‘Seismic Analysis and

Response of Bare Vs. Masonry

In-filled Frame Structures’

Researcher: Mr Constantinos Chris Andreou

BEng, MSc Civil- Subsea Graduate Engineer

RESEARCH PROPOSAL Several countries lie in areas susceptible to earthquakes and their structures

need to be designed to withstand seismic loads.

Infill panels are not considered in the design process but treated as

architectural (non-structural) components.

This study assessed the seismic performance of RC buildings by utilizing

dynamic analysis to obtain predictions of the infill panels used in their design.

The present study may assist in reducing risks of collapsed structures in case

of earthquake disasters

‘ B a r e f ra m e a n d M a s o n r y I n - f i l l e d s t r u c t u r e s ’

Research AIMS and OBJECTIVES To analyse and demonstrate the importance of masonry

infill walls against seismic loads.

To compare the available seismic design methods

proposed by Structural Eurocodes.

Research on structural seismic performance.

Evaluation of structural seismic performance of buildings using

linear structural analysis methods proposed by Structural Eurocodes

Estimation of Masonry Infill Stiffness.

Comparison of Bare and Infilled framed structure using analytical

and computer techniques.

PROPOSED MODELS FOR ANALYSIS

Bare Frame

Partially-Infilled

Fully-Infilled

Masonry infill configurations modelling

o Medium Class Ductile

Reinforced Concrete

o Regular building in Plan

and Elevation

o 6 Stories with known

heights

o 4 x 4 Frames

METHODS OF SEISMIC RESPONSE ANALYSIS

The following two types of linear-elastic analysis were contacted:

I. Equivalent static method {Lateral Force Method}

o The system response is derived by applying equivalent lateral seismic

load to the model.

o These lateral forces are applied as static loads at the position of

concentrated mass of the structure at each floor.

II. Response Spectrum Method

o Is one of the most popular methods in modern earthquake engineering.

o Offers logical results and it is more economical.

o Requires the determination of a response spectrum from measured seismic

activity.

‘Spectral

acceleration against

Periods’

MASONRY INFILL STIFFNESS VERIFICATION

Infill Wall panels are not included in structural design

Such assumption may lead to inaccurate approximation of strength,

ductility and stiffness of concrete framed buildings.

‘Research has proved that the i n f i l l s y s t em behave as a braced

frame with the wall forming ‘co m pre s s i o n s t ru t s ’

Equivalent diagonal compression ‘STRUT’

MASONRY INFILL STIFFNESS VERIFICATION {cont’d}

Infill walls replaced by Equivalent Diagonal Strut.

By determinate the diagonal strut AREA using the brick and masonry

properties, the stiffness of the wall were estimated.

Z= 0.175 [ λ . ℎ)− 0.4] dm

𝐀𝐞 = 𝐙 . 𝐭

λ =4 𝐸𝑚 . 𝑡𝑚 . 𝑠𝑖𝑛 (2θ)

4 . 𝐸𝑓. 𝐼𝑐 ℎ𝑚

Area of STRUT = Width (Z) x Thickness

SLIDING and COMPRESSION SHEAR failure

DISPLACEMENT AT YIELDING

Initial wall Stiffness = 2 x [Min. Initial shear / Displacement](Madan et al., 1997)

(Das and Murphy,2004)(Mainstone,1971)

MASONRY INFILL STIFFNESS VERIFICATION

There are many investigations and proposed verifications of masonry infill stiffness

that impediment to a reliable modeling

Limited amount of research has been undertaken on Infilled frames with openings

The initial stiffness of the masonry infill panel was defined and used in linear-elastic

analysis methods

RESULTS TAKEN FROM BARE FRAME AND MASONRY INFILL CASE WERE COMPARED

• Masonry Infilled Frames and their Seismic Behaviour at Structures

Increase Stiffness of structures

The fundamental period is decreased

The Base Shear is increased

The structural system is more reliable at seismic action as part of the load is

consumed by the infills

Energy capacity of the structure is significantly increased

RESEARCH DELIVERABLES

Comparison of

Displacements of Bare

and Infill cases

Distribution and Comparison of Results

Comparison of Seismic Analysis Methods

BASE SHEAR (KN)

MODEL T = Ct x H3/4 T = 2.(d)^0.5

Bare Frame 373.3 472.60

Partially Infilled F. 373.3 601.50

Fully Infilled 373.3 696.50

o Equivalent Static method

1. Carried out in less time by doing few and simple calculations

2. Temporal variations were neglected.

3. Considers only maximum possible responses.

4. Gives an initial idea for magnitude that will be acted due to a possible earthquake.

1) Consider the Height

2) Lateral elastic

displacement (F / k)

Can be used for preliminary design situations and for buildings up to

10 storey as mentioned by EC8.

