I-Beams

I-Beams offer a high-strength, long-span structural timber beam which can be used for residential and commercial building applications.

Overview

I-Beams are high-strength, long-span structural timber beams which are used for residential and commercial applications. They offer exceptional straightness, uniform depth and dimensional stability.

Economical to produce, the I-Beam is made from a combination of timber products. The top and bottom flanges - which make the distinct ‘I' shape, - are made from material with a high tension strength such as LVL or even graded solid timber. The flanges are separated by a vertical web, usually manufactured from structural plywood or oriented strand board (OSB). The centre of the section serves to transmit shear stresses, so a material with good shear properties is required.

The web and flanges create a lightweight beam which is both strong and durable. The flanges resist bending, tension and compressive stresses, utilising LVL's enhanced strength and stiffness properties. The web serves to transmit the shear stresses, relying on plywood's panel shear capacity and dimensional stability.

I-Beams are generally not considered to be an appearance product due to the visibility of gluelines but can be finished accordingly for architectural and design applications.

Properties

Durability

I-Beams are not suitable for weather-exposed applications, however short term exposure during construction is acceptable.

I-Beams are generally manufactured from Durability Class 4 (non-durable) softwoods and, therefore, if not preservative treated, are not termite resistant. Most I-Beams, can be made termite resistant by preservative treatment to H2 level usually with Light Organic Solvent Preservative.

Sizes

Refer to individual manufacturer's design guidelines and specifications for available sizes. The size of I-Beams vary in both depth and width between individual manufacturers.

I-Beams that are produced as ‘stock' items, are straight, with no camber and are available in lengths up to 15 m but may be less from some manufacturers. Availability of cambered beams should be checked with individual manufacturers.

Grades

Generally, I-Beams do not come in different grades. Each manufacturer has designed and tested their range of beam sizes to determine the design properties. This engineering data is available from the relevant manufacturer, together with span tables for common uses.

Regulations / Standards & Codes

Manufacturers maintain quality control programs to ensure manufacturing standards are maintained and on-going testing in accordance with AS/NZ 4063 Structural Products - Strength & Stiffness Evaluation ensures that design properties continue to meet the certified properties for the product.

The EWPAA also has a product certification scheme with includes LVL/plywood I-Beams in accordance with AS/NZS 2269 Plywood - Structural, AS/NZS 4357 Structural Laminated Veneer Lumber and AS/NZS 1720.1 Timber Structures - Design Methods.


*Disclaimer : The species mentioned here are just a guide and for specific information refer to Suppliers Section

Description

Fire Resistance

Fire resistance in the form of a fire rating can only be applied to a total building element incorporating an I-Beam. A product can not be fire rated and alone, I-Beams have little fire resistance.

I-Beams can be enclosed in fire rated materials such as plasterboard to achieve a system Fire Resistance Level (FRL).

For more information about fire resistance regulations please refer to C1.10 Fire Hazard Properties within the Building Code of Australia (BCA).

Adhesives

As I-beams are used for structural applications they are manufactured with a Type A phenolic adhesive.

Treatments

As I-Beams are proprietary products, treatments will be dependant on manufacturer.

I-Beams are not recommended for external weather exposed applications, so I-Beam treatments would be more to protect against termites and borers.

Design/Engineering Considerations

I-Beams provide a lightweight, yet strong and durable product. I-Beams are ideal for floor joists in residential applications as they are easy to install and provide floors that are more uniform.

I-Beams can also be used as rafters, however, some restraint needs to be incorporated to resist buckling when uplift forces place compression in the lower (unsupported) flange.

For commercial applications, I-Beams can be used as purlins, lintels and even as bridge girders.

Strength to weight ratio makes I-Beams ideal for long spans and offer spanning distances of up to 12 m. The ability to span further offers more flexible design options and may provide an opportunity for I-Beams to be used in place of piers, floor bearers and loadbearing walls. 

I-Beams have the same logic as "I" shaped steel beams. The higher flexural stresses on the top and bottom of the section are matched by high strength timber at those places, and in the centre of the section where the flexural stresses are low, there is a small cross section of material. The result is members with high flexural capacity, good flexural and shear stiffness that are remarkably light in weight.

The shear force per unit length can be found from the beam shear divided by the web depth.

Handling, Storage & Protection

I-Beams are not suitable for weather exposed applications, however short term exposure during construction is not detrimental.

I-Beams should not be handled or stacked flat. I-Beams have been engineered to function in the vertical orientation and therefore should be handled and stacked in that position. Care should be taken to ensure that webs and flanges are not damaged during transport and handling.

Protection - on-site storage
I-Beams should be stacked vertically and adequately supported level, clear of the ground. If covered storage is not available, the I-Beams should be covered with a suitable non-transparent plastic or tarpaulins. Cover should allow good air circulation around and under the I-Beams.

Protection - fixed in position
While I-Beams are not suitable for long-term weather exposure, short-term exposure during the construction process does not affect the I-Beams performance. Should construction be delayed, suitable protection from sun and rain needs to be provided.

Note: Not all I-Beams are the same! Where a design is based on a particular size and brand of I-Beam, substitution with another brand should not be made without engineering advice.

Cutting Holes & Notches

I-Beams have a high shear capacity, which means that holes can be cut into the webs to enable conduits, wiring and plumbing to be passed through the deep sections.

Round, square or rectangular holes can easily be cut in the web to accommodate services such as waste or utility pipes. Some manufacturers include perforated knockouts along the length of the member. Generally, the larger the hole, the further the distance from the bearing is required.

The allowable size and position of holes and notches will vary between manufacturers and the different member sizes. Reference should always be made to the manufacturers allowable practices.

Cutting into or notching of flanges should not be done, although some manufacturers permit small (12 mm max) notches in the bottom flange where it is supported on a flange of a universal beam.

Bevel cuts must not extend beyond the inside face of the members support.

Workability

I-Beams are lightweight and easy to work with due to their exception straightness, uniform depth and dimensional stability. Holes can easily be cut in the web for the placement of services.

Joints & Connectors

There are many and varied structural configurations possible when using I-Beams.

For most joints, special proprietary light metal connectors are available and each I-Beam manufacturer defines how these are to be used with their products.

Where connectors do not laterally support both the top and bottom flanges, web stiffeners are required.

At supports, it is essential that minimum bearing requirements be achieved. This will vary with the different beams.

Non-corroding fasteners, which do not cause splitting during installation, should be used and the use of morticed joints should be minimal.

Damp proof membranes should be used where I-beams are in contact with masonry.

Finishes

I-Beams are not appearance products, with gluelines often visible, both in the flanges and webs. Exposed I-Beams can be coated with an opaque finish to improve their aesthetic appearance.

Applications

  • Framing

    Since people began building simple shelters, wooden framing has played an important role in shaping structures of many kinds. One of the most popular types of wooden framing is known as lightweight timber construction.

Case Studies

All Comments (0)

Sign In or Sign Up now to post a comment!