Design Codes

Table of contents

• General Information
  • Rivet/Bolt Geometry
  • Rivet/Bolt Evaluation Properties
• Eurocode 3
  • Material Class
  • Connection Category
  • Bolt hole type
  • Class of friction surface
  • Hole Spacing
  • Rivet Design Resistance (Table 3.4)
  • Bolt Design Resistance (Table 3.4)
  • Utilization Criteria (Table 3.2)
  • Safety Factor
  • Eurocode 3 S-N Curves
  • Validity of the Eurocode 3 result
• AISC 360-16
  • Material Class
  • Connection Category
  • Bolt hole type
  • Class of friction surface
  • Hole spacing
  • Bolt Design Resistance
  • Utilization Criteria
  • Validity of the AISC 360-16 result
• User Defined

General Information

The Eurocode 3 and AISC 360-16 implementation has been reworked and the interface in Rivets/Bolts Result is updated in the 2021R1 release. When selecting “Eurocode 3” (or “AISC 360-16”) in the “Code” field additional properties are displayed.

Rivet/Bolt Geometry

When selecting a Rivet or Bolt object the dimensions for the selected object are retrieved and the values are displayed in the Rivet/Bolt Geometry group. The dimensions are used in the evaluation and can be adjusted without re-solving the model.
The used Engineering Data material name of the selected Rivet or Bolt is matched with the Rivet/Bolt Material Class.

Rivet/Bolt Evaluation Properties

Depending on selected “Connection Category” only the relevant properties are displayed.

Packing plate thickness, t_pp

If “Packing plates” (spacers) are used t_pp should be defined as the thickness of the thicker packing.

Spacing

The values for end and inner distance are checked according to the function “spacing” in the preference file.

Eurocode 3

Reference to sections and equations from Eurocode 3 are shown in brackets or italics.

Cut thread comply with EN 1090

Global resistance factor k_tv. Yes: 1.0, No: 0.85 (Section 3.6.1)(3)

Packing plate thickness, t_pp

Thickness to calculate reduction in shear resistance (Section 3.6.1)(12)

Countersunk bolt factor, k₂

Tension resistance factor No: 0.9, Yes: 0.63 (Section 3.9.1)

Material Class

The Material Class is defined in the preference file.

The values are from: “Table 3.1: Nominal values of the yield strength f_yb and the ultimate tensile strength f_ub for bolts”.
Shear strength factor, α_v, (Table 3.4).
Joint resistance partial safety factor, γ_M2, (Table 2.1).
Slip resistance partial safety factor, γ_M3, (Table 2.1).

The result “Scale Factor Value” γ_L is not defined in the tables and must be defined manual.

Connection Category

Bolt hole type

Class of friction surface

Hole Spacing

Rivet Design Resistance (Table 3.4)

Design shear resistance per plane: F_v.Rd = min(1,9·d/(8·d+3·t_pp))·0.6·f_ur·A_s/γ_M2 (Section 3.6.1)(12)
Design bearing resistance single lap joint: F_b.Rd = min(k₁·α_b, 1.5·k_b)·f_u·d·t_p/γ_M2 (Section 3.6.1)(10)
Design tension resistance: F_t.Rd = 0.6·f_ur·A₀/γ_M2

Bolt Design Resistance (Table 3.4)

Design preload: F_p.Cd = 0.7·f_ub·A_s/γ_M7 (γ_M7 = 1.1) (Section 3.6.1)
Design shear resistance per plane (i): F_v.Rd = k_tv·min(1, 9·d/(8·d+3·t_pp))·α_v·f_ub·A_s/γ_M2 (Section 3.6.1)(12)
Design bearing resistance single lap joint: F_b.Rd = min(k₁·α_b,1.5·k_b)·f_u·d·t_p/γ_M2 (Section 3.6.1)(10)
Design tension resistance: F_t.Rd = k_tv·k₂·f_ub·A_s/γ_M2
Design punching shear resistance: B_p.Rd = 0.6·π·d_m·t_p·f_u/γ_M2
Design slip-resistance per plane (nominal): F_s.Rd = k_s·μ·F_p/γ_M3 (Section 3.9.1)
Design slip-resistance per plane (reduced): F_s.Rd = k_s·μ·(F_p-0.8·F_tEd)/γ_M3 (Section 3.9.2)
Design slip-resistance per plane (actual): F_s.Rd = k_s·μ·F_cEd/γ_M3 (ii)

(i) Fv.Rd

Where the shear plane passes through the unthreaded portion of the bolt As is the gross cross section of the bolt, i.e. ds = d (nominal diameter) and αv = 0.6 must be set manually. If selecting a material class with “partially threaded” in the name αv is set accordingly.

(ii) Fs.Rd (actual)

The slip resistance is based on the actual average contact force for each bolt, F_c.Ed, instead of the nominal pretension force F_p or approximate reduced force F_p-0.8·F_t.Ed where F_t.Ed is the external axial force.

