In the 18th century, French scientists used simple-supported wooden beams to slot along the cross section of the neutral axis and fill them with wooden blocks. The flexural load capacity test showed that the upper flange of the mid-span section was in compression and the lower flange was in tension.
There is a neutral layer in the middle, which put an end to the debate on the transverse stress distribution state of materials proposed by Galileo and lasted for more than 100 years, and the calculation formula for the transverse stress distribution of materials bending elements in mechanics of materials was established in the 1840s.
In the early 19th century, the engineering structure was able to explore its working condition and reliability by proof loading. Subsequently, due to the development of production and transportation, the research and improvement of equipment and equipment, and the emergence of large-span structures, engineering structure testing began to establish quantitative testing methods and promoted the development of theory. of the calculation of engineering structures, making Proof of engineering structure an independent discipline.
China attaches great importance to the construction and development of experimental disciplines of engineering structures. Since 1956, the “Building Structure Experiment” course has been established in colleges and universities. In terms of direct production services, the Yangtze River Bridge, pressure vessels, power transmission towers and various types of buildings have been identified for new structures, new materials and new processes, and the dynamic response of various structures, including earthquake simulation, industrial. Plant micro-vibration, high-rise building structures, and wind vibration of high-rise structures have achieved a large number of actual measurement results.
In terms of scientific research on engineering structural systems, a large number of static and dynamic tests of physical objects or models have been carried out on the material properties of steel, reinforced concrete, brick, stone, wood, cold-formed steel and other structures. , basic components and general work performance of the structure, etc. (See the color image). Many test results have been obtained, and design parameters, process standards, calculation formulas, design theories and construction techniques are in line with the current reality in China. Conditions have been proposed that provide a basic basis for formulating various specifications and procedures.
Classification of test methods “According to the purpose of test research, it is mainly divided into production identification test and scientific research test. According to the load-bearing properties of the structure, it is divided into static test and dynamic test. According to the time period, it is divided into long-term observation experiment and short-term observation experiment. According to the size of the test structure, it is divided into physical test and model test. According to the allowable degree of damage of the structure, it is divided into damage test and non-destructive test. The most basic of these is the short-term static observation test.
Test Work Procedures Prepare test plans, make test designs, and select or design test objects according to the purpose of the structural (or component) test investigation. If it is a model test, it should be done based on similar theories to identify the nature of natural phenomena and simulated boundary constraints Model design (including material selection and production process). Carry out design or load selection or simulating action, select appropriate test instruments and methods, and measure and record. Put a test research report.
In addition to physical loading, loading equipment generally used for loading equipment can be used with jacks (Figure 1), hydraulic test equipment, computer systems and online vibrators, simulated seismic vibration tables (Figure 2), explosions artificial etc , to simulate structural changes or the various real functions of the component. In all test devices, there are structural test benches, reaction walls, and various load-bearing devices.
The cable-stayed bridge model (4.7 meters long, 1:160) simulates a blown test in the wind tunnel.
5-story (1:4) block house model to simulate seismic shaking table test
Seismic performance test of 12-story building structure model (1:6)
Measurement method Machine measurement method. By using mechanical instruments to measure the required data or parameters, machine measurement is highly adaptable, simple, reliable and economical, it is the most widely used measurement method in structural testing. Electrical measurement method.
The data or parameters to be measured in the test are converted into electrical parameters such as resistance, capacitance, inductance, voltage or current through the sensing element, amplified by an amplifier, and then measured, recorded and displayed by the indicator and record. The XY function recorder records structural response data and graphs, performs ductility tests on beam and column joints, and uses hydraulic loading devices for load simulation.
This conversion and measurement technology is called non-electrical electrical measurement technology, which has the advantages of precision, fast measurement, automatic control, continuous recording and remote control. Connected with the electronic computer, it can also judge and calculate by itself according to the measurement results. Light measurement method. Use light collimation to continuously amplify, convert, and record measurement parameters, with low damping and fast response (like a light oscilloscope).
It is also possible to use the optical effects of physical and chemical principles and the mechanical properties of photosensitive materials under the action of polarized light to measure strain fields (such as photoelastic instruments), which is simple, reliable and intuitive; and the application of laser displacement measurement and laser holography.
Other methods. Measure based on the relationship between indirect physical quantities such as light, electricity, magnetism and sound and a certain property of the material or structural element. For example, an ultrasonic detector uses the propagation speed of ultrasonic waves in concrete to determine the strength of the concrete. The result of analysis and processing is restored to some kind of analog quantity and displayed, to automate data collection, measurement, analysis and processing.
Data processing and analysis of results, see analysis of structure tests.
ProspectsDue to the development of the engineering structure experiment discipline, the capacity, precision and automation requirements of the equipment are getting higher and higher. Lightweight oscilloscope recording equipment, popular in the 1960s, is gradually being replaced by tape recording equipment, making manual data processing easier Earth is replaced by electronic computers; also due to the development of testing technology, it provides the conditions for a deep understanding of the actual performance of structures and components, and the effective use of material potential.
In terms of test methods, the emergence of the system identification test program, the use of tests to determine the parameters of the system equations, so that the mathematical analysis and structural tests are closely combined, especially for large structures and complex, due to the difficulty of loading the test equipment and the limited capacity of the computer.
The overall structure is decomposed into various substructures, and the mathematical models or parameters of the substructures are determined through experiments, thus replacing large-scale and complex experiments of the overall system, saving manpower and material resources. In terms of test types, dynamic and static model test research is an important topic, including model materials, model design, manufacturing technology and the like.