What Is a Haunch in Construction: Essential Insights and Uses

June 12, 2024

Portal frames use haunched connections at both the apex (rafter to rafter) and eaves (rafter to column). The haunch is an effective method to locally increase the capacity of the rafter at points of highest loading.


Design and Construction of Haunch

Haunches are typically cut from the rafter section itself. They usually extend for approximately 10 percent of the span at the eaves. This extension is crucial in enhancing the load-bearing capacity at crucial points.

Materials

In the construction of haunches, the use of materials directly cut from the rafter ensures consistency and structural integrity. This approach saves on additional materials and ensures a seamless transition in load distribution.

"First haunch install 2" by VIUDeepBay is licensed under CC BY 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/2.0/.

Extent of Haunch

The typical length of a haunch is around 10 percent of the span. This dimension helps to control and distribute the concentrated loads effectively.

Eaves Connection

The connection at the eaves, where the haunched rafter joins the column, is usually facilitated by an end plate. Due to the high load transferred to the column at this connection point, additional measures are necessary to maintain structural stability.

Method of Connection

An end plate is commonly used to securely join the haunched rafter to the column, ensuring a stable and robust connection that can handle the various forces acting on the structure.

"First haunch install 1" by VIUDeepBay is licensed under CC BY 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/2.0/.

Loading and Stability

The loads transferred to the column at the eaves connection are significant. Additional structural measures, such as stiffeners, are often required to prevent local buckling and ensure overall stability.

Column Reinforcement

Adding stiffeners in the web of the column opposite the flange of the haunch is crucial. These stiffeners prevent local buckling under high load conditions, thereby enhancing the structural integrity of the portal frame.

Stiffeners

Stiffeners are structural elements added to the column to counteract the high stress and potential buckling caused by the load transferred from the haunched rafter.

Purpose of Stiffeners

The primary function of stiffeners is to maintain the structural stability of the column under high load conditions, ensuring safety and durability.

In summary, portal frames with haunched connections are a vital component in modern construction. They offer enhanced load distribution and structural stability, especially at points of highest loading such as the eaves and apex. Proper design and construction, including the use of end plates and stiffeners, are essential to prevent structural failures and ensure the longevity of the building. By understanding these key elements, engineers and builders can effectively utilize haunched connections to create stable and robust structures.

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