The Plastic Limit Analysis And Safety Evaluationof Slot Rack Supporting Structure Of Aqueduct

Aqueduct, which guides and transports the canal water in open channel way, is the overhead cross-conveyance structure built for crossing the barriers, such as canals, valleys, ravine, depressions and roads. It is an important part of the conveyance lifeline engineerings. According to investigation statistics, plastic instability of the aqueduct’s supporting structure is one of the main failure modes of the aqueduct structure, so the plastic limit analysis of aqueduct’s supporting structure is particularly important to ensure security in the operational phase.As a new kind of numerical methods of limit analysis in recent years, elastic modules reduction method (EMRM) has been applied successfully in limit analysis and safety evaluation of the steel structure of civil and hydraulic engineering. It is adopted to plastic limit analysis theory and generalized yield criterion, and uses element bearing ratio and uniformity of bearing ratio, and combines with the principle of strain energy transformation and energy conservation of elastic modulus adjustment strategy. By this way, EMRM carries on the linear elastic iteration to obtain the maximum allowable stress field and ultimate bearing capacity. Slot rack supporting structure of aqueduct is reinforced concrete frame structure, its material properties and yield criterions of cross-section are more complex than steel structure. How to accurately simulate the material properties of the combination of steel and concrete, and to set up the calculation expression of element bearing ratio of reinforced concrete structure according to the relationship of the element-sectional internal forces and section strength, is the difficulty and critical issue of the plastic limit analysis and safety evaluation of aqueduct’s supporting structure based on elastic modules reduction method.The main research work in this paper are as following.1. According to the bearing characteristics and failure mechanism of reinforced concrete frame structure, the calculation expression of element bearing ratio of reinforced concrete structure only considering the the bending moment yield is presented. Then with elastic modulus adjustment strategy of EMRM, the EMRM for the ultimate bearing capacity analysis of reinforced concrete frame structure is set up.2. Combined with the structural characteristics of slot rack supporting structure of aqueduct, and the application of EMRM of the limit analysis of reinforced concrete frame structure, plastic limit load, component safety factor and overall safety factor of slot rack supporting structure of aqueduct are obtained, thus its safety evaluation.3. Based on elastic modules reduction method, the influencing factors of slot rack supporting structure of aqueduct that meet the requirements of safety limits is analyzed. The influences of parameters such as the rack height, the cross-section strength of the column, span of aqueduct body are discussed on the ultimate bearing capacity, the component safety factor and the overall safety factor of slot rack supporting structure of aqueduct.4. Based on EMRM of reinforced concrete frame structure that is established in this paper, the rack height of aqueduct’s supporting structure is determined quickly and accurately within the range allowed by the engineering. It provides an effective and feasible method for the engineering to determine a reasonable height of the racks.