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Timber Nailed Joint Designer to AS 1720.1

📝 This CalcTree template includes the calculation of timber nail connection capacities in accordance with AS 1720.1 - Design of Timber Structures.
This calculator designs timber nail joint connections by checking the timber species and nail group geometry. It checks the capacity of nail joints connecting two or three timber members, subject to applied axial or shear forces and moments.


Calculation

Member dimensions (i.e. width and height) are sufficiently sized to accommodate the nails. Calculator plots the minimum dimensions of the member required, based on the minimum end and edge distances calculated.

Joint Configuration

Define nail properties


Joint type
:Type 1 - Double shear​



Load direction
:Parallel to the grain​



Extra strengthening measures
:Driven through plywood gussets​



Are holes prebored
:Yes​



Are nails skewed
:No​



Nail diameter
:3.15mm​



Nail position
:Side grain​



Nail penetration length
:100mm​



Nail penetration check
:Too short ❌​



Set axis direction:


x axis
:Parallel to the grain​



y axis
:Perpendicular to the grain​


Define geometry:


Rows
:5​



Sx
:65mm​



Sx check for spacing
:✅ ​



Minimum Sx
:63.00mm​



Minimum end distance
:32mm​




Columns
:3​



Sy
:35mm​



Sy check for spacing
:✅ ​



Minimum Sy
:32mm​



Minimum edge distance
:16mm​


The plot assumes the x-axis is the axis parallel to the grain.

Can’t display the image because of an internal error. Our team is looking at the issue.



Member Properties

Define member properties and geometry:


Member #1


Stress grade 1
:F22​



Species 1
:Ash, alpine​



Condition 1
:Seasoned​



Thickness 1
:100mm​



Timber type 1
:Hardwood​



Strength_group 1
:SD4​



Joint group 1
:JD3​



Additional mechanical properties for Member #1



Characteristic strength in bearing parallel to grain, f'l1
:51MPa​



Characteristic strength in bearing perpendicular to grain, f'p1
:17MPa​



Characteristic strength in tension perpendicular to grain, f'tp1
:0.6MPa​



Characteristic strength in compression, f'c1
:42MPa​



Characteristic strength in bending, f'b1
:34MPa​



Characteristic strength in shear in a beam, f's1
:4.2MPa​



Characteristic strength in shear at joints, f'sj1
:6.1MPa​



Modulus of elasticity parallel to grain, E1
:16000MPa​



Modulus of rigidity, G1
:1080MPa​


Member #2


Stress grade 2
:F8​



Species 2
:Ash, alpine​



Condition 2
:Seasoned​



Thickness 2
:75mm​



Timber type 2
:Hardwood​



Strength group 2
:SD4​



Joint group 2
:JD3​



Additional mechanical properties for Member #2



Characteristic strength in bearing parallel to grain, f'l2
:51MPa​



Characteristic strength in bearing perpendicular to grain, f'p2
:17MPa​



Characteristic strength in tension perpendicular to grain, f'tp2
:0.6MPa​



Characteristic strength in compression, f'c2
:18MPa​



Characteristic strength in bending, f'b2
:13MPa​



Characteristic strength in shear in a beam, f's2
:2.2MPa​



Characteristic strength in shear at joints, f'sj2
:6.1MPa​



Modulus of elasticity parallel to grain, E2
:9100MPa​



Modulus of rigidity, G2
:610MPa​


Member #3 (for Double Shear only)


Stress grade 3
:F17​



Species 3
:Ash, mountain​



Condition 3
:Seasoned​



Thickness 3
:30mm​



Timber type 3
:Hardwood​



Strength group 3
:SD3​



Joint group 3
:JD3​



Additional mechanical properties for Member #3



Characteristic strength in bearing parallel to grain, f'l3
:59.0MPa​



Characteristic strength in bearing perpendicular to grain, f'p3
:19.0MPa​



Characteristic strength in tension perpendicular to grain, f'tp3
:0.6MPa​



Characteristic strength in compression, f'c3
:34.0MPa​



Characteristic strength in bending, f'b3
:25.0MPa​



Characteristic strength in shear in a beam, f's3
:3.6MPa​



Characteristic strength in shear at joints, f'sj3
:7.6MPa​



Modulus of elasticity parallel to grain, E3
:14000.0MPa​



Modulus of rigidity, G3
:930.0MPa​



Design Capacity



is dependent on the condition of the member (for Type 1) and the nail penetration length (for Type 2). The below values are as per Table 4.1 (A), (B) and Table 4.2(A), (B).
  1. 
    
