Advances in Materials Science and Engineering The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. One-Dimensional Consolidation of Double-Layered Foundation with Depth-Dependent Initial Excess Pore Pressure and Additional Stress Thu, 08 Oct 2015 07:37:07 +0000 A model for one-dimensional consolidation of a double-layered foundation considering the depth-dependent initial excess pore pressure and additional stress and time-dependent loading under different drainage conditions was presented in this study and its general analytical solution was deduced. The consolidation solutions of several special cases of single-drained and double-drained conditions under an instantaneous loading and a single-level uniform loading were derived. Then, the average degree of consolidation of the double-layered foundation defined by settlement was gained and verified. Finally, the effects of the initial excess pore pressure distributions, depth-dependent additional stress, and loading modes on the consolidation of the soft foundation with an upper crust with different drainage conditions were revealed. The results show that the distributions of initial excess pore pressure and additional stress with depth and loading rates have a significant influence on the consolidation process of the soft foundation with an upper crust. This influence is larger with the single-drained condition than that with the double-drained condition. Comparing the consolidation rate with a uniform initial pore pressure and additional stress, their decreasing distribution with depth quickens the consolidation at the former and middle stages. Moreover, the larger the loading rate is, the quicker the consolidation of the soft foundation with an upper crust is. Junhui Zhang, Guangming Cen, Weizheng Liu, and Houxuan Wu Copyright © 2015 Junhui Zhang et al. All rights reserved. Bulk Density Adjustment of Resin-Based Equivalent Material for Geomechanical Model Test Wed, 07 Oct 2015 12:46:04 +0000 An equivalent material is of significance to the simulation of prototype rock in geomechanical model test. Researchers attempt to ensure that the bulk density of equivalent material is equal to that of prototype rock. In this work, barite sand was used to increase the bulk density of a resin-based equivalent material. The variation law of the bulk density was revealed in the simulation of a prototype rock of a different bulk density. Over 300 specimens were made for uniaxial compression test. Test results indicated that the substitution of quartz sand by barite sand had no apparent influence on the uniaxial compressive strength and elastic modulus of the specimens but can increase the bulk density, according to the proportional coarse aggregate content. An ideal linearity was found in the relationship between the barite sand substitution ratio and the bulk density. The relationship between the bulk density and the usage of coarse aggregate and barite sand was also presented. The test results provided an insight into the bulk density adjustment of resin-based equivalent materials. Pengxian Fan, Haozhe Xing, Linjian Ma, Kaifeng Jiang, Mingyang Wang, Zechen Yan, and Xiang Fang Copyright © 2015 Pengxian Fan et al. All rights reserved. Preparation of U–Zr–Mn, a Surrogate Alloy for Recycling Fast Reactor Fuel Sun, 04 Oct 2015 14:40:27 +0000 Metallic fuel slugs of U–10Zr–5Mn (wt%), a surrogate alloy for the U–TRU–Zr (TRU: a transuranic element) alloys proposed for sodium-cooled fast reactors, were prepared by injection casting in a laboratory-scale furnace, and their characteristics were evaluated. As-cast U–Zr–Mn fuel rods were generally sound, without cracks or thin sections. Approximately 68% of the original Mn content was lost under dynamic vacuum and the resulting slug was denser than those prepared under Ar pressure. The concentration of volatile Mn was as per the target composition along the entire length of the rods prepared under 400 and 600 Torr. Impurities, namely, oxygen, carbon, silicon, and nitrogen, totaled less than 2,000 ppm, satisfying fuel criteria. Jong-Hwan Kim, Ki-Hwan Kim, and Chan-Bock Lee Copyright © 2015 Jong-Hwan Kim et al. All rights reserved. Output-Only Modal Analysis Based on Improved Empirical Mode Decomposition Method Sun, 04 Oct 2015 14:08:46 +0000 The output-only modal analysis for bridge structures based on improved empirical mode decomposition (EMD) is investigated in this study. First, a bandwidth restricted EMD is proposed for decomposing nonstationary output measurements with close frequency components. The advantage of bandwidth restricted EMD to standard EMD is illustrated by a numerical simulation. Next, the modal parameters are extracted from intrinsic mode function obtained