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CONTENTS
Volume 19, Number 4, April 2017
 

Abstract
The main objective of this paper was to illuminate the effect of marine environmental condition on durability of reinforced concrete (RC)-corroded columns strengthened with carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) layers. Small-scale columns were prepared and corroded by an accelerated corrosion process. After strengthening, compressive strength tests were carried out on control and weathered specimens. In this research, a marine simulator was designed and constructed similar to the tidal zone of marine environment in south of Iran which was selected as a case study in this research. Mechanical properties of wrapped specimens were studied after placing them inside the simulator for 3000 hours. Marine environment decreased ultimate strength by 4.5% and 26.3% in CFRP and GFRP-wrapped columns, respectively. In some corroded-columns, strengthening was carried out after replacing damaged cover by self-compacted mortar. In this method, by confining with one layer of CFRP and GFRP, 4.2% and 22.4% reduction in ultimate strength was observed, respectively, after exposure. Furthermore, the elastic-brittle behavior has been verified in this retrofit method. Also results of tension tests revealed, the ultimate tensile strength was degraded by 2% and 28.8% in CFRP and GFRP sheets, respectively, after applying marine exposure.

Key Words
FRP sheets; marine exposure; corroded columns; strengthening; durability

Address
Amin Kashi and Ali Akbar Ramezanianpour: Department of Civil and Environmental Engineering, Amirkabir University of Technology, Tehran, Iran
Faramarz Moodi: Department of Civil and Environmental Engineering, Concrete Technology and Durability Research Center (CTDRc), Amirkabir University of Technology, Tehran, Iran

Abstract
ANSYS is a software well accepted by professionals and academics, since it provides a variety of finite elements, material constitutive models, and linear and nonlinear analysis of structures in general. For the concrete material, for instance, the software uses an elastoplastic model with the Willam-Warnke surface of rupture (1975). However, this model is only available for finite elements that do not offer the possibility of use of the element-embedded model for rebars, demanding a much larger amount of elements to discretize structures, making numerical solutions less efficient. This study is, therefore, about the development of a computational model using the Finite Element Method via ANSYS platform for nonlinear analysis of reinforced and prestressed concrete beams under plane stress states. The most significant advantage of this implementation is the possibility of using the element-embedded rebar model in ANSYS with its 2D eight-node quadratic element PLANE183 for discretization of the concrete together with element REINF263 for discretization of rebars, stirrups, and cables, making the solutions faster and more efficient. For representation of the constitutive equations of the steel and the concrete, a proposed model was implemented with the help of the UPF customization tool (User Programmable Features) of ANSYS, where new subroutines written in FORTRAN were attached to the main program. The numerical results are compared with experimental values available in the technical literature to validate the proposed model, with satisfactory results being found.

Key Words
reinforced and prestressed concrete beams; element-embedded rebar model; ANSYS; UPF

Address
Bruna M. Lazzari, Américo Campos Filho, Paula M. Lazzari and Alexandre R. Pacheco: Civil Engineering Graduate Program, Federal University of Rio Grande do Sul, 99 Oswaldo Aranha Ave, 90035-190, Porto Alegre, RS, Brazil

Abstract
This paper conveys the effects of fly ash and silica fume incorporated in concrete at various replacement ratios on the durability properties of concretes. It is quite well known that concrete durability is as much important as strength and permeability is the key to durability. Permeability is closely associated with the voids system of concrete. Concrete, with less and disconnected voids, is assumed to be impermeable. The void system in concrete is straightly related to the mix proportions, placing, compaction, and curing procedures of concrete. Reinforced concrete structures, particularly those of subjected to water, are at the risk of various harmful agents such as chlorides and sulfate since the ingress of such agents through concrete becomes easy and accelerates as the permeability of concrete increases. Eventually, both strength and durability of concrete reduce as the time moves on, in turn; the service life of the concrete structures shortens. Mineral additives have been proven to be very effective in reducing permeability. The tests performed to accomplish the aim of the study are the rapid chloride permeability test, pressurized water depth test, capillarity test and compressive strength test. The results derived from these tests indicated that the durability properties of concretes incorporated fly ash and silica fume have improved substantially compared to that of without mineral additives regardless of the binder content used. Overall, the improvement becomes more evident as the replacement ratio of fly ash and silica fume have increased. With regard to permeability, silica fume is found to be superior to fly ash. Moreover, at least a 30% fly ash replacement and/or a replacement ratio of 5% to 10% silica fume have been found to be highly beneficial as far as sustainability is concerned, particularly for concretes subjected to chloride bearing environments.

