How should the bearing capacity of the manhole cover be tested?

The test of the bearing capacity of manhole covers generally follows relevant national standards and specifications. The following are the common test methods: I. Preparation work Determine the test samples: Select representative manhole covers as test samples. Manhole covers of different materials and specifications should be tested separately. Check the equipment: Ensure that the test equipment such as the pressure testing machine is in normal working condition and the accuracy meets the requirements. The measurement accuracy is generally required to be within a certain range (for example, within ±1%) to ensure the accuracy of the test data. II. Test equipment and environment Pressure testing machine: Adopt a special pressure testing machine that can provide vertical pressure and accurately control the loading rate and loading force. The equipment should have sufficient range to meet the maximum load test requirements that the manhole cover may bear. Test platform: There is a solid and flat test platform for placing the manhole cover samples to ensure that the manhole cover is in a stable state during the test and the test results will not be affected by factors such as the unevenness of the platform. The size of the platform should be able to adapt to the tests of manhole covers of different specifications. Environmental conditions: The tests are generally carried out indoors, and the environmental conditions such as temperature and humidity should be relatively stable to avoid the influence of environmental factors on the performance and test results of the manhole cover. For example, the temperature should be maintained within a certain range (usually at normal temperature, such as 20℃±5℃), and the humidity should be controlled at an appropriate level (such as the relative humidity not exceeding 80%). III. Test steps Place the manhole cover: Place the manhole cover sample smoothly on the test platform, ensure good contact between the manhole cover and the platform, and align the center of the manhole cover with the loading axis center of the pressure testing machine. The deviation should be controlled within a certain range (such as not exceeding 5mm) to ensure that the loading force acts evenly on the manhole cover. Preloading: First, perform preloading to eliminate the possible gaps and instabilities between the manhole cover and the test platform. The preloading force is generally 10% - 20% of the expected maximum loading force, and the loading rate is moderate (such as a loading rate of 1 - 2kN per minute). After loading to the preloading force, maintain it for a certain period of time (such as 1 - 2 minutes), and then unload. Formal loading: Gradually increase the load according to the specified loading rate (such as a loading rate of 5 - 10kN per minute) until the manhole cover reaches the failure state or the specified bearing capacity limit value. During the loading process, record the loading force and the deformation of the manhole cover in real time. For metal manhole covers such as cast iron manhole covers, usually observe whether there are obvious damage phenomena such as cracks and fractures on the manhole cover. For non-metal manhole covers such as plastic and composite materials, in addition to observing obvious damage phenomena, it may also be concerned about whether the deformation amount exceeds the specified limit value. Data recording and analysis: Record the loading force-time curve and the manhole cover deformation-time curve during the whole test process. Determine the bearing capacity of the manhole cover according to the curve. The bearing capacity generally takes the maximum load value that the manhole cover can bear before failure, or the load value corresponding to the specific deformation amount specified in relevant standards (for example, the load corresponding to when the deformation of the manhole cover reaches a certain percentage of its diameter). Analyze the test data to evaluate whether the manhole cover meets the corresponding bearing capacity standard requirements. If the test results do not meet the standards, the reasons need to be analyzed. It may be caused by factors such as uneven material of the manhole cover and defects in the manufacturing process. Through the above test methods, the bearing capacity of the manhole cover can be determined relatively accurately, providing a scientific basis for the quality evaluation and selection of the manhole cover.