P01245127138

IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE)
e-ISSN: 2278-1684,p-ISSN: 2320-334X, Volume 12, Issue 4 Ver. V (Jul. - Aug. 2015), PP 127-138
www.iosrjournals.org
DOI: 10.9790/1684-1245127138 www.iosrjournals.org 127 | Page
Strength and Behavior of Reinforced Concrete Model Beams
Containing Liquid Additives
1
Salih Elhadi Moh. Ahmed and 2
Sara Moh. A. Eimournein
1) Professor of structural engineering, Sudan University of Science and Technology, Sudan
2) Structural engineer, Thiga for Engineering consultants, Sudan.
Abstract: The aim of this paper is to study the effect of liquid additives on strength and behavior of reinforced
concrete model beams as well as cracking and deflection of these model beams .
The liquid additives (High-range water reducing/super plasticize) in different proportions by weight of cement
in the range of 0%, 0.4%, 0.8%, 1.2%. 1.6% . 2% were used.
The compressive strength of concrete •was measured at different ages (7and 28 days) and modulus of elasticity,
shear modulus, modulus of volume change. Poissons ratio, deflection and cracking at 28 days. Has been
calculated.
Best results were achieved then using the ratio’s of 1.6% by weight regarding compressive strength , modulus of
elasticity in concrete , shear modulus , modulus of volume change, Poissons ratio and deflection.
Also results showed that additives have no effect on cracking behavior (both at first cracking stage and ultimate
load).
I. Literature review
1.1 Introduction
Beams are horizontal members carrying lateral loads from roofs. floors etc. and resisting the loading in
bending, shear and bond.
This research provides an overview of the principles of design and behavior of reinforced concrete
beams. Reinforced concrete beam are designed to fail under an overload condition that has a small probability of
being exceeded during the service life(1). A beam after designed for safety is checked to assure that it will
perform in a satisfactory manner under service conditions(2). The serviceability checks usually involve assuring
that deflections and crack widths satisfy appropriate criteria for the intended use(3).
The axis of a beam deflects from its initial position under action of applied forces. The deflection of
beam depends on its length, its cross-sectional shape, and its the material, where the deflecting force is applied,
and how the beam is supported. Deflections may be calculated, but in normal cases span4o-effective depth ratios
can be used to check compliance with requirements(4).
Visible cracking occurs when the tensile stresses exceed the tensile strength of the material(5). Visible
cracking is frequently a concern since these cracks provide easy access for the infiltration of aggressive
solutions into the concrete and reach the reinforcing steel or, other components of the structure leading to
deterioration. Crack widths can be calculated, hut in normal cases cracking can be controlled by adhering to
detailing rules with regard to bar spacing in zones where the concrete is in tension.
1.2 Admixtures:
Many researchers conducted test on beams containing additives.(6) Admixtures for use in concrete are
defined as ―material added during the mixing process of concrete in small quantities related to the mass of
cement to modify the properties of the fresh or hardened state of concrete.
Admixtures are now widely accepted as materials that contribute to the production of durable and cost-
effective concrete structures. The contributions include improving the handling properties of fresh concrete,
easy-fying placing and compaction, reducing the permeability of hardened concrete, and providing freeze/thaw
resistance (7).
1.3 Compressive strength
Compressive strength is the main parameter which determine the quality of a concrete construction (8)
.
Other parameters than strength, such as durability, volume stability and impermeability are important in
evaluating the concrete quality (9)
. In general, most people think that by increasing the strength means that other
parameters are also increased. However, this assumption is not always true. For example, the use of excessive
cement will increase the strength but at the same time it also produces shrinkage and creep.

