Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 119 EFFECT OF TRANSVERSE REINFORCEMENT ON THE AXIAL COMPRESSIVE STRENGTH OF REINFORCED CONCRETE COLUMNS Haitham AL-THAIRY Civil Engineering Department, College of Engineering, University of Al-Qadissiya, Iraq. Email: haitham.althairy@qu.edu.iq Received 13 August 2015 Accepted 29 December 2015 ABSTRACT This paper presents an experimental study on the effect of transverse reinforcement on the axial compressive strength of rectangular and circular cross sectional shape reinforced concrete (RC) columns under axial compression. Twenty specimens of small scale RC columns specimens were considered in the experimental tests. Ten of the columns specimens have a square cross sectional shape with dimensions of (150×150) mm and the other ten specimens have a circular cross sectional shape with a diameter of 150mm. For each cross sectional shape, the columns are classified into two groups of five columns: the first group contains short columns according to ACI-Code requirements (ACI318, 2011) and the other group consists of long columns. Each group uses same longitudinal reinforcement ratio but with five different transverse reinforcement ratios represented as a volumetric ratio of the transverse reinforcement. An experimental test has been conducted to determine the maximum axial compressive load at which each concrete column would fail. The experimental test results have shown that increasing of the volumetric ratio of the transverse reinforcement leads to a considerable increase of the axial load resistance of the column for both rectangular and circular columns and for both cases of long and short columns. The study has also showed that using equations suggested by the ACI-Code to determine the axial compressive strength of RC columns with tie reinforcement that are spaced at distances exceed that suggested by the code, gives over- estimated predictions of the column axial resistance which may results unsafe design. Keywords: RC columns, axial strength, transverse reinforcement, experimental tests, volumetric ratio. انضغاط الحمال معرضةالكونكريتية ال لالعمدةالتسليح العرضي على مقاومة االنضغاط تاثير محورية الثائري هيثم علي بادي في قسم الهندسة المدنية/كلية الهندسة / جامعة القادسية يتدريس mailto:haitham.althairy@qadissuni.edu.iq Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 120 الخالصة عمدةاالتلك و مقاومة المسلحة يقدم المشروع دراسة عملية )مختبرية( للعالقة بين نسبة التسليح العرضي في األعمدة الخرسانية عشرة من نماذج .ة المسلحة يعمدة الخرسانوذج من االمين نتم إجراء الفحوصات المختبرية على عشر . لمحوريةاغاط ضاالنلقوة بقطر يبلغ الشكل ريةئرى بمقاطع عرضية داخو العشرة االملمتر 051× 051تمتلك مقاطع عرضية مربعة الشكل بابعاد االعمدة مجموعتين : المجموعة األولى وعددها خمس أعمدة صنفت الى واحد طع عرضي ذات مقاعمدة كل عشرة تم تقسيم . ملمتر 051 المجموعة الثانية وعددها خمس أعمدة أيضا تم و ACI 318-11 حسب متطلبات مدونة معهد الخرسانة االمريكي كأعمدة قصيرة لتسليح الحجمية لنسبة الوتغيير العمدة الخمسة من الكل مجموعة تصنيفها كأعمدة طويلة حيث تم تثبيت نسبة التسليح الطولي فحص تم . العرضي الى حجم لباب الكونكريت المحاط باالطواقللتسليح الكلي الحجم موع جالتي تمثل نسبة م العرضي )األطواق( لكل نسبة تسليح عرضي لمعرفة تأثير تغير التسليح العرضي على قابلية تحمل و لكل عمود الستاتيكية المحورية االنضغاط مقاومة مقاومة االعمدة الخرسانية ) ملحوضة في بينت الدراسة ان زيادة النسبة الحجمية للتسليح العرضي تؤدي الى زيادة .المحورية من قبل مدونة معهد الخرسانة قترحةالم التالمعاداستخدام المحورية. كما بينت الدراسة ان االنضغاط النحيفة و القصيرة ( لقوة في الحالت التي تكون فيها لالعمدة الكونكريتية المحملة محوريا المحرية لحساب مقاومة االنضغاط ACI 318-11 األمريكي األمر الذي عالية تحملتعطي قيم المسافات بين حديد التسليح العرضي ) االطواق( اكبر من الحدود العظمى المحددة من قبل الكود .لالعمدة الكونكرينية ينتج عنة تصميم غير امنقد ., نسبة حجميةاعمدة خرسانية مسلحة , مقاومة محورية , تسليح عرضي, فحوصات مختبرية :كلمات الداللة . 