0100200300400500600700800900

Bare Frame PartiallyInfilledFrame

Fully InfilledFrame

Equivalent static method(T =2.(d)^0.5)

472.613 601.507 696.482

Response spectrum method 560.82 732.42 819.96

BA

SE S

HEA

R (

KNEquivalent static

method(T =2.(d)^0.5)

Response spectrummethod

o Response Spectrum method

Comparison of Seismic Methods {cont’d}

1. Approximates better the fundamental period of vibration (T)

2. Yields more accurate and responsible results

3. Involves simplifying assumptions

4. Errs on the side of safety

Difference varies

from 15 - 18 %

Response spectrum analysis provides significant information about real-world

applications when considering a linear, elastic system that is exposed to a forcing

function (earthquakes).

WASTE OF MATERIALS

equal to

15 - 18 %

Infill Panels Behaviour

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 1 2 3 4 5 6

MA

XIM

UM

DIS

PLA

CEM

EN

T (

mm

)

FLOOR LEVELS

Bare Frame

Partially Infilled Frame

Fully Infilled Frame

Design Codes should NOT neglect the effects of masonry infills

• 2 Times smaller

(Increase in stiffness)

• P.I.F displacement at first and

second floor is bigger compared

to B.F

(Presages Soft storey effect)

• F.I.F has very small storey

displacements

(presence of infill walls)

o Displacement

o Measured Envelope of Base Shear Vs. Displacement

0

20

40

60

80

100

120

140

160

180

200

0 1 2 3 4 5

BA

SE S

HEA

R (

KN

)

DISPLACEMENT (mm)

Fully Infilled Frame

Partially InfilledFrame

Bare Frame

Maximum

Displacements

at TOP storeys

BASE SHEAR (KN)

Story Bare Frame Partially Infilled

Frame

Fully Infilled

Frame

0 0 0 0

1 47.441 93.539 77.437

2 60.745 105.405 103.375

3 81.244 122.396 134.377

4 97.656 135.562 158.472

5 123.54 140.127 171.972

6 127.058 133.264 166.855

ΣFBi 537.7 732.4 812.5

• F.I.F presented to be

34% stronger compared

to B.F

• P.I.F presents 26%

difference from B.F

• Higher amount of Shear

force is needed to

displace equal each

models top storey.

*An estimation of the overall

ductility demand can be obtained.

COMPUTER COMPUTATION TECHNIQUES

Using SAP 2000 the RESPONSE SPECTRUM ANALYSIS was carried

out for Bare model case.

Results were compared to analytical results

SAP 2000 (Linear Dynamic Procedure)

Model simulation

o SAP 2000 {cont’d}

Story SAP 2000 ANALYTICAL

1 10.3 0.178 0.27

2 18.48 0.319 0.38

3 27.9 0.481 0.527

4 37.19 0.642 0.647

5 50.19 0.866 0.881

6 57.96 1 1

T (s) 0.476 0.488

Story DISPLACEMENT

0 ANALYTICAL SAP 2000 Percentage

difference (%)

1 1.118 1.5 25

2 1.576 2.63 40

3 2.185 3.78 42

4 2.682 4.8 44

5 3.654 6.07 40

6 4.147 6.91 40

Base Shear

537.7 363.9 47

The large percentage difference caused

from:

• The different method of structural element’s

stiffness calculation .

• The reduction moment of inertia at beams

and columns equal to33% and 50%

respectively.

There is only a 4% variation of results at first vibration mode

Vibration mode shapes

The behaviour of infill frames depends on the properties of infill and

frame.

The proposal analytical procedure can be implemented in the design and

used by available computational tools.

Infilled frames can be improved by applying recommended guidelines

during their construction to achieve a better behaviour.

The non-structural infills walls can change the global seismic behaviour

of framed buildings

Masonry infill walls have major influence to the structure’s performance

ALL project Deliverables were PROVED…

CONCLUSION

REFERENCES

I. Structural Eurocodes, 2010. ‘Extracts from the

Structural Eurocodes for students of structural design’.

Third edition.

II. Thesis on ‘Seismic Analysis and Response of Bare and

Masonry In-filled Reinforced Concrete Frame

Structures’.

III. ‘Literature Survey Report’ of thesis.