Box Culvert Sizes - What is available?

If you are currently involved in the construction or design of a culvert structure, it is important to understand the available sizes and customization options to meet your project's requirements. In this blog post, we will explore the standard sizing of culverts and provide you with the necessary information for a successful project.

In Australia, culvert sizes are typically specified as a Span x Height x Length, where the span and height dimensions represent the internal dimensions of the culvert and play a crucial role in determining the hydraulic flow capacity for drainage applications.

Manufacturers of box culverts in Australia adhere to the Australian Standard AS1597, which outlines a range of standard spans and height combinations. Australian Standard AS1597 is  split into two parts:

1. AS1597.1 - Small Culverts - Up to 1200mm Span
2. AS1597.2 - Large Culverts - Over 1200mm Span

To give you an idea, the following tables presents these sizes.

Small Culvert Sizes

*Note the orange highlight indicate sizes held in stock at Modcast.

Large Culvert Sizes

As you can see from the tables above, maximum culvert heights are set by the span.

Box Culvert Lengths

While culvert lengths may vary among manufacturers, the most common sizes are 1200mm and 2400mm long. Some manufacturers may offer culverts in lengths of 1220mm or 2440mm as well.

Longer culverts can reduce the required handling and install time compared to shorter lengths, however they will be heavier.

How do I know what size I need?

Depending on the complexity and stage of your project, box culvert sizes are typically specified by a civil or design engineer. The design engineer will consider various factors, including hydraulic flow requirements, headboard levels, fill profiles, and structure length. These details will be outlined in the civil design for your project. If you are a designer, this guide will provide you with the common sizes available for box culverts.

External Dimensions

It is worth noting that external culvert dimensions can vary significantly based on factors such as manufacturers, load classes, and exposure classifications. The thicknesses of elements like walls and crowns can be increased to accommodate heavier loads or provide additional reinforcing cover for specific applications.

You may wonder why external dimensions matter. While the overall dimensions of culverts may not be critical during the design phase, they become crucial when it comes to interfacing with other elements. For instance, wider culverts may require an increase in the base slab and rebates accordingly.

What can I customize?

In terms of customization, almost any dimension of a box culvert can be tailored to suit specific applications; however, it is important to note that customization costs may vary. Generally, culvert heights and lengths can be modified easily and cost-effectively, but changing spans can be expensive due to mold limitations. If you want more detailed information on customizing culverts, we recommend checking out this comprehensive guide.

Other Limitations

When evaluating culvert sizes, it is essential to take into account any limitations regarding weight and transport dimensions. This is especially important for large culverts, as certain combinations of sizes can exceed transport limits and the capacity of available lifting equipment for installation. To address weight limitations, it may be beneficial to produce shorter length units, such as ones that are 1200mm long instead of 2400mm long, and explore other design innovations that involve multiple parts.

About Modcast

In addition to a range of common small culverts held in stock, Modcast can manufacture the entire Australian Standard size range up to 4200mm span and beyond.

Do you need further help assessing the best size combinations for your project?  Talk to our expert team today.