Lectures The various forms of connections in simple buildings are identified for both the framework and the bracing system, and the main design criteria and checking procedures are presented. Reference is also made to the economic implications concerning fabrication and erection. Detailed aspects of behaviour and design are referred back to earlier lectures in the group. Their purpose is to transfer load from the supported member into the supporting member in such a way that essentially only direct forces are involved, e. They may, therefore, only be used in situations where sufficient bracing is present that, when the joints are assumed to function as pins, adequate overall structural resistance is present.
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Lectures The various forms of connections in simple buildings are identified for both the framework and the bracing system, and the main design criteria and checking procedures are presented. Reference is also made to the economic implications concerning fabrication and erection.
Detailed aspects of behaviour and design are referred back to earlier lectures in the group. Their purpose is to transfer load from the supported member into the supporting member in such a way that essentially only direct forces are involved, e. They may, therefore, only be used in situations where sufficient bracing is present that, when the joints are assumed to function as pins, adequate overall structural resistance is present. Popular arrangements include lattice girders and bracing systems or connections between beams and columns in rectangular frames in which lateral loadings are resisted by stiff systems of shear walls, cores or braced bays.
Figures 1a and 1b illustrate multistorey frames in which simple connections may be used for each of the 6 different requirements A-E listed alongside Figure 1a. Thus the structural idealisations suitable for determining the distribution of member forces will be as shown in Figure 1c and 1d, with all lateral loading being resisted by the bracing or shear wall.
When considering the design of the frame to withstand gravity loading, the assumption of pin connections makes the overall structural analysis particularly straightforward, since loads can be traced from floors into beams into columns and eventually into the foundations using a simple statical process.
Simple joints also lead to easier fabrication and erection and as explained in Lecture Taking the example of a beam to column connection, the simple joint must: transfer the beam reaction into the column in shear have sufficient flexibility not to transfer other than small moments into the column, e.
Thus, in terms of the classification system introduced in Lecture Simple connections will normally be either fully bolted, e. Except for connections subject to vibration, e. This lecture discusses the structural design of several examples of each of the 6 connection arrangements listed in Figure 1. In doing this it makes use of basic material on weld strength and bolt strength presented in Lectures Some typical connections are illustrated in Figure 2.
Types A and C, which make use of web cleats bolted to both the girder and the beam, are the most common forms. Type B with the cleats bolted to the girder and welded to the beam, and types D and E where a flush end plate is adopted, may cause lack-of-fit problems during erection due to the dimensional tolerances.
Connection types D and E possess some predictable stiffness and strength, but their consequent partial continuity is usually neglected in design. As shown in types C and D, the beam end may be coped removing part of one or both flanges, when the beam and girder flanges meet at the same level.
The beam is thus locally weakened. The appropriate checks must be made as discussed below. Nevertheless, this solution is less expensive than type E, which requires that a tee stiffener is welded to the girder. As a variant to A the web angles may be replaced by a fin plate, as shown in Type F, a single plate which is shop welded to the primary beam and site bolted to the secondary beam. A fin plate connection is particularly simple to both fabricate and erect, but it requires careful design if it is to function as a notional pin .
In particular, there is a need to decide where the "hinge" is located as explained in Section 3 of Lecture For web cleated connections, it is good practice to place the angles as close as possible to the upper flange of the girder in order to minimise cracking of the concrete floor slab due to the beam rotation.
Bolts and welds in connections should be able to resist the beam reaction and any relevant moment due to the eccentricity of the force to the centerline of the connecting components as explained in Section 2 of Lecture When a beam is coped, as in connection type C, it should be verified that no failure may occur at the section that has been weakened block shear as explained in Section 2 of Lecture Type A, which is shown as fully bolted, may also be configured by welding the cleats to the beam end.
For lightly loaded beams, a single sided cleat may be used but the additional eccentricities must then be allowed for when checking bolt strength, etc.
The finplate Type B requires the same form of attention when deciding on the design model as discussed in the previous section where its use in beam to beam situations was discussed. Both types A and B provide some allowance for tolerance through the clearance in the beam web holes on member length.
Type B permits beams to be lifted in from one side. Types C and D require a more strict control of beam length and of squareness of the cross-section at the end of the beam. The flush end plate scheme of type D is sometimes preferred to the part depth end plate type C in order to reduce the chances of damage during transportation.
Partial depth endplates should not normally be less than about 0. Figure 4 illustrates how flexibility and rotation capacity is provided. Depending on the details, the connection behaviour of type D could change from a notational pin; it may be more appropriate to acknowledge this semi-rigid behaviour see Lecture This may be avoided by keeping the endplate thickness down to a maximum of mm and making the bolt cross-centres as large as is practical so as to ensure adequate flexibility and rotation capacity.
As for beam-to-beam connections, the bolts and the welds should be able to resist the beam reactions and the relevant moment due to the eccentricity of the force to the centreline of the connecting material as explained in Lecture Since this eccentricity is relatively small the column bending moment for such a connection is much smaller than from a moment connection as discussed in Lecture Since the general approach to the design of all forms of simple connections is essentially the same, it will be sufficient to consider only one type in some detail.
Figure 5 illustrates the 6 possible failure modes for a finplate connection; the load carrying capacity for each must be calculated and the lowest value compared with the design requirements. Methods for doing this have already been presented in Lectures It is also necessary to ensure - usually by means of appropriate detailing - that the connection will function in the manner intended, i. This may be achieved by: ensuring that strength is governed by a ductile mode of failure.
