Frontiers of Structural and Civil Engineering

ISSN 2095-2430 (Print)
ISSN 2095-2449 (Online)
CN 10-1023/X
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Modern developments related to nanotechnology and nanoengineering of concrete
Konstantin SOBOLEV
Front. Struct. Civ. Eng..  2016, 10 (2): 131-141.
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This paper reports on modern developments related to nanotechnology of cement and concrete. Recent advances in instrumentation and design of advanced nano-composite materials is discussed. New technological directions and historical milestones in nanoengineering and nanomodi?cation of cement-based materials are presented. It is concluded that there is a strong potential of nanotechnology to improve the performance of cement-based materials.

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Cited: Crossref(27) WebOfScience(27)
A concept of capillary active, dynamic insulation integrated with heating, cooling and ventilation, air conditioning system
Front Arch Civil Eng Chin.  2010, 4 (4): 431-437.
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When a historic fa?ade needs to be preserved or when the seismic considerations favor use of a concrete wall system and fire considerations limit exterior thermal insulation, one needs to use interior thermal insulation systems. Interior thermal insulation systems are less effective than the exterior systems and will not reduce the effect of thermal bridges. Yet they may be successfully used and, in many instances, are recommended as a complement to the exterior insulation. This paper presents one of these cases. It is focused on the most successful applications of capillary active, dynamic interior thermal insulation. This happens when such insulation is integrated with heating, cooling and ventilation, air conditioning (HVAC) system. Starting with a pioneering work of the Technical University in Dresden in development of capillary active interior insulations, we propose a next generation, namely, a bio-fiber thermal insulation. When completing the review, this paper proposes a concept of a joint research project to be undertaken by partners from the US (where improvement of indoor climate in exposed coastal areas is needed), China (indoor climate in non-air conditioned concrete buildings is an issue), and Germany (where the bio-fiber technology has been developed).

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Experimental study on behavior of mortar-aggregate interface after elevated temperatures
Wan WANG, Jianzhuang XIAO, Shiying XU, Chunhui WANG
Front. Struct. Civ. Eng..  2017, 11 (2): 158-168.
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A push-out test program was designed and conducted to study the meso-scale behavior of mortar-aggregate interface for concrete after elevated temperatures ranging from 20°C to 600°C with the concept of modeled concrete (MC) and modeled recycled aggregate concrete (MRAC). The MCs and MRACs were designed with different strength grade of mortar and were exposed to different elevated temperatures. Following that the specimens were cooled to room temperature and push-out tests were conducted. Failure process and mechanical behaviors were analyzed based on failure modes, residual load-displacement curves, residual peak loads and peak displacements. It is found that failure modes significantly depended on specimen type, the elevated temperature and the strength grade of mortar. For MC, major cracks started to propagate along the initial cracks caused by elevated temperatures at about 80% of residual peak load. For MRAC, the cracks appeared at a lower level of load with the increasing elevated temperatures. The cracks connected with each other, formed a failure face and the specimens were split into several parts suddenly when reaching the residual peak load. Residual load-displacement curves of different specimens had similarities in shape. Besides, effect of temperatures and strength grade of mortar on residual peak load and peak displacement were analyzed. For MC and MRAC with higher strength of new hardened mortar, the residual peak load kept constant when the temperature is lower than 400°C and dropped by 43.5% on average at 600°C. For MRAC with lower strength of new hardened mortar, the residual peak load began to reduce when the temperatures exceeded 200°C and reduced by 27.4% and 60.8% respectively at 400°C and 600°C. The properties of recycled aggregate concrete (RAC) may be more sensitive to elevated temperatures than those of natural aggregate concrete (NAC) due to the fact that the interfacial properties of RAC are lower than those of NAC, and are deteriorated at lower temperatures.

