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CONTENTS
Volume 22, Number 1, July 2018
 

Abstract
The steel fiber reinforced concrete (SFRC) shows better performance under dynamic loading than conventional concrete in virtue of its good ductility. In this paper, a series of quasi-static experiments were carried out on the SFRC with volume fractions from 0 to 6%. The compressive strength increases by 38% while the tension strength increases by 106% when the fraction is 6.0%. The contact explosion tests were also performed on the

Key Words
SFRC; blast resistant performance; spall resistant performance; damage region; blast loading

Address
Yongliang Zhang, Kai Zhao, Yongchi Li, Jincai Gu, Zhongbao Ye and Jian Ma: CAS Key Laboratory of Mechanical Behavior and Design of Materials, Department of Modern Mechanics,
University of Science and Technology of China, Hefei, Anhui 230027, China

Abstract
In this study an implicit algorithm for modeling of propagation of macrocracks in 3D concrete structures suffering from alkali-silica reaction has been developed and implemented. The formulation of the problem prior to the onset of localized deformation is based on a chemo-elasticity approach. The localized deformation mode, involving the formation of macrocracks, is described using a simplified form of the strong discontinuity approach (SDA) that employs a volume averaging technique enhanced by a numerical procedure for tracing the propagation path in 3D space. The latter incorporates a non-local smoothening algorithm. The formulation is illustrated by a number of numerical examples that examine the crack propagation pattern in both plain and reinforced concrete under different loading scenarios.

Key Words
3D crack propagation; volume averaging; alkali-silica reaction; reinforced concrete

Address
S. Moallemi and S. Pietruszczak: Department of Civil Engineering, McMaster University, 1280, Main St W, Hamilton, Ontario, Canada

Abstract
A numerical approach for the evaluation of the flexural response of Steel Fibrous Concrete (SFC) cross-sections with arbitrary geometry, with or without conventional steel longitudinal reinforcing bars is proposed. Resisting bending moment versus curvature curves are calculated using verified non-linear constitutive stress-strain relationships for the SFC under compression and tension which include post-peak and post-cracking softening parts. A new compressive stress-strain model for SFC is employed that has been derived from test data of 125 stress-strain curves and 257 strength values providing the overall compressive behaviour of various SFC mixtures. The proposed sectional analysis is verified using existing experimental data of 42 SFC beams, and it predicts the flexural capacity and the curvature ductility of SFC members reasonably well. The developed approach also provides rational and more accurate compressive and tensile stress-strain curves along with bending moment versus curvature curves with regards to the predictions of relevant existing models.

Key Words
concrete constitutive models; design codes; reinforced concrete (RC); steel fibre-reinforced concrete; structural analysis/design

Address
Constantin E. Chalioris and Thomas A. Panagiotopoulos: Department of Civil Engineering, Scholl of Engineering, Democritus University of Thrace, Laboratory of Reinforced Concrete and Seismic Design of Structures, Xanthi 67100, Greece

Abstract
Reinforced concrete structures are widely used in civil engineering projects around the world in different designs. Due to the great evolution in computational equipment and numerical methods, structural analysis has become more and more reliable, and in turn more closely approximates reality. Thus among the many numerical methods used to carry out these types of analyses, the finite element method has been highlighted as an optimized tool option, combined with the non-linear and linear analysis techniques of structures. In this paper, the behavior of reinforced concrete beams was analyzed in two different configurations: i) with welding and ii) conventionally lashed stirrups using annealed wire. The structures were subjected to normal and tangential forces up to the limit of their bending resistance capacities to observe the cracking process and growth of the concrete structure. This study was undertaken to evaluate the effectiveness of welded wire fabric as shear reinforcement in concrete prismatic beams under static loading conditions. Experimental analysis was carried out in order compare the maximum load of both configurations, the experimental load-time profile applied in the first configuration was used to reproduce the same loading conditions in the numerical simulations. Thus, comparisons between the numerical and experimental results of the welded frame beam show that the proposed model can estimate the concrete strength and failure behavior accurately.

