Zhong S.,Tongji University |
Li J.,Tongji University |
Li J.,Sinoma International Engineering Co. |
Ni K.,Tongji University |
And 2 more authors.
Construction and Building Materials | Year: 2013
In order to understand why polymer-modified mortars (PMMs) with hydroxypropylmethyl cellulose (HPMC) often show better properties than that without HPMC, the influence of HPMC on the adsorption of styrene-acrylic ester (SAE) latex particles on cement grains was studied through the particle size distribution and the zeta potential of latex modified cement paste (LMCP) with and without HPMC keep the latex/cement ratio (L/C) to 10%. The differences between the calculated and measured particle size distribution curves of LMCP indicate strong interactions between latex particles and cement grains in fresh cement pastes. The particle size distribution results show that the adsorbed rate of SAE on cement is 75.24% in LMCP, while the adsorbed rate of SAE latex particles in LMCP with HPMC is 4% lower than that in LMCP without HPMC. The zeta potential results show that the zeta potential of LMCP is negative, the equilibrium zeta potential of LMCP with HPMC is more negative than that of LMCP without HPMC and decreases with the increase of the HPMC to cement ratio (HPMC/C). The microstructures of hardened LMCP with and without HPMC were observed using scanning electronic microscopy (SEM). Without etching of LMCP with or without HPMC, the polymer films are more easily seen in pores while hard to found at the cement matrix. After etching the specimen in diluted hydrochloric acid (HCl), coherent polymer films were observed. The differences of the polymer films in samples prepared with different procedures, that is the specimens stored in absolute alcohol or not, show that they are composite films of SAE latex and HPMC in LMCP with HPMC. Higher the HPMC/C is, bigger the covered area of the polymer films is on the surface of pores, and more rigid the polymer films are, what can be confirmed from the tensile test results of films made from the HPMC and SAE latex mixture that show decreased elongation at break and increased tensile strength with the increase of HPMC to latex ratio (HPMC/L). © 2012 Elsevier Ltd. All rights reserved.
Wu Y.-F.,City University of Hong Kong |
Liu K.,City University of Hong Kong |
Liu K.,China State Construction Engineering Corporation
Journal of Composites for Construction | Year: 2013
Despite extensive research on externally bonded fiber-reinforced polymer (EB-FRP) for rehabilitation of concrete structures in the past two decades, the industry has been slow to embrace the technology owing to some difficult problems that are yet to be resolved fully. Among these, premature debonding is one of the critical problems. Since the tensile strength of concrete is inherently low and unreliable (in the long term), EB-FRP by surface adhesion might not be the final solution; augmentation of the interfacial bond by mechanical fastening may be unavoidable. To this end, the first author proposed a bond augmentation system, hybrid-bonded FRP (HB-FRP), where a special type of mechanical fasteners are used to enhance the interfacial bond. Although the HB-FRP system has been experimentally shown to increase bond strength several fold, effectively overcoming the debonding problem, there has been no systematic theoretical study of the system. In this paper, HB-FRP joints are characterized through experimental testing and analytical modeling, leading to a theory for design and construction of the HB-FRP system. © 2013 American Society of Civil Engineers.
Qu Y.-Z.,University of Jinan |
Yao M.-M.,University of Jinan |
Li F.,University of Jinan |
Sun X.-H.,China State Construction Engineering Corporation
Water, Air, and Soil Pollution | Year: 2011
Fe3+ and Ce3+ codoped titanium dioxide films with high photocatalytic activity were successfully obtained via the improved sol-gel process. The as-prepared specimens were characterized using X-ray diffraction (XRD), high-resolution field emission scanning electron microscopy (FE-SEM), X-ray energy dispersive spectroscopy, Brunauer-Emmett-Teller (BET) surface area, X-ray photoelectron spectroscopy, photoluminescence (PL) spectra, and UV-Vis diffuse reflectance spectroscopy. The photocatalytic activities of the films were evaluated by degradation of various organic dyes in aqueous solutions. The results of XRD, FE-SEM, and BET analyses indicated that the TiO2 film had nanostructure. With the codoping of Fe3+ and Ce3+, TiO2 photocatalysts with smaller crystal size, larger surface area, and larger pore volume were obtained. Moreover, codoped ions could obviously not only suppress the formation of brookite phase but also inhibit the transformation of anatase to rutile at high temperature. Compared with pure TiO2 film, Fe3+ doped or Ce3+ doped TiO 2 film, the Fe3+/Ce3+ codoped TiO2 film exhibited excellent photocatalytic activity. It is believed that the surface microstructure of the films and the doping methods of the ions are responsible for improving the photocatalytic activity. © 2011 Springer Science+Business Media B.V.
