Sep 2011, Volume 5 Issue 3
    

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  • RESEARCH ARTICLE
    Dapeng ZHU, Yang WANG, James BROWNJOHN

    Being able to significantly reduce system installation time and cost, wireless sensing technology has attracted much interest in the structural health monitoring (SHM) community. This paper reports the field application of a wireless sensing system on a 4-span highway bridge located in Wayne, New Jersey in the US. Bridge vibration due to traffic and ambient excitation is measured. To enhance the signal-to-noise ratio, a low-noise high-gain signal conditioning module is developed for the wireless sensing system. Nineteen wireless and nineteen cabled accelerometers are first installed along the sidewalk of two neighboring bridge spans. The performance of the wireless sensing system is compared with the high-precision cabled sensing system. In the next series of testing, 16 wireless accelerometers are installed under the deck of another bridge span, forming a 4 × 4 array. Operating deflection analysis is successfully conducted using the wireless measurement of traffic and ambient vibrations.

  • RESEARCH ARTICLE
    Akira WADA, Zhe QU, Shojiro MOTOYUI, Hiroyasu SAKATA

    A retrofit of an existing 11-story steel reinforced concrete frame that features the innovative use of post-tensioned rocking walls and shear steel dampers is presented. The main components of the retrofitting plan and important design considerations are described. The retrofitting system is expected to effectively control the deformation pattern of the existing structure and significantly reduce damage to the existing structure during major earthquakes.

  • RESEARCH ARTICLE
    Nattapong DAMRONGWIRIYANUPAP, Linyuan LI, Yunping XI

    Corrosion of reinforcing steel due to chloride ions is one of the severe deterioration problems in long-term performance of reinforced concrete structures. The deterioration process is frequently found in marine concrete structures, highway pavements, and bridges exposed to deicing salts. The diffusion of chloride ions is associated and strongly affected by other ions in the pore solution in concrete. In this paper, chloride penetration into concrete structures was mathematically characterized by the Nernst-Planck equation which considered not only diffusion mechanism of the chloride ions but also ionic interaction among other ions coming from externally applied deicers and within the Portland cement paste. Electroneutrality was used to determine the electrostatic potential induced by the ionic interaction. The material models of chloride binding capacity and chloride diffusion coefficient were incorporated in the governing equations. The governing equations were solved by using finite element method. A numerical example was used to illustrate the coupling effect of multi-ionic interactions and the effect of influential parameters. The numerical results obtained from the present model agreed very well with available test data.

  • RESEARCH ARTICLE
    Kazi Md Abu SOHEL, Jat Yuen Richard LIEW, Min Hong ZHANG

    This paper presents the design guide based on analytical, numerical and experimental investigation of Steel-concrete-steel (SCS) sandwich structural members comprising a lightweight concrete core with density ranged from 1300 to 1445 kg/m3 subjected to static, impact and blast loads. The performance of lightweight sandwich members is also compared with similar members with normal weight concrete core and ultra high strength concrete core (fc = 180 MPa). Novel J-hook shear connectors were invented to prevent the separation of face plates from the concrete core under extreme loads and their uses are not restricted by the concrete core thickness. Flexural and punching are the primary modes of failure under static point load. Impact test results show that the SCS sandwich panels with the J-hook connectors are capable of resisting impact load with less damage in comparison than equivalent stiffened steel plate panels. Blast tests with 100 kg TNT were performed on SCS sandwich specimens to investigate the key parameters that affect the blast resistance of SCS sandwich structure. Plastic yield line method is proposed to predict the plastic capacity and post peak large deflection of the sandwich plates. Finally, an energy balanced model is developed to analyze the global behavior of SCS sandwich panels subjected to dynamic load.

  • RESEARCH ARTICLE
    Wuchao YANG, Xudong QIAN

    This study investigates the ductile fracture resistance of 3-D external circumferential cracks in the wall of a steel pipe under remote tension, using a damage-mechanism model originally proposed by Gurson and Tvergaard. The ductile crack extension utilizes an element extinction technique implemented in the computational cell framework. The key parameter for the computational cell method, i.e., the initial porosity ratio f0, is calibrated using both the fracture resistance and the load-deformation responses obtained from fracture tests of multiple single-edge bend [SE(B)] specimens made of high-strength steel, HY80, which has a yield strength of 630 MPa. The fracture resistance along the 3-D semi-elliptical crack front is computed from the calibrated cell model. Based on the similarity concept in the near-tip stress-strain fields, this study demonstrates that an equivalent 2-D axi-symmetric model provides conservative estimations of the fracture resistance for 3-D circumferential cracks in pipes.

