AND HIGH-STRENGTH CONCRETE BEAMS Angela Salzmann

280 Pages·2017·2.81 MB·English

Damping Characteristics of Reinforced and Prestressed
Normal- and High-Strength Concrete Beams
Author
Salzmann, Angela
Published
2003
Thesis Type
Thesis (PhD Doctorate)
School
School of Engineering
DOI
https://doi.org/10.25904/1912/2687
Copyright Statement
The author owns the copyright in this thesis, unless stated otherwise.
Downloaded from
http://hdl.handle.net/10072/366888
Griffith Research Online
https://research-repository.griffith.edu.au
DAMPING CHARACTERISTICS OF REINFORCED AND
PRESTRESSED NORMAL- AND HIGH-STRENGTH
CONCRETE BEAMS

A thesis submitted in fulfilment of the
requirements for the award of the degree of

Doctor of Philosophy

by

Angela Salzmann
BEng (Hons1), J.P.

from

School of Engineering
Faculty of Engineering and Information Technology

GRIFFITH UNIVERSITY
GOLD COAST CAMPUS

November 2002
To
My Parents
Declaration i

D
eclaration

This work has not been previously submitted for a degree or diploma in any university.
To the best of my knowledge and belief, the thesis contains no material previously
published or written by another person except where due reference is made in the thesis
itself.

________________________
Angela Salzmann
November 2002

Damping Characteristics of Reinforced and Prestressed Normal- and High-Strength Concrete Beams
Acknowledgements ii

A
cknowledgements

The research from which this thesis has been composed was undertaken at the School of
Engineering, Griffith University Gold Coast Campus under the supervision of Dr. Sam
Fragomeni and Professor Yew-Chaye Loo. The author is greatly indebted to Dr.
Fragomeni and Professor Loo, whose continued support, encouragement, inspiration
and technical contributions helped to guide and shape the research effort. In particular,
the provision of significant guidance regarding the scope of the experimental work
provided invaluable assistance.

A special thankyou is given to all the technical staff and in particular to Charles Allport
without whose help, the experimental work could not have been possible. Grateful
thanks are also extended to the administrative staff of the School who provided constant
encouragement and to many final year students who enthusiastically assisted in the
laboratory testing tasks.

The author also wishes to thank the Australian Government Australian Postgraduate
Award (APA) Scholarship Scheme and the School of Engineering for providing the
financial assistance which allowed the research to be completed in this form.

Finally, her deep heartfelt thanks goes to her partner, Peter, and her parents, Gus and
Fiona and her sister Monique for their constant encouragement, understanding, financial
assistance, and belief. The completion of this research is but a small gift for their
efforts and great expectations.

Damping Characteristics of Reinforced and Prestressed Normal- and High-Strength Concrete Beams
List of Publications iii

L P
ist of ublications

Salzmann, A., Fragomeni, S. and Loo, Y.C. (2002a) Damping behaviour of reinforced
concrete beams – Review and new developments, 17th Australasian Conference
on the Mechanics of Structures and Materials, 12-14 June 2002, Gold Coast,
Australia.

Salzmann, A., Fragomeni, S. and Loo, Y.C. (2002b) The damping analysis of
experimental concrete beams under free-vibration, Advances in Structural
Engineering – An International Journal, Accepted for Publication.

Salzmann, A., Fragomeni, S. and Loo, Y.C. (2002c) Estimation of the free-vibration
damping characteristics of untested reinforced concrete beams, Electronic Journal
of Structural Engineering, Submitted for Publication.

Salzmann, A., Fragomeni, S. and Loo, Y.C. (2001a) Verification of damping formulae
using experimental results from full-scale concrete beams reinforced with 500
MPA steel, The Australian Structural Engineering Conference, Surfers Paradise
Marriott Resort, Gold Coast, Australia, 29 April – 2 May 2001, pp. 95-102.

Salzmann, A., Fragomeni, S. and Loo, Y.C. (2001b) Investigation of damping in high-
strength prestressed concrete beams, The Eighth East Asia-Pacific Conference on
Structural Engineering & Construction, 5-7 December 2001, Singapore.

Salzmann, A. and Fragomeni, S. (2000) Experimental determination of damping from
full-scale reinforced and prestressed concrete beams, Civil Engineering
Challenges in the 21st Century, Queensland Civil Engineering Postgraduate
Conference, December 12-13, 2000, Physical Infrastructure Centre Queensland
University of Technology, pp 75-84.

Damping Characteristics of Reinforced and Prestressed Normal- and High-Strength Concrete Beams
Synopsis iv

S
ynopsis

In the last few decades there has been a significant increase in the design strength and
performance of different building materials. In particular, new methods, materials
and admixtures for the production of concrete have allowed for strengths as high as
100 MPa to be readily available. In addition, the standard manufactured yield
strength of reinforcing steel in Australia has increased from 400 MPa to 500 MPa.

A perceived design advantage of higher-strength materials is that structural elements
can have longer spans and be more slender than previously possible. An emerging
problem with slender concrete members is that they can be more vulnerable to loading
induced vibration. The damping capacity is an inherent fundamental quantity of all
structural concrete members that affects their vibrational response. It is defined as the
rate at which a structural member can dissipate the vibrational energy imparted to it.

Generally damping capacity measurements, to indicate the integrity of structural
members, are taken once the structure is in service. This type of non-destructive testing
has been the subject of much research. The published non-destructive testing research
on damping capacity is conflicting and a unified method to describe the effect of
damage on damping capacity has not yet been proposed.

