Analysis and modelling of the seismic behaviour of high ... - Ingegneria

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4. SEISMIC RESPONSE OF PARTIAL-STRENGTH COMPOSITE JOINTS the S.L.S. According to a Poisson model, this corresponds to a reference return period of 95.4 years. iii. Calculating the structural demand for the pre-selected earthquake intensity. The demand parameters, such as the maximum interstory drift, are computed using standard methods of structural analysis (Non-linear Pushover analysis and Time-History analysis) taking into account possibly stiffness deterioration and strength degradation of members and connections of the structure (the effect of residual drift contributes about one-third to the loss in frame stability, and the remaining two-third drop is due to stiffness/strength degradation). iv. Determination of global and local collapse capacity, i.e. estimating the capacity of the structure and of its components (maximum rotation, interstorey, etc) for the defined limit states (damage and the collapse limit state). Local Drift Capacity will be determined from cyclic tests of full-size connection specimens conducted by the Laboratory of the University of Pisa. The cyclic tests are used to determine load-deformation hysteresis behaviour of the system and the maximum drift for which gravity loads may still be carried by the girders. This gravity-induced drift limit is reached when a low-cycle fatigue crack develops in the end plate or the load-deformation behaviour of the moment connection has completely deteriorated. A standard test protocol, based on the ECCS Procedure (1986) was used for the tests. The moment vs. plastic rotation of a beam-column assembly representative of a single test is shown in Figure 4.15. The hysteretic behaviour is characterized by gradual strength degradation with increasing plastic rotation. For the specific connection tested, it appeared that the shear-carrying capacity was reached at a plastic rotation of about 0.06 radians. In order to use such data in the reliability framework it is necessary to have several such tests, from which we can obtain statistics on the likely distribution of important design parameters, such as plastic rotation at peak load and plastic rotation at loss of capacity. Statistics that must be obtained include the median value of the parameter and the standard deviation of the logarithm of the values obtained from the testing. Global Drift Capacity of the prototype building will then be determined using the non-linear pushover analysis (NLP) or the incremental dynamic analysis (IDA) procedure that is based on the use of non-linear time-history analysis. It is important that the analytical model used for determining the global drift demand reproduces the major features of the measured response such as sudden loss of strength. This means that the measured hysteresis behaviour must be modeled reasonably well and the model must include all significant components of building stiffness, strength and damping. 125
4. SEISMIC RESPONSE OF PARTIAL-STRENGTH COMPOSITE JOINTS 126 REACTION MOMENT (kNm) 350 300 250 200 150 100 50 0 -50 -100 -150 -200 Experiment -80 -60 -40 -20 0 20 40 60 80 ROTATION (mrad) Figure 4.15. Measured moment vs. rotation behaviour of the connection v. Determining the demand-to-capacity ratio. Once calculated, the ratio between the demand obtained from aforementioned frame analyses and the obtained capacity allow to estimate the performance of the structure and of the components, i.e. the probability that the structure or a component will have less than a specified probability of exceedance of a desired performance level. The EC8 code requirements impose two primary controls on the structural design: minimum strength and minimum stiffness (as specified trough the deflection limit). These two requirements are interrelated and competing. For instance, if the stiffness of a structure is increased so that it meets the drift requirements, then the period will shorten, which often results in a larger design base shear and a correspondingly larger drift. Moreover, the strength and stiffness of the building are coupled, and thus the minimum stiffness requirement adds considerably to the system overstrength. The structural overstrength results from a number of factors including internal force redistribution, code requirements for multiple loading combinations, code minimum requirements regarding proportioning and detailing, material strength higher than that specified in the design, strain hardening, deflection, constraints on system performance, member oversize and strain rate effect.
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Dipartimento di Ingegneria Meccanic
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UNIVERSITÀ DEGLI STUDI DI TRENTO D
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Ai miei genitori
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INDEX 1 INTRODUCTION...............
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INDEX iii 4.10.3 Results of the PsD
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1.1 Introduction 1 1 INTRODUCTION I
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1. INTRODUCTION imposes precise con
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1. INTRODUCTION joints whilst 2D mo
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7 2 DUCTILITY AND SEISMIC RESPONSE
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2. DUCTILITY AND SEISMIC RESPONSE O
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3. SEISMIC BEHAVIOUR OF BOLTED END
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5. SEISMIC BEHAVIOUR OF RC COLUMNS
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6. SUMMARY, CONCLUSIONS AND FUTURE
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Analysis and modelling of the seismic behaviour of high ... - Ingegneria

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