Remove the columns from a building, and everything else is moot. There are no floors, there are no walls, there is no glossy facade that will remain standing without someone supporting it from above to the ground. In a complete Precast Concrete Columns construction system, it’s the sole business of the precast column. From residential towers to industrial warehouses, total precast construction has become common in the UAE. This guide will describe what is meant by a Total Precast System, why the column is the centre of it and what implications this has for the developer and contractors planning to work on a project.
Total Precast Concrete Columns Building System, What Is It?
A total precast building system is a system that utilises structural frame, floors and, typically, the facade too, all of which are cast in the factory and assembled together from day one. Rather than make up separate systems and hope they work together, engineers work together on footings, columns, beams, slabs, walls and stairs as a coordinated package.
Projects where there are precast parts combined with cast-in-place concrete are generally referred to as hybrid or partial precast construction. The column is usually one of the first structural components installed and a number of UAE manufacturers supply complete total precast deliveries, such as Gulf Precast, Hard Precast Building Systems (HPBS), Abu Dhabi Precast and Dubai Precast.
The Column’s Primary Function: To Carry Gravity Loads
The simplest definition of a precast column is that it is a component that acts as a vertical structural element to transfer the gravity loads (the weight of each floor, beam, wall and tenant above them) to the foundation. It is a structural member in the vertical position designed to carry both vertical and lateral loads, but made in a controlled factory environment before it is ever erected on a job site.
This load path is a fixed sequence that is always performed. The floors are made up of hollow core or double-tee slabs that are supported by precast beams. The columns support all the load down to the foundation and the corbels are built into the column from where the load is transferred to the beam. Each link in that chain relies on the correct sizing, placement and connection of the previous link.
The Structural Grid Consists of Columns.The Columns are Part of the Structural Grid
Rarely, precast columns are used without other structural elements—they establish the whole structural rhythm of the building. Their layout determines the size of the bays, floor-to-floor heights and the relationship of the architectural layout to the frame below.
It is especially important if there’s a project that requires clear and unobstructed floor space, such as a commercial office tower, logistics warehouse or multi-level parking structure. The skeletal precast frame — columns at the intersections of the grid — provides just that kind of clear span without the added structural clutter.
This is where speed really makes a difference. On actual projects, UAE precast manufacturers have achieved full-floor erection rates of approximately 10-14 days per floor, contingent on the size of the floor and site specifics. The ability to produce factories-cast columns that are delivered ready to use (no curing time, no formwork to strip after) is one of the reasons why pace is possible.
The Column as a Connection Hub
In addition to bearing loads, the column is also the point where beams, slabs, walls, staircases and foundations physically connect and share forces. The connections between columns and foundations can be either grouted pocket systems, anchor bolt base plates or grouted sleeve connections, depending on the design of the structure.
Normally, a connection to the column occurs at each floor level with cast-in corbels or steel insert plates, which in turn is designed to support the beams and the floor slabs above them. All of that loading goes back up the column.
That’s the reason connection detailing is considered a first order design consideration instead of an “on-site” detail. Yet, a poorly detailed corbel, an improperly designed grouted sleeve or a misaligned cast-in plate creates issues that trickle down the rest of the structure. Reliable manufacturers in the UAE design connection detailing in from the beginning of the project and do not wait till the project is up and running to fix it.
Precast Concrete Columns and Lateral Stability
Many people think that a column must resist lateral forces, such as wind pressure, building sway and seismic forces, completely by itself. In a properly designed total precast assembly, they are not required since shear walls are generally designed to provide this function.
Structural cores may be formed in the building by precast shear walls arranged horizontally and vertically, usually around lift shafts and stair cores, which resist lateral loads and to which the floor diaphragms transfer loads. Consequently, a system of division of labour is created: columns bear gravity loads, shear walls bear lateral loads and the floor diaphragm bears and transfers loads between the columns and the shear walls. No one is being made to fit into a compromise position, each fulfills its own role in a way best adapted for it.
Seeing is Believing: Real Project Evidence from UAE Precast Manufacturers
UAE precast producers are large enough to be able to deliver precasts on a mass scale, and not just in theory. For instance, Gulf Precast offers a range of services to its clients for the re-design of the structure, manufacturing and complete turn-key erection of a precast structure.
With a daily production rate of about 700 cubic metres of precast elements and 2,000 square metres of hollow core slab, supported by 106 trailers and trucks on site, HPBS then has the capacity to convert “total precast” from a concept into a viable production schedule.
The Column Structure and Flexibility of the Building
The general belief about precast construction is that it forces the shape of a building into a box. Well-designed precast columns generally offer a greater degree of design freedom, rather than limiting it, in practice.
It is possible to cast precast concrete in curved or radial shapes, and using high strength prestressed concrete columns can also provide smaller cross-sections and longer span lengths than some other structural systems. Short column footprints open up flexibility in the floor plan and longer spans between columns eliminate the need for more columns, creating retail floors, parking layouts, or open-plan offices. For other architectural needs in lobby and entrance canopies, circular or L-shaped columns can also be used to meet architectural needs without significant loss of structural performance.
The Speed and Commercial Benefits of Precast Concrete Columns
One of the most compelling business cases for the use of total precast systems is program speed, and the column plays a big role in achieving that. The precast erection can be performed in a coordinated manner, where several precast parts are installed one after the other, instead of building up in turn, and thereby the overall construction duration can be reduced significantly when compared with the construction time for cast-in-place works.
Most columns will be on site pre-detailed for corbelling, and connections and reinforcement projections will have been placed. The column is simply lifted by the crane onto its pre-arranged foundation connection and erected without the use of formwork, rebar fixing or curing delays. Those time savings are compounded on repeated projects, such as multi-story residential towers with repeated floor plates, because the detailing is repeated in these repeated column lifts.
This Will Have Implications for Developers and Contractors in the UAE
The column in a total precast system is commercially significant to all those involved in a project.
For developers, it translates to quicker programme delivery, cost control and floor plans free from any unessential structure. For structural engineers, it involves design rather than retrofitting connections and column-to-shear-wall interactions. For contractors, it involves reordering crane picks, deliveries, and temporary props in the order most conducive to erecting precasts, not a traditional cast in place pour sequence.
The key point for procurement teams is that they need to source columns from a certified UAE precast manufacturer, but not as a standalone element that should be separated from the beams, slabs and walls of the project.
Final Thoughts on Role of Precast Columns in Total Precast Building Systems
Each and every total precast structure is ultimately based on its columns. The vertical chain is used on beams, slabs, walls and staircases to reach the ground safely. If you size the columns correctly, detail the connections properly, and the quality of manufacturing is appropriate, the rest of the system will work just as it was designed to do.
It is quite possible that, for those who want to think about having a total precast project in the UAE, the column discussion is a task worth having early – with a precast manufacturer who considers the column conversation not merely a part of the order book, but the foundation of the whole project.