Using less concrete can have multiple benefits in reducing project costs, saving time, improving safety, and shrinking a building&#;s environmental footprint. Here are seven ways it can be done:
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Concrete is one of the major line items for many commercial construction projects, and one that usually contributes substantially to a building&#;s embodied carbon footprint. Research by Think tank Beyond Zero Emissions (BZE) found multiple ways to reduce the use of carbon-intensive Portland cement, including substitution with novel concrete mixes.
BZE&#;s Rethinking Cement report also identified tactics for reducing the use of concrete overall. According to the report, designing structures to use concrete more efficiently, utilising high-strength cement, and replacing concrete with timber could reduce overall cement consumption globally by approximately 15% within a decade.
Queensland-based structural engineer Chris Morrison has been researching ways projects can use lean design principles to reduce the quantity of concrete required in construction.
The core of lean design is engineering design refinement and smart specification of materials and methods. Lean design looks to optimise the building structure and building envelope so that the least amount of materials, time and cost is used while still delivering a structurally sound, fit-for-purpose and durable project.
Techniques used to achieve this include reducing floor slab thickness, minimising large beams and other transfer structures that transfer loads back into the building&#;s load-bearing verticals, or removing columns through utilising post-tensioning.
&#;Ask your engineer, is this design as efficient as it can be? How can we make it more efficient?&#; Morrison says.
Dr Natasha Watson, Senior Structural Engineer, Buro Happold, has written a guide for the Institution of Structural Engineers (IStructE), Lean Design &#; 10 Things to Do Now. Dr Happold states it is important for engineers to communicate to the project team &#;the value of the time and fees spent on design development and refinement, with the potential material savings leading to cost and carbon reductions.&#;
The guide also stresses the value of crystal-clear briefs in terms of the immediate post-completion use for the building. Dr Watson notes that in many cases, designs are based on conventional assumptions about loads, floor plates, and other elements that result in more material use than actually required.
A study conducted by Buro Happold investigated a simple concrete frame with initial redundancy compared to a design without redundancy in the floor slabs. The design without redundancy required an estimated 12% less material, while adding strengthening during detail design only added 3% more material back in. This equates to nearly 10% savings on material costs compared to the design based on assumptions with added redundancy.
Changing the construction method can also have benefits. Using post-tensioning approaches instead of conventional formwork and reinforcing requires less concrete. As an additional benefit, it allows for larger, open floor plates as fewer support columns are needed. There is also a material saving in reducing the number of vertical elements.
Morrison notes that this has implications for the construction program, as post-tensioning requires time to be allocated after the concrete pour. On the other hand, although conventional reinforcing has increased materials cost, a typical floor can be formed and poured in a seven-day cycle.
He says there is another consideration in favour of post-tensioning: material availability. &#;Reinforcing steel procurement is increasingly difficult and becoming extremely expensive,&#; he says.
Another concrete-saving method is utilising precast concrete elements, including precast construction for walls and columns.
&#;This puts a project along the path of prefabrication and (off-site) modular approaches,&#; Morrison says. These have advantages, including making a program less vulnerable to weather and offering improved surface finish quality. Concrete pouring and curing both require the right weather conditions. Prefab, precast, and off-site modular manufacturing are generally under cover in a climate-controlled environment. The increased cost of precast should be balanced against the construction program savings.
Many precast suppliers use high-strength concrete. This type of concrete gives the fabricator better control of the prefabricated final product quality, all while requiring less material to deliver an equivalent structural strength. High-strength concrete is also suitable for architectural applications.
Engineered timber can replace concrete in many projects and has advantages in terms of program time, safety, and environmental impact. Brock Commons at the University of British Columbia in Canada, for example, was delivered at an extremely rapid pace because of the efficiency of erecting prefabricated engineered timber components.
&#;The speed of construction with engineered timber is phenomenal,&#; Morrison says.
There&#;s another advantage to engineered timber&#;it is lighter in weight than the equivalent in structural concrete for walls and floors. Therefore, there may be a cost and materials saving in the footings and foundations required to support the building.
Recent research published by the University of Melbourne compared the use of engineered timber for the structure of a mid-rise residential project and the traditional concrete construction approach. It found the timber approach delivered a time saving of almost 50% and an overall project cost saving of 10% compared to the conventional concrete construction method.
