*2.2. Material Properties*

The tensile strength tests of steel were conducted according to the code *Metallic Materials—Tensile Testing—Part I: Method of Test at Room Temperature*. All steel was Q235B with a yield strength of 235 MPa. The grade of all steel bars was HPB300 with a yield strength of 300 MPa. The mechanical properties of the tested steel are listed in Table 2. The recycled coarse aggregate was from waste concrete specimens that had been placed in the laboratory for many years and were broken into concrete blocks. The design

strength grade of RAC was C30 and the cubic compressive strength was 30 MPa. Test cubes with a size of 100 × 100 × 100 mm were created while pouring walls and cured under the same condition as the walls. The cubic compressive strength of the RAC was measured as 32.8 MPa according to the *Standard for Test Method of Mechanical Properties of Ordinary Concrete*.


#### *2.3. Test Setup and Loading Procedure*

The test loading device is illustrated in Figure 3. The specimen was anchored on the ground beam with M30 bolts, and both ends of the ground beam were fixed in the laboratory by pressure beams. The horizontal load was applied by a 1000-kN MTS actuator, and the vertical load was applied by a 1000-kN hydraulic jack. A lateral brace was provided at the end of the MTS actuator, and the outside displacement of the specimen was limited by two groups of pulleys to ensure that the specimen and actuator moved in the horizontal direction. The displacement and strain gauges were arranged in the key parts to study the seismic behavior of the SFIRACSWs, and data were collected by a TDS-630 acquisition instrument. Concrete cracking, buckling of beams and columns, and specimen failure were constantly observed during the test.

**Figure 3.** Test setup.

In the vertical direction, 250 kN loads were applied to the steel columns, which was calculated by an axial compression ratio of 0.3. The axial compression ratio is the ratio of the design value of the axial load to the product of the total section area and design value of the axial compressive strength of concrete. The horizontal load was applied by the joint control method of force and displacement. Before the yield of the specimen, the load was controlled by force and cycled once with an increase of 20 kN each time. The load-displacement curves showed a noticeable turning point as a yield sign. After the yield of the specimen, the load was controlled by displacement and cycled thrice with an increase of 0.5 δ*y* each time, which was the estimated yield displacement. Loading stopped when the horizontal load was down to 85% of the peak load.

#### **3. Behavior of Test Specimens**

## *3.1. General Behavior*

## 3.1.1. Cast-in-Place RACSWs

## (1) Specimen SPE1

Specimen SPE1 was in the elastic stage with no observable behavior when the horizontal load was less than 200 kN. Slight oblique cracks began to appear in the middle part of the western side of the wall when the load was 220 kN. Oblique cracks appeared on the lower part of the eastern side of the wall when the load was 260 kN. Then, the specimen yielded locally, and the load was applied by controlling the displacement.

In the displacement control stage, the wall cracks continued to expand, and oblique cracks formed along the 45◦ direction in the middle of the wall when the displacement was 1.5 δ*y* (Figure 4a). The cracks continued to expand and extend at the control stage of displacement 2.0–4.0 <sup>δ</sup>*y*, and principal cracks with widths of 2–3 mm gradually formed on both sides of the wall (Figure 4b). The concrete along both sides of the principal cracks began to be crushed and fall o ff, and the width of the cracks reached 5–8 mm (Figure 4c). Local concrete fell o ff on both sides of the principal diagonal cracks, and the flange at the end of the beam bulged clearly when the displacement was 5.5 δ*y* (Figure 4d). A large area of concrete fell o ff in the middle of the wall, numerous steel bars were exposed, and the column base buckled outside when the displacement was 6.0 <sup>δ</sup>*y*. At the control stage of displacement 6.5 <sup>δ</sup>*y*, the wall was badly damaged and had holes in the middle. Finally, the horizontal load was reduced by more than 15%, and the specimen lost its carrying capacity.

**Figure 4.** Local failure of SPE1.
