Tests on steel columns filled with normal concrete and lightweight concrete were carried out to investigate the actual behavior and the load carrying capacity of such columns. Eight full scale rectangular cross-section columns filled with lightweight aggregate concrete and normal weight aggregate concrete, four specimens each, were tested under axial loads for comparison purposes. The results showed that using lightweight concrete filling instead of normal concrete filling will reduce the weight of columns. At the same time, a high load carrying capacity is achieved

Al-Ani, Hamid R.

Al-Rawi, Orabi

Ghannam, Shehdeh

English

International Institute for Science, Technology and Education (IISTE): E-Journals

Jordan Journal of Civil Engineering, Volume 4, No. 2, 2010 - 164 -  Comparative Study of Load Carrying Capacity of Steel Tube Columns Filled with Lightweight Concrete and Normal Concrete  Shehdeh Ghannam 1), Hamid R. Al-Ani 2) and Orabi Al-Rawi 3)  1) Assistant Professor, Al-Isra Private University 2) Associate Professor, Al-Isra Private University (Corresponding Author) 3) Assistant Professor, Al-Isra Private University  ABSTRACT Tests on steel columns filled with normal concrete and lightweight concrete were carried out to investigate the actual behavior and the load carrying capacity of such columns. Eight full scale rectangular cross-section columns filled with lightweight aggregate concrete and normal weight aggregate concrete, four specimens each, were tested under axial loads for comparison purposes. The results showed that using lightweight concrete filling instead of normal concrete filling will reduce the weight of columns. At the same time, a high load carrying capacity is achieved. KEYWORDS:  Failure load, Lightweight aggregate concrete, Normal weight aggregate concrete, Local buckling, overall buckling, Composite action, Tubular columns.  INTRODUCTION  Composite columns may be used for low-rise and high-rise buildings. For low-rise buildings, steel sections are often encased in concrete for the sake of appearance and for protection of steel from fire, corrosion and from vehicles in garages. For high-rise buildings, composite columns are stiffer than non-composite steel columns. The size of composite columns is often considerably smaller than required for reinforced concrete columns to support the same loads.  Although composite columns (concrete in filled steel tubulars) are often considered as a new type of column, its development has been the subject of extensive research over the past few decades. Many researchers have investigated the load carrying capacity of such composite sections, but they did not focus on the squash load (Nu). Several investigations were carried out by (Hunaiti, 1997) in order to study the behavior of short and long columns filled with foamed and lightweight aggregate concrete. Other researchers studied the slender circular columns filled with normal  concrete (Johansson and Gylltoft, 2001). Furthermore, buckling of channel beam columns was studied by (Teng, Yao and Zhao, 2002). Uy (2001) studied the behavior of concrete filled  high strength steel box columns. The purpose of this study was to study the behavior of composite columns of rectangular cross-section and to compare the load carrying capacity of lightweight aggregate concrete filled steel tubular columns with that of normal weight aggregate concrete filled steel tubular columns. All columns were tested up to failure to assess their behavior.  EXPERIMENTS  Eight full scale column specimens of rectangular hollow section were tested in this study. The column Accepted for Publication on 15/4/2010. ©  2010 JUST. All Rights Reserved.Jordan Journal of Civil Engineering, Volume 4, No. 2, 2010  - 165 - specimens were classified into two groups. The first group of specimens consisted of four specimens which were filled with lightweight aggregate concrete, and the second group consisted of four specimens that were filled with normal weight aggregate concrete. All columns were slender with various lengths and slenderness ratios and of rectangular cross-sectional dimensions as shown in Fig.1. Types and sectional dimensions of test specimens are given in Table 1.                   