Corus Tubes library publication

The contents of this publication are current, when republished it will be in the new Corus housestyle.

SHS JointingFlowdrill &Hollo-Bolt

Flow

drill

&Hol

lo-B

olt Flowdrill &

Hollo-BoltJointingfor Hollow Sections

Flowdrill and Hollo-Bolt give a choice of twomethods to produce bolted joints inHollow Sections. Both systems offer thefollowing benefits:

● They produce bolted joints of structuralcapacity in Hot Finished Rectangular HollowSections (HFRHS).

● They minimise the change in the fabricationprocess by using connection details whichare standard in the construction industry.

● They reduce fabrication by removing theneed to weld plates or other fittings onto theoutside surface of the RHS.

● They simplify erection by using fully threadedbolts -an increasing practice in theconstruction industry.

● They maintain aesthetics by producing aflush face on the RHS after fabrication.

Design GuidanceThe design guidance produced in thispublication is for Flowdrill and Hollo-Boltsystems with grade 8.8 bolts in conjunction withTubes and Pipes hot finished structural hollowsections. The design guidance, for joints insimple construction, result from Tubes & Pipesinitial research work undertaken in connectionwith CIDECT (Ref. 1). The guidancecomplements the information published by theBCSA/SCI and is presented in a formcompatible with their publication “Joints inSimple Construction” (Ref. 2).

Further test work is being undertaken toestablish design guidance for semi-rigidjoints.

Procedural checks are given for bearing, shearand local bolt pull out of the RHS wall and forthe combined effect of the column axial loadand the structural integrity tensile load ofBS 5950 : Part 1.

The combined check for the column axial loadand the structural integrity tensile loadrecognises that the flexibility of the RHS facecaused by the tensile load can, in the presenceof the column axial load, reduce the overall jointcapacity.

Flowdrill Hol

lo-B

olt

Fabrication andConstructionGeneral detailing recommendations for beamcolumn connections, given in thispublication, are in accordance with theBCSA/SCI publication -”Joints in SimpleConstruction” (Ref. 2).

Both Flowdrill and Hollo-Bolt use fully threadedbolts which allows standardisation of boltlengths throughout the construction. Wherebeams are connected to adjacent faces of anRHS column a check must be made with thechosen bolt length to ensure that assembly ispossible (see Fig. 3 and 6) and the bolts donot touch.

Both Flowdrill and Hollo-Bolt are suitable for usewith the two standard grades of Tubes & PipesSHS to BS EN10210-1 of S275J2H andS355J2H (formerly BS4360 Gr43D and 50Drespectively).

At present, application of the Flowdrill processis limited to RHS thicknesses up to andincluding 12.5mm. For thicknesses of 16mmand over, conventional drill and tap methods arerecommended, although due to the RHSmaterial strength being lower than that of thegrade 8.8 bolts, pull out strengths may be belowthe bolt tension capacity.

Reference

1. Comité International pour leDéveloppment et l’Étude de laConstruction TubulaireUK MemberBritish Steel plcTubes & PipesPO Box 101CorbyNorthants NN17 5UA

2. Joints in Simple ConstructionVolume 1 : Design methodsVolume 2 : Practical applicationsPublished jointly by:BCSA SCI4 Whitehall Court Silwood ParkWestminster AscotLondon Berks SL5 7QNSW1A 2ES

Flow

drill

The ToolsThe initial hole is made by a Flowdrill toolconsisting of a tungsten carbide bit held in aFlowdrill Morsetaper collet adaptor (Fig. 1). Thetool can be used in a conventional drillingmachine or CNC machine as found infabricators works, provided it has adequatehorsepower and spindle speed.

1st stageThe tungsten carbide bit is brought into contactwith the RHS wall where it generates sufficientheat to soften the steel. The bit is thenadvanced through the wall and in so doing themetal is redistributed (or flows) to form aninternal bush. As well as drilling the initial hole,the tool is fitted with the means of removing anysurplus material which may arise on the outsideof the RHS section. The cycle time forFlowdrilling is similar to that for conventionaldrilling. However, if done on CNC machines thefeed rate can be slow at the beginning, rapidlyincreasing as the material softens to improveefficiency.

