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Frontiers of Structural and Civil Engineering

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, Volume 11 Issue 4 Previous Issue   
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The effect of sea level rise on beach morphology of caspian sea coast
Front. Struct. Civ. Eng.. 2017, 11 (4): 369-379.   DOI: 10.1007/s11709-017-0398-6
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Study of beach morphology has been one of the most important issues in coastal engineering research projects. Because of the existence of two important coastal areas located in the north and south parts of the Iran, in the present study an analysis of the coastal zone behaviour is made. Bed level elevations are measured and compared with the theoretical equilibrium profile. It is shown that the behaviour of the coastal zone in the region is consistent with the Dean (1991) equilibrium profile. In the next stage, following extensive investigations, the bed level changes due to arise in sea level at different locations in the surf zone are estimated. The mechanism of beach re-treatment due to a rise in sea level is considered based on the simplified model of Dean (1991) in which the mass balance of the sediments is taken into account. Comparison of the equilibrium profiles for different cases of sea level rise, clearly shows that because of the sediment transport induced by the fluctuation of the water level, the beach profile in the surf zone changes accordingly resulting in an erosion in the inner region of the surf zone and an accumulation of sediments towards the offshore.

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The investigation of fly ash based asphalt binders using atomic force microscope
Rajan SAHA, Kyle MALLOY, Emil BAUTISTA, Konstantin SOBOLEV
Front. Struct. Civ. Eng.. 2017, 11 (4): 380-387.   DOI: 10.1007/s11709-017-0437-3
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Atomic Force Microscope (AFM) is a relatively new technique for investigation of construction materials. In this study AFM was used to investigate the interaction of asphalt binder with fly ash. Fly ash is a coal combustion byproduct of electric power utilities having pozzolanic properties and commonly used in Portland cement concrete. In this study, an investigation was made by using different types of fly ash with two types of asphalt binders such as PG 58-28 and PG 64-28. Asphalt microstructure is divided into four subgroups such as Saturates, Aromatics, Resins and Asphaltenes (SARA). These four phases can be distinguished by the atomic force microscope. The interaction of these phases affected by introducing fly-ash was investigated and correlation with rheological properties was observed.

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An experimental study on plunging depth of density currents
Hassan GOLEIJ, Amir Hamzeh HAGHIABI, Abbas PARSAIE
Front. Struct. Civ. Eng.. 2017, 11 (4): 388-395.   DOI: 10.1007/s11709-017-0417-7
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Mass density of the current flows is the one of the important problem in the hydraulics of the dam reservoir. Plunge point occurs when the mass density current penetrates in the stagnant fluid. Recognition the place of this point is very important because of clearing the boundary of the density current flow and ambient fluid. In this study the influences of bed slope and hydraulic parameters on plunging depth were experimentally investigated. The results show that the slope has a minor effect on the plunging depth. The height of plunging depth is increased by increasing the density of the current flow. Also increasing the densimetric Froude number caused of decreasing the plunging depth. Finally an equation was proposed to estimate the plunging depth using as function of flow characteristics.

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Application of BCP-2007 and UBC-97 in seismic vulnerability assessment of gravity designed RC buildings in Pakistan
Muhammad Usman ALI, Shaukat Ali KHAN, Muhammad Yousaf ANWAR
Front. Struct. Civ. Eng.. 2017, 11 (4): 396-405.   DOI: 10.1007/s11709-017-0436-4
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Recent earthquakes in Pakistan (Kashmir 2005, Balochistan 2008, and Balochistan 2013) revealed the vulnerability of existing building stock and the deficiencies in the then prevalent Pakistan Seismic Code (PSC-86 (1986)). This study investigates, through an analytical framework, the seismic vulnerability of these and other such buildings, in accordance with the newly developed Building Code of Pakistan – Seismic Provisions 2007 (BCP-SP 07). Detailed failure mode is presented for buildings designed as per the new code. Collapse of structures is predicted for only 8% increase in PGA after moderate damage. A previously developed method, based on Eurocode-8 (2004), is used as baseline. A deficient reinforced concrete frame, typical to local building practices, is analyzed and assessed for vulnerability using the BCP- SP 07 (2007) framework. A comparison is drawn for the same building, based on Eurocode-8 (2004). Derived vulnerability curves show that the previous framework overestimated the damage and hence the vulnerability. Comparison of vulnerability parameters with previous studies show slight difference in performance of buildings.

