12TH INTERNATIONAL

BRICK/BLOCK Masonry c O N F E R E N C E

Dro

INFlUENCES OF SHAPE AND SIZE SPECIMEN ElEMENTS ON lOAD CAPACITY AND

DEFORMATION OF UNREINFORCED ClAY BRICK MASONRY UNDER COMPRESSION

Radoslaw Jasinski', Lukasz Drobiec', Jan Kubica 2

'MSc. Eng., Silesian University of Technology, Department of Building Structures,

Akademicka 5, 44-100 Gliwice, Poland RJAS@KATKON.BUD.POLSL.GLlWICE.PL

'MSc. CEng. PhD, Silesian University of Technology, Department of Building Structures,

Akademicka 5, 44-100 Gliwice, Poland JKUB@KATKON.BUD.POLSL.GLlWICE.PL

ABSTRACT

In design practice are often used the advanced methods for analysis of building struc­tures, also made as masonry. Some of them is based on FEM and connected with mo­re respectively description of mechanical properties of materiais, used. In some causes it is necessary to make a very accurate analysis, e.g. for existing buildings. Paper pre­sents the results of carried out investigations of 5 series of test specimens of different shape, size and materiais, applied. The investigations confirmed the significant in­fluence of type of specimens, used. The most interesting is the fact that behaviour of standard models (marked as A type) was quite similar than the largest models (type CSE/ c - for cement mortar and B/ cw - for lime-cement mortar).

Key words: Masonry, unreinforced masonry walls, compressive strength, modulus of elasticity.

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1. INTRODUCTION

Applied in design practice more advanced methods for analysis of building struc­tures, also made as masonry, especially based on FEM is connecting with more respectively description of mechanical properties of materiais, used. In some cau­ses it is necessary to make a very accúrate analysis of some structures, for instan­ce when is necessary the strengthening of existing buildings.

Therefore the answer on question about influence of shape and overall dimen­sions of test specimen (also requested in standard methods) on mechanical pro­perties of masonry is very important, because shape of real masonry structures are repeatedly greater than test code specimens. For typical design situation when ensure an adequate limit of safety is requisite using only the standards' parame­ters of masonry is correct.

Differently case looks when existing the necessity of accurate analysis, often a very complicated structure, especially in state distress or at failure. Application of code properties of masonry sometimes can give the significant inaccuracies. Therefore, the most desirable is knowledge how influences on results have so-called scaling effect of test specimens for determination of material properties of masonry?

In order to answer on this question, in Department of Building Structures Silesian University of Technology were carried out a comparison investigation of different shape of test specimens made of clay brick on cement and cement - lame mor­tar. Ali models were subjected to axially compression.

2. RESEARCH

Models were made with applied of different mortar types and masonry units (bricks). Presented investigation included 5 series consisted of 5 models in each of them. Models marked as C-A/c, C-B/c, CSE/c and A/c were made of cement mortar on proportions of cement to sand 1 :3. Series of specimens made of lime­cement mortar (1:1 :6) consisted of C-A/cw, C-B/cw B/cw and A elements. Mo­deis built in cement mortar and clay brick type 1, however clay units used for spe­cimens made of lime-cement were called as type 2. Shape and overall dimensions of test specimens showed in Figure 1.

The models designated as A/c and A/cw were typically test specimens for deter­mination of compressive strength according to European standard EN-1052-1 (1) and new Polish masonry code PN-B-03200: 1999 (2) for both type of mortar.

Bricklayers made ali models from building firm for maximal similar situation on building site. In consequence of this fact was the not so high quality of bricklayer works and joints were not precise filled.

Ali models had on both against surfaces system of inductive gauges about exact to 0,002 mm, only models C-A series applied of gauges on each surfaces (Fig.1).

Figure 1. Shape and avera/l dimensians af test specimens.

