1,721,925 research outputs found
Effects of mainshock-aftershock sequences on fragility analysis of RC buildings with ageing
No full textThis paper presents the seismic vulnerability assessment of existing RC buildings designed according to previous non-seismic codes that are exposed to various levels of corrosion and mainshock-aftershock sequences. A refined finite element model of an existing four-storey reinforced concrete building is adopted. Twenty as-recorded natural ground motions are collected from international databases to perform incremental dynamic analyses for the inelastic response of the testbed building. The effects of corrosion are applied on external beams and columns to simulate a realistic exposure. The robust fragility assessment is conducted for a range of seismic intensity measures. Moreover, a new intensity measure, based on the modified acceleration spectrum intensity, is proposed. Such seismic parameter accounts for the elongation period experienced by structures during earthquake events and appears to be more reliable and accurate for corroded RC structures than the most adopted peak ground acceleration and spectral acceleration at the first natural period. The results of the comprehensive numerical simulations contribute to providing relevant indications on the non-linear response of existing corroded buildings under multiple excitations and, highlight that current seismic codes are no longer conservative for such detrimental phenomena
Base isolation of railway bridges
No full textThe seismic vulnerability assessment of existing and new lifelines, especially transportation systems, either highways or railways, is becoming of paramount importance in resilient social communities. The structural performance analysis of typical existing bridges for high speed railway is however not an easy task to accomplish. Additionally, the seismic assessment of such as-built bridges tend to emphasize the high vulnerability of the structural systems. In the present analytical work, the earthquake response analysis of typical existing bridges for high speed railway was carried out through linear and nonlinear dynamic analyses using refined finite element three-dimensional lumped-plasticity models and multiple component ground motions. The seismic vulnerability of such bridges was assessed through local and global response quantities. The retrofitting scheme adopted to augment the earthquake performance of the sample bridge structures is the base isolation system comprising either lead rubber bearings or steel dampers. The present study investigates and compares the response of such isolation devices. The outcomes of the numerical analyses proved that the use of base isolation systems lowered significantly the seismic demand, especially on the bridge piers and the foundation systems. Hysteretic metallic devices were found more suitable for the seismic isolation of railway bridges. Additionally, the need to comply with the serviceability requirements is found to be more stringent for the base isolation system in the design of retrofitting schemes for railway bridges than the fulfillment of the ultimate limit state. Further work is ongoing to account for the nonlinear modeling of the rail on the global response of base isolated railway bridges under multiple earthquake components
Effects of multiple earthquakes on inelastic structural response
No full textThe basic approach for seismic design of structures utilizes a single loading scenario and a single performance criterion; usually life-safety. In recent years, social and economic considerations have necessitated that more than one performance criterion is used, and also more than one level of earthquake intensity. This multiple load-and-limit state seismic design is the current best practice. There are a few locations around the world that warrant an alternative approach. These locations are affected by more than one earthquake within a relatively short period of time due to their special seismo-tectonic setting. Few existing studies simply assume that the first earthquake will impose the maximum damage. An opportunity has presented itself to study the effect of multiple strong earthquakes on structures as a consequence to the exceptionally rich set of records obtained from the earthquake sequence of Tohoku (Japan), starting on March 2011. In this technical note, five stations are selected to represent a set of sites subjected to multiple earthquakes of varying magnitudes and source-to-site distances. From the tens of records captured at these five sites, three are selected for each site to represent scenarios of leading and trailing strong-ground motion. A leading set is where the first earthquake has the largest peak ground acceleration (PGA) in the sequence of three, while a trailing set has the second or third records as its highest PGA signal. A short list of earthquake response parameters is selected, and the records are treated in two different manners. Inelastic constant ductility spectra for acceleration response are examined, alongside force reduction factor spectra. The final part of the technical note is a reinforced concrete (RC) frame analysis subjected to the same set of ground motions used for the response spectra. The inelastic response and force reduction factor spectra, alongside the inelastic response of the RC frame, not only confirm that multiple earthquakes deserve extensive and urgent studies, but also give indications of the levels of lack of conservatism in the safety of conventionally-designed structures when subjected to multiple earthquake
On the seismic fragility of pipe rack—piping systems considering soil–structure interaction
No full textPiping systems constitute the most vulnerable component in down- and mid-stream facilities posing immediate threat to human lives, communities financial robustness and environment. Pipe racks present several mechanical and geometrical idiosyncrasies compared to common buildings and the seismic response is governed by the pipework layout. Important design requirements e.g. dynamic interaction between pipelines and supporting structure are commonly overlooked during pipe racks design process and uncertainties relevant to modelling of soil or seismic input are not quantified. In the present work, after reviewing the technical literature and codes, a 3D RC rack was used as a testbed and analysed as coupled and decoupled with a non-seismic code conforming piping system accounting for soil–structure interaction. Incremental dynamic analysis was adopted as an assessment methodology for deriving fragility curves considering ground motions in near- and far-field conditions. It was deduced that the modelling (boundary conditions of pipes) was the most considerable uncertainty since it increased the probability of collapse limit state of structural members from 0 to 59%. It was also demonstrated that soil deformability as well as source conditions altered considerably the dispersion of intensity measure conditional on engineering demand parameter of structural and nonstructural members. The results may be another indication that code provisions should be more normative regarding industrial pipe racks
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