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Frontiers of Structural and Civil Engineering

ISSN 2095-2430 (Print)
ISSN 2095-2449 (Online)
CN 10-1023/X
Postal Subscription Code 80-968
2019 Impact Factor: 1.68

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, Volume 12 Issue 1 Previous Issue   
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In Memoriam of Professor Zuyan Shen
The Editorial Office
Front. Struct. Civ. Eng.. 2018, 12 (1): 1-2.
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Estimation of relations among hysteretic response measures and design parameters for RC rectangular shear walls
Front. Struct. Civ. Eng.. 2018, 12 (1): 3-15.
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Seismic design of RC structures requires estimation of structural member behavioral measures as functions of design parameters. In this study, the relations among cyclic behavioral measures and design parameters have been investigated for rectangular RC shear walls using numerical simulations calibrated based on the published laboratory tests. The OpenSEES numerical simulations modeling of plastic hinge hysteretic behavior of RC shear walls and estimation of empirical relations among wall hysteretic indices and design parameters are presented. The principal design parameters considered were wall dimensions, axial force, reinforcement ratios, and end-element design parameters. The estimated hysteretic response measures are wall effective stiffness, yield and ultimate curvatures, plastic moment capacity, yield and ultimate displacements, flexural shear capacity, and dissipated energy. Using results of numerous analyses, the empirical relations among wall cyclic behavioral measures and design parameters are developed and their accuracy is investigated.

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Effects of seeding nucleation agent on geopolymerization process of fly-ash geopolymer
Front. Struct. Civ. Eng.. 2018, 12 (1): 16-25.
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Geopolymer, an inorganic aluminosilicate material activated by alkaline medium solution, can perform as an inorganic adhesive. The geopolymer technology has a viability to substitute traditional concrete made of portland cement (PC) because replacing PC with fly ash leads to reduced carbon dioxide emissions from cement productions and reduced materials cost. Although fly ash geopolymer stimulates sustainability, it is slow geopolymerization reaction poses a challenge for construction technology in term of practicality. The development of increasing geopolymerization reaction rate of the geopolymer is needed. ?The purpose of this study is to evaluate seeding nucleation agents (NA) of fly ash geopolymer that can accelerate polymerization reactions such that the geopolymer can be widely used in the construction industry. Results from the present study indicate that the use of NA (i.e., Ca(OH)2) can be potentially used to increase geopolymerization reaction rate and improve performance characteristics of the fly ash geopolymer product.

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Shanghai center project excavation induced ground surface movements and deformations
Guolin XU, Jiwen ZHANG, Huang LIU, Changqin REN
Front. Struct. Civ. Eng.. 2018, 12 (1): 26-43.
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Empirical data on deep urban excavations can provide designers a significant reference basis for assessing potential deformations of the deep excavations and their impact on adjacent structures. The construction of the Shanghai Center involved excavations in excess of 33-m-deep using the top-down method at a site underlain by thick deposits of marine soft clay. A retaining system was achieved by 50-m-deep diaphragm walls with six levels of struts. During construction, a comprehensive instrumentation program lasting 14 months was conducted to monitor the behaviors of this deep circular excavation. The following main items related to ground surface movements and deformations were collected: (1) walls and circumferential soils lateral movements; (2) peripheral soil deflection in layers and ground settlements; and (3) pit basal heave. The results from the field instrumentation showed that deflections of the site were strictly controlled and had no large movements that might lead to damage to the stability of the foundation pit. The field performance of another 21cylindrical excavations in top-down method were collected to compare with this case through statistical analysis. In addition, numerical analyses were conducted to compare with the observed data. The extensively monitored data are characterized and analyzed in this paper.

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A hybrid LQR-PID control design for seismic control of buildings equipped with ATMD
Amir Hossein HEIDARI, Sadegh ETEDALI, Mohamad Reza JAVAHERI-TAFTI
Front. Struct. Civ. Eng.. 2018, 12 (1): 44-57.
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This paper presents an efficient hybrid control approach through combining the idea of proportional-integral-derivative (PID) controller and linear quadratic regulator (LQR) control algorithm. The proposed LQR-PID controller, while having the advantage of the classical PID controller, is easy to implement in seismic-excited structures. Using an optimization procedure based on a cuckoo search (CS) algorithm, the LQR-PID controller is designed for a seismic- excited structure equipped with an active tuned mass damper (ATMD). Considering four earthquakes, the performance of the proposed LQR-PID controller is evaluated. Then, the results are compared with those given by a LQR controller. The simulation results indicate that the LQR-PID performs better than the LQR controller in reduction of seismic responses of the structure in the terms of displacement and acceleration of stories of the structure.

