To study the interfacial bond-slip performance of concrete-filled square steel tubes (CFSSTs), taking the core concrete strength, slenderness ratio, and width-to-thickness ratio as the influencing factors; 9 specimens were designed with 3 factors and 3 levels for the orthogonal test method. In addition, different from the above 9 specimens, one specimen without rust removal was designed for the purpose of comparison. Based on the bond stress distribution and deformation coordination relationships between the specimens during the push-out tests, a theoretical formula for calculating the relative slip of a CFSST was deduced. e results show that with the increase of load, the relative slip at the loading ends was earlier than that at the free ends of the specimens; the interfacial bond failure and relative slip gradually developed from the two ends towards the centre of the specimens; the increase of the bond stress in the middle part was faster than that at the ends of the specimens. e order of these factors from main to secondary is the presence of rust in the inner wall of the square steel tube, the slenderness ratio, the core concrete strength, and the width-to-thickness ratio.
In order to assess the seismic performance of damaged reinforced concrete (RC) frame strengthened with carbon fiber reinforced polymers (CFRP) sheets, two experimental specimens with identical reinforcement ratio and geometric dimensions were designed following Chinese code for seismic design of buildings. Experimental specimens consist of a reference (undamaged) RC frame, namely, KJ-1, and an earthquake-damaged RC frame strengthened with CFRP sheets, namely, KJ-2. A pseudostatic test was conducted on the two specimens to simulate moderate earthquake damage. The strengthening effects of CFRP sheets on damaged RC frame were discussed in terms of hysteretic curve, skeleton curve, stiffness degradation, and ductility. In addition, numerical method based on fiber model method was utilized to analyze the seismic performance of KJ-1 and KJ-2 and it is compared with the experimental result. Both the results confirm that the method of exterior bonding CFRP sheets on the damaged RC frame has restored the seismic performance such as bearing capacity, stiffness, and ductility to its original undamaged level, and some of the seismic performance of the damaged RC frame strengthened with CFRP sheets is even better than the undamaged one, which proves that the method has significant effect in strengthening postearthquake-damaged RC frames.
In this paper, monotonic horizontal loading tests were carried out to study the bearing capacity of the cone-shaped foundation in marine fine sand. With load-controlled methods, the horizontal load was applied to the rod of cone-shaped foundation at loading eccentricity ratios of 5.0, 6.0, and 7.0. In addition, theoretical analysis was used to investigate the horizontal ultimate bearing capacity, and finite element analysis was also used in this paper to investigate the influence factors of the bearing capacity of cone-shaped foundation. Based on the theoretical analysis, the formula for horizontal ultimate bearing capacity was deduced. Test results show that, at the same loading eccentricity, cone-shaped foundation can provide higher H-M bearing capacity as well as lower lateral deflection compared to regular circular foundation for wind turbines. In addition, the deflection-hardening behavior of load-deflection curve for cone-shaped foundation is also observed. Numerical analysis results show that the H-M bearing capacity of the cone-shaped foundation increases with increasing aspect ratio and buried depth, however, and decreases with increasing loading eccentricity. Based on the results from finite element analyses, several equations to calculate the maximum moment bearing capacities are put forward, which take the aspect ratio, loading eccentricity, and embedded depth into account.
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