Until you are looking at a structural drawing and trying to correlate an engineer’s specification with what a factory can make and deliver on time, sizing a column might seem like a simple task. You will be back at the design table or paying for concrete that you didn’t need if you get it wrong. Don’t get it wrong, and the rest of the project proceeds much more smoothly. This guide details the standard dimensions of precast concrete columns in the UAE including typical cross-sections, heights, shapes, tolerances and what really influences which size you will have on your project.
Explain Why the Size of a Column is More Important Than it Sounds
The size of the column is not a fashion statement. It has a direct influence on load capacity, slenderness behavior, fire resistance and amount of clear cover the reinforcement receives. If it’s too small, it will be rejected at design review. Oversize it and you’ve paid for extra material, extra dead load… and no structural benefit; and you’ve lost usable floor area.
Precast columns are made to order, so it is more important that their size is correct during design before molds are designed and production begins as it would be in cast-in-place construction. Once the fabrication process begins, there is not much room to play around.
Typical Cross-Section Dimensions
The majority of precast concrete columns are within a rather narrow range throughout the industry. Their cross-sections are usually in the range 300×300 mm to about 1000×1000 mm, larger cross-sections available on special request.Usually, the cross-sections of these standard rectangular-shaped structural elements are between 300×300 mm and about 1000×1000 mm, with larger cross-sections available upon special request.
In UAE projects, in particular, size tends to group by building type:
- The loads are taken by 300×300 mm or 350×350 mm square sections, which are typically used in villas and low-rise residential buildings (1-4 storeys).
- For medium-rise commercial and mixed-use buildings (5 to 15 storeys), typically columns are of 400×400 mm to 500×500 mm sizes.
- Heavy industrial structures and high-rise frames: Standard 500×500, 600×600 and beyond.
Rectangular (not square) sections appear when the load distribution is not uniform or where architectural requirements necessitate this. In most UAE building projects the practical aspects of transport, crane capacity and connection detailing limit columns to about 300 mm to 700 mm, although larger sections are available should it be necessary for infrastructure and heavy industrial applications.
Standard Column Heights
Precast columns are really at their best when it comes to height. One precast column can be used for up to 5 floors, which is approximately 18 meters long, without splicing.Single precast column can be used for up to 5 floors (18 m) without any splicing.
On a typical project with 3.6m floor-to-floor heights, one column unit can be lifted by the single crane to the fifth floor in one lift. This is compared to the five separate cast-in-place pours, which would require the construction of five separate formworks, plus five curing cycles.This is in contrast to five cast-in-place pours which require five separate formworks plus five curing cycles.
In buildings exceeding 18 meters in height, columns can be produced as longer single columns or be connected together with column-to-column splicing by either grouted sleeve connections or threaded rod connectors or cast-in base plate systems, depending on the structural engineer’s preference and the loads at the column splicing point.
There are also variations in height according to the type of building. In the UAE, columns for single-storey industrial or warehouse structures are generally 6 to 9 meters tall. The column is usually the only element used in low rise residential buildings (3-5 storeys).
Circular and Non-Rectangular Columns
Not all precast columns are square or rectangular in shape. Circular columns are often seen in parking structures, building entrances and podium levels, where both appearance and traffic patterns are important.
Circular columns are usually manufactured between a diameter of 250 mm and 800 mm, although bigger sizes are used for bridge piers and other heavier infrastructure applications; in typical UAE building projects, the diameter of the circular columns generally ranges between 300 mm and 600 mm. L-shaped and T-shaped columns are also used in more complex construction, typically created as part of a larger structure rather than added from a catalogue to meet a specific beam bearing requirement, and are likely to feature corbels or ledges.
The Influence of the Strength of the Precast Concrete on the Size of the Columns
This is a surprising insight that is going to save you money in UAE projects – higher grade concrete allows engineers to specify a smaller cross section for the same load. It isn’t a secret technique or something that is only used by a few.
Lower floors may require a higher grade of concrete C30/37 to C55/67 for heavier axial loading, as well as upper floors which can be reduced to an economical mix C30/37 to C55/67. It requires a higher strength concrete, but it results in a smaller column footprint per m2 of floor space, making up for the additional cost over a building with hundreds of the same column locations.
Manufacturing Tolerances
The nominal size is only half the story. Tolerances, which are the acceptable amount of deviation from the specified dimension, are equally important and especially significant in structural connections and exposed architectural finishes, or in fit-up between adjacent precast components.
One of the more obvious reasons to check a supplier’s conformance status with Dubai Municipality’s precast conformity program before ordering a precast is that the precast column is manufactured and tested to a set of conformance tolerances, rather than the standards being estimated as they are being produced.In the UAE, a manufacturer’s conformance to Dubai Municipality’s precast conformity program involves producing and testing columns to established tolerances rather than estimating them at the time of production, which is one of the clearer reasons to check a supplier’s conformance status with Dubai Municipality’s precast conformity program before ordering a precast.
Selecting the Proper Size for Your Project
A combination of engineering calculations that your engineer controls will determine the correct size of the column, but there are a few patterns that are consistent for most types of projects in the UAE.
The most common size they appear in villa residential projects in Dubai, Abu Dhabi and Sharjah is 300×300 mm or 350×350 mm concrete columns, as they are in the C35 to C40 range. In concrete, medium-rise commercial and mixed-use buildings normally use 400mm x 400mm sections up to C40 and occasionally up to C50 or C55 at lower levels where the axial loads are highest.
The sizes of the parking structures tend to standardize on 600×600 mm columns as it fits the typical structural bay spacing used in the car parks in the UAE; where a column is required to support a heavier load across a wider bay, rectangular sections are used. In a typical industrial zone such as JAFZA or Dubai Investments Park, columns are typically required in the 9 to 14 meter range and from 400mm x 400mm up to 600mm x 600mm, depending on the roof loads calculated by the structural engineer.
Doing the Right Thing with Your Supplier
There are a few tips that can help speed up the quoting process and minimize back-and-forth communication with a UAE precast column manufacturer.
Verify design axial load for each column location, floor-to-floor height, structural grid spacing and bracing (braced or unbraced) of the frame. Know in advance if corbels or cast-in bearing plates are required as part of the column unit or not, as this increases the dimensions, weight and will impact transport planning.
It’s also important to keep in mind that a new precast column that is just installed is structurally unstable until the base connection is fully cured. That connection will require temporary props or guy wire until it is ready and a reputable UAE manufacturer will have that erection stability engineering in their shop drawings, not as an on-site afterthought.
Final Thoughts on Precast Concrete Columns
In the UAE, precast concrete columns come in a remarkably wide variety of sizes, ranging from 300 x 300 mm for villa projects to much more impressive sizes for big industrial projects; the columns can be up to 18 metres in height or higher when spliced together. These numbers are not random, they have been carefully calculated by considering the structural engineering, feasibility of manufacturing, logistics for transporting and Dubai Municipality’s certification.
Opting for a manufacturer who is certified by the DM and involves their engineering team early in the discussion can make column sizing an easy design challenge instead of a last minute scramble.