Connections - Anatomy of Steel Structure.

Connections between structural elements are similar to those in general structural practice. Specific requirements relating to industrial steel structures are considered here.

On occasions industrial plant and equipment may impose significant load variations on the structure and so consideration must be given to possible fatigue effects.

Since basic steel members themselves are not susceptible to fatigue failure in normal conditions, attention must be focused on fatigue-susceptible details, particularly those relating to welded and other connections. Specific guidance for certain types of structure is available, and where this is not relevant, general fatigue design guidance can be used.

Of general significance is the question of vibration and the possible damage to bolted connections that this can cause. It should be common practice for steelwork in close contact with any moving machinery to have vibration-resistant fixings. For main steelwork connections there is a choice between using HSFG bolts, which are inherently vibration-resistant, or using normal bolts with lock-nuts or lock-washer systems.A wide variety of locking systems is available which can be selected after consultation with the various manufacturers.

Connection design for normally-sized members should not vary from established practice, but for the large box and plate I-section members that are used in major industrial steel structures, connections must be designed to suit both the member type and the design assumptions about the joints. For particularly deep beam members, where plate girders are several times deeper than the column dimensions, assumed pin or simple connections must be carefully detailed to prevent inadvertent moment capacity. If this care is not taken, significant moments can be introduced into column members even by notional simple connections due to the relative scale of the beam depth.

In certain cases it will be necessary to load a column centrally to restrict bending on it: a typical example is where deep suspension girders on power station boilers apply very high vertical loadings to their supporting columns. Here, a rocker cap plate detail is often used to assure centroidal load transfer into the column (Fig.3.9).Conventional connections on smaller-scale members would not usually require such a precise connection as load eccentricities would be allowed for in the design.

Typical details of box columns
Fig. 3.8 Typical details of box columns

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