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\. Steel Construction Institute Qv

&:

The Steel Construction Institute develops and promotes the effective use of steel in construction. It is an independent, membership based organisation.

SCI's research and development activities cover many aspects of steel construction including multi-storey construction, industrial buildings, light gauge steel framing systems and modular construction, development of design guidance on the use of stainless steel, fire engineering, bridge and civil engineering, offshore engineering, environmental studies, value engineering and development of structural analysis systems and information technology.

Membership is open to all organisations and individuals who are involved with the use of steel in construction. Members include designers, contractors, suppliers, fabricators, academics, and government departments in the United Kingdom, elsewhere in Europe and in countries around the world. The SCI is financed by subscriptions from its members, and by revenue from research contracts, consultancy services, publication sales and course fees.

The benefits of corporate membership include access to an independant specialist advisory service and free initial copies of SCI publications as soon as they are produced. A membership Pack is available on request from the Membership Manager.

The Steel Construction Institute, Silwood Park, Ascot, Berkshire, SL5 7QN, Telephone: +44(0) 1344 623345 Fax: +44(0) 1344 622944 Email: reception@steel-sci.com

Web site: wwwsteel-sci.org Visit: www.steelbiz.org - the 24x7 online technical information system for steel design and construction

The British Constructional Steelwork Association Limited

The British Constructional Steelwork Association Limited (BCSA) was formed in 1906 and is the national organisation for the constructional steelwork industry: its Member companies undertake the design, fabrication and erection of steelwork for all forms of construction in building and civil engineering. Associate Members are those principal companies involved in the purchase, design or supply of components, materials, services, etc. related to the industry. Corporate Members are clients, professional offices, educational establishments etc., which support the development of national specifications, quality, fabrication and erection techfiuques, overall industry efficiency and good practice.

The principal objectives of the Association are to promote the use of structural steelwork; to assist specifiers and clients; to ensure that the capabilities and activities of the industry are widely understood and to provide members with professional services in technical, commercial, contractual and quality assurance matters. The services provided by BCSA work both for the overall benefit of the industry and for the direct benefit of individual companies.

A current list of members and a list of current publications and further membership details can be obtained from: The British Constructional Steelwork Association Limited, 4 Whitehall Court, Westminster, London S\VlA 2ES. Telephone: +44 (0)20 7839 8566, Fax: +U (0)20 7976 1634. Email:postroom@ steelconstruction.org Web site: www.steelconstruction.org

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Joints in Steel Construction: Simple Connections (Publication P212, 2002)

Corrigendum 1, October 2002

Tying Capacity of Fin Plate Connections with Single Line of Bolts. The values of tying capacity given in Table H.27 (pages 410 to 414) and Table H.29 (pages 420 to 424) should be amended to values that are the lesser-of the tabulated values and the shear capacity of the bolt groups. The shear capacity of the bolt group = n.P, where n is the number of bolts and P, is the shear capacity per bolt (= 91.9 kN for M20, grade 8.8 bolt from Table H.49).

The reason for this change is that, as slated in Table H.24, the tabulated tying capacities for fin plate connections were based on the minimum values from Checks I l ( i ) , I l( i i) , 12(i) and 12(ii). None of these checks relate to the shear capacity of the bolt group. Mere there is a single line of bolts, the shear capacity of the bolt group may be less than the tabulated tying capacity.

Also, when carrying out the full design procedure (in accordance with Section 6.5) an additional check for "structural integrity" should be made for the shear capacity of the bolt group. This additional check, which may be referred to as Check 13, is: Tie force I n.P,.

In practice these changes will only be of significance in the unusual case when the tie force is greater than the shear force on the beam.

8 2002 The Steel Construction Institute SCI P2 I 2 (Corrigenduni I , Oct 2002)

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9. BRACING CONNECTIONS

9. 1 INTRODUCTION 9. 2 DESIGN CONSIDERATIONS This Section gives general guidance on bracing connections and, where appropriate, refers to other publications for comprehensive detailed design.

Table9.1 shows possiblesolutionsfor bracingconnections and indicates matters relevant to each type of connection. The design method is to decide on a force path to be adopted that provides equilibrium a t the joint and check

appropriate.

Connectionsfor bracing members angles, each element for shear, tension, bearing, or buckling as channels, I-sections, RHS and CHS are included. Gusset plates incorporating kidney shaped slots are sometimes used in bracing connections for single and multi-storey frames; they are described in Section 9.3.

