ANALISIS OF INFILLED FRAME STRUCTURES
Universidad Nacional de CuyoArgentina
Francisco Crisafulli
SEMINAR ONMASONRY AND EARTHEN STRUCTURES
Universidade do Minho
Analysis of infilled frames. Why?
• New buildings, in some countries.• Old buildings that need to be retrofitted.
Argentina VenezuelaPortugal
Infilled frames
NEESR-SG: Seismic Performance Assessment and Retrof it of Non-ductile RC Frames with Infill Walls. University of California San Diego, University of Colorado at Boulder and Stanford University. http://infill.ucsd.edu/
Infilled framesDynamic test of a 3-storey RC infilled frame in Italy. Project NEARB - OPCM 3274. EUCENTRE, Pavia.
Analysis of infilled frames
In order to develop adequate and rational models we need to understand de structural response of infilled frames.
• Masonry : composite material (bricks or blocks and • Masonry : composite material (bricks or blocks and mortar joints).
• Reinforced concrete (or steel) frame .
• Panel-frame interfaces .
Structural response
80
100
120
V (
kN)
Integral infilled frame
Non-integral infilled frame
0
20
40
60
0 2 4 6 8 10 12 14 16 18 20
Bas
e sh
ear,
V (
Lateral displacement, ∆∆∆∆ (mm)
Initial Slackness
Bare frame
Structural responseB
ase
sh
ea
r
Lateral displacement
Ba
se s
he
ar
Separation starts
Structural response
Lateral displacement
Ba
se s
he
ar
Craking of masonry
Separation starts
Structural response
After separation, the structure behaves as a truss in which the masonry wall can be approximately represented by a compressive strut.
Structural response
Internal forces in the reinforced concrete frame
(a) Bending moment (b) Shear force
(c) Axial force
Structural responseB
ase
sh
ea
r
Yielding of thereinforcement
Lateral displacement
Ba
se s
he
ar
Craking of masonry
Separation starts
Structural response
Ba
se s
hea
r
Yielding of thereinforcement
Lateral displacement
Ba
se s
hea
r
Craking of masonry
Separation starts
Degradation
Structural response
The structural response is very complex and usually 4
different stages can be distinguish:
• Initial stage. Monolithic wall
• Cracking masonry.
• Yielding of the reinforcement.
• Degradation.
Truss mechanism
The wall partially separates from the frame.
The frame restrain the shear deformation of the masonry wall.
Partial separation at the panel-frame interfaces
Types of failure
Damage or failure of the masonry panel:• Shear-friction failure• Diagonal tension failure• Compressive failure
Types of failure
Damage or failure of the masonry panel:• Shear-friction failure• Diagonal tension failure• Compressive failure
Types of failure
Damage or failure of the masonry panel:• Shear-friction failure• Diagonal tension failure• Compressive failure:
1. Failure of the diagonal strut2. Crushing of the corners,.2. Crushing of the corners,.
Types of failure
Failure modes of the RC frame:
Flexural plastic mechanism
Failure due to
Plastic hinges at span length
Yielding of the reinforcement
Plastic hinges at member ends
Shear failure of the columns
Failure due to axial loads
Beam-columnjoints failure
Bar anchorage failure
Yielding of the reinforcement
Sliding shear failure
Silakhor Earthquake, Iran. March 2006 (Moghadam, 2006).
Chile Earthquake. March 1985.
Sliding shear failure
α cos f A = V ystc
At the ultimate stage, limited experimentalevidence indicates that the dowel action ismainly caused by to the kinking mechanismin the longitudinal reinforcement.
EERI, Confined Masonry Design Group. http://www.confinedmasonry.org/
Analysis of infilled frames
Infilled frames are complex structures which exhibit a highly nonlinear inelastic behaviour, This fact complicates the analysis and explains why infill panels has been considered as "non-structural elements", despite their strong influence on the global response.
Modelling techniques:
• Refined or micro-models: based on the use of many elements (usually different types).
• Simplified or macro-models: diagonal strut model (with single or multiple struts.