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Cited: Crossref(3) WebOfScience(2)
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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Design of a shaking table test box for a subway station structure in soft soil
YANG Linde, ZHENG Yonglai, ZHANG Dongliang, JI Qianqian, YANG Chao
Front. Struct. Civ. Eng..  2007, 1 (2): 194-197.
Abstract   PDF (425KB)
A reasonable choice of structure of a model box is significant for a shaking table test to be successful in geotechnical engineering. A model box has been designed for the shaking table test of a subway station structure in the soft soil of Shanghai in the paper. The reasonable geometric similarity scale of the subway station structure has been determined by a 3-D dynamic analysis under the action of lateral equivalent static loading. The shape, size and structure of the model box are chosen by considering all the involved factors comprehensively. The shape of the box is similar to that of a typical station structure, and the ratio between the plane dimension of the model ground and that of the model structure is big enough to reduce the influence of boundary condition effectively. The structure is strong enough to avoid being demolished by shaking during a test. The contact conditions between the model soil and box are clear to help the data gained from the test well fit that from numerical analysis. The total weight of the model soil and box is less than the bearing capacity of the shaking table apparatus and there is no resonance between the model soil and box. The results show that the model box can be used to simulate the dynamic response of a subway station structure very well, so it provides a firm foundation for the success of the shaking table test of a subway station structure.
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Modeling of alkali-silica reaction in concrete: a review
Front Struc Civil Eng.  2012, 6 (1): 1-18.
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This paper presents a comprehensive review of modeling of alkali-silica reaction (ASR) in concrete. Such modeling is essential for investigating the chemical expansion mechanism and the subsequent influence on the mechanical aspects of the material. The concept of ASR and the mechanism of expansion are first outlined, and the state-of-the-art of modeling for ASR, the focus of the paper, is then presented in detail. The modeling includes theoretical approaches, meso- and macroscopic models for ASR analysis. The theoretical approaches dealt with the chemical reaction mechanism and were used for predicting pessimum size of aggregate. Mesoscopic models have attempted to explain the mechanism of mechanical deterioration of ASR-affected concrete at material scale. The macroscopic models, chemo-mechanical coupling models, have been generally developed by combining the chemical reaction kinetics with linear or nonlinear mechanical constitutive, and were applied to reproduce and predict the long-term behavior of structures suffering from ASR. Finally, a conclusion and discussion of the modeling are given.

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Research review of the cement sand and gravel (CSG) dam
Xin CAI, Yingli WU, Xingwen GUO, Yu MING
Front Struc Civil Eng.  2012, 6 (1): 19-24.
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The cement sand and gravel (CSG) dam is a new style of dam that owes the advantages both of the concrete faced rock-fill dam (CRFD) and roller compacted concrete (RCC) gravity dam, because of which it has attracted much attention of experts home and abroad. At present, some researches on physic-mechanical property of CSG material and work behavior of CSG dam have been done. This paper introduces the development and characteristics of CSG dam systematically, and summarizes the progress of the study on basic tests, constitutive relation of CSG material and numerical analysis of CSG dam, in addition, indicates research and application aspect of the dam.

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Numerical study of the cyclic load behavior of AISI 316L stainless steel shear links for seismic fuse device
Ruipeng LI,Yunfeng ZHANG,Le-Wei TONG
Front. Struct. Civ. Eng..  2014, 8 (4): 414-426.
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This paper presents the results of nonlinear finite element analyses conducted on stainless steel shear links. Stainless steels are attractive materials for seismic fuse device especially for corrosion-aware environment such as coastal regions because they are highly corrosion resistant, have good ductility and toughness properties in combination with low maintenance requirements. This paper discusses the promising use of AISI 316L stainless steel for shear links as seismic fuse devices. Hysteresis behaviors of four stainless steel shear link specimens under reversed cyclic loading were examined to assess their ultimate strength, plastic rotation and failure modes. The nonlinear finite element analysis results show that shear links made of AISI 316L stainless steel exhibit a high level of ductility. However, it is also found that because of large over-strength ratio associated with its strain hardening process, mixed shear and flexural failure modes were observed in stainless steel shear links compared with conventional steel shear links with the same length ratio. This raises the issue that proper design requirements such as length ratio, element compactness and stiffener spacing need to be determined to ensure the full development of the overall plastic rotation of the stainless steel shear links.

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Safety and serviceability assessment for high-rise tower crane to turbulent winds
Zhi SUN, Nin HOU, Haifan XIANG
Front Arch Civil Eng Chin.  2009, 3 (1): 18-24.
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Tower cranes are commonly used facilities for the construction of high-rise structures. To ensure their workability, it is very important to analyze their response and evaluate their condition under extreme conditions. This paper proposes a general scheme for safety and serviceability assessment of high-rise tower crane to turbulent winds based on time domain buffeting response analysis. Spatially correlated wind velocity field at the location of the tower crane was first simulated using an algorithm for generating the time domain samples of a stationary, multivariate stochastic process according to some prescribed spectral density matrix. The buffeting forces applied to the structure were computed according to the above-simulated wind velocity fluctuations and the lift, drag, and moment coefficients obtained from a CFD computation. Those spatially correlated loads were then fed into a well calibrated finite element model and the nonlinear time history analysis was conducted to compute structural buffeting response. Compared with structural on-site response measurement, the computed response using the proposed method has good precision. The proposed method is then adopted for analyzing the buffeting response of an in-use tower crane under the design wind speed and the maximum operational wind speed for safety and serviceability assessment.

