Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : reinforced concrete

Influence of Minimum Tension Steel Reinforcement on the Behavior of Singly Reinforced Concrete Beams in Flexure

Ali A. Abdulsada; Raid I. Khalel; Kaiss F. Sarsam

Engineering and Technology Journal, 2020, Volume 38, Issue 7, Pages 1034-1046
DOI: 10.30684/etj.v38i7A.902

The requirements of minimum flexural reinforcement in the last decades have been a reason for controversy. The structural behavior of beams in bending is the best way of investigating and evaluating the minimum reinforcement in flexure. For this purpose, twelve singly reinforced concrete beams with a rectangular cross-section of (125 mm) width by (250 mm) height and (1800 mm) length were cast and tested under two-point loads up to failure. These beams were divided into three groups with different compressive strengths (25, 50, and 80 MPa). Each group consists of four beams with different amounts of tension steel reinforcement approximately equal to (0% Asmin, 50% Asmin, 100% Asmin and 150% Asmin), two bar diameters (Ø6 mm and Ø8 mm) were used as the longitudinal tension reinforcement with different yield and ultimate strengths, the minimum amount of reinforcement required is calculated based on ACI 318M-2014 code. The results show that for the reinforced concrete beams, the flexural reinforcement in NSC beams increases the first cracking load and the increment increased with an increasing amount of reinforcement, while for HSC beams the increasing in first cracking load are very little when the quantity of reinforcement less than the minimum flexural reinforcement and increased with the increasing amount above the minimum flexural reinforcement. The equation of ACI 318M-14 code gives adequate minimum flexural reinforcement for NSC and overestimate value for HSC up to (83 MPa), A new formula is proposed for HSC rectangular beams up to (90 MPa) concrete compressive strength by reducing the equation of ACI 318M-14 code for minimum flexural reinforcement by a factor depending on concrete compressive strength.

Influence of Spirals on the Behavior of Short RC Columns Strengthened by External CFRP

Kaiss F. Sarsam; Raid I. Khalel; Mohammed A. Hadi

Engineering and Technology Journal, 2018, Volume 36, Issue 2A, Pages 223-233
DOI: 10.30684/etj.36.2A.15

An experimental study was carried out to investigate the behavior of normal strength reinforced concrete (RC) circular short columns strengthened by carbon fiber reinforced polymer (CFRP) sheets. Three series comprising total of (15) specimens were loaded to failure under axial concentric compression load. Strengthening was varied by changing CFRP strips number, spacing and wrapping methods. The finding of this research can be summarized as follows; for the columns without CFRP, the influence of the spiral pitch was significant: compared with 100 mm spiral pitch, dropping the spacing to 65 mm and 30 mm increased the load carrying capacity by 25% and 43% respectively. The columns with less internal confinement (lesser amount of spirals) were strengthened more significantly by the CFRP than the ones with greater amount of internal spirals. As an example of the varying effectiveness of the fully wrapped CFRP, the column with spiral pitch at 100 mm was strengthened by 74% with the CFRP. In contrast, the ones with 30 mm spiral pitch only increased in strength with CFRP by 51%. Compared with the control specimen (no CFRP), the same amount of CFRP when used as spiral strips led to more strengthening than using CFRP as hoop strip-the former led to nearly 8% more strengthening than the latter in the case of 100 mm internal spiral pitch. In the case of 65 mm the internal spiral pitch, the difference (between the hoops &spiral CFRP strengthening)is close to 10.5%. The difference between the two methods of strengthening in the heavily spiral columns (30 mm spiral pitch) is more significant.

Effect of Re-vibration Process on Axial Capacity of Short Reinforced Concrete Circular Columns

S.A. Abbas

Engineering and Technology Journal, 2017, Volume 35, Issue 7, Pages 776-787
DOI: 10.30684/etj.35.7A.15

A considerable amount of research work has been performed on the effects of vibrating of fresh concrete on the reduction of shrinkage and creep, the improvement bond stress between reinforcing bar and concrete, reduction the concrete permeability and improvement of the mechanical properties of concrete (tension and compression). Series of tests on reinforced concrete circular column, cubes and cylinders were carried out to study the effect of re-vibration duration on axial strength of column, compression strength of concrete cubes, and tensile strength of cylinders. Different compressive strengths of concrete and different size of aggregate were considered in this investigation. The test results show that, the re-vibration operation improves the tensile and compressive strength of concrete. The stiffness of columns increased with increasing the re-vibration duration up to1.5 times the initial vibration duration. Size of aggregate has significant effect on the improvement properties of concrete due to re-vibration. Increase the time duration of re-vibration delay the appearance of first crack.