Analysis of infilled framesRefined finite element models
P. Shing, 2007)
Analysis of infilled framesRefined finite element models
P. Shing, 2007)
Analysis of infilled frames
Finite element models with ABAQUSS
Elements:
• RC frame• RC frame• Masonry• Interfaces
Analysis of infilled framesFinite element models with ABAQUSS
Maximum load
Maximum displacement
Analysis of infilled framesNEESR-SG: Seismic Performance Assessment and Retrof it of Non-ductile RC Frames with Infill Walls.
Maximum load
Maximum displacement
Equivalent strut model
The equivalent strut model was suggested by Poliakov and implemented by Holmes and Stafford Smith in the 1960s.
Later, many researchers improved the model. Today the strut model is accepted as a simple and rational way to represent the effect of the masonry panel.
A ms
msA /2
msA /2
msA /4
A /4ms
A /2ms
Macro-model for inelastic analysis
Panel element based on rational considerations of infill behavior.
Advantages and limitations.
Implemented in RUAUMOKO and SeismoStruct
Struts
Shear spring
Macro-model for inelastic analysis
(3 dof)
(3 dof)1
3
v
External node
Internal node h z
43
2
4
uϕ
Truss mechanism
Dummy node(2 dof)
h z
1
2θθθθ1111
θθθθ2222
Macro-model for inelastic analysis
Hysteretic behavior of the strut under axial load.
Axi
al s
tres
s, f
m
' θmf
Axial strain, εεεεm
Macro-model for inelastic analysis
43
u
vϕ
Shear mechanism
1
2
Macro-model for inelastic analysis
Hysteretic behavior of the shear springττ ττ
τmax
τo Bond failure
Shear strain, γγγγ
She
ar s
tres
s,
ττ ττ
Gm Gm
−τmax
Macro-model for inelastic analysis
100
Late
ral F
orce
(kN
)
Displacement history. Pushver analysis
-100
0-45 0 45
Lateral displacement (mm)
Late
ral F
orce
(kN
)
Resultados experimentales
Resultados analíticos
Experimental resultsSimulation
fn
fp
ττττ
Evaluation of the masonry strength
1. Evaluate the strength of masonry under shear and compression, based on geometrical and mechanical properties of the materials.
2. Calculate the compressive strength of masonry in the direction of the diagonal strut.
msmc AfR ' = θ θθθθ
Evaluation of the strength
Masonry strength under shear and compression:
Modified Mann-Müller Theory
ττττm
Mohr-Coulomb criterion
fnShear-frictionfailure
Diagonal tensionfailure
Compressivefailure
f'm
τoµ∗
f'to
τ∗
o
1
Evaluation of the strength
Strut compressive strength (for different angles)
6
7
8
mθθ θθ
(MP
a)
0
1
2
3
4
5
20 30 40 50 60 70
Com
pres
sive
stre
ngth
, f'
m
Angle θ θ θ θ (degs)
Shear-friction failure
Diagonal tensionfailure
Proposed macro-model
Shear and axial springs
masonry struts
Shear and axial springs :
• Hysteretic behavior.
• Axial-shear interaction.
PhD thesis Mr. G. Torrisi.
Conclusions
� The strut model gives an adequate estimation of the stiffness of the infilled frame and the axial forces induced in the surrounding frame.
� Refined finite element models may represent adequately the structural response, provided that adequately the structural response, provided that the model is properly calibrated.
� Refined model are difficult to apply in the case of multi-storey buildings.
Conclusions
� Multi-strut macro models represents a compromise solution and they can be use for the analysis of large structures.
� The main uncertainties in these models are the area of the struts and their strength.area of the struts and their strength.
Simplicity that is based on rationality is the ultimate sophistication.S. Veletsos
Thank you for your attention
IMERIS
Universidad
Nacional de Cuyo
Influence of the loading system
(a) Pushing load (b) Pulling load
New reinforcement details proposed to improve the structural response of confined masonry (Crisafulli, 1997; Crisafulli, Carr and Park 2000).