Are outrigger necessary for crawler crane?
In the heavy-duty crane industry, a common question is, “Do cranes need outriggers?” For crawler cranes, the answer is generally no. Their unique design allows them to operate stably without a crane outrigger in most conditions, making them a standout in complex terrain and large-scale projects.
Design Advantages of Crawler Cranes
Crawler cranes utilize a crawler chassis with a tank-like running mechanism, giving them unique stability. Unlike wheeled cranes that rely on outriggers, crawler cranes ensure safe operation through the following:
Low ground pressure: The crawlers distribute the machine’s weight over a larger area, adapting to soft or uneven terrain.
Integrated counterweight system: Adjustable counterweights dynamically balance load torque.
Loaded travel capability: Capable of 360° slewing and slow movement while loaded.
When is Auxiliary Stabilization Still Necessary?
While the crawler chassis of a crawler crane provides a wide support surface, its stability is not unlimited. When the overturning moment generated by external factors approaches or exceeds the crane’s inherent stabilizing moment, supplementary stabilization measures must be implemented. The following three situations are particularly critical:
1. Dealing with Extreme Loads: Approaching or Reaching the Rated Lifting Limit
This is the operating condition most in need of supplementary stabilization measures. Crane load ratings are calculated based on specific configurations and ideally flat, solid foundations, and include a certain safety factor. However, when loads approach the limit, any slight uncertainty can pose a risk.
Core Risk:
The overturning moment increases dramatically. Overturning moment = load weight × operating radius. Under extreme loads, the crane’s center of gravity shifts toward the load, significantly reducing the overall stability margin.
The function of the Crane Outrigger:
Greatly increasing the support span: The outriggers extend outward, significantly increasing the support profile. Based on the principle of leverage, this significantly increases the lever arm resisting overturning, thereby generating a greater stabilizing moment.
Operational Guidelines:
Before undertaking such a lift, a detailed lifting plan calculation and risk assessment must be conducted. The plan typically specifies the use of outriggers and the specifications of the roadbed box or pad to be laid beneath them.
2. Special or High-Precision Lifting Operations
For certain operations requiring extremely high stability and precision, outriggers may be used, even if the load is not at its limit.
Precision installation of heavy equipment: For example, installation of large generator rotors or precision machine tools requires extremely smooth lifting, where even the slightest movement can have serious consequences. Outriggers can transform the crane into a nearly “rigid” platform, minimizing movement.
Tower cranes, or those with extra-long booms and jibs, are particularly susceptible to instability in these applications due to their high center of gravity and large wind-exposed areas. The use of outriggers can significantly improve wind resistance and overall stability.
3. Working on Harsh or Uneven Ground Conditions
Situations:
Steep slope operations: When working on a sloped site, the equipment is tilted to match the slope. Using outriggers can level the crane body, ensuring it operates in a horizontal position and that all forces meet design specifications. This prevents tilting, which could reduce actual lifting capacity and increase the risk of overturning.
Extremely soft or uneven ground: Although the tracks can distribute pressure, if the foundation’s bearing capacity is severely insufficient (such as newly backfilled silt), there’s still a risk of slow subsidence. Pads or subgrade boxes under the outriggers can further distribute the pressure to deeper, more solid soil layers, preventing equipment settling during lifting.
Core Risk:
Shifted the center of gravity and reduced the effective stable surface area. When a crane is parked on a slope, its overall center of gravity shifts downhill. Simultaneously, the effective support area of
Purpose of Crane Outrigger:
Leveling the Crane Body: The primary function of the outriggers is to adjust the crane body to a completely horizontal position. This ensures that the crane’s stability in all directions meets the load table data. All lifting capacity calculations are performed with the crane level.
Compensating for Slope: Even without fully leveling, extending, and shimming the outriggers on the downside of the slope effectively increases the support area and lever arm on the downside, directly counteracting the additional overturning moment caused by the slope.
Safety Tip:
Never operate on slopes exceeding those specified in the manual. Even within the permitted slope, use an incline meter for accurate measurement and use shims under the outriggers or crawler tracks to ensure the crane is level.
4. Regulations or Manufacturer’s Requirements
Safety regulations in certain countries or regions, or the operating manual of a specific crawler crane model, may mandate the use of outriggers under specific operating conditions (e.g., certain wind speeds or boom length combinations).
Summary:
Although crawler cranes, due to their crawler undercarriage design, can operate efficiently without outriggers in most operating conditions, safety is always a non-negotiable bottom line. When dealing with critical scenarios such as extreme loads, high-precision lifting, poor foundations, and regulatory requirements, actively using a crane outrigger is a necessary measure to prevent the risk of overturning and ensure operational safety.
