Sustainability Quantitative Assessment Of Reinforced Concrete Bridges Based On Uncertainties

In its life cycle, bridge can support transport, in the meanwhile, due to the activities of construction, maintenance and demolition, it can also bring some environmental and social impact, leading to a decreasing sustainability. In this paper, a quantitative evaluation method is adopted to measure the sustainability of bridge in its life cycle, from three aspects of society, environment and economy, mainly focusing on life cycle environmental impact and life cycle cost. By multi-objective optimization, the operation phase accounting for the longest life is optimized, exploring a new approach of sustainability assessment and process management on bridge engineering. The following work is mainly conducted:(1) Make clear of the system boundary and content of bridge life cycle assessment (LCA) and the calculation formula is given by Eco-indicator. In addition, the causes of uncertainty in the stage of life cycle inventory are analyzed, and the method of LCA based on uncertainty is presented. A case is studied to give the bridge’s environmental impact in different stages and the characteristics of different environmental impact are analyzed. Besides, the LCA uncertainty of the sample bridge is calculated by statistical method, and the probability distribution of the environmental impact is obtained.(2) Bridge life cycle cost (LCC) is divided into different sectors, and the calculation formula for each part is established. By discussing the uncertainty of LCC data sources and its statistical methods, the probability distribution of the cost is drawn. In addition, a bridge LCC model based on time cost and uncertainty is established, considering preventive maintenance cost and essential maintenance cost.(3) The bridge environmental impact is calculated in a monetary form by willingness to pay by using the integrated effect of matrix operation. Through a unified computing, the bridge environmental impact and cost are integrated, obtaining a measureable bridge sustainability assessment result. At the same time, based on the fuzzy mathematic theory, a model of single index output and multi-index inputs is established.(4) In consideration of the characteristic of bridge’s long operation period, combined LCA and LCC with time-dependent reliability, the paper investigates the effect of the maintenance strategies on LCA and LCC by Monte Carlo simulation. In addition, a multi-objective optimization of the strategies of preventive maintenance and essential maintenance is conducted based on Pareto Optimization. (5) The bridge sustainability quantitative assessment software is developed by integrating with the required environmental impact and cost database and using a unified inventory. This software can be used to assess the life cycle environmental impact and the life cycle cost of bridge separately, or assess its sustainability synthetically. Besides, it can also realize the functions of schemes comparison, maintenance strategies optimization and uncertainty analysis.