Bracing is usuallydesigned assuming that all forces intersect on member centroids but if this assumption is carried out in the connection design then this may produce a large connection. It is often more convenient to arrange the member intersections to make a more compact joint and check locally for the effects of eccentricities.

Single angle bracing with welded gusset plates to beams or columns and bolted site connections are simple to fabricate. CHS bracing is also economical, being effective in both tension and compression, the connection usually being made with a 'T' shaped element welded at each end of the memberfor site bolting to gusset plates. Fabrication costs are generally higher for the other types of connections shown which have either, more elements to fabricate, or a greater weld content.

The components in the structure that attach to bracing are often the first parts to be erected since stability is then available for erection of further components. Connections should therefore be made such that erection can be made swiftly and, as far as possible, without the need of temporary supports. Care should also be taken to ensure that there are no encumbrances built into the connection which make erection difficult.

Bracing systems may include beams acting as horizontal members in bracing systems; the beams may be provided with double angle cleats, flexible end plates or fin plate connections as decribed in Sections 4, 5 or 6. It is necessary to allow for in the connection design any axial force present in the beams and induced shear forces, in addition to the normal end reactions.

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Bracing Connections - Design considerations

Table 9.1 Bracing connections

REQUIREMENT

:1) Multiple Connections Noding joints

POSSIBLE SOLUTION

(i) Extended end plates with fully welded gusset

Effect I Desiqn Gusset plates stiffen the extended end plate.

Overall connection may become a rigid connection.

Connection may be designed using loints in Steel construction: Moment Connections [241, using the combined effects of coexistent moments, shears and horizontal tension.

(ii) Full or partial depth end plates

Effect

Eonnection treated as a nominally pinned connection n Gusset plates may bevulnerable

to damage during transit. Gusset plates can be stiffened if necessary.

Design

Connection to be checked for: total shear due to bracing loads and beam loads transfer of horizontal forces eccentricity of the vertical shear from the bracing system

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Bracing Connections - Design considerations

Table 9.1 Bracing connections (continued)

REQUIREMENT

(2) Multiple Connections Non-noding joints

(3) Gusset Plates in compression and axial alignment

POSSIBLE SOLUTION

Individual bracing plates

Case 1 Y

Effect

B Additional momentsare induced in members. Gusset plates may be vulnerable to damage during transit.

B

I

Buckling

8 Case 2 Design

Check for: Additional moment due to eccentricity e, or e2. total shear due to bracing components and beam loads horizontal forces due to bracing

Eccentricity

Effect 1 Some gusset plates that are in

compression may be prone to buckling between the first bolt and the connecting member.

1 Single sided gusset connections are by their nature out of alignment

DesiQn

Plate buckling may be checked using strut cuwe C Table 24 of BS 5950-1[11. For further design guidance see reference: ClMsteel Engineering Basis [431, Cidect Cuides[281~2gl Moments due to force eccentricity 'e' can be ignored. Angle, channel and T-section struts to be designed in accordance with BS 5950-1 cl. 4.7.1 0

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Bracing Connections - Design considerations

Table 9.1 Bracing connections (continued)

REQUIREMENT

(4) Bracing Members Hollow section (CHS, RHS)

POSSIBLE SOLUTION

Design guidance for all types of CHS and RHS connections is given in Cidect Cuides[281[291

(i) Rolled or fabricated IT'

Stalks of standard rolled T sections are +--[Ei - relatively thin and therefore bolt bearing may control capacity.

(ii) Slotted tube - - - - - - - 3 Sealing plates may be required. This type

of connection involves a relatively high amount of fabrication.

sealing plate

(iii) Flattened end CHS During cold flattening longitudinal cracks/splitting may apear on the edges of the flattened CHS. Usually this has no effect on the performance of the connection.

(iv) Fork plates

Both fork plate types make more effective use of bolts (double shear) but are more expensive to fabricate. May be required for architectural reasons for single pin connections .

----

' t r - - - - i

Sealing plates may be required.

\ sealing plate (v) Castings

Castings can be economical if sufficient numbers are required. Refer to manufacturers.

Not used in orthodox buildings. For further guidance see SCI-P1 72[44].

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Table 9.1 Bracing connections (continued)

REQUIREMENT

5 ) Bracing Members Flats, angles, channel, UB/UC

POSSIBLE SOLUTION

li) Flat plate Simple tension bracing but lacks compression capability.

n Susceptible to distortion during transport and erection.

Double angle bracing can be 'back-to- back', separated by division plates spaced

[ii) Double Angle

n at intervals along the length (of same thickness as the gusset) or 'starred'

H I formation with battens in both directions spaced at intervals along the length.

n+ Double channel bracing can be 'back-to- back', separated by division plates spaced at intervals along the length of same thickness as the gusset.

