2. Design of Lacing and Battens

Lacing

Provides lateral stability by connecting the individual column elements in built-up columns.

Types: Single or double lacing, arranged diagonally.

Lacing is a crucial component in built-up columns as it helps provide lateral stability. In simpler terms, imagine a tall tower of blocks. If just one block is stacked over another, the whole tower can wobble or fall. But if we add diagonal bracing, it holds the blocks in place and prevents them from swaying. In built-up columns, lacing is designed to connect multiple pieces of steel, either in single or double arrangements, laid out diagonally, effectively stabilizing the structure from side-to-side forces.

Think of a collection of straws held together by rubber bands. If you pull the straws laterally, the rubber bands help resist the movement. Similarly, lacing acts like these rubber bands, ensuring the individual columns remain stable and don't buckle under pressure.

Design Guidelines:

Angle of lacing typically 40–70° with axis. Designed for transverse shear (usually 2.5% of axial load distributed among laces). Lacing members are designed as slender compression/tension members with appropriate slenderness limits.

When designing lacing, there are specific guidelines to follow to ensure it functions properly. The angle at which the lacing is positioned is important; a typical angle is between 40 and 70 degrees from the vertical axis. This positioning helps in effectively managing the forces acting on the laces. The laces are also designed to handle shear forces—these are forces that can cause parts of the structure to slide past each other. Generally, 2.5% of the axial load is distributed among the laces to balance the load. Also, lacing must be designed as slender members to ensure they can handle both tension (pulling forces) and compression (pushing forces) safely, within established slenderness limits.

Imagine you have a triangle made of spaghetti strands. If you pull the corners of the triangle, the angle at which the spaghetti connects has a significant effect on how stable the triangle remains. If the angles are too wide or too narrow, the triangle might collapse. This is similar to the guidelines for lacing, where specific angles and designs ensure the stability and strength of the columns.

Battens

Flat plates placed perpendicular to the axis to connect built-up sections.

Battens are flat plates that play an essential role in connecting different sections of a built-up column. They are positioned perpendicular to the main axis of the column, acting as a bridge between the individual steel elements. Think of battens as the cross-beams that help provide structural integrity by connecting the vertical columns together, ensuring they function as a single, stable unit rather than just a series of separate pieces.

Consider a bridge made of individual planks. Each plank represents a section of the column, and the battens function like the cross bracing that connects the planks. If you remove the cross braces, the structure becomes wobbly. But with battens connecting the sections, the entire formation becomes stable and secure.

Design Guidelines:

Minimum of three battens in the column length. Thickness and connections designed to carry transverse shear (typically 2.5% of axial load). Battens spaced to limit slenderness of individual component sections.

The design of battens follows clear guidelines as well. To ensure they effectively connect the column sections, a minimum of three battens must be distributed along the length of the column. This ensures adequate support and structural integrity. Each batten's thickness and the way it is connected must also be considered, as these components need to safely handle transverse shear forces—similar to how lacing does. The spacing of the battens is also critical as it must be designed to limit the slenderness of the sections, ensuring they do not buckle under loads.

Imagine stacking books on a shelf. If you stack too many books with wide gaps in between, the books may lean and fall. However, if you place enough bookends (similar to battens) closely enough together to keep the books upright, the entire stack remains stable. That’s the idea behind placing and sizing battens properly—they help keep the entire column assembly stable.

Parameter Lacing Batten Orientation Diagonal Perpendicular Function Prevent buckling, transfer shear Prevent buckling, transfer shear Common Use Tall/lighter build-ups Shorter/stockier build-ups

Lacing and battens serve similar purposes in providing stability and transferring loads, but they differ in orientation and application. Lacing is arranged diagonally and is commonly used in taller, lighter structures, while battens are placed perpendicular and are typically utilized in shorter or stockier configurations. Both work to prevent buckling and transfer shear forces, highlighting their critical roles in ensuring the safety and efficacy of built-up columns.

Think of lacing as diagonal strapping on a tall, standing tower of cards, keeping it from swaying. In contrast, battens would be like horizontal supports under a stack of heavy novels, ensuring it doesn’t topple over. Both are necessary for stability, but they are applied in different ways depending on the structure's needs.

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