from the improved EMD by both random decrement technique and stochastic subspace identification. Finally, output-only modal analysis of a railway bridge is presented. The study demonstrates the mode mixing issues of standard EMD can be restrained by introducing bandwidth restricted signal. Further, with the improved EMD method, band-pass filter is no longer needed for separating the closely spaced frequency components. The modal parameters extracted based on the improved EMD method show good agreement with those extracted by conventional modal identification algorithms. Shiqiang Qin, Qiuping Wang, and Juntao Kang Copyright © 2015 Shiqiang Qin et al. All rights reserved. Influence of Glass Powder on Hydration Kinetics of Composite Cementitious Materials Sun, 04 Oct 2015 14:01:17 +0000 The influence of glass powder (GP) on hydration kinetics of composite cementitious materials has been investigated by isothermal calorimetry test and hydration kinetics methods in this paper. The hydration heat emission rate and hydration heat decrease gradually while the induction and acceleration period increase with the increase of GP content. According to Krstulovic-Dabic model, the hydration process of composite cementitious materials containing GP is controlled by a variety of complicated reaction mechanisms, which can be divided into three periods: nucleation and crystal growth (NG), phase boundary reaction (I), and diffusion (D). The NG and I process are shortened after incorporating GP. Xiaolin Chang, Xinping Yang, Wei Zhou, Guoshuai Xie, and Shuhua Liu Copyright © 2015 Xiaolin Chang et al. All rights reserved. Metrology Needs for Predicting Concrete Pumpability Sun, 04 Oct 2015 12:52:51 +0000 With the increasing use of pumping to place concrete, the development and refinement of the industry practice to ensure successful concrete pumping are becoming important needs for the concrete construction industry. To date, research on concrete pumping has been largely limited to a few theses and research papers. The major obstacle to conduct research on concrete pumping is that it requires heavy equipment and large amounts of materials. Thus, developing realistic and simple measurement techniques and prediction tools is a financial and logistical challenge that is out of reach for small research labs and many private companies in the concrete construction industry. Moreover, because concrete pumping involves the flow of a complex fluid under pressure in a pipe, predicting its flow necessitates detailed knowledge of the rheological properties of concrete, which requires new measurement science. This paper summarizes the technical challenges associated with concrete pumping and the development in concrete pumping that have been published in the technical literature and identifies future research needed for the industry to develop best practices for ensuring successful concrete pumping in the field. Myoungsung Choi, Chiara F. Ferraris, Nicos S. Martys, Didier Lootens, Van K. Bui, and H. R. Trey Hamilton Copyright © 2015 Myoungsung Choi et al. All rights reserved. To Enhance the Fire Resistance Performance of High-Speed Steel Roller Door with Water Film System Sun, 04 Oct 2015 12:51:54 +0000 The structure of high-speed roller door with water film has improved in this study. The flameproof water film system is equipped with a water circulating device to reduce the water consumption of water film system. The water film is generated at the roller box of the high-speed roller door in this study. The heating test is done with the full-scale heating furnace. Both cases of the water film on unexposed surface and water film on exposed surface passed the fire resistance test based on ISO 834, proving that the high-speed roller door with water film system has 120A fire resistance period. The main findings indicate that the water film on exposed surface shows that as the amount of water film evaporated by high temperature inside the furnace must be greater than the evaporation capacity of water film on unexposed surface, the required water supply is 660 L more than the water film on unexposed surface. De-Hua Chung, Tien-Chih Wang, Ming-Ju Tsai, Ta-Hui Lin, and Shin-Ku Lee Copyright © 2015 De-Hua Chung et al. All rights reserved. Evaluation of an Improved Technique for Geosynthetic-Reinforced and Pile-Supported Embankment Sun, 04 Oct 2015 12:48:29 +0000 With a large number of applications of conventional technique for geosynthetic-reinforced and pile-supported (GRPS) embankment (called CT embankment), many deficiencies have been exposed. In view of the deficiencies, an improved technique, fixed-geosynthetic-reinforced and pile-supported embankment (called FGT embankment), is developed. To