Ảnh hưởng của tường chèn tới phản ứng của hệ khung bê tông cốt thép chịu động đất tt tiếng anh

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

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

1

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: αm = h m /l m≤ 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

2

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 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

non-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

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

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1.3.1.2 Micromodels

Based on finite element methods (Figures 1.13 and 1.14)

1.3.1.3 Remarks: The

single strut macromodels

are simple, easy to apply

They give approximate

results, but no results for

local effects The

accurate, but calculation

volume is large and it is difficult to determine the model's parameters

1.3.2 Main results achieved in macromodeling

1.3.2.1 Results achieved in determining the diagonal width w m

The following authors

have given the expressions

Dowling [1/6] (1988), Smith and Coull [1/10] (1991), Paulay and Priestley [0.25] (1992), Angel et al [1/8] (1994), Fardis [0.1÷0.2] (2009),

etc (The values in [] indicate the proposed w m /d m ratios)

b) The approaches for determining w m depend on both the geometric and mechanical properties of frames and MIs:

in this way: Mainstone (1974); Abdul-Kadir (1974), Henry (1998);

Nguyen Le Ninh (1980); Bazan and Meli (1980); Liauw and Kwan (1984); Decanini and Fantin (1986); Govindan (1986); Dawe and Seah (1989); Decanini et al (1993); Durrani and Luo (1994); Flanagan and Bennet (2001); Al-Chaar (2002); Tucker (2007); Amato et al (2009); Tabeshpour et al (2012); Chrysostomou and Asteris (2012); Turgay et al (2014), etc

2 In Vietnam:

Ly Tran Cuong (1991) and Dinh Le Khanh Quoc (2017) proposed the

Figure 1.13 Mallick Figure 1.14 Mehrabi

and Severn’s model and Shing’s model

Figure 1.9 Chrysostomou’s Figure 1.10

model El-Dakhakhni’s model

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3 Remarks on the results achieved in determining w m :

properties of components of infilled frames; (ii) The degree of

Among the proposed methods, the method proposed by Nguyen Le Ninh (1980) can be applied to consider all the above factors

1.3.2.2 Results achieved in establishing a simple nonlinear behavior model

of MIs

Many authors

studied this model:

Decanini, Bertoldi and

1.4 EFFECTS OF FRAME-MI INTERACTION IN THE SEISMIC STANDARDS

1.4.1 The rules take into account the influence of MIs

TCVN 9386:2012 and EN 1998-1:2004; FEMA 356 (2000); ASCE 41-13 (2013) and ASCE 41-17 (2017); NZSEE (2017) provided the rules

to consider the effects of MIs on behavior of RC frames under seismic action

1.4.2 Remarks on the rules in the design standards

• All standards state that MIs have detrimental effects on the frames, but they separate the local response calculation from the overall calculation The design rules of beams, columns and beam-column joints

do not take into account the influence of interactive forces with MIs, but when examining the columns in shear, this interactive forces must be considered

• When calculating the local response, the standards require the use of

a single diagonal strut model, but there are no instructions on how to set the model (especially TCVN 9386:2012), so it is difficult to implement

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and shear failures either at the ends or in the middle of columns; beams are often increased in stiffness, and MIs are often failed by sliding shear along the diagonal or in the midheight of MI and diagonal compression

2 The simple model using an equivalent diagonal strut is relevant to determine the overall response of the infilled frames

3 While recognizing the important influence of the frame-MIs interactive forces, the standard design regulations of infilled frames are still inadequate and unclear

CHAPTER 2 MODELING OF NONLINEAR BEHAVIOR OF MASONRY INFILLED RC

FRAMES UNDER SEISMIC ACTIONS 2.1 SELECTING THE METHODS TO MODEL MASONRY INFILLED RC FRAMES

From the literature review, the following models are selected for the analysis of infilled frames: a simple model to simulate bending behavior

in critical regions of the RC frame and the equivalent diagonal strut model

to simulate the behavior of MIs

2.2 BEHAVIOR MODEL OF THE RC FRAMES

2.2.1 At the material level: Use the behavior models of concrete and

reinforcement specified in EN 1992-1-1:2004

2.2.2 At structural element level: Use the concentrated-plasticity

modeling approach The behavior of plastic hinges is controlled through the modified Takeda model and its force-displacement curve is taken according to ASCE 41-13 (Figure 2.2)

a) b) c)

Figure 2.2 a) Plastic b) The modified Takeda c) Generalized M–θ deformation concentrated hysteresis rule relationship at plastic

on the frame components hinges of RC frame components

2.3 ESTABLISH THE NONLINEAR BEHAVIOR MODEL OF THE MIs IN

RC FRAMES

2.3.1 Setting up the force-displacement relationship of the model

The behavior of the MIs in the frame is modeled as a curve shown in Figure 2.3 In the frame model, the MIs are shown in Figure 2.4

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2.3.2 Define the basic parameters of the model

2.3.2.1 The stiffness of MIs

According to Nguyen Le Ninh (1980), the widthw m =e m(1−n)w m0 (2.1) with

0

m m

h l

d w

time when MI reaches the ultimate strength; m and k are coefficients

depending on the type of masonry; other parameters indicate the geometric and mechanical properties of frames and MIs (Figure 1.8)

of the crack (2.4) and when reaching to the ultimate strength (2.5):