Key Words
rapid chloride permeability; water depth; capillarity; mineral additives; durability

Address
Ufuk Kandil, Şakir Erdoğdu and Şirin Kurbetci: Department of Civil Engineering, Karadeniz Technical University, 61080, Trabzon, Turkey

Abstract
With the continuous evolution of the numerical methods and the availability of advanced constitutive models, it became a common practice to use complex physical and geometrical nonlinear numerical analyses to estimate the structural behavior of reinforced concrete elements. Such simulations may yield the complete time history of the structural behavior; from the first moment the load is applied until the total collapse of the structure. However, the evolution of the cracking pattern in geometrical discontinuous zones of reinforced concrete elements and the associated failure modes are relatively complex phenomena and their numerical simulation is considerably challenging. The objective of the present paper is to assess the applicability of the Applied Element Method in simulating the development of distinct failure modes in reinforced concrete walls subjected to monotonic loading obtained in experimental tests. A pushover test was simulated numerically on three distinct RC shear walls, all presenting an opening that guarantee a geometrical discontinuity zone and, consequently, a relatively complex cracking pattern. The presence of different reinforcement solutions in each wall enables the assessment of the reliability of the computational model for distinct failure modes. Comparison with available experimental tests allows concluding on the advantages and the limitations of the Applied Element Method when used to estimate the behavior of reinforced concrete elements subjected to monotonic loading.

Key Words
applied element method; nonlinear analysis; cracking pattern; RC shear walls

Address
Corneliu Cismasiu, António Pinho Ramos and Diogo F. Ferreira: CERIS, ICIST and Department of Civil Engineering, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal
Ionut D. Moldovan: CERIS, Instituto Superior Técnico, Universidade de Lisboa, 1049-001, Lisboa, Portugal
Jorge B. Filho: Department of Structures, Universidade Estadual de Londrina, Paraná, Brazil

Abstract
In the present paper experimental and numerical analysis of hook-ended steel fiber reinforced concrete is carried out. The experimental tests are performed on notched beams loaded in 3-point bending using fiber volume fractions up to 1.5%. The numerical analysis of fiber reinforced concrete beams is performed at meso scale. The concrete is discretized with 3D solid finite elements and microplane model is used as a constitutive law. The fibers are modelled by randomly generated 1D truss finite elements, which are connected with concrete matrix by discrete bond-slip relationship. It is demonstrated that the presented approach, which is based on the modelling of concrete matrix using microplane model, able to realistically replicate experimental results. In all investigated cases failure is due to the pull-out of fibers. It is shown that with increase of volume content of fibers the effective bond strength and slip capacity of fibers decreases.

Key Words
concrete; steel fibers; 3D finite element analysis; meso-scale; microplane model; bond-slip

Address
Željko Smolčić: Faculty of Civil Engineering of University of Rijeka, Radmile Matejčić 3, Rijeka, Croatia
Joško Ožbolt:
1) Faculty of Civil Engineering of University of Rijeka, Radmile Matejčić 3, Rijeka, Croatia
2) Institut für Werkstoffe im Bauwesen, Universität Stuttgart, Pfaffenwaldring 4, Stuttgart, Germany

Abstract
To study the effects of water-cement ratio changes and cracks on chloride ion transmission rate in cracked concrete, RCM method was adopted to accelerate the diffusion of chloride ion in cracked concrete, and the changes in chloride ion concentration and around the cracks are inferred by finite-element method. The test results show that as far as prefabricated cracks on concrete components are concerned, the width thresholds of two cracks on the concrete specimens with a water-cement ratio of 0.5 and 0.6 are 0.05 mm and 0.1 mm respectively, the width threshold of two cracks on the concrete specimens with a water-cement ratio of 0.4 is 0.05 mm and 0.2 mm respectively; and the results of numerical simulation show that the smaller the water-cement ratio is, the more significant effects of cracks on chloride ion transmission rate are. As a result, more attention shall be paid to the crack prevention, repairing and strengthening for high-strength concrete.

