Current Issue : April - June Volume : 2014 Issue Number : 2 Articles : 5 Articles
This paper presents a new adaptive pushover procedure to account for the effect of higher modes in order to accurately estimate the\r\nseismic response of bridges. The effect of higher modes is considered by introducing a minimum value for the total effective modal\r\nmass. The proposed method employs enough number of modes to ensure that the defined total effective modal mass participates\r\nin all increments of the pushover loading. An adaptive demand curve is also developed for assessment of the seismic demand. The\r\nefficiency and robustness of the proposed method are demonstrated by conducting a parametric study. The analysis includes 18\r\nfour-span integral bridges with various heights of piers. The inelastic response history analysis is employed as reference solution in\r\nthis study. Numerical results indicate excellent accuracy of the proposed method in assessment of the seismic response. For most\r\nbridges investigated in this study, the difference between the estimated response of the proposed method and the inelastic response\r\nhistory analysis is less than 25% for displacements and 10% for internal forces. This indicates a very good accuracy compared\r\nto available pushover procedures in the literature. The proposed method is therefore recommended to be applied to the seismic\r\nperformance evaluation of integral bridges for engineering applications....
In prestressed concrete structures, the evaluation of the safety level is generally carried out by separating the bending moment\r\nstrength and the shear force capacity. Actually interaction between bending moment (M) and shear force (V) can have significant\r\nconsequences on evaluations in service life, especially when the ultimate limit state (ULS) is considered. In this paper, the M-V\r\ninteraction is addressed for prestressed concrete girders, in the cases of both bonded and unbonded prestressing tendons. It can\r\nbe demonstrated, by drawing the interaction domains (M-V), that a significant reduction of the safety level has to be considered\r\nwhen shear force is evaluated together with bendingmoment on the ULS of the cross-section, especially for external prestressing in\r\nconcrete T-shaped or box sections of bridge girders. Interaction domains allow designers to evaluate and optimize reinforcement\r\nratios, geometric properties of the beam, and effects of shear on the ultimate state. An analytical model, based on the stress field\r\ntheory, is developed and proposed in this paper.Anumerical example is developed and interaction domains are given for an example\r\nof a box section with variation in reinforcement ratio and tendon slope. A validation of the presentedmodel is given, by comparing\r\nexperimental data in the literature with results found using the proposed analytical approach....
The structures damage conditions assessment requires numerous precautions to ensure the safety of people during site visits\r\nand inspections. Among several methods providing useful information about the conservation status of the structures, dynamic\r\nmonitoring techniques are suitable to retrieve the global behavior of the buildings. The anomalous features diagnosis of the\r\nstructural dynamic response is an index of alterations of the material state and, in the worst cases, is related to the presence of\r\ndamaged structural elements. This paper proposes the use of remote control systems for the structural evaluation of the damage\r\nstate of buildings and describes the results achieved in an interesting application: the experimental dynamic analysis carried out\r\non the inaccessible damaged bell tower of the Church of Santi Giacomo and Filippo in Mirandola (Italy). The study is based on\r\nobservations performed using the IBIS-S ground-based radar interferometer to remotely measure the displacements of several\r\nelements of the building above 0.01mm amplitude. This totally noninvasive and nondestructive approach has proved to be reliably\r\nimplemented as a useful method to structural healthmonitoring procedures and especially for extensive and fast inspection analyses\r\naiming at the first evaluation of the damage level and the soundness of slender buildings after earthquakes....
High performance fibre reinforced concrete (HPFRC) is a modern structural material with a high potential and with an increasing\r\nnumber of structural applications. Structural design of HPFRC elements is based on the post-cracking residual strength provided\r\nby fibre reinforcement, and for structural use, a minimum mechanical performance of HPFRC must be guaranteed. To optimize\r\nthe performance of HPFRC in structural members, it is necessary to establish the mechanical properties and the post-cracking\r\nand fracture behaviour in a univocal and reliable way. The best test methodology to evaluate the post-cracking and toughness\r\nproperties of HPFRC is the beam bending test. Two different types of configurations are proposed: the three-point and the fourpoint\r\nbending tests. The overall focus of this paper is to evaluate the mechanical properties and the post-cracking and fracture\r\nbehaviour of HPFRC, using the two different standard test procedures. To achieve these aims, plain and fibre concrete specimens\r\nwere tested. All the test specimens were extensively instrumented to establish the strength properties, crack tip and crack mouth\r\nopening displacement, and post-cracking behaviour. The results of the two types of bending tests were critically analysed and\r\ncompared to identify and highlight the differing effects of the bending load configurations on the mechanical parameters of HPFRC\r\nmaterial....
Various types of human running dynamic loads are numerically studied and compared to assess vibration characteristics of the light\r\nand slender composite footbridges. Running, which is a common human activity, has been categorized with respect to its intensity\r\ninto jogging, normal running, and sprinting. To explore the footbridge�s performance, the vibration responses are investigated\r\nthrough a series of analyses in terms of the peak accelerations and displacements. In the model verification, the acquired first\r\nnatural frequency of structure has shown good agreement with the value reported in the literature. The structural performance\r\nof the slender composite footbridge is then evaluated with regard to the serviceability requirement given by the current design\r\nstandards. It is generally found that the maximum acceleration of the composite footbridge due to the excitation of one person\r\nrunning varies under different running types because of diversities in the velocity and the step frequency. Furthermore, it is shown\r\nthat the investigated structure provides sufficient human comfort against vibrations for all the examined three types of running\r\nloads....
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