Strength and Behavior of Reinforced Concrete Model Beams Containing Liquid Additives
The compressive strength is the most important properly of concrete. Compressive strength in
determine by standard cubes of dimension 150 or 100 mm for aggregate not exceeding 25 mm in size crushed at
age of 28 days..
The compressive strength according to the cube strength (fcu) is defined as :
fcu = P/A where …………(1)
where : P: is the applied load A: cube area
and the relation between the cube strength and the cylinder strength f'c is
f'c=0.8lfcu ……………….(2)
1.4 Factors Affecting Concrete Strength
In general, compressive strength of concrete is influenced by the following factors:
a) Water/cement ratio used in the concrete mixture - increased in water /cement ratio will decreased the
strength
b) method of compacting concrete mixture
c) type and characteristic of cement
d) type and characteristic of aggregates
e) aggregates / cement ratio
f) Additive materials used
g) porosity content which can be affected by the above factors
h) type of specimen and geometry ( cube or cylinder and size)
i) method of testing (stress rate, moisture content)
j) sample maturity (age and type of treatment given)
1.5 Elastic Modulus
Elastic modulus is important in the calculation of beam deflection, the stress lost in pre-stress concrete
due to elastic movements., changes in stress to strain and etc. Elastic modulus (modulus Young) from non-linear
stress-strain curve is difficult to determine. The elastic modulus in a true elastic area is approximated from early
tangent modulus that is the curve at the early stage. This modulus involved a small change of strain which is
also called as dynamic elastic modulus which can be determined by ultrasonic method.
For a material such as concrete which is in general have a non -linear stress-strain curve the elastic
modulus can always be defined in four different ways(3)
as shown in Figure 1. Between the four modulus, secant
modulus is more practical and represents the average elastic modulus. Table I gives a comparison for
determination of modulus value in accordance to the various international standards According to BS8110(2)
the
relationship between elastic modulus and static (secant) modulus for normal concrete is as follows(3)
:
Ec I .25Ed ± 4 kN/mm2
…………….…………(3)
Ed (kN/mm2
) = 1.362
fcu
0.33
x 10-6
………..……(4)
Where: fcu : is cube strength in N/mm2
Ec : is the modulus of elasticity
Ed : is the secant modulus of elasticity
the elastic constants has been calculated from the following empirical formula
𝐸𝑐 = 33 𝛾𝑐
1.5
√𝑓 𝑐 … … … … … … … … … . (5)
Where 𝛾𝑐 : concrete density
The shear modulus Gc and the modulus of volume change in concrete Kc arc also calculated from the
equations:
Gc250*( 2000 ± fc )…………………….. (6)
Gc = Ec/2 (I+v) …………………….…….(7)
KcEc /3 (l-2v) ………………………….…(8)
Where v: Poissons ratio of concrete
1.6 Prediction of Deflections & Cracks:
1.6.1 Deflection :
Calculations of deflection in center of these beams δ. Can be determined from the following formula:
δ = PL3
/ 48Ec I………………………… (9)
Where I: moment of inertia, L : effective length of beam
1.6.2 Cracking:
Calculation of cracking in beam is namely governed by the following equations (see fig 1):
𝜀 𝑚 = 𝜀1 =
𝑏1(ℎ − 𝑥)(𝑎′
− 𝑥)
3𝐸𝐴(𝑑 − 𝑥)
… … … . . (10)

design crack width =
3𝑎 𝑐𝑟 𝜀 𝑚
1 + 2 (𝑎 𝑐𝑟 − 𝑐 𝑚𝑖𝑛 )/(ℎ − 𝑥)
… … … . . (1)
Where : acr is the distance of the point considered to the surface of the nearest longitudinal bar
𝜀 𝑚 is the average strain at the level where the cracking is being considered
𝜀𝐼 is the strain at the level where the cracking is being considered
𝑐 𝑚𝑖𝑛 is the cover to the tension steel
h is the overall depth of the member
x is the depth of the neutral axis
bt is the width of the section at the centroid of the tension steel
d is the effect depth
a' is the distance from the compression face to the point at which the crack width is required
Ec is the modulus of elasticity of steel
A is the area of tension reinforcement
Fig 1 (expected section - cracks )
Using equations (10) & (11) , It can be shown that the crack width at:
1) point A, acr =32.84mrn
2) point B, acr 2l.42mm
3) point C, acr 58.8mm
from equation (11)
(a) The design crack width at point 003 mm
(b) The design crack width at B 0M19 mm
(c) The design crack width at C 0.0 13 mm
II. Experimental work:
2.1 Control specimens:
The total number of the tested beam specimens was 6. All dimensions are constant and mix designs are
variable. The beams were classified into six different groups. Table (1) shows the six groups. With each beam 6
cotnrol specimens in a form of 100* 100* 100 mm cubes were casted and tested at 7 days and 28 days (10,11)
.
Table 1: Beams dimensions and additives
Beam identification Dimensions h*b*L (mm*mm*mm) Additives % added
B1 200* 100* 100 0.0
B2 200* 100* 100 0.4
B3 200* 100* 100 0.8
B4 200* 100* 100 1.2
B5 200* 100* 100 2.0
Where h, b and L are depth, width and length of the beams
2.2 The beams specimens:
In this research, a total of 6 reinforced concrete beam specimens were tested. The size of a beam is
(200* 100* 100 mm). all beams are crated and tested at 28 days. With each beam the 6 control specimens tested,
three of them tested at 7 days and the other three at 28 days (12)
. Tables (2, 3, 4 and 5) below present the result.

