Method for detecting bending moment and load deflection value of concrete poles - Master's thesis - Dissertation

Kaixin micro test

Test - lowercase jpg

Test probe PH-5H

inductance

Annular concrete poles are suitable for use in power, non-electricity, communications, and lighting pillars and signal towers that are in contact with grid lines. The main structure consists of prestressed steel bars, partially prestressed steel bars, non-prestressed steel bars and circular ring steel bars. In the actual pole inspection and testing process, in the actual situation of the manufacturer, when testing the mechanical properties of the pole, the errors should be minimized, the conditions of the test should be satisfied, and the errors of the bending moment and deflection value should be avoided. This affects our judgment of the allowable deflection value of the bearing capacity test bending moment, standard bending moment and bearing capacity.

1 fixed method

According to the test method of the National Standard GB/T 4623-2006 of the People's Republic of China, the tapered pole is a cantilever type test device, and Figure 1 is a schematic diagram of the cantilever type test device.

A, B is a U-shaped pad made of 150mm wide hardwood, so that the bottom of the pole can not move freely, even if the movement is small, can be read from the dial indicator. For our local manufacturers, one is the limitation of the site, and the other is that the inspection of the pole is not taken seriously. Most of the manufacturers in our test are on the production line or on one side of the concrete cast-in-place plate, so that the bottom of the pole is not fixed firmly (mainly the force is relatively large). If it is found on the production line or on a concrete cast-in-place board on one side, we usually use a steel wire and rivet fixing method. The advantage of the steel cord and rivet is that it will not slip or appear abnormal sound, that is, the use of a large force pull, there will be no breakage, no time waste and personal unsafe factors.

2 Do the mark, mark

When testing and testing poles, we usually use: pull a center line at the top and bottom of the pole and make a mark. Either end of the pull wire cannot be tied to the top and bottom bars, especially the bottom end, so there will be displacement, but the actual measurement is not possible because the reference object is moving at the same time. In the case of the force of the pole, the six dial gauges can be read under normal conditions. If the six dial gauges cannot be measured, the displacement generated by the top force is subtracted from the displacement generated at the bottom end. The measured data makes the standard bending distance and the deflection of the bearing capacity more realistic and reasonable.

3 Minimize friction

During the detection process, the rolling bearing keeps the pole away from the ground, reducing the friction of the ground against the detecting pole. The surface of the rolling bearing is as flat and smooth as possible, whether it is a steel seat or a wooden board. The load cell is required to be perpendicular to the pole when the force is applied, so as to avoid slipping at the top of the pole, thereby affecting the crack test coefficient, the comprehensive test coefficient of the bearing capacity and the deflection of the pole.

4 load process

In the first step, the step of 20% of the bending moment is tested by zero-cracking until 80% of the bending moment of the cracking test, and then the step is 10% of the cracking test bending moment to continue the loading to the cracking test bending moment to observe whether cracks appear. If there is a crack, stop the loading. If there is no crack under the cracking test bending moment, continue to increase the crack by 10% of the cracking test moment to the crack, measure and record the crack width and the winding value, each time stop. Time is 5 minutes. The second step is unloaded to zero by the initial cracking moment, and the static stop time is 5 minutes after unloading. The crack width and the winding value are measured and recorded. The third step is to test the crack width and the winding value by measuring the 20% step of the bending moment to the cracking test bending moment. After increasing to 160% of the cracking test bending moment, continue to load to the bearing capacity test bending moment according to the step of 10% of the cracking test bending moment. Each static stop time is 5 minutes, and each reading is observed and recorded. When the crack occurs for the first time during the loading process, the load value of the first stage should be taken as the measured value of the initial crack load. When the crack occurs for the first time within the specified load duration, the average value of the initial crack load shall be taken from the average value of the load value of the current stage and the load value of the previous stage. When the crack occurs for the first time after the end of the specified load duration, the load value of this stage should be taken as the measured value of the initial crack load.