Bolted Joints-examples

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13. BOLTED JOINTS

The calculation methods used for bolted joints

between, or to, hollow sections are basically not

different from those used for any other type of joint in

conventional steel construction.

Most details given in this chapter are presented

without (detailed) design formulae.

13.1FLANGE PLATE JOINTS

13.1.1 Flange plate joints to CHS underaxial tension load

For the flange plate joints shown in Fig. 13.1, various

investigations were carried out (Kato & Hirose, 1984;Igarashi et al., 1985; Cao & Packer, 1997).

Economical joints under tension load can be obtained

if prying force is permitted at the ultimate limit state,

with the connection proportioned on the basis of a

yielding failure mechanism of the flange plates. In

CIDECT Design Guide No. 1 (Wardenier et al., 2008a)

formulae and tables are given, based on the work of

Igarashi et al. (1985). In the context of this book, only

the failure modes are presented (Fig. 13.2). It is

preferable to design primary structural joints on the

basis of the yield resistance of the circular hollow

section.

13.1.2 Flange plate joints to RHS underaxial tension load

Research by Birkemoe & Packer (1986) and Packer et

al. (1989) on bolted RHS flange plate joints with bolts

on two sides of the RHS only, see Fig. 13.3, showed

that in principle the strength of these joints can be

analysed on the basis of the traditional prying model

developed for T-stubs by Struik & De Back (1969).

The location of the plastic hinge lines may be adjusted

for greater accuracy, i.e. the distance b in Fig. 13.4 is

adjusted to b' according to:

it2

db'b (13.1)

Detailed formulae are given by Packer & Henderson

(1997) and Packer et al. (2009a).

Many tests have been carried out on RHS flange plate

joints with bolts on 4 sides of the RHS, as shown inFig. 13.3. A thorough study of this type of bolted joint

has been undertaken by Willibald et al. (2002, 2003a).

It was revealed that RHS flange plate joints bolted on

all four sides could still be proportioned on the basis of

the two-dimensional T-stub prying model of Struik &

De Back (1969), with some minor modifications.

Following the procedure for bolted RHS flange plate

joints with bolts on two sides, the inner yield lines in

the flange plate can now be expected adjacent to the

RHS outer face and hence the term t i should be

deleted from eq. (13.1). The bolt pitch to be used is

the minimum of p from both sides. The dimension p,

the plate width or depth divided by the number of bolts

in that direction, is illustrated in Fig. 13.3. This

"minimum p" value is then used in the joint analysis

based of a two-dimensional prying model. In order for

this design model to be valid, the centres of the bolt

holes should not be positioned beyond the corners of

the RHS (as illustrated in Fig. 13.3).

Detailed information can be found in CIDECT Design

Guide No. 3 (Packer et al., 2009a).

13.1.3 Flange plate joints to CHS or RHSunder axial tension load andmoment loading

Design methods for bolted flange plate joints to date

have generally been developed for axial tension

loading. Frequently, however, hollow sections are

subjected to both axial tension load (Ni) and bendingmoment (Mi). In such cases, a hypothetical "effective"

axial load can be computed (Kurobane et al., 2004)

for use with the flange plate joint design procedures

given in Sections 13.1.1 and 13.1.2:

i

i

i

i

i AW

M

A

NaxialEffective

(13.2)

where:

Ai cross sectional area of the CHS or RHS

Wi elastic (or plastic) section modulus of the CHS orRHS

This procedure will be conservative, especially for

CHS, as it computes the maximum tensile normal

stress in the CHS or RHS and then applies this to the

whole member cross section.

13.2 END JOINTS

Some bolted end joints are shown in Fig. 13.5. The

flange of the tee in Fig. 13.5d, as well as the otherflange plates perpendicular to the CHS or RHS

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section, must be sufficiently thick to effectively

distribute the load to the cross section (Wardenier et

al., 2008a; Packer et al., 2009a), see also Section

9.7.3.

13.3 GUSSET PLATE JOINTS

For bolted gusset plate joints, the design can be

based on the various possible failure modes, e.g. for a

tension member:

- Yielding of the cross section

- Rupture of the net area

- Rupture of the effective net area reduced for shear

lag

Similar to other bolted joints, the total net area is the

sum of individual net areas along a potential critical

section of a member or gusset plate, see Fig. 13.6. If

such a critical section comprises net areas loaded in

tension and segments loaded in shear, the shear

segments should be multiplied by the shear strength

and the tension areas by the ultimate strength.

