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Steel Designers' Manual - 6th Edition (2003)
Economy of fabrication 953
• If possible select connections which avoid mixing welding and drilling in any one
piece. This avoids double handling of the member during fabrication.
Materials grade and section selection
• The designer should rationalize the range of sections and grades used in any one
structure. This will lead to benefits in purchasing and handling during all
fabrication, transportation and erection phases of manufacture.
• Make maximum use of S355 material for main sections. This is typically 8%
more expensive but up to 30% stronger than S275 steel. The exception is where
deflection governs section selection.
• The specification of small quantities of S355 or other ‘special’ grade material
should be avoided, particularly if the proposed material has poorer welding
qualities.
• Choice of fittings material grade should be left with the fabricator wherever possible.
• Structural hollow sections are approximately 60–80% more expensive than
equivalent weight open sections and have additional problems associated
with the connection requirements. Limitations on mill lengths should also be
remembered.
Connection design considerations
• Connections directly influence 40–60% of the total frame cost. They must therefore
be taken into account during the frame design.
• Least-weight design solutions are rarely the cheapest. Increasing member thickness
to eliminate stiffening at connections will often be an economic solution.
• The cost benefits from an integrated approach to frame and connection design
will only be realized if the fabricator is given a full package of information at
tender stage. Connection styles and design philosophy must be clearly marked
on drawings.
Bolts and bolting
• Non-preloaded bolting is the preferred method for site connections. Preloaded
(friction grip) bolts should only be used where joint slip is unacceptable or where
there is a danger of fatigue.
• The use of different grade bolts of the same diameter on any one contract should
be avoided.
• Threads should be permitted in the shear plane and in bearing.
• Direct and indirect cost savings can accrue by using only a small range of ‘standard’
bolts.