A new type connection with optimum stiffness configuration for very large floating platforms

A novel connection for super-scale modularized floating platforms is put forward for the purposes of suppressing the oscillation of the platform. The platform consists of multiple blocks where semi-submergible modules are flexibly connected with upper decks by elastic cushions. For the connection between adjacent blocks, neighboring decks are linked by rigid hinges and neighboring floating modules are connected by flexible linkages. Based on the linear wave theory and rigid-module-flexible-connection (RMFC) model, the governing equation of motions for the modularized floating platform is derived by using a network modeling method. In numerical case studies, a five-block platform is investigated. Taking combined responses of the platform and the connector loads as an objective function, the stiffness configuration of the connection and the elastic cushion is optimally determined by using a genetic algorithm. At last, the short-term extreme responses of the floating platform with the optimum setting of the stiffness configuration of the connection are analyzed.

Research on the Overall and Local Mechanical Behaviors of Steel Box Girder Cable-Stayed Bridge via Incremental Launching Construction

<p>In this paper, a large-span cable-stayed bridge with double pylons and double cable planes is employed to study the overall and local mechanical behaviors. The steel box girder bridge is constructed by incremental launching with the maximum span of 50 m. Through the overall stress analysis, the most unfavorable stress position of the structure in the incremental launching construction is identified; the refined local stress analysis is carried out for the girder section at this position, and the local stress characteristics of the structure are studied. The mechanical performance and the applicability of incremental launching are determined by comparing four kinds of elastic cushion. This paper aims at improving the safety of incremental launching construction of steel box girder bridge, and can provide reference for similar projects.</p>

Reconfigurable Multipoint Forming Using Waffle-Type Elastic Cushion and Variable Loading Profile

There is an increasing demand for flexible, relatively inexpensive manufacturing techniques that can accommodate frequent changes to part design and production technologies, especially when limited batch sizes are required. Reconfigurable multi-point forming (MPF) is an advanced manufacturing technique which uses a reconfigurable die consisting of a set of moveable pins to shape sheet metal parts easily. This study investigates the use of a novel variable thickness waffle-type elastic cushion and a variable punch-loading profile to either eliminate or minimise defects associated with MPF, namely wrinkling, thickness variation, shape deviation, and dimpling. Finite element modelling (FEM), analysis of variance (ANOVA), and the response surface methodology (RSM) were used to investigate the effect of process parameters pertaining to the cushion dimensions and type of loading profile on the aforementioned defects. The results of this study indicate that the most significant process parameters were maximum cushion thickness, cushion cut-out base radius, and cushion cut-out profile radius. The type of loading profile was found to be insignificant in all responses, but further investigation is required as the rate, and the thermal effects were not considered in the material modelling. Optimal process parameters were found to be a maximum cushion thickness of 3.01 mm, cushion cut-out base radius of 2.37 mm, cushion cut-out profile radius of 10 mm, and a “linear” loading profile. This yielded 0.50 mm, 0.00515 mm, 0.425 mm for peak shape deviation, thickness variation, and wrinkling, respectively.

Measurement of forces on multi-point forming tools using fibre Bragg grating sensors

Multi-point forming uses forces applied to a tool, comprising of multiple pins set at different heights, to form sheet metal for panelling in white goods, automotive bodywork, aircraft frames and so on. The use of multiple pins allows for rapid change over and flexibility in the tool making it suitable for small-batch and prototype component manufacture. To explore the relationship between ‘springback’ of the sheet metal on release from the tool, and the applied pin force, it is first necessary to understand and measure the forming forces. This article presents a novel method of measuring forming forces on individual pins in a multi-point forming tool using fibre Bragg grating sensors, monitoring the elastic strain on the selected pins during the forming process. The operating principles behind forming force measurements using fibre Bragg gratings are introduced and a relationship is developed between springback in the formed part after the final unloading and the forming force as measured on selected individual pins under different compression ratios (30%, 40%, 50% and 60%) of the elastic cushion between the tips of the pins and the workpiece. Experiments were performed to validate the proposed measuring method, and results indicate that forming forces detected by the proposed method correlated well with the results obtained by numerical simulation. This suggests the proposed method has good potential for real-time measurement and monitoring of forming force distribution in multi-point forming tools during the forming process.

Theoretical study of long elastic sleeper track to reduce vibrations induced by subway trains

Long elastic sleeper track (LEST) is a medium vibration reduction track, which is gradually used in urban rail transit in recent years. In order to analyze the structure of LEST used in subways and to study the dynamic effect of the elastic cushion stiffness and vehicle speed, a dynamic model of the vehicle–track–tunnel–soil coupling system was established based on the finite element method and vehicle–track interaction dynamics theory. The results show the following: (1) LEST is more advantageous in vibration reduction performance compared with the common slab track and the low vibration track under the same track stiffness, and LEST also has better integrity and stability than the low vibration track; (2) The lower the cushion stiffness is, the smaller the accelerations of the tunnel wall are, but the dynamic displacements of the track rise in time domain. Considering the dynamic displacements and accelerations, the cushion stiffness is recommended to be 20–30 kN/mm. (3) High vehicle speed has a detrimental effect on the dynamic response, especially the accelerations of track. It is necessary to pay more attention to vibration when the vehicle speed exceeds 100 km/h in the subway if LEST is used.

Peculiarities of calculation and design of slabs on elastic cushion reinforced with non-metallic composite reinforcement

Fiber-glass composite reinforcement becomes increasingly popular in different spheres of industry and public economy. Unique technology of the reinforcement production allows receiving the high-quality construction material which complies with modern requirements of liability, quality and safety. Pavlivska Square in Kharkiv may serve as an example of efficient application of non-metallic composite reinforcement for the reinforcement of slabs on elastic cushion during the construction of which the composite grids SKS-100/100 manufactured by Ekipage Technological Group were used as the reinforcement units. Pavement slab reinforcement scheme (including the working draft) was elaborated by the specialists of the Building Constructions Department of O.M. Beketov National University of Urban Economy. The arrangement of the pavement slab of Pavlivska Square was conducted within the short period of time. Due to this, for the purpose of mounting the two-layer reinforcing cage of the slab, the workers of Ekipage Technological Group elaborated a new mounting method which allows the essential reduction of the performance time.