What is composite construction?

Composite construction is the construction of structures in which two or more materials are used. Regarding structural engineering, composite construction is a construction where two materials are bound together in a technical manner such that both the materials act as a single unit to carry and transfer the load. The motives of composite construction are to increase the structural strength, make structures more aesthetic, and provide a sustainable environment. 

Composite materials

With advancements in the field of engineering, various types of materials are combined and new materials are designed by structural engineers to design composite materials for buildings. Some of the most popular and most widely used composite materials are given below:

• Steel-concrete composite
• Timber-concrete composite
• Timber-steel composite
• Composite wood
• Cement-polymer composite

Steel-concrete composite

The steel-concrete composite materials are used on a large scale in the construction industry. The most common example of steel-concrete composite is the Reinforced Cement Concrete (RCC). RCC is the most widely used composite material in the construction of buildings. In the reinforced cement concrete, the steel bars, often regarded as rebars are embedded into the concrete before the concrete sets. The concrete is weak in sustaining tension and very good in sustaining compression. Hence, the steel bars are provided in the member to offer resistance against the failure due to tension and the concrete offers resistance against failure due to compression.

Composite steel joists are also one of the most popular steel-concrete composites used. Composite steel joists are also known as open web steel joists. The composite joists (CJ) series of open-web steel joists is primarily used in the construction of floors and roof of buildings. The advantage of using composite steel joists is that the deflection due to live load on the slab is decreased and the requirement of material for the slab is reduced.

Timber-concrete composition

In timber-concrete composite, the composite action between timber and concrete is established to make both the materials behave as a single unit. The timber-concrete composition is primarily used in the construction of roofs and floors. The advantages of using timber-concrete composition are that the deflection of the slab is reduced and the construction is economical.

Timber-steel composition

In timber-steel or wood-steel composition, composite between wood and steel is established in a well-engineered manner. The wood-steel composition is mostly used for the construction of flitch beams in wood-framed structures constructions. In the construction of the flitch beam, a steel plate, often referred to as a flitch plate is sandwiched between two wooden beams, and the assembly is bolted together. The advantages of using flitch beams are that the larger spans of beams can be provided between two supports and the strength of beams is more than that of the traditional beams.

Composite wood

Composite wood, also known as engineered wood is a composite material made by binding wood with adhesives. The composite wood is manufactured in a well-engineered manner, meeting design criteria and tested as per standards. The most widely used composite wood material is plywood. In buildings, the composite woods are used in manufacturing wooden I-joists and I-beams, which are used for constructing floors and roofs. The composite woods are also used in manufacturing roof and floor trusses. The advantages of using composite woods are that the construction is economical and maintenance cost is less.

Cement-polymer composite

The cement-polymer composite is used as a substitute for traditional cement concrete. The cement concrete deteriorates after some time and produces cracks. Hence, the addition of crumbed rubber into the concrete mix was proposed to produce a cement-polymer composite. As per the standards, the replacement of concrete with 20% crumbed rubber is suggested. The advantages of using cement-polymer composite are that the construction becomes economical and the structures have better durability than traditional concrete structures.

Composite slab

The composite construction method is used for the construction of composite roof slabs or floor slabs. The composite slabs are designed and constructed using composite materials as a replacement for traditional RCC slabs.

In the construction of composite slabs using steel-concrete composite, the open web steel joists are provided beneath the metal decks and concrete slab to provide structural support. Shear studs are welded between the steel deck and steel joists to provide the shear connection between the slab and the joists.

In the construction of composite slabs using timber-concrete composite, timber beams or timber panels are provided beneath the slab and then the slab is constructed over it. The slab can either be pre-cast or cast-in-place. But usually, cast-in-place slabs are preferred as they are easier to construct and eliminate the shipping cost, and the margin of error is minimized. The connection between the concrete slab and timber is made using screws. The screws are half-drilled diagonally into the timber and then half are concreted into the slab after the pouring of concrete on the top, thus creating a composite structure.

Composite decks

Composite decks are the alternatives used for traditional wooden decks. The composite decks are prepared by mixing wood fibers with plastic and bonding material. All the components are melted and mixed and then cast in the shape of boards or planks and cooled. The composite decks are of two types, capped and uncapped. The capped decks are provided with an exterior coating of plastic, which makes them more durable and resistant to the fading and staining action due to the environment. The uncapped decks are not provided with an exterior coating of plastic, which makes them relatively less durable and less resistant to the fading and staining action. The advantages of using composite decks are that the decks are more durable than the traditional timber decks and the maintenance cost is less.

Composite columns and composite beams

Composite columns and beams are constructed by embedding hot rolled steel sections into the concrete casing. The composite beams and columns are alternatives for the traditional RCC beams and columns, and steel columns and steel beams. The composite columns and beams are less economical, but they provide more strength, are more ductile, and are more efficient against the loads.

Context and Applications

The composite construction is useful for the students undergoing the following courses-

• Bachelors in Technology (Civil Engineering)
• Masters in Technology (Civil Engineering)
• Masters in Technology (Construction Management)
• Masters in Science (Construction Management)

Practice Problems

1. Which of the following is not a motive of composite construction?

1. To increase structural strength.
2. To make structures uneconomical.
3. To make structures more aesthetic.
4. To provide a sustainable environment.

Answer: Option b

Explanation: To make structures uneconomical is not a motive of composite construction.

2. Which of the following is not a composite material?

1. Steel-concrete
2. Asphalt-glass
3. Timber-concrete
4. Timber-steel

Answer: Option b

Explanation: Asphalt-glass is not a composite material.

3. In RCC structures, which of the following is used to offer resistance against failure due to tension?

1. Rebar
2. Wooden plank
3. Concrete
4. PVC pipe

Answer: Option a

Explanation: In RCC structures, rebar is used to offer resistance against failure due to tension.

4. In RCC structures, which of the following is used to offer resistance against failure due to compression?

1. Rebar
2. Wooden planks
3. Concrete
4. PVC pipes

Answer: Option c

Explanation: In RCC structures, concrete is used to offer resistance against failure due to compression.

5. In the construction of a flitch beam, which of the following is often referred to as a flitch plate?

1. Steel plate
2. Wooden plank
3. Bolt
4. Steel beam

Answer: Option a

Explanation: In the construction of a flitch beam, a steel plate is often referred to as a flitch plate.