investigate the performance of the FGT embankment, the comparison analyses and parametric studies are conducted by Finite Element Method (FEM). The influencing factors investigated include elastic modulus of soil, tensile stiffness of geosynthetics, pile length, pile spacing, and pile elastic modulus. In addition, the cost evaluation for the FGT embankment and CT embankment is also made. The results show that the FGT embankment can significantly reduce the settlement and differential settlement, enhance the stability, and provide an economical and effective measure for the construction of high embankment at the bridge approach. Jun Zhang, Shao-wen Liu, and He-fu Pu Copyright © 2015 Jun Zhang et al. All rights reserved. Construction Technique of Long-Span Shallow-Buried Tunnel Considering the Optimal Sequence of Pilot-Tunnel Excavation Sun, 04 Oct 2015 12:46:44 +0000 Construction technique considering the optimal sequence of pilot-tunnel excavation was investigated in order to ensure the safety of construction process of long-span shallow-buried tunnel. Firstly, optimal comparisons of the effect of different sequence of pilot-tunnel excavation on the ground settlement were implemented by the numerical analysis. Secondly, an optimal construction method was determined and applied to the construction of a practical tunnel. Some key issues and procedure of the selected construction method were described in detail. Finally, the numerical modeling and calculation of the tunnel construction process were conducted, and the effectiveness of these simulations was demonstrated by using the measured data of the practical tunnel. Bao Jin, Yang Liu, Changxi Yang, Zhicheng Tan, and Jianyang Zhang Copyright © 2015 Bao Jin et al. All rights reserved. Effects of Seawater Corrosion and Freeze-Thaw Cycles on Mechanical Properties of Fatigue Damaged Reinforced Concrete Beams Sun, 04 Oct 2015 12:45:35 +0000 The effects of seawater corrosion and freeze-thaw cycles on the structural behavior of fatigue damaged reinforced concrete (FDRC) beams were experimentally studied. Results show that the residual strength of FDRC beams reduces as the fatigue load level (the ratio of maximum fatigue load to the ultimate static load) increases. The reduction in the loading capacity of FDRC beams in atmosphere environment was about 6.5% and 17.8% for given fatigue load levels of 0.2 and 0.3, respectively. However, if FDRC beams are exposed to the environment of seawater wet-dry cycles or to the environment of alternating actions of freeze-thaw and seawater immersion, as expected during the service life of RC bridge structures in coastal regions or in cold coastal regions, a more rapid reduction in the strength and stiffness of the beams is observed. The significance of an accurate simulation of working load and service condition RC bridge structures in coastal regions and cold coastal regions is highlighted. Zijian Liu, Bo Diao, and Xiaoning Zheng Copyright © 2015 Zijian Liu et al. All rights reserved. Development of a New Type of Alkali-Free Liquid Accelerator for Wet Shotcrete in Coal Mine and Its Engineering Application Sun, 04 Oct 2015 12:15:34 +0000 In order to address issues such as large rebound rate, high dust concentration, and low compressive strength of shotcrete when adding liquid accelerator during wet spraying, the factors influencing the efficiency of liquid accelerator were experimentally analyzed. The single-admixture, combination, and orthogonal tests were conducted on the five fundamental raw materials required to develop the new liquid accelerator. The WT-1 type liquid accelerator, which had better adaptability to different kinds of cement, was developed with the mass concentration ratio of 55% aluminum sulfate octadecahydrate, 4% sodium fluoride, 2.5% triethanolamine, 0.5% polyacrylamide, 5% bentonite, and 33% water. Experimental investigation showed that the initial setting time of the reference cement with 6% mass content of this liquid accelerator was 2 minutes and 15 seconds, and the final setting time was 7 minutes and 5 seconds. The compressive strength after 1 day of curing was 13.6 MPa and the strength ratio after 28 days of curing was 94.8%, which met the first grade product requirements of the China National Standard. Compared with the conventional type liquid accelerator, the proposed type WT-1 accelerator is capable of effectively reducing the rebound rate and dust concentration while significantly increasing the compressive strength of the shotcrete. Gang Zhou, Weimin Cheng, and Sen Cao Copyright © 2015 Gang Zhou et al. All rights reserved. Thermal Performance Analysis of Reinforced Concrete Floor Structure with Radiant Floor Heating System in Apartment Housing Sun, 04 Oct 2015 12:14:59 +0000 The use of the resilient materials in the radiant floor heating systems of reinforced concrete floor in apartment housing is closely related to the reduction of the floor impact sound and the heating energy loss. This study examined the thermal conductivity of expanded polystyrene (EPS) foam used for the resilient material in South Korea and analysed the thermal transfer of reinforced concrete floor structure according to the thermal conductivity of the resilient materials. 