Loading method of civil engineering test
1-1 Heavy load
Heavy load is one of the most frequently used loading methods in building structure tests and inspections. It is a method of applying a load to a structure or member using a bulky and easily available substance.
The advantages of loading heavy objects are: 1. Suitable for long-term building structure test, and can maintain the stability of the load value; 2. Load heavy objects are easy to obtain, the loading method is simple and convenient, economic and reliable.
In order to apply larger concentrated loads, load amplification mechanisms are often used. Lever is the simplest load amplifying mechanism, and because of its simple and convenient manufacture, the load value is constant, and it is suitable for long-term test loading.
During the test, different loading weights should be selected according to the specific situation. No matter which kind of material is used as the weight load, the load value must be weighed before the test to ensure the accuracy of the weight load value. Due to the large volume of heavy loads, measures such as safety protection should be taken during the destructive experiment of the building structure to ensure the safety of the experiment.
1-2 mechanical loading
The mechanical loading method is to use a simple mechanical device to load the structure, and the mechanical loading can apply a concentrated load to the building structure.
The advantage of mechanical loading is that the loading mechanical equipment is simple and reliable, and the loading is easy.
1-3 pneumatic loading
1. Pneumatic loading
Air pressure loading is to use compressed air or high-pressure nitrogen building structure to apply uniform load. Compressed air and high-pressure nitrogen are used to load the structure through the rubber airbag. In order to increase the test pressure load of the airbag, the supporting side wall should be built around the structure, so that the structure, the supporting side wall and the ground surround the airbag to achieve increased gas The purpose of load pressure.
2. Negative pressure loading
Another method of air pressure loading is to evacuate to form an atmospheric pressure difference to achieve uniform loading of the structure.
Air pressure loading is suitable for applying uniformly distributed loads on large-area structures such as plates and shells. Its advantages are that loading and unloading are convenient and reliable, and the load value is stable and easy to control.
1-4 hydraulic loading u
Hydraulic loading is one of the ideal loading methods in building structure tests. It can not only apply static loads to building structures, but also apply dynamic loads. The principle of hydraulic loading is clear, the loading equipment is simple and convenient to operate, safe and reliable, can produce large loads, and the loads are easy to control accurately and stable, and can achieve multi-point synchronous loading. It is currently the most widely used technology and advanced loading method one.
1. Classification of hydraulic loading
Hydraulic loaders are divided into hydraulic jacks, unidirectional hydraulic loaders, bidirectional hydraulic loaders and electro-hydraulic servo actuators based on structure and different functions.
A hydraulic jack is a simple lifting tool that can be used to apply concentrated loads. Single-acting hydraulic loaders cannot be used alone for loading, and need to be equipped with a hydraulic system to form a hydraulic loading system. The structure is simple, the working stroke of loading is large, and it can be installed upside down during use, which is easy to realize multi-point synchronous loading. The characteristic of the two-way hydraulic loader is that the area of ​​hydraulic oil on both sides of the piston is basically the same. Therefore, the double-acting hydraulic loader can apply reciprocating tensile and compressive loading, providing a loading tool for the low-cycle reciprocating loading test in the seismic structure test. The electro-hydraulic servo loader is a controllable loading device composed of an electro-hydraulic servo valve, a pulling pressure sensor and a displacement sensor based on a double-acting hydraulic loader.
2. Hydraulic system
The hydraulic loading system includes a hydraulic system and a load supporting system. The hydraulic system is composed of a hydraulic control system and a hydraulic loader. The hydraulic control system is composed of an oil tank, a high-pressure oil pump, a force measuring device and various valves. One hydraulic system can control multiple hydraulic loaders.
Equipped with different load support systems, the hydraulic loading system can be used for static load tests of various building structures (roofs, beams, columns, slabs, wall panels, etc.).
The electro-hydraulic control system of electro-hydraulic servo actuator includes hydraulic system and microcomputer control system. The hydraulic system consists of an oil pump station and electro-hydraulic servo actuators. The microcomputer control system includes: a microcomputer equipped with analog-to-digital (A / D) and digital-to-analog (D / A) conversion cards, a strain gauge and a signal amplifier. Closed-loop control is composed of resistance strain gauge, displacement sensor, tensile pressure sensor and data acquisition system.
The electro-hydraulic servo loading system has the advantages of fast frequency response, high sensitivity, good control accuracy and strong adaptability. It has a wide range of applications in building structure tests. Electro-hydraulic servo actuators and control systems can complete structural static load tests and structures. Dynamic load test, low-cycle fatigue of structure and simulated earthquake test, etc.
