Moment Connections On Hollow Structural Steel Tubes
Steel Connections -Dr. Seshu Adluri Introduction Steel Connections Many configurations are used for force transfer in connections. The configuration depends upon the type of connecting elements, nature and magnitude of the forces (and moments), available. By: Akbar Tamboli Abstract: Essential steel connection design and details for building and bridge design, fully updated with the latest codes. This fully revised guide presents steel connection design and details for building and bridge design, and includes current LRFD load information and the latest AISC and ICC codes and specifications.
Contents. Types of moment resisting connectionsMoment resisting connections are used in and in. Connections in multi-storey frames are most likely to be bolted, full depth end plate connections or extended end plate connections.
Where a deeper connection is required to provide a larger lever-arm for the bolts, a haunched connection can be used. However, as extra will result, this situation should be avoided if possible.For structures, haunched moment resisting connections at the eaves and apex of a frame are almost always used, as in addition to providing increased connection resistances, the haunch increases the resistance of the rafter.The most commonly used moment resisting connections are; these are shown in the figure below. Haunched beamInstead of bolted beam-to-column connections, welded connections can be used. These connections can provide full moment continuity but are expensive to produce, especially on site. Can be prepared in the fabrication workshop with a bolted splice connection within the beam spam, at a position of lower bending moment. Welded connections are also used for the construction of buildings in seismic areas.Other types of moment resisting connections include:. in columns and beams, including apex connections in, and.One aspect that is not covered in this article is welded joints between.
However, guidance on the hollow sections is available from Tata Steel. Joint classificationDesign of joints in steel structures in the UK is covered by BS EN 1993-1-8 and its National Annex.BS EN 1993-1-8 requires that joints are classified by stiffness (as rigid, semi-rigid or ) or by strength (as full strength, partial strength or nominally pinned). The stiffness classification is relevant for of frames, the strength classification is for frames analysed plastically.
The Standard defines joint models as simple, semi-continuous or continuous, depending on stiffness and strength. Moment-resisting joints will usually be rigid and either full or partial strength and thus the joints are either continuous or semi-continuous.In most situations, the design intent would be that moment-resisting joints are rigid, and modelled as such in the. Forces in an end-plate connectionThe resistance of a bolted end plate connection is provided by a combination of tension forces in the bolts adjacent to one flange and compression forces in bearing at the other flange. Unless there is axial force in the beam, the total tension and compression forces are equal and opposite. Vertical shear is resisted by bolts in bearing and shear; the force is usually assumed to be resisted mainly by bolts adjacent to the compression flange.
These forces are illustrated diagrammatically in the figure on the right.At the ultimate limit state, the centre of rotation is at, or near, the compression flange and, for simplicity in design, it may be assumed that the compression resistance is concentrated at the level of the centre of the flange.The bolt row furthest from the compression flange will tend to attract the greatest tension force and design practice in the past has been to assume a 'triangular' distribution of forces, pro rata to the distance from the bottom flange. However, where either the column flange or the end plate is sufficiently flexible (as defined by NA.2.7 of the UK NA ) that ductile behaviour is achieved, the full resistances of the lower rows may be used (this is sometimes referred to as a 'plastic distribution of bolt row forces'). Distribution of forces in the bolts. ‘Plastic’ distribution Design methodThe full design method for an endplate connection is necessarily an iterative procedure: a configuration of bolts and, if necessary, stiffeners are selected; the resistance of that configuration is evaluated; the configuration is then modified for greater resistance or greater economy, as appropriate; the revised configuration is re-evaluated, until a satisfactory solution is achieved.Verification of the resistance of a welded end plate connection in seven steps STEP 1Calculate the effective tension resistances of the bolt rows. This involves calculating the resistance of the bolts, the end plate, the column flange, the beam web and the column web. Methods of strengtheningThe type of strengthening must be chosen such that it does not clash with other components at the connection. Factory welded beam stub connectionA typical factory welded connection, as shown in the figure on the right, consists of a short section beam stub factory welded on to the column flanges, and a tapered stub welded into the column inner profile on the other axis.
Column manipulator for welding beam stubs to columnsContinuous are the usual choice for most small and medium sized beams with flanges up to 17 mm thick. Typical bolted cover plate splicesTypical bolted cover plate splice arrangements are shown in the figure.In a beam splice there is a small gap between the two beam ends. For small beam sections, single cover plates may be adequate for the flanges and web. For symmetric cross sections, a symmetric arrangement of cover plates is normally used, irrespective of the relative magnitudes of the design forces in the flanges.Column splices can be either of bearing or non-bearing type.
Design guidance for bearing type column splices is given in. Non-bearing column splices may be arranged and designed as for beam splices. Design basisA beam splice (or a non-bearing column splice) resists the coexisting design moment, axial force and shear in the beam by a combination of tension and compression forces in the flange cover plates and shear, bending and axial force in the web cover plates.To achieve a rigid joint classification, the connections must be designed as slip resistant connections.
It is usually only necessary to provide slip resistance at SLS (Category B according to BS EN 1993‑1‑8, 3.4.1) although if a rigid connection is required at ULS, slip resistance at ULS must be provided (Category C connection).In elastically analysed structures, bolted cover plate splices are not required to provide the full strength of the beam section, only to provide sufficient resistance against the design moments and forces at the splice location. Note, however that when splices are located in a member away from a position of lateral restraint, a design bending moment about the minor axis of the section, representing second order effects, must be taken into account.
Stiffness and continuitySplices must have adequate continuity about both axes. The flange plates should therefore be, at least, similar in width and thickness to the beam flanges, and should extend for a minimum distance equal to the flange width or 225mm, on either side of the splice. Minimum requirements for strength are given in BS EN 1993-1-8 clause 6.2.7.1 (13) and (14). Designers should also refer to SCI Advisory Desk note AD393. Design methodThe design process for a beam splice involves the choice of the sizes of cover plates and the configuration of bolts that will provide sufficient design resistance of the joint.