1. INTRODUCTION Reinforced concrete (RC) columns are main structural members of any reinforced concrete building and their failure may be cause failure of the whole structure of that building. Besides the uniaxial or biaxial bending moments that a RC column may be subjected to, columns are mainly designed to resists axial compressive loads imposed from the upper stories of the buildings. For this type of column resistance (i.e. the axial compressive load resistance) Sec. 10.3.6.1 of the American Concrete Institute design code for reinforced concrete buildings (ACI318, 2011) has suggested the following equations to predict the design axial compressive strength: 1. For columns with spiral reinforcement )AFy +)A -(Acf 0.85Ø(0.85=ØP ststgnmax  (1) 2. For columns with tied reinforcement )AFy +)A -(Acf 0.80Ø(0.85=ØP ststgnmax  (2) Where Ag is the gross cross sectional area of the RC column; Ast is the total area of the longitudinal reinforcement steel bars; Fy is the yield stress of the longitudinal reinforced steel; ́ is the compressive strength of the concrete; Ø is the strength reduction factor which is taken as 0.7 for spiral reinforcement and 0.65 for tie reinforcement. Equations 1 or 2 may be expressed in a general form as follows: )P0.8)Ø(Por (0.85=ØP Long. Conc.nmax  (3) Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 121 Where Pconc. is the axial compressive strength of the RC column comes from the concrete; PLong. is the axial compressive strength of the RC column comes from of the longitudinal reinforcement. It can be noticed from Eq 3 that the ACI-Code only considers the contribution of the concrete and longitudinal steel reinforcement in the axial compressive strength of the RC columns neglecting the contribution of transverse reinforcement (ties or spirals) which may considerably affect the total axial compressive strength of the RC columns. However, sec. 7.10.5 of ACI-Code (ACI318, 2011) suggests limits for the maximum spacing (Smax) of the transvers reinforcement to be used in the design of RC columns, which are the minimum of: 16 times the diameter of the longitudinal reinforcement steel bars (db); 48 times the diameter of transverse reinforcement steel bars (dTie) or; the minimum dimension of the column cross section. Nevertheless, as will be shown in this study, these limits gives very close spacing of the transverse reinforcement and neglects the cases of higher spacing distances which may also be applicable in many design situations. On the other hand, many research studies have been carried out to investigate the effect of transverse reinforcement on the behaviour and failure of short RC columns. However, long RC columns have rarely been considered in these previous researches. For instance, Chung et al. (2002) have suggested an equation to determine the magnitude of the increase in strength of confined concrete. The suggested equation was based on experimental data and nonlinear multiple regression method of sixty-five reinforced short concrete columns. Sharma et al. (2005) have presented an experimental study to investigate the strength of short columns with high strength concrete confined by spirals and ties reinforcement under increasing concentric compression load. The volumetric ratio, spacing, configuration and yield strength of transverse reinforcement are all considered as test variables along with the ratio of longitudinal reinforcement. Hong et al. (2006) and Junior and Giongo (2004) have also conducted an experimental study to determine the effect of low volumetric ratio of lateral tie reinforcement on the high strength concrete and steel fibre high strength concrete column respectively. It has been shown in Hong et al. study (Hong et al., 2006) that columns specimen’s with higher volumetric ratios in conjunction with lower-grade tie yield strength shows better performance than those with lower volumetric ratios in conjunction wiyh higher-grade yield strength. On the other hand, Junior and Giongo study (Junior and Giongo, 2004) have revealed that steel fibre may be help to avoid the premature concrete cover spalling. Wang and Wue (2010) carried out an experimental investigation on the effect of the confinement using Aramid Fibre-Reinforced Polymer sheets on the strength of square high-strength concrete short columns. Regression formulae were developed for strength and strain based on the experimental results. Two types of axial stress-strain curves were observed from the tests results depending on the form of AFRP wrapping. It has also been shown that the strength and ductility of the columns increases when fully wrapped AFRP sheets are used whereas only the strength increases when partially wrapped AFRP sheets are to be used Khaleek et al. (2012) has conducted an experimental study on small scale rectangular