Effect of Contact between Infill and Frame on the Behaviour of infilled Multistorey Frames

Dr.H. ACHYUTHA Assistant Professor, Structural Engineering Laboratory Indian Institute of Technology, Madras, India.

R.JAGADISH Lecturer, Faculty of Engineering - Civil Bangalore University, Bangalore. (Formerly Research SCholar, Structural Engineering Laboratory, Indian Institute of Technology, Madras)

S.S. RAffJ.AN Formerly Post-graduate student. Structural Engin~ering Labor~tory Indian Institute of Technology, Madras, India.

Summary - The composite action between infill and frame is D function of the degree of tight-fit or the length of contact "at the interface of infill and frame. The effect of type of contact between infill and frame on the behaviour of muI tistorey infilled frames is studied. Four different types of contacts are considered. For the analysis, 'simplified frame work me thod' is used. It is concluded that if there has to be composite action between the infill and the frame there has to be good contact atleast between the infill and the beam portions of the frame.

574

1. INTRODUCTION

l /i th the present knowledge of infilled fr ames, it is well established that the addition of walls a s infills improve consiJerably the strength ~nJ stiffness of a fr ame building [1-3]. This is due to the composi t e action between the infill and the frame. This compos ite 3cti on is a functi on of the degree of tight fit or the l eng th of contJct betwee n the infill and the frame . Some c onstructi on proccdures like providing shear conne ctors a t the inte rface of frame and infill or casting of concre t e me mbe rs directly on brickwork have Peen sugge sted by some earlie r investiga t ors.

In an infilled ·frame, there are f .QUI interfaces between the infill and the frame. The behaviour of infilied fr~me will be influc nce d by whether good contact ha s been provided a t alI the f our inte rfaces or at few interfaces only. Thi~ pa per reports the salivnt results of a study ma de on infillcd frame s with different types of contact be tween the infill and the fr ame [4]. F0ur categories of c ontact have bee n conside red in the present study.

2. TYPES OF CONTACT

Four categories of contacts along th c interfaces of fr ·Jmc and infill are considered as sh own in Fig .1.

1. Contact on alI the four inte rfaces of infill ~nd frame . 2. Contact along the supporting beam and two column

interface s. 3. Contact along the top and the supp orting be~m inte r­

f aces only, and

4. Contact a l ong the supporting beam inte rfa ce only.

3. TYPES OF FRAMES

For the analysis, three differcnt types of frames are c onsiJered, name ly:

1. Single storey single bay 2. Two stor ey single bay 3. Three storey single bay

Tha dime nsi ons of the frames s e lGcte d f or the an alysis are sh own in Fig.2.

4. TYPES OF LOADS

Be haviour of all the types of infilled frame s with the f our types of contact are studied for the f oll owing two types of loading:

1. latera l l oads and 2. v~rtic a l loads. (Fig.3)

575

5. METHOD Of ANALYSIS

Infilled frames are analysed making use of 'simplified frame work meth od' proposec; by Gane san et a l [5J. In this mc thod, the e l ~ stic contincum is c onsidered as an assemblage of r ectangula r pl a t e e l emen ts rigidly connected with each other a t th e mid-point of the ir sides. Ea ch e l ement is then r eplaced by the pl ane fr amework model consisting of two bar elements inte r sec ting a t right angl e s and rigidly connected ~ith the adj oining e l ements. The f orces on the e l astic continuum are r e placed by statically equival e nt nodal l oads. Using any stândard pla ne frame compute r programme, the equival ent pla ne fr ame-wo rk is then analysed f or def ormati ons, f orce s and moments at various j oints. From these r e sults the stresses in the members of the plane framewo rk and thc stresses in th e e lastic continuum (infill panel) a re interpre ted.

6. RESULIS AND CONCLUSIONS

Ihe results obta ined from the theor e tical analysis is pre se nted and discussed in detail under three groups depending oh the number of storey a nd f orms part of a the sis [4J. Ihe r esults in the f orm of axial f orce , shea r force and be nding moment in the members of the frame, stresses in the infill and the late r a l deflection of infilled frame have been studied and f or brevity the s 31ient results a r e discussed and conclusions drawn the r e fr om are presented below:

a) In one storey frame s, if there has t o be composite a ction betwee n the infill and th e frame, there has t o be good cont act atleast be t ween the infill and the beam portion of the fr ame , of cours e , in such a case the infill sh ould have regular f oundati on as proviJed in l oad bca ring construc­tions.

b) Ihere exists certa in similarities in the distribution of f orces, moments, e tc in thc t op and bottom-most storeys of two and three stor ey infilled fr ame s .

c) Of the four ca s e s of contact cons ider ed , the r educti on m f orces , moments, deflections, e tc. is highe st in the case of f our side conta ct a nd decrea ses i n the or de r of four, two, three and one side conta ct. For e xample, the influence on max imum deflections in the frame f or ea ch ca se of l o?d is given in Table 1.

d) In most of the cases , the orde r of influe nce on the moments, forces, deflections , e tc of the frame is almost same in both the cases of f our and two sides contact. But the infill is seve rely stressed in the ca se of two sides contact.