0.4

2 0

2.3.2.2 The strength of the MIs

1 The ultimate strength of masonry infill V mu is determined from the

condition V mu =min(V ms,V mc)(2.6), where:

a) V ms is the sliding shear strength of MIs selected from approaches of

following authors: Rosenblueth (1980); Smith and Coull (1991); Paulay and Priestley (1992); Decanini et al (1993); Panagiotakos and Fardis (1994), Fardis (2009); Zarnic and Gostic (1997); FEMA 356 (2000), Al-Chaar (2002), ASCE 41-06, ASCE 41-13; Galanti et al (1998), EN 1998-1:2004; FEMA 306 (1998); EN 1996-1-1:2005; according to TCVN 5573:2011 (2.10)

1

1 0.72

bs m m ms

f t l V

n tgµ θ

=

− (2.10)

Figure 2.3 The force-displacement relationship Figure 2.4 Position of plastic

of the MI’s behavior model hinges in the model of infilled frames

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b) V mc is the diagonal compression strength of MIs selected from

approaches of following authors: Smith and Coull (1991); Decanini et al (1993); Galanti et al

(1998); FEMA 306;

Al-Chaar (2002); Tucker

(2007); ASCE 41-13

In order to select the

appropriate strengths for

MI’s model, comparative

analyses are performed on

the infilled RC frame

consistent with the object

and objectives of the

research The results are

the curves representing

relationships of V ms and

h m /l m ratios of MIs in Figures 2.9

and 2.10 Since then, choose the

3 The residual strength of

the masonry infill V mr :

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2.3.2.3 Steps to establish the force-displacement curve of the model

Step 1 Determine K my using (2.4) Step 2 Determine V mu using (2.6)

Step 3 Determine ∆ =mu V mu K mu∗ (2.14) Step 4 Determine V my using

using (2.13) Step 7 Determine

mr mu V mr V mu K mr

2.3.2.4 Axial nonlinear response of

equivalent diagonal strut

relationship of masonry proposed by

Kaushik, Rai and Jain (2007) (Figure

2.3.3.1 Kakaletsis and Karayannis (2008)

Based on the parameters of the

experimental models, we establish the

behavior models of the MIs based on the

steps in section 2.3.2.3 (Figure 2.16)

Using these models together with the

behavior models of the RC materials and

structural elements selected in section

2.2, performing a nonlinear pushover

analysis of the experimental frame

models The capacity curves obtained

from analyses are compared with the

envelopment (Figure 2.18) The results

show a good fit between them

Figure 2.18 Comparison between

experimental results and analytical results using the proposed method

a) Weak MI (S) b) Strong MI (IS)

Figure 2.16

Force - displacement relationship of the proposed MIs’ models

Figure 2.13 Idealized stress-strain

relationship for masonry under uniaxial compression

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2.3.3.2 Morandi et al (2014-2018)

Figure 2.20 Force - displacement

relationship of the proposed MI’s

model

Similarly, set up a behavior

model of the MI using the

proposed method (Figure 2.20)

and perform a nonlinear pushover

analysis of the experimental frame models The results show that the capacity curves obtained from the analyses are quite consistent with the experimental envelopment (Figure 2.21)

2.4 REMARKS ON CHAPTER 2

A simple model is established to simulate the behavior of the MIs in

RC frames taking into account the decrease in strength and stiffness of frame and MIs The verification results on the infilled RC frame models designed according to the current seismic conception exhibit good results

So, the calibration of the model is not necessary

CHAPTER 3 EFFECTS OF MASONRY INFILLS TO THE CONTROL OF THE FAILURE MECHANISM OF RC FRAME STRUCTURES UNDER SEISMIC ACTIONS 3.1 MODERN CONCEPTION AND DESIGN RULES FOR FRAMES IN THE CURRENT SEISMIC DESIGN STANDARDS

3.1.1 Modern conception in design of structures for earthquake resistance

According to the current seismic conception, the design purpose of a building is to protect directly both human life and social properties When

a strong earthquake occurs, the buildings are allowed to work beyond the elastic limit, but they are not collapsed suddenly

3.1.2 Basic design principles according to modern seismic conception

From the aforementioned goals, the structure must be designed to experience plastic failure, and shear failure must happen after flexural failure when a strong earthquake occurs

Figure 2.21 Comparison between experimental results and analytical results using the proposed method

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3.1.3 Design RC frames according to current seismic standards

To carry out the above design principles, the capacity design method

is used By using this method, the forces used to design a frame must be

as follows, for example, according to TCVN 9386:2012 (the “so-called” basic design principle of strong columns - weak beams):

a) Beam: The bending moment M and the axial force N are taken from

the results of structural analysis, while the shear force Q is determined

from the bending resistance of the beam

b) Column: The bending moment M is redefined from the following

condition:

∑M Rc ≥1.3∑M Rb (3.1)

resistances of the columns framing to the joint, taking into account the

the design values of the moment resistances of the beams framing to the joint

Shear force Q is redefined from the flexural strength of columns Remarks: (i) The frame design process must follow a very strict

process; (ii) Frame design rules do not take into account frame-MI interaction

3.2 EFFECTS OF MIs TO THE BEAM RESPONSE

Experimental studies on the infilled frames show that the interactive forces with the MIs make the beams behave more stiffly than that of bare frames To clarify this phenomenon, consider a RC frame without MI

(bare frame) as shown in Figure 3.2a The external force H causes the

bending moment at the ending section C of the beam:

I h

I l

a) Bare frame; b) Infilled frame; c) Equivalent infilled frame

Figure 3.2 Models for calculation of the frame

The curvature of the beam at the end C has the following value:

ω

+ (3.4)