and circular cross section short columns to determine the effect of volumetric ratio of the transverse reinforcement on the axial compressive strength. It has been shown that the column axial compressive resistance significantly increases when the volumetric ratio of transverse reinforcement has been increased. However, since the study has only considered short columns, as defined by ACI-Code classification of columns, their results could not be generalized to include other cases of long columns because of the difference in behavior and failure modes between two types of columns. Shin et al. (2012) have also conducted experimental tests on eight small scale rectangular cross section short columns subjected to axial compressive load to cause column failure. It has been Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 122 concluded that increasing of the volumetric ratio of transverse reinforcement results to a considerable increase of the column ductility which is indicated by the number of cyclic loading that the column can sustain before experiencing failure. It has also been found that the increasing in ductility of the column was due to increasing of the compressive strength of the column owing to increasing of the confinement resulted from the transverse reinforcement (ties). Öztekin (2012) suggested a method to predict the confined compressive strength of square concrete columns using artificial neural networks (ANN). The ANN model has been developed by using experimental test results of normal and high strength square concrete columns. Several parameters have been addressed in the developed model including numbers and diameters of longitudinal and transverse reinforcements, spacing and configuration of the transverse reinforcement. The validation results have shown that the developed ANN model predicted more accurate results compared to the available analytical models. Radnić et al. (2013) have recently presented an experimental study to investigate the effect of concrete confinement on the compressive strength and ductility of concrete beam subjected to pure bending. The effect of the form and spacing of stirrups on the capacity and ductility of RC beams were investigated in the study. It has been shown that the ultimate strength capacity and deflection of RC beam increase with decreasing of stirrups spacing. Moreover, it has been concluded that the stirrup form has a considerable effect on the ultimate load carrying capacity and ductility of RC beam. It is clear that all the previous research studies have only considered the short reinforced concrete columns in their investigations. Therefore, the main objective of the present research is to investigate the effect of transverse tie reinforcement on the axial compressive strength of the RC short and long columns. Series of experimental test will be conducted on twenty small scale rectangular and circular cross section long and short columns specimens. All RC columns specimens will be subjected to an incremental increasing static axial load up to column failure. The experimental test results will be compared with the corresponding ACI-Code design equations. 2. EXPERIMENTAL PROGRAM AND TEST SETUP This section describes in details the experimental program including test setup and column specimens used in experimental tests of this study and present the experimental test results. 2.1. Concrete mixture ingredients All material used in the concrete mixture used to cast the concrete column specimens (fine aggregate, coarse aggregate) are tested in the constructional material laboratory at Civil Engineering Department/College of Engineering/The University of Al-Qadissiya as follows: 2.1.1. Cement: The ordinary Portland cement type (I) available in local markets in Iraq and conform to the Iraqi specification No. 5/1984 was used in the present study. 2.1.2. Fine aggregate (Sand): Natural sand with maximum size of 10 mm was used in this study. Experimental tests have been carried out to determine the grain size distribution; sulfate and fine material contents and the results are shown in Table 1. Test results have shown that the grain size distribution conform to the Iraqi specification No.45/1984. On the other hand, sulfate and the fine materials contents are comply to the requirements of the Iraqi specification No.45/1984. Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 123 2.1.3. Table 2. Test results have shown that the grain size distribution conform to the Iraqi specification No.45/1984. On the other hand, sulfate and the fine materials contents are comply to the requirements of the Iraqi specification No.45/1984. 2.1.4. Reinforcement steel bars: The mild steel bars have been used to reinforce the concrete columns with diameters of 10mm and 8mm for longitudinal reinforcement and 6 mm for transverse reinforcement. A uniaxial tensile test has been conducted to determine the yield stress of the reinforcement steel (Fy) to be used thereafter in the ACI equations (i.e. Eq. 1 and Eq. 2). Error! Reference source not found. shows the uniaxial tensile test results of the reinforcement steel bars. 2.1.5. Water: Tap water was used in this study for mixing and curing test specimens. 2.2. RC columns specimens. All the ingredients of the concrete mixture were mixed with each other using a mix ratio of 1:1.75:3.5 (cement: sand: aggregate). A tap water was added using water to cement ratio (w/c) equal to 0.48 to form a fresh concrete mixture. The concrete mixture with the aforementioned properties has been used to cast twenty reinforced concrete columns with dimensions, longitudinal and transverse reinforcements as shown in Table 4 and Figure 1. Ten of RC column specimens have a square cross section with dimensions of (150×150) mm and the other ten columns have a circular cross section with a diameter of 150mm. For each cross sectional shape, the columns are divided into two groups of five columns: the first group contains short columns defined according to Sec. 10.10.1 of AIC- Code (AIC318, 2011) and have a total length of 800mm for rectangular section column which are designated as (RS0- RS4) and 750 mm for circular section columns which are designated as (CS0- CS4). The other group contains long column (AIC318, 2011) with a length of 1200mm for square cross section columns which are designated as (RL0- RL4) and of 1300mm for circular cross section column which are designated as (CL0- CL4). Each group of five RC columns uses same longitudinal reinforcement ratio but with five different transverse tie reinforcement ratios represented as a ratio of the tie reinforcement volume to the concrete core volume. The transverse tie reinforcement ratio has been changed by changing number of ties in each column as shown in Table 4. Ply-wood and PVC pipes were used as forms to cast the rectangular and circular columns respectively. Due to the limitation in resources available in the laboratory, each ten columns with same cross sectional shapes were cast in two different batches. For each cast batch, twelve concrete cubes with dimensions of (150×150×150) mm have also been case to determine the compressive strength of concrete corresponding to each ten columns. After casting, all RC column specimens and concrete cubes have been remolded, marked and cured for time duration of 28 days by immersing in a warm water basin (at 20 C o to gain the maximum concrete strength and to be ready for the test. 2.3. Testing and loading of RC column specimens. 2.3.1. Concrete cubes: After curing, axial compressive tests have been carried out on the twelve concrete cubes to obtain the compressive strength of concrete corresponding to each ten Coarse aggregate (gravel): Natural coarse aggregate with maximum size of 20 mm was used in this study. Experimental tests have been carried out to determine the grain size distribution; sulfate and fine material contents and the results are shown in Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 124 column. The compression test machine available at constructional material laboratory at Civil Engineering Department/ College of Engineering/ The University of Al-Qadissiya was used to perform the tests; Table 5 shows the compressive strength of the concrete cubes corresponding to each concrete batch with the average values used for each group of ten columns. 