Alternative sodium sources for Cu(In,Ga)Se2 thin-film solar cells on flexible substrates

Sodium (Na) is an important doping element for Cu(In,Ga)Se₂ (CIGS) solar cells. However, when using Na-free flexible substrates like steel foil or polyimide film, it is necessary to ensure an efficient supply of sodium to achieve high cell efficiencies. The common incorporation methods for Na on these Na-free substrates are either to deposit a Na-containing precursor layer (e.g. NaF) onto the molybdenum (Mo) back contact prior to CIGS growth or to coevaporate a Na compound during CIGS growth. Another way is to incorporate sodium after CIGS growth by a post-deposition treatment with NaF. In this work, we tested two alternative Na doping methods which are well suited for a production line due to their easy controllability. One approach is to dope the molybdenum target with Na. With Na-doped Mo layers (Mo:Na) as the back contact, we could achieve efficiencies of 13.1% both on titanium (Ti) and stainless Cr steel foil using a single-stage inline CIGS process. With a low-temperature single-stage CIGS process on polyimide (PI) we reached an efficiency of 11.2% using a Mo:Na back contact. Another doping method involves sol-gel-deposited silicon oxide layers which contain Na (SiO_x:Na). We have successfully deposited these sol-gel layers onto stainless steel foil by a roll-to-roll (R2R) method with short annealing times as needed in production. With these SiO_x:Na layers we could achieve efficiencies of 13.7% on stainless steel foil and 11.5% on mild steel sheet using a single-stage inline CIGS process.     

抗弯钢框架P-Δ效应稳定系数的应用

为分析抗弯钢框架中的P-Δ效应,提出2个稳定系数。在弹性阶段,弹性稳定系数θme是框架的基本周期、振型的函数。在塑性阶段,非弹性稳定系数θmi仍与基本周期、振型有关,通过回归分析得到。结果表明:使用这两个稳定系数,可精确模拟考虑P-Δ效应的钢框架荷载-位移曲线,包括:初始刚度、强度、后屈服刚度等。以22个抗弯框架为例,验证稳定系数的正确性。     

组合剪力墙的滞回性能研究

组合型钢剪力墙刚度大、延性好,在土木工程中应用广泛。组合型钢剪力墙一般通过铺设与钢板连接的混凝土层或纤维增强复合板形成。本试验和数值研究主要分析剪力钉间距、中间梁刚度、梁柱连接方法对组合型钢剪力墙性能的影响。结果表明:增大剪力钉间距可减小荷载-位移曲线的斜率,并提高结构韧性。中间梁刚度和梁柱连接对组合型钢剪力墙性能的影响是非常微小的,可以忽略。     

福州市螺洲大桥主桥钢箱梁顶推施工技术

结合福州市螺洲大桥工程介绍步履式平移顶推施工技术的特点和工艺设备,以及采用的集中控制系统。同时根据本工程实际情况,分析顶推平台与临时支墩的布置与设计的合理性以及经济性。     

Pushdown resistance as a measure of robustness in progressive collapse analysis

This paper presents a technique termed ‘pushdown analysis’ that can be used to investigate the robustness of building systems by computing residual capacity and establishing collapse modes of a damaged structure. The proposed method is inspired by the pushover method commonly used in earthquake engineering. Three variants of the technique, termed uniform pushdown, bay pushdown and incremental dynamic pushdown, are suggested and exercised using nonlinear analysis on 10-story steel moment frames designed for moderate and high levels of seismic risk. Simulation results show that the frame designed for high seismic risk is more robust than the corresponding one designed for moderate seismic risk. The improved performance is attributed to the influence of seismic detailing, specifically, the presence of reduced beam sections and stronger columns. It is shown that the dynamic impact factors associated with column removal are significantly lower than the commonly used value of 2.0 and are in line with lower values in the guidelines recently proposed by the US Department of Defense. The study suggests that seismic ‘fuses’ can play a role in the design for robustness and a discussion of the implications of this observation is provided.     

EMD-based random decrement technique for modal parameter identification of an existing railway bridge

Vibrational measurement data are often nonstationary and modal parameter identification based on these data is of practical value for structural health monitoring and condition assessment. The empirical mode decomposition (EMD) is a most recent tool for analysis of nonstationary signals. An EMD-based random decrement (RD) technique is presented to identify modal parameters from monitoring vibrational data. The nonstationary measurement data are first decomposed into a series of quasi-stationary intrinsic mode functions (IMFs) by EMD. The RD technique is then applied to the selected IMFs to obtain the free-decay response. The modal frequencies and damping ratios are finally identified from the free-decay response by minimizing the error between the measured free-decay responses and the predicted responses from a parametric model. The present method is applied to extract the modal parameters of the Nanjing Yangtze River Bridge from the measured responses. The identification result is compared to those from finite element analysis as well as from the experimental result identified with the peak-picking (PP) method. In addition, the modal frequencies of the bridge loaded with heavy trains are also identified and compared to the ‘empty’ bridge. The EMD-based random decrement (RD) technique provides an effective and promising tool for modal parameter identification for large bridges and other structures.     

