Issue 46

W. Hao et alii, Frattura ed Integrità Strutturale, 46 (2018) 391-399; DOI: 10.3221/IGF-ESIS.46.36 392 ratios and improve the section forms of the columns, but also need to make sure they are filled with high-performance concrete. Reactive powder concrete (RPC) is a new ultra-high-performance cement-based composite [1] with excellent mechanical properties such as ultra high strength, toughness and durability. Compared with high-strength concrete (HSC), the 200MPa- level RPC has 2-4 times its compressive strength, 3-10 times its flexural strength and 200 times its fracture energy. The RPC filled steel tube can significantly improve the strength and deformation performance of the RPC as the steel tube can constrain its deformation. Compared with ordinary concrete filled steel tubes, the RPC filled ones, have obvious mechanical advantages in reducing the cross-sectional dimensions of components and improving their bearing capacity and lateral stiffness. Therefore, as a new type of composite structure, RPC filled square steel tube has a broad application prospect in civil engineering. At present, there are few researches on RPC filled square steel tubular columns at home and abroad. By carrying out an eccentric loading experiment on RPC filled square steel tubular columns, this paper attempts to study the mechanical behavior of eccentrically loaded RPC filled square steel tubular columns as well as their influencing factors. At the same time, it compares and analyzes the experimental results and the theoretical values of bearing capacity which were calculated with relevant specifications (or codes), and finds the calculation formula of bearing capacity suitable for RPC filled square steel tubular columns. In addition, this paper utilizes the finite element software Abaqus to carry out numerical simulation of the eccentrically loaded RPC filled square steel tubular columns, which provides a theoretical basis for engineering practice. O VERVIEW OF THE EXPERIMENT Preparing the specimens PC materials include P.O 42.5 ordinary Portland cement (C), silica fume (SF), quartz sand (QU), Super plasticizers (SU), steel fiber (with a diameter of about 0.18~0.20mm and a length of 12~14mm) and water (W). By reference to relevant documents [2-3], the mix ratios are shown in Tab. 1, where B=C+SF, the proportion of steel fiber is volume ratio, and the others are mass ratios. The mechanical properties of RPC are shown in Tab. 2. Cement C Silica fume SF/C Quartz sand QU/C Super-plasticizers SU/B Water-binder ratio W/B Steel fiber Vs/V 1 0.21 1.8 0.035 0.23 1% Table 1: Mix Ratios of RPC. Strength type Cube compressive strength f cu /N/mm 2 Axial compressive strength f c /N/mm 2 Splitting tensile strength f ct /N/mm 2 Value 93.49 69.0 11.43 Table 2: Mechanical properties of RPC. The steel tubes are all straight-seam square steel tubes. The cross-section dimensions of all specimens are all 100mm×100mm. According to GB/T 228.1-2010 and GB/T 228-2002 Metallic Materials-Tensile Experimenting at Ambient Temperature, the mechanical properties of these specimens were experimented, as shown in Tab. 3. Nominal wall thickness t/mm Measured wall thickness t/mm Yield strength f y /N/mm 2 Tensile strength f st /N/mm 2 Modulus of elasticity E s /N/mm 2 3 2.63 390.3 429.9 2.17×105 4 3.70 383.7 423.6 2.20×105 5 4.71 354.9 396.6 2.44×105 Table 3: Mechanical properties of steel tube. By reference to relevant documents [4-7], 12 RPC filled square steel tubular column specimens were designed in this experiment, whose detailed parameters are shown in Tab. 4. Pressure-bearing cover plates were welded at both ends of the R