KENYA STANDARD      DKS 2802-12:2019 
ICS  
  
 
 
  
 
  
 
 
 
  
 
  
Masonry units — Methods of test  
 
Part 12:  
Determination of initial shear strength
 
 
   
 
  
 
  
 
  
 
   
 
  
 
   
 
  
 
  
 
 
© KEBS 2019 First Edition, 2019 DKS 2802-12:2019  
ii  © KEBS 2019 — All rights reserved TECHNICAL COMMITTEE REPRESENTATION 
 
The following organizations were represented on the Technical C ommittee:  
 
National Housing Corporation 
Kenya Clay Products Ltd 
Coast Clay Works Ltd Consumer Information Network 
University of Nairobi  
Kenya Industrial Research & Development Institute 
Architectural Association of Kenya 
M&O Consulting Engineers 
Kenya Association of Manufacturers, 
Kenya National Federation of Jua Kali Association 
Lake Basin Development Authority 
Kenya Bureau of Standards — Secretariat 
 
 
 
 
 
    
 
 
 
  
 
 
 
  
 
REVISION OF KENYA STANDARDS 
 
In order to keep abreast of progress in industry, Kenya Standar ds shall be regularly reviewed. Suggestions for 
improvements to published standards, addressed to the Managing Director, Kenya Bureau of Standards, are 
welcome.  
 
  
© Kenya Bureau of Standards, 2017 
 Copyright. Users are reminded that by virtue of Section 25 of the Copyright Act, Cap. 130 of 2001 of the Laws of Kenya, copyrig ht subsists 
in all Kenya Standards and except as provided under Section 25 of this Act, no Kenya Standard produced by Kenya Bureau of Stand ards KENYA STANDARD                                       DKS 2802-12:2019 
ICS  
© KEBS 2019 — All ri ghts reserved   iii may be reproduced, stored in a retrieval system in any form or transmitted by any means without prior permission in writing fro m the 
Managing Director.   DKS 2802-12:2019  
iv  © KEBS 2019 — All rights reserved Masonry units — Methods of test  
 
Part 12: 
 
Determination of initial shear strength  
 
  
 
  
 
  
 
  
 
  
 
  
 
 
  
 
  
 
  
 
  
 
  
 
  
 
  
KENYA BUREAU OF S TANDARDS (KEBS) 
 
Head Office: P.O. Box 54974, Nairobi-00200, Tel.: (+254 020) 605490, 602350,  Fax: (+254 020) 604031 
E-Mail: info@kebs.org, Web:http://www.kebs.org  
 
Coast Region    Lake Region    Rift Valley Region  
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Fax: (+254 041) 229448   Fax: (+254 057) 21814 
 
Foreword KENYA STANDARD                                       DKS 2802-12:2019 
ICS  
© KEBS 2019 — All rights reserved   v  
This Kenya Standard was prepared by the Clay and Clay Products Technical Committee under the guidance 
of the Standards Projects Committ ee and in accordance with the procedures of the Kenya Bureau of 
Standards. 
 During the development of this standard, reference was made to the following documents: 
 
BS EN 1052 – 3:2002 Methods of test for masonry - Part 3: Deter mination of initial shear strength. 
 
Acknowledgement is hereby made for the assistance received from  these sources. 
  
KENYA STANDARD        DKS 2802-12:2019 
 
 
© KEBS 2019 — All rights reserved   1  
Masonry units — Me thods of test  
 
Part 12:  
Determination of ini tial shear strength 
 
1. Scope  
 
This Kenyan Standard specifies a method for determining the in plane initial shear strength of horizontal bed 
joints in masonry using a specimen tested in shear. 
 
 
2. Normative references 
 The  following  referenced  documents  are  indispensable for  the  application  of  this  document.  For dated 
references, only the edition cited applies.  For undated refere nces, the latest edition of the referenced 
document (including any amendments) applies. 
 DKS 2802-1, Methods of test for masonry units - Part 1: Determi nation   of compressive strength. 
 
EN 772-10,  Methods  of test for  masonry  units - Part  10: De termination   of moisture  content of calcium 
silicate  and autoclaved  aerated  concrete  units. 
 
DKS 2802 - 8, Methods of test fo r masonry units - Part 16: Dete rmination   of dimensions. 
 EN 998-2, Specification for mortar for masonry - Part 2: Masonr y mortar. 
 