Key Words
cracks; finite element method; nonlinear concrete; prismatic beam; steel frame; welded stirrups

Address
Wagner L. Goncalves: University Center of the Guaxupe Educational Foundation (UNIFEG), Avenue Dona Floriana, 463, Guaxupe, Brazil
Guilherme F. Gomes: Mechanical Engineering Institute, Federal University of Itajuba (UNIFEI), Avenue BPS, 1303, Itajuba, Brazil
Yohan D. Mendez: Mechanical Engineering Institute, Federal University of Itajuba (UNIFEI), Avenue BPS, 1303, Itajuba, Brazil
Fabricio A. Almeida: Institute of Industrial Engineering and Management, Federal University of Itajubá (UNIFEI), Avenue BPS, 1303, Itajuba, Brazil
Valquiria C. Santos: Institute of Natural Resources, Federal University of Itajubá (UNIFEI), Avenue BPS, 1303, Itajuba, Brazil
Sebastiao S. Cunha Jr.: Mechanical Engineering Institute, Federal University of Itajubá (UNIFEI), Avenue BPS, 1303, Itajubá, Brazil

Abstract
This study introduces a new algorithm to determine size independent values of fracture energy, fracture toughness, and fracture process zone length in three-point bending specimens with shallow to deep notches. By using the exact beam theory, a concept of equivalent notch length is introduced for specimens with no notches in order to predict the peak loads with acceptable precisions. Moreover, the method considers the variations of fracture process zone length and effects of higher order terms of stress field in each specimen size. In this paper, it was demonstrated that the use of some recently developed size effect laws raises some concerns due to the use of nonlinear regression analysis. By using a comprehensive fracture test data, provided by Hoover and Bazant, the algorithm has been assessed. It could be concluded that the proposed algorithm can facilitate a powerful tool for size effect study of three-point bending specimens with different notch lengths.

Key Words
concrete; fracture mechanics; civil engineering structures; fracture toughness; notch length

Address
Mohammad Karamloo and Moosa Mazloom: Department of Civil Engineering, Shahid Rajaee Teacher Training University, Lavizan, Tehran, Iran

Abstract
Cracking of concrete cover induced by reinforcement corrosion is a critical issue for life-cycle design and maintenance of reinforced concrete structures. However, the critical degree of corrosion, based on when the concrete surface cracks, is usually hard to predict accurately due to the heterogeneity inherent in concrete. To investigate the influence of concrete heterogeneity, a modified rigid-body-spring model, which could generate concrete sections with randomly distributed coarse aggregates, has been developed to study the corrosion-induced cracking process of the concrete cover and the corresponding critical degree of corrosion. In this model, concrete is assumed to be a three-phase composite composed of coarse aggregate, mortar and an interfacial transition zone (ITZ), and the uniform corrosion of a steel bar is simulated by applying uniform radial displacement. Once the relationship between radial displacement and degree of corrosion is derived, the critical degree of corrosion can be obtained. The mesoscale model demonstrated its validity as it predicted the critical degree of corrosion and cracking patterns in good agreement with analytical solutions and experimental results. The model demonstrates how the random distribution of coarse aggregate results in a variation of critical degrees of corrosion, which follows a normal distribution. A parametric study was conducted, which indicates that both the mean and variation of critical degree of corrosion increased with the increase of concrete cover thickness, coarse aggregates volume fraction and decrease of coarse aggregate size. In addition, as tensile strength of concrete increased, the average critical degree of corrosion increased while its variation almost remained unchanged.

Key Words
concrete cover cracking; steel corrosion; mesoscale model; random distribution of aggregate; critical degree of corrosion

Address
Junyu Chen, Weiping Zhang and Xianglin Gu: Key Laboratory of Performance Evolution and Control for Engineering Structures, Ministry of Education, Tongji University, 1239 Siping Road, Shanghai 200092, PR China

Abstract
Introduction of prestressed concrete slabs based on post-tensioned (PT) method aids in constructing larger spans, more useful floor height, and reduces the total weight of the building. In the present paper, for the first time, simulation of 32 two-way PT slab-edge column connections is performed and verified by some existing experimental results which show good consistency. Finite element method is used to assess the performance of bonded and unbonded slab-column connections and the impact of different parameters on these connections. Parameters such as strand bonding conditions, presence or absence of a shear cap in the area of slab-column connection and the changes of concrete compressive strength are implied in the modeling. The results indicate that the addition of a shear cap increases the flexural capacity, further increases the shear strength and converts the failure mode of connections from shear rigidity to flexural ductility. Besides, the reduction of concrete compressive strength decreases the flexural capacity, further reduces the shear strength of connections and converts the failure mode of connections from flexural ductility to shear rigidity. Comparing the effect of high concrete compressive strengths versus the addition of a shear cap, shows that the latter increases the shear capacity more significantly.