2nd stageThe 2nd and final stage is to tap the Flowdrillbush. This is done by roll threading the bushwith a Coldform Flowtap. The complete cycle isshown in Figure 2.

TheProcess

Flowdrill data :The Flowdrill system was developed by Flowdrill BV in Holland, and is available in the UK fromtheir agent - Robert Speck Ltd,. Little Ridge, Whittlebury Road, Silverstone, Northants NN12 8UD.Tel: 01327 857307 Contact Mr Mike Carpenter.

Flowdrill Flowdrilling is basically a thermal drillingprocess which makes a hole through thewall of a structural hollow section withoutthe removal of metal normally associatedwith a drilling process. The formed hole isthen threaded by the use of a roll threadforming tool, leaving a threaded hole whichwill accept a standard fully threaded bolt.

Tool holder

Collet

Flowdrill bit

Fig. 1

Fig. 2

1st Stage 2nd Stage

Drilling machine parameters :Table 1 gives a guide to required machineparameters for producing Flowdrill holes forM12 to M24 bolts:

Note: The Flowdrill process is not suitable forhand held or magnetic clamp type drillingequipment when used in the sizes shown.

Flowdrill detailing requirements.See Fig. 3 and Table 3.

Note:

● Flowdrilled joints used atlocations exposed to theweather should not beconsidered as water tight.

● Flowdrilling is not suitablefor use with pre-galvanisedmaterials.

Drill length: The recommended length ofFlowdrill bits varies with the thread size andthickness of material as given in Table 2.

Drill care: Flowdrills are made from tungstencarbide. They are extremely hard but cannotwithstand shock loads. After drilling each hole,FD KS paste should be applied to the Flowdrillwhilst it is still hot, so minimising oxidation andpreventing ‘build up’ on the surface.

Flat surface: the raised rim on the outer surfaceof the RHS material caused during Flowdrillingshould be removed using Flowdrills with cuttingedges provided on the collar. One rotation of thecutter is all that is required to remove the rim.

Table 1

Table 2

Table 3 (See Fig. 3 for nomenclature)

Thread size

Flowdrill size

M/c spindlespeed rpm

M/c feed rate

Motor powerKW Min

Tapping speedrpm

M12

10.9

1000-1500

2

250

M16

14.8

700-1100

2.5

200

M20

18.7

600-1000

3.5

150

M24

22.5

500-800

5

100

0.1/0.15mm (0.004/0.006 inches) per rev

Flowdrill Length

Thread SizeMax materialthickness

(mm)

3

5

6

8

10

12

16

M12

Short

Long

Long

Long

-

-

-

M16

Short

Short

Long

Long

Long

-

-

M20

Short

Short

Short

Long

Long

Long

-

M24

Short

Short

Short

Long

Long

Long

-

Dimensions(mm)

A1

B1

C1

D1

E1 Minimum

Min Bolt Centres

M12

7

13

18

30

M16

10

17

20

40

M20

12

22

26

50

M24

15

25

29

60

Thread size/Bolt diameter

Varies with overall bolt length (Lb) specified

C1/2 + tc (for connection made to a single face or opposite faces)

B1/2 + A1 + D1 + tc (for connection made to adlacent faces)

E1

tp

tc

Lb

E1

B1

A1

D1

C1

Min bolt centres

Width

Fig. 3

Hollo

-Bol

tHollo-Bolt

The pre-assembled unit (Fig. 4) isinserted through normal tolerance holesin both the attatchment plate and theRHS. As the bolt is tightened the cone isdrawn into the body, spreading the legs,and forming a secure fixing. Onceinstalled only the Hollo-Bolt head andcollar are visible (Fig. 5).

The Hollo-Bolt

HOLLO-BOLT is a pre-assembledthree part fitting consisting of body,cone and bolt.

Further information onHollo-Bolt is available from

Lindapter InternationalA Division of Victaulic plc.,Lindsay House, Brackenbeck Road,Bradford, West Yorkshire, Tel: 01274 521444England, BD7 2NF Fax: 01274 521130

Hexagon Head

Location Flats

Body

Cone Knurling

Collar

Fixture

RHS

Cone

Legs

Central Bolt

Fig. 4

Fig. 5

Drilling requirements:Hollo-Bolt uses a plain drilledhole which can be made onsite or in the fabrication shopusing all normal drillingequipment. The finished holeshould have a tolerance of-0.2mm to +1.0mm from thenominal given in the data table(Table 4).