EN 1015-3, Methods of test for mor tar for masonry-   Part 3: De termination   of consistence of fresh mortars 
(by flow  table). 
 
EN 1015-7, Methods of test for mor tar for masonry - Part 7: Det ermination   of air content of fresh mortar. 
 
EN 1015-11, Methods of test for mortar for masonry-   Part  11:  Determination of flexural and compressive 
strength  of hardened  mortar. 
 
3. Principle 
 The initial shear strength of masonry is derived from the stren gth of small masonry specimens tested to 
destruction. The specimens are tested in shear under four-point  load. 
 Four different failure modes are considered to give valid resul ts. 
 
Two procedures, A and B are included. Procedure A involves test ing specimens at different precompressions 
and the initial shear strength is defined by a linear regressio n curve to zero prestress. Procedure B involves 
testing specimens at zero precompression and determining a char acteristic initial shear strength from a simple 
or a statistical consideration of the results.  
 
4. Terms, definitions and symbols 
 
4.1. Terms and definitions 
 
For the purpose of this Kenyan S tandard, the following terms an d definitions apply. 
  
2  © KEBS 2019 — All rights reserved 4.1.1.  masonry 
assemblage of masonry units laid in a specified pattern and joi nted together with mortar 
 
4.1.2. shear  strength of masonry 
strength of masonry subj ected to shear forces 
 
4.2. Symbols 
 
Ai                 is the cross-sectional area of a specimen para llel to the bed joints, in square millimetres (mm2) 
e                 distance between centre lines of the mortar bed  and the loading roller, in millimetres (mm) 
fvoi               is the shear strengt h of an individual sample, in  Newton per square millimetres (N/mm2) 
fpi                is the precompressive stress of an individual sa mple, in Newton per square millimetres (N/mm2) 
fvo               is the mean initial shear strength, in Newton per  square millimetres (N/mm2) 
fvko              is the characteristic initial shear strength, in Newton per squ are millimetres (N/mm2) 
F                  is the representation of the force applied to  the specimen, in Newton (N) 
Fi,max           is the maximum shear load, in Newton (N) 
Fpi                is the precompressive force, in Newton (N) 
h1 and h2    are the heights of cut units, in millimetres (mm) 
hu                is the height of the units according to DKS 2802  -8, in millimetres (mm) 
ls                is the length of s pecimen, in m illimetres (mm) 
lu               is the length of the units according to  DKS 2802 -8, in millimetres (mm)  
tbj               is the thickness of the bed joint, in millimetre s in millimetres (mm)  
ts               is the thickness of the steel loading plates, in millimetres (mm) 
α                i s the angle of internal friction, in degrees 
αk             is the characteristic angle of internal friction, in degrees  
5. Materials 
 
5.1. Masonry units 
 
5.1.1.  Conditioning of the units 
 
The conditioning of masonry units shall be as specified: 
 
Record the method of conditioning the masonry units prior to la ying.  Measure the moisture content by mass 
of autoclaved aerated concrete and calcium silicate units in ac cordance with EN 772-10.  Record the age of 
non-autoclaved concrete units at the time of testing the masonr y specimens. 
 DKS 2802-12:2019  
© KEBS 2019 — All rights reserved   3 5.1.2.  Testing 
 
Determine the compressive strength of a sample of masonry units , using the test method given in DKS 2802-
1.  For non autoclaved concrete units determine the compressive  strength at the time of testing th masonry 
specimens. 
 
5.2. Mortar 
 
The mortar, its mixing procedure and its flow value shall confo rm with the requirements of EN 998-2, unless 
otherwise specified, and these shall be reported in the test re port. 
 Take representative samples of fresh mortar from the mason's bo ard to make mortar prism specimens, to 
determine the flow value in accordance with EN 1015-3 and to de termine the air content in accordance with 
EN 1015-7. Use the prism specimens to determine the mean compre ssive strength at the time of testing the 
masonry specimens in accordance with EN 1015-11. 
 
6. Apparatus 
  
The testing machines used to apply the shear loads and precompr ession shall comply with the requirements 
given in Table 1. 
 
The testing machine to apply the shear loads shall have adequat e capacity but the scale used shall be such 
that the ultimate load on the specimen exceeds one fifth of the  full scale reading. The machine shall be provided 
with a load pacer or equivalent means to enable the load to be applied at the rate specified. 
 