Key Words
water-cement ratio; cracks; concrete; chloride ion; numerical simulation

Address
Yue Li, Xiaohan Chen and Guosheng Zhang:
1) The Key Laboratory of Urban Security and Disaster Engineering, MOE, Beijing University of Technology, 100124, Beijing, PR China
2) Beijing Key Lab of Earthquake Engineering and Structural Retrofit, Beijing University of Technology, 100124, Beijing, PR China

Abstract
In this paper, the mechanical property of CFRP, BFRP, GFRP and their hybrid FRP was experimentally studied. The elastic modulus and tensile strength of CFRP, BFRP, GFRP and their hybrid FRP were tested. The experimental results showed that the elastic modulus of hybrid FRP agreed well with the theoretical rule of mixture, which means the property of hybrid composites are linear with the volumes of the corresponding components while the tensile strength did not. The bearing capacity, peak strain, stress-strain relationship of circular concrete columns confined by CFRP, BFRP, GFRP and hybrid FRP subjected to axial compression were recorded. And the confinement effect of hybrid FRP on concrete columns was analyzed. The test results showed that the bearing capacity and ductility of concrete columns were efficiently improved through hybrid FRP confinement. A strength model and a stress-strain relationship model of hybrid FRP confined concrete columns were proposed. The proposed stress-strain model was shown to be capable of providing accurate prediction of the axial compressive strength of hybrid FRP confined concrete compared with Teng et al. (2002) model, Karbhari and Gao (1997) model and Miyachi et al. (1999) model. The modified stress-strain model was also suitable for single FRP confinement cases and it was so concise in form and didn\'t have piecewise fitting, which would be easy for use in structural design.

Key Words
hybrid FRP; confined concrete column; axial compressive test; mechanical behavior; stress-strain model

Address
Li-Juan Li, Lan Zeng, Shun-De Xu and Yong-Chang Guo: School of Civil and Transportation Engineering, Guangdong University of Technology, 100 Waihuan Xi Road, Panyu District, 510006, Guangzhou, China

Abstract
Carbon Fiber Reinforced Plastic (CFRP) has commonly been used to strengthen existing RC structures. Wrapping the whole component with CFRP is an effective method and simple to execute. Besides, specific configuration of CFRP sheets (L, X and T shape) has also been considered in some experiments to examine CFRP effects in advance. This study aimed to provide an optimal CFRP configuration to effectively retrofit the beam-column connection using continuous material topology optimization procedure. In addition, Moved and Regularized Heaviside Functions and penalization factors were also considered. Furthermore, a multi-material procedure was also used to compare with the results from the single material procedure.

Key Words
topology optimization; 99-line matlab code; multi-material; stress concentration; beam-column joint; retrofitted

Address
Hoang V. Dang, Dongkyu Lee and Kihak Lee: Department of Architectural Engineering, Sejong University, 98 Gunja-dong, Gwangjin-gu, Seoul 143-747, Republic of Korea

Abstract
Concrete is a material popularly used in construction. Due to the load-bearing and external environmental factors during utilization or manufacturing, its surface is prone to flaws, such as crack and leak. To repair these superficial defects and ultimately and avoid the deterioration of the concrete\'s durability, numerous concrete surface protective coatings and crack repair products have been developed. Currently, studies are endeavoring to exploit the mineralization property of microbial strains for repairing concrete cracks be the repairing material for crack rehabilitation. This research aims to use bacteria, specifically B. pasteurii, in crack rehabilitation to enhance the flexural and compression strength of the repaired concrete. Serial tests at various bacterial concentrations and the same Urea-CaCl2 medium concentration of 70% for crack rehabilitation were executed. The results prove that the higher the concentration of the bacterial broth, the greater the amount of calcium carbonate precipitate was induced, while using B. pasteurii broth was for crack rehabilitation. The flexural and compression strengths of the repaired concrete test samples were the greatest at 100% bacterial concentration. Compared to the control group (bacterial concentration of 0%), the flexural strength had increased by 32.58% for 1-mm crack samples and 51.01% for 2-mm crack samples, and the compression strength had increased by 28.58% and 23.85%, respectively. From the SEM and XRD test results, a greater quantity of rectangular and polygonal crystals was also found in samples with high bacterial concentrations. These tests all confirm that using bacteria in crack rehabilitation can increase the flexural and compression strength of the repaired concrete.

Key Words
concrete crack; biological rehabilitation; enzyme; flexural strength; compression strength

Address
How-Ji Chen, Pang-Hsu Tai, Ching-Fang Peng and Ming-Der Yang: Department of Civil Engineering, National Chung Hsing University, 145 Xingda Rd., Taichung City 402, Taiwan

