A new damage index for seismic fragility analysis of reinforced concrete columns

In the fragility analysis, researchers mostly chose and constructed seismic intensity measures (IMs) according to past experience and personal preference, resulting in large dispersion between the sample of engineering demand parameter (EDP) and the regression function with IM as the independent variable. This problem needs to be solved urgently. Firstly, the existing 46 types of ground motion intensity measures were taken as a candidate set, and the composite intensity measures (IMs) based on machine learning methods were selected and constructed. Secondly, the modified Park–Ang damage index was taken as EDP, and the symbolic regression method was used to fit the functional relationship between the composite intensity measures (CIMs) and EDP. Finally, the probabilistic seismic demand analysis (PSDA) and seismic fragility analysis were performed by the cloud-stripe method. Taking the pier of a three-span continuous reinforced concrete hollow slab bridge as an example, a nonlinear finite element model was established for vulnerability analysis. And the composite IM was compared with the linear composite IM constructed by Kiani, Lu Dagang, and Liu Tingting. The functions of them were compared. The analysis results indicated that the standard deviation of the composite IM fragility curve proposed in this paper is 60% to 70% smaller than the other composite indicators which verified the efficiency, practicality, proficiency, and sufficiency of the proposed machine learning and symbolic regression fusion algorithms in constructing composite IMs.

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Proposed Model of Predicting the Reduced Yield Axial Load of Reinforced Concrete Columns Due to Casting Deficiency Effect

Transactions of the VŠB - Technical University of Ostrava Civil Engineering Series ◽

10.2478/tvsb-2014-0015 ◽

2014 ◽

Vol 14 (2) ◽

pp. 120-128

Author(s):

Dimitra Achillopoulou ◽

Athanasios Karabinis

Keyword(s):

Reinforced Concrete ◽

Axial Load ◽

Load Capacity ◽

Concrete Strength ◽

Damage Index ◽

Concrete Columns ◽

International Standards ◽

Reinforced Concrete Columns ◽

Nominal Strength ◽

Proposed Model

Abstract The study deals with the investigation of the effect of casting deficiencies- both experimentally and analytically on axial yield load or reinforced concrete columns. It includes 6 specimens of square section (150x150x500 mm) of 24.37 MPa nominal concrete strength with 4 longitudinal steel bars of 8 mm (500 MPa nominal strength) with confinement ratio ωc=0.15. Through casting procedure the necessary provisions defined by International Standards were not applied strictly in order to create construction deficiencies. These deficiencies are quantified geometrically without the use of expensive and expertise non-destructive methods and their effect on the axial load capacity of the concrete columns is calibrated trough a novel and simplified prediction model extracted by an experimental and analytical investigation that included 6 specimens. It is concluded that: a) even with suitable repair, load reduction up to 22% is the outcome of the initial construction damage presence, b) the lower dispersion is noted for the section damage index proposed, c) extended damage alters the failure mode to brittle accompanied with longitudinal bars buckling, d) the proposed model presents more than satisfying results to the load capacity prediction of repaired columns.

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