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Steel Designers' Manual - 6th Edition (2003)
Analysis 827
holding-down bolts should not exceed pygZg, where Zg is the elastic modulus of the
gusset and pyg is the design strength of the gusset (pgy � 270 N/mm 2 ).When the effective
area of the baseplate is less than its gross area, the connections of the gusset
should be checked for the effects of a nominal distribution of bearing pressure on
the gross area as well as for the distribution used in the design.
27.2.2.3 Beam bearing plates
Bearing plates at beam seatings are required to distribute the beam reaction to the
masonry support at stress levels within the capacity of the masonry and to ensure
that the web-crushing capacity of the beam is not exceeded. The distribution of
bearing stresses under the plate is extremely complex although simplifying assumptions
are usually made in appropriate cases.
The bending of the plate, shown in Fig. 27.9 in the direction transverse to the
beam, will depend on the stiffness of the beam flange and the fixing of the flange
to the plate. It is usual to assume that the position of maximum bending is the
outside edge of the root of the web and that the plate carries the whole of the
bending.
In the longitudinal direction, shown in Fig. 27.10, the deflection and rotation of
the beam due to its loading will cause a concentration of bearing at the front edge
and, depending upon the load from above the bearing, a possible lifting of the back
edge of the plate. It is often assumed, therefore, that the distribution will be either
trapezoidal or triangular; possibly the triangle may not reach the back of the
bearing. If it is expected that the front edge concentration will be high the plate is
set back from the front of the pier as shown in Fig. 27.11. This is to reduce the possibility
of spalling at the front of the pier but also has the advantage of applying the
beam reaction more centrally to the masonry.
A method of assessing the rotation of the bearing has been proposed by Lothers.
From this a more accurate estimate of the stress distribution can be made. The
method, however, can only be applied in cases of isolated masonry piers and is
dependent on the homogeneity of the masonry. It may be justified in cases of very
heavy beam reactions provided the workmanship in constructing the pier can be
reasonably guaranteed.
27.3 Analysis
27.3.1 Bolt forces
The area required to transmit the compressive forces under the baseplate is
calculated at the appropriate bearing strength of the concrete. The stress block may
be assumed to be rectangular with a maximum stress of 0.6 fcu where fcu is the char-