2.3.2. Concrete Columns: After a 28 day of curing, a static axial compressive load bearing tests were conducted for the reinforced concrete columns specimen to capture the axial compressive strengths to each column. The universal test machine available at constructional material laboratory at Civil Engineering Department/ College of Engineering/ The University of Al-Qadissiya was used to perform the tests, see Figure 2. The ends supports of all tested columns simulate the simply support conditions with no sideways movement (braced columns) because the top and bottom ends of the columns are not capable to move laterally. To ensure a uniform distribution of the axial compressive load, a square steel bearing plate with dimensions of (200×200×5) mm (width ×length× thickness) was fixed at the top end of each column during the test. An incremental increasing axial static load has been applied to each RC column until the column experienced failure represented by a reloading of loading gages of the test machine. The axial load at which failure occurs was recorded for each tested column and the results will be presented and discussed in the next section. 3. DISCUSSION OF THE TEST RESULTS 3.1. Failure modes Figure 3 and Figure 4 show the RC column specimens shapes after failure. As can be seen from these figures, all tested columns have experienced similar failure pattern represented by concrete crushing at the top of the column followed by generating of cracks and splitting of the concrete cover surrounding the transverse reinforcements at the top quarter of the RC column. It can also be noticed from Figure 3 and Figure 4 that the longitudinal reinforcement bars have also experienced global buckling particularly near to the loaded end of the column. This can be attributed to the effect of the axial load and because the longitudinal reinforcement bars have no lateral support when the concrete surrounding the longitudinal reinforcement bars have been crushed at the beginning of loading. One of the functions of transverse reinforcements in columns is preventing the main longitudinal bars from buckling outward, spalling the concrete and causing early collapse. Without ties being properly spaced, the main steel could not be relied upon to reach its yield stress. 3.2 Axial compressive strength. As mentioned before, each column specimen has been subjected to an increment axial static load until the column experienced failure using a load increment of 5kN. Failure of each column was detected by a reloading of the loading gage of the test machine which occurs when the RC column crushes or buckles. Table 6 and Table 7 and Figure 6 to Figure 8 show the relationship between failure load and the volumetric ratio of transverse reinforcement for all tested columns. It can be seen form Table 6, Figure 5 and Figure 6 which demonstrate the relationship between the axial compressive strength of short columns and volumetric ratio of the transverse reinforcement that increasing of the volumetric ratio of the transverse reinforcement resulted increasing of the axial compressive load at which the columns have failed. Increasing of the volumetric ratio of the transverse reinforcement from 1.4961×10 -3 to 3.9896×10 -3 for rectangular sections and from 3.16×10 -3 to 9.49×10 -3 for circular sections has increased the column axial compressive resistance from 316.5kN to 410. 8kN and from 292.4kN to 394.7kN for rectangular and circular sections respectively with increasing rate of 30% and 35% for rectangular and circular sections respectively. Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 125 Similarly, Table 7, Figure 7 and Figure 8 show that increasing of the volumetric ratio of the transverse reinforcement from 3.23.0×10 -3 to 6.3156×10 -3 for rectangular sections long column and from 5.48×10 -3 to 16.45×10 -3 for circular sections long columns has increased the column axial compressive resistance from 385kN to 523kN and from 270kN to 455.6kN for rectangular and circular sections respectively with increasing rate of 36% and 68.7% for rectangular and circular section respectively. This is an expected behavior since increasing of the volumetric ratio of the transverse reinforcement causes increasing of the confinement of the concrete core surrounded by the transverse reinforcement hence results increasing of the concrete compressive resistance (Cusson, D. Paultre, P., 1994, Öztekin, 2012, Radnić at al., 2103) and then increasing of the column axial compressive load strength. Moreover, increasing of the transverse reinforcement may also increase the strength of longitudinal steel bars and prevent the steel bars from buckling out and causing early failure, see Figure 3 and Figure 4. 