Seismic vulnerability of reinforced concrete buildings in sliding slopes

Abstract

Seismically triggered landslides represent one of the most devastating collateral hazardsassociated with earthquakes, as they may result in significant direct and indirect lossesto the population and built environment. Predicting the expected degree of damage toaffected built structures subjected to earthquake-induced landslides is thus important fordesign, urban planning, and for seismic and landslide risk assessment and mitigationstudies.Stemming from the general lack of comprehensive methodologies to assess buildingvulnerability to slides as well as the inherent uncertainties associated with them, one ofthe most significant challenges of the present research is the proposition andquantification of a new analytical methodology to estimate the physical vulnerability ofreinforced concrete (RC) frame buildings subjected to earthquake triggered slow-movingslides. According to the suggested method, the damage caused by a slow moving slide ona single building is attributed to the cumulative permanent (absolute or differential)displacement and it is concentrated within the unstable or moving area. A RC buildinglocated next to the crown of a potential unstable slope, is subjected to forced differentialdisplacement and subsequently to structural distress and damage. In terms of numericalcomputations, a two-step uncoupled analysis is performed. In the first step, thedifferential permanent deformation demand at the building’s foundation level is estimatedusing a dynamic non-linear finite difference slope-foundation model. To enhance thereliability of the dynamic analysis results, the computed permanent displacements at theslope area are compared with Newmark-type displacement methods. In the second step,the calculated differential permanent displacements are statically imposed at thebuilding’s nonlinear finite element model at the foundation level to assess the building’sresponse to differing permanent seismic ground displacements. Structural limit states aredefined in terms of threshold values of strains for the reinforced concrete structuralcomponents. Various sets of probabilistic fragility curves are proposed both in terms ofpeak ground acceleration (PGA) and permanent ground displacement (PGD) based on thesuggested methodological framework, via an extensive parametric investigation and sensitivity analysis of various slope geometries, soil properties and distances of thebuilding with respect to the slope’s crown. Τhe slope inclination in conjunction with theslope soil material are proved to be the most influential features on the vulnerability ofthe building exposed to the seismically induced landslide. The slope height may alsogreatly influence the building’s fragility for sand steep slope configurations. Thedeveloped curves might be used by scientists and practitioners for efficientimplementation within a probabilistic risk assessment framework from site specific tolocal scales. To gain confidence on the proposed methodological framework and therespective fragility functions, representative fragility curves developed in this study arecompared with literature ones and recorded building damages from real past events.Traditionally, the structural vulnerability implicitly refers to the intact, as-built structureassuming an optimum plan of maintenance. However, structures deteriorate due tovarious time-dependent mechanisms after they are put into service, without alwayssubjected to the necessary interventions during their lifetime. These issues are becomingeven more crucial in presence of natural hazards striking the structure, such as landslidesand/or earthquakes. To bridge this gap, the proposed approach is also extended toaccount for the evolution of building vulnerability over time by proposing time-dependentfragility curves for RC buildings exposed to the earthquake -induced landslide hazard. Inparticular, the progressive aging of typical RC buildings due to exposure to aggressivecorrosive environment was investigated by including probabilistic models of corrosiondeterioration of the RC elements within the vulnerability modeling framework. It is shownthat the fragility of the structures may increase over time due to corrosion.