Bearing of the bolts in either the finplate or the beam web is usually arranged to form the governing condition. When performing the structural checks it is necessary to be consistent in the assumption of the location of the line of shear transfer, i. One approach 1 that removes the need for a decision is to design both the bolt group and the welds for the combination of shear and eccentricity moment. Alternatively, the location can be chosen as the bolt group for the stiff support arrangement illustrated in Figure 5 or the weld if the support is more flexible as would be the case, for example, if a RHS column were used due to bending of the column face as a plate.
In theory no splice connection is required, since the compression force is transmittable by direct bearing. Due to the presence of geometric imperfections lack of straightness of the column as well as of unavoidable eccentricities, and to the fact that even carefully machined surfaces will never assure full contact, connections have to be provided. They should be designed to resist the internal forces other than compression determined in the column at the point where they are located.
Even when the column is subject to simple compression, and full contact in bearing is assumed, codes specify stiffness and strength requirements to be fulfilled. The location of the splice should be selected so that any adverse effect on column stability is avoided, i. If this requirement cannot be fulfilled, account should be taken of the second order moment induced by member imperfections. More significant bending resistance may be required in splices when columns are subject to primary moments, as in a frame model assuming hinges at, or outside, the column outer face.
In addition, in columns acting as chords of cantilever bracing trusses, tensile forces may arise uplift in some loading conditions, which must be transmitted by splices. Typical column splices suitable for use in simply designed frames are shown in Figure 6. They are of two basic types: A, B and C all transmit the whole of the force through the cover plates, whilst D-G rely on direct bearing. When a bolted solution is adopted types A, B and C , both flanges and the web are usually connected.
Type A uses a double cover plate, whilst type C uses single cover plates for the flanges. These may be positioned on the outside faces of the flanges so as to reduce the plan area occupied by the splice. Forces are distributed among the connecting plates in proportion to the stress resultant in the cross-sectional elements, e.
Differences in column flange thickness may be accommodated by the use of packs. When the surfaces of the end cross-sections of the two column shapes are sawn and considered to be flat, and squareness between these surfaces and the member axis is guaranteed, the axial force may be assumed to be transmitted by bearing. Fillet welds type D or light cover plates type E are provided to resist possible secondary shear force and bending moment when the upper and lower columns differ in serial size.
A plate may be interposed, and welded to both column sections as in connection type F, or, alternatively, two welded plates bolted to each other may be used type G.
Plates are flattened by presses in the range of thicknesses up to 50m, and machined by planing for thicknesses greater than mm. For intermediate thicknesses either working process may be selected.
Where there is a significant variation of cross-sectional dimensions in the arrangement of type F, the plate s must be checked for bending resistance. A possible conservative model assumes the plate is a cantilever of breadth equal to the width of, and clamped to, the upper column flange. The axial force, which is transmitted between the corresponding column flanges, is applied as an external load at the mean plane of the flange of the lower column. Full details of this approach are presented in ref.
For larger differences in column size, a short vertical stiffener may be located directly below the flange s of the upper column to directly assist in transferring the locally high force. Since the triangulated bracing arrangement will have been designed on the basis that each member carries only axial forces apart from any relatively small bending effects due to non-coincidence of centroidal axes , the design requirement for the bracing connections is essentially the transfer of direct forces between a number of differently oriented members.
Two basic arrangements are illustrated in Figure 7: Type A attaches the bracing to the main framing, Type B is an internal bracing connection. Types C and D combine both functions by making the beams part of the bracing system. Details of the design considerations and the calculations necessary to effect these have already been provided in Section 1. A second, usually rather thicker, steel plate is normally incorporated into the top of the foundation, as illustrated in Figure 8.
It helps both to locate the foot of the column accurately and in spreading the load into the weaker concrete or masonry foundation material. Baseplate connections in simple construction are generally modelled as pins, and designed to transfer either concentric force compression or tension or a combination of axial and shear force usually when the column is part of the bracing system Figure 8c.
In some instances they may, however, be designed to transmit also bending moments due to moderate load eccentricity, or for erection stability. The plate is always attached to the column by means of fillet welds. However, if the column carries only compression loads, direct bearing may be assumed, provided that the contact surfaces are machined or can be considered to be flat. No verification of the welds is then required. Machining may be omitted if loads are relatively small. Where there are moderate tension forces or no net tension the holding down bolts are usually cast into the foundation Figure 9.
They anchor the baseplate by bonding Figure 9a , by bonding and bearing Figure 9 b, c , or by bearing Figure 9d. When tensile forces are significant, it is necessary to provide appropriate anchorage to the bolts. For example threaded bolts may be used in conjunction with channel sections embedded in the concrete.
In tension connections the baseplate thickness is often dictated by the bending moments produced by the holding down bolts. The bending moments may require the use of stiffeners Figures 8c and 8d.
Such an arrangement significantly increases the fabrication content and therefore the cost of the column base as compared with the "simple" case. Attaching the steel frame to a concrete core is mainly a practical problem, since the two systems are built with dimensional tolerances of a different order of magnitude. Special care should be taken to account for the relative sequence of erection of the concrete and steel system, the method of construction of the core on which concrete tolerances also depend , as well as the feasibility of compensating for misalignments.
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For LUH campus users we will be happy to check if free access is available for you. Scientific Data Management Research Staff. Computer Aided Learning in Structural Engineering: The table of contents of the conference proceedings is generated automatically, cohrse it can be incomplete, although all articles esdsp available in the TIB. The University ; The course will be given in Swedish Aim The course shall give understanding and knowledge about the behaviour of advanced steel and timber structures, tools for modelling and design and the ability to weigh pros and cons for different structural systems. Press and information Press releases Press Archives.
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