Lacing bars are essential components in bolted steel construction, particularly in built-up compression members. These members often consist of two or more main components (like angles, channels, or plates) placed at a distance from each other and connected by lacing bars or battens.

Lacing Bars in Bolted Construction

Lacing bars play a crucial role in ensuring the structural integrity and stability of built-up compression members. Their primary functions include:

• To hold the components of the built-up section together, preventing their relative displacement.
• To resist the transverse shear force, which arises due to the applied loads and the slenderness of the compression member.
• To ensure that the entire built-up section behaves as a single, stiff unit, thereby increasing its overall buckling strength.

Proper design of lacing bars, including their dimensions and connections, is vital for the safe and efficient performance of the structure.

Minimum Width Requirements for Lacing Bars

The dimensions of lacing bars are specified by design codes to ensure they have adequate strength and stiffness. For bolted connections, the minimum width of lacing bars is directly related to the diameter of the bolts used for the connection.

According to standard design practices and codes (such as IS 800:2007, which is the Indian Standard for general construction in steel), the minimum width of lacing bars in bolted construction must be sufficient to accommodate the bolt and provide adequate edge distance and strength around the bolt hole.

Specifically, the minimum width of lacing bars is generally specified as a multiple of the nominal diameter of the end bolt. This ensures that there is enough material around the bolt hole to prevent tear-out or excessive deformation under load.

The code stipulates that the minimum width of lacing bars shall be 3 times the nominal diameter of the end bolt. This requirement helps in maintaining sufficient bearing and shear capacity at the bolt connections, preventing localized failure.

Let's denote:

• \(w\) as the minimum width of the lacing bar.
• \(\phi\) as the nominal diameter of the end bolt.

Then, the relationship can be expressed as:

\[w \ge 3 \times \phi\]

This minimum width ensures not only structural adequacy but also practical considerations for drilling and installation.

Code Provisions for Lacing Bar Design

While the minimum width is a critical dimension, other factors also govern the design of lacing bars. These include:

• Thickness: The thickness of flat lacing bars should not be less than \(\frac{1}{40}\) of its effective length for single lacing and \(\frac{1}{60}\) of its effective length for double lacing.
• Angle of Inclination: The angle of inclination of lacing bars with the longitudinal axis of the member should generally be between \(40^\circ\) and \(70^\circ\).
• Slenderness Ratio: The maximum slenderness ratio of the lacing bar itself should not exceed 145.
• Connection Details: Lacing bars are connected to the main components either by bolts or welds. The connections must be designed to transfer the lacing forces effectively.

Adhering to these code provisions ensures that the lacing system effectively carries the transverse shear and prevents the buckling of individual components of the built-up column, contributing to the overall stability and safety of the structure.