The static load test shall be carried out according to the following procedures and requirements.
- Park the クレーン at the column.
- 初め, start the hoisting mechanism to conduct no-load lifting and lowering operations, and make the trolley run back and forth along the whole journey. This no-load trial operation shall be carried out no less than three times, and there should be no abnormal phenomena.
- Park the trolley in the middle of the crane span, gradually apply loads to conduct the hoisting test until the rated load of 50t is reached. Then, make the trolley run back and forth several times along the whole bridge girder travel. There should be no abnormal phenomena in all parts. After removing the load, there should be no abnormal phenomena in the bridge girder structure.
- Park the trolley in the middle of the crane span, lift the 62.5t load without impact, and suspend it at a height of 200mm above the ground for no less than 10 minutes. There should be no instability phenomenon. After removing the load, drive the trolley to the end of the span and inspect the metal structure of the クレーン bridge girder. There should be no defects such as cracks, weld cracking, paint peeling, or other damages or looseness that affect safety. This test shall not exceed three times, and there should be no permanent deformation in the third test. Measure the actual upward camber of the main girder, which should be greater than 0.7S/1000mm = 9.45mm (where S is the crane track span).
- Inspect the static stiffness of the crane (the downward deflection of the main girder). Drive the trolley to the middle of the bridge girder, lift a 50t load to a height of 200mm above the ground. After the crane and the load are stationary, measure the upward camber value. The difference between this value and the result of item 4 is the static stiffness of the crane. The allowable value of the static stiffness should be less than S/700 (mm).
When it comes to crane safety, static load tests play a pivotal role. These tests are designed to mimic the real-world stresses that a crane will endure during its operational lifespan, but in a controlled environment. Let’s delve deeper into each step of this crucial testing process.
Regarding the initial positioning in step 1, parking the クレーン at the column is not just a simple placement. The column’s position is often chosen because it provides a stable and known reference point. This stability is essential as any slight movement of the crane during the test could lead to inaccurate readings and misinterpretations of the crane’s performance. It also allows for easy access to power sources and control systems, facilitating the smooth progression of subsequent test steps.
The no-load trial in step 2 serves multiple purposes. By running the hoisting mechanism and trolley multiple times without any load, engineers can check for any mechanical hitches right from the start. It helps in identifying issues like misaligned gears, uneven tracks, or faulty electrical connections that could cause problems once the crane is under load. This step is like a pre-flight check for an aircraft; it gives an initial thumbs-up or a heads-up about potential problems.
As we move on to step 3, the gradual application of load is a carefully orchestrated process. Starting from zero and ramping up to 50t mimics how a crane would be used in a real construction or industrial scenario. Each increment of load tests the integrity of different components, from the hoisting cables to the bridge girder’s load-bearing capacity. The full-span runs of the trolley further stress-test the overall structure, ensuring that all parts work in harmony under this standard load.
Step 4 is where the real stress-testing intensifies. Lifting a 62.5t load, which is above the rated load, is a way to push the crane to its limits in a safe, test environment. The 200mm suspension height and 10-minute hold time are carefully selected parameters. This height is sufficient to isolate the crane from any ground interference while still being manageable in case of an emergency. The 10-minute hold checks for any slow-developing issues like gradual deformation or stress relaxation in the metal structure. And the subsequent inspections for cracks, weld failures, and other defects are crucial for ensuring long-term safety.
ついに, step 5 focuses on the static stiffness, a key indicator of a crane’s structural integrity. Measuring the upward camber under different load conditions and calculating the difference gives engineers a quantitative value to compare against industry standards. A static stiffness within the allowed limit, less than S/700 (mm), means that the crane can resist deflections well, which is vital for accurate and safe load handling during actual operations.
さらに, in modern crane manufacturing, data from these static load tests are often fed back into the design process. If a particular model consistently shows issues during the static load test, such as excessive deflection or unexpected stress points, designers can modify the next generation of the crane. This could involve changing the shape of the main girder, upgrading the material used, or improving the connection points between components. Static load tests also have implications for maintenance schedules. If a crane passes the test with flying colors, maintenance intervals can be optimized, saving both time and cost. On the other hand, if there are marginal failures, more frequent inspections can be scheduled to catch any potential problems before they escalate into major safety hazards.
