Key Indicators Of Design Theory On Engineering Structures In The Whole Life-Cycle

Construction of engineering structures usually demands relatively higher investment and more resource. In order to insist on a goal of sustainable development, to improve economic return, effectively to save resource, to reduce various risks and to obtain long-term benefits, it's much necessary to carry on a life cycle research on engineering structures and its application with a global perspective. With the norm of structural safety, serviceability, durability and economical efficiency achieving an optimization, the fundamental frame of life cycle research on engineering structures is established, the research methods of the key indictors and their optimization are put forward and the basic optimization of life cycle design and management of engineering structures is studied. The content includes1) The concept of life cycle on engineering structures is defined by the whole life of engineering structures including planning, design, construction, operation, aging and decommissioning. The characteristic of structural life cycle cost in different stages is illustrated and the connotative meaning of life cycle research on engineering structures is studied with structural timing, probability and cost.2) The fundamental frame of the life cycle research on engineering structures is set up with the concept of research being from goals to content then to methodology. The key goals, which including performance optimization, timing optimization and economy optimization, and the green goals, which taking harmoniousness, environmental protection, energy saving and successiveness into account, constitute the goal system. According to the key goals the basic content of the life cycle research on engineering structures is proposed based on the three key indictors of structural service life, structural life cycle performance and structural life cycle cost.3) The indictor of structural service life, having a global effect of guidance, is the most important indictor of timing. The factors to determine the design reference life of a structure is analyzed and several prediction model of residual service life with probability is proposed with the norm of determining structural service life.4) The indictor of structural life cycle reliability performance is the fundamental indictor among the three key ones. The model of structural time-dependent reliability is established according to the models of time-dependent load effect and structural resistance updated by the service load and actual test information with the Bayesian method. The reliability models in different stages of engineering structures are also defined. In addition, the fuzzy partition and the fuzzy evaluation for the grades of structural durability performance are proposed, the corresponding prediction method is established with the Markov chain and the parameters of structural durability is also predicted based on a path probability method.5) The indictor of structural life cycle cost is the decision-making indictor among the three key ones. The prediction models of main cost including initial construction, inspection, maintenance, repair, failure, deficiency of functionality, decommissioning and income are proposed and the prediction model of structural life cycle cost for engineering structures is established based on theoretic analysis and event tree method according to change of structural life cycle reliability performance.6) Suppose the design reference life is determined, the method to optimize the target reliability index for structural life cycle design on engineering structure:; is proposed based on the structural performance and structural life cycle cost. The method to optimize the initial design of durability level is put forward according to the comparison of structural life cycle cost. And the method to control and manage the main parameters of structural design is established based on the target reliability and the correlative cost so as to increase robust of a structure.7) The target reliability index of the foundation structures of sea-crossing bridges on serviceability limit states is suggested and a new method of calibrating factors of live loads, which is based on the contributed ratio of tensile stresses of reinforcing bars produced by various loads to the maximum crack width of concrete, is proposed. The calibration of the reliability-based factors of the frequent value and the quasi-permanent value of live loads is conducted through an analysis of an actual sea-crossing bridge and its main design parameters are also controlled and managed.8) The decision-making method of life cycle management on engineering structures in service life is established. Within this method, the target reliability index of life cycle management for existing structures is obtained and the planning and the timing of decision-making for the actions of inspection, maintenance and repair are optimized based on the prediction and the comparison of structural life cycle cost according to the norm of various actions carrying out.