Choosing the Best Material for Beam Design: Timber, Steel, or Concrete?

Selecting the right material for beam design is a fundamental aspect of structural engineering.

The choice directly impacts the safety, functionality, and aesthetics of a building and the cost-effectiveness of a project. A well-designed beam must meet the load requirements specified by the building codes while being efficient in terms of engineering design, material use, and construction cost.

The most common materials used for beam design include timber, steel, and reinforced concrete.

Each material has unique material properties that make it suitable for different applications, and selecting the right one requires a thorough understanding of the structural demands, space constraints, and aesthetic goals of the project.

Engineers often struggle to select a material to begin beam design, and the material selected is important as it determines which standard the beam should be designed in accordance with. If engineers select the wrong beam material, then they can waste time designing a beam that is structurally inadequate, has size issues, or a beam that cannot be procured easily from a manufacturer or construction.

In this guide, we will explore the critical factors that influence material selection in the design of beams so that engineers can select the correct material type for their beam and ensure the time spent on their beam design is efficient. We will examine load requirements, space considerations, aesthetic preferences, and the complexities of combined actions. We will close out the discussion by detailing how modern software tools like ClearCalcs can simplify the design process.

Disclaimer: All beams must be designed by a suitably qualified engineer and the information below is intended to be an article for information only.

Table of contents:

• Understanding load requirements
• Space and dimension considerations
• Aesthetic considerations
• Combined actions and complex loads
• Case studies

Figure 1: Beam material selection is important in residential structural design (Reference)

Section 1: Understanding load requirements

Key terms defined

Axial loads: These are forces applied along the length of a beam, either in tension (pulling apart) or compression (pushing together). Axial loads are relatively rare in beam design compared to other load types but can be significant in certain structural elements like trusses or columns.

Bending moments: A bending moment is the reaction induced in a beam when an external force or moment is applied, causing the beam to bend. The magnitude of the bending moment varies along the length of the beam and is a critical factor in determining the beam's strength and deflection.

Shear forces: Shear forces act perpendicular to the length of the beam and are caused by external loads that try to slide one section of the beam relative to the other. Shear forces are particularly important near the supports of a beam.

Figure 2: Examples of Applied Moments on Beams (Reference)

Load capacities for common beam materials

Timber beams

Timber is one of the oldest construction materials and remains popular due to its sustainability, ease of use, and aesthetic appeal. However, its strength is generally lower than that of steel or concrete. The typical load capacity for a timber beam can vary significantly depending on the wood species, grade, and cross-sectional size.

Axial load capacity: Timber beams can handle axial loads in the range of 10-20 kN for typical residential applications. Higher-grade timber or engineered wood products can achieve greater capacities.

Bending moment capacity: Timber beams usually have a bending moment capacity ranging from 5 to 20 kNm, depending on the span and cross-sectional area.

Shear force capacity: The shear capacity of timber beams typically falls between 2 and 10 kN, depending on the cross-sectional size and type of wood.

Laminated Veneer Lumber (LVL) beams

LVL beams are engineered wood products made from multiple layers of thin wood veneers bonded together with adhesives. LVL offers higher strength and stiffness compared to traditional timber, making it suitable for larger spans and higher loads.

Axial load capacity: LVL beams can handle axial loads in the range of 20-40 kN, depending on the grade and cross-sectional area.

Bending moment capacity: LVL beams typically offer a bending moment capacity of 10 to 40 kNm.

Shear force capacity: The shear capacity for LVL beams generally ranges from 5 to 15 kN.

Steel beams

Steel is widely used in beam design due to its high strength-to-weight ratio, durability, and ability to withstand significant loads with relatively small cross-sectional areas. Steel beams are particularly suited for applications with large spans or high load requirements.

Axial load capacity: Steel beams can handle axial loads in excess of 100 kN, making them ideal for heavy-duty applications.

Bending moment capacity: Steel beams typically offer a bending moment capacity of 50 to 500 kNm, depending on the section size and shape (e.g., I-beams, H-beams).

Shear force capacity: The shear capacity of steel beams generally ranges from 20 to 100 kN, depending on the cross-sectional area.

Reinforced concrete beams

Reinforced concrete beams combine the compressive strength of concrete with the tensile strength of steel reinforcement. This combination makes them ideal for a wide range of applications, particularly in buildings where fire resistance and durability are critical.

Axial load capacity: Reinforced concrete beams can handle axial loads in the range of 50-200 kN, depending on the reinforcement and cross-sectional size.

Bending moment capacity: Reinforced concrete beams typically offer a bending moment capacity of 50 to 500 kNm.

Shear force capacity: The shear capacity of reinforced concrete beams generally ranges from 15 to 75 kN, depending on the size and amount of shear reinforcement (stirrups).

