فهرست مطالب

Civil Engineering - Volume:16 Issue: 5, 2018
  • Volume:16 Issue: 5, 2018
  • تاریخ انتشار: 1397/02/30
  • تعداد عناوین: 10
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  • The Church of the Nativity in Bethlehem: Analysis of a Local Structural Consolidation
    Claudio Alessandri *, Jessica Turrioni Pages 457-474
    An innovative technique for reinforcing a wall of the Church of the Nativity in Bethlehem against earthquakes is proposed. The use of such a technique was required due to the peculiarity of the site, recently added to the UNESCO list of World Heritage sites, which is important to both Christian and Islamic religions. Local seismicity data and the parameters of an equivalent Italian site provided the input data for a design earthquake, and 3D modal analysis of the entire Church revealed that the structure is characterized by clear local modes of vibration. As per the most recent studies on masonry structures, local assessment based on limit analysis procedures was performed. This showed that in the event of an earthquake, a Crusade-era wall addition is at risk of collapse via simple overturning around its own base, due to the lack of firm connections with the orthogonal walls of the façade and the transept. Hence, a novel double system of horizontal steel tension structures was designed to consolidate the wall, conforming to the main restoration Charter requirements, i.e. lightness, non-invasiveness and reversibility, and being hidden from the sight of visitors. In the absence of reliable local regulations, all analyses, computations and checks on the proposed intervention were carried out with reference to the Italian technical regulations.
    Keywords: Tension structures, Masonry, Church of the Nativity, Local collapse mechanisms
  • Numerical Simulation of the Flow and Local Scour Process around Single and Complex Bridge Piers
    Mahdi Alemi *, Rodrigo Maia Pages 475-487
    The present work is focused on the flow and clear-water scour process around single and complex bridge piers using the computational fluid dynamics (CFD) approaches. In CFD, the use of large time steps may accelerate the simulation process but the effects of the unsteady flow structures may not be considered in the computations. In this case, the computational method is defined as a steady-state solution. In the present study, the capability and accuracy of the steady-state solution of the flow equations are investigated by employing the SSIIM code which is numerically stable for large time steps. For this purpose, several simulations were performed for different piers and bed configurations and the corresponding numerical results were compared with experimental ones obtained from referenced bibliography. Overall, the steady-state solution of the flow equations could predict fairly well the scour geometry at the upstream side and lateral sides of the bridge pier but not downstream side of the pier. Moreover, the local scour around a single pier was also predicted by performing an unsteady-state solution (where the vortex shedding effects are taken into account) by using the Flow-3D code. The major difference between the results from the two mentioned CFD codes was observed downstream of the pier such that, compared to the physical model, the scour depth was under-predicted by the steady-state calculations while it was over-predicted by the unsteady-state calculations.
    Keywords: Numerical simulation, Local scour, Bed shear stress, Complex bridge pier, SSIIM Flow, 3D
  • Study on Mechanical Behavior of Negative Bending Region Based Design of Composite Bridge Deck
    Lu Peng-Zhen *, Cheng Lin-Feng, Li Yang, Li Zheng-Lun, Shao Hua Pages 489-497
    Steel–concrete composite decks are paved by grid beams on the superstructure of Dongping Bridge. Bridge deck grid beams consist of three main longitudinal girders, secondary longitudinal girders, main beams, secondary beams, and composite decks (which consist of profiled steel sheet, shear connectors with perfobond strips, steel rebar and concrete with steel fiber). Shear connectors with perfobond strips are designed in Dongping Bridge to improve the longitudinal shear capability between profiled steel sheet and concrete. For the performance of deck system in structural negative bending region, three typical forms of load, namely, service load, fatigue load and failure load, are applied. The results show sufficient stiffness and high load-carry capacity of the deck system. The stress of shear connectors with perfobond strips under 10000 cycles and 2.99 million cycles of fatigue load appeared to be invariable, which indicates that PBL is of good anti-fatigue performance as shear connectors with perfobond strips reaches the corresponding yield strength before destroyed, with the yield load of 359.10 kN.
    Keywords: Steel–concrete composite Bridge deck, Perfobond rib shear connector, Fatigue, ultimate bearing capacity, Test, Optimization design
  • Influence of the Drag Coefficient on Communication Towers
    Edgar Tapia-Hern, Aacute, Ndez *, JosE A. Cervantes-Castillo Pages 499-511
    This paper discusses some of the recent wind loading procedures for the design of lattice towers. In particular, the paper focuses the attention on the drag coefficient of communication towers with square and triangular cross-section and with flat-sided and circular elements. It provides some background behind the normative methodology of the current specialized codes and its relationship with results of experimental tests. For this purposes, different load patterns were adopted from the application of the normative methodology of the following countries: Mexico, United States, India, Japan and Australian–New Zealand Code. Additionally, the paper provides examples based on actual communication towers to illustrate the lack of consensus and to identify uncertainties in the procedures. The paper concludes that the complexity of most current wind design procedures is not justified and it pretends to help to make rational decision by designers.
