What Is a Rigid Frame?

A rigid structure is an earthquake-resistant structure that is set on a building or structure. Relatively flexible structure. Its columns and beams have a solid structure and are designed with high-strength seismic walls, which can enhance the overall rigidity of the building and withstand the impact of strong seismic forces. Compared with flexible structure buildings, rigid structure buildings have a short natural vibration period and small deformation.

In the study of structural engineering, we can divide the structure into two categories: flexible structure and rigid structure based on whether the structure needs prestress to maintain stability. Among the many forms of space scaffolding, the grid structure and the shell structure are the most typical rigid structures. These structures have been widely used for their reasonable load, simple calculation, large rigidity, low material, single rod, and convenient fabrication and installation. Further, according to the connection mode of the members and the internal force transmitted by them, the net frame and the net shell structure can be divided into three types of rod structure, beam structure and beam-rod combination structure.

Rod system

The pseudo-dynamic test method is a relatively new type of structural seismic test method. This method uses a computer and a loading actuator in combination, and there are many ways to achieve this. At the same time, this method gives great development space. In essence, the pseudo-dynamic test is actually a time-history analysis process. The only difference is that the stiffness characteristic parameters of the structure required in the calculation are obtained by the test, rather than assumed by selecting a certain restoring force model before calculation. In this way, by applying the calculated displacement using an actuator in an online test, the true response-related structural restoring force can be measured.

The pseudo-dynamic test method combines the advantages of both the pseudo-static test and the shaking table test. Of course, it also has its own specific limitations, mainly including: the stiffness of the structure cannot be too large; the test system error (especially the control error) needs to be strictly limited; it is not suitable for structures with a large distributed mass (including concrete dams); The response is very sensitive to the viscous damping characteristics, and it is difficult to accurately identify, the pseudo-dynamic test method is not applicable; it is not possible to test on test pieces made of strain rate sensitive materials. The pseudo-dynamic test of a rigid multi-degree-of-freedom system also has the following difficulties:

The stability conditions are too strict: For rigid tests, the highest natural frequency of the structure is very large. Due to the stability conditions required by the standard explicit integration algorithm, the integration time interval may be too small.

The displacement increment is small: even if the integration time interval is acceptable, applying a small displacement increment will introduce a high displacement control error in the degree of freedom being controlled. In the worst case, the increment may be smaller than the resolution of the hydraulic actuator.

Displacement measurement error: Because the test displacement range of a rigid structure is small, relatively speaking, the displacement measurement error may be very high, leading to error accumulation and errors in the final structure response.

Test error growth: False high-order effects caused by test error sources and error propagation effects may reach unacceptable levels. This effect may even lead to the failure of the test method. In addition, if the time integration interval is small, the response simulation with a certain length of time requires more integration and loading steps, which will also cause serious test error accumulation problems ^[2]

Seismic structure

Earthquake-resistant structures are those which are designed to resist earthquakes to a certain extent or reduce their destructiveness.

Judging the structural system and geometric stability is an ancient subject. With the continuous development of building technology, more and more new theories have been proposed in the field of structural safety research. Spatial structures have developed vigorously in recent years, and the safety of these structural systems is novel, huge, and complicated. Began to get more and more attention. In order to evaluate the performance of these complex structures under frequent and occasional loads, scholars have introduced the concept of structural robustness by referring to the practices of industries such as automatic control, power systems, and lifeline engineering. The so-called structural robustness mainly refers to the robustness of the structural components' distribution topological relationship, and its antisense is the vulnerability of the structure. Earlier research on robustness still rested on qualitative analysis based on design experience. However, with the advancement of building technology, more and more complex structures such as large-span spatial structures have begun to be applied more and more to engineering practice. The original design experience has been difficult to meet the design requirements. Began to attract more and more attention. Each structure is a whole composed of units. In theory, as long as each rod can be guaranteed to work in the normal range, the overall safety of the structure can be guaranteed. Therefore, the importance of the members in the evaluation structure is the key to quantitative evaluation of robustness. It is also based on this thinking that scholars at home and abroad have conducted a lot of research on the coefficient of structural importance. In general, from the perspective of whether or not external loads are considered, the quantitative judgment methods of component importance can be divided into two categories. One type is an evaluation method that has nothing to do with external load. The evaluation target of this method is the properties of the structural system itself. Generally, the importance level of structural members is analyzed from the topological relationship and stiffness distribution of the structure. The other is an evaluation method related to the external load. This method not only considers the structure's own properties, but also considers the load distribution on the structure and the influence of the force transmission path.