A concrete volumetric system for multistorey buildings with a unique loadbearing structure
For decades the construction industry has been pursuing ways of moving construction from building sites and into factories. We’ve had panelised wall systems, precast concrete modules, structural sandwich panels, insulated concrete formwork, bathroom and kitchen pods and volumetric buildings.
You would expect that most ideas have been exhausted, but now a firm has come up with an idea to build multistorey buildings faster and cheaper than before. The brains behind it is Ole Bjerre, a Danish furniture designer who also trained as an architect and worked as a troubleshooter for Ikea. Bjerre expected his idea to have been thought of already, but when he investigated it and found nothing he quickly took out a patent.
The advantages of off-site construction are well documented – speed on site, quality control, less waste and all-round greater efficiencies. And it’s these advantages that Bjerre’s company Bpod International aims to exploit with its concrete volumetric system.
The single biggest difference with the Bpod system is that it is aimed specifically at multistorey structures – up to 20 storeys in height. For these types of scheme, the company says, concrete is the most viable building material for strength and fire safety reasons. The room-sized building modules are constructed from lightweight concrete panels, but what makes the concept unique is the way the loadbearing structure is created.
The Bpod starts off in the factory, where what looks like a conventional concrete panel is cast. However, because the modules aren’t loadbearing, only the outer edges of the panel need to be made from dense concrete to give it structural rigidity and strength. The centre of the panel is filled with lightweight concrete that, says Bjerre, has good acoustic and thermal properties.
Where necessary, steel reinforcement bars are clipped onto the back of polystyrene insulation panels, which are then pressed into the wet concrete to form a composite wall or ceiling panel. The smooth side of the concrete panel facing into the mould will eventually form the finished surface of the wall or ceiling. Floor panels are cast with a steel reinforcement mesh and can also include piping for underfloor heating as well as wet room drains.
A floor panel, four wall panels and a ceiling panel are then joined to form a room-sized unit with high levels of airtightness. According to Bjerre, the size of the unit ultimately depends on transportation but he says the maximum width is 4.8m and the length 12m. The weight of a fitted-out pod will be about 30 tonnes.
Individual pods can be divided into several rooms by installing partitions, or several can be combined to create a single room. At this stage the room is fitted out. Water, power and wiring for communications are run in channels in the insulation on the outside of the Bpod and a service riser can be incorporated into the design to carry drainage, water, power, communications and ventilation up through the building.
Finishes, internal doors, kitchens and bathrooms are also installed where required.
The external cladding is factory built. This can be fitted with doors and windows and, unlike traditional facing elements, can accommodate any thickness of insulation as they are not supported by the walls of the pod but the structural frame. This gives the potential to improve the building’s thermal efficiency.
Delivery to site
The pods are then ready to be transported to site where they are placed next to each other on ready-installed foundations using a mobile or fixed crane. The facades are fitted and steel reinforcement cages inserted where necessary into channels in the insulation. These are then filled with concrete to form the loadbearing structure. Levelling bolts on top of the Bpods are aligned using lasers to provide accurate levelling for the next storey and steel brackets are fitted to guide the positioning.
Next, super-plasticised concrete is pumped into the insulation channels to create the loadbearing columns and beams. This is done one floor at a time to avoiding vertical construction joints in the loadbearing structure. “The lightweight Bpod walls act simply as permanent shuttering,” says Bjerre.
The building carries on upwards, and the final stages are to fit the pre-assembled roof and connect the services. The company claims the time needed on site is reduced by up to 80% compared with traditional construction techniques, and that virtually all dependence on the weather is removed.
Martin Goss, managing director of specialist off-site consultants Mtech, says there is nothing quite like Bpod on the market with its mix of precast twin wall and volumetric module technologies. “There doesn’t appear to be any technical reason why this shouldn’t work – though there is an immense amount of detail design that I suspect hasn’t yet been done to verify that the product does actually work in reality.”
The next stage is to build a prototype. For this to happen Bpod needs to find a manufacturer to license the technology. “We want to license it and that way get it used as widely as possible,” says Ole Henriksen, head of Buildpod International.
This could be a challenge. Goss says there are many novel building technologies waiting in the wings for the construction sector to adopt but many never reach the stage of commercial exploitation. “The big challenge for these embryonic factory-based technologies is achieving a successful route to market. This means finding the client base which want to use the product and then establishing the means of delivering that product reliably at the right cost point.”
Bpod International is initially targeting the UK and Denmark but Henriksen concedes that the biggest barrier, other than the downturn, is convincing a company to take it on board. “We’re experiencing some resistance from the precast concrete manufacturers because they see a system like this as competing with their customers. For us it’s really important to find a client such as a large developer or housing association which has the interest and power to get the system adopted.”
1 Lightweight, 80mm-thick concrete panels are cast …
Original print headline: 'Prefab just got fabber'