4. COMPARISON WITH ACI318-2011 CODE EQUATIONS In this section, a comparison is presented and discussed between the column axial compressive strength recorded from the experimental test with that calculated using the equations suggested in Sec. 10.3.6.1 of ACIM318-11 code (i.e. Eq 1 and Eq. 2 in present study). As mentioned before, the sec. 7.10.5 of ACI-Code has suggested maximum spacing limits between the transverse reinforcement which is equal to 150mm for RC column specimens used in the presents study However, the actual spacing used in the present study exceed this limit as listed in Table 6 and Table 7. Nevertheless, in order to investigate the applicability of the ACI equations for spacing values higher that maximum spacing limits suggested by ACI -code, the following comparisons were conducted. Firstly, the axial compressive strength of RC columns was calculated according to the equations Eq. 2. The average of the experimental values of concrete compressive strength corresponding to each cast batch as listed in Table 8 were substituted in Eq. 2. One the other hand, the experimental value of the yield stress of the reinforcement steel bars obtained from the uniaxial tensile test of steel bars as presented in Table 8 has also been used in Eq. 2 to calculate the axial compressive strength of RC columns. Table 6 and Table 7 list the calculated axial compressive strength for each column along with the experimentally recorded values. Table 6, Table 7, Figure 9 and Figure 10 compare the experimentally recorded values of the column axial compressive strengths with those calculated by ACI – Code equation. It can be noticed from Table 5 and Table 6 along with Figure 9 and Figure 10 that the ACI-Code equation gives overestimated values of the axial compressive strength of the rectangular shape RC columns compared with the values recorded experimentally particularly for long RC columns specimens. However, the ACI-Code equations predict underestimated values of the axial compressive strength of circular shape column especially for high values of the volumetric ratio of transverse reinforcements. The axial compressive strength values calculated by ACI-Code equations do not account the effects of transverse reinforcement of the RC columns strength. It only accounts for the compressive strength of concrete and strength of the longitudinal reinforcement steel bars. The overestimated perdition of the column’s axial compressive strength of the RC column may result unsafe design of the column. On the other hand, the underestimated prediction of the column’s axial strength may results uneconomic design particularly when high values of the volumetric ratio of transverse reinforcements would be used. Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 126 5. SUMMARY AND CONCLUSIONS. This study has presented, in detail, the research undertaken by the author to investigate the effect of transverse reinforcement on the axial compressive strength of reinforced concrete columns subjected to axial compressive load. The study is also aimed to assess the accuracy of equations suggested by ACI-Code to determine the design axial capacity of RC column. The main findings and conclusions that may be extracted from the study are as follows: 1. Increasing of the volumetric ratio of the transvers reinforcement of the RC column results increasing of the axial compressive strength of the RC column. This behavior is valid for short and long columns. 2. Failure of the RC column under axial compressive load starts by bearing or crushing at the loaded end followed by splitting of the concrete cover. For long column specimens with low transverse reinforcement ratios, the aforementioned failure is accompanying with buckling of the longitudinal reinforcement, particularly near the loaded end of the column caused by increasing of the effective length of the longitudinal reinforcement due to crushing the concrete surrounding it. 3. Using the ACI-Code equations for RC column with transverse or ties reinforcements spaced at distances exceed the maximum limits suggested by the code may give either over estimated or underestimated prediction of the axial compressive strength of the column. This could result unsafe or uneconomical design. 