An Experimental Study on the Shear Strength of High-performance Reinforced Concrete Deep Beams without Stirrups

Sinan Abdulhkaleq Yaseen

Engineering and Technology Journal, 2016, Volume 34, Issue 11, Pages 2123-2139
DOI: 10.30684/etj.34.11A.17

High-performance fiber-reinforced concrete is a new class of concrete that has been developed in recent decades. It exhibits enhanced properties such as high compressive strength and improved tensile strength. Three types of concrete with different compressive strengths, namely, normal-strength concrete, high-strength concrete, and high-performance concrete, were used in this study. The experimental program included casting and testing sixteen reinforced concrete deep beams without stirrups to study the shear strength and behavior of these beams under two-point loading. The variables considered were the compressive strength of concrete (f′c ) (40–120 MPa), shear span-to-depth ratio (1, 1.5, 2, 2.5, and 3), and the ratio of the amount of flexural steel bar ratio (1.35%, 2.40%, 3.76%, and 6.108%). Experimental results showed that increasing concrete compressive strength and flexural steel bar ratio increased ultimate shear capacity. By contrast, increasing shear span-to-depth ratio and span-to-depth ratio reduced ultimate shear capacity. Based on the test results of this investigation (16 beams) and those of available literature (233 deep beams), an equation that considered the parameters affecting shear stress (f′c, l/d, a/d, andw) was proposed using SPSS software. The proposed equation was compared with predictions made by the American Concrete Institute (ACI) and the works of other researchers, including that of Zsutty and Aziz. The ACI predictions were conservative and the proposed equation had a lower coefficient of variation.

Direct Shear Behavior of Carbon Fiber Reinforced Self- Compacting Concrete

Kaiss F. Sarsam; Tareq S. Al-Attar; Ghzwan Ghanim Jumah

Engineering and Technology Journal, 2014, Volume 32, Issue 10, Pages 2491-2513
DOI: 10.30684/etj.32.10A.13

This paperrepresents an experimental and statistical investigation for the behavior of connectionpoints produced by using self-compacting concrete and subjected to direct shear. The investigation also includes the effect of carbon fiber inclusion as reinforcement on self-compacting concrete (SCC) behavior in direct shear.
This study gives results of sixteen push-off or direct shear specimens in four groups. Variations include volume fraction for carbon fiber (V_f= 0.00, 0.50, 0.75 and 1.00) % for every percentage change in the steel reinforcement. The steel reinforcement parameter ρ_vf f_y values are (0.00, 2.66, 5.33 and 7.99) MPa(where ρ_vf varies from 0.00 to 0.0173 and f_y=585.7MPa) . The main material properties studied include compressive strength, splitting tensile strength and modulus of rupture. Measurements of deformations were made throughout testing of shear specimens.
The dimension of the shear plane in the push-off specimenswas 170x185 mm. The shear reinforcement was normal to the shear plane. Specimens were cast by using SCC which is a type of high performance concreteand reinforced with carbon fiber.
This work aims to investigate the direct shear behavior of SCC with or without carbon fiber at constant water to cementitious materials ratio of 0.3 by weight. It is found that using carbon fiber increased the direct shear strength. However, carbon fiber alone (without reinforcement) leads to brittle failure. In contrast, adding rebars leads to higher strain and more ductile behavior-increased shear capacity is obtained when higher steel quantity is used. The aim of adding carbon fibers was the increase of the horizontal strain (displacement). It was found that the optimum percentage of volume fraction was 0.75 % for fresh and hardened concrete.
In addition, the effects of carbon fiber on compressive strength of SCC lead to a drop in compressive strength (f_c^') compared with reference specimens. This drop in f_c^' was 2.39, 8.38 and 13.58% for V_f=0.50, 0.75 and 1.00%, respectively. In contrast, the splitting tensile strength increased by 3.34, 31.2 and 18.2 as compared with the cylinder strength without carbon fibers atV_f equal to0.50, 0.75 and 1.00% respectively. The modulus of rupture increased by [11.9, 21.99 and 13.83%] as compared with SCC without carbon fibers at〖 V〗_f equal to 0.50, 0.75 and 1.00% respectively.
Based on push-off tests results for this work and those available in the literature, two statisticalmodels have been established using regression analysis. Four variables f_c^',f_ct,ρ_vf f_y and V_f, were included in these models. Both models showed good representation according to their coefficients of variation (COV)values. Verification of the models were done by using 273 observations from literature and the present work.