Series C-S/C Series C-S/ew

Series CSE/e

0-..Pc"

Series C-Ale Series C-Alew

Series S/ew

Ali gauges were connected with automatically recording apparatus. Investigations made in press transmitted loads through washers reducing the friction. Ali mo­deis loaded temporary in one cycle to failure recorded volume of deformations for each load leveI.

3. RESULTS OF MATERIAL INVESTIGATIONS

Also the specimens of mortar and masonry units (brick) for determination of ma­teriais properties were taken. Investigations for mortar included: mean compres­sive strength according to PN-85/B-04500 (3). For clay brick: mean value of com­pressive strength with measurement secant modulus of elasticity (with the aid of gauges about 20 mm measure base) according to prEN-772-1 :1995 (4). Test re­sults of materiais covered table 1.

The clay brick type 7 characterise twice as big modulus of elasticity and about 24% more compressive strength than clay brick type 2.

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Table 7. Main mechanical parameters af martar and brick

MORTAR CLAY BRICK

SERIES fm v, E. v" f. v"

[N/mm'] [%] [N/mm'] [%] [N/mm'] [%]

1:3 TYPE 1

Ale 11,7 11,3

C-Ale

C-B/e 12,5 12,2 8176 2,8 23,8 7,7

CSE/e

1:1:6 TYPE 2

A/ew 4,3 9,2

C-A/ew 6,1 13,4 4617 15,1 19,2 7,8

C-B/ew

B/ew 4,2 10,8

Table 2. Results af main investigatians

SERIES FkttH v, E ItU 0,33 Eu

lf" Ve

[N/mm2] [%] [N/mm2) [mm/m] [%)

CEMENT MORTAR

Ale 6,43 5,7 7891 1,788 8,5

C-Ale 14,54 13,0 12961 2,971 32,0

C-B/e 11,54 12,0 9408 1,688 28,0

CSE/e 9,16 15,0 8723 1,492 38,0

LIME - CEMENT MORTAR

A/ew 6,1 6,3 2616 2,810 22,5

C-A/ew 4,3 4,7 3884 4,310 14,4

C-B/ew 4,6 5,1 1777 3,789 16,4

B/ew 6,8 11,0 2711 3,336 3,2

4. RESULTS OF MAIN INVESTIGATIONS

Describing of the compressive strength in direction perpendicular to the bed joint, secant modulus of elasticity and maximal strains for specimens under com­pression was the main aim of presented investigations. Model failure according to expectations through produced vertical individual"columns" as a result of verti­cal cracks. Only the smallest models of C-A series fa ilure thought strong vertically bursting and next 11 crushed". For both mortar types and clay bricks the failure mechanism was observed. Main test results in the form of relationships s-e are shown in Figures 2 to 5, however value of compressive strength, secant modulus of elasticity and maximal strains in the ultimate phase is shown in table 2.

5. ANALYSIS

Stress-strain relationships characterise considerable non-linear behaviour of tested masonry. 80th in case of wall specimens made of cement and lime-cement mor-

Figure 2. The <J-E relationship for A series.

Figure 4. The <J-E relationships for C-B series.

0.0 0,5 1,0 1,5 '20 1,~ 3.0 3,5 4.0 '1"' ........ 1

Figure 6. Comparison af compressive strength.

Figure 3. The <J-E relationships for C-A series.

:: r-:-:;.---;-.-;.-:>-:;~-,;:-: .... :;:a; -'-.. -;-..,.--' [ =:~ I ___ .' __ •• J.

:::::::::::::::._ .. '~"".' .. ' ~ < ••.•....• ; 1

0.0 0,5 1,0 1,5 2.0 '25 3,0 3,5 4.0 4.5 '1 ... ..,., ... 1

Figure 5. The <J-E relationships for Blew and CSEle series.

" ,--,--,---,-----.,.--,

~ ,~~~J~i[T'~~~· ~ , .... ... ~

I ..... _~ .. _ ..... _ ........ .

1.5 2 2.$ 3.' ·1"' ..... "'1

Figure 7. Comparison of secant modulus of elasticity.