Load Type	Timber	LVL	Steel	Concrete
Axial	10-20kN	20-40kN	20-100kN	50-200kN
Bending	5-20kNm	10-40kNm	50-500kNm	50-500kNm
Shear	2-10kN	5-15kN	20-100kN	15-75kN

Table 1: A summary of typical load capacities for different beam materials

Note: the above ranges are guides only, not all beams in those materials will satisfy those requirements. The table is only intended to guide the early stages of beam design. True beam capacity has many more factors such as connection types, material grades, sectional area, span and more that must be considered for a conforming design.

Section 2: Space and dimension considerations

Space constraints and material choice

The available space in a building or structure can significantly influence the choice of beam material. In some cases, the need to minimize beam depth to preserve headroom or the desire to reduce the width of structural elements can drive the material selection process.

Timber and LVL beams: Timber and LVL beams tend to have larger cross-sectional dimensions compared to steel for the same load-bearing capacity. This makes them less suitable for spaces with tight height restrictions. However, they can be advantageous in wide, open spaces where deeper beams can be accommodated without compromising headroom.

Steel beams: Steel beams, with their high strength-to-weight ratio, can support large loads with smaller cross-sections, making them ideal for spaces with limited headroom or width constraints. For instance, in high-rise buildings where floor-to-floor height is limited, steel beams are often preferred for their compact size.

Reinforced concrete beams: Reinforced concrete beams require larger cross-sectional areas than steel but can be molded into various shapes, offering some flexibility in design, as they can be constructed in-situ. However, their larger dimensions might not be suitable for all projects, especially in retrofit scenarios where space is limited.

Size comparisons

When comparing the size of beams made from different materials, it's essential to consider the material's mechanical properties and the required load-bearing capacity. For example:

A timber beam supporting a 20 kN load over a 5-meter span might require a cross-section of 250x100 mm, whereas a steel beam might only need a cross-section of 150x50 mm.

It’s vital to discuss with the builder whether they have a preference on material type, as construction methodology can influence the material selection.

For example, if the builder is building a residential property, they may have a preference for timber members, which are lightweight and can be lifted in place without the need for a crane or mechanical plant which can be costly. They may also have supplier preferences that could mean that one particular material type is cheaper. The builder is usually the client of the structural engineer and it is important to provide a design that meets their needs.

Section 3: Aesthetic considerations

Visual impact of material selection

The material selected for a beam not only affects the structural performance but also contributes to the overall aesthetics of the building. Different materials offer unique visual qualities that can enhance or detract from the architectural intent.

Timber beams: Timber beams are often chosen for their natural appearance and warmth. They are commonly used in residential and hospitality projects where a rustic, traditional, or eco-friendly aesthetic is desired. Exposed timber beams can become a central design feature, adding character to the space. An example of a use case for a timber beam would be residential home with an open-plan living area featuring exposed timber beams might aim for a cozy, traditional aesthetic. The natural wood grain and warm tones of the timber contribute to a welcoming atmosphere.

Figure 3: Timber beams are commonly used in residential construction (Reference)

LVL beams: LVL beams, while still wooden, have a more uniform and engineered appearance compared to traditional timber. They are often used in modern or contemporary designs where a cleaner, more consistent look is desired. They are used to achieve the timber warmth aesthetic whilst providing higher strength than standard timber beams which means they can be used on spans larger than typical timber beams.

Figure 4: LVL beams are commonly used in large spans in residential buildings of low-rise commercial buildings (Reference)

Steel beams: Steel beams are typically used in industrial or minimalist designs. Their sleek, metallic finish can contribute to a high-tech or industrial aesthetic. Exposed steel beams are popular in loft-style apartments and commercial spaces where the structural elements are celebrated as part of the design. Steel beams are often used in modern office buildings and can be painted black or left in their natural finish, complementing other modern materials like glass and polished concrete.

Figure 5: Steel beams are commonly used in industrial buildings (Reference)

Reinforced concrete beams: Reinforced concrete beams are often hidden within the structure but can be exposed in certain designs to create a brutalist or industrial look. The rough, raw texture of concrete can add a sense of solidity and permanence to a space. Often reinforced concrete beams are clad with plasterboard for aesthetics.

Figure 6: Reinforced concrete beams are the strongest beams and commonly used in high-rise buildings or civil structures exposed to high loads and adverse weather conditions like bridges (Reference)

Section 4: Combined actions and complex loads

Introduction to combined actions

In many real-world scenarios, beams are subjected to multiple types of loads simultaneously, such as axial loads, bending moments, and shear forces. These combined actions can complicate the design process, as the interaction between different forces must be considered to ensure the beam's structural integrity.

