Performance and Calculations of Recycled Aggregate Concrete-filled Steel Tubular (RACFST) Short Columns under Axial Compression

Zongping Chen,Jinjun Xu,Jianyang Xue,Yisheng Su 한국강구조학회 2014 International Journal of Steel Structures Vol.14 No.1

This paper describes a series of tests on steel tubular short columns of circular section filled with normal concrete (NA) andrecycled aggregate concrete (RAC). Twenty-two specimens, including 11 small diameter of RAC-filled steel tubular (RACFST)columns named CA series and 11 larger diameter of RACFST columns called CB series, were tested to research the influenceof variations in confinement index and replacement ratio of recycled coarse aggregate (RCA), from 0% to 100% with 10%increasing. The test results show that both types of RACFST columns and normal concrete-filled steel tubular (CFST) columnsfailed due to oblique shear pressure damage with a drum-like. Comparisons are made with predicted bearing capacities ofRACFST columns using the existing theories, such as Unified Strengthen theory (I), Confinement theory (II) and Superpositiontheory (III). The equation for axial compression stress-strain curves of the whole process are proposed in this investigation forRACFST short columns, which can be directly used in theoretical and numerical analysis as well as practical engineering designand evaluation of RACFST structures.

Bond behaviors of shape steel embedded in recycled aggregate concrete and recycled aggregate concrete filled in steel tubes

Zongping Chen,Jinjun Xu,Ying Liang,Yisheng Su 국제구조공학회 2014 Steel and Composite Structures, An International J Vol.17 No.6

Thirty one push-out tests were carried out in order to investigate the bond behavior between shape steel, steel tube (named steels) and recycled aggregate concrete (RAC), including 11 steel reinforced recycled aggregate concrete (SRRAC) columns, 10 recycled aggregate concrete-filled circular steel tube (RACFCST) columns and 10 recycled aggregate concrete-filled square steel tube (RACFSST) columns. Eleven recycled coarse aggregate (RCA) replacement ratios (i.e., 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100%) were considered for SRRAC specimens, while five RCA replacement ratios (i.e., 0%, 25%, 50%, 75% and 100%), concrete type and length-diameter ratio for recycled aggregate concretefilled steel tube (RACFST) specimens were designed in this paper. Based on the test results, the influences of all variable parameters on the bond strength between steels and RAC were investigated. It was found that the load-slip curves at the loading end appeared the initial slip earlier than the curves at the free end. In addition, eight practical bond strength models were applied to make checking computations for all the specimens. The theoretical analytical model for interfacial bond shear transmission length in each type of steel-RAC composite columns was established through the mechanical derivation, which can be used to design and evaluate the performance of anchorage zones in steel-RAC composite structures.

Seismic behavior of steel reinforced concrete cross-shaped column under combined torsion

Zongping Chen,Xiang Liu 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.26 No.4

Experiments were performed to explore the hysteretic performance of steel reinforced concrete (SRC) cross-shaped columns. Nine specimens were designed and tested under the combined action of compression, flexure, shear and torsion. Torsion-bending ratio (i.e., 0, 0.14, 0.21) and steel forms (i.e., Solid - web steel, T - shaped steel, Channel steel) were considered in the test. Both failure processes and modes were obtained during the whole loading procedure. Based on experimental data, seismic indexes, such as bearing capacity, ductility and energy dissipation were investigated in detail. Experimental results suggest that depending on the torsion-bending ratio, failure modes of SRC cross-shaped columns are bending failure, flexure-torsion failure and torsion-shear failure. Shear - displacement hysteretic loops are fuller than torque - twist angle hysteretic curves. SRC cross-shaped columns exhibit good ductility and deformation capacity. In the range of test parameters, the existence of torque does not reduce the shear force but it reduces the displacement and bending energy dissipation capacity.What is more, the bending energy dissipation capacity increases with the rising of displacement level, while the torsion energy dissipation capacity decreases.

Seismic behavior and strength of L-shaped steel reinforced concrete column-concrete beam planar and spatial joints

Zongping Chen,Deyi Xu,Jinjun Xu,Ni Wang 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.39 No.3

The study presented experimental and numerical investigation on the seismic performance of steel reinforced concrete (SRC) L-shaped column- reinforced concrete (RC) beam joints. Various parameters described as steel configuration form, axial compressive ratio, loading angle, and the existence of slab were examined through 4 planar joints and 7 spatial joints. The characteristics of the load-displacement response included the bearing capacity, ductility, story drift ratio, energy-dissipating capacity, and stiffness degradation were analyzed. The results showed that shear failure and flexural failure in the beam tip were observed for planar joints and spatial joint, respectively. And RC joint with slab failed with the plastic hinge in the slab and bottom of the beam. The results indicated that hysteretic curves of spatial joints with solid-web steel were plumper than those with hollow-web specimens. The capacity of planar joints was higher than that of space joints, while the opposite was true for energy-dissipation capacity and ductility. The high compression ratio contributed to the increase in capacity and initial stiffness of the joint. The elastic and elastic-plastic story deformation capacity of L-shaped column frame joints satisfied the code requirement. A design formula of joint shear resistance based on the superposition theory and equilibrium plasticity truss model was proposed for engineering application.

