Seismic Performance of Precast Columns Connected with Two Different Connection Modes

The precast reinforced concrete building is made of precast components, which are connected at the joints via reliable connection approaches. Therefore, the study on the stability and reliability of the connections should be conducted to improve the safety and integrity of the precast structure. In this paper, experiments on two connection modes, i.e. corrugated pipe confined with spiral stirrup connection and steel sleeve connection, were carried out. The experimental tests consisted of six specimens, including one cast-in-situ specimen, three precast specimens using steel sleeve connection and two precast specimens using corrugated pipe confined with the spiral stirrup. The influence of artificially unbonded length at the connection joint is also studied. All specimens were tested under low-frequency cyclic repeated loading to analyse their seismic performance under different connection modes. The experimental results showed that the precast columns using the two proposed connections have a similar or even better seismic performance compared with the cast-in-situ column. The installation of proper unbonded treatment on the longitudinal reinforcement in the connection is beneficial in improving the seismic performance of precast columns and the length of 5 times of the longitudinal reinforcement’s diameter is recommended

Retrofitting of infilled RC frames using collar jointed masonry

Masonry is a composite material made of masonry units bonded together with mortar. A large number of historical buildings constructed using masonry can be found all over the world. Little or no seismic loading was considered when they were built. Therefore, masonry structures often need to be retrofitted or strengthened. This research proposed a new strengthening approach using a collar-jointed technique. Namely, the approach is implemented by building another masonry wall parallel to the existing single-leaf wall and bonding the two together using a mortar collar joint. Furthermore, collar-jointed masonry wall construction is also a popular construction system in reality. This thesis considers two different types of collar wall strengthening applications: pre- and post-damaged walls. The results found out that the pre-damaged strengthening could improve the lateral resistance by about 50% while the post-damaged retrofitting can only restore the initial strength. A simplified micro-scale finite element model for fracture in masonry walls was developed. The mortar joints and the brick-mortar interfaces are taken to have zero-thickness. The bricks were modelled as elastic elements while the brick-mortar interfaces were represented using a Mohr-Coulomb failure surface with a tension cut-off and a linear compression cap. One feature of the research was to identify the material parameters for the constitutive model. The material parameters were tuned by minimizing the difference between the experimental and numerical results of a single leaf wall panel. The model was then validated by assigning the parameters to the single-leaf masonry wall as well as to the double-leaf wall to predict its mechanical behaviour. Good agreement with experimental results was found. Furthermore, masonry is also widely used in the form of infill panels within RC frames. Therefore, the collar-jointed technique has also been extended and applied to the infilled RC frame. The numerical results showed that the collar-jointed technique could provide some benefits to the composite structure

A novel alkali-activated cement from mineral admixture, superabsorbent polymers, and alkali-doped carboxylate glass

Acknowledgments We gratefully acknowledge the financial support of China National Key R&D Program (Grant No. 2018YFE0106300) and National Nature Science Foundation of China (No: 51925205). We gratefully acknowledge the financial support of “111” project (No. B18038). We gratefully acknowledge the Dr. Helle Rüsz Hansen for her contribution to the development of the slow release glasses used in this paper.Peer reviewe

Catheter-directed thrombolysis for patients with acute lower extremity deep vein thrombosis: a meta-analysis