    Keywords: Communication tower, Wind load, Drag coefficient, Lattice tower, Solidity ratio
  • Evaluation of Ductility of RC Structures Constructed with Bubble Deck System
    Seyed Shaker Hashemi *, Kabir Sadeghi, Mohammad Vaghefi, Seyed Alireza Siadat Pages 513-526
    Since in bubble deck (BD) system, the concrete in the middle of deck’s cross sections, mainly in the middle of the spans, is removed, the slabs become lighter compared to the traditional slabs. The application of this type of structural system has been recently increased. In the researches, the ductility factor is expressed generally for the reinforced concrete (RC) structures, with moment-resisting system (MRS), and dual systems. These include particularly, the MRSs, shear walls, and the flat slabs having mainly the BD system. In this research, the variations of the ductility of RC structures constructed with BD are assessed by applying the numerical modeling and nonlinear static analysis. Based on the evaluation of the obtained results, it can be concluded that the ductility of structures with dual systems, including MRS and shear wall (MRSSW), is more than the ductility of the structures with single MRSs. In the structures with MRSSW by increasing the ratio of the span length to story height (L/H) and also the number of stories, ductility factor will decrease and the rates of these decreases are considerable, while in MRS the number of stories and also the L/H ratio have less effect on the ductility factor. Among the structures with dual systems, including MRSSW, the low-rise structures with high ratios of span length to story height have the least value of ductility. As a conservative approach, a ductility factor of 3 for MRS structures is proposed. In addition, in MRSSW structures, for 4, 8 and 12 story structures, as a representative of low-rise, mid-rise and high-rise structures, the ductility factors of 6, 4 and 3 are suggested.
    Keywords: Bubble deck Ductility Nonlinear static analysis Reinforced concrete
  • Durability of CFRP-Wrapped Concrete Exposed to Hydrothermal Environment
    Zhihong Xie, Jianhe Xie *, Yongchang Guo, Yaohong Huang Pages 527-541
    In recent years, it has become increasingly common to strengthen concrete by wrapping carbon fibre reinforced polymer (CFRP) laminates to improve its compressive strength and ductility. However, studies on the durability of CFRP-confined concrete are relatively scarce, which could significantly hinder the application of CFRP in structural reinforcement. An experimental study was conducted to investigate the effect of exposure to natural hydrothermal environment on the confinement system of CFRP-wrapped concrete in this study. Three kinds of specimens were prepared and tested after natural exposure to the subtropical environment in South China, including 35 CFRP flat coupons, 35 epoxy adhesive flat coupons and 60 CFRP-wrapped concrete cylinders. The test parameters included the exposure duration (0, 6, 12, 18 and 30 months) for all specimens and the number of CFRP layers (0, 1, 2 and 3) for the CFRP-wrapped concrete specimens. Based on the experimental results, a compressive strength model for the CFRP-confined concrete exposed to hydrothermal environment was proposed. The results show that hydrothermal environment had a significant effect on the mechanical properties of the epoxy adhesive, but a relatively slight effect on that of the CFRP. Due to the deterioration of the CFRP, the compressive strength of CFRP-wrapped concrete gradually decreased with the increase of exposure duration. After a 30-month exposure, the compressive strength of CFRP-wrapped concrete has a decrease of approximately 10%.
    Keywords: Durability, Carbon fibre reinforced polymer (CFRP), Hydrothermal environment, Natural exposure, Confined concrete
  • A Numerical Implementation of the Three-Dimensional Viscoelastic Model for Asphalt Mastic
    Wenke Huang, Xiaoning Zhang *, Yingmei Yin, Shaofan Cai Pages 543-551
    This paper presents a numerical implementation of the three-dimensional viscoelastic model to describe the behavior of asphalt mastic. Details of the numerical viscoelastic constitutive formulation implemented in a finite element code are presented and illustrated. Then, uniaxial tensile tests and torsion tests were conducted to determine the viscoelastic constitutive parameters at a temperature of 20 °C. Both the capability of the model and the accuracy of the parameter determination of the displacement-based constitutive numerical model were examined by comparing the numerical predictions with the observed laboratory tests under two basic loading paths. The presented results show that the numerical predictions exhibit a rather good agreement with the experimental results for three primary modes of bending and compression loading. Therefore, the presented numerical implementation of constitutive model may be appropriate for describing the mechanical behavior of asphalt mastic when the viscoelastic constitutive parameters became available.