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Properties of cement grout modified with ultra-fine slag
Front. Struct. Civ. Eng.. 2018, 12 (1): 58-66.
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The purpose of the study is to obtain a cement grout with improved performance. The grout mixes of the present study contain cement, ultra-fine slag (UFS), super plasticizer and water. Properties like flowability, bleeding, compressive strength and shrinkage of cement grouts have been studied. Rheological parameters were also studied in order to explain the grout workability. The results show that, cement replacement with slag in grouts could reduce bleeding substantially without affecting the workability of the mixes. Introduction of slag enhanced the compressive strength and reduced shrinkage reasonably. Ultra-fine slag can be used as a supplementary cementitious material in cementitious grouts in order to improve the grout behavior.

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Assessment of an alternative to deep foundations in compressible clays: the structural cell foundation
Front. Struct. Civ. Eng.. 2018, 12 (1): 67-80.
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The new type of deep foundation for buildings on saturated, compressible-low strength clayey soil deposits, branded structural cell essentially consists of a rigid concrete top slab, structurally connected to reinforced concrete peripheral walls (diaphragms) that enclose the natural soil. Accordingly, as the initial volume of the confined soft clays within the lateral stiff diaphragms will remain constant upon loading, the hollowed structural cell will be “transformed” into a very large cross-section pillar of unit weight slightly higher than that of the natural soft clayey soil. This type of foundation seems to be a highly competitive alternative to the friction pile-box foundations (widely used in Mexico City clays), due to its economic and environmental advantages. Economies result, for example, from the absence of huge excavations hence sparing the need of earth retaining structures. Further savings result from appreciably smaller concrete volumes required for building the structural cell than the friction pile-box foundation; moreover, the construction time of the former is much shorter than that of the latter. Regarding the impact to the environment, less air contamination follows from the fact that both traffic jams and soil excavation lessen appreciably. Considering these facts and others regarding scheduling, it was decided to replace 48-friction pile-box foundations specified in the master plan project by this new type of foundation. The overall behavior of these cell foundations over a five-year period is fared from close visual observations and their leveling during the first three years after their construction.

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In-plane transversal normal stresses in the concrete face of CFRD induced by the first-dam reservoir filling
Front. Struct. Civ. Eng.. 2018, 12 (1): 81-91.
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To evaluate the effects of dam height, valley narrowness and width of concrete slabs on the first-dam reservoir filling in-plane transversal normal stresses in the concrete face of CFRD´s, 3D finite difference analyses were carried out. Behavior of rockfill dams considered in this study was defined from the monitoring of a number of 3D sets of pressure cells and extensometers installed in three large dams in Mexico. The 3D analyses results show that high in-plane transversal compressive stresses develop within the concrete panels located in the central concrete face zone upon dam reservoir filling loading. Likewise, in-plane induced tensile transversal stresses in the zones near the abutments increase the potential of slabs cracking and damaging the waterstops in-between the vertical and perimetral joints. From the results of the 3D finite difference analyses, a simple method to estimate in-plane normal stresses in the concrete face is advanced and through comparisons with the results of a 3D case numerical study, its accuracy assessed.

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A combination of damage locating vector method (DLV) and differential evolution algorithm (DE) for structural damage assessment
Front. Struct. Civ. Eng.. 2018, 12 (1): 92-108.
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In this study, a two-stage method is presented for identifying multiple damage scenarios. In the first stage, the damage locating vector (DLV) method using normalized cumulative energy (nce) is employed for damage localization in structures. In the second stage, the differential evolution algorithm (DE) is used for damage severity of the structures. In addition, in the second stage, a modification of an available objective function is made for handing the issue of symmetric structures. To verify the effectiveness of the present technique, numerical examples of a 72-bar space truss and a one-span steel portal frame are considered. In addition, the effect of noise on the performance of the identification results is also investigated. The numerical results show that the proposed combination gives good assessment of damage location and extent for multiple structural damage cases.