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Behavior of compacted clay-concrete interface
R. R .SHAKIR, Jungao ZHU
Front Arch Civil Eng Chin.  2009, 3 (1): 85-92.
Abstract   HTML   PDF (209KB)

Tests of interface between compacted clay and concrete were conducted systematically using interface simple shear test apparatus. The samples, having same dry density with different water content ratio, were prepared. Two types of concrete with different surface roughness, i.e., relatively smooth and relatively rough surface roughness, were also prepared. The main objectives of this paper are to show the effect of water content, normal stress and rough surface on the shear stress-shear displacement relationship of clay-concrete interface. The following were concluded in this study: 1) the interface shear sliding dominates the interface shear displacement behavior for both cases of relatively rough and smooth concrete surface except when the clay water content is greater than 16% for the case of rough concrete surface where the shear failure occurs in the body of the clay sample; 2) the results of interface shear strength obtained by direct shear test were different from that of simple shear test for the case of rough concrete surface; 3) two types of interface failure mechanism may change each other with different water content ratio; 4) the interface shear strength increases with increasing water content ratio especially for the case of clay-rough concrete surface interface.

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A critical review of preparation design and workability measurement of concrete material for largescale 3D printing
Guowei MA, Li WANG
Front. Struct. Civ. Eng..  2018, 12 (3): 382-400.
Abstract   HTML   PDF (2267KB)

In recent few years, significant improvement has been made in developing largescale 3D printers to accommodate the need of industrial-scale 3D printing. It is of great feasibility to construct structural components and buildings by means of 3D concrete printing. The major issues of this innovative technique focus on the preparation and optimization of concrete materials which possess favourable printable properties as well as the measurement and evaluation methods of their workability. This paper firstly introduces three largescale 3D printing systems that have been successfully applied in construction industry. It then summarizes the commonly used raw materials in concrete manufacturing. Critical factors that should be particularly controlled in material preparation are specified. Easy-extrusive, easy-flowing, well-buildable, proper setting time and low shrinkage are significant for concrete mixture to meet the critical requirements of a freeform construction process. Thereafter, measuring methods that can be employed to assess the fresh and hardened properties of concrete at early stages are suggested. Finally, a few of evaluation methods are presented which may offer certain assistance for optimizing material preparation. The objective of this work is to review current design methodologies and experimental measurement and evaluation methods for 3D printable concrete materials and promote its responsible use with largescale 3D printing technology.

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Cited: Crossref(34) WebOfScience(28)
Dynamic analysis of rail transit elevated bridge with ladder track
He XIA, Yushu DENG, Yongwei ZOU, Guido DE ROECK, Geert DEGRANDE
Front Arch Civil Eng Chin.  2009, 3 (1): 2-8.
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In this paper, a dynamic analysis model of an elevated bridge with ladder tracks under moving train load is established. The whole process of a train running through an elevated bridge at different speeds is simulated. The dynamic responses of the elevated bridge with ladder track and the running safety and comfort index of train vehicles are evaluated. Compared with the dynamic responses of an elevated bridge with ordinary non-ballasted slab track, the ladder track’s effect on reducing the vibration of an elevated bridge is analyzed. The analysis results show that the ladder track has good vibration reduction characteristics as compared to ordinary non-ballasted track.

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Shear design of high strength concrete prestressed girders
Emad L. LABIB,Hemant B. DHONDE,Thomas T. C. HSU,Y. L. MO
Front. Struct. Civ. Eng..  2014, 8 (4): 373-387.
Abstract   HTML   PDF (1660KB)

