind, and seismic loads through the structure while accommodating wood shrinkage effects. Using dowel-type bolted joints, here is an overview of proven design principles:
- Perpendicular-to-grain bolts in the column effectively engage timber’s excellent bearing strength. Multiple staggered rows of bolts spread load into the column.
- Parallel-to-grain bolts through the beam resist dowel-type bending stresses. Higher bolt densities near the column increase moment resistance.
- Compression pegs perpendicular to the grain allow for longitudinal shrinkage at the joint interface. The pegs take up shrinkage over time.
- Balancing compression and tension bolt numbers/locations creates symmetry and resists eccentric loads. Staggering avoids bolt groupings.
- Ends of beams and columns are precisely machine cut for full contact. Steel side plates provide clamping force and reinforce joints.
- Ductile failure modes like bolt yielding are preferable to brittle timber crushing. It provides redundancy and energy dissipation under seismic loads.
The future looks bright for timber construction as bolted joints enable stronger, taller, and safer timber buildings. Bolted joint technology will elevate timber from a niche material to a primary choice for sustainable and resilient structures. Timber construction is leveling up.