Advanced Materials Research Vols. 243-249

Abstract: Shape memory alloys (SMAs) are unique class materials that have the ability to undergo large deformations, while returning to their undeformed shape through either the applications of heat (SME) or removal of stress (SE). The unique properties lead to their wide applications in the biomedical, mechanical, aerospace, commercial industries, and recently in civil engineering. The paper presents two case studies of structural seismic vibration control using SMAs. The first one is a study of the SMA reinforced RC members. Two innovative applications in RC members, such as SMA-based Precast Concrete Frame Connection (SMA-PCFC), and SMA reinforced RC short column, were proposed. Moreover, the self-rehabilitation properties of SMAs-based Intelligent Reinforced Concrete Beams (SMA-IRCBs) were further experimentally investigated. The results show that SMAs can improve the mechanical properties of concrete members. SMA reinforced RC members have unique seismic performance compared to ordinarily steel reinforced concrete members. The second one is a study of the structural energy dissipation system using SMAs damping device. An innovative hybrid SMAs friction device (HSMAFD) which consists of pre-tensioned superelastic SMA wires and friction devices (FD) was presented. The results of cyclic tensile tests show that the HSMAFD exhibits stable large energy dissipation capacity and re-centering feature. The effectiveness of the HSMAFD in reducing horizontal response of structures subjected to strong seismic excitations was verified through shaking table tests carried out on a reduced-scale symmetric steel frame model with and without the HSMAFD.

Abstract: The paper has made a maximum Lyapunov exponent and Lyapunov exponent spectrum entropy analysis of ASCE Benchmark using non-linear theory and chaos time sequence. The maximum Lyapunov exponents in the two kinds of structural monitored data are both over zero, indicating that in the structural system chaos phenomenon has appeared. And, experiments have shown that the maximum Lyapunov exponent is sensitive of the amount of samples and the time delay. So, to compute the chaos index, the amount of samples and the time duration are of importance. Meanwhile, the Lyapunov exponent spectrum entropy is effective to measure the chaotic characteristic of the system, but ,the entropy is less sensitive to state recognition more than the max Lyapunov exponent.

Abstract: In this paper, the blast vibration was monitored and the data from an underground engineering were analyzed. The empirical formula of the relation between the maximum vertical direction vibration velocity and the scaled explosive charge, the maximum horizontal radius direction vibration velocity and the scaled explosive charge, the maximum horizontal tangential direction vibration velocity and the scaled explosive charge were determined. According to the blasting safety regulations, the safety standard of the blasting vibration velocity is less than 7.0 cm/s. Through monitoring and inspection, the safety evaluation of the secondary lining of the highway tunnel was made. The safety evaluation of the protected highway tunnel is safety under the blasting vibration.

Abstract: A method for modal parameter identification of time-varying structures based on Hilbert- Huang transform (HHT) is presented. Theoretical formulas for identifying the modal frequency and damping radio using the displacement response of a time-varying SDOF structure are deduced. Taking advantage of modal filtering characteristics of empirical mode decomposition (EMD), the presented method is expanded to identify the modal parameters of MDOF structures. Numerical simulation of a three degrees of freedom structure with time-varying stiffness and damping show the validity of the method. Finally, a time-varying structure experiment is designed to further study the method. The experimental device is a cantilever beam. By adjusting the adjunctive mass and stiffness, two kinds of time-varying structures with continuous mass change and stiffness change is realized respectively. Modal parameters are identified from the free acceleration response of the beam.

Abstract: The paper proposes a new variable friction system, of which the friction force can increase linearly with the displacement of system. This new system can be used in TMD to avoid the disadvantage of Coulomb friction TMD. Using first order harmonic balance method, the equivalent damping ratio and frequency of SDOF variable friction system is deduced and analyzed. The frequency response characteristics of SDOF variable friction system is discussed. The control effectiveness of variable friction TMD under harmonic excitation is analyzed theoretically. The results demonstrate that the frequency response curves of variable friction TMD and classically damped TMD are similar and both can effectively reduce structural response under harmonic excitation.

Abstract: Since the pioneering work of Paris and Erdogan (1963), the fatigue crack growth (FCG) model has been being modified by worldwide researchers. Research efforts have been devoted by a number of investigators for assessing the fatigue condition of structural components by means of residual stress at the crack tip, threshold stress intensity factor, load ratio, and so on. The parameter C is always as a constant about material and structure, and almost no further research on it. In this paper, we proposed a novel analytical approach to predict the effect of the parameter C on fatigue performance. The inertial effect coefficient model for FCG under constant amplitude (CA) loading is briefly described and then used to verify the parameter C is a variable and analyze the relation between the parameter C and FCG rate. The prediction of the parameter C in this model is in good agreement with experimental data taken from the literature.

Abstract: In engineering structures, it is a new approach to evaluate the structural health situation by use of optic fiber sensor. In this paper, a standard specimen beam, 200mm×300mm×3000mm, is chosen and the comparative experiment is executed for strain testing by FBG sensors and vibrating wire sensors which were widely used in bridge health monitoring. Experimental results show that the FBG sensors have a higher measurement precision, higher linearity and better noise resistance. Then we use traditional electrical resistance strain gage to calibrate the FBG sensors and obtain the strain degree of sensitivity, and apply them into bridge strengthening in the Wuhuang Highway in order to collect the strains of reinforcement bar in the deck pavement and the beams before and after the bridge strengthening. The above work is also to evaluate the effects of strengthening projects and carry out long-term structural health monitoring. The monitoring results show that the safety condition can be monitored conveniently with the FBG sensors testing system whose durability and stability can satisfy the need of bridge health monitoring. Finally, we also discuss the key problems and practical approaches in structural health monitoring process by use of embedded FBG sensors.

Abstract: In order to test the applicability of the strength curves of rebound method and ultrasonic-rebound combined method of common concrete in estimating the strength of recycled concrete, basis on the C30 recycled concrete specimens with 70% of recycled coarse aggregate replacement are designed, then changing the replacement ratio of recycled coarse aggregate for experimental verification. The results show that It will lead to a large error if using the strength curves of common concrete to estimate the strength of recycled concrete, and the error grows with the growth of the replacement ratio of recycled coarse aggregate. So It is necessary to establish the special purpose strength curves of recycled concrete with the rate of recycled coarse aggregate. Finally, the strength curves of recycled concrete with recycled coarse aggregate are 30%,50%,70% and 100% are given in this test conditions in this paper.

Abstract: Modals of BP neural networks with different inputs and outputs are presented for different damage detecting schemes. To identify locations of structural damages, the regular vectors of changes in modal flexibility are looked on as inputs of the networks, and the state of localized damage are as outputs. To identify extents of structural damage, parameters combined with changes in flexibility and the square changes in frequency are as inputs of the networks, and the state of damage extents are as outputs. Examples of a simply supported beam and a plate show that the BP neural network modal can detect damage of structures in quantitative terms.

Abstract: This study is the second part of investigation into the interface mechanical performances of cracked reinforced concrete (RC) beams strengthened with prestressed hybrid fiber reinforced polymer (HFRP). Four cases of difference crack location are considered by establishing finite element analysis models to discuss the effort of crack location on the interface stresses in the strengthened beams. The analysis results indicate that the flexural crack obviously changes the distributing of the interface stresses, and an abrupt increase of the stresses arise at the crack location. Moreover, when the crack location is closer from the interface end, the change rate of the stresses is larger.