Table 2: Compressive strength of control cubes at 7 days
Specimen
designation
Average wt of . cube
(gm)
Average density
(kg/m3
)
Average failure load
(PKN)
Average compressive strength
(fcu N/mm2
)
B1 2650 2650 290.00 29.00
B2 2700 2700 320.00 32.00
B3 2700 2700 341.67 34.16
B4 2700 2700 360.00 36.00
B5 2700 2700 400.00 40.00
B6 2650 2750 281.67 28.16
Table 3: Compressive strength of control cubes at 28 days
Speci
design
Ave
weight
(gm)
Ave.
density
(kg/m3
)
Ave.
failure
load (KN)
Ave. fcu
N/mm2
fc=0.81 fcu
N/mm2
Ec N/mm2
G N/mm2
K N/mm2
V
B1 2650 2650 373 37.3 30.237 27.0 11.007 16.071 0.22
B2 2700 2700 415 41.5 33.615 28.5 11.852 15.833 0.20
B3 2700 2700 540 45.0 36.45 29.7 12.650 15.468 0.18
B4 2700 2700 480 48.0 38.88 31.0 13.168 15.656 0.17
B5 2700 2750 533 53.3 43.19 32.0 14.245 14.035 0.12
B6 2650 2700 370 37.0 29.97 26.9 10.940 16.011 0.00
Where for concrete: Ec is the modulus of elasticity, G is the shear modulus, k is the modulus of volume change
and v s Poissons ratio.
Table 4: Load- deflection for all beams
Load kN Deflection B1
(mm)
Deflection B2
(mm)
Deflection B3
(mm)
Deflection B4
(mm)
Deflection B5
(mm)
Deflection B6
(mm)
0 0 0 0 0 0 0
2 0.09 0.16 0.05 0.02 0.01 0.02
4 0.2 0.27 0.05 0.09 0.06 0.04
6 0.35 0.27 0.07 0.2 0.11 0.25
8 0.46 0.34 0.19 0.33 0.12 0.39
10 0.54 0.45 0.21 0.44 0.12 0.49
12 0.63 0.48 0.32 0.5 0.12 0.6
14 0.72 0.76 0.9 0.54 0.19 0.7
16 1.1 0.91 0.67 0.88 0.19 0.79
18 1.1 1.06 0.8 1.13 0.2 0.92
20 1.27 1.18 0.94 1.22 0.26 0.95
22 1.52 1.27 1.09 1.34 0.54 1.04
24 1.62 1.31 1.19 1.43 0.68 1.17
26 1.97 1.46 1.24 1.45 0.78 1.45
28 2.16 1.79 1.36 1.59 0.88 1.6
30 2.36 1.96 1.67 1.88 0.98 1.75
32 2.5 2.08 1.89 2 1.08 1.9
34 2.63 2.17 2.04 2.15 1.09 1.97
36 3.09 2.25 2.17 2.29 1.16 2.02
38 3.27 2.3 2.22 2.4 1.22 2.37
40 3.38 2.44 2.39 2.43 1.58 2.55
42 3.49 2.58 2.74 2.52 1.66 2.7
44 3.64 2.95 2.91 2.85 1.73 2.9
46 4.44 3.11 3.15 3 1.83 2.95
48 4.44 3.19 3.2 3.15 2.03 3.17
50 4.44 3.31 3.39 3.3 2.08 3.62
52 4.72 3.53 3.79 3.41 2.17 3.92
54 4.01 3.89 3.55 2.33
56 2.63
58 2.98