3. Hydraulic load loader standard
The hydraulic loader must be calibrated by a qualified testing laboratory or testing station certified by the National Quality and Technical Supervision Bureau. When calibrating the hydraulic loader, the actual use method should be used for calibration, and the relationship curve of the load-pressure representation value should be established to ensure the test The accuracy of the load value. "
When calibrating a hydraulic loader, since the low end and high end of the pressure indication value belong to the low sensitivity area of ​​the pressure gauge, the calibration of the hydraulic loader cannot be performed in the area where the pressure indication value is insensitive. Take more than 6 measuring points uniformly in the sensitive area of ​​the pressure indicating value, measure the pressure indicating value and the corresponding test machine load indicating value, repeat the test three times and take the average value of each measuring point, and then perform a one-dimensional linear regression analysis to give The fitted straight line equation between the expressed value of the output pressure and the ejector force of the hydraulic loader is loaded by the relationship of the straight line equation during the test.
1-5 Dynamic load method
1. Inertial force loading
The initial displacement loading method is a method that applies a load to a structure or member to deform it, and then suddenly unloads the load to cause the structure or member to vibrate freely. This loading method has no additional mass effect on structural vibration and is suitable for measuring the natural frequency of the structure.
Tension sudden unloading method Another loading method is to use the heavy object to generate the initial displacement of the structure, and the automatic decoupling device makes the heavy object load unload suddenly, producing free vibration. Since the mass of the weight does not affect the structure's additional mass, it is an ideal loading method for measuring the natural frequency of the structure.
The initial velocity loading method is to increase the potential energy level of the loading appliance, and then the potential energy of the loading appliance is converted into kinetic energy. After the loading appliance obtains a certain speed, it impacts the test structure to obtain the impact load of the structure.
2. Vibrator loading method
According to the different loading methods of the shaker, it is divided into mechanical shaker and electromagnetic shaker. The mechanical vibration exciter uses the centrifugal force to apply the periodic load, while the electromagnetic vibration exciter uses the nature of the magnetic pole to apply the load.
The mechanical vibration exciter has strong adaptability, and the base of the vibration exciter needs to be fixed at the loading point of the test structure and used for direct loading. The mechanical vibration exciter can also be connected with the movable platform to form a mechanical vibration platform. The frequency of the mechanical vibration exciter is low, the degree of distortion of the vibration waveform is large, and the loading equipment is bulky and heavy, and the noise generated is very large, which is a defect of the mechanical vibration exciter.
The electromagnetic vibration exciter is installed on different supports to achieve horizontal excitation loading or vertical excitation loading, and is an important loading device for dynamic testing of building structures.
The advantages of electromagnetic vibration exciter are: wide frequency range, generally 0 ~ 200Hz, individual products can reach 1000Hz; light weight, convenient control, excitation force from tens of kilos to hundreds of kilos. The disadvantage is that the excitation force is small, and it is only suitable for small-scale building structure model tests.
3. Explosive loading
Explosive loading is the use of gunpowder or explosives to burn or cause an explosion, generating an impact load on the test structure or building. After the explosive explodes, it acts on the test structure or building in the form of stress wave or shock wave, and the combustion of the gunpowder acts on the structure or building in the form of excitation force through the rocket excitation load.
Explosive loading uses the ground and underground for explosive explosive loading, which causes an instantaneous dynamic effect on the ground. Under normal circumstances, when the test structure is far away from the initiation center, the dynamic effect of the earthquake on the test structure can be well simulated, and satisfactory test results can be obtained.
Rocket excitation loading is also known as recoil shaker loading, which uses the principle of the rocket engine to apply a load to the test structure. Rocket excitation loaders are particularly suitable for use in field self-vibration frequency and power reflection tests. During the test using rocket excitation loaders, the rocket excitation loaders should be fixed firmly and fire prevention should be noted.
l1-6 loading auxiliary equipment
1. Load supporting device
The load supporting device must have sufficient strength and rigidity to be competent to ensure the smooth progress of the experiment. The load supporting device is divided into a vertical load supporting device and a horizontal load supporting device.
The load supporting device used in the test room is assembled by building blocks. The characteristic of this type of test load supporting device is to adapt to different sizes of test pieces through different combinations to meet different test conditions. When carrying out structural experiment inspection on the construction site, simple load balancing support devices can be used, such as: foundation piles or accumulated heavy objects on the site to balance the vertical loading force.