Durability Characteristics of Concrete and Reinforcing Bars Exposed to Harsh Environments

Sanaa Abdul Hadi Hafad; Farah Hamed Rashed

Engineering and Technology Journal, 2014, Volume 32, Issue 5, Pages 921-937
DOI: 10.30684/etj.32.5B.9

Saline pollution attack is an important factor that leads to the deterioration of the concrete, especially in industrial plants. In spite of research address the sustainability of concrete and particularly steel rebar submeserged in it steel rebar is the most important causal factors the deterioration in the reinforced concrete the main aim of this research is study the effect of additives added to reduce superior degree water and two types of mineral additives that include silica fumes and steel fiber, as well as the combined effect of these additives on the properties of concrete. The experimental work of this measure include concrete specimens have been partially submerged in a solution of chlorides and sulfates in concentrations similar to those found in aggressive conditions. The properties of concrete specimens were evaluated through the properties investigated included ultrasonic plus velocity, compressive strength electrochemical potential for various types of mixes. Concrete mixed with 10% of silica shown development all properties of concrete, while these properties deceases values of mix reference coated with natural rubber (RFCNR) and steel fiber coated with natural rubber (STFCNR). The result coated specimens has shown resistance to corrosion greater than specimens without coated when immersion in salt solution. Thus group (RFCNR )shown more develops in all properties as compared with all other mixture immersed in salt solution for 180 days at odds with group ( SF-SP) which had development in all properties as compared with the reference mixture at 180 days of immersion in salt solution .

Mechanical Properties and Dynamic Response of Lightweight Reinforced Concrete Beam

AzizI brahimAbdulla; a A. Ali; Alya; Ahmed Adnan Ghanee

Engineering and Technology Journal, 2012, Volume 30, Issue 2, Pages 293-311
DOI: 10.30684/etj.30.2.9

The study is conducted to perform two goals: The first geal is to produce a
lightweight concrete using major components which are locally available with
some standard admixtures.Many mixtures are prepared using many ratios of
superplasticizer (SP) and silica fume (SF) admixtures to yield a lightweight
aggregate concrete, the effects of using different ratios of these admixtures on unit
weight, compressive strength and flexural strength are studied individually and
accumulatively. The secondis to study the dynamic specifications of normal and
lightweight reinforced concrete beams.
The results showed that the increasing in dosage of superplasticizer (SP) for
(LWAC) increases the density of (LWAC), and the increasing in dosage of silica
fume (SF) decreases the density of (LWAC). The experimental impact tests for
R.C. beams shows that the lightweight R.C. beams have a better response under
impact loading with respect to the maximum dynamic deflection (2.955mm for
normal weight beam and 1.58mm for lightweight beam). Also,Impact force
transferred to supports reactions of lightweight beams is smaller within 45% than
the impact force transferred to reaction of normal weight concrete under the same
impact load, and the time to reach 90% damping equal to 1.223 sec and 1.6 sec for
lightweight and normalweight R.C. beams respectively. Also, the reinforced
concrete beams are tested under repeated impact load up to failure. The tests
showed that the no. of blows to cause first crack for lightweight concrete beams
more than twice of this for normalweight concrete beams.