Table 5: Moment- rotation (in radians) for all beams
Moment kN.m Rotation*
(radians) B1 (10-
4
)
Rotation*
(radians) B2 (10-
4
)
Rotation*
(radians) B3
(10-4
)
Rotation*
(radians) B4
(10-4
)
Rotation*
(radians) B5
(10-4
)
Rotation*
(radians) B6
(10-4
)
0.0 0.00 0.0 0.0 0.0 0.0 0.0
0.5 1.80 3.2 1.0 0.4 0.2 0.4
1.0 4.00 5.4 1.0 1.8 1.2 0.8
1.5 7.00 5.4 1.4 4.0 2.2 5.0
2.0 9.20 6.8 3.8 6.6 2.4 7.8
2.5 10.8 9.0 4.2 8.8 2.4 9.8
3.0 12.6 9.6 6.4 10.0 2.4 12.0
3.5 14.4 15.2 7.8 10.8 3.8 15.8
4.0 22.0 18.2 13.4 17.6 3.8 14.0
4.5 24.0 21.2 16.0 22.6 4.0 18.4
5.0 25.4 23.6 18.8 24.4 5.2 19.0
5.5 30.4 25.4 21.8 21.8 26.8 20.8
6.0 32.4 26.2 23.8 28.6 23.6 23.4
6.5 39.4 29.2 24.8 29.0 15.6 29.0
7.0 43.2 35.8 27.2 31.8 17.6 32.0
7.5 47.2 39.2 33.4 37.6 19.6 35.0
8.0 50.0 41.6 37.8 40.0 21.6 38.0
8.5 52.6 43.4 40.8 43.0 21.8 39.4
9.0 61.8 45.0 43.4 45.8 25.0 40.4
9.5 65.4 46.0 44.4 48.0 30.0 47.4
10.0 67.6 48.8 47.8 48.6 31.6 51.0
10.5 69.8 51.6 54.8 50.4 33.2 54.0
11.0 72.8 59.0 58.2 57.0 34.6 58.0
11.5 73.0 62.2 63.0 60.0 36.6 59.0
12.0 75.0 63.8 64.0 63.0 40.6 63.4
12.5 88.8 66.2 67.8 66.0 41.6 72.4
13.0 94.4 70.6 75.8 68.2 43.4 78.4
13.5 80.2 77.8 71.0 46.6
14.0 52.6
14.5 59.6
*As the beam is symmetrical the rotation of each beam is calculated at left support.
III. Discussions of Results:
* From table 2, and of results table 3, fig:2 has been drawn. The compressive strength of control
specimen and thus beam increases by increase in additives in the range (0% - 1.6%) and decreases by increase in
additives in the range (1.6% - 2%) for the both ages of 7 day and 28 days. For both ages of 7 days and 28 days,
the best results has been achieved in the ratio of 1.6%.
Fig 2: Effect of additives on compressive strength of control specimens of beams
* From Table 3 modulus of elasticity of concrete (Ec) , shear modulus (0) , modulus of volume change (K) were
increased by increase in additives in the range (0% - 1.6% ) and decreased by increase in additives in the range

(1.6% - 2%) . Again best results have been achieved at the ratio of 1+6%. Fig. 3 shows the effect of additives on
the prescribed elastic moduli.
* From Table 3 Poissons ratios (v) decreases by increase in additives in the range (0% - 1.6%) and increases by
increase in additives in the range (1.6% -- 2%) , and best results has been achieved at the ratio of 1.6% . (see fig.
3 (a & b)) .
* From Table 4 and Table 5 , fig 4 and fig 5 has been drawn (12) As shown deflection decreases as additives
increases in the range (0% - 1.6% ) and increases as additives increases in the range (1.6%-2%) and best results
has been achieved at the ratio of 1.6% .
* From fig. 6.1 and fig 6.2 the failure crack patterns are found to be nearly similar both theoretical and
experimental. The same phenomena has been noticed in all the other tested beams, which means that addition of
additives has no effect on the failure pattern of the tested beams.
Fig. 3: Effect of additives on elastic modullii
Fig 4: Load-deflection curve for all beams

