In order to improve the energy dissipation capacity and self-centering capacity of the frame structure, a functional self-centering beam-column joint based on superelastic SMA bar was proposed. In this paper, based on OpenSees finite element software platform, the finite element numerical model of self-centering SMA reinforced concrete beam-column joints was established by using SMA material self-centering double flag constitutive model, and the finite element simulation under low-cycle reciprocating action was carried out to obtain the hysteretic curve and skeleton curve of the joints. The validity of the joints analysis model is verified by comparing with the existing experimental results. The parameter analysis was carried out, and the parameters such as the quantity, length and yield strength of SMA material were considered respectively. The influence of SMA material parameters on the hysteretic performance and self-centering ability of the joints was analyzed. The results show that the superelastic SMA reinforced concrete beam-column joints have high energy dissipation capacity and self-centering capacity. The numerical analysis model can well simulate the hysteretic behavior of self-centering SMA joints under low cyclic reciprocating loads. The mechanical parameters of SMA bars have a great influence on the seismic performance of joints: under the condition of proper reinforcement, the larger the number of SMA configurations, the smaller the residual displacement and the stronger the centering capacity. Under the same condition, after the SMA bar exceeds the plastic hinge length, it has little effect on the joint performance. Under the condition of proper reinforcement, increasing the yield strength of SMA will improve the bearing capacity and selfcentering capacity of the joints.
Shape memory alloys (SMAs) are a relatively new class of functional materials, exhibiting unique
thermo-mechanical behaviors, such as shape memory effect and superelasticity, which enable their great potentials in
seismic engineering as energy dissipation devices. This paper presents a study of the mechanical behaviors of
superelastic SMAs, specially emphasizing on the influence of strain rate under various strain amplitudes. Cyclic
tensile tests on superelastic NiTi SMA wires with different diameters under quasi-static and dynamic loadings were
carried out to assess their dynamic behaviors. An internal temperature variable which indicates the influence of
loading frequency under various strain amplitudes and different temperatures was introduced to the Liang's
constitutive equation of SMA. Numerical simulation results based on the proposed constitutive equations and
experimental results are in good agreement. The findings in this paper will assist the future design of superelatic
SMA-based energy dissipation devices for seismic protection of structures.
Superelastic shape memory alloys (SMAs) are a class of materials that have the ability to undergo large deformations
while reverting back to their original shape through removal of stress. The unique material can be utilized as key
components for seismic energy dissipation in earthquake engineering. In this paper, an innovative recentering SMAsbased
damper (RSMAD) is introduced. Cyclic tensile-compressive tests on the damper with various pre-strain under
different loading frequency and displacement amplitude are conducted. To assess the effectiveness of the damper in
reducing dynamic response of structures subjected to strong seismic excitations, an extensive experimental program and
main results of shaking table tests performed on reduced-scale steel frame model with and without RSMAD are
presented. In the shaking table tests, several representative seismic signals as well as white noise motion are utilized as
input energy. The comparisons of dynamic behaviors, i.e. storey displacements, interstorey drifts and storey
accelerations, of structural model with and without RSMAD under seismic loading are conducted. The results show that
RSMAD is effective in suppressing the dynamic response of building structures subjected to strong earthquakes by
dissipating a large portion of energy through their hysteretic loops.
Smart precast concrete frame connection based on unbonded shape memory alloy (SMAPCFC) was proposed as a
possible seismic resistance measure for reinforced concrete frame buildings. To investigate the restoring force
characteristics of SMA wire, cyclic tensile tests on superelastic NiTi SMA wires with three diameters were carried out.
The effects of the different loading conditions, namely: cyclic loading-unloading number, strain amplitude, loading
frequency and ambient temperature, on the mechanical behavior described by some fundamental quantities, such as
energy dissipation per cycle, secant stiffness, equivalent damping, residual strain, were examined. The temperature
changes of the SMA wires due to the latent heat under different loading conditions were also discussed.
Energy dissipation technique, relying on the absorption and dissipation of big amount of energy by devices, provides
a very effective passive method of protecting structures from the hazard of earthquakes. An innovative hybrid
damper combining friction device with superelastic shape memory alloy (SMA) wires was proposed. The most
important property of the damper is the integration with stable energy dissipation capacity mostly provided by the
friction device and re-centring feature profited from the superelastic pre-tensioned SMA wires. To investigate the
mechanical behaviors of the damper as a function of pre-displacement, displacement amplitude and loading
frequency, cyclic tensile tests on a scale model under various loading conditions were conducted. The effectiveness
of the damper to reduce the seismic vulnerability of structures is assessed through nonlinear time history analysis on
a steel frame with the innovative dampers subjected to representative earthquake ground motions. The experimental
and analytical results show that the hybrid SMA damper has both the stable energy dissipating and recentring
features with the hysteretic loop under cyclic loading-unloading, and it is effective in reducing the seismic response
of structures.
Shape memory alloys (SMAs) are a relatively new class of functional materials, exhibiting special thermo-mechanical behaviors, such as shape memory effect and superelasticity, which enables their applications in seismic engineering as energy dissipation devices. This paper investigates the properties of superelastic shape memory alloys and highlights the influence of strain rate on superelastic behavior under various strain amplitudes by cyclic tensile tests on NiTi SMA wires. A novel constitutive equation is proposed to describe the strain-rate dependent hysterestic behavior of superelastic SMAs at different strain levels. This development is based on the Graesser and Cozzarelli's model, which has the advantage of simplicity. To verify the effectiveness of the proposed constitutive equation, experiments on a superelastic NiTi wire with different strain rates and strain levels are conducted. Experimental results and the numerical simulation based on the proposal constitutive equation are in close agreement. The results in this paper are useful for future design of superelatic SMA-based energy dissipation devices for seismic protection of structures.
In this paper, we propose a new featured-based geo-registration technique for aerial images that helps nearly real-timely calibrate and update the telemetry data and sensor model on flight. Firstly by using the available telemetry information, we bring both images into a common projection space. Second, we use the distribution of local geometric properties to guess the initial rotation and translation parameters. After the coarse alignment, the Harris operator is adopted to produce the initial feature points set, while the corresponding feature points set in the target image can be established through normalized correlation in local neighborhood of the selected points' position. Finally after the matched feature point sets are well constructed, the transform parameters can be solved by least square error estimation. The experiment shows our algorithm can effectively reduce the error in telemetry data caused by various noises.
The paper brings forward a new method for identifying and annotating erotic films based on content analysis. First, the film is decomposed to video and audio stream. Then, the video stream is segmented into shots and key frames are extracted from each shot. We filter the shots that include potential erotic content by finding the nude human body in key frames. A Gaussian model in YCbCr color space for detecting skin region is presented. An external polygon that covered the skin regions is used for the approximation of the human body. Last, we give the degree of the nudity by calculating the ratio of skin area to whole body area with weighted parameters. The result of the experiment shows the effectiveness of our method.
The paper discusses practical aspects of LED measurements and problems about how to improve the measurement accuracy of LED spectral properties when using linear CCD sensor. Designed and implemented an instrument for LED spectral measurement based on linear CCD sensor. The CCD sensor has 2048 pixels and ultra-high sensitivity. The duration of one measurement is about 10ms. For reducing the effect of CCD output noise, a software filtering method is introduced. After software calibration, the accuracy of color temperature is 40K in the range of 1300K to 25000K, and accuracy of wavelength is 0.2nm in the range of 360nm to760nm. The accuracy of chromaticity coordinated (x, y) or (u, v) is better than 0.003.
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