Impact loads can have major adverse effects on the safety of civil engineering structures, such as concrete-filled steel tubular (CFST) columns. The study of mechanical behavior and stress analysis of CFST columns under impact loads is very important to ensure their safety against such loads. At present, the internal stress monitoring of the concrete cores CFST columns under impact loads is still a very challenging subject. In this paper, a PVDF (Polyvinylidene Fluoride) piezoelectric smart sensor was developed and successfully applied to the monitoring of the internal stress of the concrete core of a CFST column under impact loads. The smart sensor consists of a PVDF piezoelectric film sandwiched between two thin steel plates through epoxy. The protection not only prevents the PVDF film from impact damages but also ensures insulation and waterproofing. The smart sensors were embedded into the circular concrete-filled steel tube specimen during concrete pouring. The specimen was tested against impact loads, and testing data were collected. The time history of the stress obtained from the PVDF smart sensor revealed the evolution of core concrete internal stress under impact loads when compared with the impact force–time curve of the hammer. Nonlinear finite element simulations of the impact process were also carried out. The results of FEM simulations had good agreement with the test results. The results showed that the proposed PVDF piezoelectric smart sensors can effectively monitor the internal stress of concrete-filled steel tubular columns under impact loads.

This paper presents the results of a series of pullout tests that were performed on Glass-fiber-reinforced polymer (GFRP) bars embedded in concrete, while providing a detailed report on the influence of various variables that impinge upon bond behavior, such as the surface characteristics and diameter of the bars, concrete strength, as well as the confined effect of stirrups. The Bertero-Popov-Eligehausen (BPE) and Cosenza-Manfredi-Realfonzo (CMR) models analyzed the bond stress (τ)–slip (s) relationship between GFRP bar and stirrups-confined concrete. The tests results indicate that when the bond failure interface only occurs on the surface of a GFRP bar, the bond strength is not dependent upon the concrete strength. Moreover, the results indicate that in comparison to specimens without stirrups, their stirrup-containing counterparts are more prone to pullout failure with greater ductility and higher bond strength and corresponding slip. The BPE and CMR models are able to investigate the τ-s relationship between GFRP bars and the stirrups-confined concrete with accuracy. With the experimental data, the specific parameters in the models classified by surface characteristics have been suggested.

The purpose of this research is to study the effect of both transverse impact, and ratio of outer diameter to thickness of outer steel tube (D/t), on the residual axial bearing capacity of concrete-filled circular steel tubular columns (CFCSTCs). A total of sixteen samples, including four samples left untreated for comparison, are experimentally studied to investigate the effect of both drop-hammer transverse impact height (H), and D/t ratio, on the residual axial bearing capacity of CFCSTCs. The failure mode, load-displacement curves, load-strain curves, and residual axial bearing capacity of those samples are extensively investigated. A finite element analysis (FEA) model is established to predict the effect of D/t ratio on the residual axial bearing capacity of CFCSTCs. The results indicate that the H and the D/t ratio have noticeable effects on the axial compression performance of CFCSTCs. Failure mode of samples is commonly local buckling. In addition, maximum reduction of the axial bearing capacity of columns reaches about 35% compared with that of untreated columns. The results also show that the bearing capacity of the column increases with a decreasing D/t ratio of the same diameter (D).

Tuned mass dampers (TMD) have been widely used in passive vibration control, but their main disadvantage is that the vibration reduction effect may be greatly affected by the natural frequency of the main structure. In order to solve this limitation, we designed a frequency adjustable tuned mass damper (FATMD) based on a magneto rheological elastomer (MRE), which is a new type of magneto rheological smart material, with adjustable stiffness, obtained by changing the magnetic induction. We used MRE to change the stiffness of FATMD to track the natural frequency of the main structure. However, adding TMD will change the natural frequency of the system. Therefore, we combined Hilbert–Huang transform (HHT) and a natural excitation technique (NExT), with Simulink/dSPACE, to identify the natural frequency of the system in real time, and then calculated the natural frequency of the main structure through the TMD optimal design theory. This can help adjust FATMD to its optimum tuning state. To verify the applicability and effectiveness of FATMD, this paper compares the FATMD and traditional TMD experimental results. The natural frequency of steel beams can be changed by adding mass blocks. The experimental results indicate that FATMD, using the frequency tracking method, can effectively track the natural frequency of the main structure to ensure that the system is always in the optimum tuning state. In addition, FATMD can still achieve a good vibration reduction effect when the natural frequency of the main structure changes.

Due to the difficulty in adopting the conventional centralized control method for seismic response control of high-rise buildings with complex structures and large sizes, the decentralized control method is applied. The challenge is that the control model of the high-rise structure divided into multiple subsystems changes as large nonlinear deformation under strong earthquakes. Therefore, with an application of the long short-term memory neural network, the long short-term memory intelligent decentralized control method is proposed for seismic response control of high-rise buildings. On the basis of the decentralized control theory for high-rise buildings, a long short-term memory network deep-learning framework is established to construct different types of decentralized controllers, and to determine the sufficient conditions for the stability of the decentralized controllers using the Lyapunov stability theory. The long short-term memory intelligent decentralized control system of a 20-story benchmark building mode is simulated, and its fault tolerance is studied. The simulation results show that the decentralized control method can reduce the complexity of the structure model by dividing the high-rise building structure into multiple subsystems. Compared with the centralized control method, the long short-term memory intelligent decentralized control method can effectively avoid the overall failure of the control system. The long short-term memory intelligent decentralized control method can still have a satisfactory performance under sensor noise and control devices failures. This verifies that the long short-term memory intelligent decentralized control system has a better fault tolerance and can provide an innovative solution for the decentralized control of high-rise buildings.

A new piezoelectric composite, macro fiber composite (MFC) is recombined with piezoceramic fibers, an epoxy resin basal body, and an interdigitated electrode. It has been widely applied in vibration reduction and deformation control of thin-walled structures, due to its great deformability and flexibility. Research on its actuation performance is mostly concentrated on the MFC actuating force calculation based on classical plate theory (CPT), and the overall modeling of MFC and its structure. However, they have some deficiencies in the tedious calculating process and neglect of shear deformation, respectively. To obtain a precise MFC actuating force, the sinusoidal shear deformation theory (SSDT) is adopted to deduce the MFC actuating force formula, and global–local displacement distribution functions are introduced to help the MFC laminated plate structure satisfy the deformation compatibility and stress balance. For instance, in the end displacement calculation of the MFC laminated beam structure. The experimental result of the MFC laminated beam is compared with those of the MFC actuating force based on SSDT and on CPT, which indicates that the MFC actuating force formula based on SSDT can reach higher computational accuracy.