Swansea
Print Workshop @
Kings
Lane Warehouse
now viewing: Kings Lane Warehouse / The New Building / Structural Engineers Proposal
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Structural Engineers Proposal
King Shaw Associates have been commissioned to support Sarah Wigglesworth Architects providing structural and building services concept advice in developing a scheme against which a budget can be estimated. This information plus the client’s business plan will be submitted as a funding application to the Welsh Arts Council.
The proposal is to re-house the client in new larger premises that will become an artist commune in an area identified for regeneration. The project interfaces with a large development to be constructed by the Swansea Housing Association with this project forming one of the faces of the new urban square to be created.
In respect to producing a sustainable design the philosophy has been to retain substantially the external masonry wall and drop a new engineered structure within it. This structure will stabilise the existing and as it reaches levels the wall is pealed back and the new structure and cladding project up from the original masonry enclosure.
Outstanding Engineering Information:
- Soil investigation
- Exact details of intended temporary and permanent works to be carried out by Swansea Housing Association on their adjoining development. (Their design will have to take into account the surcharge of our building in its final form and needs to be conveyed to them at an early date. As the formation level to this excavation is below our structure the design of their retaining structure needs to take into account loads generated by our structure in its final form.
- Utilities information from Swansea Housing Association
- Confirmation of Swansea Housing Association’s security arrangements with respect to the adjoining urban space they are creating
Appraisal of Existing Structure
Using as a basis the existing Structural Condition survey made available through the client, we carried out a further visual inspection of the building to review items identified and also to obtain information on the structural elements. Using this information we carried out a structural analysis of these elements to ascertain if there was any redundancy in the existing structure to sustain the intended revised configuration. The visual inspection also enabled us to take a view as to the status of the fabric deterioration and the level of remediation required to return it to safe and secure structure.
The existing structure is constructed on 4 floors with the top level formed within the roof truss zone. The ground floor is stepped to marry in with the external sloped road levels. Brick piers run up to the first floor level and above this there is a central row of wrought iron columns off which steel beams run centrally down the building with beams running laterally to the external walls. The steel beams are set on top of the other with deep timber joists spanning between them. To the West elevation a concrete stair is set within a brick core to this end with the west elevation formed as what appears to be a more modern brick elevation.
The external walls to the building are load bearing masonry with window openings punched through this with exposed steel lintels to some openings. These walls appear to be fairly serviceable which would appear to indicate their foundations are adequate however externally they have suffered organic degradation.
In Situ Items Requiring Substantial Remedial Action
The areas noted in the original report had degraded further due to the ingress of damp through the failed areas in the external envelope. We also noted that in some of the areas where the main beams were pulling out of the masonry had appeared to have progressed further and were at some locations reaching a critical state. This is particularly evident in the East and North elevations where the masonry walls are pulling outwards resulting in excessive eccentricities of loading.
The roof itself is in poor condition suffering extensive damage from water ingress. The floor to this 3rd floor area is very dynamic and is not suitable to sustain the intended use as an auditorium space with partitioned private areas for staff, storage and possible library. The physical access to this area when we visited site was very limited and in areas dangerous.
The floor structure is constructed as a grid of steel beams supporting substantial timber joists with floor boarding over. The columns appear to be cast iron and the connections at the joints have bolts missing. Generally as a sustainable structure it would require extensive remedial works to ensure its integrity in ensuring load transfer and rigidity. The structure would also require being fire protected.
When we visited site our external access was limited to viewing the East, South and West elevations from street level. We noted the various aspects indicated in the condition survey with respect to areas where extensive damage can be noted to the brickwork which will require remedial action. The east elevation, which was previously restrained by the demolished extension, is now pulling away from the floor plates. Currently we have available very little information on the soil structure below the site but are in the process of obtaining this from the Swansea Housing Association to verify our current assumptions with respect to the load capacity of the underlying soils.
Calculation Checks Carried Out
for this exercise we took the following loads as:
| Dead | Live | |
| Self Weight timber structure | 0.5KN/m2 | Light Industrial |
| 2.5KN/m2 | ||
| Finishes plus services | 0.6KN/m2 | |
| Partitions | 1.5KN/m2 |
Using these values we proved by calculations that the existing timber joists could sustain the loading on a 3.0m span. However, the existing steel beams and columns failed.
We also carried out an investigation into the strength of the existing roof structure to review whether this contained sufficient redundancy to support the new loading requirements. The loads generated in the truss elements and their deflections proved that this structure was unsatisfactory.
Generally with the issue of strengthening the existing and providing acoustic and fire separation the existing structure is inappropriate and would require substantial cost and remedial work to bring it up to an adequate standard. As such it is cost effective to insert a prefabricated steel and precast structure. At steel to steel connections particularly column heads there are numerous bolts omitted and an inability to establish mechanical fixings because of the lack of drilled holes.