Hu B.,Hefei University of Technology |
Li G.-Q.,State Key Laboratory for Disaster Reduction in Civil Engineering |
Li G.-Q.,Tongji University |
Sun J.-Y.,China State Construction Engineering Corporation
International Journal of Impact Engineering | Year: 2014
Preventing unauthorized vehicles from approaching a protected area by anti-ram bollard systems installed in the perimeter of buildings and infrastructures would consequently reduce blast and debris threats of vehicle borne improvised explosive devices. In this paper, an explicit finite-element model, which is more comprehensive than existing numerical models, was developed to simulate the performance of fixed anti-ram bollard system subjected to vehicle impact. Different materials for different locations of the foundation support, differences in weight and configuration between test vehicles and vehicle model, and more accurate contact algorithm used between truck and bollards were taken into account. The accuracy of the developed model was validated through comparing the impact results with four existing crash tests. Based on the verified numerical model, 72 numerical experiments of K4-rating shallow footing fixed anti-ram bollard systems (SFFABSs) were investigated according to orthogonal design. The minimum height of the bollard H min during the impact was proposed as a new deformation tolerance for K4-rating SFFABS. The new deformation tolerance is defined as the H min value of 564 mm or above according to SD-STD-02.01 Revision A, and a more reliable deformation tolerance is defined as the Hmin value of 587 mm or above. Orthogonal analysis for the experimental factors with respect to Hmin showed that height of the bollard, diameter of the bollard, and strength of the steel tube have greatly significant influences on Hmin. © 2013 Elsevier Ltd. All rights reserved.
Chang C.-M.,Urbana University |
Spencer Jr. B.F.,Urbana University |
Shi P.,China State Construction Engineering Corporation
Structural Control and Health Monitoring | Year: 2014
Passive isolation has been widely accepted as an effective means for the protection of structures against seismic hazards. The isolation bearings, typically placed at the base of the structure, increase the flexibility of the structure and shift its fundamental frequency away from the dominant frequency of seismic excitations, resulting in significantly reduced interstory drifts and floor accelerations. During severe earthquakes, the performance of passive isolation systems is usually achieved at the expense of having large base displacements. Alternatively, active isolation combines isolation bearings with adaptive actuators to effectively mitigate the base displacements, while maintaining reasonable interstory drifts and floor accelerations. Despite successfully theoretical proof documented in previous studies, most experimental implementations only verified active isolation with unit-axial actuators under unidirectional excitations. Earthquakes are intrinsically multidimensional, resulting in out-of-plane responses such as torsional responses. Therefore, the focus of this paper is the development and experimental verification of active isolation strategies for multistory buildings subjected to bidirectional earthquake loadings. First, a model building is designed to be dynamically similar to a representative full-scale structure. The selected isolation bearings feature low friction and high vertical stiffness, providing stable behavior. In the context of the multidimensional response control, three custom-manufactured and appropriately scaled actuators are employed to mitigate both in-plane and out-of-plane responses. In addition, the structure is subjected to multi-directional earthquake ground motion. To obtain a high-fidelity model of the active isolation systems, the authors propose a hybrid identification approach, which combines the advantages of the lumped mass model and nonparametric methods. Control-structure interaction is also included in the identified model to further enhance the control authority. By employing the H2/LQG control algorithm, the controllers for the hydraulic actuators are shown to offer high performance and good robustness. Active isolation is found to possess the ability to reduce base displacements and produce comparable accelerations and interstory drifts to passive isolation. The proposed active isolation strategies are validated experimentally for a six-story building tested on the six-degree-of-freedom shake table in the Smart Structures Technology Laboratory at the University of Illinois at Urbana-Champaign. Copyright © 2013 John Wiley & Sons, Ltd. Copyright © 2013 John Wiley & Sons, Ltd.