82 EPS specimens were used to measure the thermal conductivity. The measured apparent density of EPS resilient materials ranged between 9.5 and 63.0 kg/m3, and the thermal conductivity ranged between 0.030 and 0.046 W/(m·K). As the density of resilient materials made of expanded polystyrene foam increases, the thermal conductivity tends to proportionately decrease. To set up reasonable thermal insulation requirements for radiant heating floor systems, the thermal properties of floor structure according to thermal insulation materials must be determined. Heat transfer simulations were performed to analyze the surface temperature, heat loss, and heat flow of floor structure with radiant heating system. As the thermal conductivity of EPS resilient material increased 1.6 times, the heat loss was of 3.4% increase. Young-Sun Jeong and Hae-Kwon Jung Copyright © 2015 Young-Sun Jeong and Hae-Kwon Jung. All rights reserved. An Impact Vibration Experimental Research on the Pretension Rectangular Membrane Structure Sun, 04 Oct 2015 11:49:59 +0000 The pretension of the membrane is applied with biaxial tension bracket; the digital dynamometer is used for measuring the change of the tension; the concentrated impact load is applied on the surface of rectangular membrane; the displacement change of each feature point on the membrane surface is measured by noncontact laser displacement sensor. Through this experiment, the vibration displacement-time curve of the rectangular membrane under the fixed boundary condition is obtained. Further, the vibration frequency is given, according to the power spectral density function. The results of the experimental research are used to verify and correct theoretical formula and make the foundation for further theoretical research. Jianjun Guo, Zhoulian Zheng, and Song Wu Copyright © 2015 Jianjun Guo et al. All rights reserved. Experimental Study on Bond Behavior between Plain Reinforcing Bars and Concrete Sun, 04 Oct 2015 11:33:39 +0000 To evaluate the bond behavior between the reinforcing bar and surrounding concrete, a total of six-group pullout specimens with plain steel bars and two-group specimens with deformed steel bars, serving as a reference, are experimentally investigated and presented in this study. The main test parameters of this investigation include embedment length, surface type of reinforcing bars, and bar diameter. In particular, the bond mechanism of plain steel reinforcing bars against the surrounding concrete was analyzed by comparing with six-group pullout specimens with aluminium alloy bars. The results indicated that the bond stress experienced by plain bars is quite lower than that of the deformed bars given equal structural characteristics and details. Averagely, plain bars appeared to develop only 18.3% of the bond stress of deformed bars. Differing from the bond strength of plain steel bars, which is based primarily on chemical adhesion and friction force, the bond stress of aluminium alloy bars is mainly experienced by chemical adhesion and about 0.21~0.56 MPa, which is just one-tenth of that of plain steel bars. Based on the test results, a bond-slip model at the interface between concrete and plain bars is put forward. Guohua Xing, Cheng Zhou, Tao Wu, and Boquan Liu Copyright © 2015 Guohua Xing et al. All rights reserved. Locally Corroded Stiffener Effect on Shear Buckling Behaviors of Web Panel in the Plate Girder Sun, 04 Oct 2015 11:31:11 +0000 The shear buckling failure and strength of a web panel stiffened by stiffeners with corrosion damage were examined according to the degree of corrosion of the stiffeners, using the finite element analysis method. For this purpose, a plate girder with a four-panel web girder stiffened by vertical and longitudinal stiffeners was selected, and its deformable behaviors and the principal stress distribution of the web panel at the shear buckling strength of the web were compared after their post-shear buckling behaviors, as well as their out-of-plane displacement, to evaluate the effect of the stiffener in the web panel on the shear buckling failure. Their critical shear buckling load and shear buckling strength were also examined. The FE analyses showed that their