Experimental Validation of Finite Element Models for Reinforced Concrete Beams with Discontinuities That Form Dowel-Type Joints

Marios Filippoupolitis,Carl Hopkins

doi:10.3390/vibration4030032

Abstract

Earthquakes have the highest rate of mortality among the natural disasters and regularly lead to collapsed structures with people trapped inside them. When a reinforced concrete building collapses due to an earthquake, many of the concrete elements (i.e., beams and columns) are damaged and there are large sections where the concrete is missing and the steel reinforcement is exposed (i.e., concrete discontinuities). The prediction of vibration transmission in collapsed and severely damaged reinforced-concrete buildings could help decisions when trying to detect trapped survivors; hence there is need for experimentally validated finite element models of damaged concrete elements. This paper investigates the dynamic behaviour of damaged reinforced concrete beams using Experimental Modal Analysis (EMA) and Finite Element Methods (FEM). FEM models are assessed using two beams with one or more concrete discontinuities that form dowel-type joints. These models used either beam or spring elements for the exposed steel bars and were experimentally validated against EMA in terms of eigenfrequencies and mode shapes. Improved agreement was achieved when using springs instead of beam elements in the FEM model. The comparison of mode shapes used the Partial Modal Vector Ratio (PMVR) as a supplement to the Modal Assurance Criterion (MAC) to confirm that spring elements provide a more accurate representation of the response on all concrete parts of the beams.

Highlights

Earthquakes have the highest rate of mortality among the natural disasters [1] and most of the casualties occur in collapsed buildings [2] where concrete elements are severely damaged and there are large sections where the concrete is missing and the steel reinforcement is exposed
For junctions of beams with and without concrete discontinuities it was found that the use of beam elements for modelling the steel reinforcement was less effective where the reinforcement was exposed and the steel bars were behaving as dowels
This paper focuses on the validation of Finite Element Methods (FEM) models for bending and torsional motion of reinforced concrete beams where there are discontinuities in the concrete with dowel-type joints due to the steel reinforcement

Summary

Introduction

Earthquakes have the highest rate of mortality among the natural disasters [1] and most of the casualties occur in collapsed buildings [2] where concrete elements are severely damaged and there are large sections where the concrete is missing and the steel reinforcement is exposed (e.g., see [3,4,5]). Previous work by Filippoupolitis and Hopkins [9] investigated the potential to predict vibration transmission across unbonded contacts between concrete beams in collapsed buildings This used experimentally validated finite element models of beams junctions at frequencies up to a few kilohertz. A ‘smeared approach’ to the modelling of reinforced concrete [18] considers the steel reinforcement by using solid elements with equivalent properties calculated as weighted averages of the properties of reinforcement and concrete For this reason, it is not appropriate for modelling beams with discontinuities where the exposed reinforcement bars can act as dowels [10,11]. To simulate idealized fractures that could occur in a collapsed building, Beam 1 and Beam 2 were designed to have one and two discontinuities that were 100 mm wide, respectively

Material Properties

Test Setups

Reinforced Concrete Beams with Dowel-Type Joints

Findings

Conclusions