Another methodology that is starting to get attention is the use of steel-timber hybrid floor and wall cassettes. Morrison says this approach has been proven on multiple projects in the US, Europe, UK and Canada. The use of steel in combination with engineered timbers, such as laminated veneer lumber (LVL), glue-laminated timber (GLT), and cross-laminated-timber (CLT), means the structural design can take advantage of the strength of steel to reduce the size of key structural members while still giving the project the time savings and safety benefits of timber pre-fab.
Achieving the most efficient design means ensuring the delivery pathway has sufficient collaboration at the front end. It can be facilitated by models such as early Contractor Involvement (ECI).
Morrison notes that traditional lump-sum contracting can be more challenging, as the geometry of the project is often &#;locked-in&#; at the point the client goes out to tender. BIM can help address these limitations, as the process of developing and collaborating on the BIM model can allow opportunities for refining design at the least-cost, lowest-risk stage of the project delivery.
Another approach builders can use is to have engineering designs peer-reviewed, Morrison says. This is not currently a legal requirement for most projects. However, the small outlay in consulting fees for an engineering design peer review can deliver significant cost savings in design optimisation.
It also ensures the design is &#;sense-checked&#; for buildability, safety and compliance, as well as providing an additional level of quality control. The Opal Tower investigation found, for example, that there were inadequacies in the project engineering design. Peer review may have found those issues before work commenced, reducing the level of reputational damage and costly legal fees suffered by Opal&#;s builder and developer.
Morrison says that moving into 3D modelling for design rather than using 2D drawings allows the project team to more easily identify opportunities to optimise the design.
&#;Manufacturers have been using 3D design for decades,&#; he says.
It is also easier to see what can be prefabricated when using a 3D model. Morrison notes that the need for having shop drawings produced based on the architectural plans is a potential barrier to projects utilising prefab. However, with 3D modelling, this process is streamlined as the design is already digitised and more compatible with manufacturing technologies, such as CAD.
A 3D model also helps the project team fine-tune tolerances and control and track the quality of design and delivery more effectively.
&#;The efficiency you can achieve with some pretty simple technology makes people&#;s lives easier [on projects],&#; Morrison says. &#;And the end result is better quality.&#;
Commercial concrete management, including post-tensioning systems, is critical to any residential or commercial high-rise and multi-level parking garage construction project. Post-tensioning involves placing prestressed steel &#;tendons&#; tightened once the concrete hardens. The additional stress of tightening compresses the concrete into its strongest state, ensuring it can support the external service loads (weight) once using the structure.
Failing to factor in the load-bearing capability of a structure can lead to catastrophic events, such as the collapse of the Hotel New World in Singapore in . The six-story building collapsed in 60 seconds, resulting in 33 deaths. More recently, investigators are still trying to determine the cause of a partial parking garage collapse in Baltimore in July .
This article looks closer at post-tensioning systems, explaining what they are, how they work, and their benefits to construction and architecture. We&#;ll also present some practical applications of post-tensioning concrete, criteria to consider when evaluating such systems, and where to turn for post-tensioning repairs.
Post-tensioning is a unique design technique that reinforces concrete in commercial building construction. This process helps strengthen concrete, allowing it to hold up better post-construction, keeping structures secure and stable. Post-tensioning tendons generally consist of stainless steel and reinforced cable bundles. These run inside plastic coatings or sleeves, placed inside the casings where concrete is poured before filling. Afterward, the cables are tensioned and anchored against the other concrete edges.
The post-tension acts much the same as support beams and improves the safety and stability of concrete pillars, foundations, columns, and other structures. Post-tensioning concrete is critical in the commercial building process, and proper execution gains maximum benefits.
Post-tensioning works within commercial building structures as a form of prestressing. Steel is stressed and put under tension before the concrete has hardened to support the service loads and stress of the building. Most precast, prestressed concrete has this process done as well. Post-tensioned concrete means that the concrete gets poured, and then tension is applied&#;but there is stress before applying the loads, leaving it prestressed. It is a way of preparing the structure to support the loads and stress of large commercial systems adequately.
Reasons concrete is popular in commercial buildings and commonly seen in post-tensioning construction include:
High durability and resiliency over long periods.
Relatively low maintenance and upkeeps are required.
Affordable and easy
maintenance and repairs
.
Affordable for mass projects and large-scale production.
The versatility of applications allows greater design creativity.
Easy to source locally for more affordable rates.
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It can be used in all climates and temperature extremes.
Highly resistant to rust and corrosion.
It is fire resistant and doesn&#;t burn easily.
Fewer issues with pests, mold, and other issues.
With so much in favor of concrete construction, the ability to improve the features of stability, durability, and longevity with post-tensioning only adds to the appeal of concrete usage in commercial structures.