The process has a number of distinct stages, which are outlined below.The design process for a beam splice outlined in five steps STEP 1Calculate design tension and compression forces in the two flanges, due to the bending moment and axial force (if any) at the splice location. These forces can be determined on the basis of an elastic stress distribution in the beam section or, conservatively, ignoring the contribution of the web.Calculate the shear forces, axial forces and bending moment in the web cover plates. Typical bolted end plate splicesBolted end plate connections, as splices or as apex connections in, are effectively the beam side of the beam-to-column connections, mirrored to form a pair. This form of connection has the advantage over the cover plate type in that (and the consequent required preparation of contact surfaces) are not required.
However they are less stiff than cover plate splice details.The 'portal apex haunch' splice is regularly used in single storey and is commonly assumed to be 'Rigid' for the purposes of. Design methodThe design method is essentially that described for, omitting the evaluation of column resistances. The relevant steps and the corresponding calculations are described in Section 4.3. Beam-through-beam moment connections Connection detailsBeam-through-beam joints are usually made using end plate connections with non-preloaded bolts; typical details are shown in the figure below. Non-preloaded bolts may be used when there are only end plates but when a cover plate is used as well, should be used, to prevent slip at ULS. Typical beam through beam splices. Design methodWhere there is no cover plate, the design method for may be used.
Where a cover plate is used, it should be designed as for a; it may be assumed conservatively that the end plate bolts carry only vertical shear.The connection between the cover plate and the supporting beam is usually only nominal, as the moment transferred in torsion to the supporting beam is normally very modest.The relevant steps and the corresponding calculations are described in Section 4.4. Welded splices Connection details. Typical welded column splicesWhere the sections being joined are not from the same 'rolling' and consequently vary slightly in size because of rolling tolerances, a division plate is commonly provided between the two sections.
When joining components of a different serial size by this method, a web stiffener is needed in the larger section (aligned to the flange of the smaller section), or a haunch may be provided to match the depth of the larger size.A site splice can be made with fillet welded cover plates, as an alternative to a butt welded detail. A typical unstiffened column base plateAn example of a column base which is able to transmit moment and axial force between steel members and concrete substructures at the base of columns is shown in the figure on the left. The example shows a column base with an unstiffened base plate.
Stiffened base plate connections and column bases cast in pockets are other options available. ↑ BS EN 1993-1-8:2005. Eurocode 3: Design of steel structures. Design of joints, BSI. ↑ NA to BS EN 1993-1-8:2005.
UK National Annex to Eurocode 3: Design of steel structures. Design of joints, BSI.
↑ P207 Joints in steel construction: Moment connections, SCI, 1995 Further reading. Editors B Davison & G W Owens.
Moment Connections On Hollow Structural Steel Tubes Sizes
The Steel Construction Institute 2012, Chapter 28. Architectural Design in Steel – Trebilcock P and Lawson R M published by Spon, 2004 Resources. See also.
By Jason McCormickAssociate Professor, Civil & Environmental Engineering, University of Michigan, Ann Arbor, MI, USAMoment connections made of rectangular and square hollow structural sections (HSS) have received less consideration compared to HSS-to-HSS connections made up of axially loaded members (T-, Y-, cross-, and K-connections). The majority of static studies focusing on these connections have considered Vierendeel truss systems. These systems are often formed by square or rectangular top and bottom chords that are connected with square or rectangular vertical web (branch) members (Figure 1).
As a result of this configuration, the chord-to-web connection undergoes significant bending along with shear and axial loads and is not considered a pinned connection as is commonly done in typical truss systems. Originally conceived in 1896 by Arthur Vierendeel, it was not until HSS were developed that the potential for Vierendeel trusses started to be realized (Korol et al. 1977), but their use required an understanding of how to transfer moment between HSS-to-HSS T-connections.Many of the early studies of these connections focused on the ability of the connection to develop the full moment capacity of the branch member.
Jubb and Redwood (1966) showed that when the branch section had an equal width to the chord section (b=1) the full moment capacity of the HSS member could be achieved without reinforcement. However, this study did not consider the potential loss of moment capacity due to the presence of axial load.
On the other hand, Korol et al. (1977) showed that connections with a smaller branch width than the chord could not develop the full moment capacity of the branch without reinforcing through a series of 29 different connection tests considering 5 different configurations (unreinforced, branch flange reinforcing plates, chord flange stiffeners, haunch, and truncated pyramid). In general, the strength and rigidity of unreinforced Vierendeel type connections decreases with an increase in chord slenderness ratio (B/t) and decrease in branch-to-chord width ratio (b). As a result, unstiffened Vierendeel truss type connections can only be considered rigid (i.e. Undergo minimal relative rotation between the chord and branch) when the branch-to-chord width ratio is 1.0 and the chord slenderness ratio is low or the connection is reinforced (Packer 1993).Because the maximum moments in these joints can occur at excessively large deformations, a similar approach to that used for axially loaded square and rectangular HSS joints is adopted, where by an ultimate bearing capacity or a deformation or rotation limit is used to characterize the design moment (Wardenier 1982). AISC 360-10 (Chapter K3) considers three limit states for square and rectangular HSS T-connections under static in-plane bending: chord wall plastification, sidewall local yielding, and local yielding of the branch due to uneven load distribution. Chord wall plastification occurs as a result of the width of the branch member being less than the width of the chord (b ≤ 0.85) requiring the tension and compression loads produced by the bending moment to be transferred through the relatively flexible face of the chord rather than directly to the stiffer sidewalls.