Figure (1): Concrete-filled rectangular steel hollow section  The columns were of different sizes, shapes, lengths and slenderness ratios. From the prototype sections of 200x100x5mm and 150x90x3mm, four specimens of each section were prepared, two of them were filled with normal weight aggregate concrete, and the other two were filled with lightweight aggregate concrete . Two different concrete mixes were used with a max. aggregate size of 10 mm. For normal concrete, a concrete mix of 1: 1.4: 2.8 with w/c=0.6 was used. Ordinary Portland cement, medium crushed limestone aggregate gravel and fine sand (2mm size) were used. For lightweight concrete, pumice of 10mm size was used with expanded perlite.  Concrete mixes and material properties of the columns are summarized in Tables 2 and 3. The column specimens were tested under axial monotonic loading in a 2000 kN capacity compression hydraulic jack (M 1000/RD), with a deformation rate of 0.01 mm/sec. All specimens were prepared and placed axially with a high degree of accuracy to ensure that the load application is in the required position as shown in Fig. 2 and Fig. 3 (1&2). DESIGN CONSIDERATIONS  The ultimate load carrying capacity of a composite column can be calculated by several methods, which exist in codes of practice. The Bridge Code (BS 5400,2000), (The Eurocode 4, 2000) and the American Standard (AISC-LRFD Methods, 1993) contain rules of the design of composite columns. In calculating the squash load, Nu, (According to the Bridge Code) for rectangular cross section, the following formulae can be used:  Nu= As fsk / γms + Ac fck/ γmc                                    Eq.  (1)  The material partial safety factors for steel and concrete, γms and γmc, were taken as unity. Moreover, the value of the characteristic concrete strength fck was taken as                  fck =  0.83 fcu                     Eq. (2a) instead of              fck  = 0.67   fcu                    Eq.   (2b) where fcu is the 28 day cube strength of concrete. The value of 0.83 fcu is recommended by ECCS for experimental   work.  Furthermore,  the ratio  between 90 (100) mm 150 200) mm( Comparative Study…                                                              Shehdeh Ghannam, Hamid R. Al-Ani and Orabi Al-Rawi  - 166 - Ac fck / γmc and Nu is called the concrete contribution factor αc, and for a filled composite section it varies between 0.1 and 0.8 which is considered in this paper.  fsk was taken as  fsk = 0.91 fy.   A pin ended hydraulic jack  Upper loading plates Tested specimen Lower loading plates Base plate                                                                                   Steel ball Steel floor plate    Figure (2): General scheme of the test rig  RESULTS  The column specimens behaved very well under load, and as shown in Table 4, the experimental failure loads of all columns were mostly well in excess of design values estimated by most composite codes. According to the visual observations and due to the experimental failure loads shown in Table 4, The failure modes of the tested columns are summarized as follows: a. Sections filled with lightweight aggregate concrete failed due to local as well as overall buckling, and they supported more than 92% of the squash load.  b. Sections filled with normal weight aggregate concrete failed due to overall buckling at mid height, and they supported more than 87% of the squash load.  It can obviously be seen that columns with lightweight aggregate concrete filled steel tubulars support similar loads as columns filled with normal weight aggregate concrete. On the other hand, the weight of the column with lightweight concrete was 30% less than that of the column with normal concrete of the same cross-section. Jordan Journal of Civil Engineering, Volume 4, No. 2, 2010  - 167 -   Figure (3.1): Data acquisition system   Figure (3.2): General view of the test rig Comparative Study…                                                              Shehdeh Ghannam, Hamid R. Al-Ani and Orabi Al-Rawi  - 168 - Table (1): Types and sectional dimensions of test specimens Column type Section dimensions(mm) Effective length (mm) Slenderness ratio Kle /r C1-N