## 2 Experimental Program  
### Specim Design  
The specimens were designed in accordance with concrete design code of China, Both the live load, LL, and the dead load, DD, of the floor were taken as 2.5 kN/m\({}^{2}\) for the prototype structure, and the combined design load is calculated by 1.2 DD + 0.5 LL. The position of the beam-column sub-assembages in the prototype structure is enclosed with dotted lines, as shown in Figure 1. Six 1/4 reduced scaled sub-assembages, named as S1 to S6, were designed referring to the prototype, and each sub-assembage consists of two beams and three columns. The dimensions and reinforcement details of the control specimen, S1, are shown in Figure 2. Longitudinal steel reinforcement in the columns was welded on steel plates embedded in the columns, BFRP bars were used as longitudinal reinforcement of the frame beams. The design details of the sub-assembages are listed in Table 1, in which S2 and S3 were designed to investigate the influence of prestress action modes, including unbonded prestress (UP) and bonded prestress (BP). The steel prestressing strand is 9.5 mm in diameter and arranged in parabolic shape as shown in Figure 3. Figure 4 illustrates the anchorage of BFRP bars in the frame beam stubs, i.e., BFRP bars were anchored in steel hollow tubes with 40 mm in diameter and 200 mm length, which were filled with epoxy mortar. BFRP bars were manufactured in the factory in advance and used as the alternative of steel stirrups of the frame beams for S5. The actually measured average axial compressive strength of the concrete after 28 days according to Chinese code from tests of three prismatic specimens was 29.3 MPa, and the concrete tensile strength, as well as the elastic modulus, were 2.6 MPa and \(3.5\times 10^{4}\) MPa respectively. The mechanical properties of steel reinforcement and the prestressing strand are listed in Table 2, and the nominal mechanical values of BFRP bars reported in the manufacturer data sheet is also listed in Table 3.  
Figure 1: Prototype structure.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Test Identifier**} & **Span of the Frame Beam** & **Span to Depth** & **Initial** & **Action Modes** & **Types of** \\  & **Frame Beam** & **Ratio of the** & **Effective** & **of Prestress** & **Stirrups in the** \\  & **(mm)** & **Frame Beams** & **Prefress** & **Beams** \\ \hline S1 & 2600 & 12.0 & NA & NA & SRB \\ S2 & 2600 & 12.0 & 0.6\(f_{ptk}\) & UP & SRB \\ S3 & 2600 & 12.0 & 0.6\(f_{ptk}\) & BP & SRB \\ S4 & 2300 & 10.5 & NA & NA & SRB \\ S5 & 2600 & 12.0 & NA & NA & BFRP(B8) \\ S6 & 2900 & 13.5 & NA & NA & SRB \\ \hline \hline \end{tabular} \(f_{ptk}=\) the ultimate tensile strengthen of the prestressing strand, NA = the data is unavailable, and SRB = steel reinforcing bars.  
\end{table}
Table 1: Specim design.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Items**} & **Nominal** & \multirow{2}{*}{**Yield Strength**} & **Ultimate Tensile** & **Elastic** & \multirow{2}{*}{**Elongation (\%)**} \\  & **Diameters** & **(MPa)** & **Strength (MPa)** & **(MPa)** & **(MPa)** \\ \hline R8 & 8 & 371.0 & 550.2 & 2.1\(\times 10^{5}\) & 10.8 \\ D16 & 16 & 539.0 & 711.4 & 2.0\(\times 10^{5}\) & 14.3 \\ Prestressing & 9.5 & 1812 & 1926 & 1.9\(\times 10^{5}\) & 5.5 \\ strand & & & & & \\ \hline \hline \end{tabular}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Items**} & **Nominal** & \multirow{2}{*}{**Yield Strength**} & **Ultimate Tensile** & **Elastic** & \multirow{2}{*}{**Flongation (\%)**} \\  & **Diameters** & **(MPa)** & **Strength (MPa)** & **(MPa)** & **(MPa)** \\ \hline R8 & 8 & 371.0 & 550.2 & 2.1\(\times 10^{5}\) & 10.8 \\ D16 & 16 & 539.0 & 711.4 & 2.0\(\times 10^{5}\) & 14.3 \\ Prestressing & 9.