on the seismic fragility of pipe rack piping systems considering soil structure interaction

Piping 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

Petrochemical Steel Pipe Rack: Critical Assessment of Existing Design Code Provisions and a Case Study

Abstract The investigation of the seismic integrity of petrochemical plant steel structures should be commensurable to their importance given the high necessity for human life safety and financial robustness. To date, it is demonstrated in the existing literature that still many grey areas of knowledge exist upon the appropriate application of code provisions on non-building structures design. Indeed, the selection of seismic design parameters such as system performance factors or important classes are still vague aspects, in contrast with those for common building structures, either because of the paucity of information of seismic codes or due to the structural peculiarities that characterise the industrial structures resulting in the difficulty of defining 'all-encompassing' design parameters. The present paper aims at highlighting those parameters considering also a case-study that pertains to a steel pipe rack. The pipe rack is designed and analysed in the linear and nonlinear regime, both statically and dynamically, according to the Italian and European codes. American code provisions are examined as well so as possible inconsistencies might be found. It is demonstrated that the common nonlinear static analysis (pushover analysis) cannot be used to assess the response of the rack and the behaviour factor selection from current standards could be unjustifiable. Also, common engineering demand parameters, e.g. interstorey drift ratio, need further assessment vis-à-vis the response of nonstructural components of which the current design method does not comply with modern methods

CRITICAL REVIEW OF MODELS FOR THE ASSESSMENT OF THE DEGRADATION OF REINFORCED CONCRETE STRUCTURES EXPOSED TO CORROSION

Exposure to aggressive environments is one of the main causes of reinforced concrete (RC) civil infrastructure degradation and damage, which can become critical if such structures are unprotected, as in the case of bridges, and even more crucial if subjected to seismic loading. This paper aims at analysing the models and approaches currently used for the assessment of RC structures exposed to different levels of corrosion. Furthermore, a specific section will be devoted to the evaluation of ageing on the seismic performance of bridges. A few numerical and analytical models of aged reinforced concrete structures have been chosen among thousands the proposed in the literature based on chronological time criteria. The methodological approach consists in comparing the results provided in the literature, based on experimental tests, with the outputs of Finite Element. These analyses were conducted by changing the mechanical properties of both concrete and steel rebars at different corrosion rates, which affect concrete strength, yielding stress, ultimate stress and stiffness of embedded steel rebars, and thus, bearing-capacity and seismic performance. New relationships for concrete strength and steel properties according to the level of corrosion are given. The results confirm the pivotal role and evolutionary nature of the impact of corrosion on the lifecycle of concrete structure

Seismic risk of typical ageing petrochemical steel structure in harsh atmospheric conditions

AbstractThis paper addresses the evaluation of the effects of corrosion on the performance of ageing steel industrial infrastructures. A novel probabilistic risk assessment method is presented with respect to a case study of a real petrochemical structure located in an atmospheric environment with high severity of corrosion. The results of damage assessment derived from refined fragility analyses revealed that long-term corrosion mass reduction can increase the probability of damage to the structure by an average of 40%. Furthermore, the risk analysis demonstrated that the annual failure rate of the corroded structure is at most 2.80 times that of the uncorroded counterpart. The vulnerability analysis showed that the difference in annual repair costs between corroded and uncorroded cases gradually increased as the severity of ground motion raised. Moreover, the results of comprehensive and refined nonlinear analyses indicated that the corroded structure after 50 and 100 years can increase the likelihood of causing corrosion repair costs in the first year by about 40 and 60 times, respectively. The evaluation of the ratio of construction to maintenance and retrofitting was also carried out; it was based on innovative retrofitting measures with the use of Carbon Fibre Reinforced Polymers for steel structures. The findings illustrated in the present numerical study can help owners and insurance companies to predict more reliably maintenance and repair costs, thus they can provide an efficient roadmap for industrial asset management.</jats:p

A critical review on the vulnerability assessment of natural gas pipelines subjected to seismic wave propagation. Part 1:Fragility relations and implemented seismic intensity measures

© 2019 Elsevier Ltd Natural gas (NG) pipeline networks constitute a critical means of energy transportation, playing a vital role in the economic development of modern societies. The associated socio-economic and environmental impact, in case of seismically-induced severe damage, highlights the importance of a rational assessment of the structural integrity of this infrastructure against seismic hazards. Up to date, this assessment is mainly performed by implementing empirical fragility relations, which associate the repair rate, i.e. the number of repairs/damages per unit length of the pipeline, with a seismic intensity measure. A limited number of analytical fragility curves that compute probabilities of failure for various levels of predefined damage states have also been proposed, recently. In the first part of this paper, a thorough critical review of available fragility relations for the vulnerability assessment of buried NG pipelines is presented. The paper focuses on the assessment against seismically-induced transient ground deformations, which, under certain circumstances, may induce non-negligible deformations and strains on buried NG pipelines, especially in cases of pipelines crossing heterogeneous soil sites. Particular emphasis is placed on the efficiency of implemented seismic intensity measures to be evaluated or measured in the field and, more importantly, to correlate with observed structural damage on buried NG pipelines. In the second part of this paper, alternative methods for the analytical evaluation of the fragility of steel NG pipelines under seismically-induced transient ground deformations are presented. Through the discussion, recent advancements in the field are highlighted, whilst acknowledged gaps are identified, providing recommendations for future research