To protect the external wall panel of the steel frame in prefabricated construction, a kind of ring-shaped energydissipating device (RSED) was proposed and further studied, which can connect the wall panel and steel frame. The hysteretic performance of steel frame-external wall panel system (SFEWPS) with RSED as the joint is analyzed via the finite element method, to quantify the protective effect of RSED on a wall panel. The results are that even under extremely rare earthquakes, RSED can still effectively control the energy consumption of wall panels, and play a protective role for it. In addition, combined with failure mechanism analysis, this paper proposes the best parameter selection for RSED.

The reliability of stern shaft sealing in large ships is affected by the large pressure fluctuation caused by changes in immersion depth. To investigate the dynamic performance of the pressure adjustable air seal system for stern shaft, a mathematical model is established by segmenting the system according to the position of valves and chambers, and a constant pressure difference control strategy is devised. The simulation results reveal the effects of various factors on system response. The results indicate that the sealing flow rate decreases by 2.5 g/s for every 5 μm decrease in the width of lip seal gaps; The overshoot of intake flow is influenced by both the change rate of immersion depth and the volume of air chambers; The maximum overshoot flow rate increases by 2.1 g/s for every 1 m/s increase in the depth change rate, and by 0.05~0.1 g/s for every 0.001 m 3 increase in chamber volume; The rapid change rate of immersion depth can prolong the pressure response time, which extends by 0.4~0.5 seconds at 4 m/s, and by 2 seconds at 6 m/s. Based on the findings, the required widths of the lip seal gaps to achieve rapid pressure relief at different depth change rates are summarized, providing references for the design and engineering practice.

Thin-walled cold-formed steel (TWCFS) structures have a great application prospect and are widely adopted in low-rise residential constructions due to great mechanical and economical properties. Since TWCFS member has low flexural rigidity and is hard to weld, it is rarely used in bridge engineering. In Poyang Lake Wetland of Jiangxi Province, China, a TWCFS footbridge was built. In this paper, Serial tests including static loading test, natural frequency test and pedestrian comfort test were conducted. At the same time, finite element analysis (FEA) models were built with Midas/Civil software. The data shows that although natural frequency is far greater than the range of pedestrian walking frequency and will not lead to the resonance of bridge, the peak acceleration under crowd load reflects poor pedestrian comfort. The structure was modified for improving pedestrian comfort and the results after modification verify that the comfort can be ensured.

为了准确模拟RC(reinforced concrete)矩形空心桥墩的刚度退化特性,为桥梁震后可恢复性能研究提供理论基础,进行了不同设计参数的14个RC矩形空心墩模型拟静力试验.通过引入峰值位移影响系数体现刚度退化与峰值位移的关联,建立修正的Bouc-Wen-Baber-Noori (BWBN)滞回模型;基于粒子群-引力搜索混合智能优化算法(combination of particle swarm optimization and gravitational search algorithm,PSOGSA)识别实测滞回曲线对应的滞回参数,并建立桥墩设计参数与滞回参数间的对应关系,进而总结滞回参数的经验预测方法.研究结果表明:修正的BWBN滞回模型曲线与实测滞回曲线吻合程度高,相关性系数在0.98以上,且新型滞回模型能准确地反映出桥墩侧向刚度随墩顶位移退化的特性;PSOGSA算法能精确地识别实测滞回曲线的模型参数;采用经验预测方法得到的模型曲线与实测滞回曲线的相关性系数为0.83,该方法适用于缺乏实测滞回曲线的桥墩.

Hexavalent chromium contamination is a global environmental issue and usually reoccurs in alkaline reduced chromite ore processing residues (rCOPR). The oxidation of Cr(III) solids in rCOPR is one possible cause but as yet little studied. Herein, we investigated the oxidation of Cr(OH)3, a typical species of Cr(III) in rCOPR, at alkaline pH (9-11) with δ-MnO2 under oxic/anoxic conditions. Results revealed three pathways for Cr(III) oxidation under oxic conditions: (1) oxidation by oxygen, (2) oxidation by δ-MnO2, and (3) catalytic oxidation by Mn(II). Oxidations in the latter two were efficient, and oxidation via Pathway 3 was continuous and increased dramatically with increasing pH. XANES data indicated feitknechtite (β-MnOOH) and hausmannite (Mn3O4) were the reduction products and catalytic substances. Additionally, a kinetic model was established to describe the relative contributions of each pathway at a specific time. The simulation outcomes showed that Cr(VI) was mainly formed via Pathway 2 (>51%) over a short time frame (10 days), whereas in a longer-term (365 days), Pathway 3 predominated the oxidation (>78%) with an increasing proportion over time. These results suggest Cr(III) solids can be oxidized under alkaline oxic conditions even with a small amount of manganese oxides, providing new perspectives on Cr(VI) reoccurrence in rCOPR and emphasizing the environmental risks of Cr(III) solids in alkaline environments.

