Study On Environmental Actions And Performance Degradation Of Structures For The Needs Of Structural Life-Cycle Design

The feature of structural life-cycle design is that it can consider the post-investment resulting from the maintenance, detection, repair, etc. of the constructed structure in the design stage, and minimize the total resource investment through evaluating building cost, customer cost and social cost comprehensively. To achieve the ultimate goal of sustainable structural engineering, it is necessary to introduce the life-cycle method in the structural design. Comparing with the existing design method, the structural life-cycle design mainly includes five research fields, such as the continuing action of design loads, the decay behavior of structural resistance, the reliable index of performance evaluation, the system model of operation and management and the economic benefits of life-cycle design.Since the lack of basic data about the environmental actions, the development of the structural life-cycle theory is severely hindered and meanwhile the relevant researches about the degradation laws of structural resistance and Performance Evaluation are immature, which also limit the application of life-cycle design. Thus around the key scientific issues of structural life-cycle design, we have investigated the attenuation principles of the structure/component function due to the action of various environmental loads and the applicability of the performance evaluation. The main work and research results are as follows:1) The fatigue wind speed is the main fatigue load of large bridge and high-rise building. The current researches primarily focus on the statistic of extreme wind speed, and the fatigue wind speed, which is the base of wind-induced fatigue research, is ignored. To get environmental action spectrums for life-cycle structure design, the continuous wind speed data were employed to compile the fatigue-wind-speed spectrum, which were provided by Changhai wind farm of Liaoning, Luohu weather station etc. of Shenzhen and the stations in Bohai sea. Weibull distribution was adopted herein, and its applicability and the characteristics of the joint distribution of wind Speed and wind Direction are analyzed as well. Based on these results, region division of fatigue wind speed was established to provide wind-induced fatigue action and its parameters for research of life-cycle design.2) Freezing temperature plays an important role in the freezing-thaw damage of the concrete, but is always neglected in counting and analyzing Freeze-thaw action. Considering the effect of the freezing temperature on the freeze-thaw damage, we have investigated the probability distribution of freeze-thaw action of Harbin, Beijing, Hohhot, Yining and Zhengzhou using the temperature data from 1951 to 2009, and a way to compile the freeze-thaw action spectrums was proposed herein. Thus we established freeze-thaw action zones in China through selecting appropriate indicators.3) Utilizing the temperature data of Harbin, Bohai sea, Shenzhen and Guangzhou, we have analyzed the probability distribution of daily extreme temperature (namely, daily maximum and minimum temperature) and diurnal temperature range, and then established temperature action zones in China. In view of the existing regulations did not consider the influence of the climatic differences between south China and north China on the temperature action of the bridges, we have investigated the parameter selection of temperature gradient of sunshine and cold wave on hollow components of large bridge by analyzing meteorological data and generating finite element model, and proposed the prediction formulas.4) Fiber model can not be used to investigate the bond slip of steel directly. Based on the Opensees and fiber model, the bond slip of joint steel in footing was simulated accompany with the zero length element and Bond_sp01 material. By precise modeling with ANSYS, the change law of the parameters of Bond_sp01 under corrosion was studied, and the deterioration of steel bond performance can be considered when analyzing performance degradation of the joint in footing. Thus we proposed a way to consider the descending effects of bonding capacity in fiber-based analysis.5) The function indexes (eg. reliable index) of the current design method, cannot directly reflect the deterioration of structural performance. Therefore we chose the service life of structure/component as index, and the concept of life index was introduced. The service life of structural component under fatigue wind load and freeze-thaw action was predicted, in which the relationship of material performance obtained from laboratory and nature environment, the information of environmental action spectrums and the material performance degradation from experimental results are all involved.6) From the structure level, we have compared the earthquake resistant capability of multi-aged buildings in Dujiangyan City through investigating the seismic damage information of more than 2000 buildings during Wenchuan earthquake in this area. It is helpful in testing and verifying the numerical simulation results through comprehensively considering the effect of various factors such as structure type, design code and aging process on the seismic capacity of buildings. The analysis results can provide reference for investigating the rule of structural behavior deterioration.