    = capacity for a nail parallel to the grain in member
    
    
  1. 
    
    = capacity for a nail perpendicular to the grain in member
    
    

Member #1


Qk1_1
:1135N​



Qk2_1
:16N/mm​

Member #2


Qk1_2
:1135N​



Qk2_2
:16N/mm​

Member #3


Qk1_3
:1135N​



Qk2_3
:16N/mm​

❗Capacity for Member #3 is only applicable for joints in double shear

Type 1 joint:

ϕNj≥ϕ k1 k13 k14 k16 k17 nQkϕM=ϕ k1 k13 k14 k16 k17 rmax Qk [Σ(rirmax)]32\phi N_j \geq \phi \space k_1 \space k_{13} \space k_{14} \space k_{16} \space k_{17} \space nQ_k \\ \phi M = \phi \space k_1 \space k_{13} \space k_{14} \space k_{16} \space k_{17} \space r_{max} \space Q_k \space [\Sigma (\frac{r_i}{r_{max}})]^\frac{3}{2}
Type 2 joint:

ϕNj=ϕ k13 lp n Qk\phi N_j = \phi \space k_{13} \space l_p \space n \space Q_k


N*
:3.0kN​



ΦN
:1.00kN​



N_Utilisation
:300%​



N_check
:❌ ​




M*
:0.05​



ΦM
:0.22kN m​



M_Utilisation
:0.23​



M_check
:✅ ​



Parameter Values



phi
:0.85​



k1
:1.00​



k13
:1.00​



k14
:2.00​



k16
:1.00​



k17_M
:1.20​



k17_N
:0.94​




Explanation

Timber nail connections are widely used in both residential and commercial construction, offering versatility and ease of installation. The method is favored for its cost-effectiveness, speed and reliability, making it a popular choice for framing, truss assembly, and other applications in timber structures.
Timber framing for residential complex (Source: YourHome)

Nail connections rely on the simplicity and effectiveness of nails driven into wood to create secure bonds between different components, such as beams, joists, and columns. The process involves strategically placing nails to ensure structural integrity and stability while considering factors like load-bearing capacity and resistance to forces such as tension and shear.
Nails driven into the timber spread the fibres apart. Generally, nails don't cut or break the timber fibres, so the strength of the member is not compromised. The tensile strength of the timber member therefore remains unaffected by the nailed connection.
Common timber nail connections (Source: MTC Solutions)


Code Parameters and Equations

AS 1720.1 categorises a connection type into either "type 1" or "type 2" for the purpose of design. The code also prescribes minimum dimensions for the nail set-out and for the timber thickness.

Type 1 Joint

A type 1 joint is a system where nails are resisting shear forces,

.
Type 1 joints

The capacity of a type 1 joint to resist direct shear loads and in-plane moments are calculated as:

ϕNj≥ϕ k1 k13 k14 k16 k17 nQk(Cl. 4.2.3.2)ϕM=ϕ k1 k13 k14 k16 k17 rmax Qk [Σ(rirmax)]32(Cl. 4.2.3.3)\large \phi N_j \geq \phi \space k_1 \space k_{13} \space k_{14} \space k_{16} \space k_{17} \space nQ_k \hspace{0.5cm} \text{(Cl. 4.2.3.2)} \\ \phi M = \phi \space k_1 \space k_{13} \space k_{14} \space k_{16} \space k_{17} \space r_{max} \space Q_k \space [\Sigma (\frac{r_i}{r_{max}})]^\frac{3}{2} \hspace{0.5cm} \text{(Cl. 4.2.3.3)}
Where:
  1. 
    
    accounts for duration of applied loads determined in accordance with Cl. 2.4.1.1. Longer load duration decreases the capacity of the joint.
  2. 
    
    accounts for the location of the nail penetration. The end grain of a member is structurally weaker than the side grain and more prone to splitting and failure. Hence, if nail is embedded in the end grain of a member, the capacity is reduced.