A large amount of salt waste accompanied with contaminants (e.g., organic pollutants) is produced in chemical production process, causing serious environmental hazards and waste of salt resources. However, there have been few satisfactory treatments for this hazardous waste until now. In this work, a novel strategy for NaCl recovery and organic pollutants removal from the salt waste containing pyridine derivatives was developed by using acetone in salt waste solution. The results showed NaCl was effectively recovered (recovery rate, 99.12%), and the TOC value of its saturated solution was reduced from 806.2 to 145.4 mg/L, below the limits (200 mg/L) for chlorine gas and caustic soda production in chlorine alkali plant. Moreover, no pyridine derivatives can be identified through Fourier transform infrared spectroscopy (FTIR) test. Mechanism analysis demonstrated the dual effects of acetone as following: 1) acetone and NaCl formed aqueous two-phase systems (ATPS) to remove organic pollutants; 2) acetone, as a crystal regulator, induced NaCl crystals to recrystallize in cubic morphology with a smooth surface, which enhanced the removal of pollutants. Besides, the acetone-water phase split facilitated the separation of organic pollutants as well as the reuse of acetone. This work proposes a promising and feasible method for salt waste to remove organic pollutants and recover recrystallized NaCl solids, and also provides new insights into the function of acetone on the crystal regulation of salts. (C) 2020 Elsevier Ltd. All rights reserved.

The quantification of thermal action is important to the analysis of structural-fire performance of bridges. This study evaluates the parameters for the localized fire model adopted in SFPE Handbook for application to the fire scenario of a tanker truck burning beneath a bridge. Modification is applied first to the flame length and then to the distribution of gauge heat flux using the simulation results of various fire models established in Fire Dynamics Simulator considering parameters, including the sectional dimensions of bridge, bridge headroom, truck size and heat release rate. Spatially varied gauge heat flux or adiabatic surface temperature of the bridge can be predicted with this fire model. Implementation of this modified fire model in structural-fire analysis is illustrated with a sequentially coupled thermo-mechanical modelling of a post-tensioned segmental concrete box girder bridge exposed to tanker truck fire. The adiabatic surface temperature calculated from the modified fire model is applied as thermal boundary to the bridge. Simulation results show that, although the global structural responses are seldom influenced by fire, localized damage in concrete and tendon may result. The prestress in tendons near mid-span may be reduced even after the bridge is cooled down to ambient temperature, which may adversely affect its load-carrying capacity. The damage to concrete may also induce localized separation between adjacent segments, possibly affecting the durability of tendons.

Complete extraction of Cr(vi) from rCOPR which involved ion exchange in ion channels of Cr(vi)–ettringite, formation and growth of nano-CaCO3.

采用SAP2000建立了基于大质量法的动力分析模型,选取了4条NGA-West2数据库中与实际工程场地条件类似的地震波通过调幅后作为输入地震动,研究了行波效应对大跨度铁路劲性骨架混凝土拱桥地震响应的影响规律.研究结果表明:大跨度铁路劲性骨架混凝土拱桥在非一致激励下交界墩伸缩缝位移和主拱拱脚及主拱L/4处弯矩随相位差的变化具有周期性,且变化周期与结构1阶纵向自振周期基本一致,在相位差为结构1阶纵向自振周期的2n倍(n为整数)时结构响应处于峰值,在(2n+1)/2时结构响应处于谷值;跨中伸缩缝位移、拱顶轴力在非一致激励下分别为一致激励下的50～150倍,100～300倍;由于行波效应加剧了结构地震响应,在进行大跨度劲性骨架混凝土拱桥抗震设计时应考虑行波效应对结构关键部位的影响.

The issue that the residual Cr(VI) in the reduced chromite ore processing residue (rCOPR) is slowly released during deposition has attracted increasing attention. However, the speciation and leaching behaviors of Cr(VI) in rCOPR are still not clear, which is essential for revealing the release mechanism of Cr(VI). In this study, ettringite was determined to be the host phase of Cr(VI) in ferrous sulfate-reduced COPR by scanning electron microscopy (SEM), microfocus X-ray fluorescence spectroscopy (μ-XRF) and aberration-corrected scanning transmission electron microscopy (Cs-STEM). This is because the channel structure of ettringite makes it relatively easy for sulfate to be replaced by chromate with similar structure and thermochemical radius. Furthermore, the investigation on the leaching behavior and mechanism of Cr(VI) in rCOPR eroded by environmental factors showed that carbonates, sulfates and acid can promote the release of Cr(VI). Among them, the erosion effect of HCl on rCOPR is weaker than that of Na2CO3 and Na2SO4 because rCOPR possesses a high buffering reserve of alkalinity. In addition, the erosion of rCOPR by Na2CO3 and Na2SO4 can change Cr(VI) speciation in rCOPR. The results implied that the environmental risk of Cr(VI) release during the deposition of rCOPR should deserve careful assessment.