Table 1 - Requirements for testing machines 
Maximum  permissible 
repeatability  of forces as  
percentage  of indicated force  Maximum permissible mean error  
of forces as percentage of 
indicated force  Maximum permissible error 
of zero force as percentage  of 
maximum force of range 
 
2,0± 2,0± 0,4   
 
Apparatus  capable of measuring the cross sectional area of the specimens  to an accuracy of 1 %.  
 
7. Preparation  and curing  of specimens 
 
7.1. Preparation of masonry specimens 
 
Prepare    type I specimens according to Table 2 and Figure 1. If hu > 200 mm, type II specimens may be 
used.  Where for practical purposes it is necessary to cut unit s, ensure that the faces of the unit to be mortared 
are representative of the unit as a whole. 
  
4  © KEBS 2019 — All rights reserved  
 
Build the specimens within 30 min after completion of the condi tioning of the units.  Use mortar mixed not more 
than 1 h beforehand unless it is designed to be used over a mor e prolonged period. 
  
The bearing surfaces of the masonry units shall be wiped clean of any adherent dust. The lower unit shall be 
laid on a clean level surface. The next unit shall be laid so t hat a final mortar joint thickness of 8 mm to 15 mm, 
representative of masonry with conventional mortar joints, or o f I mm to 3 mm, representative of masonry with 
thin layer mortar joints, is attained. The masonry unit shall b e checked for linear alignment and level using a 
set-square and spirit level. Excess mortar shall then be struck  off with a trowel. 15) In the case of Type I 
specimens according to Figure 1, the procedure for the second u nit shall be repeated for the top unit. 
 
 
  
 
DKS 2802-12:2019  
© KEBS 2019 — All rights reserved   5 7.2. Curing and conditioning of the specimens 
 
Immediately after building, pre-compress each specimen by an un iformly distributed mass to give a vertical 
s t r e s s  b e t w e e n  2 , 0  x  1 0-3  N / m m2 a n d  5 , 0  x  1 0-3  N / m m2. Then cure the specimens and maintain them 
undisturbed until testing. For other than lime based mortars, p revent the test specimens from drying out during 
the curing period by close covering with polyethylene sheet, an d maintain the specimens undisturbed until 
testing, unless otherwise specified. Test each specimen at an a ge of 28 d ± 1 d, unless otherwise specified for 
lime based mortars, and determine the compressive strength of t he mortar at the same age following EN 1015-
11. 
 
8. Procedure 
 
8.1. Placing the specimens in the testing machine 
 
Support the end units of each specimen in the test apparatus in  accordance with Figure 2. For this, use pieces 
of steel at least 12 mm thick, with an appropriate capping if n ecessary, to ensure good contact. The diameter 
of the roller bearings shall be 12 mm with a length of at least  the width of the unit. 
 
Apply the load through a ball hinge placed in the centre of the  top central steel plate.  
  
6  © KEBS 2019 — All rights reserved  
DKS 2802-12:2019  
© KEBS 2019 — All rights reserved   7 8.2. Loading 
 
8.2.1.  Procedure A 
 
Test at least three specimens at each of three precompression l oads. For units with compressive strengths 
greater than 10 N/mm 2, use precompression loads that give appr oximately 0, 2 N/mm2, 0,6 N/mm2  and 
1,0 N/mm2.   For units with compressive strength less than 10 N/mm2 use precompression loads that give 
approximately 0,1N/mm2, 0,3  N/mm2and 0,5 N/mm2. The precompression load shall be kept within± 2 % of 
the initial value. The pre-compression shall be applied accordi ng to Figure 3. 
 
The stiffness of the loading beams that are used for the precom pression shall be sufficient to ensure an equally 
distributed stress. If the platens of the machine are shorter t han the length of the specimen, loading beams 
may be used. These shall have a length equal to the length of t he specimen/, and a depth greater than or 
equal to the length beyond the edge of the plate.  
 
8.2.2.  Procedure B 
 Test at least six specimens at zero precompression. 
 
8.2.3.  Loading rate 
 
Increase the shear stress at a rate between 0, 1 N/(mm
2/min) and 0,4 N(mm2 / min). 
 
8.3. Measurements and observations 
 
Record the following: 
 
- the age of non-autoclaved concrete units 
- the cross-sectional area Ai of the specimens parallel to the shear force with an accuracy of 1% 
- the maximum load Fi,max 
- the precompression load Fpi  for procedure A 
- the type of failure (see annex A). 
 
