Torque Shear Bolt

Torque Shear Bolt Introduction

High Strength Torque Shear Bolts (also known as Twist-off Bolts) are commonly abbreviated as TC, which originates from the English abbreviation TCB (Tension Control Bolts) to differentiate them. The ends of these bolts have a spline end and the bolt heads are generally circular (mushroom-shaped) with a spline design. A torque shear-style high-strength bolt assembly consists of one high-strength bolt, one nut, and one washer.

The specifications of the steel structure torque shear style high strength bolts range from M16 to M30 (available in six different thread sizes: M16, M20, M22, M24, M27, M30), with lengths ranging from 40mm to 220mm. The performance grades include 10.9 and 12.9s, and the surface treatments can be phosphatized, plain, galvanized, or blackened. The performance indicators comply with the GB/T 3632-2008 standard for torque shear-style high-strength bolts.

Torque Shear Bolt Dimension Details

During the installation of torque shear-style high-strength bolt connections, only one washer should be added on the side of the nut. The formula for calculating the initial torque value is: Tc = 0.065 * Pc * d, where Tc is the initial torque value in N·m, Pc is the construction pretension in kN, and d is the diameter of the high-strength bolt thread in mm. The final tightening is done using a wrench until the spline end breaks. Emphasis should be placed on quality inspection during the construction process supervision. Torque shear-style high-strength bolts are an improved version of large hexagon high-strength bolts for better construction. Large hexagon high-strength bolts consist of one bolt, one nut, and two washers, while torque shear-style high-strength bolts consist of one bolt, one nut, and one washer.

Features of Structural Torque Shear Bolts:

• The bolt’s manufacturing process, including the head, tail, thread, and groove, is all carried out in the same factory using cold forging. The precision and stability of the manufacturing process are excellent.
• Continuous steel strip heat treatment furnaces are used for heat treatment. Standard temperature and carbon concentration are automatically recorded to effectively control quenching temperature and gas concentration, preventing carburization or decarburization and ensuring the required mechanical properties of the bolts.
• Process control is thoroughly implemented through the use of control charts and process capability analysis methods to track processing and quality conditions, providing comprehensive data for engineering designers’ reference.
• Considering the special characteristics of torque shear-style bolts, to prevent sliding and spinning during installation, an anti-slip treatment is added beneath the bolt head during the design and manufacturing process. This effectively avoids safety and quality accidents caused by improper installation due to bolt slippage.

Dimension of High Strength (10.9) Structural Torsion Shear Bolt

Thread d		M16	M20	M22	M24	M27	M30
Thread pitch		2	2.5	2.5	3	3	3.5
da	max	18.83	24.4	26.4	28.4	32.84	35.84
ds	max	16.43	20.52	22.52	24.52	27.84	30.84
	min	15.57	19.48	21.48	23.48	26.16	29.16
dw	min	27.9	34.5	38.5	41.5	42.8	46.5
dk	max	30	37	41	44	50	55
k,	Norminal	10	13	14	15	17	19
	max	10.75	13.9	14.9	15.9	17.9	20.05
	min	9.25	12.1	13.1	14.1	16.1	17.95
k’	min	12	14	15	16	17	18
k"	max	17	19	21	23	24	25
r	min	1.2	1.2	1.2	1.6	2	2
db	max	11.3	14.1	15.6	16.9	19.3	21.4
	min	11	13.8	15.3	16.6	18.7	20.8
dc ≈		12.8	16.1	17.8	19.3	21.9	24.4
de ≈		13	17	18	20	22	24

Torsion Shear Bolt Mechanical Property

Mechanical Property	Tensile Strength	Yield Strength σ0.2	Elongation δ5	Shrinkage Ψ
	σь	Mpa	%	%
	Mpa	min
10.9S	1040～1240	940	10	42
8.8S	830～1030	660	12	45

Torsion Shear Bolt Physical Tensile Load

Thread Size d		M16	M20	M22	M24	M27	M30
Stress cross-sectional area(mm2)		157	245	303	353	459	561
Tensile Load       KN	10.9S	163～195	255～304	315～376	367～438	477～569	583～696
	8.8S	130～162	203～252	251～312	293～364	381～473	466～578

When the bolt l/d≤3, if the wedge load test cannot be done, the core hardness test is allowed. The core hardness value should comply with the table below.

Tensile Strength	Rockwell Hardness		Vickers Hardness
	HRC		HV30
	min	max	min	max
10.9S	33	39	312	367
8.8S	24	31	249	296

Fastening Axial Force of Torsional Shear Bolt

Thread d		M16	M20	M22	M24	M27	M30
Average value of each batch of fastening axial force （kN）	Pitch	110	171	209	248	319	391
	min	100	155	190	225	290	355
	max	121	188	230	272	351	430
Standard Deviation of Fastening Axial Force ≤   /kN		10	15.5	19	22.5	29	35.5

When l is less than the value in the table below, the fastening axial force test may not be carried out. The unit is: millimeter (mm）  

Thread d	M16	M20	M22	M24	M27	M30
L	50	55	60	65	70	75

Steel Materials for Structural Bolt Nut and Washer

Type	Tensile Strength	Thread Size	Material
Bolt	10.9S	M12～M24	20MnTiB
		M27～M30	35VB
	8.8S	M12～M16	35#
		M20～M24	20MnTiB
		M27～M30	35VB
Nut	8H  10H	M12～M30	35#
Washer	35～45 HRC	12～30	45#

Torsion Shear Bolt Chemical Composition

Material	C%	Si%	Mn%	Ti%	V%	B%	P%	S%
20MnTiB	0.17～0.24	0.17～0.37	1.30～1.60	0.04～0.10		0.0005～0.0035	≤0.035	≤0.035
35VB	0.31～0.37	0.17～0.37	0.50～0.90		0.05～0.12	0.001～0.004	≤0.04	≤0.04
35#	0.32～0.40	0.17～0.37	0.50～0.80				≤0.035	≤0.035
45#	0.42～0.50	0.17～0.37	0.50～0.80				≤0.035	≤0.035