4. The effect of increasing the transverse reinforcement on increasing the axial compressive strength of RC column is more visible in short columns than that in long columns. This can be attributed to the confining due to transverse reinforcement which has more effect in short columns than long columns. REFERENCES [1] ACI Committee 318 2011. Building Code Requirements for Structural Concrete. American Concrete Institute, Farmington Hills, USA. [2] Chung H.S., Yang K.H, Lee Y.H, and Eun H.C, 2002. Strength and Ductility of Laterally Confined Concrete Columns, Can. J. Civ. Eng., 29:820–830. [3] Cusso D. and Paultre, P.1994. High-Strength Concrete Columns Confined by Rectangular Ties. J. Struct. Eng., 10.1061/(ASCE)0733-9445,120:3(783), 783-804. [4] Hong K.N., Han S.H. and Yi, S.T. 2006. High-Strength Concrete Columns Confined By Low-Volumetric-Ratio Lateral Ties, Engineering Structures, 28:1346–1353. [5] Junior H.C.L and Giongo, J.S.2004. Steel-Fibre High-Strength Concrete Prisms Confined by Rectangular Ties Under Concentric Compression, Materials and Structures, 37:689-697 [6] Khaleek A., Yadav R. K. and Chandak R. 2012. Effect of Lateral Confinement on Strength of Concrete, ISCA Journal of Engineering Sciences, 1: 40-44. [7] Öztekin E. 2012. Prediction Of Confined Compressive Strength Of Square Concrete Columns By Artificial Neural Networks. International Journal Of Engineering & Applied Sciences (Ijeas), Vol.4, Issue 3:17-35. Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 127 [8] Radnić J., Markić R., Harapin A. and Matešan D. 2013. Effect of confined concrete on compressive strength of RC beams. Advances in Concrete Construction, Vol. 1, No. 3 :215- 225. [9] Sharma U.K., Bhargava P. and Kauskik S.K. 2005. Behaviour of confined high strength concrete column under axial compression. Journal of Advanced Concrete Technology. 3: 267- 281. [10] Shin S., Kim J. and Ahn J. 2010. Transverse Reinforcement of RC Columns Considering Effective Lateral Confining Reduction Factor. Journal of Asian Architecture and Building Engineering/November/508. [11] Wang Y. f. and Wue H. l. 2010. Experimental Investigation on Square High-Strength Concrete Short Columns Confined with AFRP Sheets. Journal of Composites for Construction, 14: 3:346–351. [12] Zahn, Franz . 1985. Design of reinforced concrete bridge columns for strength and ductility. .University of Canterbury. Department of Civil Engineering. Table 1: Experimental test results of the fine aggregate Sieve size analysis Fine minerals Sieve size % A cumulative passing Materials finer than75μm, % % (SO3) Sulphate contents 01mm 011 3 0.149 4..5mm 89 3.26mm 82 0.09mm 99 611micron .3 211 micron 36 051micron 5 http://ir.canterbury.ac.nz/browse?type=author&value=Zahn%2C+Franz+August http://ir.canterbury.ac.nz/browse?type=author&value=Zahn%2C+Franz+August Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 128 Table 3: Mechanical properties of the reinforcement steel bars form uniaxial tensile test. Fy (N/mm 2 ) (%) (N/mm 2 ) Fu (N/mm 2 ) (%) 647.89 0.00318 204×10 3 742.76 0.134 Table 4: Dimensions and reinforcement details of the RC column specimens Column specimen designation Dimensions (m) H×W×L or D×L KL/r Longitudinal reinforce. Volumetric ratios of transverse reinforce.(ties) ×(10 -3 ) No. of ties used (Ø6mm) RS0 1.05×1.05 ×0.8 17.78 4Ø10 2.23 2 RS1 1.05×1.05 ×0.8 17.78 4Ø10 2.01 3 RS2 1.05×1.05 ×0.8 17.78 4 Ø10 2.98 4 RS3 1.05×1.05 ×0.8 17.78 4 Ø10 4.66 5 RS4 1.05×1.05 ×0.8 17.78 4 Ø10 6.31 6 RL0 1.05×1.05 ×1.2 26.67 6 Ø10 0.50 2 RL1 1.05×1.05 ×1.2 26.67 6 Ø10 0.88 4 RL2 1.05×1.05 ×1.2 26.67 6 Ø10 3.88 6 RL3 1.05×1.05 ×1.2 26.67 6 Ø10 2.48 7 RL4 1.05×1.05 ×1.2 26.67 6 Ø10 2.89 8 CS0 0.15×0.75 20 4 Ø8 5.48 2 CS1 0.15×0.75 20 4 Ø8 8.23 3 CS2 0.15×0.75 20 4 Ø8 10.97 4 CS3 0.15×0.75 20 4 Ø8 13.71 5 Table 2: Experimental test for the coarse aggregate Sieve size analysis Fine minerals Sieve size % A cumulative passing Materials finer than75μm, % % (SO3) Sulphate contents .5mm 011 1 0.03 62mm 011 2..5mm 011 31mm 011 04mm 94 01mm 40 5mm 0.3 3.26mm 1.4 Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 129 CS4 0.15×0.75 20 4 Ø8 16.45 6 CL0 0.15×1.3 34.67 4 Ø8 3.16 2 CL1 0.15×1.3 34.67 4 Ø8 4.75 3 CL2 0.15×1.3 34.67 4 Ø8 6.33 4 CL3 0.15×1.3 34.67 4 Ø8 7.91 5 CL4 0.15×1.3 34.67 4 Ø8 9.49 6 Table 6: The experimentally recorded values of the axial compressive