typical shear buckling failures were affected by the structural relationship between the web panel and each stiffener in the plate girder, to resist shear buckling of the web panel. Their critical shear buckling loads decreased from 82% to 59%, and their shear buckling strength decreased from 88% to 76%, due to the effect of corrosion of the stiffeners on their shear buckling behavior. Thus, especially in cases with over 40% corrosion damage of the vertical stiffener, they can have lower shear buckling strength than their design level. Jungwon Huh, In-Tae Kim, and Jin-Hee Ahn Copyright © 2015 Jungwon Huh et al. All rights reserved. Preparation and Mechanical Properties of Continuous Carbon Nanotube Networks Modified Cf/SiC Composite Sun, 04 Oct 2015 11:21:47 +0000 Continuous carbon nanotube (CNT) networks were formed in Cf/SiC composites via freeze-drying method. Composites were fabricated by precursor infiltration and pyrolysis (PIP) process afterwards. The different distribution morphologies of CNTs in the preforms originating from the different CNT contents were analyzed while the influence of the distribution of CNTs was discussed in detail. Compared to composites without CNTs, the interfacial shear strength (ILSS) and the flexural strength of Cf/1%CNTs/SiC were increased by 31% and 27%, respectively, but the values of Cf/2.5%CNTs/SiC decreased as a result of lots of defects caused by excess CNTs. With the analysis of ILSS, the flexural strengths, and the fracture morphologies, CNTs effectively improved the weak interfacial strength between T700SC carbon fibers and SiC matrix. Lei Wang, Feng Hou, Xin Wang, Jiachen Liu, and Anran Guo Copyright © 2015 Lei Wang et al. All rights reserved. Numerical Investigation on Stress Concentration of Tension Steel Bars with One or Two Corrosion Pits Sun, 04 Oct 2015 11:20:29 +0000 Pitting corrosion has been observed in steel bars of existing reinforced concrete (RC) structures in different erosion environments and has been identified as a potential origin for fatigue crack nucleation. In the present study, under uniaxial tension loading, stress distribution in the steel bars with one or two semiellipsoidal corrosion pits has systematically been investigated by conducting a series of three-dimensional semiellipsoidal pitted models. Based on the finite element analyses, it is shown that stress concentration factor (SCF) increases linearly with increasing pit aspect ratio (a/b) and increases nonlinearly with increasing pit relative depth (a/R) for single corrosion pit problem. For double corrosion pits problem, the SCF decreases nonlinearly with increasing angle of two transverse pits (θ). The interaction of two longitudinal pits can be ignored in the calculation of SCF even if the distance of two pits (d) is very small. Jian Hou and Li Song Copyright © 2015 Jian Hou and Li Song. All rights reserved. Prediction of Chloride Penetration into Hardening Concrete Sun, 04 Oct 2015 10:25:04 +0000 In marine and coastal environments, penetration of chloride ions is one of the main mechanisms causing concrete reinforcement corrosion. Currently, most of experimental investigations about submerged penetration of chloride ions are started after the four-week standard curing of concrete. The further hydration of cement and reduction of chloride diffusivity during submerged penetration period are ignored. To overcome this weak point, this paper presents a numerical procedure to analyze simultaneously cement hydration reaction and chloride ion penetration process. First, using a cement hydration model, degree of hydration and phase volume fractions of hardening concrete are determined. Second, the dependences of chloride diffusivity and chloride binding capacity on age of concrete are clarified. Third, chloride profiles in hardening concrete are calculated. The proposed numerical procedure is verified by using chloride submerged penetration test results of concrete with different mixing proportions. Wei-Jie Fan and Xiao-Yong Wang Copyright © 2015 Wei-Jie Fan and Xiao-Yong Wang. All rights reserved. Durability Indicators in High Absorption Recycled Aggregate Concrete Sun, 04 Oct 2015 10:19:35 +0000 The use of recycled aggregates in structural concrete production has the inconvenience of increasing the fluid transport properties, such as porosity, sorptivity, and permeability, which reduces the resistance against penetration of environmental loads such as carbon dioxide and chloride ion. In this paper, behavior of ten concrete mixtures with different percentages of coarse aggregate replacement was studied. The recycled material was recovered by crushing of concrete rubble and had high absorption values. The results showed that it is