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Modeling considerations in seismic assessment of RC bridges using state-of-practice structural analysis software tools
Ricardo MONTEIRO, Miguel ARAÚJO, Raimundo DELGADO, Mário MARQUES
Front. Struct. Civ. Eng.. 2018, 12 (1): 109-124.
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The increasing awareness of the general society toward the seismic safety of structures has led to more restrictive performance requirements hence, many times, to the need of using new and more accurate methods of analysis of structures. Among these, nonlinear static procedures are becoming, evermore, the preferred choice of the majority of design codes, as an alternative to complete nonlinear time-history analysis for seismic design and assessment of structures. The many available software tools should therefore be evaluated and well understood, in order to be easily and soundly employed by the practitioners. The study presented herein intends to contribute to this need by providing further insight with respect to the use of commonly employed structural analysis software tools in nonlinear analysis of bridge structures. A comparison between different nonlinear modeling assumptions is presented, together with the comparison with real experimental results. Furthermore, alternative adaptive pushover procedures are proposed and applied to a case study bridge, based on a generic plastic hinge model. The adopted structural analysis program proved to be accurate, yielding reliable estimates, both in terms of local plastic hinge behavior and global structural behavior.

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Fracture model for the prediction of the electrical percolation threshold in CNTs/Polymer composites
Yang SHEN, Pengfei HE, Xiaoying ZHUANG
Front. Struct. Civ. Eng.. 2018, 12 (1): 125-136.
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In this paper, we propose a 3D stochastic model to predict the percolation threshold and the effective electric conductivity of CNTs/Polymer composites. We consider the tunneling effect in our model so that the unrealistic interpenetration can be avoided in the identification of the conductive paths between the CNTs inside the polymer. The results are shown to be in good agreement with reported experimental data.

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Pore structure of cementitious material enhanced by graphitic nanomaterial: a critical review
Front. Struct. Civ. Eng.. 2018, 12 (1): 137-147.
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Carbon nano tubes (CNT) has been introduced as an efficient nanomaterial in order to improve the mechanical and durability properties of concrete. The effect of CNT on the microstructures of cementitious materials has been widely reported. This paper combines a critical review on the effect of CNT on the pore and microstructure of cement composite with a discussion on the porosity measurement of pastes containing CNT using mercury intrusion porosimetry techniques (MIP). It was found that, surface treatment by H2SO4 and HNO3 solution forms carboxyl acid groups on CNTs’ surfaces that lead to the improvement of reinforcement. In this scope, this review paper involves analyzing the effect of CNT on the microstructure and the pore structure of cementitious materials. The existing methods of measuring the porosity of cementitious material are reviewed, in particular, the contact angle measurement is discussed in detail in which the most effective parameters and possible errors of calculation is presented.

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Intermediate HSS bracing members during seismic excitations: modeling, design, and behavior
Front. Struct. Civ. Eng.. 2018, 12 (1): 148-162.
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Concentric hollow structural section (HSS) bracing members are used frequently in steel framed structural systems to resist seismic excitations. Finite element modeling of the HSS braces that utilizes the true stress-strain curves produces hysteresis responses that are reasonable matches to the experimental response. True stress-strain curves are obtained from coupon tests or stub-column tests while utilizing an exponential function or strain hardening rule with a trial and error procedure to obtain the hysteresis behavior. In the current study, the true stress-strain curves are directly obtained from tests on stub-columns extracted from the full scale HSS bracing members away from the mid-length plastic hinge after cyclic testing. Two experimental tests (Shaback 2001 and Haddad 2004) were used to validate the model. Results indicate that the stress-strain curves for these braces are not unique. A refined damage accumulation model for ultra-low-cycle fatigue is implemented to predict fracture of the brace tests. The refined damage model is then used in the finite element modeling to predict fracture of braces in a chevron braced frame of an eight-storey building subjected to selected ground motions analyzed using OpenSees program. Results indicate that all braces could sustain the selected earthquake records without fracture.

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Probabilistic safety assessment of self-centering steel braced frame
Front. Struct. Civ. Eng.. 2018, 12 (1): 163-182.
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The main drawback of conventional braced frames is implicitly accepting structural damage under the design earthquake load, which leads to considerable economic losses. Controlled rocking self-centering system as a modern low-damage system is capable of minimizing the drawbacks of conventional braced frames. This paper quantifies main limit states and investigates the seismic performance of self-centering braced frame using a Probabilistic Safety Assessment procedure. Margin of safety, confidence level, and mean annual frequency of the self-centering archetypes for their main limit states, including PT yield, fuse fracture, and global collapse, are established and are compared with their acceptance criteria. Considering incorporating aleatory and epistemic uncertainties, the efficiency of the system is examined. Results of the investigation indicate that the design of low- and mid-rise self-centering archetypes could provide the adequate margin of safety against exceeding the undesirable limit-states.

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14 articles