Utilization Criteria (Table 3.2)

The “Utilization Factor”, Uf, is calculated for each criterion in the selected category, Uf = F_Ed/F_Rd.
The maximum utilization, Uf_max, is saved from the evaluated criteria for each bolt or rivet.
If Uf_max > 1.0 the joint does not fulfil the Eurocode 3 criteria.

The following Result Items are available depending on selected category and are printed in the output file used in the results summary in the Bolt Report.

(i)

Uf_pretension and Uf_contact are not Eurocode 3 criteria but can be enabled in the preference file.

(ii)

For slotted holes Uf_bearing does not evaluate parallel and perpendicular loads separately but conservatively uses the magnitude of F_v.Ed and F_b.Rd defined in the weakest direction.

(iii)

Uf_slip is based on actual contact force, F_cEd, and if a contact is open and F_cEd is zero Uf_slip is set to 99.
If no preload is used, Fp = 0, then Uf_slip = 0 in the evaluation of Category F.

Safety Factor

To plot results as “safety factor” (SF) instead of “utilization factor” (Uf), SF = 1/Uf, a new option in the preference can be set: “UfsafetyFactor = True”, see Bolt Settings or the preference section.

Eurocode 3 S-N Curves

The Eurocode 3 S-N curves are defined in the preference file.

Figure 7.1: Fatigue strength curves for direct stress ranges, Constant amplitude.

Slope m₂ = 1e6 is used from knee point at N_c = 5e5 up to N = 1e8. N_cutoff = 1e8 cycles is used.

Figure 7.1: Fatigue strength curves for direct stress ranges, Variable amplitude.

N_cutoff = 1e8 cycles is used.

Figure 7.2: Fatigue strength curves for shear stress ranges.

N_cutoff = 1e8 cycles is used.

Validity of the Eurocode 3 result

Please pay attention to chapter 2 “Basis of design” in Eurocode 3. The evaluation supports rivets, bolts and preloaded bolts according to category A-E according to section 3.4 and table 3.2 Eurocode 3. It is the user’s responsibility to ensure that the FE-model, chosen method, input values and results obtained by this application is suitable for his/her intended purpose, e.g. to evaluate according to a selected joint category and to apply load safety factors according to use case, e.g. operational vs. ultimate limit.

A verification model is included in the Downloads section under “Demo and verification models” where the different joints and results are tested and compared with the expected values. Solve the model and click “Bolt Report” to get the verification report.

AISC 360-16

The AISC 360-16 implementation follows the same structure as Eurocode 3 and is based on “Load and Resistance Factor Design” (LRFD) or “Allowable Strength Design” (ASD).

Reference to sections and equations from the code are shown in brackets.

The design tensile or shear strength, R_d = Φ·R_n (LRFD), and the allowable tensile or shear strength, R_d = R_n/Ω (ASD), of a snug-tightened or pretensioned high-strength bolt or threaded part shall be determined according to the limit states of tension rupture and shear rupture as:

R_n = F_n·A_b (J3-1)
Φ = 0.75 (LRFD) Ω = 2.0 (ASD)

where
F_n = nominal tensile stress, F_nt, or shear stress, F_nv, from Table (J3.2) A_b = nominal unthreaded body area of bolt or threaded part.

Material Class

The Material Class defined in the preference file is used to select if “Allowable Strength Design” (ASD) or “Load and Resistance Factor Design” (LRFD) is used to calculate the design strength, F_Rd.

The adoption of AISC to the structure and naming in the app is done by the following definitions:

• Nominal tension stress; F_nt = f_yb
• Ratio of nominal shear stress to tension stress; α_v = F_nv/F_nt
• Partial safety factor; γ_M2 = Ω = 2.00 (ASD) or γ_M2 = 1/φ = 1/0.75 = 1.3333 (LRFD)
• Load scaling factor; γ_L= 1.0 (ASD) or γ_L= 1.5 (ASD)
• Design shear load; F_v.Ed = f_rv·A_b

The resulting design resistance differ between ASD and LRFD. In ASD all safety factors are applied on the material resulting in an “allowable strength” value and loads are taken with their nominal value. In LRDF material safety factors are applied on the material resulting in a “design strength” value in combination with a load factor, γ_L (similar to Eurocode 3). The LRDF method is designed to give the same Wuf as ASD by using γ_L = φ·Ω = 0.75·2.0 = 1.5.

When selecting a Material Class the results “Scale Factor Value” is defined. If selecting a different Material Class without the γ_L defined the “Scale Factor Value” is unchanged!

Connection Category

The evaluation of bolt joints is based on selecting a joint category that defines the criteria to use.