Objetivos: Evaluar estudios de series de casos y evaluar cuantitativamente los efectos de la trombólisis dirigida por catéter (TDC) y comparar la eficacia entre la TDC y anticoagulación en pacientes con trombosis venosa profunda (TVP) aguda de las extremidades inferiores para el tratamiento futuro. Métodos: Se realizaron búsquedas en bases de datos relevantes, incluyendo PubMed, Embase, Cochrane, Ovid MEDLINE y Scopus hasta enero de 2017. Los criterios de inclusión se aplicaron a pacientes seleccionados con TVP aguda de extremidad inferior tratados con TDC o comparados con TDC y anticoagulación. En estudios de series de casos, las estimaciones agrupadas de los resultados de eficacia para la tasa de patencia, la lisis completa, la retrombosis y el síndrome postrombótico (SPT) se calcularon a través de los estudios. En estudios que compararon la TDC con la anticoagulación, se calculó el resumen de las razónes de posibilidades (RP). Resultados: 25 artículos (seis que comparan TDC con anticoagulación y 19 series de casos) que incluyeron 2254 pacientes qienes cumplieron los criterios de elegibilidad. En los estudios de series de casos, los resultados agrupados fueron: tasa de patencia 0,87 (IC 95%: 0,85; 0,89), lisis completa 0,58 (IC 95%: 0,40; 0,75), retrombosis 0,11 (IC 95%: 0,06; 17,0), SPT 0,10 (IC 95%: 0,08; 0,12). Seis estudios que compararon los resultados de eficacia entre la TDC y anticoagulación mostraron que la TDC se asoció con una reducción de SPT (RP 0,38; IC 95%: 0,26; 0,55; pObjectives: To evaluate case series studies that quantitatively assess the effects of catheter-directed thrombolysis (CDT) and compare the efficacy of CDT and anticoagulation in patients with acute lower extremity deep vein thrombosis (DVT). Methods: Relevant databases, including PubMed, Embase, Cochrane, Ovid MEDLINE and Scopus, were searched through January 2017. The inclusion criteria were applied to select patients with acute lower extremity DVT treated with CDT or with anticoagulation. In the case series studies, the pooled estimates of efficacy outcomes for patency rate, complete lysis, rethrombosis and post-thrombotic syndrome (PTS) were calculated across the studies. In studies comparing CDT with anticoagulation, summary odds ratios (ORs) were calculated. Results: Twenty-five articles (six comparing CDT with anticoagulation and 19 case series) including 2254 patients met the eligibility criteria. In the case series studies, the pooled results were a patency rate of 0.87 (95% CI: 0.85-0.89), complete lysis 0.58 (95% CI: 0.40-0.75), rethrombosis 0.11 (95% CI: 0.06-0.17) and PTS 0.10 (95% CI: 0.08-0.12). Six studies comparing the efficacy outcomes of CDT and anticoagulation showed that CDT was associated with a reduction of PTS (OR 0.38, 95%CI 0.26-0.55, pObjetivos: Avaliar os estudos de séries de casos e avaliar quantitativamente os efeitos da trombólise dirigida por cateter (TDC) e comparar a eficácia entre TDC e anticoagulação nos pacientes com trombose venosa profunda aguda das extremidades inferiores (TVP) para tratamento futuro. Métodos: Foram pesquisadas as seguintes bases de dados relevantes: PubMed, Embase, Cochrane, Ovid MEDLINE e Scopus​. Os critérios de inclusão foram aplicados para pacientes selecionados com TVP aguda de extremidades inferiores tratados com TDC comparada a TDC com anticoagulação. Nos estudos de série de casos, as estimativas agrupadas de resultados de eficácia para a taxa de permeabilidade, lise completa, retrombose e síndrome pós-trombótica (SPT) foram calculadas em todos os estudos. Em estudos comparando TDC com anticoagulação, foi calculada a razão de chance de resumo (summary odds ratio - OR). Resultados: Vinte e cinco artigos (seis comparando TDC com anticoagulação e 19 séries de casos), incluindo 2.254 pacientes, preencheram os critérios de elegibilidade. Nos estudos da série de casos, os resultados agrupados foram: taxa de permeabilidade 0,87 (IC95%: 0,85-0,89), lise completa 0,58 (IC95%: 0,40-0,75), e retrombose 0,11 (IC95%: 0,06-0,17), SPT 0,10 (IC95%: 0,08-0,12). Seis estudos que compararam os resultados de eficácia entre TDC e anticoagulação mostraram que TDC foi associada à redução da SPT (OR 0,38; IC95%: 0,26-0,55;

Influence of Water-Cement Ratio and Type of Mixing Water on the Early Hydration Performance of Calcium Sulphoaluminate (CSA) Cement