strength for short RC columns with the values calculated using ACI-Code equations Column designation Volumetric ratio ×10 -3 Experimental values of the axial compressive strength, kN Spacing between tie reinforcement (mm) Calculated values of the axial compressive strength, kN RS0 3.23.0 295 748 465.2 RS1 2.0139 401 371 465.2 RS2 2.9.95 401 245 465.2 RS3 4.6543 496.2 183 465.2 RS4 6.3156 523 145 465.2 CS0 5.48 270 698 301.3 CS1 8.23 310.6 349 301.3 CS2 10.97 327.5 229 301.3 CS3 13.71 358.7 170 301.3 CS4 16.45 455.6 135 301.3 Table 7: The experimentally recorded values of the axial compressive strength for long RC columns with the values calculated using ACI-Code equations Column designation Volumetric ratio ×10 -3 Experimental values of the axial compressive strength, kN Spacing between tie reinforcement (mm) Calculated values of the axial compressive strength, kN RL0 0.4860 206.5 1198 515.5 RL1 0.8849 246 395 515.5 RL2 3.8833 254.4 295 515.5 RL3 2.4818 282.2 195 515.5 RL4 2.8986 401.9 166 515.5 CL0 3.16 292.4 1248 301.3 CL1 4.75 319.8 621 301.3 CL2 6.33 348.6 412 301.3 CL3 7.91 373.2 307 301.3 CL4 9.49 394.7 245 301.3 Table 5: Compressive test results of the concrete cubes Section Cast batch Compressive strength( ́ (N/mm 2 ) ́ Average (N/mm 2 ) Rect. 1 37.1 37.5 40.5 34.7 41.8 40.74 33.9 35.0 34.7 34.6 37.1 32.3 36.64 Circ. 2 31 29 31 31 27 32 31 31 30 26 31 32 30.25 Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 130 Table 8: Concrete compressive strengths and steel yield stress used to calculated the compressive strength of column specimens according to ACI-Code. Cast Batch Section shape fc ’ Average (N/mm2) Fy (N/mm 2 ) Axial strength (kN) Short columns Long columns 1 Rect. 36.64 648 465.156 515.54 2 Circ. 30.25 648 301.337 301.337 (A) (B) Figure 1: Reinforcement details of rectangular sections (A) and circular sections (B) RC columns Figure 2: Universal test machine used in experimental tests. Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 131 Figure 3: Failure modes of square and circular short columns Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 132 Figure 4: Failure modes of square and circular long columns. Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 133 Figure 5: Relationship between the axial compressive load and the volumetric ratio of the transverse reinforcement of short columns with rectangular sections. Figure 6: Relationship between the axial compressive load and the volumetric ratio of the transverse reinforcement of short columns with circular sections. Figure 7: Relationship between the axial compressive load and the volumetric ratio of the transverse reinforcement of long columns with rectangular sections. 300 350 400 450 500 550 2.33E-03 3.10E-03 3.88E-03 4.65E-03 6.21E-03 Volumetric ratio of transverse reinforcement A x ia l c o m p re s s iv e s tr e n g th ( k N ) Rect. short column 200 255 310 365 420 475 5.48E-03 8.23E-03 1.10E-02 1.37E-02 1.65E-02 Volumertic ratio of transverse reinforcement A x ia l c o m p re s s iv e s tr e n g th ( k N ) Circ. short column 300 325 350 375 400 425 1.50E-03 1.99E-03 2.99E-03 3.49E-03 3.99E-03 Volumetric ratio of transverse reinforcement A x ia l c o m p re s s iv e s tr e n g th ( k N ) Rect. long column Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 1 ….2016 134 Figure 8: Relationship between the axial compressive load and the volumetric ratio of the transverse reinforcement of long columns Figure 9: Comparison between the recorded and the calculated values of the column axial compressive strength for short columns Figure 10: Comparison between the recorded and the calculated values of the column axial compressive strength for long columns 200 240 280 320 360 400 3.16E-03 4.75E-03 6.33E-03 7.91E-03 9.49E-03 Volumertic ratio of transverse reinforcement A x ia l c o m p re s s iv e s tr e n g th ( k N ) Circ. long column 250 310 370 430 490 550 0.0E+00 4.0E-03 8.0E-03 1.2E-02 1.6E-02 Volumetric ratio of transverse reinforcement A x ia l c o m p re s s iv e s tr e n g th ( k N ) Experimenta- Rect. Experimenta- Circl. ACI318-Rect. ACI318-Circl. 250 295 340 385 430 475 520 565 0.E+00 2.E-03 4.E-03 6.E-03 8.E-03 1.E-02 Volumetric ratio of transverse reinforcement A x ia l c o m p re s s iv e s tr e n g th ( k N ) Experimenta- Rect. Experimental- Circl. ACI318- Rect. ACI318- Circl.