(a) Bolts are permitted to be installed to the snug-tight condition when used in:

1. Bearing-type connections, except as stipulated in Section E6. (Category A)
2. Tension or combined shear and tension applications, for Group A bolts only, where loosening or fatigue due to vibration or load fluctuations are not design considerations. (Category D or Category F)

(b) Bolts in the following connections shall be pretensioned: (Category E)

1. As required by the RCSC Specification.
2. Connections subjected to vibratory loads where bolt loosening is a consideration.
3. End connections of built-up members composed of two shapes either interconnected by bolts, or with at least one open side interconnected by perforated cover plates or lacing with tie plates, as required in Section E6.1.

(c) The following connections shall be designed as slip critical: (Category C)

1. As required by the RCSC Specification.
2. The extended portion of bolted, partial-length cover plates, as required in Section F13.3.

Bolt hole type

Class of friction surface

Hole spacing

The hole spacing is an adoption of the “clear distance”

(i) e₁

Using actual hole size, d₀ instead of nominal bolt size.

Bolt Design Resistance

Design preload (minimum): F_p.Cd = T_b = 0.7·f_yb·A_b (Table J3.1M)

Design tension resistance: F_t.Rd = Φ·F_nt·A_b = f_yb·A_b/γ_M2 (J3-1)

Design shear resistance per plane: F_v.Rd = Φ·F_nv·A_b = α_v·f_yb·A_b/γ_M2 (J3-1)

Combined tension and shear resistance: F’_t.Rd = Φ·F’_nt·A_b = Φ·(1.3·F_nt - f_rv·F_nt/(Φ·F_nv))·A_b ≤ F_t.Rd (J3-2)
where: F’_nt = min(F_t.Rd, F_t.Rd·(1.3 - F_v.Ed/F_v.Rd)) (J3-3a)

Design slip-resistance per plane (nominal): F_s.Rd = Φ·μ·D_u·h_f·T_b·n_s (J3-4)

1. For standard size and short-slotted holes perpendicular to the direction of the load: Φ = k_s = 1.00
2. For oversized and short-slotted holes parallel to the direction of the load: Φ = k_s = 0.85
3. For long-slotted holes: Φ = k_s = 0.70

D_u = 1.13, T_b = F_p.Cd, h_f(one filler plate) = 1.0, h_f(many fillers) = 0.85
n_s = number of slip planes (= 1)
Mean slip coefficient: μ(Class A surfaces) = 0.30, μ(Class B surfaces) = 0.50
F_s.Rd = k_s·μ·1.13·h_f·F_p.Cd

Slip-resistance reduction factor: k_sc = 1 - T_u/(D_u·T_b·n_b) (J3-5a)

• T_u = required (external) tension force, n_b = number of bolts carrying the applied tension.
  The external load per bolt is not known direct, instead the reduction factor is re-written to use the actual remaining contact force per bolt, F_c.Ed, to scale the slip resistance.

Design slip-resistance per plane (actual): F’_s.Rd = k_sc·F_s.Rd = (F_c.Ed/(D_u·F_p.Cd))·F_s.Rd

Design bearing resistance: F_b.Rd = Φ·k_b·d·t_p·f_u = k_b·d·t_p·f_u/γ_M2 (J3-6a) (J3-6e)

• When deformation at the bolt hole at service load is a design consideration.
  Hole type: “Long Slotted (perpendicular)”; k_b = 2.0, All other; k_b = 2.4

Design tearout shear resistance: B_v.Rd = Φ·k_v·l_c·t_p·f_u = k_v·l_c·t_p·f_u/γ_M2 (J3-6c) (J3-6f)

• When deformation at the bolt hole at service load is a design consideration.

Hole type: “Long Slotted (perpendicular)”; k_v = 1.0, All other ; k_v = 1.2
Clear distance, in the direction of the force, between the hole edges; l_c = min(e₁ - 0.5·d, p₁-d)

Utilization Criteria

The “Utilization Factor”, Uf, is calculated for each criterion in the selected category, Uf = F_Ed/F_Rd.
The maximum utilization, Uf_max, is saved from the evaluated criteria for each bolt or rivet.
If Uf_max > 1.0 the joint does not fulfil the AISC 360-16 criteria.

The following Result Items are available depending on selected category and are printed in the output file used in the results summary in the Bolt Report.

(i) Uf_bearing

Uf_bearing is evaluating bearing and tearout

(ii) Uf_slip

Uf_slip is based on actual contact force, F_c.Ed, and if a contact is open and F_c.Ed is zero Uf_slip is set to 99.

Validity of the AISC 360-16 result

It is the user’s responsibility to ensure that the FE-model, chosen method, input values and results obtained by this application is suitable for his/her intended purpose, e.g. to evaluate according to a selected joint category and to apply load safety factors according to use case, e.g. operational vs. ultimate limit.

A verification model is included in the Downloads section under “Demo and verification models” where the different joints and results are tested and compared with the expected values. Solve the model and click “Bolt Report” to get the verification report.

User Defined

The existing codes can be used as base for a user defined code by using the Bolt Settings object.