Material Options

Standard product is manufactured from mildsteel and is electro-zinc plated with the additionof JS500 1000 hour saltspray corrosionprotection. The central fastener is a grade8.8 bolt.

For special applications, the Hollo-Bolt isavailable manufactured from 316 stainless steel,with a grade A4-80 central bolt. This will not be astocked item, and would be manufactured toorder.

Installation

The only tools required to fit Hollo-Bolt are twospanners - an open ended spanner to hold thecollar and a torque wrench to tighten the centralbolt. Alternatively a power operated electrichand tool is in development.

Should the steelwork need to be adjusted,the fixing can simply be removed and thehole reused with another Hollo-Bolt.

Sealing Options

In certain applications, it may be necessary toseal the Hollo-Bolt to prevent ingress of water orother corrosive agents. For details of sealingoptions available, please contact Lindapter.

Special Options (manufactured to order)

● Stainless steel● Button head setscrew ● Socket head capscrew● Countersunk setscrew/body ● Special body lengths

Table 4 (See Fig. 6 for nomenclature)

Boltsize

M8

M10

M12

M16

M20

Boltlength

(V)

mm

45

49

53

57

80

Fixingthickness

(W)Min Max

mm

3 22

3 22

3 25

3 28

3 34

Boltcentres

(X)Minmm

35

40

50

55

70

Internalmin. edgedistance

(Y)mm

13

15

18

20

25

Edgedistance

(E1)Minmm

50-tp

55-tp

60-tp

65-tp

90-tp

Bolthole dia.(Dh)

mm

14

18

20

26

33

Acrossflats mainbody

mm

19

24

30

36

46

Tighteningtorque

Nm

21

40

78

190

300

E1

tp

tc

V

YX

W

Width

Fig. 6

Fig. 7

Simple connections between Universalbeams and RHS columns can be madeusing double angle web cleats orflexible end plates.

The following procedural checks arecompatible with the BCSA/SCI rules forJoints in Simple Construction (Ref. 2).

Double Angle Cleats Flexible End Plates

Notes

● The cleats or end plates are generally positioned as close to the top flangeof the beam as possible to provide adequate positional restraint and a platelength of at least 0.6D is usually adopted to give adequate torsional restraint(BS 5950: Part 1, Table 9).

● Bolt gauge g: 90mm ≤ g ≤ 140mm, but g ≥ 0.3 x RHS face width B.

● Although it may be possible to satisfy the design requirements with tp< 8mm,it is not recommended in practice because of the likelihood of welddistortion during fabrication and damage during transportation.

● The plate thickness and gauge limitations apply equally to partial depth andto full depth end plates.

If necessary, to comply with structural integrity requirements for a 75 kN tie force,the connection must have at least 2 no. M20, Grade 8.8 bolts in tension with/ ≥ 140mm, t ≥ 8mm and g ≤ 140mm.

Design ofJoints inSimpleConstruction

Face of column Face of column

ID ID

g g

Length of cleatI ≥ 0.6D

Length of plateI ≥ 0.6D

Cleat thickness, tptp= 8mm or 10mm

Plate thickness, tptp= 8mm or 10mm

Flowdrill hole diameter, DhDh = d+2mm for d ≤ 24mmDh = d+3mm for d > 24mmFor Hollo-Bolt Dh see Table 4.

Bolt diameter, d Bolt diameter, d

End projection t1, approx 10mm

Basic RequirementFor Shear

Local shear and bearing capacity of the RHS column wall and bolts.

