Civil Engineering Reference
In-Depth Information
'Secondary steelwork is by others, it is probably in the QS's clad-
in specifications if unresolved details exist which are likely to
compromise architectural criteria or to have cost implications.
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ding cost provision. It will be sorted out by the architect.'
'Access, site conditions, propping and erection will be sorted out
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18.3.3 Case 3
A waste transfer station had refuse containment walling con-
nected to the portal frame columns. In addition to unanticipated
impact load from front end loaders, the frame sway deflections
were excessive due to a combination of column under-sizing
and frame assumptions being detailed designed by the steel-
work contractor for rigid based fixity. Neither were provided
in the foundation design by the designer.
The message here is that the designer needs to properly
understand the client's intended use and provide adequate def-
inition of frame design parameters even if parts of the struc-
tural design are by others.
by the contractor.'
18.3.1 Case 1
The steelwork contractor's claim for the costs of plating and
strengthening beams and columns 1-1.5 m out from each con-
nection was refused, leading to litigation. The designer had
changed the frame's stability concept from 'simple' to 'rigid'.
The 8-storey frame was a 'minimum weight' design with a
column section change at each floor. There was no reserve of
bending strength in the beams and columns, and the selected
sections were unable to sustain the bending moments without
extensive modification. The steelwork contractor won the argu-
ment that the tendered design required a price for 'simple con-
nections' and could not be considered to include costs for rigid
connections.
The message here, is that risk of compartmentalisation of
design, between connections and frame member selection
column, and beam selection and the need to provide a design
consistent with pricing information, needs to be monitored dur-
ing design development. The designer needs to retain control
of the frame design philosophy in most building types (see sec-
tion 18.1.4 describing CASE's view of the roles of the engineer).
Exceptions may be in single-storey construction where the
overall engineer may be the steelwork contractor.
18.3.4 Case 4
Universal beam (UB) sections used to support brickwork over
openings twisted during wall construction, leading to postpone-
ment of the work pending redesign and site work including sec-
tion stiffening, connection strengthening and in some instances
replacement with hollow box sections. The main design and
build (D&B) contractor claimed delay and repair costs.
The message here is that the designer needs to be alert to
torsion control of steelwork in critical locations such as per-
imeter support of cladding. Closed hollow sections are often
the most effective solution but the material cost is approxi-
mately double open section costs. While this might discourage
their use the cost of open sections with stiffening often proves
more costly particularly when the need is identified late in the
programme. Lack of resolution of so-called 'secondary' steel-
work is a common cause of unsuccessful steel construction.
The designer should provide weight and/or cost estimates if
not clearly identified in tender/pricing information.
18.3.2 Case 2
The main contractor involved in a design and build contract
had unexpected costs to resolve the dimensional coordination
of staircases in a multi-storey frame. Escape widths speci-
fied on the architect's layouts could not be accommodated
between columns that had heavy externally plated column
splices not anticipated by the team until after the frame was
constructed. The splices had to be cut back and the column
flanges site butt-welded to avoid increasing the outside
dimensions of the columns. Other site modifications were
needed to resolve late coordination problems including doors
clashing with bracing, inadequate headroom, and additional
steelwork needed on site to suit the architect's layouts issued
late in the programme and not reflected on the structural
drawings that were issued early in the programme for steel-
work manufacture.
The message here is to be aware of the support other team
members can anticipate from the structural designer during
design development. Initial structural design information issued
for tender/pricing without proper guidance on the allowances
for design development is common. The steel contractor may
be involved late in the design programme and required to price
information not knowing it might be partially coordinated.
Resolution of structural details such as column splices and
their interface with architectural requirements is the design-
er's role. Guidance should be provided on the drawings and
18.3.5 Case 5
Concreting of a composite deck forming an industrial mezza-
nine floor was abandoned when efforts to level the slab led
to progressive deflection of the floor beams under load from
the concrete placing operation. The composite floor beams had
been designed to be propped during construction but there was
no construction guidance on the designer's drawings.
It is not unusual for the temporary support required by the
design assumptions not to be transferred from design software
to the pricing and construction information. If the designer
retains control of the frame design philosophy as described
by CASE (Section 18.1.4) above, this will improve communi-
cation of key construction information. Construction (Design
and Management) (CDM) requirements (HSE, 2007) apply in
the UK for the designer to communicate construction meth-
ods.
Figure 18.16
shows the temporary support arrangement
needed to erect a frame requiring support of beam ends prior
to site welding. Other common situations requiring temporary
stability of steelwork are long span roof beams with long span