  • RESEARCH ARTICLE
    Yan-Gang ZHAO, Zhao-Hui LU

    Load and resistance factors are generally obtained using the first order reliability method (FORM) in which the design point should be determined and derivative-based iterations used. In this article, the third-moment reliability index, based on the three-parameter lognormal (3P-lognormal) distribution, is investigated. A simple method based on the third-moment method for estimating load and resistance factors is then proposed, and a simple formula for the target mean resistance is also presented to avoid iterative computations. Unlike the currently used method, the proposed method can be used to determine load and resistance factors, even when the probability density functions (PDFs) of the basic random variables are not available. Moreover, the proposed method does not require the iterative computation of derivatives or any design points. Thus, the method provides a more convenient and effective way to estimate load and resistance factors in practical engineering applications. Numerical examples are presented to demonstrate the advantages of the proposed third moment method for determining load and resistance factors.

  • RESEARCH ARTICLE
    Chung-Che CHOU, Jun-Hen CHEN

    Post-tensioned (PT) self-centering moment frames have been developed as an alternative to typical moment-resisting frames (MRFs) for earthquake resistance. When a PT frame deforms laterally, gaps between the beams and columns open. However, the gaps are constrained by the columns and the slab in a real PT self-centering building frame. This paper presents a methodology for evaluating the column restraint and beam compression force based on the column deformation and gap openings at all stories. The method is verified by cyclic tests of a full-scale, two-bay by one-story PT frame. Moreover, a sliding slab is proposed to minimize restraints on the expansion of the PT frame. Shaking table tests were conducted on a reduced-scale, two-by-two bay one-story specimen, which comprises one PT frame and two gravitational frames. The PT frame and gravitational frames are self-centering throughout the tests, responding in phase with only minor differences in peak drifts caused by expansion of the PT frame. When the specimen is excited by a simulation of the 1999 Chi-Chi earthquake with a peak ground acceleration of 1.87 g, the maximum interstory drift and the residual drift are 7.2% and 0.01%, respectively.

  • RESEARCH ARTICLE
    Nicholas KEAGE, Christopher MAIOLO, Rebecca PIEROTTI, Xing MA

    In this paper, a practical test and finite element analysis has been undertaken to further investigate the effects of contact buckling. A test rig was designed and constructed to record vertical and transverse deflections of compressively loaded steel skin plates. The boundary conditions were modeled as fully fixed. A finite element analysis was also undertaken using the software package Strand7. Results from both analyses have been examined and compared to data established from previous studies on contact buckling. Both the finite element analysis and practical results correlate well with this data. The result of the investigation has confirmed contact buckling theories and has foreshadowed the onset of the newly observed phenomenon of secondary contact buckling.

  • RESEARCH ARTICLE
    Ivan Gomez ARAUJO, Esperanza MALDONADO, Gustavo Chio CHO

    An ambient vibration test on a concrete bridge constructed in 1971 and calibration of its finite element model are presented. The bridge is characterized by a system of post-tensioned and simply supported beams. The dynamic characteristics of the bridge, i.e. natural frequencies, mode shapes and damping ratios were computed from the ambient vibration tests by using the Eigensystem Realization Algorithm (ERA). Then, these characteristics were used to update the finite element model of the bridge by formulating an optimization problem and then using Genetic Algorithms (GA) to solve it. From the results of the ambient vibration test of this type of bridge, it is concluded that two-dimensional mode shapes exist: in the longitudinal and transverse; and these experimentally obtained dynamic characteristics were also achieved in the analytical model through updating. The application of GAs as optimization techniques showed great versatility to optimize any number and type of variables in the model.

  • RESEARCH ARTICLE
    Ling LI, Xianzhong ZHAO, Ke KE

    Intersecting connection plays an important role in the new diagrid structural system for high-rise buildings. To investigate the static behavior of the intersecting connection of concrete-filled steel tubular (CFST) columns, a typical reduced-scale planner connection specimen is tested under monotonic axial compression. The failure modes, force mechanism and bearing capacity of intersecting CFST connections are analyzed further in the follow-up numerical simulation, considering influences of intersecting angle, elliptical plate and ring plate. Test and simulation results prove that, intersecting connection can develop fully plastic deformation and provide sufficient bearing capacity. Parametric analysis indicates that bearing capacity of planar intersecting CFST connection mainly depends on intersecting angle and thickness of elliptical plate, while the ring plate affects that little. Capacity estimation method for planar intersecting CFST connection is proposed basing on the capacity of the critical section which is located near intersecting center for a distance of steel tube radius, and the design suggestions is provided in the end of this paper.

