Etude experimentale et analytique du comportement en compression-flexion de poteaux composites partiellement enrobes de betons haute performance et de betons renforces de fibres metalliques

The main objectives of this research project is to evaluate the impact on partially encased composite columns of: (1) axial compression or axial compression-flexure loading; (2) prior cyclic loading history; (3) normal concrete or high performance concrete; (4) steel fibres reinforced concrete.;Experimental program A total of 16 partially encased composite columns with a cross section of 400x400x7.94 mm and a 2000 mm height were tested in the laboratory. From these: (1) 2 were tested in pure axial compression; (2) 7 were tested in axial compression-flexure under static loading; (3) 7 were initially subjected to a cyclic load in axial compression-flexure and then to an axial compression-flexure static load; (4) 3 were made of normal strength concrete (38 MPa); (5) 5 were made of normal strength concrete (38 MPa) reinforced with steel fibres (SFRC with V F = 1,0 %); (6) 4 were made of high performance concrete ( HPC of 50 MPa); (7) 4 were made of high performance concrete reinforced with steel fibres (HPFRC of 50 MPa with VF = 1,0 %).;The principal conclusions drawn from these tests are as follows: (1) Prediction of the composite columns axial resistance: The average value of the ratio Pexperimental /Panalytical is 1.033 excluding local buckling and 1.123 when considering local buckling. Consequently, the inclusion of the local buckling in the analyses led to over-conservative results for the composite columns studied. Moreover, the columns bent along their weak axis exhibit slightly more sensitivity to local buckling than the columns bent along their strong axis. (2) Cyclic loading: Negligible differences in resistance and failure mode were observed between the columns tested under static and cyclic loading histories. Hence, this parameter can be neglected in the evaluation of the composite columns axial capacity. (3) Concrete types: (a) HPC vs normal concrete: For the same concrete strength, the residual capacity at a given transverse deflection is very similar after the maximum axial load is reached. However, the columns made with high performance concrete show a greater capacity under combined axial and flexure loading. (b) SFRC vs normal concrete: The addition of steel fibres increases the column axial capacity by 10 % in average. An important increase of the residual axial capacity is observed at two times the peak axial strain (+/- 28 %), and a 1.8 times increase of the area under the column axial load vs the axial strain curve is also noted. (c) HPC vs HPFRC: The addition of steel fibres does not increase the column axial capacity. An increase of the residual axial capacity is observed at two times the peak axial strain, 2deltaaxial (+/- 24 %) and the flexural capacity from the P-M curves is increased 1.3 in average. (4) Failure mode: The failure of all the columns tested have been initiated either by the simultaneous compressive crushing of the concrete and the local buckling of the steel flanges or by the compressive crushing of the concrete followed by the local buckling in the post-peak range.;Axial compression and axial compression -- flexural capacity prediction of partially encased composite columns The relations proposed by CAN/CSA-S16-01 (Cl. 18.3.2) but modified to use F1 = 1.025psi for concrete without steel fibres, and F1 = 1.155psi for concrete with steel fibres, instead of F1 = 0.8 in the Crc equation give very good results to predict both the axial capacity for partially encased composite columns under axial compression and axial compression -- flexural loadings.;The relations given by the CAN/CSA-S16-01 (Cl. 18.2.4) standard for concrete-filled hollow structural sections is adapted to evaluate the axial capacity of partially encased composite columns subjected to axial compression -- flexural loadings. An addionnal parameter is also proposed to reduce the flexural capacity of columns subjected to bendings moments along their weak axis.;Original scientific contributions The main scientific contributions of this research project are: (1) To make the synthesis of the knowledge on the partially encased composite column system; (2) To broader the use of the partially encased composite columns by proposing design equations and rules, to include composite columns made of SFRC and/or HPC and composite columns subjected to axial compression and flexural loading, for possible inclusion in the Canadian Design Standard CAN/CSA-S16. (Abstract shortened by UMI.).