1. The Test Equipment And Test Conditions
The standard temperature of test laboratory should be 23±5℃， there should be no corrosive gases or vibration sources,because these factors may influence the testing result,it affect the detection. It should be noted that before the experiment, the sample should be directly placed to the standard temperature, and the samples should be placed for 24 hours to ensure that the temperature inside and outside the sample is consistent.
The ultimate compressive strength is one of important test item to test elstomeric bearing pad, it is specified the ultimate compressive strength, and is mainly used to determine the safety of the bearing under the specified ultimate compressive strength. The test is carried out according to the following steps: place the specimen on the bearing plate of the testing machine, align it with the center position, and continuously load it at a rate of 0.1MPa/s until the ultimate compressive strength Ru of the specimen is not less than 70MPa. Observe the stress state and changes of the specimen at any time to determine whether it is intact.
When testing the compressive strength of elstomeric bearing pads,we need to use compressure shear testing machine, Before conducting the index test, it is necessary to ensure that the load position of the compression shear testing machine can meet the ultimate compressive strength , The max testing compression range of the machine should be larger than the max requested test pressure of the bridge bearing pads. in order to avoid production accidents such as test interruption or damage to the testing machine due to insufficient load position during the test process. During the testing process, it is necessary to observe the changes in the sample at any time. As the outer layer of the plate rubber support is wrapped in natural rubber, if the rubber layer is subjected to compression and cracks, it will be more obvious during the loading process. After unloading, due to the reducibility of the natural rubber itself, the cracked and damaged parts will be blurred, which will affect the final result judgment. So at the process of the testing ,we need to strictly follow the test requests of the machine and process, or we can not tell if the test is in the right way, this will affect the test results too.
2.2 How to Test Elstomeric Bearing Pad Of Compressive Modulus Of Elasticity
Test steps for compressive modulus of elasticity: Place the tested sample on a testing supporting plate, continuously increase the compressive stress to 10MPa at a rate of (0.03~0.04) MPa/s, hold for 2 minutes, then unload the compressive stress to 1.0MPa, hold for 5 minutes, and start the formal loading after preloading three times. Each loading cycle starts from 1.0MPa, and each 2MPa is loaded step by step, holding for 2 minutes. Collect the deformation value of the support until the compressive stress reaches 10MPa, and then unload continuously and uniformly at a rate of 1.0MPa. After repeating the loading process three times, the compressive elastic modulus E1 of each sample is the arithmetic mean of the three measured results obtained from the three loading processes.
The compressive modulus test requires the installation of displacement sensors at the four corners of the bearing plate to collect deformation data of each level of load support. The average of the changes measured at the four corners is taken as the cumulative vertical compression deformation of the specimen under each level of load. So the correct installation of displacement sensors and the sensitivity of the sensors will have a decisive impact on the final results.
Three rubber bearing pads should be used to test The compressive modulus of elasticity. and the compressive modulus of elasticity E1 for each support is the arithmetic mean of three measured results obtained during three loading processes. However, the deviation between a single result and the arithmetic mean should not exceed 3% of the arithmetic mean, otherwise a re verification test is required. According to the new standard of the Ministry of Transport, if the measured compressive elastic modulus E1 of the three bearings meets E ± EX20%, it can be judged that the batch of bearings has qualified compressive elastic modulus. E is the standard allowable compressive modulus of elasticity, calculated according to equation 2.
E=5.4XS2 (2).In the formula: S - shape factor of the rubber bearing pad.
2.3 Shear modulus Testing of elastomeric bearing pad
The shear modulus of elasticity is tested according to the following steps. The sample and the middle rigid tension plate are configured in a double shear combination as shown in Figure 3. To prevent slipping, high friction plates should be pasted on the upper and lower bearing plates and the middle steel tension plate (P36 grit sandpaper should be pasted instead in this test) to ensure the accuracy of the test; Continuously increase the compressive stress at a rate of (0.03~0.04) MPa/s to the average compressive stress o, and maintain it constant throughout the entire shear test process; Pre apply horizontal force, continuously apply horizontal shear stress at a rate of (0.002-0.003) MPa/s to 1.0 MPa, hold for 5 minutes, then unload at a continuous and uniform speed to 0.1 MPa, hold for 5 minutes, and so on for 3 times; Perform formal loading, starting from 0.1MPa per loading cycle, with an increase in shear stress at each level
0.1MPa, hold the load for 1 minute, collect deformation data of the support until it reaches 1.0MPa, and then unload
The next cycle should be carried out 10 minutes after the shear stress reaches 0.1 MPa, and the loading process should be repeated three times continuously.
For the testing of laminated rubber bearings, normally we test three important items: ultimate compressive strength, compressive elastic modulus, and shear elastic modulus. All three indicators meet the requirements of the specifications and are commonly tested in the mechanical performance testing of laminated rubber bearings.
Other mechanical performance testing indicators include shear aging resistance, shear bonding performance, etc. This article mainly discusses the testing process of ultimate compressive strength, compressive elastic modulus, and shear elastic modulus, and points out common problems and precautions in the testing. Of course, the more important aspect of the testing is the objective and rigorous attitude of the testing personnel, who strictly follow the requirements of the specifications to conduct the testing. Only in this way can the accuracy of the final testing results be guaranteed. Rubber bearings, as an important component in bridge engineering,
We mainly discuss about the testing elastomeric bearing pad process. And appoint the main problem of the test, of course, for the testing of elastomeric bearing pad, the more important is the testing personnel attitude, should strictly follow the requirements of the specifications of the tests, to make to the final testing result of laminated bearing pad is accuracy. Rubber bearing pad as the main part of bridge construction, should make sure the accuracy of testing results and ensure the safety of rubber bearing in the bridge construction.