Normal strength prestressed concrete I-girders are commonly used as the primary superstructure components in highway bridges. However, shear design guidelines for high strength PC girders are not available in the current structural codes. Recently, ten 7.62 m (25 feet) long girders made with high strength concrete were designed, cast, and tested at the University of Houston (UH) to study the ultimate shear strength and the shear concrete contribution (Vc) as a function of concrete strength (f\hskip -3ptc). A simple semi-empirical set of equations was developed based on the test results to predict the ultimate shear strength of prestressed concrete I-girders. The UH-developed set of equations is a function of concrete strength (f\hskip -3ptc), web area (bwd), shear span to effective depth ratio (a/d), and percentage of transverse steel (ρt). The proposed UH-Method was found to accurately predict the ultimate shear strength of PC girders with concrete strength up to 117 MPa (17000 psi) ensuring satisfactory ductility. The UH-Method was found to be not as overly conservative as the ACI-318 (2011) code provisions, and also not to overestimate the ultimate shear strength of high strength PC girders as the AASHTO LRFD (2010) code provisions. Moreover, the proposed UH-Method was found fairly accurate and not exceedingly conservative in predicting the concrete contribution to shear for concrete strength up to 117 MPa (17000 psi).

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Cyclic stress-strain behavior of structural steel with yield-strength up to 460 N/mm2
Yiyi CHEN,Wei SUN,Tak-Ming CHAN
Front. Struct. Civ. Eng..  2014, 8 (2): 178-186.
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This paper presents a constitutive model based on Ramberg-Osgood equation to describe the hysteresis material behavior of structural carbon steel with nominal yield strength between 235 to 420 N/mm2. The proposed model was calibrated against a series of cyclic material tests with strain amplitude varying from 0.5% to 2.0%. A simple relationship between the modular parameter K and the yield strength fy was proposed. The calibrated Ramberg-Osgood model revealed excellent agreement with the experimental results and captured further the experimental behavior of test specimens with nominal yield strength of 460 N/mm2. The proposed constitutive model was also adopted in conjunction with the combined kinematic/isotropic materials description in ABAQUS to mimic a full scale experimental test under cyclic loading. The numerical results revealed close agreement with the experimental observations.

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Simulation model based on Monte Carlo method for traffic assignment in local area road network
Yuchuan DU, Yuanjing GENG, Lijun SUN
Front Arch Civil Eng Chin.  2009, 3 (2): 195-203.
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For a local area road network, the available traffic data of traveling are the flow volumes in the key intersections, not the complete OD matrix. Considering the circumstance characteristic and the data availability of a local area road network, a new model for traffic assignment based on Monte Carlo simulation of intersection turning movement is provided in this paper. For good stability in temporal sequence, turning ratio is adopted as the important parameter of this model. The formulation for local area road network assignment problems is proposed on the assumption of random turning behavior. The traffic assignment model based on the Monte Carlo method has been used in traffic analysis for an actual urban road network. The results comparing surveying traffic flow data and determining flow data by the previous model verify the applicability and validity of the proposed methodology.

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Vibration analysis of multi-walled carbon nanotubes embedded in elastic medium
Pattabhi R. BUDARAPU,Sudhir Sastry YB,Brahmanandam JAVVAJI,D. Roy MAHAPATRA
Front. Struct. Civ. Eng..  2014, 8 (2): 151-159.
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We propose a method to estimate the natural frequencies of the multi-walled carbon nanotubes (MWCNTs) embedded in an elastic medium. Each of the nested tubes is treated as an individual bar interacting with the adjacent nanotubes through the inter-tube Van der Waals forces. The effect of the elastic medium is introduced through an elastic model. The mathematical model is finally reduced to an eigen value problem and the eigen value problem is solved to arrive at the inter-tube resonances of the MWCNTs. Variation of the natural frequencies with different parameters are studied. The estimated results from the present method are compared with the literature and results are observed to be in close agreement.

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3D finite element method (FEM) simulation of groundwater flow during backward erosion piping
Front. Struct. Civ. Eng..  2014, 8 (2): 160-166.
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Backward erosion piping is an important failure mechanism for cohesive water retaining structures which are founded on a sandy aquifer. At present, the prediction models for safety assessment are often based on 2D assumptions. In this work, a 3D numerical approach of the groundwater flow leading to the erosion mechanism of backward erosion piping is presented and discussed. Comparison of the 2D and 3D numerical results explicitly demonstrates the inherent 3D nature of the piping phenomenon. In addition, the influence of the seepage length is investigated and discussed for both piping initiation and piping progression. The results clearly indicate the superiority of the presented 3D numerical model compared to the established 2D approach. Moreover, the 3D numerical results enable a better understanding of the complex physical mechanism involved in backward erosion piping and thus can lead to a significant improvement in the safety assessment of water retaining structures.