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Compressive strength and stability of sustainable self-consolidating concrete containing fly ash, silica fume, and GGBS
Osama Ahmed MOHAMED, Omar Fawwaz NAJM
Front. Struct. Civ. Eng.. 2017, 11 (4): 406-411.   DOI: 10.1007/s11709-016-0350-1
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This paper presents the findings of an experimental program seeking to understand the effect of mineral admixtures on fresh and hardened properties of sustainable self-consolidating concrete (SCC) mixes where up to 80% of Portland cement was replaced with fly ash, silica fume, or ground granulated blast furnace slag. Compressive strength of SCC mixes was measured after 3, 7, and 28 days of moist curing. It was concluded in this study that increasing the dosage of fly ash increases concrete flow but also decreases segregation resistance. In addition, for the water-to-cement ratio of 0.36 used in this study, it was observed that the compressive strength decreases compared to control mix after 28 days of curing when cement was partially replaced by 10%, 30%, and 40% of fly ash. However, a fly ash replacement ratio of 20% increased the compressive strength by a small margin compared to the control mix. Replacing cement with silica fume at 5%, 10%, 15%, and 20% was found to increase compressive strength of SCC mixes compared to the control mix. However, the highest 28 day compressive strength of 95.3 MPa occurred with SCC mixes in which 15% of the cement was replaced with silica fume.

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Research Article
Instantaneous deflection of light-weight concrete slabs
Front. Struct. Civ. Eng.. 2017, 11 (4): 412-423.   DOI: 10.1007/s11709-017-0416-8
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Construction loading before the age of 28 d can have the most significant effects on the slabs, especially for multi-story structures. The changing properties of the young concrete complicate the prediction of serviceability design requirements also. An experimental investigation is performed on four simply supported Light-Weight Concrete (LWC) one-way slabs subjected to immediate loading at 14 d. Effects of aggregate type, loading levels and cracking moment together with the influences of ultimate moment capacity and service moment on the instantaneous deflection of slabs are studied. Comparison of the obtained results with predictions of existing models in the literature shows considerable differences between the recorded and estimated instantaneous deflection of LWC slabs. Based on sensitivity analysis of the effective parameters, a new equation is proposed and verified to predict the instantaneous deflection of LWC slabs subjected to loading at the age of 14 d.

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Numerical study on the seismic response of the underground subway station- surrounding soil mass-ground adjacent building system
Guobo WANG, Mingzhi YUAN, Xianfeng MA, Jun WU
Front. Struct. Civ. Eng.. 2017, 11 (4): 424-435.   DOI: 10.1007/s11709-016-0381-7
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Ground buildings constructed above metro station have increased very quickly due to the limited land resources in urban areas. In this paper, the seismic response of the Underground subway station-Surrounding soil mass-Ground adjacent buildings (USG) system subjected to various seismic loading is studied through numerical analysis. The numerical model is established in terms of the calculation domain, boundary condition, and contact property between soil and structure based on the real project. The reciprocal influence between subway station and ground adjacent building, and their effects on the dynamic characteristics of surrounding soil mass are also investigated. Through the numerical study, it is found that the impact of underground structure on the dynamic characteristics of the surrounding soil mass depends on its own dimension, and the presence of underground structure has certain impact on the seismic response of ground adjacent building. Due to the presence of underground structure and ground adjacent building, the vertical acceleration generated by the USG system cannot be ignored. The outcomes of this study can provide the references for seismic design of structures in the USG system.

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The effect of SiO2 nanoparticles derived from hydrothermal solutions on the performance of portland cement based materials
Front. Struct. Civ. Eng.. 2017, 11 (4): 436-445.   DOI: 10.1007/s11709-017-0438-2
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The nanoparticles of SiO2 were used in cement systems to modify the rheological behavior, to enhance the reactivity of supplementary cementitious materials, and also to improve the strength and durability. In this research, low-cost nano-SiO2 particles from natural hydrothermal solutions obtained by membrane ultrafiltration and, optionally, by cryochemical vacuum sublimation drying, were evaluated in portland cement based systems. ??The SiO2-rich solutions were obtained from the wells of Mutnovsky geothermal power station (Far East of Russia). The constant nano-SiO2 dosage of 0.25% (as a solid material by weight of cementitious materials) was used to compare the cement systems with different nanoparticles against a reference mortar and a commercially available nano-SiO2. Nanoparticles were characterized by X-Ray Diffraction (XRD), BET Surface Area, Scanning Electron Microscope (SEM) and Fourier Transform Infrared (FTIR) spectroscopy techniques. It was demonstrated that the addition of polycarboxylate ether superplasticizer and the dispersion treatment using an ultrasound processor can be used to facilitate the distribution of nano-SiO2 particles in the mixing water. The effect of nano-SiO2 particles in portland cement mortars was investigated by evaluating the flow, heat of hydration and compressive strength development. It was demonstrated that the use of nano-SiO2 particles can reduce the segregation and improve strength properties.