Fig 5: moment- Rotation curve for all beams.
Fig. 6.1 the actual experimental cracks of beam B1
Fig. 6.2: The expected theoretical section- cracks of B1
IV. Conclusions:
The additive under investigation has the following effects in concrete cubes and beams:
 In the range of 0.4- 1.6% addition it increases the compressive strength (at age of 7 and 28 days), density,
modulus of elasticity of different types in compression, in shear and in volume.
 Also in the above mentioned range it decreases poission ratio and deflection.
 Beyond 1.6% addition the above mentioned results were reversed i.e. at 1.6% addition the optimum good
results are obtained.
 The additive increases the width of the first crack and its early appearance.
References
[1]. Mosley W. H. Bungey J. H. & Hulse R . ― Reinforced concrete design‖ Pitman. 1997 385 PP.
[2]. British Standard Institution. Code of practice for design and construction. BS 8110: Part 1. London: BSI Publication 1979.
[3]. Reynolds C.E,and Steadman J.C, ―Reinforced Concrete Designers’ Johnuiley. . -1981. -
[4]. Macginley T.J. & Choo B.S. - ―Reinforced Concrete Design Theory and Examples‖ - First published by E & FN Spon First edition
1978 Second edition 1990.
[5]. Nicholas Carino J. & James Clifton R. - « Prediction of Cracking in Reinforced Concrete Structures‖ Pitman 1987 .
[6]. Rixom M. R. and Mailvaganam N. P. ― Chemical Admixtures for Concrete‖ Second Edition 1986, Published by E. & F.N. Spon
Ltd., USA, 306 pp.
[7]. Steven Kosrnatka I-i. , Beatrix Kerkhof C.f, and William Panarese ―Design and Control of Concrete Mixtures‖ .longman group ,
UK, 224 PP.

[8]. Neville A.M. , & Brooks J.J. , ― Concrete Technology ―. Cetak ulang. Singapore: Longman Singapore Publishers (Pte.) Ltd, 1990 .
438 PP
[9]. John Newman & Ban Seng Choo Advanced Concrete Technology Concrete Properties‖ - Elsevier Ltd. All rights reserved , 2003 .
[10]. Ken W. Day ―Concrete Mix Design, Quality Control and Specifications‖, Chapman & Hall, London, UK, 1995, 350 pp.
[11]. ASTM 169 A ―Tests and Properties of Concrete and Concrete Making Materials‖, American Society For Testing And Materials,
USA, 1966 , 571 pp.
[12]. Sara mob. A. Mom. ―Cracking & Deflection Of R.C. Beam Models Including Additive master of science Sudan University of
Science & Technology , March 20 11 .
[13]. Mansur , Eisa , A. and Other‖ Introduction to Pure and Applied Statistics‖ , English Book Library , Cairo 2001 .
1.1 Other types of crack in buildings maybe summarized as:
- Shrinkage cracks in buildings are unlikely to be of any structural concern but can be a source of water entry
or radon entry in buildings and may form a tripping hazard.
- Settlement cracks in a slab indicate inadequate site preparation, such as failure to compact fill on which a
foundation was poured.
- Frost heaves or expansive soil damage can cause substantial damage to basement, crawl space, or garage
floor slabs in some conditions.
- Crack from settling of new addition. Anew addition has experienced settling as a result of soil consolidation
at the new foundation.
- Crack formation due to soil related influences. Ground water can cause soil erosion and reduction of soil
compressive strength, reduction load bearing capacity of the foundation, stressing and cracking building
materials.
- Illustrate of structural member, which can occur for variety of reason such as defect or deterioration. This
stresses on other building components, promoting crack formation.
- Partial collapse of foundation, which is common among older stone foundation. Mortar has deteriorated and
stones have fallen into the basement area. The loss of structural foundation support has caused cracking of
drywall in the building interior. This is a form of deterioration.
- Cracks in wallboard due to settling.
- Cracks formed instantaneously as a result of a natural gas leakage fueled explosion in the building.
- Cracks in block wall about halfway up the wall. This is an indicator of soil and! or water pressure causing
inward deflection of the wall and impending failure. In this case, water drainage toward the foundation had
caused an excessive hydraulic load. Lock of maintenance of gutter drainage and grade near the wall has
increased hydraulic loading against the wall over time. (see Fig. 2 for the differenftypes of cracks in
buildings).
1.2 Limits on crack width:
It is necessary to identify limits of acceptability for crack widths. Max allowable in range of 0.1 mm to
0.4 mm, one reason often given for limitation of crack width is prevention of corrosion of reinforcing steel.
Table (1) present the permissible limits of crack widths (3).
Table (1): Permissible crack width:
Member Crack width (mm)
Dray air protection members 0.4
Humility, moister, soil 0.3
Deicing chemicals sea water and sea water spray 0.15
Water retaining structures 0.1

