## 2 Specim Design and Test Method
### Material Property Test  
The chemical compositions of test materials are given in Table 2. The content of carbon and manganese in low-yield-point steel was much lower than that in ordinary steel. The lower the carbon content, the better the plasticity, cold bending performance, weldability, and corrosion resistance of steel, but the lower the strength of steel. Manganese can significantly improve the strength of steel,  
Figure 4: Energy absorbers (unit mm). (**a**) Front; (**b**) side. Figure 3: Beam–column joint. (**a**) 3D; (**b**) plane. Figure 2: Detailed connections at the bottom of columns (unit: mm). (**a**) 3D; (**b**) plane; (**c**) section A–A. but reduce the weldability of steel. These indicate that the yield strength of low-yield-point steel is lower, whereas the plasticity and weldability are better than that of ordinary steel. The uniaxial tensile test on steel coupons had been carried out to obtain fundamental mechanical properties of the materials including the yield strength, ultimate tensile strength, modulus of elasticity, elongation, and yield ratios. The typical steel coupons designed as the shape of the plate shown in Figure 5 for the material tensile test were cut from the base metals. Table 3 presents the detailed sizes of different geometric parameters about the coupons, and three tensile coupons with the actually measured sizes listed in Table 4 were tested for the LYP steel with the nominal yield strength of 100 MPa. These steel coupons for tensile tests were respectively installed on the electro-hydraulic universal material-testing machine, which can automatically record the maximum load, yield strength, and ultimate strength at the end of the test (Figure 6). The tensile coupons of LYP steel were observed to stretch considerably long, from the initial elasticity to the yield and then to the strain hardening stage until the necking fracture. The cross-sectional area was reduced to a sufficiently small section, and the fractured surface was uneven and jagged after tensile fracture of LYP steel coupons, as shown in Figure 7, which indicates that this LYP steel exhibits superior ductile performance. Table 5 presents the different mechanical behaviors of low-yield-point and ordinary steel specimens under quasi-static tensile tests. In comparison, the ratios of yield strength, ultimate tensile strength, and yield ratio of LYP steel to Q235 steel were approximately 0.41, 0.64, and 0.63, respectively, whereas the elongation of LYP steel was approximately 1.36 times that of Q235 steel. The actual engineering stress-strain curves of LYP steel could then be calculated and achieved based on the test results, as shown in Figure 8. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Number** & **M1** & **M2** & **M3** \\ \hline Measured thickness \(a\) & 7.56 & 7.57 & 7.57 \\ Measured width \(b\) & 25.02 & 25.01 & 24.98 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Measured sizes of LYP steel coupons (unit: mm). Figure 5: Fabricated coupon. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Test Materials** & **C** & **Si** & **Mn** & **P** & **S** & **N** \\ \hline Low-yield-point steel & 0.01 & 0.06 & 0.08 & 0.007 & 0.01 & 0.0024 \\ Ordinary steel & 0.16 & 0.15 & 0.33 & 0.028 & 0.021 & 0.045 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Chemical compositions of test materials (unit: %). The characteristics of LYP steel regarded as an ideal material for energy absorption and its advantages in engineering applications can be summarized as follows: (i) the yield strength of LYP steel is much lower than that of ordinary steel, which will enable metallic energy absorbers made of LYP steel to form the plastic deformation, prior to other structural members, for energy dissipation when  
Figure 8: Stress–strain curves of the LYP steel. Figure 6: Material tensile test. (**a**) Installation; (**b**) fracture. Figure 7: Fractured LYP steel coupons.