Composite Beams - Types of shear connection.

The modern form of shear-connector is the welded headed stud ranging in diameter from 13 to 25mm and from 65 to 125mm in height.The most popular size is 19mm diameter and 100mm height before welding.When used with steel decking, studs are often welded through the decking using a hand tool connected via a control unit to a power generator. Each stud takes only a few seconds to weld in place. Alternatively, the studs can be welded directly to the steel beams in the factory and the decking butted up to or slotted over the studs.

There are, however, some limitations to through-deck welding: the top flange of the beam must not be painted, the galvanized steel should be less than around  1.25mm thick, the deck should be clean and free of moisture, and there should be no gap between the underside of the decking and the top of the beam.The minimum flange thickness must not be less than the diameter of the stud  divided by 2.5  (typically, 19/2.5 = 7.6mm). The power generator needs 415V electrical supply, and the maximum cable length between the weld gun and the power control units should be limited to around 70m to avoid loss of power. Currently, only 13, 16 or 19mm diameter studs can be through-deck welded on site.

Where precast concrete planks are used, the positions of the shear-connectors are usually such that they project through holes in the slab which are later filled with concrete.Alternatively, a gap is left between the ends of the units sitting on the top flange of the beam on to which the shear connectors are fixed. Reinforcement (usually in the form of looped bars) is provided around the shear-connectors.

There is a range of other forms of welded shear-connector, but most lack practical applications. The ‘bar and hoop’ and ‘channel’ welded shear-connectors have been use in bridge construction.

Shot-fired shear-connectors may be used in smaller building projects where site power might be a problem.All shear-connectors should be capable of resisting uplift forces; hence the use of headed rather than plain studs.

The number of shear-connectors placed along the beam is usually sufficient to develop the full flexural resistance of the member. However it is possible to reduce the number of shear-connectors in cases where the moment resistance exceeds the applied moment and the shear-connectors have adequate ductility (or deformation capacity).

0 comentarios:

Post a Comment