Investigation of the Behavior for Reinforced Concrete Beam Using Non-Linear Three-Dimensional Finite Elements Model

Israa Kh. AL-Shimmari; Nagham T.Hamad; Waleed A Waryosh

Engineering and Technology Journal, 2011, Volume 29, Issue 10, Pages 1870-1885
DOI: 10.30684/etj.29.10.1

This study presents theoretical investigation that reinforced concrete and composite construction might be suitably combined to give a new structural material: composite reinforced concrete. To study theoretically the composite beam, nonlinear three-dimensional finite elements have been used to analyze the tested beam.
The 8-node brick elements in (ANSYS) are used to represent the concrete, the steel bars are modeled as discrete axial members connected with concrete elements at shared nodes assuming perfect bond between the concrete and the steel. The results obtained by finite element solution showed good agreement with experimental results.

Evaluation of Elastic Deflections and Bending Moments for Orthotropically Reinforced Concrete Rectangular slabs Supported on Three Edges Only

Hisham M. AL-Hassani; Husain M. Husain; Aama; a Ali Ahmad

Engineering and Technology Journal, 2009, Volume 27, Issue 7, Pages 1247-1259
DOI: 10.30684/etj.27.7.2

This paper deals with the evaluation of the elastic deflections and bending moments
for orthotropically reinforced concrete rectangular slabs supported on three variously
restrained edges with the fourth edge free and subjected to uniformly distributed load.
Six cases are considered for such slabs to cover all possible restraining conditions at the
three supported edges. Based on the finite difference approach, equations are derived to
calculate the maximum values of the positive and negative bending moments as well as
the maximum deflection in any of these six slab cases caused by the applied uniform

Experimental Tests on Orthotropically RC Rectangular Slabs Having Various Restrained Edges and Subjected to Uniform Load

Husain M. Husain; Hisham M.AL-Hassani; Sarmad S. Abdul-Qader AL-Badri

Engineering and Technology Journal, 2009, Volume 27, Issue 5, Pages 913-929
DOI: 10.30684/etj.27.5.6

In this research, nine orthotropically reinforced concrete (RC) rectangular slabs
having various boundary restraints at the edges are tested under uniformly distributed
load. The main aim of these tests is to show that when some or all edges of a slab are
restrained against rotation and horizontal translation the ultimate load carrying capacity
of the slab will be enhanced greatly above that suggested by the simple Johansen ,s yield
line theory(1). For this purpose, a specially designed rig is constructed and used for
providing slabs with various boundary restraints along their edges.
The results of tests, which are presented in the form of load-deflection curves plotted
non-dimensionally, show that for restrained slabs the enhancement in load above
Johansen ,s load ranges between 50% and 100% depending on the number and positions
of the slab restrained edges. These results are also used to examine the accuracy of a
recently submitted elastic-plastic theoretical model(2).

Design charts for channel shaped reinforced concrete short columns subjected to axial compressive load and uniaxial bending

Asma; a A. Ahmad; Sarmad S. Abdul-Qader AL-Badri

Engineering and Technology Journal, 2009, Volume 27, Issue 4, Pages 809-820
DOI: 10.30684/etj.27.4.17

Eight design charts are presented for reinforced concrete short C-columns subjected to
axial compressive load plus uniaxial bending. For design these charts can be used for
determining the required column dimensions and amount of steel, while for analysis
these charts can be used for estimating the loaded column capacity.
Four examples are given to explain the use of design charts for both design and
analysis, two of which are design examples while the other two are analysis. It has been
shown by these examples that the new proposed charts are very simple to use in
structural applications.

Flexural Rigidity of Slender RC Columns

Sabeh Z. Al-Sarraf; Ihsan A. S. Al-Shaarbaf; Bassman R. Al-Bakri; Kaiss F. Sarsam

Engineering and Technology Journal, 2009, Volume 27, Issue 1, Pages 96-115
DOI: 10.30684/etj.27.1.8

166320 hypothetical reinforced concrete (RC) columns, each with a different
combination of variables, were used to investigate the major variables that affect the
flexural rigidity (EI) of slender RC columns. Using linear regression analysis, new EI
expression was statistically developed for 131 slender RC columns. These columns were
experimentally tested and available in the literature. This proposed EI expression were
introduced into the ACI 318M-05 Code column design procedure to make comparisons
between 150 column experimental data with theoretical estimates of the nominal
strength using theoretical other methods. These estimates include, in addition to the proposed
EI expression, other calculations from the literature.