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318 Barry’s Advanced Construction of Buildings
Mass concrete foundation to columns
The base of columns carrying moderate loads of up to, say, 400 kN bearing on soils of good
bearing capacity can be formed economically of mass concrete. The size of the base depends
on the bearing capacity of the soil and load on the column base, and the depth of the
concrete is equal to the projection of the concrete beyond the base plate, assuming an angle
of dispersion of load in concrete of 45°.
Reinforced concrete base
The area of the base required to spread the load from heavily loaded columns on subsoils
of poor to moderate bearing capacity is such that it is generally more economical to use a
reinforced concrete base than a mass concrete one. The steel column base plate is fixed as
it is to a mass concrete base. Where column bases are large and closely spaced, it is often
economical to combine them in a continuous base or raft. When a heavily reinforced concrete
base is used, it may be possible to tie and position the bolt boxes to the reinforcement
cage prior to pouring the concrete, rather than erecting a temporary timber frame.
Steel grillage foundation
Steel grillage foundation is a base in which a grillage of steel beams transmits the column
load to the subsoil. The base consists of two layers of steel beams, two or three in the top
layer under the foot of the column and a lower cross layer of several beams so that the area
covered by the lower layer is sufficient to spread column loads to the requisite area of
subsoil. The whole of the steel beam grillage is encased in concrete. This type of base is
rarely used today as a reinforced concrete base is much cheaper.
Hollow rectangular sections
Beam to column connections
Bolted connections to closed box section columns may be made with long bolts passing
through the section. Long bolts are expensive and difficult to use as they necessitate raising
beams on opposite sides of the column at the same time in order to position the bolts.
Beam connections to hollow rectangular and square section columns may be made through
plates, angles or tees welded to the columns. Standard beam sections are bolted to T-section
cleats welded to columns and lattice beams by bolting end plates welded to beams to plates
welded to columns, as illustrated in Figure 5.44.
Flowdrill jointing
A recent innovation in making joints to hollow rectangular steel (HRS) sections is the use
of the flowdrill technique as an alternative to the use of either long bolting through the
hollow sections or welding and site bolting. The flowdrill technique depends on the use of
a tungsten carbide bit (drill) which can be used in a conventional power operated drill. As
the tungsten carbide bit rotates at high speed on the surface of the steel, friction generates
sufficient heat to soften the steel. As the bit penetrates the now softened wall of the steel
section, it redistributes the metal to form an internal bush, as illustrated in Figure 5.45.
Once the metal has cooled, the formed internal bush is threaded with a coldform flowtap
bit to make a threaded hole ready for a bolt. The beam connection to the hollow steel
column is completed by bolting welded on end plates or bolting to web cleats welded to
the column through the ready drilled holes. The execution of this form of connection
requires a good deal of skill in setting out centre punched holes accurately in the face of