Advanced Materials Research Vols. 163-167

Abstract: In order to discuss the mechanical behaviour differences between the two-tower and three-tower suspension bridges, based on the Taizhou Yangtze River Bridge, three dimensional space finite element models of two-tower, three-tower with concrete mid-tower and with steel mid-tower were constructed. Through the comprehensive analysis, main conclusions are got as follows: due to the mid-tower lack of effective restraint from side cable, compared with two-tower suspension bridges, three-tower suspension bridges have lower total stiffness and natural frequency, with larger deflection-to-span ratio of main girder. So, some factors such as anti-slipping safety factor between the main cable and saddle, deflection-to-span ratio of main girder and force in mid-tower, which are not important in two-tower design, become controlling ones in three-tower suspension bridges. These factors are related to anti-pushing rigidity of mid-tower, but in contradictory demanding for the rigidity of mid-tower. After comprehensive analysis, steel tower with shape of upside-down ‘Y’ meets all demands, and then, was selected as appropriate structure for the mid-tower.

Abstract: In order to improve dimensional stability of cementitious materials, synergistic effect of shrinkage reducing admixtures (mixture of glycol ethers and siloxane, SRA) and MgO-based expansive agent (MEA) burned at 850 °C, 950 °C, 1050 °C and 1200 °C for 1 h on the deformation of cement paste was investigated while being cured in water of 20 °C, 40 °C and 60 °C, sealedly by polyethylene sheet at 20 °C, 40 °C and 60 °C as well as in simulated using environment. The results illustrated that combined use of SRA and MEA (burned at 850 °C and 950 °C) could compensate the shrinkage of cement paste effectively, and MEA also could make up for the shortage of SRA whose shrinkage-reducing ratio decreased at later age. In the simulated using environment, the paste both with SRA and MEA (burned at 850 °C and 950 °C) was in micro-expansion condition, and the average deformation increased slowly till 240d, and the deformation amplitude reduced to the half of the control sample. Then hydration of MEA in the present of SRA was examined by gravimetry. The results indicated that the presence of SRA retarded the hydration of MEA, but with prolonged curing, the hydration degree of MEA with or without SRA tended to be the same.

Abstract: With the aim of finding the optimum design that maximizes the stiffness of shell structures, an suitable approach for combined shape and topology optimization of free-form surface is presented. For numerical expression for the configuration of free form shell, NURBS (Non Uniform Rational B-Spline) is utilized. For shape optimization, the approach is employed to calculate the differential of total structural strain energy corresponding to surface height parameters. The surface height is adjusted iteratively according to its sensitivity to total structural strain energy. For topology optimization, the OC algorithms which are derived from the necessary optimality conditions are used and element connectivity is taken as design variable. The method has been implemented into a computational 3D model and example is provided to show the applicability of the present method.

Abstract: The size optimization of truss-plate composite structure is presented in this paper. Two improved random optimization algorithms, heuristic particle swarm optimizer (HPOS) and quick search optimizer (QGSO), are combined with finite element method to achieve the optimal design of truss-plate structure. The discrete variables are converted by the mapping function method. An example of the composite structure is given to test this two improved random optimization algorithms. The results show that the QGSO have a better convergence rate than the HPSO in the early time. They are all converged at the same fitness value and feasible on composite structure optimization.

Abstract: In this paper, determinate beam and indeterminate beam with multiple span are optimized by using genetic algorithm, the mathematic model of optimize beam is built and the processing method of constraint conditions is given. The examples show that the algorithm could be used for optimizing determinate structure, and also optimizing indeterminate structure. Compared to the linear approximation method, genetic algorithm has advantages of being simple, easy, fast convergence and has no use for changing the objective function and constraint conditions to linearity or other processing. Its results agree with linear approximation method’s. It is the other method that can be adopt in engineering field.

Abstract: The stress state of finished bridge and service stage is influenced by various closure schemes in cantilever construction of multi-span prestressed concrete box-girder bridge. Two typical bridges—multi-span prestressed concrete continuous rigid frame bridge and girder bridge are investigated, The stress state in different closure schemes are analyzed using finite element(FE) analysis. Meanwhile, compared the healthy monitoring data, it has been found that taking the closure sequence from side span to middle span in cantilever construction of multi-span prestressed concrete box-girder bridge can lower stress of girder and pier in finished bridge stage, as well as reducing deformation of girder in service stage. Hence, the closure sequence from side span to middle span is more suitable for cantilever construction of multi-span prestressed concrete box-girder bridge.

Abstract: Reinforced PHC piles make use of nonprestressed steel bars to reinforce the initial steel cage, with the intent being to invent novel piles that have better flexural properties than the conventional PHC piles. In this study, a comprehensive test program was carried out with 12 full-scale test piles to compare the flexural properties of two different types of PHC piles. The flexural stiffness of the reinforced PHC pile is greater than the flexural stiffness of the conventional PHC pile. The Reinforced PHC pile and the conventional PHC pile exhibited similar axial stress development, planar section remained in pile mid-span during the initial period and the neutral axis shifted upward after concrete cracking. The cracking patterns and failure modes for two different types of PHC piles are evidently different. The moment capacities for reinforced piles were significantly higher than the values for the conventional piles, and the improvements increase in order from the pile specification of B to the AB to the A.

Abstract: This paper introduces the basic principle and characteristic of genetic algorithm (called GA), and it points out the shortcoming of ordinary optimum algorithm and the merit of GA. Comparing the optimum results of GA with accurate value by exemplification, and it is good. This paper provides a systematic thought model and a good method for readers.

Abstract: To reach the optimum mechanics state of long span cable-stayed bridge after it erected, a method is proposed to predict and adjust parameter in construct control of cable-stayed bridge, which integrates the grey prediction theory model and influence matrix adjustment method compositively. The selection of parameters of construct control, reasonable objects of adjustment and determination of state variable during prediction data process are also studied deeply, and a perfect procedure and method is established to identify, predict and optimizing adjust parameters. The method is also verified by construct control of the longest span pre-stressed concrete bridge in Asia, and the effect of construct is very successful. This work of construct control can absolutely demonstrate the validity and practicability of the method.

Abstract: Current guidelines such as TM5 and ASCE use a trial and error procedure to design RC slabs against blast loads. Although the trial and error procedure is easy to implement, it may not result in a optimal to resist blast loads. In this study, SDOF system recommended by TM5 and ASCE was adopted to simplify RC slabs; the bilinear model was selected to simulate the resistance-deflection curve for dynamic response analysis. After comparing the areas under the resistance-deflection curves of RC slabs with different reinforcement ratios, the reinforcement ratio responding to the biggest area can be defined as the optimal reinforcement ratio. These derived relationships are useful to facilitate a design with maximum capacities to resist blast loads.