Experimental evaluation of the seismic performance of steel MRFs with compressed elastomer dampers using large-scale real-time hybrid simulation

Real-time hybrid simulation combines experimental testing and numerical simulation, and thus is a viable experimental technique for evaluating the effectiveness of supplemental damping devices for seismic hazard mitigation. This paper presents an experimental program based on the use of the real-time hybrid simulation method to verify the performance-based seismic design of a two story, four-bay steel moment resisting frame (MRF) equipped with compressed elastomer dampers. The laboratory specimens, referred to as experimental substructures, are two individual compressed elastomer dampers with the remainder of the building modeled as an analytical substructure. The proposed experimental technique enables an ensemble of ground motions to be applied to the building, resulting in various levels of damage, without the need to repair the experimental substructures, since the damage will be within the analytical substructure. Statistical experimental response results incorporating the ground motion variability show that a steel MRF with compressed elastomer dampers can be designed to perform better than conventional steel special moment resisting frames (SMRFs), even when the MRF with dampers is significantly lighter in weight than the conventional MRF.     

An experimental study on steel-caged RC columns subjected to axial force and bending moment

Among the different methods of strengthening RC columns, steel caging is one of the most extensively used, for square or rectangular cross-section columns. Few studies have been carried out on steel caging and most of these have focused on axially loaded strengthened columns, without taking the effects of bending moments into account. This paper presents the results of a series of experimental tests on full-scale specimens strengthened with steel caging including simulation of the beam-column joint under combined bending and axial loads. Capitals were applied to all the specimens to connect the caging with the beam-column joint either by chemical anchors or steel bars to improve the transmission of forces. In all the specimens tested it was observed that steel caging increases both the ultimate load and ductility of the strengthened columns. The specimens fitted with steel bars reach higher ductility and strength than those with chemical anchors. The laboratory results were compared with three design proposals and the degree of fit with each one was analysed.     

A simplified analytical procedure for assessing the worst patch load location on circular steel silos with corrugated walls

Silos are widely used in the food and chemical industries for the storage of granular materials. The calculation of their wall dimensions is complicated since the interaction between the stored material and that from which the silo is made is complex, a consequence of their very different mechanical behaviours. The loads exerted on the silo walls by stored materials must be taken into account in silo design, and the means for calculating them is contemplated in Eurocode EN 1991-4. The complexity of the phenomena that occur within silos often leads to the appearance of unexpected and asymmetrically distributed pressures. This is taken into account in the above Eurocode via the concept of the patch load, which is asymmetric and can be exerted at any point on the silo wall. A finite element model has been developed in order to check that the stress resultants derived from the patch load on steel silos with corrugated walls may be predicted by using the well-known expressions of shell theory. Then, a simplified analytical procedure has been developed for predicting the worst location of patch loads for all metal silos, but with special application to corrugated steel silos in Action Assessment Class 3. It has been found that significant differences may be found for most cases with the worst location for the patch load defined in Eurocode for welded silos in Action Assessment Class 2. On the other hand, the values obtained for the maximum meridional membrane stress resultant do not significantly differ, except for high slenderness values in intermediate slenderness silos.     

Numerical and experimental study on the interaction cable structure during the failure of a stay in a cable stayed bridge

Corrosion, abrasion and fretting fatigue may cause deterioration and, eventually, the failure of a post-tensioning tendon or a stay cable on a cable supported structure. In the present study, the stress acting during the rupture on the remaining portion of the stay which fails is derived, and the role of the rupture time on the response of the structure is discussed from a theoretical and a numerical point of view. In addition, the load-time curve during the rupture and the total time of the rupture of undamaged and damaged wires of seven-wire steel strands are investigated in an experimental program defined on the basis of the previous theoretical results. In the locally damaged specimens, a notch is machined into their outer wires. The specimens are tested under tension at three different strain rates in order to determine the influence of this parameter on the rupture time and on the load-time curve. The damaged specimens also allow us to determine the influence of a local reduction of the cross section on the stiffness and ultimate load of the specimen.