The project’s upper
floors nearing
completion
Modifying existing frames
Significant modifications to the existing steel frame are a key feature of the work to reconfigure the Post Building. David Brown of the SCI
discusses some of the issues with refurbishment projects.
The first concern is always to discover details of the existing structure,
likely that design calculations are available. Comprehensive surveys are
needed, recognising that modifications through the years may have been
undertaken with no records at all. Assessment of the existing structure
must follow, acknowledging the design Standards and material quality of
the time.
At the Post Building, significant site fabrication and welding was
undertaken to reduce the depth of the existing transfer beams. For any
form of welding, procedures must be developed and followed to minimise
the risk of defects, which in turn demands that the composition of the
original material be known. Site welding sometimes carries with it the
idea of slightly shoddy work, but this should not be the case. Site welding
should be completed to the same demanding standards of shop welding,
involving weld procedures, qualified welders and post weld inspection.
Another feature of the refurbishment of the Post Building is the change
in loading regime for many members. Design forces have been modified,
in phases, and the resistance of the member must be carefully considered
at each stage. Additional steel reinforcement to increase member
resistance will not carry the stress from the existing loads, unless some
form of jacking is undertaken to temporarily relieve the member. Unless
the existing load is relieved, the stress in the original member must be
considered in the verification of any site-fabricated compound members.
The Post Building is also notable for the complete remodelling of the
building’s stability system and the careful thought required to transfer
the loads and to develop the temporary works requirements. Stability
is of fundamental importance to the structure, addressed under the
CDM regulations and the National Structural Steelwork Specification.
20 NSC
which will often demand site investigation – it is very uncommon
to find sufficient drawings to describe the structure, and even less
March 18
The NSSS calls for an outline of the method of erection envisaged by the
structural designer, together with information on the assumed temporary
works and the erection stage when the temporary works are no longer
necessary.
Designers undertaking refurbishment or adapting existing structures
will find the first reference particularly helpful, as it provides guidance on
historic steelwork, but also on the principles to be followed when working
on the modification of structures of any age.
Appraisal of existing iron and steel structures, P138, SCI
Appraisal of steel structures, SN41, Steelbiz
Guide to site welding, P161, SCI
National Structural Steelwork Specification, 6th edition, BCSA
Mixed-use
19 paint, all of which had to be carefully removed.”
In total, the mixed-use development creates 44,000m2
of floorspace, with eight floors of offices and seven floors
of adjacent residential (including 100% of the required
affordable housing provision on-site) above two floors and
a basement containing a variety of public uses including
shops, cafés, galleries, and a GP surgery for the local
community.
The development also makes a significant contribution
to the public realm by creating a new public space on
Museum Street, reactivating the historic route of Dunn’s
Passage, and providing a public roof terrace.
The Post Building is scheduled to complete by
December 2018.
One of the existing
transfer beams that
was reduced in depth
from 1.8m to 500mm
/Design_codes_and_standards
/Fabrication
/Construction#Site_welding
/Welding#Weld_procedure_specifications
/Welding#Welder_qualification
/Welding#Inspection_and_testing
/Concept_design#Structural_options_for_stability
/Construction#Health_.26_safety
/Steelwork_specification#The_National_Structural_Steelwork_Specification_for_Building_Construction
/Construction#Steel_erection
/Construction#Temporary_works
/Multi-storey_office_buildings#Mixed_use_commercial_buildings