Assessing combined load effects

To assess the impact of combined loads on a beam, engineers must calculate the resulting stresses and compare them to the material's allowable stress limits. The basic steps include:

1. Determine the individual loads: Calculate the axial load, bending moment, and shear force separately based on the applied loads and support conditions.
2. Calculate the resulting stresses: Use the relevant formulas to calculate the axial stress, bending stress, and shear stress in the beam.
3. Check for interaction effects: In some cases, the combined effect of axial stress and bending stress (or other combinations) may exceed the material's allowable limits. Interaction equations, such as those found in design codes, help assess these effects.

Material suitability for complex loads

Timber and LVL beams: Timber and LVL beams can handle combined actions but are generally more sensitive to high shear forces and bending moments. Additional considerations, such as lateral-torsional buckling (which timber performs poorly when subjected to), may be required when designing timber beams for complex loads.

Steel beams: Steel beams are well-suited for handling combined actions due to their high strength and ductility. They are particularly effective in scenarios where high bending moments and shear forces are present, such as in multi-story buildings or industrial structures.

Reinforced concrete beams: Reinforced concrete beams excel in handling combined actions, particularly when axial loads are combined with bending moments. The reinforcement can be tailored to resist specific load combinations, making concrete a versatile choice for complex loading scenarios.

Figure 7: In complex projects composite beams can be designed (Reference)

Section 5: Case studies

Case Study 1: Residential timber beam design

A residential project in a rural area required exposed beams for an open-plan living space. The architect wanted to maintain a rustic aesthetic while ensuring the beams could support the roof load.

Timber was chosen due to its natural appearance and the relatively light loads involved. The use of timber allowed for easy installation for the builder and provided the desired aesthetic without compromising structural integrity.

Case Study 2: Steel beam in an office building

In a 4 storey office building, the design team faced space constraints that required minimizing beam depth to maintain ceiling height.

Steel beams were chosen for their high strength-to-weight ratio and compact cross-sections. The beams had to support floor loads of 50 kN/m over a 10-meter span. The design incorporated 300x150 mm steel I-beams, which provided the necessary strength while keeping the overall structural depth to a minimum.

Case Study 3: Reinforced concrete beam in a parking garage

A 5 storey car park required beams that could support heavy vehicle loads and resist environmental conditions like moisture and temperature fluctuations.

Reinforced concrete was selected for its durability and fire resistance. The beams had to support a live load of 30 kN/m2 over a 7-meter span. The final design used 400x200 mm reinforced concrete beams with sufficient shear reinforcement to handle the combined actions of axial loads and bending moments.

How ClearCalcs simplifies beam design

The ClearCalcs free beam analysis calculator offers a user-friendly interface that makes it easy to perform beam analysis.

By following a simple three-step process, structural engineers can input key properties, loads, and obtain calculation summary outputs. This includes valuable data such as shear and moment diagrams, bending moments, shear forces, beam deflections, and more.

Figure 8: An example of summary outputs from a ClearCalcs beam analysis.

These outputs help engineers visualize and understand the behavior of the beam under different load conditions. A detailed explanation on how to use the ClearCalcs free beam analysis calculator can be found here.

By reviewing the summary outputs (shear force diagrams, bending moment diagrams), users can gauge an assessment of which material is likely going to be required based on the above guidance.

Then, the specific beam design calculators by material type and building standards can be referred to for detailed design. These calculators are specific to the relevant standards and specifications based on the jurisdiction where the design is being completed.

These calculators provide access to extensive member databases of timber, steel, and concrete products, allowing engineers to quickly find and compare different members and materials from suppliers that meet their design specifications. All designs are programmed to be built to the latest codes and standards, reducing the risk of non-compliance and improving the overall safety of the structure.

Even if you are designing a beam, for example, a timber beam, and find that you need to switch to a steel or concrete beam because all of the timber beams in the member selector tool do not have the capacity to resist the applied loads (as below), ClearCalcs has the ability to change materials.

Figure 9: An example of ClearCalcs member selector tool.

See a video example of how the change material functionality works. This ensures all your input parameters (such as span, loading and connection types) are transferred to the new beam design (steel or concrete) which saves lots of time in manual calculations.

It also allows engineers to quickly check for a more efficient design by changing material and not having to perform the entire calculations again, as this is automatically done in ClearCalcs to the relevant material standard.

Figure 10: ClearCalcs change material feature makes it easy to switch between material types for the same design specifications.

Conclusion

Choosing the best material for beam design is a complex decision that requires careful consideration of load requirements, space constraints, aesthetic goals, and the potential for combined actions. Timber, LVL, steel, and reinforced concrete each offer unique advantages and limitations, making them suitable for different types of projects.

By understanding the strengths and weaknesses of each material, engineers and architects can make informed decisions that enhance the safety, functionality, and visual appeal of their designs. Additionally, leveraging modern design tools like ClearCalcs can streamline the process, ensuring that the optimal material is selected for every application.

In conclusion, the right material choice can make all the difference in the success of a structural design. By considering all relevant factors and using advanced tools, professionals can create structures that are not only safe and functional but also aesthetically pleasing and efficient.

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