2. Crack with calcuations
2.1 Standard Formula:
Fig. 3.b: Definition of A
Fig. 3. Crack width calculations
Taking fig.. (a & b) under consideration, Welch and Janjua (4) proposed that the crack spacing S is given by:
𝑆 = 1.5ℎ + 3.0𝑑 … … … … … … … … . (1)

Where h is the concrete cover measured to the bar centre and db is diameter; the same authors proposed
the following formula for the maximum crack width;
𝑊𝑚𝑎𝑥 = 1.5 1.5ℎ + 3.0𝑑 𝑏 ℎ +
𝜎𝑠𝑡
𝐸𝑠
+ 0.0001
𝑦1
𝑦𝑠𝑡
… … … … (2)
The CEB- FIP model code (5) proposed the following formula for the crack spacing:
𝑆 = 2 ℎ +
𝜎
10
+ 0.6
𝑑 𝑏
𝑝𝑟
… … … … … (3)
Where a is the spacing of the reinforcing bars and pr is the ratio of steel bar to effective surrounding area of
concrete in tension.
Gergely and Lutz (6) has proposed that
𝑊𝑚𝑎𝑥 = 0.011(ℎ𝐴)0.33
𝐷 − 𝑘𝑑
𝑑 − 𝑘𝑑
+ 0.0001 𝜎𝑆𝐼 × 10−3
… … … … … (4)
Where h is the minimum cover to the centre of the bar and A is the concrete tension area surrounding
each bar.
ACI (7) proposed the following formula for the maximum crack width in fully cracked tensile
members.
𝑊𝑚𝑎𝑥 = 0.10𝑓𝑠3
𝑑 𝑐 𝐴 × 10−3…………………(5)
Or
𝑊𝑚𝑎𝑥 = 0.076𝛽𝑓𝑠3
𝑑 𝑐 𝐴 × 10−3…………………(6)
Where 𝛽= ratio of distance between neutral axis and tension face to distance between neutral axis and centroid
of reinforcing steel 1.2 in beams.
fs = actual tensile strength of concrete in psi dc = distance from centre of bar to extreme tension fiber in (in.)
A = area of concrete symmetric with reinforcing steel divided by the number of bars (in2).
2.2 Effect of cracking on members stiffness:
When a symmetrical un-cracked reinforced concrete member is loaded in tension the tensile force is
distributed between the reinforcing steel and concrete in proportion to their respective stiffness. The load carried
across the crack by reinforcement is gradually transferred by the bond to the concrete on each site of crack. As
the applied load increases additional cracks form at distance intervals along the member and the stiffness is drop
down, as a result of this drop, the member under cracking may finally fail. The contribution of concrete between
cracks to the net stiffness of a member is known as tension stiffening.
2.3 Finite element applications:
Extensive researches has been done in recent years on the application of finite elements to modeling the
behavior of reinforced concrete and is summarized in a report of the ASCE task committee on finite element
analysis of reinforced concrete (8). Two basic approaches, the discrete crack approach and the smeared crack
approach have been used to model cracking and tension stiffening.
2.4 Deflection - calculation:
Prediction of deflection is very important in order to avoid damage to finishes and services, although the
estimation of exact deflection may be difficult due to some considerable effects on deflection calculation, such
as:
 The long term creep effects.
 The effect of finishes, partitions ... etc.
 Shrinkage of the concrete.
 The precise duration of the live load. However, the max deflection (a) in concrete may be calculated using
the following formula (9);
𝑎 = 𝐾
𝐿2 𝑀
𝐸 𝑐 𝐼 𝑐𝑒
…………………………….(7)
where K is a coefficient that depends on the load distribution and the end fixity conditions.
L = length of the concrete member.
M = bending moment.
Ec = modulus of elasticity of concrete.
Ice = second moment of area of the section in equivalent concrete units.
The permissible deflection in the building elements should not exceed the values given in table (2)