Concrete is the most popular construction material in the world, and for a good reason. It&#;s widespread in commercial buildings, not only for basements and foundations but also for exterior walls. And, of course, it&#;s used frequently for sidewalks, ramps, and parking garages. The concrete used in commercial buildings is often subject to more significant pressures and stressors than concrete for residential use. When used in massive commercial building projects, this requires additional support and design considerations.
Concrete may be among the most common construction materials, but it can still come with a high price tag. Industry estimates show that a concrete parking garage could range between $4 and $7 per square foot. This price typically includes the cost of materials and labor. A smaller structure may run $5,000 to $14,000, whereas a larger building could be as much as $174,000-$490,000. Larger commercial structures, whether office buildings or parking garages, require more structural performance, which may change how you need to utilize concrete. This is where post-tensioning makes its impact.
Considering all these features and benefits, one critical aspect of commercial concrete management and upkeep regarding degradation makes all the difference post-tensioning.
Post-tensioned concrete has a variety of benefits, including:
Allowing concrete to be used in higher and longer spans to create larger spaces
Providing increased strength and support for load-bearing areas of construction
Compensates for poor site conditions and improves structural stability
Installs and hardens faster than other conventionally reinforced concrete structures
It uses much less concrete, saving money and resources
Provides flexibility and options for primary formwork and final aesthetic touches
Increases the overall safety and durability of the structure
Provides a faster and more practical manufacturing option
Safe to use in nearly every building situation
Reliable structure strength with post-tensioning
Easily scalable for use in small, medium, and large commercial buildings
Finding the balance between affordable concrete usage and durable post-tension elements remains crucial in planning and maintaining commercial structures.
The post-tensioning concrete method was first developed in the early s by industry specialists such as VSL in Switzerland. Post-tensioning is often a solution for addressing design and engineering issues. It enables the operational definition of the internal load path in concrete structures by superposing a favorable state for the internal stresses. This stress reduction minimizes deformations, reduces the thickness of concrete segments, reduces reinforcement congestion, joins components without relying on wet joints, and allows high-strength steel to reinforce structural components further.
The post-tensioning system is a structural support mechanism essential to many commercial concrete structures built today. Experts who specialize in concrete repair and upkeep utilize this system for three main reasons:
Post-tensioning lightens the structure&#;s weight, reduces load-bearing packages, and helps improve the overall aesthetic appearance.
It can be used in a wide variety of structures and often occurs in a wide range of systems that vary in size and usage.
Post-tensioned construction offers the most suitable solution for combining production and application to create a final uniform structure.
This act of prestressing has several advantages over standard rebars:
Significantly removes the risk of shrinkage cracks, so fewer joints are required. Shrinkage cracks occur naturally in poured concrete during the curing process as the concrete loses its moisture.
Cracks that do occur are held tightly together and do not grow and spread.
It allows structural concrete pieces to be thinner and lighter than they would normally.
Engineers and designers can build slabs over expansive areas or on softer soils.
Post-tensioning supports longer spans in elevated areas like floors, beans, and ceilings.
Building designers looking for a post-tensioning system should first consider three factors to avoid costly damages and repairs down the road.
Type of structural element &#; the depth of the structural component plays a key role:
Use of slab tendons with flat designs for thin structural elements such as floor flaps and ceilings.
Multi-strand tendons can be used for any other application and are common in thicker heavy construction areas.
Structural design &#; taking into account specific structural design requirements:
Post-tensioning can be introduced and might utilize internal or external tendons or, in some cases, a combination.
Concrete slab post-tensioning tendons are bonded or unbonded based on the location, application, and desired results.
Protection against corrosion &#; Protection needed to safeguard cables against corrosion:
The tendon encapsulation depends on the required protection level (PL) &#; PL1, PL2, PL3, typically subject to location and environmental exposures.
Corrosion protection is the application of anti-corrosion chemicals to prevent damage to equipment or facilities caused by corrosive processes.
Finding the balance between affordable yet durable materials is vital in planning and maintaining commercial structures. Post-tensioning concrete systems allow the utilization of the durable and versatile nature of concrete, while the addition of steel cables and tension support add required structural stability.
The post-tensioning system is the structural support working behind the scenes to provide long-lasting strength, durability, safety, and protection. Professional building management services are integral in maintaining post-tensioning systems to guard against building collapses.
Make sure your team is ready to deal with the maintenance and upkeep of post-tensions systems. Contact The Valcourt Group today and work with industry experts who can keep your building in good working order.
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