Abstract
With the rising global environmental awareness on energy saving and carbon reduction, as well as the environmental transition and natural disasters resulted from the greenhouse effect, waste resources should be efficiently used to save environmental space and achieve environmental protection principle of \"sustainable development and recycling\". This study used recycled cement mortar and adopted the volumetric method for experimental design, which replaced cement (0%, 10%, 20%, 30%) with recycled materials (fly ash, slag, glass powder) to test compressive strength and ultrasonic pulse velocity (UPV). The hyperbolic function for nonlinear multivariate regression analysis was used to build prediction models, in order to study the effect of different recycled material addition levels (the function of Rm(F, S, G) was used and be a representative of the content of recycled materials, such as fly ash, slag and glass) on the compressive strength and UPV of cement mortar. The calculated results are in accordance with laboratory-measured data, which are the mortar compressive strength and UPV of various mix proportions. From the comparison between the prediction analysis values and test results, the coefficient of determination R2 and MAPE (mean absolute percentage error) value of compressive strength are 0.970-0.988 and 5.57-8.84%, respectively. Furthermore, the R2 and MAPE values for UPV are 0.960-0.987 and 1.52-1.74%, respectively. All of the R2 and MAPE values are closely to 1.0 and less than 10%, respectively. Thus, the prediction models established in this study have excellent predictive ability of compressive strength and UPV for recycled materials applied in cement mortar.

Key Words
compressive strength; ultrasonic pulse velocity; prediction model; recycled materials; cement mortar

Address
Chien-Chih Wang: Department of Civil Engineering and Geomatics, Cheng Shiu University, Kaohsiung, 833, Taiwan, R.O.C.
Her-Yung Wang and Shu-Chuan Chang: Department of Civil Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung, 807, Taiwan, R.O.C.

Abstract
Failure of basic structures material is usually accompanied by expansion of interior cracks due to stress concentration at the cracks tip. This phenomenon shows the importance of examination of the failure behavior of concrete structures. To this end, 4 types of mortar samples with different amounts of nano-silica (0%, 0.5%, 1%, and 1.5%) were made to prepare twelve 50x50x50 mm cubic samples. The goal of this study was to describe the failure and micro-crack growth behavior of the cement mortars in presence of nano-silica particles and control mortars during different curing days. Failure of mortar samples under compressive strength were sensed with acoustic emission technique (AET) at different curing days. It was concluded that the addition of nano-silica particles could modify failure and micro-crack growth behavior of mortar samples. Also, monitoring of acoustic emission parameters exposed differences in failure behavior due to the addition of the nanoparticles. Mortar samples of nano-silica particles revealed stronger shear mode characteristics than those without nanoparticles, which revealed high acoustic activity due to heterogeneous matrix. It is worth mentioning that the highest compressive strength for 3 and 7 test ages obtained from samples with the addition of 1.5% nano-silica particles. On the other hand maximum compressive strength of 28 curing days obtained from samples with 1% combination of nano-silica particles.

Key Words
failure behavior; micro-crack growth; acoustic emission; nano-silica particles

Address
Amin Nazerigivi, Hamid Reza Nejati, Abdolhadi Ghazvinian: Rock Mechanics Division, School of Engineering, Tarbiat Modares University, Iran
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Abstract
In recent years, the use of supplementary cementing materials, especially in addition to concrete, has been the subject of many researches. Rice husk ash (RHA) is one of these materials that in this research, is added to the roller compacted concrete as one of the pozzolanic materials. This paper evaluates how different contents of RHA added to the roller compacted concrete pavement specimens, can influence on the strength and permeability. The results are compared to the control samples and determined optimal level of RHA replacement. As it was expected, RHA as supplementary cementitious materials, improved mechanical properties of roller compacted concrete pavement (RCCP). Also, the application of adaptive neuro-fuzzy inference system (ANFIS) in predicting the permeability and compressive strength is investigated. The obtained results shows that the predicted value by this model is in good agreement with the experimental, which shows the proposed ANFIS model is a useful, reliable, fast and cheap tool to predict the permeability and compressive strength. A mean relative error percentage (MRE %) less than 1.1% is obtained for the proposed ANFIS model. Also, the test results and performed modeling show that the optimal value for obtaining the maximum compressive strength and minimum permeability is offered by substituting 9% and 18% of the cement by RHA, respectively.

Key Words
rice husk ash; roller compacted concrete pavement; servopac gyratory compactor; mechanical properties; adaptive neuro-fuzzy inference system¬; modeling

Address
Ebrahim Khalilzadeh Vahidi and Maryam Mokhtari Malekabadi: Department of Civil Engineering, Faculty of Engineering, Razi University, Kermanshah, Iran
Abbas Rezaei and Gholam Hossein Roshani: Department of Electrical Engineering, Kermanshah University of Technology, Kermanshah, Iran
Mohammad Mahdi Roshani: Young Researchers and Elite Club, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran


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