Al-Qadisiyah Journal For Engineering Sciences, Vol. 10……No. 1….2017 26 EFFECT OF ADDITION THE CONDUCTIVE SCREWS ON THE BEHAVIOR OF REINFORCED CONCRETE BEAMS AND COLUMNS Khamail Abdul-Mahdi Mosheer Department of Civil Engineering Al-Qadisiyah University / Lecturer kh20072011@gmail.com Received on 01 June 2016 Accepted on 30 November 2016 Abstract In the present paper, experimental investigations were used to study the effect of the addition conductive screws on the behavior of reinforced concrete columns and beams. Screws with 25.4mm (1 inch) length were used. These screws were made of iron coated with Zinc-Aluminium alloy (called Al-Clad), which is resistant to corrosion and rust. The volume fractions of the conductive screws were 0%, 0.5%, 1%, and 1.5% by volume of concrete mix with water/cement ratio equal to 0.55. The results show that the use of the conductive screws enhanced the strength. The strength in tested beams was increased by 15.78%, 44.73%, and 76.31% for 0.5%, 1%, and 1.5% screws content respectively compared to the reference beam with no screws. The same trend was observed with the columns results, where the strength was increased by 12.44%, 26.79%, and 50.71% for 0.5%, 1%, and 1.5% screws content respectively compared to the reference column with no screws. Key words: Screws, reinforced concrete columns, reinforced concrete beams. على تصرف العتبات الخرسانیة المسلحة واالعمدة اضافة الصوامیل الموصلة تأثیر دراسة الخرسانیة المسلحة خمائل عبد المھدي مشیر مدرس/ كلیة الھندسة/قسم الھندسة المدنیة/جامعة القادسیة الخالصة الخرسانیة المسلحة واالعمدة الخرسانیة المسلحة. تصرف العتبات على الصوامیل الموصلة اضافة تأثیر دراسة ھو البحث ھذا من الھدف انج). -١ملم ( ٢٥.٤. تم استخدام صوامیل موصلة بطول من حجم الخلطة الخرسانیة). ,and 1% %1.5 ,%0.5 ,%0وبنسب مختلفة ( للتآكل والصدأ والتي تعطي القوة المقاومة (Al-Clad)المنیوم والمسماة -ھذه الصوامیل الموصلة مصنوعة من الحدید المطلي بسبیكة زنك ) والنسبة الحجمیة للصوامیل الموصلة التي اضیفت للخرسانة w/c=0.55والمرونة للصوامیل. نسبة الماء الى سمنت التي استخدمت كانت ( العتبات واالعمدة. من حجم الخلطة الخرسانیة). النتائج بینت ان وجود الصوامیل زاد من مقاومة تحمل and 1.5% ,%1 ,%0.5 ,%0كانت ( ,%0.5 ) عن العتب المرجعي الخالي من الصوامیل الموصلة وللنسب (%76.31 ,%44.73 ,%15.78حیث زاد تحمل العتبات بمقدار ( ) عن العمود %50.71 , %26.79,%12.44من حجم الخلطة الخرسانیة) على التوالي. كما زاد تحمل االعمدة بمقدار (,1.5%, 1% من حجم الخلطة الخرسانیة) على التوالي. ,%1.5, %1 ,%0.5 من الصوامیل وللنسب ( المرجعي الخالي الكلمات المفتاحیة: صوامیل الموصلة، العتبات الخرسانیة المسلحة، االعمدة الخرسانیة المسلحة. Al-Qadisiyah Journal For Engineering Sciences, Vol. 10……No. 1….2017 27 1. Introduction. Concrete is relatively a brittle material and has poor toughness. Addition of randomly distributed fibres improves concrete structural characteristics such as, strength, ductility and flexural toughness etc., which depend upon fibre type, size, aspect ratio and volume fractions of the fibres used (Singh et al. 2010). Steel fibre is one of the most commonly used fibres. The effect of using steel fibres on the behavior of concrete has been studied by many researchers. (Craig et al. 1984) reported that adding steel fibers to a reinforced concrete column improved its compressive strength, shear strength, and ductility. The study carried out by (Oh 1992) indicates that ductility and ultimate resistance of reinforced concrete beams are remarkably enhanced due to the addition of steel fibres. (Casanova et al. 1997) shown that steel fibers can be used to significantly reduce the amount of transverse shear reinforcement in beams while maintaining the required shear resistance. (Cohen 2012) show that if steel fibres added in sufficient quantity can be used to replace traditional shear reinforcement and promote flexural failure and ductility . ( Namdar et al. 2013) indicated that steel fiber improves flexural strength of beams and controlled crack morphology. (Aoude et al. 2014) Show that the addition of steel fibres in concrete columns enhances confinement and cover spalling. The results obtained by (Mosheer 2015) showed that the addition of conductive screws to plain concrete led to enhancement mechanical properties of concrete. In this study, conductive screws made from iron coated with Zinc-Aluminium alloy (called Al-Clad), which is resistant to corrosion and rust, were used as a short fibre to reinforce conventional concrete. The screws were used in different volume fractions. Experimental investigations were conducted to study the effect of addition conductive screws on columns and beams. 