APPENDIX 13.5 STRUCTURAL APPRAISAL

APPENDIX 13.5
STRUCTURAL APPRAISAL

Crest Nicholson
18 September 2006

QM
Issue/revision Issue 1 Revision 1 Revision 2 Revision 3
Remarks
Draft
Date 18 September 2006
Prepared by
Gary Tutt
Signature
Checked by
Stephen Punt
Signature
Authorised by
Stephen Punt
Signature
Project number 24540241
File reference 24540241/07
WSP Buildings
9 Parchment Street
Winchester
Hampshire
SO23 8AT
Tel: +44 (0)1962 844 944
Fax: +44 (0)1962 843 770
http://www.wspgroup.com
Reg. No: 1383511

Contents
1. Introduction
2. Building structure
3. Condition of Structure
4. Dismantling Structure and Remedial Works
5. Re-Erecting Frame
6. Dismantling Sequence of Works
7. Conclusion
Appendix - Photographs

1 Introduction
WSP were appointed to carry out a condition survey and report on a historic blister
hangar situated on the Former DERA site in Chertsey. The purpose of the visual
inspection was to determine the building condition and the possibility of dismantling the
hangar and relocating it on another site for re-use. The inspection consisted of a site
visit to the hangar with access to both the outside and inside of the building. This report
relates to the site survey and provides recommendations for moving the structure only.
24540241 Chertsey Building 10 1

2 Building Structure
The building is approximately 27.5m x 13.75m in plan and is arch shaped with a
maximum height of approximately 6.5m. The front and rear elevations consist of
brickwork walls with piers and inset doors (photos 1 & 2). Large folding doors are
situated in the front elevation of the building with a smaller standard access door to the
rear.
The structure of the building consists of 7 number steel arch frames at approximately
3.0m centres, spanning from one side to the other down to ground level. The frames are
made up of sections of curved lattice beams approximately 3.8m in length made from
steel flange plates and lattice rods connecting the plates. The sections are bolted
together to form the arch shape of the building. Purlins are bolted to the tops of the main
frames which in turn support the corrugated metal roof and ceiling.
The stability of the structure is achieved by diagonal bracing at the front and rear of the
building in the plane of the arch. Loads are transferred through the structure using
purlins and longitudinal bracing. Both bracing and purlins are made from steel angles
measuring approximately 50mm x 50mm, (photos 3, 4 & 5).
The ends of each of the steel arches are restrained at ground level with horizontal lattice
beams fixed to the ground floor slab and with angles which appear to be cast into the
foundation below the slab (photo 6). Vertical lattice columns provide additional support
to reduce the effective length of the arches.
The ends of the building are constructed from brickwork walls which support the doors
as mentioned above. The building also has some 2.5m high free standing dividing walls
in two corners which create sectioned off areas within the main building (photo 7).
The floor construction is a concrete slab with raised areas to both sides made up with a
concrete screed. This screed partially encases the ground level steel lattice beams
(photo 8).
24540241 Chertsey Building 10 2

3 Condition Of Structure
The steel structure generally appears to be in a good condition with only the exposed
end frame to the rear of the building showing any signs of corrosion (photos 9 & 10).
This frame is on the external side of the rear masonry wall and is heavily corroded at
both connections to the ground floor slab. The internal frames, purlins and bracing are
not showing any significant signs of corrosion.
Two areas of minor mechanical damage to the main frames were seen at high level, see
photographs (photos 11 & 12)
24540241 Chertsey Building 10 3

4 Dismantling Structure And Remedial
Works
The steel frame is generally in a good condition, which could be dismantled and erected
on a different site without major remedial works. This would include the lattice arch
frames, purlins and diagonal bracing. Remedial works would be needed to the two
bases of the rear frame and this is likely to be achievable by welding additional steel
plates to the frame to act as a repair to the base box section.
It is likely that the steel frame which is embedded in the screed will be in a good
condition and can be cleaned using a high pressure hydro demolition system. This
technique involves the use of hand held jetting guns which breaks the concrete up into
large lumps and small particles but leaving the steelwork clean and intact. The anchors
which are cast into the foundations will need to be replaced as it will be difficult to
remove them from the concrete slab and foundations.
24540241 Chertsey Building 10 4

5 Re-Erecting Frame
New foundations and ground floor slab will be required to support/fix the frame onto and
new end walls will need to be constructed. The large doors to the front of the building
may be re-useable as they appear to be in a good condition. The nature of the
foundations and ground slab would be dependant on ground conditions of the new site.
We would recommend that the steelwork is cleaned and repainted using a zinc-rich
epoxy primer and appropriate top coat. The exact nature of any repainting would need to
be subject to discussion with the new users as to the best approach.
24540241 Chertsey Building 10 5

6 Dismantling Sequence Of Works
The following is a suggested sequence of how to dismantle the hangar. The contractor
should provide a method statement for his preferred sequence of works.
1. Service strip of all internal and external mechanical and electrical services
and main hangar doors.
2. Removal of all roof and ceiling cladding (excluding purlins).
3. Demolition of all masonry, including internal and end walls
4. Removal of main frames, bracing and purlins down to approximately 3m
high. The frames are to be dismantled in sections from the top down, while
supporting the lower sections of the frame with temporary works. The
frames should be removed from the rear of the building first as these have
the most corrosion and are therefore the weakest frames. The temporary
stability of the building should be maintained with temporary works to allow
the bracing and purlins to be removed.
5. Removal of screed finishes encasing steel frame to sides of hangar to allow
frames to be removed.
6. Removal of the final part of the steel frame (excluding angles which are cast
into the foundations).
7. Angles protruding from the slab to be cut off and ground down to slab level.
24540241 Chertsey Building 10 6

7 Conclusion
In conclusion it is recommended that the steel frame is suitable for dismantling, removal
and re-erection on an alternative site without the need for major remedial works.
24540241 Chertsey Building 10 7

Appendix-
Photographs
24540241 Chertsey Building 10 8

Photo 1 - Front elevation
Photo 2 - Rear elevation
24540241 Chertsey Building 10 9

Photo 3 - Internal View on front wall showing bracing & purlins
Photo 4 - Internal View on side showing bracing & purlins
24540241 Chertsey Building 10 10

Photo 5 - Diagonal bracing to front of building
Photo 6 - View on vertical columns & horizontal restraints
24540241 Chertsey Building 10 11

Photo 7 - Internal masonry walls
Photo 8 - Floor screed encasing lattice beams
24540241 Chertsey Building 10 12

Photo 9 - Corrosion to rear frame base
Photo 10 - Corrosion to rear frame base
24540241 Chertsey Building 10 13

Photo 11 - Mechanical damage
Photo 12 Mechanical damage
24540241 Chertsey Building 10 14