Fly ash 168

Silica fume 35

Water 262

Fine sand 460

Coarse sand 920

Water reducer 9。1

Fig。 3。 Schematic diagram of  loading

Fig。 4。 Test  setup

In this test, to study the seismic behavior of the columns in practical engineering, the axial compression ratio was considered。 Because the maximum load of laboratory equipment is limited, the axial load on the tested columns was 580 kN, and the axial compression ratio was 0。15。 The axial force was applied to a pre- determined value before the low cyclic loading was applied, and then it was kept constant。 The loading procedure was controlled by the incremental method, which was jointly controlled by the stresses and the displacements。 The load increased by increments of 4 kN and looped one time before the steel bar yielded。 The

Fig。 5。 Layout of measuring  point

displacement control was adopted after the  steel  bar  yielded。 The displacement of each stage increased by the value of the yield displacement and looped three times。 The failure of the specimen occurred when the load of the specimen fell to 85% of the peak load, and the loading was then  finished。

The horizontal force, horizontal displacement of the column top, middle horizontal displacement of the column, column base dis- placement, longitudinal steel strain of the column root, and the stirrup strain of the shear regions were measured in the test。 The displacement meters were indexed as 1–3, and the strain-gauge measuring points were indexed as S1–S12。 The specific details are shown in Fig。 5。 These mentioned data were automatically gath- ered by the collecting  devices。

Experimental  Results  and Analysis

Experimental Phenomenon

Specimen C1

Specimen C1 showed more rust spots than Specimens C2 or C3 in the corrosion region。 Two cracks appeared along the longitudinal reinforcement in the concrete surface, which  had  a  length  of 400 mm and a width of 0。1 mm。 When the horizontal force reached 60 kN, horizontal cracks appeared 130 and 70 mm from the root of the column, with widths of 0。2 mm。 The number of the cracks in- creased, and the horizontal cracks ran through the whole section during the loading procedure。  When  the  horizontal  force  was 76 kN, the steel bar reached its yield strain, and the width of the existing corrosive cracks expanded to 0。34 mm。 In the first loop of the 2Δy (yield displacement) loading, the horizontal load reached its peak value, and the concrete at the root of the column concurrently spalled。 In the 4Δy loading, the horizontal bearing capacity fell below 85% of the peak load, and the rust of the internal

© ASCE 04016231-4 J。 Struct。 Eng。

concrete fragments was obvious。 The longitudinal reinforcements were chiseled out after the test, and the actual corrosion rate of the steel was 4。12%。

Specimen C2

Specimen C2 showed corrosive cracks in the surface of the reinforc- ing layer that were much smaller than those of Specimen C1。 The length of the corrosive cracks was 300 mm, and their width was

0。04 mm。 When the horizontal force reached 76 kN, the first hori- zontal crack appeared 330 mm from the root of the column, but it did not extend to both sides。 When the horizontal force was 92 kN, the steel bars yielded, but the number of cracks was not great。 The existing corrosive cracks widened, and dense vertical cracks ap- peared at right angles to the column root。 In the first loop of the 2Δy loading, the horizontal load reached its peak value, and frac- ture sound of the textile increased, with a small amount of mortar spalling from the reinforcement layer。 In the 6Δy loading, the hori- zontal bearing capacity fell rapidly。 Compared with Specimen C1, the number of displacement cycles of specimen C2 increased by a factor of 6, which meant that the seismic deformation capacity was improved。 The longitudinal reinforcements were chiseled out after the test, and the measured corrosion ratio of the steel was   3。08%。