→k13=1.0for nails in side grain→k13=0.6for nails in end grain\hspace{0.5cm} \rightarrow \hspace{0.5cm}k_{13}=1.0 \hspace{0.5cm}\text{for nails in side grain}\\\hspace{0.5cm} \rightarrow\hspace{0.5cm}k_{13}=0.6 \hspace{0.5cm}\text{for nails in end grain}
  1. 
    
    accounts for the number of members assisting in load-resisting action. Lapping multiple layers reduces the shear stress on the nails.

→k16=1.0for single shear joint (i.e. two-member joint)→k16=2.0for double shear joint (i.e. three-member joint)\hspace{0.5cm} \rightarrow \hspace{0.5cm}k_{16}=1.0 \hspace{0.5cm}\text{for single shear joint (i.e. two-member joint)}\\\hspace{0.5cm} \rightarrow\hspace{0.5cm}k_{16}=2.0 \hspace{0.5cm}\text{for double shear joint (i.e. three-member joint)}

  1. 
    
    accounts for the effect of a nail group (i.e. joint system with multiple nails) and is interpolated from AS1720.1 Table 4.3 (A) and (B) for joints resisting direct loads and in-plane moments, respectively.
AS1720.1 - Table 4.3 (A) and (B)

Important thing to note in the above tables is that the value of

is different for calculating

and

. When using Table 4.3 (A),

is the number of rows of nails, whereas for Table 4.3 (B),

refers to the number of nails outside a perimeter of

as depicted in the diagram below:
Adopted from AS1720.1 - Figure 4.5

  1. 
    
    denotes the radial distance from the centroid of the nail group, consisting of
    
    number of nails, to centroid of each nail with
    
    being the maximum.
  2. 
    
    is the characteristic strength per nail and is a function of the joint group classification and nail diameter.
AS1720 - Table 4.1 (A) and (B)


Type 2 Joint

A type 2 joint is a system where nails are resisting withdrawal (axial) forces,

.
Type 2 joints

The strength of a type 2 joint is primarily governed by the nail embedment depth, unlike type 1 joints which depend on the nail diameter.
Capacity of a type 2 joint to resist direct axial or tension loads causing withdrawal is calculated as:

ϕNj=ϕ k13 lp n Qk(Cl. 4.2.3.4)\large \phi N_j = \phi \space k_{13} \space l_p \space n \space Q_k \hspace{0.5cm} \text{(Cl. 4.2.3.4)}
Where:
  1. 
    
    , again, accounts for the effect of the nail position.

→k13=1.0for withdrawal from side grain→k13=0.25for withdrawal from end grain\hspace{0.5cm} \rightarrow \hspace{0.5cm}k_{13}=1.0 \hspace{0.5cm}\text{for withdrawal from side grain}\\\hspace{0.5cm} \rightarrow\hspace{0.5cm}k_{13}=0.25 \hspace{0.35cm}\text{for withdrawal from end grain}
  1. 
    
    is the depth of nail penetration, into primary member (i.e. the member in which the nail ends)
  2. 
    
    is determined from Table 4.2 (A) and (B):
AS1720.1 - Table 4.2 (A) and (B)


Minimum Spacing, Edge and End Distance

Nail Length and Minimum Timber Thickness



Related Resources

  1. 🔗 Timber Screwed Joint Designer to AS 1720.1
  2. 🔗 Timber Beam Calculator to AS1720.1
  3. 🔗 Timber Column Calculator to AS1720.1
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