In order to study probability of plastic hinge formation of a reinforced concrete (RC) high pier under near-field seismic action, a certain RC high pier with a height of 90m was taken as the study object. Firstly, the support vector machine algorithm was used to predict the equivalent yield curvature of its cross section. Then, considering pier parameters and the randomness of near-field seismic action, the software OpenSees was used to build the high pier model to do the increment dynamic nonlinear analysis. Finally, the equivalent yield curvature was taken as the critical index, and dynamic responses of the pier’s cross section were equivalently normalized with JC method to calculate and analyze the probability of plastic hinge formation of the pier’s cross section. The results showed that equivalent yield curvature of RC high pier cross section in forward bridge direction and that in transverse bridge one have obvious discreteness and obey normal distribution; under near-field seismic action in forward bridge direction, probabilities of plastic hinge formation in pier bottom area and pier middle part are larger to form plastic hinges, plastic hinge length in pier middle part is 31.7m and 84.3% longer than that determined only considering the randomness of seismic action; under the near-field seismic action in transverse bridge direction, probability of plastic hinge formation in pier bottom area is larger, and plastic hinge length is basically consistent to that determined only considering the randomness of seismic action; the probability analysis method for plastic hinge formation can be used to more accurately evaluate plastic hinge formation and distribution of RC high-piers.

Here, Aiming at problems of lower signal amplitude and secondary harmonic waves being uneasy to be effectively excited and easy to be interfered in nonlinear ultrasonic longitudinal wave detection, a nonlinear standing wave detection method was proposed. The nonlinear ultrasonic longitudinal wave method and the nonlinear standing wave one were used to detect 0Cr17Ni4Cu4Nb martensitic stainless steel tensile specimens, respectively. The detection results showed that compared to the nonlinear ultrasonic longitudinal wave method, the nonlinear standing wave one can raise signal amplitude, effectively excite secondary harmonic waves generated due to non-linear interaction inside material, and improve signal-to-noise ratio of ultrasonic signals and frequency resolution of frequency spectra; the test results are basically consistent to the finite element simulation ones. Three-point bending fatigue specimens of 0Cr17Ni4Cu4Nb martensitic stainless steel were detected with the nonlinear standing wave method. It was shown that when the fatigue time is smaller than the fatigue life of 50%, normalized ultrasonic nonlinear coefficients increase with increase in fatigue life under different fatigue stresses; so the nonlinear standing wave method can better detect early damage of 0Cr17Ni4Cu4Nb stainless steel.

Structural load and parametric identification are important contents in structural dynamics field. At present, there are some studies focusing on joint identification of them. The extended GDF (EGDF) method presented here by the authors has the ability to continuously identify unknown loads and parameters. However, it is necessary to know acceleration responses at locations unknown loads exerted on. Besides, like other identification methods based on the least square, the EGDF method has low frequency drift phenomena of identified unknown loads and displacements. Here, a modified method was proposed to convert this recognition problem into the recognition of modal displacements and modal loads in modal space, and then the modal truncation technique was used to obtain the real-time EGDF method. Furthermore, taking displacement and acceleration as measured responses, the data fusion technique was used to solve low frequency drift problems in identification results.

 

To promote the effective application of ultrasonic wave technique in quantitative evaluation of bolt tightening state, combining with requirements of actual detection, an appropriate finite element (FE) model was established for the bolt axial stress measurement method based on acoustoelastic effect. A 2-D axisymmetric mode was used to simulate bolt M8×25, and a 10 MHz ultrasonic transducer was placed on the bolt head. In FE simulation, a hyper-elastic material with Murnaghan third-order elastic constants was used to do coupling analysis for structural field and acoustic one. Through two studying steps, the ultrasonic waveform signal for bolt axial tension state was determined. The FE computation results showed that there is a linear relationship between time difference of ultrasonic wave propagation (ns) and bolt axial stress (MPa), and this relationship varies with change of bolt clamped length and its material; for the bolt axial stress measurement method based on acoustoelastic effect, the linear coefficient’s correct measurement is very important. The FE computation results were analyzed deeply, it was shown that bolt stress state has a superposition effect on ultrasonic wave propagation change in bolt; different bolt clamped length causes larger change of acoustoelastic effect, this should be paid enough attentions to; the FE computation results agree well with those of analytical calculation and practical test measurement; the proposed FE model for bolt axial stress measurement with the ultrasonic wave method can be used to solve the difficult problem of acoustoelastic effect’s numerical simulation and analysis, and provide a technical guidance for analysis of detection methods and development of specific instruments.

Effects of periodic gust flow on super-cavitation morphology and hydrodynamic characteristics of ventilated vehicle were numerically simulated with the dynamic grid technique. Firstly, comparing the numerical computation results with test data, the feasibility of the dynamic grid technique being used to simulate periodic gust flow was verified. Then, based on this simulation method, the super-cavitation morphology evolution process and hydrodynamic change features of a ventilated vehicle under the action of periodic gust flow were investigated. The results showed that under the action of periodic gust flow, super-cavitation morphology of the ventilated vehicle reveals a periodic change, size and position of wetted area of the vehicle also change to cause periodic change of hydrodynamic coefficient; the proportion of the vehicle’s wetted area resistance in total resistance increases with increase in wetted area; the proportion of wetting area lift in total lift is larger, there is a high pressure zone near cavitation closing line ofwetted area to make small wetted area provide a very big lift for vehicle.

Many factors, such as, dynamic characteristics of hydro-cylinder, structural flexibility, excavating objects and excavator-soil interaction affect digging dynamic behavior of hydraulic excavators during their operation. Here, to solve digging dynamic load calculation problems, an excavator’s digging dynamic model comprehensively considering factors mentioned above was proposed. To achieve a good balance between accuracy and efficiency, all slender structures including movable arms, bucket rods and connecting rods were simplified as beam elements. Complex shape structures like bucket, etc. were simply modeled using the sub-structure DOF condensation method. The bucket-excavating object relation was modeled as a spring-damper element. Hydro-cylinders were modeled as two-node elements containing variables of pressure, displacement and velocity, etc. Then, all structural elements and hydro-cylinder elements were assembled to form a global finite element system model, and perform dynamic computation using Newmark algorithm. Finally, a 50t excavator’s movable arm lifting under impact condition was taken as a case study to do computation and test analysis. The results showed that the computed dynamic loads agree well with measured ones in tests, the error of dynamic load peak values is less than 6%, these verify the correctness of the proposed method and model; compared with using the displacement driven model to simulate hydro-cylinder in dynamic computation, the accuracy of applying the proposed hydro-cylinder model in dynamic computation is increased by 5 times, while structural flexibility has a smaller effect on digging dynamic load. 

Based on the LS-DYNA software, nonlinear finite element simulations of truck collisions with typical reinforced concrete piers were conducted in this study. The dynamic responses and damage characteristics of the piers with different boundary conditions and stirrup ratios were focused, especially the typical damage patterns of reinforced concrete bridge piers under the actions of truck collisions. The analysis results revealed that: 1) piers mainly fail in shear, and when the fixed constraint position at the bottom of the piers lowers by 1 m from the ground, the main damage area of piers expand from 1.2 m to 2.5 m above the ground; 2) when the diameter of pier stirrups increases from 8 mm to 24 mm, the maximum horizontal displacement of the piers reduces by an average of 71.3%; 3) due to the gravity loads of the upper structures, the stress of the tensile longitudinal rebar of the piers at the range of the nominal impact height reduces significantly.