BEHAVIOUR OF HIGH STRENGTH CONCRETE COLUMNS REINFORCED WITH STEEL FIBRES UNDER DIFFERENT ECCENTRIC LOADS

Transcription

1 BEHAVIOUR OF HIGH STRENGTH CONCRETE COLUMNS REINFORCED WITH STEEL FIBRES UNDER DIFFERENT ECCENTRIC LOADS Emdad K.Z. Balanji, M. Neaz Sheikh, Muhammad N.S. Hadi School of Civil, Mining and Environmental Engineering, University of Wollongong, Australia November 2016

2 Table of Content Introduction Objectives Experimental Program Results and Discussions Conclusions

3 Introduction Definition of High Strength Concrete (HSC) The term of HSC is used for concrete which has higher durability, excellent environmental resistance and a higher compressive strength than Normal Strength Concrete (NSC). Australian Standard (AS ) if the compressive concrete strength at 28 days is greater than 50 MPa, the concrete shall consider as special class concrete. ACI 363R-10 if the concrete compressive strength at 28 days is higher than 55 MPa, the concrete shall consider as HSC Chicago s Water Tower Place (1976) South Wacker Drive Concrete Buildings Constructed in (1990)

4 Introduction Advantages of HSC in structural members Columns Beams Slab Others applications Increased Load Carrying Capacity Reduced Cross Sectional Area Allows For Longer Spans Reduction in Dead Load Lower Permeability Reduced Column Cross Section Increased Resistance to Freeze-Thaw Higher Corrosion Resistance Jobes et al. (1984)

5 Introduction Disadvantages of HSC Columns Early Cover Spalling Lower Ductility

6 Introduction Steel Fibre Reinforced Concrete (SFRC) To Delay Cover Spalling Using Steel Fibres To Enhance Ductility To Prevent Brittle Failure Types of Fibres 6

7 Introduction NSC HSC Existing Research Studies of Using Fibres Reinforced Concrete Columns Square Columns Circular Columns Load Condition Craig et al Concentric Mangat and Azari Concentric Ganesan and Murthy Concentric Hsu et al Cyclic Nagarajah and Sanders Lateral cyclic Sarkar and Rangan Eccentric Foster and Attard Concentric and Eccentric Lima and Giong Concentric - Hadi 2005 Concentric Lee Concentric Sharma et al Concentric - Djumbong et al Concentric Togoz 2009 Compression Cyclic Hadi 2009 Concentric Paulter et al Concentric Khalil et al Concentric Palanivel and Sekar Concentric - Osorio et al Compression Cyclic

8 Objective To investigate the effect of different types of steel fibres (micro and macro) on the behaviour of the HSC columns under different eccentric loads.

9 Experimental Program Test Matrix Steel fiber Reinforcement Specimens Type Volume content Longitudinal Helix Load conditions (v f %) RC Concentric RC mm eccentric RC mm eccentric MI-0 Concentric MI-25 MI 3 6N12 60 mm 25 mm eccentric MI mm eccentric MA-0 Concentric MA-25 MA 2 25 mm eccentric MA mm eccentric

10 Experimental Program Material Selection 1. Concrete A local ready mix concrete with compression strength of 60 MPa. Mix Cement (kg/m 3 ) Mix proportion for 1m 3 of Plain HSC. Water (kg/m 3 ) Fly ash (kg/m 3 ) Fine aggregate (kg/m 3 ) Coarse aggregate (kg/m 3 ) Plain HSC Steel bars Deformed steel bars N12 Plain steel bars R10

11 Experimental Program 3. Steel Fibres Type of steel fibres Micro steel fibres (GDMF, 2014) Macro steel fibres (Fibercon, 2014) Length Diameter Tensile Density Aspect ratio (l) (d) strength of fibre (l/d) (mm) (mm) (MPa) (kg/m 3 ) 6±1 0.2± >

12 Experimental Program Geometry of the Columns

13 Experimental Program Preparation and Casting of The Specimens

14 Experimental Program Preparation and Testing of The Specimens Under concentric load Under eccentric load

15 Results and Discussions Specimens Tested under Concentric Axial Load

16 Axial load (kn) Results and Discussions Specimens Tested under Concentric Axial Load RC-0 MI-0 MA Axial deformation (mm)

17 Results and Discussions Specimens Tested under 25 Eccentric Axial Load

18 Axial load (kn) Results and Discussions Specimens Tested under 25 Eccentric Axial Load RC-25 MI-25 MA Lateral deformation (mm) Axial deformation (mm)

19 Axial load (kn) Results and Discussions Specimens Tested under 50 Eccentric Axial Load RC-50 MI-50 MA Lateral deformation (mm) Axial deformation (mm)

20 Conclusions The inclusion of steel fibres into HSC specimens leads to improvement in the maximum load of eccentrically loaded columns more than that of concentrically loaded columns. A higher improvement in the maximum load for the specimens under eccentric load was observed for Specimens MI. However, the maximum load slightly increased for Specimens MA. Higher enhancement in ductility for specimens under eccentric load was observed for Specimens MA. Finally, the inclusion of 3% by volume of micro steel fibres, into HSC columns improves the strength of the HSC. However, adding 2% by volume of macro steel fibres onto HSC specimens improves the ductility of the specimens.

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