Hong Nan Li

Lessons Learnt from Building Damages in the Wenchuan Earthquake

The earthquake Ms=8.0 at Wenchuan county of Sichuan Province in China happened on May 12, 2008. In the strong seismic area, engineering structures were badly damaged in various grades or collapsed. This paper focuses on the description and analysis of the damage phenomena of engineering geology, buildings and lifeline engineering structures based on the on-site investigation of the earthquake damage. Finally, some valuable lessons learned from this big earthquake are presented including the suitable building structures should be chosen for important buildings to resist the seismic action in the strong earthquake area when the building is designed; the concept design and applications of energy-absorbed and vibration-reduced techniques should be paid attention; the comprehensive safe evaluations for the existing buildings should be done in the strong seismic active area; the seismic designs and researches on bridges and pavement should be emphasized, and the seismic design and research on facilities of communication, and power and water supplies should be regarded as key issues to make the facilities expedite for disaster rescue after earthquake. The content in this paper may be as a reference to seismic design of buildings, reconstruction of disaster area and revision of corresponding codes and regulations.

On Optimal Sensor Placement Criterion for Structural Health Monitoring with Representative Least Squares Method

A novel sensor placement criterion is proposed for structural health monitoring after five influencing criteria are critically reviewed. The objective of the proposed criterion is to achieve best identification of modal frequencies and mode shapes through almost unbiased estimation of modal coordinates. The proposed criterion derived by the Representative Least Squares method depends on both the characteristics and the actual loading situations of a structure. It selects sensor positions with the best subspace approximation of the vibration responses from the linear space spanned by the mode shapes. Furthermore, the connection between the Effective Independence and the approximate Representative Least Squares estimator is obtained through matrix perturbation analysis. It is found that the Effective Independence is a step-by-step approximation to that of the Representative Least Squares criterion.

Impact of Flood on a Simple Masonry Building

AbstractIn this paper, the impact action of a flood on rural mountain buildings is systematically studied. First, based on the one-dimensional Saint-Venant water equation explicit-difference scheme, a new explicit-difference scheme is deduced to establish the evolutionary routing model of a flood. A computational formula about the impact loading of the flood model is deduced. Secondly, an impact experiment of a flood on buildings is carried out in a large wave-current tank. The heights of the water are 0.6, 0.9, and 1.2 m, and the distances between the building and floodgate are 3, 6, and 9 m, respectively. The model scale of the buildings is 1:6, and three buildings with different ratios of holes are designed to simulate the buildings in countries and villages. Based on the experimental results, the effects of the heights of the water, the distances between buildings and floodgates, and the ratios of holes on the impacting pressure are investigated. The numerical results are compared with the experimenta...

Estimation of Hysteretic Energy of MDOF Structures Based on Equivalent SDOF Systems

It is important for obtaining the relationship between seismic energies of single degree-of-freedom (SDOF) systems and multiple degree-of-freedom (MDOF) structures in engineering. In this paper, the formula of hysteretic energy between the MDOF structures and equivalent SDOF systems is developed. Here is also presented the procedure for estimating hysteretic energy of MDOF structures subjected to severe ground motions employing the energy relation equation based on equivalent SDOF systems. Eight examples for two regular and six irregular MDOF structures show that the procedure to obtain the hysteretic energy demands of MDOF structures may be used as a simple and effective energy estimation method.

Hysteresis Model for Superelasticity of Shape Memory Alloy Based on ANN

Superelasticity is one of the most important properties of shape memory alloy. In this paper, the superelastic deformation behavior of NiTi shape memory alloy subjected to cyclic loading with stable superelasticity is experimentally investigated. According to test data, a constitutive model for the superelasticity of shape memory alloy is presented based on the artificial neural network (ANN). Numerical results agree well with experimental observations that verified the constitutive model being of high accuracy. This model can avoid the difficulties of other models on the determination of the parameters and is suitable for practical engineering application. Thus, a new method is provided for building the constitutive model of shape memory alloy.

Treatments with Fracture Mechanics in Debonding of FRP-Strengthened Concrete Beams

External bonding fiber reinforced polymers (FRP) to the tension faces of reinforced concrete (RC) beam as an effective approach of rehabilitation and strengthening of reinforced structures have attracted significant interests of researchers in the past decade. Since the load-carrying capacity of RC beams strengthened with the FRP is dominated by interfacial delaminated failure, the anchorage strength in FRP to concrete bonded joints under shear and the debonding stress transferring behavior at the end parts of flexural concrete members bonded with FRP have been deeply studied. Recently, methods of fracture mechanics have been introduced into analyzing the above issues. Compared with the traditional methods, the analytical models of existing fracture mechanics are reviewed and analyzed. Based on them the debonding bearing capacity of FRP-strengthened RC beams is calculated and the corresponding finite element models are created. These models of fracture mechanics are then evaluated with the finite element results and the experimental data from author’s and the literature. Some conclusions with engineering significance are drawn.

Model of Transmission Tower-Pile-Soil Dynamic Interaction Under Earthquake: In-Plane

In this paper, the mechanical model of Soil-Pile-Structure interaction of transmission tower-cable system in in-plane is presented and the corresponding equations of motion are derived, in which the nonlinear characteristics of soil is included in the dynamic time history analysis. The computer program for the system is complied and used to calculate the earthquake response of an actual transmission tower. The results of numerical calculation are compared with and without considering soil-pile-structure interactions, which show that the dynamic interaction should be taken into account in the soft foundation.© 2002 ASME

Health monitoring system for a tall building with Fiber Bragg grating sensors

Fiber Bragg grating (FBG) sensors demonstrate great potentials for structural health monitoring of civil structures to ensure their structural integrity, durability and reliability. The advantages of applying fiber optic sensors to a tall building include their immunity of electromagnetic interference and multiplexing ability to transfer optical signals over a long distance. In the work, FBG sensors, including strain and temperature sensors, are applied to the construction monitoring of an 18-floor tall building starting from its construction date. The main purposes of the project are: 1) monitoring the temperature evolution history within the concrete during the pouring process; 2) measuring the variations of the main column strains on the underground floor while upper 18 floors were subsequently added on; and 3) monitoring the relative displacements between two foundation blocks. The FBG sensors have been installed and interrogated continuously for more than five months. Monitoring results of temperature and strains during the period are presented in the paper. Furthermore, the lag behavior between the concrete temperature and its surrounding air temperature is investigated.

Lag Time and Working Frequency of FBG Strain Sensor

This paper investigates the lag time and the highest working frequency of Fiber Bragg Grating strain sensor in which strain wave transfers to bare FBG by analyzing the transmit course of the strain wave. The results show that the FBG strain sensor is applicable to the measurement of low frequency vibration in engineering. As its application, FBG strain sensors are used in the shake table test of offshore platform model and show good capability in measuring the dynamic strain of vibration system with low frequency.

Seismic Damage Characteristics of RC Shear Wall with Diagonal Profile Steel Braces by Experiment

This paper focuses on an experimental investigation and theoretical analysis of different types of RC shear wall with the profile steel braces in two side columns and diagonal profile steel braces of walls subjected to applied repeated cyclic loads. Fifteen RC shear walls with different shear span ratio are tested and their aseismic charactertics are studied. The effect of profile steel bracings on failure property, bearing capacity, ductility and hysteretical characteristic of shear wall is investigated based on experimental results. It is shown that adding the profile steel braces on the boundary column and inner of walls can obviously enhance the ultimate strength of specimens and improve their aseismic characteristics. Finally, the mechanical model of the shear wall is presented and the formulae for calculating the load-carrying capacity are developed. Numerical analyses indicate that the theoretical results agree well with those from experiments.