  • RESEARCH ARTICLE
    Yun WU, Qilin ZHANG

    This paper presents an experimental investigation of longitudinally welded aluminum alloy I-section columns subjected to pure axial compression. The specimens were fabricated using 6061-T6 heat-treated aluminum alloy. The test program included 20 column tests which were separated into 2 test series of different types of welding sections. Each test series contained 10 columns. All the specimens were welded using the Tungsten Inert Gas welding method. The length of the specimens ranged from 442 to 2433 mm in order to obtain a column curve for each test series. The observed failure mode for the column tests includes mainly flexural buckling around the minor axis and the major axis by applying support except for one column (ZP1217-1) which buckled in the local zone and some columns which failed in the weld. The test strengths were compared with the design strengths predicted by the European Code and China Code for aluminum structures. The purpose of this paper is to present the tests results of two typically longitudinally welded I-section columns, and to check the accuracy of the design rules in the current specifications.

  • RESEARCH ARTICLE
    Youliang DING, Aiqun LI

    This paper addresses the problem of condition assessment of bridge expansion joints using long-term measurement data under changing environmental conditions. The effects of temperature, traffic loading and wind on the expansion joint displacements are analyzed and interpreted, which reveal that measured displacements are observed to increase with an increase in temperature and to decrease with increased traffic loading, while the correlation between displacement and wind speed is very weak. Two regression models are developed to simulate the varying displacements under the changes in temperature and traffic loadings. Based on these models, the effects of the environmental conditions are removed to obtain the normalized displacement. Statistical process control using mean value control charts is further used to detect damage to the bridge expansion joints. The results reveal that the proposed method had a good capability for detecting the damage-induced 1.0% variances of the annual changes in the expansion joint displacements.

  • RESEARCH ARTICLE
    Faxing DING, Xiaoyong YING, Linchao ZHOU, Zhiwu YU

    This paper presents a unified calculation method and its application in determining the uniaxial mechanical properties of concrete with concrete strengths ranging from 10 to 140 MPa. By analyzing a large collection of test results of the uniaxial mechanical properties of normal-strength, high-strength and super high-strength concrete in China and performing a regression analysis, unified calculation formulas for the mechanical indexes of concrete are proposed that can be applied to various grades of concrete for determining the size coefficient, uniaxial compressive strength, uniaxial tensile strength, elastic modulus, and strain at peak uniaxial compression and tension. Optimized mathematical equations for the nonlinear stress-strain relationship of concrete, including the ascending and descending branches under uniaxial stress, are also established. The elastic modulus is almost constant throughout the elastic stage for the ascending branches of the stress-strain relationship for concrete. The proposed stress-strain relationship of concrete was applied to the nonlinear finite element analysis of both a steel-concrete composite beam and a concrete-filled steel tubular stub column. The analytical results are in good agreement with the experiment results, indicating that the proposed stress-strain relationship of concrete is applicable. The achievements presented in this paper can be used as references for the design and nonlinear finite element analysis of concrete structures.

  • RESEARCH ARTICLE
    Yuanqing WANG, Hui ZHOU, Yongjiu SHI, Yi HUANG, Gang SHI, Siqing WEN

    Horizontal strengthened storeys are widely used in super high-rise steel structures to improve the lateral structural rigidity. This use has great effects on the seismic properties of the entire structure. The seismic properties of the Wuhan International Securities Building (a 68-storey super high-rise steel structure with three horizontal strengthened storeys) were evaluated in this study. Two approaches, i.e., mode-superposition response spectrum analysis and time-history analysis, were employed to calculate the seismic response of the structure. The response spectrum analysis indicated that transition parts near the three strengthened storeys were weak zones of the structure because of the abrupt change in rigidity. In the response spectrum analysis approach, the Square Root of Sum of Square (SRSS) method was recommended when the vertical seismic effects could be ignored. However, the complete quadratic combination (CQC) method was superior to SRSS method when the vertical seismic effects should be considered. With the aid of time-history analysis, the seismic responses of the structure were obtained. The whiplash effect that spectrum analysis cannot reveal was observed through time-history analysis. This study provides references for the seismic design of super high-rise steel structures with horizontal strengthened storeys.