Key Words
prestressed concrete slab; post-tensioned; shear cap; unbonded; bonded

Address
Farshad Janghorban: Civil Engineering Department, Kish International Campus, University of Tehran, Niyayesh St., Mirmohanna Blvd., Kish Island, Iran
Abdollah Hoseini: Civil Engineering Department, University of Tehran, 16th Azar St., Enghelab Sq., Tehran, Iran

Abstract
Various systems for simulating particulate matter are developed and used in concrete technology for producing virtual cementitious materials on the different levels of the microstructure. Basically, the systems can be classified as two distinct families, namely random sequential addition systems (RSAs) and discrete element methods (DEMs). The first type is hardly being used for this purpose outside concrete technology, but became popular among concrete technologists. Hence, it is of utmost relevance to compare the two families in their capabilities, so that the reliability of produced data can be estimated. This paper pursues to do this on the basis of earlier published material of work performed by a succession of PhD students in the group of the second author. Limited references will be given to external sources.

Key Words
cementitious materials; aggregate; hydration; porosimetry; permeability; structure-sensitivity

Address
Kai Li: Key Laboratory for Green & Advanced Civil Engineering Materials and Application Technology of Hunan Province, College of Civil Engineering, Hunan University, 410082 Changsha, China
Piet Stroeven: Faculty of Civil Engineering and Geosciences, Delft University of Technology, Stevinweg 1, 2628 CN, Delft, The Netherlands

Abstract
It is seldom possible that geotechnical materials like rocks and concretes found without joints, cracks, or discontinuities. Thereby, the impact of micro-cracks on the mechanical properties of them is to be considered. In the present study, the effect of micro-crack on the failure mechanism of rock specimens under uniaxial compression was investigated experimentally. For this purpose, thermal stress was used to induce micro-cracks in the specimens. Several cylindrical and disk shape specimens were drilled from granite collected from Zanjan granite mine, Iran. Some of the prepared specimens were kept in room temperature and the others were heated by a laboratory furnace to different temperature levels (200, 400, 600, 800 and 1000 degree Celsius). During the experimental tests, Acoustic Emission (AE) sensors were used to monitor specimen failure at the different loading sequences. Also, Scanning Electron Microscope (SEM) was used to distinguish the induced micro-crack by heating in the specimens. The fractographic analysis revealed that the thin sections heated to 800oC and 1000oC contain some induced micro-fractures, but in the thin sections heated to 200oC, 400oC and 600oC have not been observed any micro-fracture. In the next, a comprehensive experimental investigation was made to evaluate mechanical properties of heated and unheated specimens. Results of experimental tests showed that induced micro-cracks significantly influence on the failure mode of specimens. The specimens kept at room temperature failed in the splitting mode, while the failure mode of specimens heated to 800oC are shearing and the specimens heated to 1000oC failed in the spalling mode. On the basis of AE monitoring, it is found that with increasing of the micro-crack density, the ratio of the number of shear cracks to the number of tensile cracks increases, under loading sequences.

