Installation issue of vehicle hoist and expansion joints

"A strip cut into a concrete slab, often called a control joint, contraction joint, or, locally, an expansion joint, is a deliberate cut made in the concrete to manage cracking. These cuts are strategically placed and timed to encourage cracking to occur along those specific lines rather than randomly across the slab."

A heavy-duty blue two-post car lift stands ready for use in a spacious, organized automotive workshop.

This helps minimise unsightly cracks and maintain the overall appearance of the concrete surface.

Purpose:

Concrete shrinks as it cures, and this shrinkage can cause cracking. Control joints are designed to allow these cracks to form along predetermined lines, preventing random cracks that could damage the concrete or affect its structural integrity.

Placement and Spacing:

The placement and spacing of control joints depend on the slab thickness, the concrete type, and the overall design requirements.

Timing:

Control joints are usually cut within a few hours of pouring, when the concrete has hardened enough to support the cut but is still relatively soft.

Cutting Method:

Control joints can be created using a saw, a grooving tool, or by placing plastic strips into the wet concrete.

Sealing:

After the control joints are created, they are typically sealed to prevent moisture from entering and causing further damage.

Mounting Close to Joints

In essence, control joints are a crucial part of concrete construction, helping to control cracking and maintain the structural integrity and appearance of the concrete.

It’s generally best to avoid drilling or mounting objects directly onto a contraction joint in concrete, as it can weaken the joint and potentially cause cracking or movement.

If you need to mount something, try to position it at least 2 inches (50mm) away from the joint, or consider using a different attachment method. The depth, diameter and applied load on the anchor point could dictate the required minimum distance above.

Why avoid drilling/mounting directly on contraction joints?

Weakened Structure:

Contraction joints are designed to allow concrete to shrink and expand without causing cracks in the main slab. Drilling through or mounting directly onto a joint can weaken it, potentially leading to premature cracking or movement.

Stress Concentration:

The joint itself is a point of stress concentration in the concrete. Adding the weight or force of a mounted object can exacerbate this stress, increasing the likelihood of cracking.

Disrupting Joint Function:

Contraction joints are essential for controlling cracking in concrete slabs. If you disrupt the joint, you can shift where cracks will occur and potentially create uncontrolled cracks elsewhere.

Offset the Mounting Point:

If possible, position the mounting point a few inches (or more, depending on the situation) away from the joint. This will allow the joint to move without being directly impacted by the mounting.

Use a Different Mounting Method:

Not Applicable

Reinforce the Slab:

If the area around the joint needs to support a heavy load, you might consider reinforcing the slab with additional steel or concrete to ensure stability.

Consult an Engineer:

In some cases, especially for critical installations or high-load applications, it’s best to consult a structural engineer to determine the most appropriate way to attach your object without compromising the integrity of the concrete slab. Over the years, I have read up and investigated this issue many times. Some installers/OEMs have spoken about distances of up to 400mm, but we all know that the latter is not practical due to wasted space in the already overcrowded workshop.

1. RAV – No expansion joints to break the continuity of the upper reinforcement.

2. Nussbaum - If there are defects (cracks or hairline cracks) in the zone of influence Ø200 mm, the foundation cannot be used to install the lift on it.

3. Rotary – ANSI minimum distance to edge = 114mm.

4. Stertil Koni - The minimum distance from the anchor to the edge of the concrete slab is 150 mm.

5. A good rule of thumb is the distance from the edge of a slab should be at least 6 to 8 times the diameter of the hole drilled. So 20mm x 8 = 160mm.

6. Many OEM manuals do not indicate a minimum distance but cover themselves by clearly indicating that an engineer needs to be consulted to verify concrete strength and positioning points of the machine.

Concrete thickness, strength and baseplate width and sizes will also affect the required distance.

Would the 150mm average derived from the mention above be a sufficient distance?

While the 150mm average seems reasonable in many scenarios, it remains crucial to consider the specific dynamics of each installation. Factors such as localised stresses, variations in slab composition, and the type of machinery being anchored must all be evaluated. Furthermore, consulting with experienced structural engineers ensures compliance with all safety regulations, especially in high-risk zones such as workshops with heavy equipment. By prioritising precision in placement, not only can the integrity of the concrete be preserved, but the overall functionality and durability of the installation can be optimised.

More input is not only welcome but also requested.

LEEASA,

+27 (0) 82 859 7384,

gert@leeasa.co.za,

www.leeasa.co.za