Significantly, there is not one method in the published literature or national design
codes, including the Australian Standard AS 3600-2001, available to predict the
damping capacity of concrete beam members at the design stage. Further, little
research has implemented full-scale testing with a view to developing damping
capacity design equations, which is the primary focus of this thesis.

To examine the full-range damping behaviour of concrete beams, two categories of
testing were proposed. The categories are the ‘untested’ and ‘tested’ beam states.
These beam states have not been separately investigated in previous work and are
considered a major shortcoming of previous research on the damping behaviour of
concrete beams.

Damping Characteristics of Reinforced and Prestressed Normal- and High-Strength Concrete Beams
Synopsis v

An extensive experimental programme was undertaken to obtain residual deflection and
damping capacity data for thirty-one reinforced and ten prestressed concrete beams.
The concrete beams had compressive strengths ranging between 23.1 MPa and 90.7
MPa, reinforcement with yield strengths of 400 MPa or 500 MPa, and tensile
reinforcement ratios between 0.76% and 2.90%. The full- and half-scale beams tested
had lengths of 6.0 m and 2.4 m, respectively. The testing regime consisted of a series of
on-off load increments, increasing until failure, designed to induce residual deflections
with increasing amounts of internal damage at which damping capacity (logarithmic
decrement) was measured.

The inconsistencies that were found between the experimental damping capacity of the
beams and previous research prompted an initial investigation into the data obtained.
It was found that the discrepancies were due to the various interpretations of the
method used to extract damping capacity from the free-vibration decay curve.
Therefore, a logarithmic decrement calculation method was proposed to ensure
consistency and accuracy of the extracted damping capacity data to be used in the
subsequent analytical research phase.

The experimental test data confirmed that the ‘untested’ damping capacity of reinforced
concrete beams is dependent upon the beam reinforcement ratio and distribution. This
quantity was termed the total longitudinal reinforcement distribution. For the
prestressed concrete beams, the ‘untested’ damping capacity was shown to be
proportional to the product of the prestressing force and prestressing eccentricity.
Separate ‘untested’ damping capacity equations for reinforced and prestressed concrete
beams were developed to reflect these quantities.

To account for the variation in damping capacity due to damage in ‘tested’ beams, a
residual deflection mechanism was utilised. The proposed residual deflection
mechanism estimates the magnitude of permanent deformation in the beam and
attempts to overcome traditional difficulties in calculating the damping capacity during
low loading levels. Residual deflection equations, based on the instantaneous
deflection data for the current experimental programme, were proposed for both the
reinforced and prestressed concrete beams, which in turn were utilised with the
proposed ‘untested’ damping equation to calculate the total damping capacity.

Damping Characteristics of Reinforced and Prestressed Normal- and High-Strength Concrete Beams
Synopsis vi

The proposed ‘untested’ damping, residual deflection and total damping capacity
equations were compared to published test data and an additional series of test beams.
These verification investigations have shown that the proposed equations are reliable
and applicable for a range of beam designs, test setups, constituent materials and
loading regimes.

Damping Characteristics of Reinforced and Prestressed Normal- and High-Strength Concrete Beams
Table of Contents vii
T C
able of ontents

Declaration ....................................................................................................... i
Acknowledgements .......................................................................................... ii
List of Publications .......................................................................................... iii
Synopsis ............................................................................................................ iv
Table of Contents ............................................................................................ vii
List of Figures .................................................................................................. xi
List of Tables ................................................................................................... xv
List of Plates .................................................................................................... xvi
Notation ............................................................................................................ xvii

CHAPTER

1. Introduction ..................................................................................................... 1-1
1.1 General Remarks ................................................................................... 1-1
1.2 Research Objectives .............................................................................. 1-2
1.3 Research Methodology ......................................................................... 1-2
1.4 Layout of the Thesis .............................................................................. 1-3
1.5 Summary ............................................................................................... 1-4

2. Damping in Concrete ....................................................................................... 2-1
2.1 General Remarks ................................................................................... 2-1
2.2 Undamped Systems ............................................................................... 2-2
2.2.1 Single-DOF and multi-DOF structures .................................. 2-2
2.3 Damped Systems ................................................................................... 2-4
2.3.1 The idealized MDOF system ................................................. 2-4
2.3.2 Viscous damping .................................................................... 2-5
2.3.3 Coulomb damping ..................................................................2-11
2.3.4 Hysteretic damping ................................................................2-12
2.3.5 Equivalent viscous damping ..................................................2-14
2.4 Experimental Determination of Damping .............................................2-15
2.4.1 Free-vibration damping ..........................................................2-15
2.4.2 Forced excitation damping .....................................................2-16
2.4.2.1 Half-power (bandwidth) method ...............................2-17
2.4.2.2 Resonant amplification .............................................2-17
2.4.2.3 Energy loss per cycle ................................................2-18
2.5 Literature Review of Damping in Concrete............................................2-21
2.5.1 Material damping.....................................................................2-21
2.5.2 Member damping.....................................................................2-24
2.5.3 Structural damping...................................................................2-32
2.6 Summary ...............................................................................................2-34

3. Theoretical Consideration ............................................................................. 3-1
3.1 General Remarks ................................................................................... 3-1
3.2 Pilot Study............................................................................................... 3-1
3.2.1 Verifying the accuracy of logdec ........................................... 3-2

Damping Characteristics of Reinforced and Prestressed Normal- and High-Strength Concrete Beams