possible to achieve good resistance to carbonation and chloride penetration with up to 50% replacement of recycled coarse aggregate for 0.5 water/cement ratio. Finally, new indexes for porosity and sorptivity were proposed to assess the quality of concrete. Luis F. Jiménez and Eric I. Moreno Copyright © 2015 Luis F. Jiménez and Eric I. Moreno. All rights reserved. Micromechanism Underlying Nonlinear Stress-Dependent of Clays at a Wide Range of Pressures Sun, 04 Oct 2015 10:15:58 +0000 In order to investigate the mechanism underlying the reported nonlinear at-rest coefficient of earth pressure, of clays at high pressure, a particle-scale model which can be used to calculate vertical and horizontal repulsion between clay particles has been proposed. This model has two initial states which represent the clays at low pressure and high pressure, and the particles in this model can undergo rotation and vertical translation. The computation shows that the majority of particles in a clay sample at high pressure state would experience rotation during one-dimensional compression. In addition, rotation of particles which tends to form a parallel structure causes an increase of the horizontal interparticle force, while vertical translation leads to a decrease in it. Finally, the link between interparticle force, microstructure, and macroscopic is analyzed and it can be used to interpret well the nonlinear changes in with both vertical consolidation stress and height-diameter ratio. Xiang-yu Shang, Chen Yang, Guo-qing Zhou, and Xiu-zhong Zheng Copyright © 2015 Xiang-yu Shang et al. All rights reserved. Stability of Three-Dimensional Slurry Trenches with Inclined Ground Surface: A Theoretical Study Sun, 04 Oct 2015 09:43:52 +0000 Stability of slurry trenches is an important issue during the construction of the groundwater cutoff walls and diaphragm walls, and thus gradually draws attention. In this paper, a theoretical method for a three-dimensional trench model with an inclined ground was proposed. Based on the Coulomb-type force equilibrium, a safety factor assessing the stability was derived. The results showed that the existing two-dimensional model was conservative compared to the present three-dimensional model; concretely, a greater inclined angle of the inclined ground and trench length decreased the safety factor. This work could be used to assess the trench stability for both 2D and 3D cases with inclined ground surfaces. Xiao-Fei Jin, Shu-Ting Liang, and Xiao-Jun Zhu Copyright © 2015 Xiao-Fei Jin et al. All rights reserved. The Influences of Iron Ore Tailings as Fine Aggregate on the Strength of Ultra-High Performance Concrete Sun, 04 Oct 2015 09:11:34 +0000 The present study looks for the feasibility of preparing UHPC with iron ore tailings (IOT for short) as fine aggregate. To enhance outstanding high performances, some influences on UHPC mortars were investigated such as different kinds of sands, different mix ratio of sands, and different largest particle size of fine aggregate. The results show that IOT have negligible poorer aggregate performance than silica sands but better than river sands. The strength of UHPC reaches the highest point when silica sands were instead 60% by IOT. As the largest particle size of fine aggregate is decreasing, the strength and frost resistance of UHPC were improved, but the liquidity was decreased. Micropowder of IOT affects the strength and the optimal content was 4%. Zhigang Zhu, Beixing Li, and Mingkai Zhou Copyright © 2015 Zhigang Zhu et al. All rights reserved. A Study on the Evaluation of Field Application of High-Fluidity Concrete Containing High Volume Fly Ash Sun, 04 Oct 2015 07:58:56 +0000 In the recent concrete industry, high-fluidity concrete is being widely used for the pouring of dense reinforced concrete. Normally, in the case of high-fluidity concrete, it includes high binder contents, so it is necessary to replace part of the cement through admixtures such as fly ash to procure economic feasibility and durability. This study shows the mechanical properties and field applicability of high-fluidity concrete using mass of fly ash as alternative materials of cement. The high-fluidity concrete mixed with 50% fly ash was measured to manufacture concrete that applies low water/binder ratio to measure the mechanical characteristics as compressive strength and elastic modulus. Also, in order to evaluate the field applicability, high-fluidity concrete containing high volume fly ash was evaluated for fluidity, compressive strength, heat of hydration, and drying shrinkage of concrete. Yun-Wang Choi, Man-Seok Park, Byung-Keol Choi, and Sung-Rok Oh Copyright © 2015 Yun-Wang Choi et al. All rights reserved. Shear Strengthening