    Keywords: Viscoelastic, Constitutive, Numerical implementation, Numerical simulation, Asphalt mastic
  • Serviceability Performance Analysis of Concrete Box Girder Bridges Under Traffic-Induced Vibrations by Structural Health Monitoring: A Case Study
    Alessandra Fiore *, Giuseppe Carlo Marano Pages 553-565
    The perceptible vibration of concrete box girders under traffic loads is an important topic in existing bridges, on which vehicle movement often cause vibrations too strong from the viewpoints of travelers. In this paper, the results of an extensive program of full-scale ambient vibration tests involving a 380 m concrete box girder bridge, the Cannavino bridge in Italy, are presented. The human safety assessment procedure of the bridge includes ambient vibration testing, identification of modal parameters from ambient vibration data, comparison with a detailed finite element modeling as validation of experimental measurements, comparison of peak accelerations to reference values from technical standards/literature in order to estimate the vibration level, and evaluation of safety by the use of histograms. A total of nine modal frequencies are identified for the deck structure within the frequency range of 0–10 Hz. The results of the ambient vibration survey are compared to the modal frequencies computed by a detailed three-dimensional finite element model of the bridge, obtaining a very good agreement. It emerges that a linear finite element model appears to be capable of capturing the dynamic behavior of concrete box girder bridges with very good accuracy. For each direction, experimental peak accelerations are compared to acceptable human levels available in technical standards/literature, showing that traffic loads mainly induce a vertical component of vibration on the bridge deck. Finally, the elaboration of histograms allows to assess that the bridge is exposed to clearly perceptible vertical vibrations, requiring the adoption of suitable vibration reduction devices.
    Keywords: Concrete box girder bridge Traffic load Ambient vibration testing Dynamic identification Structural vibration Acceptable human levels
  • Tall Hybrid Coupled Structural Walls: Seismic Behavior and Design Suggestions
    Chung-Chan Hung *, Wei-Ting Lu Pages 567-582
    The seismic behavior of tall hybrid coupled wall systems is studied. For this purpose, nonlinear time history analyses are carried out to investigate the seismic response of eight example systems that are designed in accordance with the current design regulations. The results show that the shear and overturning moment magnification values are 1.6 and 1.4 for 10-story systems, and 1.8 and 1.2 for 30-story systems, due to the dynamic effect. In light of the analysis results, design suggestions are made for the system base shear, lateral force distribution, and coupling beams. In particular, based on the obtained detailed structural response and yielding mechanism, the necessity of adopting different coupling beam designs elaborately tuned to meet the actual vertical beam demand distribution along the structural height is discussed. It is found that a tall coupled wall structure with uniform steel coupling beam sections over the structural height ultimately leads to an average proportion of yielding coupling beams about 80%, which is as satisfactorily as the one with the beam designs carefully tuned according to the vertical demand distribution obtained using effective lateral load analysis.
    Keywords: Coupled wall systems, RC structural walls, Steel coupling beams, Seismic behavior, Computational analysis
  • Pore Structure Indicators of Chloride Transport in Metakaolin and Silica Fume Self-Compacting Concrete
    Parviz Ghoddousi *, Leyla Adelzade Saadabadi Pages 583-592
    The aim of this paper is to investigate the microstructure indicators and more effective durability mechanisms of SCCs (Self-Consolidating Concretes) containing supplementary cementitious material. The reference SCC mixture at constant water-to-cementitious material (W/CM) ratio of 0.45 and total cementitious material content of 450 kg/m3 was prepared. The other mixes containing binary (92% PC  8% SF, 88% PC  12% SF, and 80%PC  20%MK) and ternary (72%PC  8%SF  20%MK) cementitious blends of metakaolin and silica fume were studied. The effect of using MK and SF in SCCs made with binary and ternary cementitious blends of metakaolin and silica fume and cement on chloride transport and electrical properties was investigated by measuring electrical resistivity parameters such as pore surface conductivity, pore solution conductivity, and tortuosity of pores as chemical and physical indicators of durability. Observations indicated a stronger relationship between the chloride migration coefficient and pore surface conductivity. A new parameter τσs (multiplication of tortuosity and pore surface conductivity), called pore chemi-physical factor, was introduced. Results indicate that the addition of pozzolanic materials such as silica fume and metakaolin leads to a remarkable increase in pore surface conductivity. The correlation coefficient between τσs and the chloride migration coefficient was 0.97. So, if chloride ions are absorbed by pore surfaces, the chloride migration coefficient will decrease in greater tortuosity.
    Keywords: Chloride transport, Electrical resistivity, Pore surface conductivity, Supplementary cementitious material