West Hill Special School
The McAvoy Group were appointed as principal contractors for the design & build of West Hill Special School. The new school, which will incorporate classrooms, teaching training areas, a food technology room, a library and staffroom, is connecting two separated buildings currently on site.
Construction of the new school building began in January 2017, at McAvoy's manufacturing facility in Lisburn. McAvoy were on site on 21st March 2017 to begin installation of the bespoke modules, with the project on schedule to be handed over on 8th August. Due to an offset height difference of 870mm from one existing building to the other, McAvoy was able to incorporate a ramped gradient within the design, nullifying the height difference. McAvoy is facing a number of other challenges on this project, namely the need to use a neighbouring school for access, which along with the two current buildings on site, are all live.
The building consists of self-supporting steel modular units. The modules are corner supported and constructed with a primary steel framework designed as a simple beam and column structure with no moment resisting connections. The framework consists of hot rolled square hollow section corner posts supporting cold formed folded C-section longitudinal beams and tie beams. Roof purlins and floor joists between main beams are light gauge cold formed C-sections. Stability is achieved by the OSB roof and floor decks acting as horizontal diaphragms transferring horizontal loads to OSB sheathed vertical internal and external shear walls.
3D Point cloud surveys were done to map the project site. The project is located between 2 existing buildings with different levels, heights, and different construction methods (modular and traditional). The survey was used to create a 3D representation of the site where our design model was placed and the initial design process started. We started setting our modular grid to suit the initial clients’ brief, due to the nature of the site and the level differences, module sizes had to be designed in a bespoke way to suit the location and the floor levels as they had to be stepped.
The resulted building structural modules had different heights and therefore we had to create ramps to connect the building parts to ensure accessibility in line with the building regulations. The detailing and the ‘stepping’ process of the modules was extremely challenging as it was not the usual modular structure that the McAvoy group generally use.
The foundations were challenging as well due to the level differences. To avoid multiple steps and level differences in the foundations themselves we designed ‘stub columns’ to provide support off the foundations and to transfer the building loads in a more effective way. Where they were instances that numerous different modules shared the same support point, the varying lengths of stub columns enabled the top of the foundation to be level. After the building footprint and the modular grid were agreed, the next challenge was to ensure each module fitted within the transport limits. The maximum transportable height of a module is 3950mm.Due to the 870mm difference in levels between the existing buildings, this proved even more challenging at the ground floor modules of the 2 storey element. This is where the 3D modelling became essential, especially when trying to accommodate services etc. in the ceiling void.
As one of the group rooms in the school was ‘land-locked’ and not on an external wall, we were unable to install a window therefore we installed a roof light to get the day light in. When the specification and size of the roof light was agreed, our steel detailer in conjunction with the structural engineer were able to design the steelwork in a suitable way that accommodated the roof light in line with the architectural details, including exact location that was determined using the Tekla BIM model.
As the building was a 2 storey building, a lift was needed and an opening for the lift was required in the structure. After the location was determined, various elements of the steelwork were adjusted to accommodate this specific lift. This included recessing of the floor joists below the lift shaft, as well as the various PFC trimmers formed in the GF Ceiling and FF Floor modules. These trimmers allowed stud walls/partitions to be installed, creating the lift shaft offsite prior to modular installation.
As there were acoustic limitations at the site due to the proximity to the main road, a mechanical ventilation system had to be installed. To keep with the client’s brief and planning drawings; we had to provide a louvered openings incorporated within the windows and above ceiling level. This again was a constraint to the usual modular methods used by McAvoy.
Through the use of multiple BIM Software including Tekla structures for the steel structural design, ArchiCAD for the architectural design, Revit MEP for the services and Mitek wood engine for timber wall panels. We were able to output separate IFC Models which were then federated using Tekla BIM Sight for Clash detection. Clash detection allowed us to identify any clashes between the various elements to enable removing any errors in the building before it gets to the production and construction stages. This proved invaluable as errors which weren’t identified on the separate software applications, were identified visually via the federated model.
Once steel design was progressed sufficiently, this allowed the other designers to progress with their own detailing and coordination. The IFC Output was easily brought into the other software platforms which proved successful IFC Export without any loss of information. The use of the IFC export allowed accurate construction details to be produced, again ensuring coordination between the various disciplines.
The Tekla Model of the steel structure of the building was able to be sent to the internal stair manufacturer, who in turn were able to produce the accurate stair design in conjunction with the architectural IFC model, this proved very successful as we were able to show the client exactly how the stair would look. The fully coordinated BIM model was able to be converted to VR to show the building to the client and have them explore a different type of visualisation and it allowed us to offer an immersive virtual reality experience.
BIM led to better design decisions being made, and allowed these decisions to be made much earlier due the enhanced co-ordination that is necessary through the BIM processes. Model Management Methodology was set so that each discipline is responsible for authoring their 3d models in compliance with the technology strategy, and publishing the coordination .IFC files in compliance with the data drops as defined within the MIDP & TIDP – The Information manager coordinated this, alongside the project delivery manager and the Lead designer.
We were able to federate our Tekla structural model with the architectural and M&E models and we ran clash detection using Tekla BIMsight. The development of the new BCF file outputs to communicate issues throughout the design team allowed for streamlined co-ordination workflow, that all led to savings in time against the overall project programme. The ability to pass on the BIM models throughout the lifecycle of the project provides the whole supply chain with a better understanding of the building design, and hence allows them to better plan and carry out their elements of the build process.
Using Tekla structures helped reduce the risk of error & rework within the factory during the design phase, reference models from all disciplines were imported and overlaid to ensure the steelwork frames were correct. The steelwork model was also exported from Tekla to provide the disciplines a reference model to work from and interrogate their own designs. Using Tekla structures also helped reduce lead-in times for our steelwork manufacturer, a preliminary copy of the .DB1 file was shared to allow them to procure material and book factory time slots for manufacture. Once the structure had been finalised copies of the fabrication drawings, NC data and a latest .DB1 file were supplied, this allowed our supplier to fabricate and phase the delivery of steelwork to our factory for assembly. Tekla structures was also instrumental in helping produce clear and concise assembly drawings for out teams to build the steel frames, plans where created along with 3D-GA’s to allow our production teams to assemble the modules correctly, as the building was bespoke additional items were required within each unit. During manufacture our production team were able to view the steelwork model using Tekla BIMsight, this helped them identify issues both during the design and build phase by being able to visualize the building as a whole.