C2-N C3-LW C4-LW 200x100x5 200x100x5 200x100x5 200x100x5 2000 2000 2000 2000 20 20 20 20 C5-N C6-N C7-LW C8-LW 150x90x3 150x90x3 150x90x3 150x90x3 2250 2250 2250 2250 25 25 25 25  Table (2): Concrete mixes Type of concrete Cube strength (fcu MPa) Density, ρ (kg/m3) Concrete mix proportions Normal weight aggregate concrete 33.4 2081    Cement : sand : medium aggregate         1      :   1.4   :        2.8 w/c = 0.6  Light weight aggregate concrete   10  1390 Cement    :    pumice                         1      :       1.53    Exp. Perlite 0.92 L/kg of pumice w/c = 0.85  Table (3): Details of sectional properties of columns Steel section Dimension of section (mm) Area of steel As (mm2) Area of concrete  Ac (mm2) Yield strength  Fy (MPa) Steel modulus of elasticity Est (MPa) Rectangular cross section 200x100x5 150x90x3 2900 1404 17100 12096 360 320 229300 201000  Table (4): Column properties and results Col. No. and type Concrete contribution factor (αc) (Bridge Code) Squash  load  Nu  (kN) Bridge Code Experimental  load Ne (kN) C1-N C2-N C3-LW C4-LW 0.303 0.333 0.139 0.116 1356 1417 1103 1048 1242 1242 1062 1022  Jordan Journal of Civil Engineering, Volume 4, No. 2, 2010  - 169 - CONCLUSIONS  The steel tubes filled with lightweight aggregate concrete showed acceptable strength under the applied loads when compared to design calculations. According to the experimental and design code calculations, the behaviours of both lightweight concrete –filled steel tubular columns and normal concrete-filled steel tubular columns were very similar. Column specimens filled with lightweight aggregate concrete developed the ultimate axial capacity and significantly enhanced the strength of steel sections. The load carrying capacity of the column was increased in the view of the fact that the concrete core, in addition to its own strength contribution, also helped prevent the effect of local buckling of the steel tube. This increased the strength contribution of the tube portion over the hollow section.  Notation The following symbols are used in this paper: Ac      = concrete cross section;   As      = steel cross section; Ec      = modulus of elasticity of concrete; Es       = modulus of elasticity of steel; fck      = characteristic strength of concrete;  fsk      = characteristic strength of steel; K      = restraint column factor;  Le      = effective length of a column;  Nu      = squash load of a column; r         = radius of gyration of the column cross-section; αc       = concrete contribution factor; γm      = partial coefficient of material.  REFERENCES  American Institute of Steel Construction (AISC). 2000. Load and Resistance Factor Design Specification for Structural Steel Buildings (LRFD), Chicago, USA. British Standards Institution BS5400, Part 5. 2000. Concrete and Composite Bridges, U.K. Hunaiti, Y. M. 1996. Composite Action of Foamed and Lightweight Aggregate Concrete. ASCE-Journal of Materials in Civil Engineering, 8 (3):111-113. Hunaiti, Y. M. 1997. Strength of Composite Sections with Foamed and Light-weight Aggregate Concrete.  ASCE-Journal of Materials in Civil Engineering, 9 (2): 58-61. Johansson, M. and Gylltoft, K. 2001. Structural Behavior of Slender Circular Steel under Various Means of Load Applications, Steel and Composite Structures, I: 393-410.  Teng, J.G., Yao, J. and Zhao, Y. 2003. Distortional Buckling of Channel Beam-Columns. Thin Walled Structures, 41: 595-617. Uy, B. 2001. Strength of Short Concrete Filled High Strength Steel Box Columns, J. Constructional Steel Research, 57:113-134. Uy, B. 1998. Concrete Filled Fabricated Steel Box Columns for Multi-storey Buildings, Progress in Structural Engineering and Materials, 150-158. Zhang, W. and Shahrooz, B.M. 1999. Comparison between ACI and AISC for Concrete-Filled Tubular Columns. Journal of Structural Engineering, 125 (11): 1213-1223.  

Comparative Study of Load Carrying Capacity of Steel Tube Columns Filled with Lightweight Concrete and Normal Concrete

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Comparative Study of Load Carrying Capacity of Steel Tube Columns Filled with Lightweight Concrete and Normal Concrete

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