Performance of Hybrid FRP-FRCM Sun, 04 Oct 2015 07:57:34 +0000 The effectiveness of a hybrid fiber reinforced polymer- (FRP-) fabric reinforced cementitious matrix (FRCM) for shear strengthening was investigated though an experimental study. FRP materials of FRCM are usually fabricated in the form of a fabric to enhance the bond strength between the FRP material and the cementitious matrix. The hybrid FRP fabric used in this study consisted of carbon FRP (CFRP) and glass FRP (GFRP) in warp and weft directions, respectively. A total of 11 beams were fabricated and 8 beams among them were strengthened in shear with externally bonded hybrid FRP-FRCM. The number of plies, the bond types, and the spacing of the hybrid FRP fabric were considered as experimental variables. Additionally, a shear capacity model for a FRCM shear strengthened beam was proposed. The values predicted by the proposed model were compared with those by the ACI 549 code and test results. It was confirmed from the comparison that the proposed model predicted the shear strengthening performance of the hybrid FRP-FRCM more reliably than the ACI 549 code did. Kyusan Jung, Kinam Hong, Sanghoon Han, Jaekyu Park, and Jaehyun Kim Copyright © 2015 Kyusan Jung et al. All rights reserved. On the Durability of Sealable Circular Concrete Structures under Chloride Environment Sun, 04 Oct 2015 07:56:28 +0000 Reinforcement corrosion resulting from chloride attack is one major mechanism that compromises concrete durability. Numerical methods were commonly used for tackling Fick’s diffusion equations. In this paper, we developed a Crank-Nicolson based finite difference scheme suitable for circular concrete structures. Both a time-dependent surface chloride model and diffusivity were considered. The impact of an ideal sealer on chloride redistribution was further investigated. Results suggested that the chloride threshold depth in a concrete structure is greatly affected by the radius of curvature, environment severity, and diffusivity. For sealable concrete structures, both the sealer application timing and location are of great importance. Changwen Mi, Kaikai Shao, and Xiaobao Li Copyright © 2015 Changwen Mi et al. All rights reserved. Experimental Study on Sandwich Bridge Decks with GFRP Face Sheets and a Foam-Web Core Loaded under Two-Way Bending Sun, 04 Oct 2015 07:53:52 +0000 In recent years, the sandwich bridge decks with GFRP face sheets and light weight material core have been widely used in the world due to their advantages of low cost, high strength to weight ratios, and corrosion resisting. However, as the bridge decks, most of them are used in foot bridges rather than highway bridges because the ultimate bending strength and initial bending stiffness are relatively low. To address this issue and expand the scope of use, a simple and innovative sandwich bridge deck with GFRP face sheets and a foam-web core, manufactured by vacuum assisted resin infusion process, is developed. An experimental study was carried out to validate the effectiveness of this panel for increasing the ultimate bending strength and initial bending stiffness under two-way bending. The effects of face sheet thickness, foam density, web thickness, and web spacing on displacement ductility and energy dissipation were also investigated. Test results showed that, compared to the normal foam-core sandwich decks, an average approximately 657.1% increase in the ultimate bending strength can be achieved. Furthermore, the bending stiffness, displacement ductility, and energy dissipation can be enhanced by increasing web thickness, web height, and face sheet thickness or decreasing web spacing. Ruili Huo, Weiqing Liu, Li Wan, Yuan Fang, and Lu Wang Copyright © 2015 Ruili Huo et al. All rights reserved. Survival Analysis of Factors Influencing Cyclic Fatigue of Nickel-Titanium Endodontic Instruments Thu, 01 Oct 2015 13:04:20 +0000 Objective. The aim of this study was to validate a survival analysis assessing the effect of type of rotary system, canal curvature, and instrument size on cyclic resistance. Materials and Methods. Cyclic fatigue testing was carried out in stainless steel artificial canals with radii of curvature of 3 or 5 mm and the angle of curvature of 60 degrees. All the instruments were new and 25 mm in working length, and ISO colour coding indicated the instrument size (yellow for size 20; red for size 25). Wizard Navigator instruments, Mtwo instruments, ProTaper instruments, and Revo-S instruments were passively rotated at 250 rotations per minute, and the time fracture was being recorded. Subsequently, fractographic analysis of broken tips was performed by scanning electron microscope. The data were then analysed