Eurocode 3 (EN 1993-1-1, 2005) specifies a Mfactor

of 1,0 for yielding and 1,25 for ultimate strength

(rupture).

A failure mode of the gusset plate which also must be

checked is yielding across an effective dispersion

width of the plate, which can be calculated using theWhitmore (1952) effective width concept illustrated in

Fig. 13.7. For this failure mode (for one gusset plate),

the strength is given by:

M

o

pyp

1p)30(tan2gtfN

Rd,i (13.3)

where the term p represents the sum of the boltpitches in a bolted connection or the length of the

weld in a welded connection, and M=1,1.

If the member is in compression, buckling of the

gusset plate must also be prevented.

Fig. 13.8 shows some examples of bolted gusset plate

joints. It must be borne in mind that fitting of these

connections is very sensitive with regard to

dimensional tolerances and to deformations of the

welded gusset due to weld-induced distortions. Thus,

care has to be taken to ensure fitting at site.

When a member is connected by some, but not all

parts of its cross section elements and if the netsection includes elements which are not connected,

the net area perpendicular to the load has to be

multiplied by a shear lag factor which depends on the

shape of the section, the number of connected faces

and the number of transverse rows of fasteners.

Such a case is illustrated in Fig. 13.8b where bolting

plates are welded to the sides of the RHS brace

member. For welds parallel to the direction of load (as

the four flare groove welds would be in Fig. 13.8b,

along the four corners of the RHS), the shear lag

factor is a function of the weld lengths and the

distance between them. For the RHS, the shear lag

reduction factors can be applied to each of the four

sides (two of width w = bi- ti, and two of width w = h i-

ti), to produce a total effective net area of the RHS

reduced by shear lag. Suggested shear lag reduction

factors for these four element areas, in terms of the

weld length Lw, are (CSA, 2009):

- 1,00 when the weld Iengths (Lw) along the RHS

corners are 2bi(or 2hi as applicable)- (0,5 + 0,25Lw/bi) when the weld lengths along the

RHS corners are biLw< 2bi, or- (0,5 + 0,25Lw/hi) when the weld lengths along the

RHS corners are hiLw< 2hi- 0,75Lw/bi when the weld lengths along the RHS

corners are Lw< bi(or hi as applicable)

13.4 SPLICE JOINTS

Fig. 13.9 shows a splice joint for circular hollowsections. This type of connection can, for example, be

executed with four, six or eight strips welded

longitudinally on the periphery of the hollow sections

and connected by double lap plates, one on each

side.

Lightly loaded splice joints in tension can be made as

shown in Fig. 13.10 and for architectural appearance

the bolts can be hidden. Using one plate on each side,

instead of the solution in Fig. 13.10, provides a more

fabrication-friendly solution. Such an eccentric joint,

however, may have little stiffness and resistance toout-of-plane flexure under compression loading, thus

the designer should be confident that such a condition

has been considered. Experimental and numerical

research on this RHS joint type, under tension loading,

has been conducted by Willibald et al. (2003b).

13.5 BEAM-TO-COLUMN JOINTS

Bolted beam-to-column joints can be designed in

various ways, mainly depending on the type of load

that has to be transmitted. In general, shear joints aresimpler to fabricate than moment joints. Typical joints

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are given in Figs. 13.11 to 13.15 without detailed

description.

13.6 BRACKET JOINTS

Some typical joints for lightly loaded beams are shownin Fig. 13.16.

13.7 BOLTED SUBASSEMBLIES

Lattice structures are often connected to columns by

bolted flanges, plates or Tee profiles. Some examples

are shown in Fig. 13.17.

13.8 PURLIN JOINTS

Fig. 13.18 shows some examples of purlin joints for

trusses with CHS or RHS chords.

13.9 BLIND BOLTING SYSTEMS

Due to the closed nature of hollow sections, in many

cases additional welded plates are used for bolted

joints. However, solutions are then not aesthetically

appealing. Nowadays, bolting systems are available

which can be used when only one side of the

connection is accessible. Blind bolting systems make

use of either special types of bolts or inserts or special

drilling systems.

