Members of MPA Precast provide a wide range of structural precast products. Structural precast concrete is manufactured in modern factories and can form part of complete offsite building systems. Many of the structural solutions on offer are fully compatible with the principles of design for manufacture and assembly (DfMA). Solution details:
Crosswall construction is a modern and effective method of construction that employs factory precast, precision engineered, concrete components. Each component is custom-designed and manufactured to suit the specific project. This method of construction was developed to facilitate swift and adaptable residential buildings such as hotels, student residences, prisons and military barracks.
The elements are made to order, often manufactured in the UK, using locally sourced materials. Their design is based on an established system of details that have been honed through experience offering quality, safety and efficiency. Services can be embedded if required, and high levels of surface finish are available. Walls and floors are designed to be as slender as possible without the need for structural downstands.
The panels are delivered to site in a “just-in-time” operation and are lifted directly from the lorry into their final position when they are tied together using a series of hidden joints that are grouted as the works progress, minimising need of temporary works. With quick assembly clients are thus offered a rapid room occupancy programme.
Being concrete, the structural elements are durable, non-combustible and virtually maintenance free, having little impact from the effects of water. These are all benefits available during construction but also over the life of the building. The concrete offers excellent acoustic performance, security, airtightness and thermal mass.
Twinwall consists of two precast concrete panels held apart by a lattice girder, manufactured from steel reinforcement. The precast concrete panels form both a permanent shutter for the in-situ concrete and contribute to the final structural element. The surface finish of the panels are good quality and may only require a skim coat of plaster, or paint finish. The advantage of using an in-situ concrete infill is that the elements can be readily tied together to form a robust structure. Potential uses for twinwall panels include:
Precast concrete beams are reinforced with either steel reinforcement or prestressed with steel strand. They may be designed to act compositely with the floor. They can also be designed to be monolithic with columns especially where these are in-situ concrete elements. Where the beams are supporting precast concrete floor units the beam profiles are generally inverted T-beams or L-beams with the nib designed to support the floor unit. However, other profiles can be manufactured.
Precast columns are generally square, rectangular or circular, although other shapes are possible and can be cost-effective where there are a large number of repetitions. Increments of 50mm on the dimensions of faces of square and rectangular columns are preferred. The preferred increment for the diameter of circular columns is 50mm. Circular columns are routinely cast vertically in the factory, limiting them in most cases to single-storey height. Rectangular and square columns can be cast horizontally and the maximum height of columns without splices is generally between 20m and 24m although 15m to 16m is often more economic. Where the columns are continuous through one or more floor levels they can have corbels or structural inserts to provide support for beams
Precast concrete stairs offer a quick method of providing robust, safe access routes during construction. They remove the need for complicated on-site shuttering and provide a high quality finish. They generally do not require temporary propping and are often connected to floors and landings using steel angle joints. Other connections such as continuous halving joints and intermittent halving joints are also used. Combined stairs and landing units are also available. Precast concrete stairs are particularly cost-effective when duplicated or based on manufacturers’ standard, but adjustable, mould sizes. The greater the number of identical units required, the lower the cost.
The structure for a bathroom pod can be manufactured in precast concrete. The structure generally consists of thin concrete walls and floor with a single layer of reinforcing mesh. Services such as electrical conduits and pipework can be incorporated into the concrete structure. After casting the concrete pod the bathroom is fully fitted out, including all the finishes. The finished pod is delivered to site and lifted into position ready for final connection of the services.
Precast concrete balconies are manufactured mainly for use in flats and high-rise developments. Units have steel reinforcing bars projecting from the back which tie in with the steel reinforcement in the concrete floor structure. Balcony units are temporarily supported until the structural floor or screed has been placed and reached sufficient strength. Precast concrete balcony units typically have integral drainage slots to receive drainage outlets and an upstand to facilitate weatherproofing details at door thresholds. They may also incorporate tiled upper faces and cast-in fittings for balustrades. There are proprietary systems available to minimise cold bridging which can be incorporated into precast balconies.
Precast concrete is used extensively for terracing in grandstands, stadia and auditoria. Precast concrete provides a strong, durable and versatile terracing unit that is quick and easy to install. Importantly, it can easily be designed to meet the vibration criteria for sports grounds. There is a large range of associated products including stairs, vomitories, steps, raking beams and columns that will enable the structure, as well as terracing, to be constructed in precast concrete if required.
Concrete structure can be supplied in a volumetric form, either as two planes (floor and wall) or more commonly as a four-sided box, with or without the floor or roof, depending on the intended use. They are particularly beneficial for stair and lift cores or prison accommodation but with potential for further applications. The modules will generally be delivered to site on low loaders, with the ground floor units being erected onto a prepared ground floor slab. The subsequent units are then successively erected onto the roofs of the units below. Units can be fitted out at the factory with windows, vents, bathroom and other fittings, plus plumbing and electrical fixtures and fittings.
Precast retaining walls are used to retain soils at different levels where a site condition would not allow for a slope to be provided. Retaining walls are used in different infrastructure, flood control and road construction applications. Members of MPA Precast Architectural and Structural produce different types of retaining walls, either as gravity block-based systems or as “L” shaped units.
Retaining walls (either gravity based or cantilevered) are designed in accordance with EN 15258: Precast Concrete Products – Retaining Wall Elements.