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From understanding to designing soundscapes
Front Arch Civil Eng Chin.  2010, 4 (4): 403-417.
Abstract   HTML   PDF (337KB)

Soundscape represents a step change in the field of environmental acoustics in that it combines physical, social, and psychological approaches. Although the term soundscape was introduced in the 1960s, significant attention to it has mainly been paid in the last decade or so in the community of environmental acoustics by researchers and recently by practitioners including policy makers. This paper explores the current situation and future challenges in soundscape. Starting with a framework on research and practical needs in soundscape and a brief introduction of some recent/current networks, activities, projects, and publications, this paper then presents a systematic review of recent progress in soundscape research and practice. A short review of the soundscape research in China is also given.

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Strain localization analyses of idealized sands in biaxial tests by distinct element method
Mingjing JIANG, Hehua ZHU, Xiumei LI,
Front. Struct. Civ. Eng..  2010, 4 (2): 208-222.
Abstract   PDF (1317KB)
This paper presents a numerical investigation on the strain localization of an idealized sand in biaxial compression tests using the distinct element method (DEM). In addition to the dilatancy and material frictional angle, the principal stress field, and distributions of void ratio, particle velocity, and the averaged pure rotation rate (APR) in the DEM specimen are examined to illustrate the link between microscopic and macroscopic variables in the case of strain localization. The study shows that strain localization of the granular material in the tests proceeds with localizations of void ratio, strain and APR, and distortions of stress field and force chains. In addition, both thickness and inclination of the shear band change with the increasing of axial strain, with the former valued around 10–14 times of mean grain diameter and the later overall described by the Mohr-Coulomb theory.
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Experimental study on concrete box culverts in trenches
Baoguo CHEN, Junjie ZHENG, Jie HAN
Front Arch Civil Eng Chin.  2009, 3 (1): 73-80.
Abstract   HTML   PDF (353KB)

Concrete box culverts are widely used in expressways in mountain areas. Many problems frequently take place due to improperly estimated vertical earth pressures on culverts. The prevailing Chinese General Code for Design of Highway Bridges and Culverts (CGCDHBC) stipulates the computation of the design load on culverts primarily based on the linear earth pressure theory, which cannot accurately describe the variation of the vertical load on culverts in trenches. In this paper, a full-scale experiment and numerical simulation were conducted to evaluate the variation of vertical earth pressures on culvert and soil arching in backfill. The variations of foundation pressure and settlement were also analyzed. The result revealed that the soil arch forms when the backfill on the culvert reaches a certain height. The soil arching effect reduces the stress concentration on the crown of the culvert but it is unstable. The vertical earth pressure on top of the culvert is significantly different from that recommended by the CGCDHBC

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A model reference adaptive control based method for actuator delay estimation in real-time testing
Cheng CHEN, James M. RICLES
Front. Struct. Civ. Eng..  2010, 4 (3): 277-286.
Abstract   PDF (479KB)
Real-time testing provides a viable experimental technique to evaluate the performance of structural systems subjected to dynamic loading. Servo-hydraulic actuators are often utilized to apply calculated displacements from an integration algorithm to the experimental structures in a real-time manner. The compensation of actuator delay is therefore critical to achieve stable and reliable experimental results. The advances in compensation methods based on adaptive control theory enable researchers to accommodate variable actuator delay and achieve good actuator control for real-time tests. However, these adaptive methods all require time duration for actuator delay adaptation. Experiments show that a good actuator delay estimate can help optimize the performance of the adaptive compensation methods. The rate of adaptation also requires that a good actuator delay estimate be acquired especially for the tests where the peak structural response might occur at the beginning of the tests. This paper presents a model reference adaptive control based method to identify the parameter of a simplified discrete model for servo-hydraulic dynamics and the resulting compensation method. Simulations are conducted using both numerical analysis and experimental results to evaluate the effectiveness of the proposed estimation method.
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Urban design based on public safety-Discussion on safety-based urban design
Kaizhen CAI, Jianguo WANG
Front Arch Civil Eng Chin.  2009, 3 (2): 219-227.
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Because of public safety problems in construction of urban surroundings, this paper expounds the necessity of the study on public safety-based urban design in perspective of modern city. It brings forward the concept of safety-based urban design and attempts to explore the basic connotation and contents with framework for studies.

