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Timber Bolted Connection Design

Introduction

Bolted timber connections are essential in wood-framed structures, especially when transferring high loads between beams, columns, or other framing elements. Properly designed bolted joints ensure structural integrity, accommodate deformation, and help prevent brittle failure modes.

In this post, we walk through the essentials of bolted connection design in timber construction in accordance with the National Design Specification (NDS 2018). We'll highlight the key factors that influence connection strength — including material properties, geometry, fastener placement, and adjustment factors — and show how a typical design is carried out step by step.


The Essentials of Timber Bolted Connection Design

A bolted connection typically involves steel side plates (or wood-to-wood bearing), bolts as the load-transfer elements, and wood members under bearing and shear. These joints must be designed to prevent both fastener and wood failure, while complying with spacing, edge distance, and group action requirements per NDS.





Key Factors in Bolted Connection Design

Load Identification

As with any structural design, the process begins with identifying applied loads — tension, shear, or combined actions. Load combinations per ASCE 7 are used with LRFD or ASD provisions to determine design demands.

Material Selection

  • Wood members: May be sawn lumber, glulam, or other engineered products. Design values are affected by species, grade, and loading conditions.

  • Steel side plates: Often A36 or similar structural steel.

  • Bolts: Typically ASTM A307 or equivalent, with standard diameters and yield strengths specified.


Connection Geometry

  • Bolt diameter (Db), number of bolts, and bolt spacing all influence capacity.

  • Member thickness, edge distances, and end distances must satisfy NDS minimums to prevent premature failure.

  • The configuration (e.g., single shear vs. double shear) also impacts design strength.


Practical Applications in Bolted Connection Design

Bolted connections are used in:

  • Beam-to-column joints

  • Girder hangers

  • Timber trusses

  • Moment-resisting frames with steel side plates


Engineers rely on bolted connection design to:

  • Transfer large axial or shear forces safely

  • Provide predictable ductile failure modes

  • Meet code and detailing requirements with full transparency

  • Optimize for cost and performance with clear span and unbraced length considerations.




Example Problem

(Solutions Provided Using CalcBook) Design Basis:


Problem Statement:


Design Inputs:


Preliminary Design Calculations:


K Factors:


Rd Reduction Factors:


Nominal Yield Mode Capacities:


Adjustment Factors:



Design Strength:




Conclusion

Bolted timber connection design is a critical aspect of safe and reliable wood construction. With the many factors involved — from material selection to yield mode checks and adjustment factors — it’s essential to follow NDS provisions methodically.

CalcBook simplifies this process by automating NDS 2018 bolted connection design, with fully transparent calculations, clear factor breakdowns, and professional-grade documentation.


Try CalcBook today for fast, accurate timber connection design.



 
 
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