Hi there! I’m Russell McCarthy, the lead building inspector and founder of WA Building Inspections Perth. In this article, I’m going to talk about beam bearing length—a crucial aspect of construction that ensures the stability and safety of your structure. Whether you’re dealing with steel or timber beams, it’s essential to get the bearing length right; somethig that the builder of this house in the PCI inspection video below clearly failed to do.

What is Beam Bearing Length?

Beam bearing length is the portion of the beam that rests on a support, like a wall or column. This length is crucial because it helps distribute the load carried by the beam to the supports, ensuring your structure can handle the intended loads without any issues.

Minimum Bearing Length

The minimum bearing length is the shortest length over which the beam must rest on its support to safely transfer the load without causing undue stress or deformation.

As I mentioned in the video, “So the national construction codes state that no beam, not some beams, but no beam can be bearing down on something less than 150 millimeters?”

Calculating Minimum Bearing Length

Here’s a simple step-by-step guide to calculate the minimum bearing length:

1. Determine the Load: Calculate the total load the beam will carry.
2. Material Strength: Identify the material’s allowable stress.
3. Support Conditions: Assess the support’s capacity to bear the load.
4. Apply Formula: Use engineering formulas to calculate the bearing length.

For example, for a timber beam carrying a uniform load of 5000 N/m over a span of 6 meters, with an allowable stress of 10 N/mm², the minimum bearing length can be calculated as follows:

$\text{Minimum Bearing Length} = \frac{\text{Total Load}}{\text{Allowable Stress} \times \text{Width of Beam}}$

Minimum Bearing Length=Allowable Stress×Width of BeamTotal Load​

Bearing Length of Steel Beam

Steel beams are commonly used in construction due to their strength and durability. Ensuring the correct bearing length is vital to maintain structural integrity.

As I highlighted in the video, “Now it is pretty common that garage piers are only 90 millimeters, which I totally understand, but let’s take a look at this one because sometimes things get a little bit wrong, and sometimes they get a lot wrong.”

Bearing Length of Timber Beam

Timber beams are less dense than steel, requiring different calculation methods to ensure adequate support.

In the video, I pointed out, “Then we’ve got another beam, same problem, and then we go along, we go along, and this beam, same problem. But also collects another beam with way less than 90 mils, just a whole bunch of steel members that are welded together, and it’ll probably be okay once the engineer approves it, but remember that value is supposed to be 150 mil.“

Comparison of Steel and Timber Beam Bearing Lengths

Differences:

• Material Strength: Steel is stronger, allowing for shorter bearing lengths.
• Weight: Timber beams are lighter but may require longer bearing lengths.

Similarities:

• Both require accurate calculations to ensure safety and structural integrity.

Factors Affecting Beam Bearing Length

Several factors can influence the required bearing length:

1. Load Distribution: Uniform versus point loads.
2. Material Strength: Different materials require different bearing lengths.
3. Structural Design: Overall design impacts bearing length requirements.

Importance of Accurate Bearing Length Calculations

Accurate calculations are crucial for:

• Safety: Prevents structural failures.
• Structural Integrity: Maintains the building’s stability. p.s. check out an example of very poor structural integrity in the video of a recent new build inspection in Midland where the lengths of this builders dodginess knew no bounds.

Common Mistakes in Bearing Length Calculations

Common mistakes include:

• Ignoring Load Types: Different loads require different calculations.
• Incorrect Material Properties: Using wrong values for material strength.
• Oversimplification: Skipping steps in the calculation process.

From the video: “That top member there is 35 mil. This one here is an off-cut of an LVL and has been measured at 50 mil, and also continues to support other loads, so sorry about the unclear image. So it’s one thing that they can’t achieve 150. It’s another thing that they had the ability to, at the very least, achieve 90 mil bearing.”

How to Avoid Them: Double-check calculations, use correct values, and follow all steps meticulously.

Advanced Techniques for Bearing Length Calculation

Software Tools: Utilise engineering software for precise calculations. Engineering Methods: Advanced methods such as finite element analysis.

Regulatory Standards and Codes

In Australia, the standards for beam bearing length are dictated by several regulations and codes of practice to ensure the structural integrity and safety of buildings. One of the key documents is the Australian Standard AS 4100-1998, which covers the design of steel structures. This standard provides guidelines for the minimum bearing length requirements based on the type of material, the load conditions, and the support structure.

Key Points of Australian Standards for Beam Bearing Length

1. Material-Specific Requirements:
   • For steel beams, AS 4100 specifies that the bearing length should be sufficient to prevent local crushing of the support and to distribute the load evenly.
   • For timber beams, standards such as AS 1720.1 provide similar guidelines, ensuring the bearing length is adequate to prevent excessive deformation or failure.
2. Load Considerations:
   • The bearing length must account for the maximum loads the beam will experience during its lifetime, including live loads (e.g., people, furniture) and dead loads (e.g., the weight of the structure itself).
   • Special considerations are given for dynamic loads and point loads, which can affect the distribution of stress on the supports.
3. Support Conditions:
   • The type of support (e.g., concrete, masonry, timber) significantly influences the required bearing length. Each material has different strength and deformation characteristics, which must be considered in the design.
   • For concrete supports, standards such as AS 3600-2018 (Concrete Structures) provide additional guidelines on how the bearing length should be calculated to prevent local failure.
4. Safety Margins:
   • Australian standards emphasize the inclusion of safety factors in the design process. These factors account for potential variations in material properties, construction tolerances, and unforeseen load conditions.
   • The standards ensure that even under the worst-case scenarios, the bearing length will be sufficient to maintain the integrity of the structure.

For more detailed insights on regulatory standards, check out AS4349.1: Understanding the Basics of Inspection of Buildings – A Comprehensive Guide.

Practical Tips for Ensuring Correct Bearing Length

• Best Practices: Follow industry standards and guidelines.
• Quality Assurance: Regularly check and verify calculations.

As I noted in the video, “So it’s one thing that they can’t achieve 150. It’s another thing that they had the ability to, at the very least, achieve 90 mil bearing, but to do this and this and on the other side, not so much that side, but there, I don’t get it. I don’t understand why these builders are so why they are struggling with the most minor of concepts.”

My Final Say

Understanding and accurately calculating beam bearing length is crucial in construction. By following the outlined steps and considerations, you can ensure the safety and stability of your structures. Remember, whether you’re working with steel or timber, precise calculations are the foundation of any successful building project.

For more information about comprehensive building inspections across Perth, visit our WA Building Inspections Perth pages:

1) WA Building Inspections Perth

2) WA Building Inspections Rockingham to Mandurah

 3) WA Building Inspections Midland

FAQs About Beam Bearing Length

What is the bearing length of a beam?

The bearing length of a beam is the portion of the beam that rests on a support, distributing the load safely to the structure.

How do you calculate the bearing length of a steel beam?

Calculate the load on the beam, determine the material’s allowable stress, assess the support conditions, and apply the appropriate engineering formula.

What factors influence the minimum bearing length?

Factors include the load type, beam material, and support conditions.

Why is accurate bearing length important?

Accurate bearing length ensures the safety and structural integrity of the building, preventing potential failures.

Can software help in calculating beam bearing length?

Yes, engineering software tools can provide precise calculations, enhancing accuracy and efficiency.