ThesisPresentation

City University LondonSchool of Mathematics, Computer Science &

Engineering

Seismic Assessment of Existing Reinforced Concrete Structures with Inelastic Finite Element Models

by

Panagiotis D. Panas

MSc Structural Engineering

Panagiotis Panas - MSc Thesis 1

• A large number of existing reinforced concrete (RC) structures have been designed according to old codes andconstruction practices which included provisions only for vertical loading. The seismic response of such structures duringan excitation event is expected to be unsatisfactory due to limited lateral load resistance capacity and inadequateductility.

• For the purposes of this study, the performance of a two dimensional RC frame structure, which is considered arepresentative of the design practices used in Southern Europe in the 1950s and 1960s, is assessed with the aid ofnonlinear dynamic time-history and inelastic static analyses.

• The seismic assessment is mainly performed in the "fibre based" finite element package Seismostruct v7 where prior tothe analysis of the frame structure an investigation on the influence of different finite element formulations for themodelling of the nonlinear response of RC structures is being made through the use of an experimental test asbenchmark. The examined RC frame structure is then modelled with distributed inelasticity force based elements andsubjected to nonlinear dynamic time-history analysis under two different input motions accounting for 475 and 975 yearsreturn period. Afterwards, the structure is subjected to inelastic static (pushover) analysis using again Seismostruct v7 butalso the commercial computer software SAP2000 v15 where the "lumped - inelasticity" approach is followed and plastichinges are calculated and inserted to the software according to the provisions of Eurocode 8 - Part 3

1. Introduction


• Literature review relative to seismic design codes (mainly Eurocode 8) and the suggested performance assessment methods

• Literature survey for previous studies containing nonlinear dynamic and inelastic static analyses in order to gain anunderstanding for the theoretical background of the nonlinear analysis methods

• Investigation of different FE formulations proposed by Seismostruct for the modelling of the nonlinear response of RCstructures

• Subject the RC frame structure to nonlinear dynamic and inelastic static analyses through the use of two commercialcomputer softwares

• Comparisons between the analytical results and the experimental ones obtained at ELSA Laboratory (Ispra, Italy)

• Discussion about the failure modes and the damages identified from the nonlinear analyses

1.1 Steps - Objectives


2. Investigation of Seismostruct Models

Examined SpecimenColumn 415 - (adopted from Lehman & Moehle, 2000)


2.1 Inelastic Static Analysis (FB Element)

Modelling of column & Section discretization“Single force based inelastic element “

Nonlinear static curves - Force based element


2.2 Inelastic Static Analysis (DB Element)

Subdivision of structural Member Displacement based elements

Nonlinear static curves - Displacement based elements


2.3 Inelastic Static Analysis (Different Formulations)

• Force based with 4 IPs• Displacement based with 4 elements• Displacement based plastic hinges• Force based plastic hinges

Comparisons between different formulations

Length of plasticity


2.4 Static Time - History Analysis (FB Element)

Force-displacement diagrams for distributed inelasticity FB elements


2.5 Static Time - History Analysis (DB Element)

Force - displacement diagrams for distributed inelasticity DB elements


2.6 Static Time - History Analysis (Plastic Hinges)

Force - displacement diagrams for plastic hinge FB element


Force - displacement for plastic hinge DB element

2.7 Static Time - History Analysis (Plastic Hinges)


2.8 Investigation of Material Models

Uniaxial steel models: a) Menegotto - Pinto (1973), b) Monti - Nuti (1996), c) Bilinear and d) Dodd -

Restrepo (1995) (adopted from Seismosoft, 2014

Concrete Models: a) Mander et al (1988), b) Kappos and Konstantinidis (1999), c) Chang and Mander (1994) and d)

Simplified Trilinear (adopted from Seismosoft, 2014)


2.9 Investigation of Material Models (Steel)

Force displacement diagrams - Comparisons of steel models


2.10 Investigation of Material Models (Concrete)

Force displacement diagrams - Comparisons of concrete models


2.11 Investigation of Material Models

Pushover Curves - Experiment Comparisons


3. The ICONS Frame

Examined Structure - Elevation view


3.1 Original Structural Drawings

Plan and elevation - Four storey, three bay reinforced concrete frame (adopted from Pinto et al., 2002)



Beam reinforcement details (adopted from Pinto et al., 2002)



Column reinforcement details (adopted from Pinto et al., 2002)


3.2 Modal Analysis (Seismostruct)

Model of ICONS frame for modal analysis in Seismostruct


3.2 Modal Analysis (Seismostruct)

The first, second and third mode shapes with their corresponding natural periods and modal masses ratios (Seismostruct)


3.3 Modal Analysis (SAP2000)

Scheme of vertical loading (adopted from Carvahlo et al., 1999)


3.3 Modal Analysis (SAP2000)

Natural Periods of Structure - Comparisons


3.4 Nonlinear Dynamic Analysis

Nonlinear dynamic analysis model in Seismostruct



Inelastic FB frame elements Discretization of RC cross-sections



Artificial acceleration time-history for 475 and 975 years return periods


3.5 Results and Comparisons

Analytical storey displacements for Acc475 and Acc975



Top Storey Displacements Comparison between Acc475 and Acc975



Comparisons between analytical and experimental storey displacements for Acc475 and Acc975



Comparisons between analytical and experimental top storey displacements for Acc475 and Acc975



Third Storey Drift for Acc475 & Acc975



Maximum interstorey drifts for Acc475 and Acc975



Storey shear vs interstorey drift diagrams for Acc475 and Acc975



Maximum storey shear for Acc475 and Acc975



Maximum response values for Acc475 and Acc975 (summary table)


3.6 Seismic Assessment

Yielding of reinforcement for Acc475


3.6 Seismic Assessment

Deformed Shape of the structure at maximum displacement

Shear Capacity (yellow) and Yielding of Reinforcement (red) for Acc975


3.7 Pushover Analysis (Seismostruct)

Model in Seismostruct



Pushover Curve & Target Displacements



Interstorey drift Tr = 475 and Tr = 975

Maximum storey shearTr = 475 and Tr = 975


3.8 Seismic Assessment (Pushover Analysis)

Shear capacity (yellow) and yielding (red) for Tr = 475


3.8 Seismic Assessment (Pushover Analysis)

Chord Rotation Capacity, Shear Capacity (yellow) & Yielding (red) for Tr = 975


3.9 Pushover Analysis (SAP2000)

Model in SAP2000


3.9 Pushover Analysis (SAP2000)

Acceleration Response Spectra for Tr = 475 and Tr =975


3.10 Seismic Assessment (SAP2000)

Deformed shapes and plastic hinge formations for Tr = 475 and Tr = 975


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