576

e) In usual mUltistorey frame constructions, wal ls are built on beams as partitions making no provisions for good bonding or connections with the side columns and t op be am • Even in such cases, a~_~bservod from the c,se s of fr3mes with infills having~8ff"one side (i. o. on the supporting beam), there is redQction in horizontal sway, in moments, forces, vertical .deflections of the supporting bo am, in all cases of loads.

f) When there is good interaction betwe en the infill and the frame, there are tensilc stresses (in the infill) of the order that will cause cracking and hence this calls for reinforcing the infill to take up the tensile stresses.

REFERENCES

(1] J.R.BENJAlviIN and H.A. WILLIAMS: Ihe Behaviour of One-storey Reinforced Concreto Shear Walls ~ Proc. of A.S.C.E •• Vol.a3, May 1957.

(2] A.COULL: Ihe Influence of Concrete 1nfilling on the Strength and Stiffness of Steel Frames - Cement and Concrete, Oct-Dec.1966, pp 162-169.

(3] D.V.MALLICK and R.P.GARG: Effect of Openings on the Lateral Stiffness of 1nfil1ed Frames - Proc. of Ihe Institution of Civil Engineers, Vol.49, 1971, pp 193-209.

[4] S.S.RA!f;,AN: Effect of Cont3ct between 1nfill and Frame on the Behaviour of Infilled Multistorey Frames -M.Iech Ihesis, 1ndian Instituto Df Iechnology, Madras, July 1979.

(5] I.P.GANESAN, P.C. VARGHESE and H.ACHYUIHA : Simplified Framework Method for c'2 rtain Pl i'1 no Stress Probloms -Journal of Institution of Engineers, Vol.57, Part CI-5, pp 250-254, 1977.

577

TABLE 1

-------------------------------------------------------------Number Loa d Absolute Numbe r of side s of contact*

of cas e valu e in --------------~-------------Storeys simple frnme Four Thr EOe Two One without infill -------- ---------------- ---------------- --------------------One l..Cl 5.1 1.2 62.6 1.2 99.6

LC2 0.2 48.0 62.0 63.8 99.8 l..C3 51.8 0.7 1.0 0.9 92.0

Two LCl 5. 5 2.1 60.3 2.1 98.0 LC2 0.3 39.4 63.8 49.1 99.9 l..C3 295 . 3 0.9 1.1 1.0 68.0 LC4 4.1 1.3 3.9 1.4 9.2

Three l..Cl 5.7 2.9 60.4 3.0 97.7 LC2 0.5 36.4 65.4 43.0 99.7 LC3 83 .5 1.2 1.5 1.2 38.3 l..C4 4.3 2.4 6.4 2.6 12.4 l..C5 3.8 1. 4 4.2 1.5 9.7

===============================================;============~

* The de fl ec tions i n th esc cases a r e expr e ssed as a percentage of th c abso l ute maximum val ue of the deflecti ons in a simple fram e without any infill.

j

.....

o. Fu 11 contoct

.i"'''''''~ " " S; : : : : ª " ; S X)('(.I(XXXXXX~

xxx XXXXX )t')(xJt "

: " : : : " : " " " " " " " " xxxxxxxxxxxx X)Qt')()()C)(X X. xxx~

: : : : :! x .... xxxJ

'/"/// '"",,,

o. FuI! contoe!

" " ~~i ~:: :~:: " ~xxxxxxxxx

b. Three sides contoct

! : i xxxx. ,.

c. Two sides contoct

ONE STOREYED INFILLED FRAME

I" ...... .,"

: : : : :

txxxx",x.J!J

: : : : :

xxx)C,xxxxxxxx

~ : ~ : : : : : :S : : : : :

" " " " xxxxxxxxxxxxx xxxxxxxxxxxx> )C)(xxxxx)('xxx)('

: : : : : : : : I I :

IJÓr"xxxxxxxx~ XXXX)(

',,'// "" " " ,.,r ",,,/////,

: : : :: XXXXXXXXXX

d . One side contoe!

: : : : : :

XXXXX)(XXXXX)I

: : : : : :

XXXXXXXX1.OCX

I

: : : : (:-

xxxxxxxxxxxx '//// / / /

b. Three sides contoct

c . Two sides d. One side contoct contoct

THREE STOREYED INFILLED FRA ME

FIG. 1 . TYPES OF CONTAC T.

I 580

Frame members : 200 x 200

Infi 11 : 2700 x 2700 x 200

Econcrete : 0 .206 N/mm2

E infill : 0.069 NI mm2

:~

.10 J ~/::;: //;:;;: / ;:;;:;;/;; // /!,J,

f--- 3100 -------1 a . O ne st oreyed

inf i Iled frame

I : : : : :

,-

: : : : ': eeoo

5900

: : : : : : i I

,//,/// , ~;;;;;;:;;77;;TT7~! _L-

1---3100 ~ ~3100 ~

b . Two storeyed c . Three storeyed infilled frame infilled frame

FIG. 2. DETAILS OF FRAMES.

------------------

W

CCl

W W/2 W/2 P

n W

LCl

W/2

LCl

LC2

LC2

W/2 W/2 P

t----l 2'-P ...... ___ 1

LC 2

W/2

P

2P

2P

LC 3

LC 3

LC3

LC4

FIG.3. LOADING CASES.

W=P=9S.1kN

W

LC4

W

LCS

581