MINISTRY OF EDUCATION AND TRAINING
NATIONAL UNIVERSITY OF CIVIL ENGINEERING
Phan Van Hue
EFFECTS OF MASONRY INFILLS ON THE
RESPONSES OF REINFORCED CONCRETE FRAME
STRUCTURES UNDER SEISMIC ACTIONS
Major: Civil Engineering
Code: 9580201
SUMMARY OF DOCTORAL DISSERTATION
Ha Noi - 2020
The Dissertation has been completed at
the National University of Civil Engineering
Academic advisor: Assoc. Prof. Dr. Nguyen Le Ninh
Examiner 1: Prof. Dr. Nguyen Tien Chuong
Examiner 2: Assoc. Prof. Dr. Nguyen Ngoc Phuong
Examiner 3: Dr. Nguyen Dai Minh
The doctoral dissertation will be defended before Doctoral Defence
Committee held at the National University of Civil Engineering at
……… on ……………….…………, 2020.
This Dissertation is available for reference at the Libraries as
follows:
- National Library of Vietnam
- National University of Civil Engineering’s Library
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PREFACE
1. REASON FOR SELECTING THE TOPIC
Earthquake researches and engineering site observations over the past
seven decades show that masonry infills (MIs) significantly affect
response of the surrounding frame structures under seismic actions. The
modern seismic standards, including TCVN 9386:2012, admit this
phenomenon, but the design regulations for the infilled frames still have
many shortcomings:
(i) Conflicts between design of the whole structure (ignoring the
interactive forces with the MIs) and design of structural members locally
(considering the interactive forces with the MIs);
(ii) The models to calculate the infilled frames are unclear and
uncompleted.
Therefore, the study on "Effects of masonry infills on the responses of
reinforced concrete frame structures under seismic actions" is necessary
and meaningful.
2. RESEARCH PURPOSES
(i) To establish the behavior model of the MIs and to employ this
model to determine the seismic behavior of infilled frames;
(ii) To study how to control the failure mechanisms of reinforced
concrete (RC) frames under seismic actions, considering the interaction
between the frame and the MIs;
(iii) To study the effects of the MIs on the control of the local response
of RC frame columns under seismic actions.
3. RESEARCH OBJECTS AND SCOPE OF WORK
3.1. Research objects
Multi-storey monolithic RC frames with MIs in the frame plane:
(i) The frames are designed according to the modern seismic
conception;
(ii) Unreinforced MIs (solid and hollow clay bricks, AAC bricks)
without openings are constructed after the hardening of the RC frames.
The MIs are in contact with the frame (i.e. without special separation
joints) but without a structural connection to it.
3.2. Scope of work: (i) Impacts are in the frame plane;
(ii) The aspect ratio of MIs:
α
m = hm/lm ≤ 1.0
4. SCIENTIFIC BASIS OF THE TOPIC
(i) Research results of infilled frames in the last seven decades;
(ii) The modern seismic design conception;
(iii) Regulations on designing the RC frames subjected to earthquakes
in some common building codes worldwide, including Vietnam.
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5. RESEARCH METHODOLOGY
Theoretical research and numerical simulation analysis are used.
6. NEW CONTRIBUTIONS OF THE DISSERTATION
(i) Established the nonlinear behavior model of the MIs and employed
this model to determine the seismic behavior of infilled RC frames;
(ii) Established the condition to control failure mechanisms of the RC
frames and proposed the method to design RC frames when considering
the interaction with the MIs based on the modern seismic design
conception;
(iii) Proposed a method to determine the interactive forces between
the frame and the MIs as well as a method to design RC frame columns
in shear considering these interactive forces.
7. LAYOUT OF DISSERTATION
The thesis consists of preface, four chapters, and conclusions,
presented in 116 pages with 29 tables, 55 figures, 149 references
(Vietnamese: 10, English, Romanian: 139). The appendix has 21 pages.
CHAPTER 1
INTERACTION BETWEEN FRAMES AND MASONRY INFILLS AND
DETERMINATION OF RESPONSES OF THE MASONRY INFILLED RC
FRAMES UNDER LATERAL IMPACT
1.1. INTRODUCTION
Contrary to the previous conception that considers MIs as non-
structural elements, the field observation results showed that MIs are the
cause of failures: columns, beam-column joints, and the collapse of
buildings, etc. under seismic action. This issue has attracted many studies
worldwide.
1.2. INTERACTION BETWEEN FRAMES AND MASONRY INFILLS AND
BEHAVIOR OF MASONRY INFILLED RC FRAMES UNDER LATERAL
IMPACT
1.2.1. Interaction between frames and MIs under lateral impact
The behavior of MIs in the frames
under lateral impact can be divided
into two stages. At the first stage,
before the frame-MI contact surfaces
are cracked, the structure behaves like
a monolithic vertical cantilever; and at
the second stage after the contact
surfaces are cracked at the unloaded
corners (Figure 1.3a). In the remaining
contact regions, interactive forces appear (Figure 1.3b).
a) b)
Figure 1.3. The behavior of MI RC
frames and interactive forces in the
contact regions
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1.2.2. Consequences of frame-MI interaction for the behavior of MI RC
frames
1.2.2.1. RC frames are designed not according to the seismic standards
The impact of the frames-MIs interaction forces has resulted in failure
of MIs and of the frame components.
1. Types of failure in MIs: (i) Shear cracking (cracking along mortar
joints, stepped cracks or horizontal sliding; diagonal cracks); (ii)
Compression failure (failure of the diagonal strut; corner crushing).
2. Types of failure of RC frames: (i) Flexural failure (at member ends;
in span length); (ii) Failure due to axial force (yielding of the longitudinal
reinforcement; bar anchorage failure); (iii) Shear failure of columns; (iv)
Beam-column joint failure.
1.2.2.2. The RC frames are designed according to modern seismic
standards
The extensive experimental researches by the authors: Mehrabi et al.
(1996), Kakaletsis and Karayannis (2008), Morandi et al. (2014-2018),
Basha (2017) gave the failure types as follows:
1. Types of failures in MIs: Strong MIs-strong frames: diagonal sliding
shear and compression failure. Weak MIs-strong frames: sliding shear
failure along the diagonal or in the midheight of MIs.
2. Types of failure of RC frames:
a) Column: Plastic hinges appear at the ends of columns; shear cracks
occur simultaneously with flexural cracks.
b) Beams: Flexural and shear cracks rarely appear. Frame beams
behave more stiffly when considering the interaction with MIs.
1.3. MODELING OF BEHAVIOR OF MIs UNDER LATERAL LOADING
1.3.1. Behavior models of MIs in frames
1.3.1.1. Macromodels
Replace MIs with one or
more equivalent diagonal
struts.
1. Single-strut models
(Figure 1.8): parameters of
diagonal struts: width wm and
thickness tm (tm is equal to
MI’s thickness).
2. Multiple-strut models:
Divide a diagonal strut into
multiple equivalent struts (Figures 1.9 and 1.10).
a) Deformation due to b) The equivalent diagonal
lateral force strut model
Figure 1.8. The equivalent diagonal strut model