High precision structural displacement monitoring is challenging, but an effective method for structural health monitoring and particularly damage evaluation. In this paper, a high precision fiber Bragg grating (FBG) displacement sensor with embedded spring is developed to monitor structural displacement variation even at very small ranges. The principle of such monitoring is based on the central wavelength shifts in accordance with the displacement between measuring points. Calibration experiments are conducted to examine the performance of the innovative displacement sensor. The result indicates that the sensor has excellent linearity and repeatability, with the sensitivity coefficient being 23.96[Formula: see text]pm/mm, and the static relative error is 4.94% after three loading and unloading cycles. The displacement sensor therefore shows an excellent sensitivity and high precision for application. Moreover, it has been verified that this sensor is suitable and applicable for displacement monitoring in quasi-static experiment of structures.

The limitation of height-to-width ratio (HWR) for a base-isolated building with elastomeric rubber bearings is of considerable concern to structural design engineers. Guidelines and codes on this type of building have to deal with this issue. Nevertheless, until now, no systematical and quantitative studies have been done on this problem for base-isolated buildings. For this reason, the main objective of this paper is to focus on investigations on the limit of the HWR for the isolated building with rubber bearings under different conditions subjected to earthquake excitations. The simplified formulation is derived to explore the rules of seismic responses for the structural system and some influential factors, such as the site soil conditions, seismic ground motion intensity, period of the isolated system, period of the superstructure and layout of isolators, are studied and discussed. According to the numerical results, it has been found that the effects of site soil conditions on the HWR limit values are important: the softer the site is, the smaller the HWR limit value is under different seismic intensities. The predominant period of an isolated building also plays a considerable role in the HWR limit value, namely, the isolated building with a longer period may have a relatively large HWR value; and the stiffness of the superstructure affects the HWR limit value little. Furthermore, an effective method to improve the HWR limit value is proposed.A time-history calculational method, i.e., the Newmark b method (with coefficients a = 1/2; b = 1/4), is applied to quantitatively analyse the factors influencing the HWR limit of the base-isolated building with rubber bearings. Theses factors include the site soil conditions, seismic ground motion intensity, period of the isolated system, period of the superstructure and layout of isolators. In computations, different structures have been chosen within the range of periods of the practical medium-low-storey buildings.In order to explore the effects of different site soil conditions on the HWR limits of the isolated building, nine seismic acceleration records have been employed, listed in detail in Table 1, which belong to three different types of soil site conditions: hard site, medium site and soft site. Each case of HWR limit at the different sites is calculated with three seismic acceleration inputs. The mean value and variation coefficient (standard variance/mean value) of the results will be given for each site. Effect of site condition and seismic intensityIn this section, the analysis is based on a base-isolated building, whose predominant period is 1·4 s, while 0·65 s before the corresponding building was isolated. Here, the effect of peak accelerations on LIMITATIONS OF HEIGHT-TO-WIDTH RATIO 283

More and more applications exist of base-isolated buildings. So far much attention has been paid to the improvement of design approaches. In this paper, the equation of motion is derived for a torsionally coupled base-isolated structure under the action of seismic ground motion. Based on numerical analyses of the structure, torsional responses and influencing parameters have been investigated and some rules obtained for sites with different soils, in which the superstructure is idealized as a series-rigid floor model, while the isolation system adopts the Bi-linear resilience curve. Applying the method of least squares to the numerical results, three simplified formulae have been produced to approximately calculate the torsional seismic accelerations of base-isolated structures. The results calculated by the practical method proposed in this paper approximate to those obtained by time history analyses. It is shown that the method is of good accuracy in comparative terms and suffices for the needs of engineering designs for base-isolated eccentric structures with rubber bearings under earthquake action.

Multiphase flow measurements have become increasingly important in a wide range of industrial fields. In the present study, a dual needle-contact capacitance probe was newly designed to measure local void fractions and bubble velocity in a vertical channel, which was verified by digital high-speed camera system. The theoretical analyses and experiments show that the needle-contact capacitance probe can reliably measure void fractions with the readings almost independent of temperature and salinity for the experimental conditions. In addition, the trigger-level method was chosen as the signal processing method for the void fraction measurement, with a minimum relative error of −4.59%. The bubble velocity was accurately measured within a relative error of 10%. Meanwhile, dynamic response of the dual needle-contact capacitance probe was analyzed in detail. The probe was then used to obtain raw signals for vertical pipe flow regimes, including plug flow, slug flow, churn flow, and bubbly flow. Further experiments indicate that the time series of the output signals vary as the different flow regimes and are consistent with each flow structure.

The limit of height-to-width ratio (HWR) for base-isolated building with the elastomeric rubber bearings is of considerable concern to structural design engineers. And guidelines and codes on this building in the world have to deal with this issue. Nevertheless, until now, no systematical and quantitative study has been done on this problem for the base-isolated buildings. For this reason, the main objective of this paper is to focus on investigations on the limit of the HWR for isolated building with the rubber bearings under different conditions subjected to earthquake excitations. The simplified formulation is derived and some influenced factors, such as the site soil conditions, seismic ground motion intensity, period of the isolated system, period of the superstructure and layout of isolators, are studied and discussed. According to the numerical results, it has been found that the effects of site soil conditions on the HWR limit values are important, in which the softer the site is, the smaller the HWR limit value is under different seismic intensities; the predominant period of isolated building also plays a considerable role in the HWR limit value, namely, the isolated building with a longer period may have a relatively large HWR value; and the stiffness of superstructure affects the HWR limit value little. Furthermore, an effective method to improve the HWR limit value is proposed.