Appraisal And Reinforcement Research On Existing Reinforced Concrete Structure Based On Target Service Life And Overall Reliability

Current appraisal standard and reinforcement design specification for existing building are inadequate for engineering practice in the following aspects. Firstly, the service life requirement from owners is hard to meet for existing buildings. Secondly, there are no any quantified indices to appraise existing structure. Thirdly, the appraisal standard is inconsistent with reinforcement design specification. In addition, with little development, methodology of reinforcement design does not introduce target reliability. To address these problems, this paper deals with the reliability analysis and appraisal of existing structure member, overall reliability appraisal, reinforcement design methodology as well as reinforcement design based on structure member reliability to achieve the reasonable and economical result. The main study is as follows.1. In the reliability analysis of structural member, stationary binomial random load model of current specification is adopted and existing structure loads corresponding to different target service life are compared with counterparts of specification. Therefore, load statistical characteristics and correction factor of live load normal value are obtained based on various target service life. In addition, wind load and earthquake action characteristics are studied. According to the load action feature and super probability theory, important parameter of existing building in Guangzhou region such as basic wind pressure conversion factor and maximum value of horizontal earthquake influence coefficients are derived. As a result, the load and action computation in reliability analysis can be adjusted on the basis of target service life.2. In the research on reliability appraisal of structure member, reliability appraisal expression by subitem coefficient method is established for existing frame structure based on the characteristics of resistance and load. Through calibration method for target reliability and optimized load and computation equation for resistance subitem coefficients in current specification, load and resistance subitem coefficients are derived for different target service life. Therefore, reliability appraisal of structure member can be made corresponding to different target service life.3. In the overall reliability appraisal of structure, membership grade is introduced to the reliability appraisement grade set so as to avoid the large gap between grades. And improved analytic hierarchy process is applied to determine the weight of each system member. Related factors are put into the principle layer. So the appraisal scope is extended in contrast to the simple classification of general analytic hierarchy. Finally, the overall reliability appraisement set is determined by appraisement grade set and weight of structure member. In this way, reliability appraisal can be conducted to guide further maintenance and reinforcement design. This approach is compared with current specification and proved effective in engineering examples. Its obvious advantage lies in the convenience and high efficiency of electronic computation by program compilation.4. In the study on reinforcement design methodology, integrity theory is applied to reliability reinforcement design of building and integrity methodology of reliability reinforcement design is established. Combined the safety, applicability with durability, structure reinforcement design is conducted from single member to integral structure and even the whole environment, which is useful for building reinforcement research. Taking account of the characteristics of reliability-based reinforcement design, a comprehensive integration method for building reinforcement is proposed and a flow chart is made to illustrate reliability reinforcement design procedure based on integrity theory. Consequently, an effective mechanism is built to connect reliability appraisal and reliability reinforcement design.5. Reliability-based reinforcement design research is carried out in three aspects. Firstly, from the concept of super probability, reverse-reliability computation equation in the reinforcement design is derived from lognormal distribution of initial resistance. However, reverse-reliability is still not put into practice, so normal algorithm reinforcement design method is also presented by iteration and approach target reliability. Secondly, with the frame of normal algorithm, member reinforcement design software package is developed based on specification. Moreover, this software package includes input and output visualization function and it enables equation in calculation account to output in word format which enhances the efficiency of engineers and makes foundation for computerizing the reliability analysis of reinforced member. Lastly, reliability of reinforced structure members is analyzed and compared with member reliability of new-built structure. As a result, reliability computation method for reinforced member is proposed due to inadequate bearing capacity and function alteration respectively. A program is developed for reliability analysis and the result shows that for given target service life, the reliability influence factors of reinforced axially compressed column are concrete strength variation coefficient of existing structure, the load increase factor as well as the ratio of construction load to design load by the order of importance. This result provides useful and practical information for reinforcement design. Different from leap grading in structure appraisement and bearing capacity-based reinforcement design in the present engineering practice, this paper deals with existing building appraisement and reinforced design based on target service life and reliability. And a bridge is established between appraisal and reinforcement design, contributing to reliability-based reinforcement design research. Furthermore, the engineering examples are given in the attachment to compare the proposed method in this paper with the current method in the terms of economy. It turns out that this method can reduce the engineering cost significantly for the given target service life and target reliability, which is helpful and meaningful for guiding reinforcement engineering practice.