AXIAL LOAD CAPACITY OF CELLULAR LIGHTWEIGHT CONCRETE-FILLED STEEL SQUARE TUBE COLUMNS Jaksada THUMRONGVUT Department of Civil Engineering, Rajamangala University of Technology Isan, THAILAND Sittichai SEANGATITH School of Civil Engineering, Suranaree University of Technology, THAILAND

Outline Statement of the Problem Experimental Program Test Results Comparison with Design Equation Conclusions

1) Statement of the Problem 1) Need for a precast construction method for new buildings due to the lack of laborers and high cast-in-place construction cost, resulting from Aging Society. 2) Need for an effective strengthening or rehabilitation method for “functionally obsolete” buildings and “structurally deficient” buildings.

1) Statement (Cont.) Concrete-filled steel tube column (CFT column) is a type of composite column and comprises the combination of concrete and steel.

1) Statement (Cont.) Comparisons of different types of columns

1) Statement (Cont.) CFT column is subjected to axial load “both on the steel tube and concrete core”. The steel tube performs as primary longitudinal main reinforcement to the concrete core.

1) Statement (Cont.) Cellular lightweight concrete (CLC) is produced by mixing the portland cement, sand and water with gas-forming chemicals. Its lightweight appropriate for precast construction. Also, its low strength and stiffness can simulate the old concrete in old building.

1) Statement (Cont.) Objectives : 1) To present the results of the experimental investigation on cellular lightweight concrete-filled steel tube columns (CLCFT columns) under monotonic concentric axial loading. 2) To compare the obtained axial load capacity results with those of the reference CLC columns and with ones, predicted by the ACI 318 design equation.

2) Experimental Program Variables : The compressive strengths (f’c) of the CLC are 15, 20 and 25 MPa. The wall thicknesses of the steel tube (t) are 3.0, 4.5 and 6.0 mm.

2) Experimental Prog. (Cont.) Table of the test specimens XX-YY-ZZ Thickness (mm) SC = CLC Column (reference) SS = CLCFT Column Compressive Strength (MPa)

2) Experimental Prog. (Cont.) Schematics diagram for the test specimens

2) Experimental Prog. (Cont.) CLC stress-strain diagram 25.5 MPa 20.9 MPa 15.8 MPa

2) Experimental Prog. (Cont.) Steel stress-strain diagram t = 3.0 mm; fy = 387.1 MPa t = 4.5 mm; fy = 382.3 MPa t = 6.0 mm; fy = 384.1 MPa

3) Test Setup

Axial load versus axial shortening of test columns 4) Test Results (Cont.) t = 6.0 mm t = 4.5 mm t = 3.0 mm t = 0 mm (reference) Axial load versus axial shortening of test columns

4) Test Results (Cont.) Mode of Failures CLC columns CLCFT columns

4) Test Results (Cont.) Axial load capacity, Mode of failure and the Comparisons ACI design equation can estimate the axial compressive load of the CLCFT columns with sufficient accuracy

5) Conclusions CLCFT columns with steel square tube have a linear elastic behavior up to 80-90% of their axial compressive load. Then, the behavior of the columns is gradually becoming nonlinear with the strain-softening type. Failure mechanism of the columns was identified as the crushing of concrete core and the yielding of hollow steel tube. ACI design equation can estimate the axial compressive load of the CLCFT columns with sufficient accuracy in the range of 3-6%.

Q & A Thank You For Your Attention Jaksada THUMRONGVUT Department of Civil Engineering, Rajamangala University of Technology Isan, THAILAND Sittichai SEANGATITH School of Civil Engineering, Suranaree University of Technology, THAILAND