Key Words
failure mechanism; micro-crack; thermal stress; acoustic emission

Address
Amin Khodayar and Hamid Reza Nejati: Rock Mechanics Division, School of Engineering, Tarbiat Modares University, Tehran, Iran

Abstract
As one of the most important engineering structures, arch dams are huge constructions built with human hands and have strategical importance. Because of the fact that long construction duration, water supply, financial reasons, major loss of life and material since failure etc., the design of arch dams is very important problem and should be done by expert engineers to determine the structural behavior more accurately. Finite element analyses and non-destructive experimental measurements can be used to investigate the structural response, but there are some difficulties such as spending a long time while modelling, analysis and in-situ testing. Therefore, it is more useful to conduct the research on the laboratory conditions and to transform the obtained results into real constructions. Within the scope of this study, it is aimed to determine the structural behavior of arch dams considering experimentally validated prototype laboratory model using similitude and scaling laws. Type-1 arch dam, which is one of five arch dam types suggested at the \"Arch Dams\" Symposium in England in 1968 is selected as reference prototype model. The dam is built considering dam-reservoir-foundation interaction and ambient vibration tests are performed to validate the finite element results such as dynamic characteristics, displacements, principal stresses and strains. These results are considered as reference parameters and used to determine the real arch dam response with different scales factors such as 335, 400, 416.67 and 450. These values are selected by considering previously examined dam projects. Arch heights are calculated as 201 m, 240 m, 250 m and 270 m, respectively. The structural response is investigated between the model and prototype by using similarity requirements, field equations, scaling laws etc. To validate these results, finite element models are enlarged in the same scales and analyses are repeated to obtain the dynamic characteristics, displacements, principal stresses and strains. At the end of the study, it is seen that there is a good agreement between all results obtained by similarity requirements with scaling laws and enlarged finite element models.

Key Words
arch dam; finite element analyses; scaling laws; similarity requirements

Address
Ahmet Can Altunisik, Ebru Kalkan and Hasan B. Basaga: Department of Civil Engineering, Karadeniz Technical University, Trabzon, Turkey

Abstract
The use of nanotechnology materials and applications in the construction industry should be considered for enhancing material properties. However, in this paper, the technical and economical assessment of applying silica nanoparticles for construction of concrete structure is studied. In order to obtain the equivalent material properties of the structure, the Mori-Tanaka model is used considering agglomeration of nanoparticles. The effect of using these nanoparticles on mechanical properties of concrete, such as the modulus of elasticity, compressive strength, as well as its indirect effect on armature percentage is investigated. Finally, the price of silica nanoparticles and its effect on the price increase of concrete structure is investigated. The results show that increasing the volume percent of silica nanoparticles up to 10% improves elastic modulus 111% and reduces amateur percentage up to 72%.

Key Words
silica nanoparticles; concrete structures; technical and economical assessment; Mori-Tanaka model

Address
Sajad Shariati Rad: Department of Civil Engineering, Jasb Branch, Islamic Azad University, Jasb, Iran

Abstract
Reinforced concrete (RC) columns which are the main vertical structural members are exposed to several static and dynamic effects such as earthquake and wind. However, impact loading that is sudden impulsive dynamic one is the most effective loading type acting on the RC columns. Impact load is a kind of impulsive dynamic load which is ignored in the design process of RC columns like other structural members. The behavior of reinforced concrete columns under impact loading is an area of research that is still not well understood; however, work in this area continues to be motivated by a broad range of applications. Examples include reinforced concrete structures designed to resist accidental loading scenarios such as falling rock impact; vehicle or ship collisions with buildings, bridges, or offshore facilities; and structures that are used in high-threat or highhazard applications, such as military fortification structures or nuclear facilities. In this study, free weight falling test setup is developed to investigate the behavior effects on RC columns under impact loading. For this purpose, eight RC column test specimens with 1/3 scale are manufactured. While drop height and mass of the striker are constant, application point of impact loading, stirrup spacing and concrete compression strength are the experimental variables. The time-history of the impact force, the accelerations of two points and the displacement of columns were measured. The crack patterns of RC columns are also observed. In the light of experimental results, low-velocity impact behavior of RC columns were determined and interpreted. Besides, the finite element models of RC columns are generated using ABAQUS software. It is found out that proposed finite element model could be used for evaluation of dynamic responses of RC columns subjected to low-velocity impact load.

Key Words
ABAQUS; dynamic analysis; impact effect; RC columns; weight falling drop test

Address
Ozgur Anil: Department of Civil Engineering, Gazi University, Ankara, Turkey
Tugrul Erdem: Department of Civil Engineering, Celal Bayar University, Manisa, Turkey
Merve Nilay Tokgoz: Department of Civil Engineering, Gazi University, Ankara, Turkey

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