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Soil arching effect of Lattice-Shaped Diaphragm Wall as bridge foundation
Jiujiang WU, Lingjuan WANG, Qiangong CHENG
Front. Struct. Civ. Eng.. 2017, 11 (4): 446-454.   DOI: 10.1007/s11709-017-0397-7
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As a new type of bridge foundation, Lattice-Shaped Diaphragm Wall (hereinafter for LSDW) is highly concerned in relevant construction area but its research is far from achievement. Based on PFC2D, the soil arching effect of LSDWs is studied thoroughly in this paper and the special attention is given to its influencing factors. It turns out to be that a differential wall-soil settlement can be found at the lower location of soil core of an LSDW which is one of the trigger factors of soil arching; meanwhile, the differential settlement degree can reflect the exertion degree of soil arching; the shape of soil arching is basically a hemisphere which can be explained by the theory proposed by Hewlett and Randolph; normally, the chamber number is a negative factor for the development of soil arching; the soil arching effect is significantly influenced by the distance of two adjacent wall elements and the foundation depth, and a relatively large or small value of these factors is disadvantageous to the exertion of soil arching; in addition, the soil arching effect increase with the growth of stiffness and friction coefficient of particles and the friction coefficient of particles has insignificant influence on the development of soil arching effect compared with particle stiffness.

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Seismic analysis of semi-gravity RC cantilever retaining wall with TDA backfill
Il-Sang AHN, Lijuan CHENG
Front. Struct. Civ. Eng.. 2017, 11 (4): 455-469.   DOI: 10.1007/s11709-017-0392-z
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The seismic behavior of Tire Derived Aggregate (TDA) used as backfill material of 6.10 m high retaining walls was investigated based on nonlinear time-history Finite Element Analysis (FEA). The retaining walls were semi-gravity reinforced concrete cantilever type. In the backfill, a 2.74 m thick conventional soil layer was placed over a 3.06 m thick TDA layer. For comparison purpose, a conventional all soil-backfill model was also developed, and the analysis results from the two models under the Northridge and Takatori earthquakes were compared. The FEA results showed that both models did not experience major damage in the backfill under the Northridge earthquake. However, under the Takatori earthquake, the TDA-backfill model developed substantially large displacement in the retaining walls and in the backfill compared with the soil-backfill model. Regions of large plastic strain were mainly formed in the TDA layer, and the soil over the TDA layer did not experience such large plastic strain, suggesting less damage than the soil-backfill model. In addition, the acceleration on the backfill surface of the TDA-backfill model decreased substantially compared with the soil-backfill model. If an acceleration sensitive structure is placed on the surface of the backfill, the TDA backfill may induce less damage to it.

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An efficient stochastic dynamic analysis of soil media using radial basis function artificial neural network
Front. Struct. Civ. Eng.. 2017, 11 (4): 470-479.   DOI: 10.1007/s11709-017-0440-8
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Since a lot of engineering problems are along with uncertain parameters, stochastic methods are of great importance for incorporating random nature of a system property or random nature of a system input. In this study, the stochastic dynamic analysis of soil mass is performed by finite element method in the frequency domain. Two methods are used for stochastic analysis of soil media which are spectral decomposition and Monte Carlo methods. Shear modulus of soil is considered as a random field and the seismic excitation is also imposed as a random process. In this research, artificial neural network is proposed and added to Monte Carlo method for sake of reducing computational effort of the random analysis. Then, the effects of the proposed artificial neural network are illustrated on decreasing computational time of Monte Carlo simulations in comparison with standard Monte Carlo and spectral decomposition methods. Numerical verifications are provided to indicate capabilities, accuracy and efficiency of the proposed strategy compared to the other techniques.

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Kinetic energy based model assessment and sensitivity analysis of vortex induced vibration of segmental bridge decks
Nazim Abdul NARIMAN
Front. Struct. Civ. Eng.. 2017, 11 (4): 480-501.   DOI: 10.1007/s11709-017-0435-5
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In this paper, semi 3D models for segmental Bridge decks are created in ABAQUS CFD program with the support of MATLAB codes to simulate and analyze vortex shedding generated due to wind excitation through considering the stationary position of the deck. Three parameters (wind speed, deck streamlined length and dynamic viscosity of the air) are dedicated to study their effects on the kinetic energy of the system in addition to the shapes and patterns of the vortices. Two benchmarks from the literature Von Karman and Dyrbye and Hansen are considered to validate the vortex shedding aspects for the CFD models. Good agreement between the results of the benchmarks and the semi 3D models has been detected. Latin hypercube experimental method is dedicated to generate the surrogate models for the kinetic energy of the system and the lift forces. Variance based sensitivity analysis is utilized to calculate the main sensitivity indices and the interaction orders for all the three parameters. The kinetic energy approach performed very well in revealing the rational effects and the roles of each parameter in the generation of vortex shedding and predicting vortex induced vibration of the deck.

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12 articles