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Code-check of bolts and preloaded bolts according to Chinese standard

Steel

Connection

CBFEM

Bolts

GB (China)

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Bolts

Bolts are checked according to GB 50017, Cl. 11.4. The tensile and shear force in each bolt is determined by finite element analysis. Prying forces are determined by finite element analysis and taken into account. Each shear plane is checked individually. The plate in the bearing is checked against the sum of shear forces at nearby planes.

Design tensile and shear strengths of a bolt; f_ub[MPa] – ultimate strength of a bolt; derived from Table 4.4.6

\(f_{ub}\) [MPa]	\(f_t^b \)	\(f_v^b\)
\(f_{ub} \le 400 \)	\(0.425 \cdot f_{ub}\)	\(0.35 \cdot f_{ub}\)
\(400<f_{ub}<830\)	\(0.42 \cdot f_{ub}\)	\(0.38 \cdot f_{ub}\)
\(830 \le f_{ub}\)	\(40/83 \cdot f_{ub}\)	\(32/83 \cdot f_{ub}\)

Bolt in tension

A bolt subject to a tensile force is designed according to Cl. 11.4.1.2 and shall satisfy:

\[ N_t \le N_t^b = A_s \cdot f_t^b \]

where:

N_t – tensile force in a bolt
N_t^b – design tension capacity
\( A_s = \frac{\pi d_e^2}{4} \) – tensile stress area of a bolt
d_e – effective diameter of a bolt at threaded section
f_t^b – design tensile strength of a bolt

Bolts in shear

A bolt subject to a shear force is designed according to Cl. 11.4.1.1 and shall satisfy:

\[ N_v \le N_v^b = A_g \cdot f_v^b \]

where:

N_v – shear force in a bolt in investigated plane
\( A_g = \frac{\pi d^2}{4} \) – gross cross-section area of a bolt
d – nominal diameter of a bolt
f_v^b – design shear strength of a bolt

Each shear plane is checked individually, i.e. number of shear planes n_v = 1.

Bolts in combined tension and shear

A bolt loaded in shear and tensile forces at the same time is designed according to Cl. 11.4.1.3 and shall satisfy:

\[ \sqrt{\left ( \frac{N_v}{N_v^b} \right ) ^2 + \left ( \frac{N_t}{N_t^b} \right ) ^2} \le 1.0 \]

where:

N_v – shear force in a bolt in investigated plane
N_t – tensile force in a bolt
N_v^b – design shear resistance of a bolt
N_t^b – design tensile resistance of a bolt

Bolts in bearing

A plate subject to a bearing force due to a bolt in shear is designed according to Cl. 11.4.1.1 and shall satisfy:

\[ N_v \le N_c^b = d\cdot t \cdot f_c^b \]

where:

N_v – shear force in acting on a plate; vector sum of shear forces in nearby planes
d – nominal bolt diameter
t – plate thickness
f_c^b – design bearing strength of a plate

Design bearing strength of a plate; f_u – ultimate strength of a plate; derived from Table 4.4.6

Preloaded bolts

High strength bolt in friction type joint is designed according to Cl. 11.4.2.

Preloaded bolts in tension

The tensile resistance of a preloaded bolt is determined as:

\[ N_t \le N_t^b = 0.8 \cdot P \]

where:

N_t – tensile force in a bolt
N_t^b – design tension capacity
P – pretension of a high strength bolt – Table 11.4.2-2

Table 11.4.2-2 – pretension of a high strength bolt P [kN]

Bolt grade	M16	M20	M22	M24	M27	M30
8.8	80	125	150	175	230	280
10.9	100	155	190	225	290	355

A preloaded bolt which is not in Table 11.4.2-2 subject to a tensile force is designed according to Cl. 11.4.1.2 and shall satisfy:

\[ N_t \le N_t^b = A_s \cdot f_t^b \]

where:

N_t – tensile force in a bolt
N_t^b – design tension capacity
\( A_s = \frac{\pi d_e^2}{4} \) – tensile stress area of a bolt
d_e – effective diameter of a bolt at threaded section
f_t^b – design tensile strength of a bolt

Preloaded bolts in shear

The design resistance of a preloaded bolt in shear is determined according to Cl. 11.4.2.1:

\[ N_v \le N_v^b = 0.9 k \mu P \]

where:

N_v – shear force in investigated plane
N_v^b – design shear resistance of a bolt
k – factor for bolt holes; k = 1 for normal holes, k = 0.85 for oversized holes, k = 0.6 for slotted holes
μ – slip coefficient at friction interface taken from Table 11.4.2-1; editable in Code setup
P = N_t^b / 0.8 – pretension of a high strength bolt for bolts which are not in Table 11.4.2-2