2. Experimental Program Experimental program was mainly designed to examine the effect of addition conductive screws with different volumetric ratios on the behavior of reinforced concrete beams and columns. 2.1 Specimen details The experimental work involved testing of four beams and four columns. The dimensions of beams and columns are 1200 × 150 × 150 mm. Geometry and reinforcement detail for beams and column are shown in Fig1. 2.2 Materials Properties 2.2.1 Concrete Sulphate-resistant Portland cement (Type V) was used, coarse aggregate have a (5-19) mm size crushed gravel and the fine aggregate was natural river sand, zone 2 according to IQS:45 1984 with 2.85 fineness modulus. 2.2.2 steel reinforcement Arrangement of steel bar used in tested beams and columns are indicted in Fig1. Sample of steel bars was tested by tensile testing machine to product some properties of them, results of test were listed in Table 1. 2.2.3 Screws The conductive screws were used throughout the experimental program, made from iron coated with Zinc-Aluminium alloy, which is resistant to corrosion and rust. The screws were used with length 25.4 mm (1 inch) as shown in Fig 2. Some properties of the screws are listed in Table 2. Al-Qadisiyah Journal For Engineering Sciences, Vol. 10……No. 1….2017 28 2.3 Mix proportions Volumetric mixing ratio of (1:2:4) was used, with water/cement ratio (w/c) = 0.55. Cylinders and prisms for each mix were cast and stored with each beam and column. Average results of cylinder strength !c and modulus of rupture f r are given in Table 3. The screws were added in volume fractions of 0%, 0.5%, 1%, and 1.5% by volume of the total mix for the beams (B0, B1, B2,and B3) respectively, and for columns (C0, C1, C2,and C3) respectively as indicted in Table 4. The beam and column with no screws were considered as a reference sample. After a 28 day of curing, a tests were conducted for the reinforced concrete members. 3. Testing Procedure 3.1 Reinforced concrete beams test All the tested beams were simply supported under one point load at mid span which incrementally loaded up to maximum load capacity by means of a hydraulic jack with maximum capacity of 200 kN. Dial–gage placed vertically at mid span of beams to measure the deflection at each increment of the load. 3.2 Reinforced concrete columns test All columns were tested for concentric axial loads by an universal testing machine with capacity of (200) ton. 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. The load was applied through a bearing plate in small increments up to failure. A dial-gage placed vertically at the top face of column to recorded the axial deformation, while the lateral deflection was measured using dial-gages placed horizontally at the mid height of column in each side. After each increment, the load was kept constant until the required measurements were recorded. 4. Discussion of the results 4.1 Reinforced concrete beams From the test results shown in Table 5 and Fig 3 and 5, it can be seen that ultimate axial load increases with increasing the screws content. The ultimate axial load increased by 15.78%, 44.73%, and 76.31% for B1, B2, and B3 respectively from reference beam with no screws B0. The increase in ultimate axial load appears more clearly with screws contents of 1.5% for beam B3 compared to the reference beam B0. From Fig 5 it can be observed that cracks width decreases and number of cracks increase with increasing the volume fraction of the screws compared with the reference beam B0 (0.0% added ratio). This is due to the fact that the load path is intercepted by the conductive screws, which leads to a change in its direction. 4.2 Reinforced concrete columns The reinforced concrete columns test results are illustrated in Table 5 and Fig 6 to 8. The ultimate axial load increased by 12.44%, 26.79%, and 50.71% for C1, C2, and C3 respectively from reference beam with no screws C0. Fig 9 show the reinforced concrete column specimens shapes after failure. As can be seen from this Fig, 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. 5. Conclusions From the experimental results, the following conclusions can be stated: Al-Qadisiyah Journal For Engineering Sciences, Vol. 10……No. 1….2017 29 1. The use of conductive screws works to increasing the strength capacity for reinforced concrete columns and beams. This is due to the ability of screws to control and redistribute the stresses after cracking. 