2. The vibration isolation design of the anechoic chamber has been estimated. The total load of the box above the spring is 3108.72KN.
2.1 Selection of spring and determination of quantity The whole inner box of the anechoic chamber is placed on the spring. First, the spring can meet the requirements of the vertical bearing capacity of the upper box. Since the spring is limited by the manufacturer's processing technology and spring accuracy, the design first selects the spring that meets the accuracy requirements, and then determines the number and arrangement of the spring according to the bearing capacity of the spring.
After comparison, the design uses the following specifications of vibration isolation spring: d = 40mm, D = 190mm, spring free height H = 300 ± 1mm, total number of turns N = 5.5, effective number of turns n = 4, spring steel 60SiMn, shear The modulus of elasticity G = 93.3 Gpa, and its ultimate bearing capacity is 79.6 KN (the spring modulus of the spring is constant under this load condition). Taking into account the fatigue characteristics of the spring under long-term stress conditions, 70% of the ultimate bearing capacity of the spring is selected as its working load, ie 79.6kN *70%=55.72KN, then the number of springs required is (G+P)/55.72=3108.72 / 55.72≈56. Under this working load, the compression of the spring is 60.0 mm.
2.2 Vibration isolation design and construction measures The weight of the anechoic chamber is basically evenly distributed on the spring and transmitted to the lower foundation beam through the spring. Due to the damping effect of the spring, the influence of various internal and external factors such as external noise and ground vibration on the anechoic chamber is greatly reduced, thereby achieving the purpose of vibration isolation and noise reduction. The key design and construction measures are as follows:
(1) Considering that the anechoic chamber is a symmetrical structure, the load has symmetry. To ensure the balance of the box, the arrangement of the spring must be strictly uniform and symmetrical.
(2) In order to ensure uniform spring force, easy connection, anchoring and installation, the springs are arranged in pairs in the design and welded to the embedded steel plate.
(3) A vibration isolation joint is arranged between the test bench and the bottom plate of the anechoic chamber, the slit width is about 15 mm, and the joint is filled with sponge rubber, and a rubber vibration isolating pad is arranged between the test bench and the foundation of the building.
(4) In order to ensure the stability of the box, all springs should be strictly and accurately at the same level, and the horizontal deviation of the vibration spring base and the top should be ≤ L/1000 (L is the horizontal length of the box).
3. Vibration isolation spring construction The vibration isolation spring is tested one by one before leaving the factory. Under the same load, the compression height is basically the same. The installation base of the vibration isolation spring should be strictly leveled, and then the spring should be anchored. After checking one by one, the upper anechoic chamber bottom plate and ring beam are started.
The upper wall of the anechoic chamber should be built up by circle, and the load around the same level should be controlled as much as possible to ensure that the compression deformation of the spring is as uniform as possible, avoiding large inclination, and requiring vertical deviation of the four walls ≤ 10mm (total height range Inside).
3.1 Determine the spring load frequency of the anechoic chamber construction? 48*3.5mm ordinary scaffolding steel pipe, 160 poles and 80 crossbars are tightened and fixed with right angle fasteners, together with the spring to withstand the upper constant load and the upper construction load. The 56 springs are mounted simultaneously with the ±0.000 bottom plate beam formwork. The dead load + formwork and construction load of the box above the spring is 2824.45KN.
48*3.5mm ordinary scaffolding steel pipes should meet the following requirements. (1) According to the axial compressive strength condition, the bearing capacity of each pole is 81.52 KN, and the vertical bearing capacity of 160 poles is 13043.2 KN, which can meet the requirements of receiving upper constant load and construction load; (2) The friction between the fastener and the steel pipe pole is such that, in the case of tightening the bolt, sufficient frictional force can be generated between the fastener and the steel pipe to transmit the load from the crossbar and ensure that the joint is not deformed. The friction of each pole is 6.0 KN, the friction of 160 poles is 960 KN, and the number of classifications is 2824.45/960=2.94, so the scaffolding steel pipe can be loaded into the spring three times.
3.2 The sequence of spring graded loading is the first time: ±0.000 height of the bottom plate constant load +2.1m high wall, the gravity load of the ring beam and the structural column is 949KN, after the concrete age 28d (intensity is 100%), Start the first loading of the spring, that is, the fastener on the steel pole is moved down 18mm (two times, each time down 9mm), the spring is loaded 935.4KN. It is also calculated that the vertical bearing capacity of each spring is 0.928KN when the compression is 1mm, and the vertical bearing capacity is 0.928*18*56= 935.4KN when the compression of 56 springs is 18mm.
The second time: the wall around the box, the ring beam and the structural column were completed, and the gravity load was 945 KN. Actually, the fastener on the steel pole is moved down by 18mm, and the spring load is 935.4 KN.
The third time: the construction of the 6.28m elevation roof was completed, and the gravity load was 523.4 KN. Then, the fastener on the steel pole is moved down by 10mm, and the spring load is 0.928*10*56=519.68 KN.
3.3 The loading process of the spring is completed after the 7.800m elevation roof panel is completed. After the template is removed and the construction load is released, the average spring compression of the anechoic chamber is 18+18+10=46mm under the self-weight load.
At present, the building noise reduction and vibration isolation is a new topic of construction engineering. The above is a little insight in the construction, and it is hoped that it will be able to throw bricks and attract jade, so that this subject can be continuously improved.
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