Heavy metal-containing gypsum is a widespread hazardous waste. In this work, H+ was found to be the most essential factor of the mineralizers in hydrothermal treatment to completely (≥99.8%) extract Cr(VI) from gypsum waste to the supernatant, where the significant growth (from several μm to several hundreds of μm) and perfection of the gypsum crystals were observed. Moreover, with increasing concentration of H+, the crystal growth (undergoing Ostwald ripening process) was accelerated and the phase transformation temperature of gypsum was decreased from 110℃ (at 0.2 mol/L of HCl) to 100℃ (at 0.3 mol/L of HCl), which are favorable to enhance Cr(VI) extraction efficiency. Pilot experiments further certified this method to be practicable even in ton-scale. This work proposes a practicable and universal method to completely extract Cr(VI) from gypsum waste, and would also inspire the recycle of gypsum waste containing other heavy metals, such as As, Pb, Cd, and Hg.

This paper studied the cause of rainstorm occurred in the Haihe River Basin during 18-20 July, 2016 based on the meteorological data, and made comparison between the "1963.8" and "1996.8" storms. The results show that the rainstorm was caused by superimposing of different weather systems and special terrain. It is closely related to water vapor transmission from the South China Sea and East China. The moving path of the rainstorm was from southwest to northeast along the Taihang Mountains. The main influence weather system was similar to the "1963.8" storm, but different from the "96.8" storm. The moving path was between the "1963.8" and "1996.8" storms.

Purpose This study aims to investigate the influence of tendon layout, pre-stressing force, bond condition and concrete spalling on the structural behaviour of two-way post-tensioned flat slabs at elevated temperatures. Design/methodology/approach Fire tests of four scale specimens of two-way post-tensioned concrete flat slabs were performed and analysed. Three of them were provided with bonded tendons, while the other was unbonded for comparison. The fabrication of specimens, phenomena observed during testing, temperature distributions, deflections and occurrence of concrete spalling were examined. Findings Different degrees of concrete spalling observed at the soffit had significant effects on the temperature distribution and stress redistribution. This was the major reason for the progressive concrete spalling observed, resulting in loss of structural integrity and stiffness. Originality/value The structural behaviour of two-way post-tensioned concrete flat slabs at elevated temperatures is less understood compared to their one-way counterparts. Therefore, the present study has focused on the structural behaviour of two-way post-tensioned concrete flat slabs with bonded tendons in fire, a field in which relatively little information on experimental work can be found.

Based on the urban rail transit design and relevant specifications, this paper studies the rail transit bridge seismic design in the light of the principle of energy conversion.The results conclude that reducing the stiffness of the structural system and increasing the energy output is an effective way to reduce the structural seismic response.Structural system stiffness can be effectively reduced by controlling the size of the structure and mounting plastic hinge and seismic isolation bearing.The energy output can be increased by placing high damping bearing and shock proof block.The actual earthquake damages show that it is hardly possible to get accurate structural response value and difficult to understand the structure internal force and deformation characteristics simply by seismic calculation in case of rare earthquakes.According to the failure mechanism of the bridge, concept design should be prioritized to achieve the structural seismic performances in case of rare earthquake.

Fire tests of three reduced-scale two-way post-tensioned concrete slabs with bonded tendons were carried out. This study was intended to investigate the influence of the layout of prestressing tendons, prestressing force and concrete spalling on the structural response of two-way post-tensioned concrete slabs with bonded tendons in fire. The material used to fabricate the specimens, the phenomena observed during the tests, the temperature distributions, the deflections and occurrence of concrete spalling were investigated.

According to current engineering practice, Confined Masonry (CM) buildings are weak in earthquake resistance and difficult in post-quake restoration. A new form of structure, i.e. Hybrid Masonry – Reinforced Concrete Structure (HMRCS), is investigated. By slightly increasing the sizes and reinforcement ratios of the RC members, i.e. beams and columns, which normally only act as confinement in a CM structure, now play an essential role in resisting the gravity load in HMRCS, while the masonry wall mainly resists the lateral earthquake load. To investigate the seismic-resistant behavior, pseudo-static tests on two full-scale HMRCS specimens were conducted, and the measured hysteretic curves were analyzed. Finite Element (FE) simulation was performed to verify the working mechanism and seismic response of the HMRCS specimens. The lateral displacement ductility factor obtained from the experimental results can fully satisfy the seismic requirement of structures. Therefore, HMRCS is reliable if its RC frame members and masonry walls are designed properly. Furthermore, the feasibility of using FE software to study the proposed HMRCS has been validated by comparing the experimental and simulation results.