"'<w Blcw

tar the falling branch of relationships (beyond point of maximal compressive stresses) was not observed as in (5, 6). Tables 3 include parameters with referen­ce to "code's" models A type (according to (1) and (2)). However what a very im­portant is, that the value of compressive strength described for model type A we­re only about 42% smaller than obtained for large specimens (SE/c, which good reflected the real wall. Similar results were observed for models built in lime-ce­ment mortar.

The results of compressive strength obtained for A model are about 12% greater for series B/cw. In case of others series the deficit of compressive strength about 29-25% has got. In Fig.6 the results of compressive strength for ali models and mortar types were presented.

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Table 3. Comparison main parameters of models from test

CEMENT MORTAR LIME - CEMENT MORTAR

A/c C-Ale C-B/e CSE/e A/ew C-A/ew C-B/ew B/ew

t Inr

" 1,0 2,79 1,78 1,42 1,0 0,71 0,75 1,12 {, /fl!

" E Itll

1,04 O.H,' 1,0 1,64 1,19 1,11 1,0 1,48 0,68 E (tIl O,JJ,A

Eu,/t1l 1,0 1,67 0,95 0,84 1,0 1,54 1,35 1,19

Eu,A,nr

Figure 8. Comparison of ultimate strains.

In the ease the mean values of modulus of elastieity (Fig. 7) for models built in eement and lime-eement mortar are similar. The greatest values were obtained for slender elements (C-Ale and C-A/ew). Maximal differenees with referenees to A models in this ease was sinee 64% for eement mortar in C-Ale models to 10% - for CSE/e models. For elements made of lime-eement mortar these dif­ferenees were mueh less and similarly for models C-A/ew - 48% and B/ew - 4%.

Differenees between modulus of elastieity value for elements C-B/ew and A series were about 30%.

Opposite situation was observed for C-B/e speeimen's, when this differenee is less than 20%. Comparison of maximal strains in the ultimate loads for ali models was shown in table 3 and Fig.8.

Both types of test elements, built in eement and lime-eement mortar, the grea­test value of ultimate strains was obtained for "eolum" type specimens (C-A). Ho­wever measured strains on larger test models (CSE/e and B/ew series) were sma­lIer ea . 5 ( 20% than getting for standard speeimens (A type). The strains of models CSE/e series were less than A speeimen, for elements on lime-eement mortar (series B/ew) - greater about 20%.

6. CONCLUSIONS

By the reason of small number of test speeimens and types of masonry units and mortars, the results of presented investigations should be analysed mainly in qua­litative mining.

It seems, that it can be possible to formulate the following conclusions:

• the a-E relationships for ali models have not a linear form;

• shape and overall dimensions of test specimens gives the significant influence on values of compressive strength, modulus of elasticity and ultimate strain;

• the mean values of properties analysed above, obtained for standard (accor­ding to [1, 2]) specimens A type are quite similar then determined for the lar­gest specimens (CSE/c series for elements built in cement mortar and B/cw ele­ments for masonry ma de of lime-cement mortar).

7. REFERENCES

1. EN 1052-1, Methods of test for masonry - Part 1: determination of compressive strength. CEN 1998.

2. PN-B-03002:1999, Unreinforcement masonry structures. Analysis and structural designo PKN, 1999.

3. PN-85/B-04500, Mortars. Physical and mechanical tests. PKN 1985.

4. PrEN 772-1 :1995, Methods of test for masonry units - Part 1: Determination of compressive strength. CEN 1995.

5. KNUTSSON H. H., NIELSEN I. On the modulus of elasticity for masonry. foumal of the British Masonry Society. Masonry Intemational, Vo1.9, No2, 1995, pp.57-61.

6. BROOKS I.]" ABU BAKER B.H., The modulus of elasticity of masonry. foumal of the British Ma­sonry Society. Masonry Intemational, Vo1.12, No 12, pp 58-63.

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