(iii) Double Channel

UB/UC The flanges on one side can be removed to allow the gusset plate to be bolted to the web. A web reinforcing plate can be used if it is necessary to increase connection capacity.

(iv) UB/UC

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Bracing Connections - Kidney shaped slot connections

4 24

>24

9.3 KIDNEY SHAPED SLOT CONNECTIONS Kidney shaped slots used in bracing connections provide a practical solution for connecting members of varying lengths and angles with standardised components. The kidney shaped slot is generally formed in the gusset plate rather than a t the end of the bracing member, as shown in Figure 9.1.

Non-preloaded bolts (ordinary bearing bolts) are used rather than preloaded (friction grip) bolts.

Width Length

d + 2 d +2 3d see Note 1

d + 3 d +3 3d see Note 1

Figure 9.1 Gusset plate with kidney shaped slot

;pacing s between circular hole and kidney slot:

End and edge distances e

Practical Considerations The three common methods of forming the kidney shaped slot are:

2.5 d

2 d

Punching full size, in one operation, using a die that matches the slot dimensions.

The advantages of a connection incorporating a kidney shaped slot are that:

Drilling two holes and completed by cutting.

Machine operated plasma or flame cutting.

A standard end connection can be used for bracing mem bers.

Standard gusset plates which accommodate a range of bracing member may be used.

A two bolt connection allows one bolt to be inserted in the connection whilst locating and maintaining alignment with a podger spanner through the other hole.

Standard details encourage a batch production approach to the fabrication of the connection components, and save time in design, detailing, checking and fabrication.

Recommended Geometry The recommended geometry for the single circular hole and the kidney shaped slot is as shown in Figure 9.2 and given in tables 9.2 and 9.3.

/ /

I

Figure 9.2 Recommended geometry for gusset plate with kidney shaped slot

Table 9.2 Hole and slot dimensions (see Figure 9.2

c.2 117

Note 1 : but angle 8 should not exceed 30

Table 9.3 Spacing dimensions

I Minimum

I

ree Figure 9.2)

Maximum

Lesser of 14t and 200 mm

Lesser of 1 1 tE and 40 mm + 4t

d = bolt diameter

t = thickness of gusset plate

py = design strength of gusset plate

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Bracing Connections - Kidney shaped slot connections

Design Rules For a two-bolt connection where one of the holes is kidney shaped, the following rules are recommended, in accordance with BS 5950-1 :2000:[1 clause 6.3.2.4 and 6.3.3.3.

Connection Capacity Total shear capacity = 1.6P,

P, = shear capacity of a single bolt in standard clearance hole.

Total bearing capacity = 1 S P b S

P,, = bearing capacity of a gusset plate for a single bolt in standard clearance hole.

Effective Length of Bracing Member Since the kidney shaped slot allows rotation of the connection, the connection detail cannot be assumed to provide directional restraint equivalent to that of two bolts in standard clearence holes.

When effective lengthsfor hollow section bracing members aredeterminedfromTable22 of BS 5950-1 [I, a connection incorporating a kidney shaped slot should not be assumed to provide any directional restraint in the plane of the gusset.

When angles are used as bracing members and the connections incorporate kidney shaped slots, the provisions for single bolt connections in Table 25 of BS 5950-1[] should be adopted, though the reduction to 80% in compression resistance stated in Note 3 to Table 25 need not be applied.

Provision of Washers Clause 6.1 .5(ii) of the National Structural Steelwork Specification (NSSS)[8] specifies that a plate washer or heavy duty washer be used under the bolt head and nut when bolts are used to assemble components with oversize or slotted holes. The origin of this clause concerned slots which were provided to permit movement in service. Shouldered bolts would normally be used in such joints.

The use of kidney shaped slots in bracing connections is a different situation to the one intended to be addressed by Clause 6.1.5(ii) of the NSSS[8]. Ordinary washers are considered to besatisfactory for use in bracing connections with kidney shaped slots.

Further information Further information can be found in the, SCI Publication 249 Design Capacity of Kidney Shaped Slotted Connections (1 998)[45].

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Design and page make-up by The Steel Construction Institute, Ascot, SL5 7QN Typeset by Richard Stainsby, 1 Linden Road, Great Ayton, TS9 6 A N Printed in Europe by the Alden Group, Oxford 09-02 2000 (BCC 7710)

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P212

Joints in Steel Construction: Simple Joints

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