by the Kaplan-Meier estimator of the survival function, the Cox proportional hazards model, the Wald test for regression covariates, and the Wald test for significance of regression model. Conclusion. The lifespan registered for the tested instruments was Mtwo > Wizard Navigator > Revo-S > ProTaper; 5 mm radius > 3 mm radius; and yellow > red in ISO colour coding system. Eva Fišerová, Martina Chvosteková, Silvie Bělašková, Michal Bumbálek, and Zdeněk Joska Copyright © 2015 Eva Fišerová et al. All rights reserved. Experimental and Theoretical Research on the Stress-Relaxation Behaviors of PTFE Coated Fabrics under Different Temperatures Thu, 01 Oct 2015 13:03:18 +0000 As polymer composites, the stress-relaxation behaviors of membrane materials have significant effects on the pattern cutting design, the construction process analysis, and the stiffness degradation of membrane structures in the life cycle. In this paper, PTFE coated fabric is taken as the research object. First, the stress-relaxation behaviors under different temperatures (23°C, 40°C, 50°C, 60°C, and 70°C) are studied, and the variations of main mechanical parameters are got. Then, a simple review of several current viscoelastic models is presented. Finally, several common models for the material viscoelasticity are used to compare with the test results. Results show PTFE coated fabric is typically viscoelastic. The stress relaxation is obvious in the initial phase and it decreases with time increasing. The stress decreases significantly and then tends to a stable value. With temperature increasing, the decrease rate of membrane stress decreases and the final stable value increases. This material performs obvious hardening with temperature increasing. Most of the current models can make good prediction on the stress-relaxation behaviors of PTFE coated fabrics under different temperatures. The results can be references for the determination of pattern shrinkage ratio and construction process analysis of membrane structures. Yingying Zhang, Shanshan Xu, Qilin Zhang, and Yi Zhou Copyright © 2015 Yingying Zhang et al. All rights reserved. Shear Failure of RC Dapped-End Beams Thu, 01 Oct 2015 13:01:30 +0000 Reinforced concrete dapped-end beams (RC-DEBs) are mainly used for precast element construction. RC-DEBs generally are recessed at their end parts and supported by columns, cantilevers, inverted T-beams, or corbels. The geometric discontinuity of dapped-end beams evokes a severe stress concentration at reentrant corners that may lead to shear failure. Therefore, stress analysis is required at the reentrant vicinity for design requirement of these beams. Four large-scale RC-DEBs specimens were prepared, cast, and tested up to failure. Three parameters were investigated: amount of nib reinforcements, main flexural reinforcements, and concrete type at the dapped-end area. Finite element analysis using Vec2 was also conducted to predict the behavior of RC-DEBs. It has been found that highest stresses concentration factors occur at the reentrant corners and its vicinity. By using engineered cementitious composite (ECC) in the dapped-end area, the failure load has increased by 51.9%, while the increment in the failure load was 62.2% and 46.7% as the amount of nib reinforcement and main flexural reinforcement increased, respectively. In addition, Vec2 analysis has been found to provide better accuracy for predicting the failure load of RC-DEBs compared to other analysis approaches. Muhammad Aswin, Bashar S. Mohammed, M. S. Liew, and Zubair Imam Syed Copyright © 2015 Muhammad Aswin et al. All rights reserved. Progress in Research on Carbon Nanotubes Reinforced Cementitious Composites Thu, 01 Oct 2015 12:59:33 +0000 As one-dimensional (1D) nanofiber, carbon nanotubes (CNTs) have been widely used to improve the performance of nanocomposites due to their high strength, small dimensions, and remarkable physical properties. Progress in the field of CNTs presents a potential opportunity to enhance cementitious composites at the nanoscale. In this review, current research activities and key advances on multiwalled carbon nanotubes (MWCNTs) reinforced cementitious composites are summarized, including the effect of MWCNTs on modulus of elasticity, porosity, fracture, and mechanical and microstructure properties of cement-based composites. The issues about the improvement mechanisms, MWCNTs dispersion methods, and the major factors affecting the mechanical properties of composites are discussed. In addition, large-scale production methods of MWCNTs and the effects of CNTs on environment and health are also summarized. Qinghua Li, Jintao Liu, and Shilang Xu Copyright © 2015 Qinghua Li et al. All rights reserved.