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Shear-flexural strength mechanical model for the design and assessment of reinforced concrete beams subjected to point or distributed loads
Front. Struct. Civ. Eng..  2014, 8 (4): 337-353.
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A mechanical model recently developed for the shear strength of slender reinforced concrete beams with and without shear reinforcement is presented and extended to elements with uniformly distributed loads, specially focusing on practical design and assessment in this paper. The shear strength is considered to be the sum of the shear transferred by the concrete compression chord, along the crack, due to residual tensile and frictional stresses, by the stirrups and, if they exist, by the longitudinal reinforcement. Based on the principles of structural mechanics simple expressions have been derived separately for each shear transfer action and for their interaction at ultimate limit state. The predictions of the model have been compared to those obtained by using the EC2, MC2010 and ACI 318-08 provisions and they fit very well the available experimental results from the recently published ACI-DAfStb databases of shear tests on slender reinforced concrete beams with and without stirrups. Finally, a detailed application example has been presented, obtaining each contributing component to the shear strength and the assumed shape and position of the critical crack.

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Study of bond strength between various grade of Ordinary Portland Cement (OPC) and Portland Pozzolane Cement (PPC) mixes and different diameter of TMT bars by using pullout test
Front Struc Civil Eng.  2013, 7 (1): 39-45.
Abstract   HTML   PDF (387KB)

Since last two decades, the Portland Pozzolane Cement (PPC) is extensively used in structural concrete. But, till to date, a few literature is available on bond strength of concrete using PPC mixes. There are many literatures available on bond strength of concrete mixes using Ordinary Portland Cement (OPC). Hence, a comparative study was conducted on bond strength between OPC and PPC mixes. In the present investigation, total 24 samples consisting of M20, M35 and M50 grades of concrete and 16 and 25 mm diameter of TMT bar were tested for 7 and 28 days. The pullout bond test was conducted on each specimen as per IS: 2770-1967/1997 [1] and the results were observed at 0.25 mm slip at loaded end called as critical bond stress and at maximum bond load called as maximum bond stress. It was observed that the critical bond strength of PPC mixes is 10% higher than OPC mixes. Whereas, marginal improvement was noticed in maximum bond strength of PPC mixes. Hence, based on these findings, it could be concluded that development length for PPC mixes could be reduced by 10% as compared with same grade of OPC mixes.

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Nonlinear experimental response of non-conventional composite steel and concrete connection
Front Arch Civil Eng Chin.  2009, 3 (1): 42-49.
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An experiment was carried out on a set of full-scale specimens of a non-conventional connection between a concrete column and a composite steel and concrete beam defined on the basis of a number of requirements. The proposed connection, conceived in the ambit of semi-rigid joints, is aimed at combining general ease of construction with a highly simplified assembly procedure with a satisfying transmission of hogging moment at supports in continuous beams. For this purpose, the traditional shear studs used at the interface between the steel beam and the upper concrete slab, are also employed at the ends of the steel profiles welded horizontally to the end plates. The test is aimed at investigating the hogging moment response of the connection under incremental loads until failure.

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Prediction of cyclic large plasticity for prestrained structural steel using only tensile coupon tests
Liang-Jiu JIA, Tsuyoshi KOYAMA, Hitoshi KUWAMURA
Front Struc Civil Eng.  2013, 7 (4): 466-476.
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Cold-formed steel members, which experience complicated prestrain histories, are frequently applied in structural engineering. This paper aims to predict cyclic plasticity of structural steels with tensile and compressive prestrain. Monotonic and cyclic tests on hourglass specimens with tensile and compressive prestrain are conducted, and compared with numerical simulations using the Chaboche model. Two approaches are taken in the simulation. The first requires only the monotonic tensile test data from the prestrained steels, and the second requires both the monotonic tensile test data from the virgin steel and the prestrain histories. The first approach slightly overestimates the compressive stress for specimens with tensile prestrain, while the second approach is able to accurately predict the cyclic plasticity in specimens with tensile and compressive prestrain.