Q ≤ Pv_2

Pv = local shear capacity ofRHS column wall

= smaller of 0.6pyc Av and0.5 Usc Avnet

Av = [g/2 + (n -1) p = et] tcwith [et ≤ 5 d]

Avnet = Av - n d tc

n = number of rows of boltsp = bolt pitchd = nominal bolt diameter (or

hole diameter in RHScolumns for Hollo-Bolt)

g = bolt gauge widthtc = RHS column wall

thicknesspyc = design strength of RHS

colunm wall (S275 = 275N/mm2 : S355 =355 N/mm2)

Usc = ultimate tensile strengthof RHS column wall

For bearing

Q ≤ Pbsc_2

Pbsc = bearing capacity of the RHScolumn wall per bolt = d tc pbsc

pbsc = bearing strength of the RHScolumn wall (S275 =460 N/mm2 : S355 = 550 N/mm2)

Bolt Check (Table 5)

The single shear capacity for Flowdrill and Hollo-Bolt can be taken as follows:-

Flowdrill

Bolt diameter

-

-

M12

M16

M20

M24

kN

-

-

31.6

58.9

91.9

132

Bolt diameter

M8

M10

M12

M16

M20

-

kN

12

25

38

75

100

-

Flowdrill

tc

p

p

p

g

Q/2 Q/2

Q

et

n rowsof bolts

Critical sections

Structural integrity-local bolt pull-outof RHS colmn wall.

Note: This check is only needed if it is necessary to comply with structuralintegrity requirements.

Basic Requirement

Tie force ≤ ∑ Local bolts pull-outresistances

∑ Local bolt pull-out resistances= 2 n Pp(si)

The local bolt pull-out design resistancein kN of a grade 8.8 bolt in a flowdrilledhole or a Hollo-Bolt should be taken from the following tables which are based ontest results:

Note:

1. The tension capacity of Grade 8.8 bolts fornormal design and for structural integritydesign is shown in the shaded areas.

2. The pull-out resistances for structuralintegrity Pp(si) are less than those for normaldesign because the design methodpresented here for structural integrity leadsto thinner cleats or end plates than fornormal design methods, based on BS 5950:Part 1, and, as a result, will lead to higherprying forces. This has been taken intoaccount in the quoted resistances.

Flowdrill normal design strength (Pp(n)kN

RHS column wall thickness tc mm

Grade S275 (Grade 43) Grade S355 (Grade 50)Bolt

diametermm

M16

M20

M24

6.3

60

85

101

8

95

122

10

70

97

134

12.5

110

159

5

59

102

103

6.3

130

70

110

8-12.5

159

5

46

70

80

Flowdrill structural integrity design strength (Pp(si)kN

RHS column wall thickness tc mm

Grade S275 (Grade 43) Grade S355 (Grade 50)Bolt

diametermm

M16

M20

M24

6.3

40

56

67

8

63

81

10

46

65

89

12.5

73

106

5

39

68

68

6.3

86

46

73

8-12.5

106

5

30

46

53

Hollo-Bolt design strengths

Boltdiameter

mm

M8

M10

M12

M16

M20

Normal designstrength (Pp(n))

kN

16

26

38

70

110

Structural integritydesign strength (Pp(si))

kN

10

17

25

46

73

Table 6

Table 7

Table 8

n rows ofbolts (criticalbolts arethose inthe column)

Tie force

Basic Requirement

Tie force ≤ Tying capacity of RHS columnwall

Tying capacity of RHS column wall8 mu

= (�1+ 1.5 (1 - �1)0.5 (1 - �1)0.5)(1 - �1)

Mu = moment capacity of RHScolumn wall per unit lengthpyctc2

=4

pyc = design strength of the RHS column(S275 = 275 N/mm2 : S355 = 355 N/mm2)

tc = thickness of RHS column wall

n�1 = (n - 1)p - d

2(B - 3tc)

g�1 =

(B - 3tc)

d�1 =

(B - 3tc)

B = overall width of RHS columnwall to which the connection ismade.

d = bolt diameter (or hole diameterin RHS column for Hollo-Bolt)

g = bolt gauge width

n = number of rows of bolts

p = bolt pitch

Structural integrity - tie forcecapacity of RHS column wall in thepresence of axial compression in thecolumn.

Note: This check is only needed if it is necessary to comply with structuralintegrity requirements.

tc

1.5 tc

Tie force(applied at

bolt positions)

Bolt holesdeducted

Yield lines

B

p

g

(n-1)p

British SteelTubes & PipesPO Box 101, Weldon Road, Corby, Northants, NN17 5UA

Tel: 01536 402121 Fax: 01536 404111

British Steel plc Registered Office: 9 Albert Embankment, London, SE1 7SN Reg. in England No: 2280000

TD 3

84.1

2E.9

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