SUBSTRUCTURE
To the East end of the building a basement plant and storage area is to
be created by excavating and dropping the levels locally. Prior to
taking the levels down we have assumed it will be necessary to underpin
the existing side walls, the East elevation wall itself having a
formation level below the adjoining 8.35m ground level. The extent of
the underpinning relates to ensuring its formation is below the new slab
level and will only be required if the existing wall is stepped as the
adjoining street level rises. This needs to be proved on site by
exploratory pitting exercise. The final levels and loads from our
structure need to be confirmed to ensure the retaining works to the new
basement of the adjoining structure are designed to sustain these.
SUPERSTRUCTURE
The proposed use of the building is as a print workshop, gallery space
with associated café, artist’s studio spaces with residential units, a
large multipurpose studio and staff facilities. The floors need to be
solid, provide acoustic and fire separation, reasonable dynamic response
and also act as tie diaphragms for the surrounding load bearing walls.
The project brief is to develop a sustainable solution and to this end
we propose reusing as much as possible of the existing floor timbers to
form a new roof shape whilst forming the lower levels as a steel frame
with composite exposed concrete precast planks.
Prior to commencing any works the building will have to be temporarily shored to ensure the stability of the external walls as work progresses on them. These props are to remain until such time as the new construction has been completed up to second floor level. The props may require a closing order be placed on the adjoining street dependent on their actual size.
The proposal is to use a prefabricated steel structure that can be craned in quickly within the existing masonry walls onto the completed ground floor and integral foundations. The steels are either to be the slim floor system with asymmetric flanges or be beam units with a steel plate welded to the bottom flange. Asymmetric beams are required to enable the precast planks to be lifted into position with their required bearing. The planks themselves come with preformed void formers attached so that when the concrete topping is cast onto this the volume of concrete is reduced and thereby the structural weight. Once the concrete has been cast the propping system can be removed resulting in the planks and beams acting compositely providing a flat soffit.
This form of structure with exposed concrete soffits acts as a climate modulator by providing exposed thermal mass. This mass assists in maintaining a thermal balance during occupation which can be improved if the building management allows through ventilation during the night which will partially purge the heat from the slab.
The steel frame is fairly simple except where there is a step in the floor plate. At this point the lower beams are supported off columns connected to the beam of the level above. The lift shaft is in this area and is formed as a rectangular box of steelwork made of square hollow sections set within the lightweight partitioning. We propose that the stairs adjoining these areas are formed in proprietary precast elements.
There also some expressed stair and bridge elements around the project and these are to be constructed to an architectural finish standard along with some large glazed elements to some of the re-modelled openings.
The North and East elevations are to be substantially remodelled with new and larger openings introduced into them. Architecturally the roof springs vertically from the masonry box, the top of which is set at a single level apart from the West elevation brickwork gable which remains and the North elevation where a large section of wall is removed down to ground level over grids 1 to 3. This will mean that certain areas such as from first floor up on the east elevation will need to be re-built. The advantage is that the new build will provide better thermal values and be fully integrated into the new structure.
The intention is to use any suitable arisings from the excavations or remodelling of the facades as fill material around the north and east perimeters of the building to raise these levels.
The large opening on the North elevation is supported on a double steel beam infilled with concrete for fire protection. The cladding wall above the masonry bands is formed as timber panels supported off either timber or steel horizontal and vertical purlins attached to the steel frames set on grid. The proposal is to recycle as much of the existing floor timbers to form the secondary elements for the cladding supports.
To ensure the robustness of the final construction remaining elements of the masonry wall are to be tied to the insitu concrete floor plates by steel tie plates expressed on the external elevation. The through bolts from the 300mm diameter plate are to have ragged ends to ensure tension anchorage into the concrete substrate.
ROOF
The intention with the roof is to re-use as much of the existing roof
timber as possible in the new structure, given its relatively good
condition. The sectional profile of the roof is to provide an asymmetric
pitched roof with the short pitch providing roof lights and a large
sloped roof plan across most of the span. As far possible the existing
timbers provided they are long enough, are to be used to this roof scape.
The new internal frame structure rises up past the original walls to support a primary frame of ridge beam and purlins, which will become trusses that span larger spaces formed from reclaimed timber or steel elements. Prop/ tie trusses 2.5m act as primary rafters spanning between the ridge and purlins with conventional rafters at 400mm centres forming the final roof construction. The bays of the roof will be constructed as ladder trusses to carry the new gable cladding system.
The roof cross stability will be provided by the internal cross walls acting as shear elements and longitudinally by a mixture of the side wall panels and possible diagonal bracing to the sloped planes to support the Architectural vision that these be transparent.