13.9.1 Systems using bolts and inserts

Special types of bolts and systems allow one to bolt

from one side of a hollow section. A number of

patented blind bolting systems is available, e.g. Huck

"Ultra Twist Blind Bolt" and Lindapter "HolloFast" and

"HolloBolt". The latter, which uses a special insert and

a standard bolt, has been investigated by CIDECT

(Sidercad & British Steel, 1996; Yeomans, 1998) with

regard to its axial, shear and bending capacity (see

Fig. 13.19).

The systems are based on the principle that after

bringing them in from one side, the bolts are torqued

and a "bolt head" forms on the inside of the connected

plies.

The design rules for blind bolting systems are based

on typical failure modes, i.e.- Punching shear of the fastener through the column

face

- Yielding of the column face (yield line pattern

around the bolts)

- Bolt failure in shear, tension or a combination of

both

13.9.2 Drilling system

The Flowdrill system, see Fig. 13.20, is a special

patented method for extruded holes. CIDECT has

carried out research (Yeomans, 1994; British Steel,

1996) to assess the load bearing capacity of this type

of joint in structural hollow sections.

Flowdrilling is a thermal drilling process (Fig. 13.21) to

make a hole through the wall of a hollow section by

bringing a tungsten carbide bit into contact with the

hollow section wall and generating sufficient heat by

friction to soften the steel. As the bit moves through

the wall, the metal flows to form an internal bush. In

the next step, the bush is threaded using a roll tap.

Conventional bolts are then used in this tapped hole.

Bolting to hollow sections with wall thicknesses up to

12,5 mm can be recommended by using the Flowdrill

method, see Yeomans (1994).

13.10 NAILED JOINTS

As an alternative to bolting or welding, steel circular

hollow sections can be nailed together to form reliable

structural joints. Up to now, this method of connection

has only been verified for splice joints between two

co-axial tubes (see Fig. 13.22). In such a joint, one

tube can fit snugly inside the other, in such a way that

the outside diameter of the smaller equals the inside

diameter of the larger. Nails are then shot fired and

driven through the two wall thicknesses and arranged

symmetrically around the tube perimeter.

As an alternative, two tubes of the same outsidediameter can be joined by means of a tubular collar

over both tube ends; in this case nails are again

inserted by driving them through the two tube walls.

Research to date has covered a range of tube sizes

with various diameter-to-thickness ratios, tube wall

thickness and lack of fit (Packer, 1996). The observed

failure modes were nail shear failure, tube bearing

failure, and net section fracture of the tube. These

failure modes have been identified for both static and

fatigue loading. Simple design formulae, derived from

bolted and riveted joints, have been verified for boththese load cases.


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Fig. 13.1 Bolted CHS flange plate joint

Fig. 13.2 Failure modes for bolted CHS flange plate joints

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p p p

p

p

p p p

p

p

Fig. 13.3 Bolted RHS flange plate joints

Fig. 13.4 RHS flange plate joint with bolts at two sides of the RHS

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Fig. 13.5 Bolted end joints

Bolt hole diameter d

Shear segmentsInclined segments

Tension segment Bolt hole diameter d

Shear segmentsInclined segments

Tension segment

Total net area for critical section A-A is the sum of the individual segments:

For tension segment : An= (g1- d/2)t

For shear segment : Agv= L t

For each inclined segment : An= (g2- d)t + (s2/4g2)t

Fig. 13.6 Calculation of total net area for a gusset plate

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,,

Fig. 13.7 Whitmore criterion for gusset plate yielding

Fig. 13.8 Some examples of bolted gusset plate joints

Fig. 13.9 Bolted splice joint for CHS

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Fig. 13.10 Hidden bolted splice joint

IPE or HE cut offIPE or HE cut off

Fig. 13.11 I section beam-to-CHS column joints

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a b

c d

e fFig. 13.12 I section beam-to-RHS column simple shear joints

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a b

c d

Fig. 13.13 Moment joints between open section beams and CHS or RHS columns

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Fig. 13.14 RHS sections connected to I section columns

Fig. 13.15 Knee joint assemblies for portal frames

Fig. 13.16 Bracket joints

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a b

c d

e f

Fig. 13.17 Bolted joints for lattice girder supports

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a b

c d

e f

Fig. 13.18 Purlin joints

Fig. 13.19 Lindapter "HolloFast" connection

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Fig. 13.20 Flowdrill connection for joining end plates or angles to RHS

Fig. 13.21 Flowdrill process

Fig. 13.22 Nailed CHS joint

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