Table (2) Permissible Deflection
Member Deflection
Cantilever beam Length/180
Beams carrying plaster Span/ 360
All other beams Span /200
Columns in multi-storey buildings Height/ 300
Crane girders Span/ 600
Table (3): the studied buildings
Building No.
Location No. of Floors
Type of
slab
Beams size
cm
Column size cm Type of foundation
1.
AlGeraif- KRT 11 Flat -
70 × 30
120 × 30
Raft
2.
Riadh – KRT 7 Flat -
70 × 30
90 × 30
Raft
3.
Riadh – KRT 6 Flat -
70 × 30
90 × 30
Raft
4. alGeraif- KRT 3 FLAT 50 × 20 50 × 20 ISOLATED
5. AlNuzha- KRT Footings - - - -
6.
Algeraif- KART 3
Slab-
Beam
50 ×25 40 × 40 Isolated
7. Khartoum centre 7 Slab-beam 40 ×25 60 × 25 Isolated
8. Mamoura- KRT 1 Flat - 50 × 25 Isolated
9. Thawora- Omdurman 2 Flat - 50 × 25 Isolated
10. Sinaat- Omdurman 3 Slab- beam 50 ×25 50 × 25 Isolated
11. Saifa- KRT-N Footings - - - -
12.
3rd
Class-KRT 6 Flat -
70 × 30
90 × 30
Raft
13. Amarat-KRT 11 Flat - 60 × 30 Raft
14. Arkawit-KRT Footings - - - -
15. Khartoum Center 3 Slab- beam 50 ×25 50 × 25 Isolated
16.
Amarat-KRT 2 Flat -
60 × 30 Isolated
17.
Magran-KRT 4 Slab-Beam 50 ×25
60 × 30 Isolated
Table (4): Types of failures in the different buildings:
4. Discussion of Results:
The crack width calculations in the different buildings has ranged between 0.7 mm-15mm, all of it is
more greater that the permissible crack width shown in table (1).
Regarding deflection in some members it has been recorded in two of the cantilevers of lengths 160 cm
as 60 mm which is very excessive in comparison to table (2).

In reference to table (3) and table (4) that 17 reinforced concrete structures has been studied and the
main type of failure has been presented and it has been found that the main types of failure is due to construction
and lack in design and regarding the structural elements, the slabs and walls are suffering failure more than the
other elements. Table (5) present the percentage comparison for the different causes of failure in the studied
reinforced concrete elements in tables (3) and (4).
Table (5). Failure % age comparison
5. Conclusions:
From the case study in this research, the following conclusions can be drawn:
1) The main cracks in reinforced concrete buildings are due mainly to lack in construction process.
2) Soil testing is very important before the design process of the reinforced concrete building.
3) The flat slab may be one of the main causes of failure in reinforced concrete structures due to the punching
shear developed at the column face.
4) Insufficient design and poor detailing may lead to failure in reinforced concrete structures.
5) In design the ability requirements like the expansion joints, the reinforced concrete cores, and the shear
walls should be taken under consideration.
6. References:
[1]. Future Engineering Group ―Design of high rise building to resist wind and seismic loads‖ in Arabic, walid printing press, Egypt
1994, 480 pp.
[2]. Abu — Almagd. .et..al ―Cracks in Reinforced Concrete Structures and its Repair‖, Egyptian Universities Printing Press, Cairo,
2007.
[3]. Concrete manual, 8th edition, U.S. Bureau of Reclamation, Denver, 1975, 627 pp.
[4]. Janjun, M.A and Welch, G.B ―Magnitude and Distribution of concrete cracks in Reinforced concrete Flexural Members‖, UNICJV.
Report No. R 78, Univ. of NSW, Kensington, 1972.
[5]. CEB-FIP Model Code for Concrete Structures, C&CA, London, 1979.
[6]. Gergely P., and Lutz, L.A ―Maximum crack width in reinforced concrete flexural member‖, ACT publications, sp-20, Detroit, 87-1
17 pp. 1968.
[7]. 7. ACI 224 — 2R — 92, ―Cracking of Concrete Members in Direct Tensiontt, re-approved 1997.
[8]. Finite Element Analysis of Reinforced Concrete, American Society of Civil Engineers, New York, 1982, 545 pp.
[9]. Morell, P. ―Design of Reinforced Concrete Elements‖, Granda,U.K,1984.

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