2. The strength of beams and columns increased with increasing the screws content. 3. The cracks width in reinforced concrete beams decreases with increasing the screws content, instead, there was an increase in the number of cracks. References Aoude, H., Hosinieh, M., Cook, W., and Mitchell, D. (2014), "Behavior of Rectangular Columns Constructed with SCC and Steel Fibers." Journal of Structural Engineering, 10.1061/(ASCE)ST.1943-541X.0001165 , 04014191. Casanova, P., Rossi, P., and Schaller, I. (1997), “Can Steel Fibers Replace Transverse Reinforcements in Reinforced Concrete Beams?” ACI Materials Journal, V. 94, No. 5, Sept.-Oct., pp. 341-354. Cohen, M. (2012) “Structural Behaviour of Self Consolidating Steel Fiber Reinforced Concrete Beams,” M.S. thesis, Dept. Civil. Eng., Ottawa. Univ., Ottawa. Craig, R. J., Dunya,S., Riaz, J., and Shirazi ,H. (1984), “Torsional Behavior of Reinforced Fibrous Concrete Columns” Fiber Reinforced Concrete-International Symposium. SP-81. American Concrete Institute. Detroit. SP-81, pp.17-49. Mosheer, K. A., (2015) “Addition of conductive screws to improve the mechanical properties of concrete” Al-Qadisiyah Journal For Engineering Sciences, Vol. 8, No. 2, pp.211-224. Namdar, A., Zakaria, I. B., Hazeli, A. B., Azimi, S. J., Bin, A. S., and Razak, A., (2013), “An experimental study on flexural strength enhancement of concrete by means of small steel fibers” Frattura ed Integrità Strutturale,V. 26, DOI: 10.3221/IGF-ESIS.26.03., pp. 22-30. Singh, S.P., Singh, A.P., and Bajaj, V. (2010), “Strength and flexural toughness of concrete reinforced with steel – polypropylene hybrid fibres” Asian Journal of Civil Engineering (Building And Housing) Vol. 11, No. 4, pp. 495-507. Oh, B.H. (1992), “Flexural Analysis of Reinforced Concrete Beams Containing Steel Fibres” Journal of Structural Engineering, ASCE, Vol. 118, No. 10, pp. 2821–2836. Material type fy MPa fu MPa Ø 12 bar 447 731 Ø 10 bar 452 729 Table 1: Test results of steel bars (MPa) Al-Qadisiyah Journal For Engineering Sciences, Vol. 10……No. 1….2017 30 Material type Average Diameter (mm) Head Diameter (mm) Length mm Density kg/m 3 Modulus of Elasticity GPa Screw 3 6.5 25.4 7500 200 Fibre content % !" MPa # MPa 7 days 28 days 0.0 14.91 19.4 2.75 0.5 15.32 21.37 2.84 1.0 15.72 22.41 2.90 1.5 17.69 23.82 2.94 Member Type Member No. Screws content % !" MPa Beam B0 0.0 19.4 B1 0.5 21.37 B2 1.0 22.41 B3 1.5 22.92 Column C0 0.0 19.4 C1 0.5 21.37 C2 1.0 22.41 C3 1.5 23.82 Table 3 : Test results of Concrete (Mixing ratio=1:2:4) Table 2 : Properties of conductive screws Table 4: Details of reinforced concrete beams and columns Al-Qadisiyah Journal For Engineering Sciences, Vol. 10……No. 1….2017 31 Member Type Member No. Screws content % ! MPa Ultimate load Pu (kN) Increasing rate in ultimate load % Beam B0 0.0 19.4 38 -- B1 0.5 21.37 44 15.78 B2 1.0 22.41 55 44.73 B3 1.5 22.92 67 76.31 Column C0 0.0 19.4 418 - C1 0.5 21.37 470 12.44 C2 1.0 22.41 530 26.79 C3 1.5 22.92 630 50.71 Table 5: Test result of beams and columns 31 Figure 1: Geometry and reinforcement detail for (a): Beams, (b): Columns Al-Qadisiyah Journal For Engineering Sciences, Vol. 10……No. 1….2017 32 Figure 2: Screws used Figure 3: Load-deflection curve for beams B0(0%) ,B1 (0.5%), B2 (1%), and B3 (1.5%) 32 Figure 4: The relationship between ultimate load in beams and the screws content Al-Qadisiyah Journal For Engineering Sciences, Vol. 10……No. 1….2017 33 ` B0 (0.0%) B1 (0.5%) B2 (1.0%) B3 (1.5%) Figure 5: Failure mode of reinforced concrete tested beams Al-Qadisiyah Journal For Engineering Sciences, Vol. 10……No. 1….2017 34 0.0 0.5 1.0 1.5 Screw Addition % 400 450 500 550 600 650 U lt im a te A x ia l L o a d ( k N ) 0.0 1.0 2.0 3.0 4.0 5.0 6.0 Axial Deflection (mm) 0 100 200 300 400 500 600 700 A x ia l L o a d ( k N ) C0 (0.0%) C1 (0.5%) C2 (1.0%) C3 (1.5%) Figure 6: Load- Lateral deflection curve for columns C0 , C1, C2, and C3 Figure 7: Load-Axial deflection curve for columns C0 ,C1, C2, and C3 34 Figure 8: The relationship between ultimate load in columns and the screws content Al-Qadisiyah Journal For Engineering Sciences, Vol. 10……No. 1….2017 35 C0 (0.0%) C1 (0.5%) C2 (1.0%) C3 (1.5%) Figure 9: Failure modes of reinforced concrete columns