The shear wall is the ideal horizontal load supporting structure in the laboratory. The truss type horizontal load support device is made of section steel, it can only withstand not too large horizontal loads, and is usually used in the test of small and medium-sized structural specimens. The truss type horizontal load support device is a movable test bracket, which can be fixed at a specified position according to the test needs, and can also be loaded in two directions of XY in the horizontal plane by using two reaction force frames.
2. Load transfer device
The function of the load transfer device is to correctly transfer the force generated by the loading device to the test structure according to the requirements of the test load pattern. The structure of the load transfer device is simple, such as: lever, horizontal beam and distribution beam, but it plays an important role in the structural test. The function of the horizontal beam is to convert the concentrated load of several loading devices into a uniform load on the loading surface of the test piece during the test. The function of the distribution beam is to divide a concentrated load applied by the loading device into two concentrated loads according to a certain ratio. In order to divide a concentrated load into multiple concentrated loads, a multi-layer distribution beam can be used.
1-7 Test piece support device
The support device of the test piece is one of the key test devices to achieve the force boundary conditions and displacement boundary conditions of the test structure. Therefore, only the correct use of the support device in the structural test can ensure the smooth progress of the structural test. The specimen supporting device includes: support and support.
1. Support
The working condition of the support is that the support contacts the surface of the test structure to support the test structure, the reaction force of the support acts on the test structure, and the support itself is supported by the support pier. The frequently used bearings are divided into rolling hinge bearings, fixed hinge bearings, fixed ball hinge bearings, movable ball hinge bearings, and fixed-end bearings according to different action forms. The rolling hinge support allows the structure to move freely in the lateral direction at the support point, and the action direction of the support reaction force is on the common normal line at the contact point and points to the test structure. The difference between the fixed hinge bearing and the rolling hinge bearing is that the test structure is not allowed to produce lateral displacement at the bearing point. The fixed spherical hinge support allows the test structure to rotate in three directions, the reaction force of the test makes the test structure uniaxially compressive load, and the movable spherical hinge support has five degrees of freedom. The fixed-end bearing does not allow the test structure to rotate and move. When conducting structural tests, the corresponding supporting force should be selected according to the actual stress of the structure to obtain correct experimental data.
2. Piers
The support pier is in contact with the ground and is a support device for the support. The laboratory uses steel or reinforced concrete piers, which can move freely. The piers used in the field structural test are made of bricks or cast in concrete. These piers are often used once, so their structure is simple.
Steel plates should be embedded on the upper surface of the pier. The pier itself should have sufficient strength and greater rigidity, and the bottom area of ​​the pier should ensure that there is no excessive uneven settlement during the test.
SHORE WESTERN
the company
Shore Western
The company is headquartered in California, USA
Monrovia
The city's high-tech enterprises have a worldwide reputation for providing cost-effective structural and material testing systems. It has surpassed in the design and manufacture of high-performance electro-hydraulic servo systems
35
Years of experience.
It provides a wide range of products and services for users in scientific research, product development, quality control and other fields. Its fields mainly include: civil engineering structure test, material test system, auto parts test system, aircraft structure test system, biological structure
/
Material testing and simulation system, servo control system, dynamic and static hydraulic cylinder, oil source, electric control oil separator, etc.
As a system supplier,
Shorewestern
The outstanding achievements are also reflected in its continuous innovation, leading new technologies, and assisting users to achieve their unique test goals. As it launched
SC6000
High-performance electro-hydraulic servo controller can be directly connected to the network to realize remote monitoring and control and remote diagnosis.
SC6000
Users can download the function module expansion capability directly from the server.
Electro-hydraulic servo structure loading test system
Shore Western is a high-tech enterprise headquartered in Monrovia, California, USA. It has a worldwide reputation for providing cost-effective structural and material testing systems. He has over 35 years of experience in designing and manufacturing high-performance electro-hydraulic servo systems. It provides a wide range of products and services for users in scientific research, product development, quality control and other fields. Its products mainly include: structural loading system, material test system, dynamic and static hydraulic cylinder, oil source, electronic control oil separator and so on.
Shore Western electro-hydraulic servo structure loading system is mainly used in: civil engineering structure test, auto parts test, aircraft structure test, biomechanical structure test and friction simulation system.
Shore Western electro-hydraulic servo structure loading system mainly includes electro-hydraulic servo controller, dynamic and static electro-hydraulic servo cylinder, hydraulic oil source, pipeline distribution system, etc.
The SC6000 high-performance electro-hydraulic servo controller launched by Shorewestern can be directly connected to the network to realize remote monitoring and control and remote diagnosis. Users of SC6000 can download function module expansion capabilities directly from the server.
Electro-hydraulic servo structure loading test system
Electro-hydraulic servo material test system
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