Types of Beams in Construction: Supports and Sections

Beams are the horizontal members that carry floors and roofs across open space and deliver their loads to columns and walls. There are many types of beams, and engineers classify them in two main ways: by how they are supported, which determines how they bend, and by their cross-section and material, which determines how efficiently they resist that bending. Understanding both helps students read structural drawings and helps homeowners see why some beams are deeper, heavier or more critical than others.

This article covers the support types first, then the section and material types, gives a short worked comparison, and finishes with the mistakes most often made. The emphasis is on intuition and plain formulas, not detailed design.

What a beam does

A beam takes load acting across its length and carries it sideways to its supports. In doing so it bends, putting one face in compression and the other in tension, and it resists shear near its supports. The size of the bending moment, the shear force and the deflection all depend on how the beam is supported. Our articles on bending moment and beam vs column explain the underlying behaviour.

Types of beams by support

Simply supported beam

Rests on two supports that resist vertical movement but allow rotation. Maximum moment under a uniform load w over span L is wL²/8 at midspan. Common in timber joists, precast planks, steel beams with simple connections and lintels. The sibling article on simply supported vs fixed beams covers this in depth.

Fixed (built-in) beam

Both ends restrained against rotation. Moments are wL²/12 hogging at supports and wL²/24 sagging at midspan, and deflection is one fifth of the simply supported value. Requires supports and connections capable of resisting the end moments.

Cantilever beam

Fixed at one end and free at the other, like a balcony or canopy. Maximum moment is wL²/2 at the support, four times that of a simply supported beam of the same span and load. Cantilevers need a robust backspan or anchorage; see our article on cantilever structural design.

Continuous beam

Runs over three or more supports. Sagging moments in the spans are reduced, and hogging moments develop over the internal supports. Very common in cast-in-place reinforced concrete. Covered in the sibling article on continuous beams.

Propped cantilever

Fixed at one end and simply supported at the other. Its behaviour sits between a cantilever and a fixed beam, with a hogging moment of wL²/8 at the fixed end under uniform load.

Overhanging beam

A simply supported beam that extends past one or both supports. The overhang creates hogging over the support, which reduces the sagging moment in the main span.

Types of beams by cross-section

Rectangular beam. The basic solid section in concrete and timber. Simple to form and build.
T-beam. A concrete beam cast monolithically with a slab, so part of the slab acts as a wide compression flange. Very efficient in sagging regions.
L-beam. The edge-beam version of a T-beam, with the slab on one side only.
I-beam and H-section. Rolled steel sections that concentrate material in the flanges, far from the neutral axis, where it is most effective in resisting bending. The web resists shear.
Box and hollow sections. Good in torsion and in bending about both axes; used for long spans and where twisting loads occur.
Channel and angle sections. Lighter steel sections used for secondary members, trimmers and lintels.

The common thread is that bending resistance grows with depth squared. Placing material as far as possible from the neutral axis, as an I-section does, gives the highest stiffness and strength for the least weight.

Types of beams by material and function

Reinforced concrete beams. Concrete takes compression, steel bars take tension. The default in Singapore residential and commercial frames.
Prestressed concrete beams. Steel tendons are tensioned to pre-compress the concrete, reducing cracking and allowing longer, shallower spans.
Steel beams. Rolled or fabricated sections, light and fast to erect, needing fire and corrosion protection.
Composite beams. Steel beams connected by shear studs to a concrete slab so the two act together.
Timber and glulam beams. Used in houses, roofs and mass-timber buildings.
Lintels. Short beams over door and window openings.
Ground beams. Beams at foundation level linking pile caps or pads and supporting walls.
Transfer beams. Heavy beams that pick up columns or walls from above and carry them to supports below, allowing a change of layout. See our article on the transfer beam.
Deep beams. Beams whose depth is large relative to span, behaving more like walls; they are designed differently from ordinary beams.
Ring and bond beams. Beams running round a structure or along masonry walls to tie it together.

A worked comparison

A 5 m span carries a uniform load of 8 kN/m. The maximum bending moment depends on support type alone:

Simply supported: wL²/8 = 8 × 25 / 8 = 25 kNm at midspan.
Fixed both ends: wL²/12 = 200 / 12 ≈ 16.7 kNm at the supports, with about 8.3 kNm at midspan.
Cantilever of the same length: wL²/2 = 200 / 2 = 100 kNm at the support.

The same load on the same span can produce maximum moments ranging from about 17 to 100 kNm. Choosing the right support arrangement, and correctly identifying the one that actually exists, matters more than almost any other decision in sizing a beam.

Common mistakes

Misidentifying the support condition. Assuming a beam is fixed when it rests on masonry, or continuous when it has been cut, understates its moment.
Forgetting hogging reinforcement. Continuous, fixed and cantilever concrete beams need top bars over supports.
Underestimating cantilevers. Their moments are much larger and their deflections more visible.
Coring or notching beams. Holes for services through webs or near supports can weaken a beam in shear or bending if not designed for.
Treating a transfer beam like an ordinary beam. It may carry several floors; any alteration needs careful engineering.
Ignoring deflection. A beam can be strong enough yet sag enough to crack finishes and partitions.

Frequently asked questions

What are the main types of beams?

By support, the main types of beams are simply supported, fixed, cantilever, continuous, propped cantilever and overhanging. By section and material they include rectangular and T-beams in concrete, I and box sections in steel, composite, prestressed and timber beams, along with functional types such as lintels, ground beams and transfer beams.

Which type of beam is strongest?

No beam type is strongest in general. For a given span and load, a fixed beam has smaller maximum moment and deflection than a simply supported one, and a steel I-section is very efficient for its weight. The best choice depends on span, loads, supports, material and construction method.

What is a T-beam?

A T-beam is a reinforced concrete beam cast together with the slab it supports, so a strip of slab acts as a wide compression flange on top of the beam. This makes it more efficient in sagging bending than a rectangular beam of the same depth.

Why do steel beams have an I shape?

Bending stresses are greatest at the top and bottom of a beam, so placing most of the material in flanges far from the centre gives high bending strength and stiffness for little weight. The thin web connects the flanges and resists shear.

Can I drill a hole through a concrete beam for services?

Only after an engineer has checked it. A hole can cut reinforcement or reduce shear and bending capacity, particularly near supports or in the tension zone. Openings should be positioned and sized to the engineer’s advice, with any strengthening that is required.

Planning to cut, core, extend or remove a beam? Talk to our consultancy or get in touch for an accountable assessment.