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CONTENTS
Volume 3, Number 2, June 2016
 

Abstract
It is a challenging problem of assessing the location and extent of structural damages with vibration measurements. In this paper, an improved Extended Kalman filter (EKF) with Tikhonov regularization is proposed to identify structural damages. The state vector of EKF consists of the initial values of modal coordinates and damage parameters of structural elements, therefore the recursive formulas of EKF are simplified and modal truncation technique can be used to reduce the dimension of the state vector. Then Tikhonov regularization is introduced into EKF to restrain the effect of the measurement noise for improving the solution of ill-posed inverse problems. Numerical simulations of a seven-story shear-beam structure and a simply-supported beam show that the proposed method has good robustness and can identify the single or multiple damages accurately with the unknown initial structural state.

Key Words
extended Kalman filter; structural damage identification; Tikhonov regularization; ill-posed inverse problem

Address
Chun Zhang, Jie-Zhong Huang, Gu-Quan Song, Lin Dai and Huo-Kun Li: Department of Civil Engineering and Architecture School, Nanchang University, Nanchang, China

Abstract
We present a methodology to validate with monitoring data finite element models of existing concrete dams: numerical analyses are performed to assess the structural response under the effects of seasonal loading conditions, represented by hydrostatic pressure on the upstream-downstream dam surfaces and thermal variations as recorded by a thermometers network. We show that the stiffness effect of the rock foundation and the surface degradation of concrete due to aging are crucial aspects to be accounted for a correct interpretation of the real behavior. This work summarizes some general procedures developed by this research group at Politecnico di Milano on traditional static monitoring systems and two significant case studies: a buttress gravity and an arch-gravity dam.

Key Words
existing concrete dams; thermal analysis; finite element model; validation; monitoring data

Address
Martina Colombo, Marco Domaneschi and Aldo Ghisi: Department of Civil and Environmental Engineering, Politecnico di Milano, Italy

Abstract
The Pulse-Pre Pump Brillouin Optical Time Domain Analysis (PPP-BOTDA) technique is introduced to implement the multi-direction strain measurement. The monitoring principle is stated. The layout scheme of optical fibers is proposed. The temperature compensation formula and its realizing method are given. The experiments, under tensile load, combined bending and tensile load, are implemented to validate the feasibility of the proposed method. It is shown that the PPP-BOTDA technique can be used to discriminate the multi-direction strains with high spatial resolution and precision.

Key Words
multi-direction strain measurement; PPP-BOTDA; distributed optical fiber; experimental study

Address
Huaizhi Su: State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University,
Nanjing 210098, China
Meng Yang: College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, China
Zhiping Wen: Department of Computer Engineering, Nanjing Institute of Technology, Nanjing 211167, China


Abstract
Based on classical viscoelastic damper, a brand-new damper is designed by the change of simple construction to implement vibration control for both translational vibration and rotational vibration simultaneously. Theoretic analysis has been carried out on the restoring force model and the control parameters. Two improved models are presented to obtain high simulation precision. The influence of the size, shape of the viscoelastic material, the ambient temperature and the response frequency on the vibration control effect is analyzed. The numerical results show that the new type viscoelastic damper is capable of mitigating the multi-dimensional seismic response of offshore platform and the response control effect has complicated relations with aforementioned related factors.

Key Words
viscoelastic damper; platform; multi-dimensional seismic response; seismic control

Address
Xiao-Yu He: Zhejiang Provincial Planning, Design & Research Institute of Communications, Hangzhou 310006, P.R. China
Hong-Nan Li: State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Ganjingzi District, Linggong Road 2, Dalian, 116024, P.R. China
Jun Zhang: State Grid Zhejiang Electric Power Company, Hangzhou, 310007, P.R. China

Abstract
Based on the change of traditional viscoelastic damper structure, a brand-new damper is designed to control simultaneously the translational vibration and the rotational vibration for platforms. Experimental study has been carried out on the mechanical properties of viscoelastic material and on its multi-dimensional seismic response control effect of viscoelastic damper. Three types of viscoelastic dampers with different shapes of viscoelastic material are designed to test the influence of excited frequency, strain amplitude and ambient temperature on the mechanical property parameters such as circular dissipation per unit, equivalent stiffness, loss factor and storage shear modulus. Then, shaking table tests are done on a group of single-storey platform systems containing one symmetric platform and three asymmetric platforms with different eccentric forms. Experimental results show that the simulation precision of the restoring force model is rather good for the shear deformation of viscoelastic damper and is also satisfied for the torsion deformation and combined deformations of viscoelastic damper. The shaking table tests have verified that the new-type viscoelastic damper is capable of mitigating the multi-dimensional seismic response of offshore platform.

Key Words
viscoelastic damper; platform; multi-dimensional seismic response; seismic control

Address
Xiao-Yu He: Zhejiang Provincial Planning, Design & Research Institute of Communications, Hangzhou 310006, P.R. China
Tie-Wei Zhao: Ningbo Port and Waterway Administration, Ningbo, 315041, P.R. China
Hong-Nan Li: State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Ganjingzi District, Linggong Road 2, Dalian, 116024, P.R. China
Jun Zhang: State Grid Zhejiang Electric Power Company, Hangzhou, 310007, P.R. China


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