CAPABILITY OF THE CENTRE OF GRAVITY (COG) TO CHANGE / SHIFT DURING TANDEM LIFTING OPERATIONS

The center of gravity (COG) in a tandem lifting operation can change due to several factors. This can impact the stability and load distribution between the cranes. Here’s why and how it might happen:

1. Load Movement

If the load is not rigid and shifts during the lift, the COG of the system changes. External forces such as wind or vibrations can cause the load to sway or rotate, altering the COG.

2. Asymmetrical Lifting

If the cranes do not lift the load evenly or at the same rate, it can lead to a shift in the COG. Misalignment or differing hoisting speeds can cause one crane to bear more weight than the other.

3. Weight Distribution of the Load

For irregularly shaped or non-uniform loads, the initial estimation of the COG might be incorrect. Changes in how the load is rigged or secured can also affect its weight distribution.

4. Dynamic Effects

During lifting, movements such as acceleration, deceleration, or slewing can temporarily shift the COG.

5. Ground Conditions

Uneven or unstable ground under one of the cranes can cause tilting, which may indirectly affect the overall COG.

This is the mitigation steps to minimal and avoid the COG shifting during tandem lifting operations

Pre-lift Planning: Conduct a detailed lift study to determine the load's exact COG and ensure cranes are positioned correctly.

Load Monitoring: Use load cells and sensors to monitor real-time weight distribution on each crane.

Coordination: Ensure synchronized operation of both cranes through proper communication and training.

Stability Check: Verify the ground conditions and crane outriggers for stability before the lift.

this is very serious consideration need to monitor, If not properly managed, a shifting COG during tandem lifting can lead to uneven load distribution, crane instability, or even failure.

Mathematical / Calculation Prove for The Shifting COG During Lifting Operations

To demonstrate how the center of gravity (COG) can shift during a tandem lift with two mobile cranes, let’s consider an example calculation.

Scenario:

Two mobile cranes (Crane A and Crane B) are performing a tandem lift of a 20-ton load. The initial load distribution is evenly split, with each crane lifting 10 tons. The load’s COG is initially at the center of the load. A shift in the load occurs, moving the COG 1 meter towards Crane A.

Assumptions:

The load is rigid but shifts dynamically. Each crane has sufficient lifting capacity and boom angles are consistent. The total distance between the cranes is 10 meters. The original COG is at the midpoint (5 meters from each crane).

Calculation Steps:

Original Distribution (Even Load):

Total Load (W): 20 tons

1. Load Distribution:

Crane A: WA=10 tons

Crane B: WB=10 tons

2. New Load Distribution (COG Shift):

The COG shifts 1 meter toward Crane A. The new distances of the COG from the cranes are:

Distance from Crane A (dA): 5?1=4 m

Distance from Crane B (dB): 5+1=6 m

Using the principle of moments:

WA× dA = WB × dB

Substituting:

WA×4=WB×6

3. Solve for WA and WB:

Total Load: W=WA+WB

Substituting WB=W?WA×4=(20?WA)×6

Expand and simplify:

4WA=120?6WA

10WA=120

WA=12 tons, WB=20?12=8 tons

4. Results:

After the COG shift, the load distribution is:

Crane A: 12 tons

Crane B: 8 tons

Implications:

The COG shift caused an imbalance in the load distribution. Crane A now bears a higher load (12 tons) than initially planned (10 tons). This could exceed its safe lifting capacity if not accounted for. The structural stability of both cranes needs to be re-evaluated for the new load distribution.

Conclusion:

This calculation shows that a 1-meter COG shift results in a significant change in load distribution. Proper monitoring and planning are critical to prevent accidents during tandem lifting operations.