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A hypothesis for crack free interior surfaces of Longyou caverns caved in argillaceous siltstone 2000 years ago
Zhong Qi YUE, Shaopeng FAN, Zhifa YANG, Lihui LI, Luqing ZHANG, Zhongjian ZHANG,
Front. Struct. Civ. Eng..  2010, 4 (2): 165-177.
Abstract   PDF (1272KB)
Five complete caverns were discovered in Longyou in 1992. They were manually caved in argillaceous siltstone at shallow depths more than 2000 years ago. When they were un-watered, their integrity was maintained completely, and their interior rock surfaces were free of old cracks. Since then, however, the rock’s interior faces have initiated and propagated more and more cracks. This paper attempts to address the question of why the rock interior faces were free of old cracks once they were unearthed. To address this question, this paper proposes a hypothesis that the argillaceous siltstone has the ability of self-healing its cracks over a short period of time under weak acid water environment. Data and evidence are presented herewith to prove the hypothesis. They include observations and measurements in the field and test results in the laboratory. Specifically, a three-point bending test is used to form a tensile crack in a rectangular rock specimen and a dead load test for the specimen immersed in initially weak acid water is used for self-healing its crack. The results have shown that the argillaceous siltstone is in a state of weak alkalinity and the rain water at the site is in a state of weak acidity. Therefore, when it is immersed in weak acid water for some time, the argillaceous siltstone would be able to make chemical reactions to generate new minerals such as calcite. The new minerals would be able to infill the cracks and then heal the crack within a few years. Once the crack is self-healed, the rock can regain its strength and integrity. Consequently, the rock interior surfaces could be free of old cracks when the water was pumped out of the caverns.
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A FEniCS implementation of the phase field method for quasi-static brittle fracture
Front. Struct. Civ. Eng..  2019, 13 (2): 380-396.
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In the recent years, the phase field method for simulating fracture problems has received considerable attention. This is due to the salient features of the method: 1) it can be incorporated into any conventional finite element software; 2) has a scalar damage variable is used to represent the discontinuous surface implicitly and 3) the crack initiation and subsequent propagation and branching are treated with less complexity. Within this framework, the linear momentum equations are coupled with the diffusion type equation, which describes the evolution of the damage variable. The coupled nonlinear system of partial differential equations are solved in a ‘staggered’ approach. The present work discusses the implementation of the phase field method for brittle fracture within the open-source finite element software, FEniCS. The FEniCS provides a framework for the automated solutions of the partial differential equations. The details of the implementation which forms the core of the analysis are presented. The implementation is validated by solving a few benchmark problems and comparing the results with the open literature.

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Simulation of blast induced crater in jointed rock mass by discontinuous deformation analysis method
Youjun NING, Xinmei AN, Jun YANG, Guowei MA,
Front. Struct. Civ. Eng..  2010, 4 (2): 223-232.
Abstract   PDF (1084KB)
Rock blasting is a dynamic process accompanied with the propagations of shock waves and the dispersion of the explosion gas. This paper adopts the discontinuous deformation analysis (DDA) method to simulate the rock blasting process. A dynamic parameter adjustment and the non-reflecting boundary condition are implemented in the DDA method. The sub-block DDA method to simulate fracture problems is used. The blasting process in jointed rock mass is simulated by application of the explosion gas pressure on the expanding borehole walls and induced connected fracture surfaces around the boreholes. The blast craters with different overburdens are derived. The whole process including the explosion gas dispersion, borehole expansion, rock mass failure and cast, and the formation of the final blasting piles in rock blasting are well reproduced numerically. Parametric study for different overburdens is carried out, and the results are analyzed and discussed.
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Theoretical and experimental study on seismic response control on top of Three-Gorges ship lift towers using magnetorheological intelligent isolation system and its key technique
Weilian QU, Jianwei TU
Front Arch Civil Eng Chin.  2009, 3 (1): 32-41.
Abstract   HTML   PDF (309KB)

A vertical ship lift under earthquake excitation may suffer from a whipping effect due to the sudden change of building lateral stiffness at the top of the ship lift towers. This paper proposes a roof magnetorheological (MR) intelligent isolation system to prevent the seismic whipping effect on machinery structures. Theoretically, the dynamic models of MR damper and the mechanical model of ship lift was established, the inverse neural network controlling algorithm was proposed and the fundamental semi-active control equation for the Three-Gorges ship lift where the MR intelligent isolation system was installed was deduced. Experimentally, the experimental model of the ship lift was given, the vibrating table experiment of the MR intelligent isolation system controlling the whipping effect was carried out and the results of the inverse neural network control strategy and passive isolation strategy were compared. In practical aspect, the large-scale MR damper (500 kN) and a sliding support with limited stiffness were designed and fabricated. It was proven that the MR intelligent isolation system with proper control strategy can greatly reduce the seismic whipping effect on the top workshop of the ship lift and be simple and effective enough to be applied to real engineering structures.

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