Composite HSS, or concrete-filled tubes (CFT) as it is sometimes referred, is an underutilized form of design and construction that has several advantages.  The most common use is for columns supporting traditional steel framing or other floor systems such as Delta Beam with precast concrete planks. Let’s explore the top five reasons you will want to consider Composite HSS on your next design.

1. Increase in axial capacity: An HSS filled with concrete can give you more capacity compared to the same size HSS without concrete. This may allow you to utilize a smaller column for a specific load and potentially increase your interior space
2. Improved performance: When a composite HSS is used to resist bending, the steel is located in the best possible place which is as far from the neutral axis as possible. This makes the steelwork as efficiently as possible.   The steel on the outside confines concrete on the inside, which will lead to more efficient axial load carrying by the concrete.  This also leads to improved local buckling behavior of the steel. When you use composite HSS members, you’ll achieve an increase in strength, ductility, and damping under cyclic loading
3. Improved Cost: The HSS acts as permanent formwork for the concrete which will reduce labor cost and increase the speed of construction at the job site.  The cost of a composite HSS member roughly equates to that of reinforced concrete on a strength per dollar basis.  This can also lead to simpler, more cost-effective connections to the composite HSS because of the improved local buckling behavior of the steel
4. Fire Protection: Composite HSS gives you an increase in fire resistance endurance which can lead to the reduction in protective coatings. Based on research, concrete filled HSS can achieve up to two and three-hour fire ratings!
5. Blast Resistance: Square and round sections filled with concrete are ideal for blast resistant structures. Because the section properties are the same for all axes, they can provide the same level of strength regardless the direction of the blast. Having the steel confine and protect the concrete prevents any spalling of the concrete

These are just some of the advantages that incorporating Composite HSS into your next design could offer you. Want to learn more about Composite HSS? Sign up for my lunch and learn on the subject today!