The present work studies the influence of water-cement ratio and types of mixing water on the hydration process and microstructure of calcium sulphoaluminate (CSA) cement. Experimental tests on the setting time, physical properties, compressive strength, chemical shrinkage, X-ray diffraction (XRD), and scanning electron microscopy (SEM) of CSA cement paste were carried out. The XRD analysis confirmed that the main hydration product is ettringite in both freshwater and seawater mixed CSA cement with different w/c ratios. The SEM analysis and physical properties test show that both low w/c ratio and seawater can improve the microstructure of CSA cement. The test results also find out that the high w/c ratio can accelerate the hydration process, extend the setting time, lower the compressive strength, and increase the chemical shrinkage of CSA cement, and the seawater presents a similar influence except for the mechanical property. The seawater increases the compressive strength of CSA cement in the early stage of hydration but will increase the microcracks at the later hydration stage of CSA cement and reduce its mechanical properties

Influence of Fiber Shape and Volume Content on the Performance of Reactive Powder Concrete (RPC)

This research studied the influence of three types of open (short-straight, long-straight, semicircular) and three different shapes of closed steel fibers (triangular, rectangular, circular) with different fiber contents by volume (0, 0.5%, 1%, 1.5%, and 2%) on the working and mechanical performance of reactive powder concrete (RPC). The results indicated that (1) the number of steel fibers and the enclosed area formed by closed steel fibers would remarkably impact the performance of RPC; (2) the semicircular fiber improves RPC’s strength the most among the three open shapes; (3) the short-straight fiber works more effectively than the closed steel fibers; (4) the circular fiber works the most efficiently in improving RPC’s mechanical performance while the triangular ones have the least effect among the three closed steel fibers; (5) both the closed and open steel fibers improve their compressive strength more than their flexural strength; (6) the closed steel fiber works more efficiently in improving the flexural strength but less efficiently in improving the compressive strength; (7) the open steel fibers enhance the mechanical performance of RPC via their anchoring performance while the closed steel fibers work by confining the concrete; (8) the hybrid utilization of steel fibers improves RPC’s mechanical performance to a higher level via combing the advantages of open and closed steel fibers

Energy Conversion Stage Design of Solar Water Pump in a Nanofiltration System

AbstractStandalone solar power system provides simple yet flexible solution to certain applications which demand high mobility. This paper introduces the design of a single solar panel powered induction machine-driven water pump system, which is used in an on-board nanofilteration system. The system configuration is evaluated at the first stage to provide high ratio voltage step-up; and complementary PWM and space vector PWM scheme is chosen for dc-dc stage and dc-ac stage respectively; V/F based control scheme is designed and integrated with maximum power point tracking algorithm for the best use of solar panel. The control system is implemented digitally in a TMS320F2812 DSC. Meaningful mode of operation is tested and satisfactory experimental results are collected

A novel composite nonlinear controller for stabilization of constant power load in DC microgrid

Transportation electrification involves the wide utilization of power electronics based dc distribution networks and the integration of a large amount of power electronic loads. These power electronic loads, when tightly controlled, behave as constant power loads (CPLs) and may cause system instability when interacting with their source converters. In this paper, a composite nonlinear controller is proposed for stabilizing dc/dc boost converter feeding CPLs by integrating a nonlinear disturbance observer (NDO)-based feedforward compensation with backstepping design algorithm. First, the model is transformed into the Brunovsky's canonical form using the exact feedback linearization technique, to handle the nonlinearity introduced by the CPL. Second, the NDO technique is adopted to estimate the load power variation within a fast dynamic response, serving as a feedforward compensation to increase the accuracy of output voltage regulation. Then a nonlinear controller is developed by following the step-by-step backstepping algorithm with strictly guaranteed large signal stability. The proposed controller not only ensures global stability under large variation of the CPL but also features fast dynamic response with accurate tracking over wide operating range. Both simulations and experiments are conducted to verify the proposed strategy.Accepted versio