8.4. Replications 
 
If failure is by:  
- shear failure in the unit para llel with the bed joint (see Fi gure A.3) or; 
- crushing or splitting of the units (see Figure A.4), then; 
 either 
  
- further  specimens may be tested until shear failures of the types shown in Figure A.1 or Figure  A.2  
have  been  achieved  for  each  precompression level  (Procedu re  A)  or  six  times (Procedure B) or 
alternatively;  
 
- the result may be used as a lower bound to the shear strength  for each precompression level. 
 Lower bound results should not be used in the evaluation of res ults in clause 10. If necessary, an alternative 
precompression may be needed for Procedure A so that sufficient  failures are achieved.  
  
  
8  © KEBS 2019 — All rights reserved  
 
9. Calculations 
 
For each specimen calculate the shear strength and for Procedur e A the precompression stress to the nearest 
0,01 N/mm2  using the following  equations:  
 
           
 
where  
 
10.  Evaluation of results 
 
10.1.  Procedure A 
 
Plot a graph of the individual shear strength fvoi against the normal compressive   stress fpi as shown in Figure 
4.  Plot the line determined   from a linear regression   of th e points.  Record the mean initial shear strength 
fvo at zero normal stress to the nearest 0,01 N/mm2.   Obtain this from the intercept of the line with the vertica l 
axis.  Record also the angle of i nternal friction to the neares t degree, from the slope of the line. 
 
   
The characteristic    value  of the  initial  shear  strength  is fvok where  fvok = 0,8 fv0   and the   characteristic 
angle  of internal  friction  from tan αk = 0,8 tan α.  
 
DKS 2802-12:2019  
© KEBS 2019 — All rights reserved   9 10.2.  Procedure B 
 
10.2.1. General 
 
Calculate the mean initial shear strength fvo  to the nearest 0,01 N/mm2. 
 
The characteristic   initial shea r strength may be calculated u sing 10.2.2 or 10.2.3. 
 
10.2.2. Simple method 
 
The characteristic   shear strength, fvok,  shall be calculated  as: 
 
       f vok  =  0,8   X fvo 
 
or fvok  shall  be  taken  as  the  lowest  individual   result  which ever   is the  lower,   and  shall  be  given  to 
the nearest  0,01 N/mm2. 
 
10.2.3. Statistical method 
 
Calculate for each individual bond strength fvo1, fvo2………………… fvon the values of Y1, Y2 ……………Yn 
  
 
 
NOTE           The characteristic value derived is based upon a  95 % confidence level.  
 
 
10  © KEBS 2019 — All rights reserved  
11.  Test report 
 
 The test report shall contain the following information: 
 
a) the number, title and date of i ssue of this Kenyan Standard;  
b) name of the testing laboratory; c) the Test Procedure used, A or B;  
d) date of building and number of specimens; e) curing conditions (e.g. tim e, temperature, humidity); 
f) date of testing the specimens; 
g) description of the specimens including dimensions; h) descriptions of the masonry units and the mortar, preferably  consisting of the appropriate test reports, 
securely attached, or of extract s taken from these reports; 
i) age of non-autoclaved  concret e units at the time of testing  the specimens; 
j) type of mortar and the mixing procedure of the mortar; 
k) the method of conditioning the units prior to the time of la ying and for autoclaved aerated concrete and 
calcium silicate units the moisture content by mass;  
l) maximum load reached by the test specimens; 
m) mean compressive strength of the masonry units in N/mm
2  the nearest 0,01 N/mn1 and the coefficient 
of variation; 
 
n) mean compressive strength of the mortar in N/mm2  the nearest 0,01 N/mm2 and the coefficient of 
variation; 
 
o) individual  values for the shear strength and for Procedure A precompression stress for each specimen 
in N/mm2 to  the nearest 0,01 N/mm2 and the description of the failure mechanism of each specimen 
and whether any lower bound values have been recorded; 
 
p) mean and characteristic initial shear strength in N/mm2 to the nearest 0,01 N/mm2 and in the case of 
Procedure B whether the simple or statistical method has been u sed; 
 
q) if Procedure A is used the angle of internal friction and ch aracteristic angle of internal friction; 
 
r)  remarks, if any.  
  
 
  
 
  
 
  DKS 2802-12:2019  
© KEBS 2019 — All rights reserved   11 Annex A 
(informative)