Flexural bearing capacity and stiffness research on CFRP sheet strengthened existing reinforced concrete poles with corroded connectors

Chen, Zongping,Song, Chunmei,Li, Shengxin,Zhou, Ji Techno-Press 2022 Structural monitoring and maintenance Vol.9 No.1

In mountainous areas of China, concrete poles with connectors are widely employed in power transmission due to its convenience of manufacture and transportation. The bearing capacity of the poles must have degenerated over time, and most of the steel connectors have been corroded. Carbon fiber reinforced polymer (CFRP) offers a durable, light-weight alternative in strengthening those poles that have served for many years. In this paper, the bearing capacity and failure mechanism of CFRP sheet strengthened existing reinforced concrete poles with corrosion steel connectors were investigated. Four poles were selected to conduct flexural capacity test. Two poles were strengthened by single-layer longitudinal CFRP sheet, one pole was strengthened by double-layer longitudinal CFRP sheets and the last specimen was not strengthened. Results indicate that the failure is mainly bond failure between concrete and the external CFRP sheet, and the specimens fail in a brittle pattern. The cross-sectional strains of specimens approximately follow the plane section assumption in the early stage of loading, but the strain in the tensile zone no longer conforms to this assumption when the load approaches the failure load. Also, bearing capacity and stiffness of the strengthened specimens are much larger than those without CFRP sheet. The bearing capacity, initial stiffness and elastic-plastic stiffness of specimen strengthened by double-layer CFRP are larger than those strengthened by single-layer CFRP. Weighting the cost-effective effect, it is more economical and reasonable to strengthen with single-layer CFRP sheet. The results can provide a reference to the same type of poles for strengthening design.

Investigation on compression properties of seawater-sea sand concrete

Chen, Zongping,Mo, Linlin,Song, Chunmei,Zhang, Yaqi Techno-Press 2021 Advances in concrete construction Vol.12 No.2

This paper introduces the experimental results of the influence of sea sand replacement rate and mixing water on the basic mechanical properties of sea sand concrete. A total of thirty test blocks were designed for uniaxial compression test. In this test two parameters were considered: (a) sea sand replacement ratio (i.e., 0%, 25%, 50%,75%, 100%); (b) water for mixing (i.e., freshwater, seawater). The entire stress-strain curve of sea sand concrete under uniaxial compression was obtained. Based on the test results, the influence of sea sand replacement rate and mixing water on the peak stress, peak strain, and deformation performance of sea sand concrete were analyzed. Test results showed that the stress-strain curves of seawater sea sand concrete were steeper than that of ordinary concrete, which indicated that seawater sea sand concrete was slightly more brittle. On the whole, the sea sand replacement rate had no significant effect on the axial compressive properties of sea sand concrete. Under the same sea sand replacement rate, the deformation performance of freshwater sea sand concrete (FSC) was slightly greater than that of seawater sea sand concrete (SSC). Seawater had an enhanced effect on the early strength development of sea sand concrete.

Residual bond behavior of high strength concrete-filled square steel tube after elevated temperatures

Zongping Chen,Xiang Liu,Wenxiang Zhou 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.27 No.4

This paper presents experimental results on the residual bond-slip behavior of high strength concrete-filled square steel tube (HSCFST) after elevated temperatures. Three parameters were considered in this test: (a) temperature (i.e., 20°C, 200°C, 400°C, 600°C, 800°C); (b) concrete strength (i.e., C60, C70, C80); (c) anchorage length (i.e., 250 mm, 400 mm). A total of 17 HSCFST specimens were designed for push-out test after elevated temperatures. The load-slip curves at the loading end and free end were obtained, in addition, the distribution of steel tube strain and the bond stress along the anchorage length were analyzed. Test results show that the shape of load-slip curves at loading ends and free ends are similar. With the temperature constantly increasing, the bond strength of HSCFST increases first and then decreases; furthermore, the bond strength of HSCFCT proportionally increases with the anchoring length growing. Additionally, the higher the temperature is, the smaller and lower the bond damage develops. The energy dissipation capacity enhances with the concrete strength rasing, while, decreases with the temperature growing. What is more, the strain and stress of steel tubes are exponentially distributed, and decrease from the free end to loading end. According to experimental findings, constitutive formula of the bond slip of HSCFST experienced elevated temperatures is proposed, which fills well with test data.

Residual behavior of recycled aggregate concrete beam and column after elevated temperatures

Zongping Chen,Ji Zhou,Ying Liang,Peihuan Ye 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.76 No.4

This paper presents the results of an experimental study on the residual behavior of reinforced recycled aggregate concrete (RRAC) beam-columns after exposure to elevated temperatures. Two parameters were considered in this test: (a) recycled coarse aggregate (RCA) replacement percentages (i.e. 0, 30, 50, 70 and 100%); (b) high temperatures (i.e. 20, 200, 400, 600, and 800°C). A total of 25 RRAC short columns and 32 RRAC beams were conducted and subjected to different high temperatures for 1 h. After cooling down to ambient temperature, the following basic physical and mechanical properties were then tested and discussed: (a) surface change and mass loss ratio; (b) strength of recycled aggregate concrete (RAC) and steel subjected to elevated temperatures; (c) bearing capacity of beam-columns; (d) load-deformation curve. According to the test results, the law of performance degradation of RRAC beam-columns after exposure to high temperatures is analyzed. Finally, introducing the influence coefficient of RCA replacement percentage and high temperatures, respectively, to correct the calculation formulas of bearing capacity of beam-columns in Chinese Standard, and then the residual bearing capacity of RRAC beam-columns subjected elevated temperatures is calculated according to the modified formulas, the calculated results are in good agreement with the experimental results.

Seismic behavior of T-shaped steel reinforced high strength concrete short-limb shear walls under low cyclic reversed loading

Zongping Chen,Jinjun Xu,Yuliang Chen,Yisheng Su1 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.57 No.4

This paper presents an experimental study of six steel reinforced high strength concrete T-shaped short-limb shear walls configured with T-shaped steel truss under low cyclic reversed loading. Considering different categories of ratios of wall limb height to thickness, shear/span ratios, axial compression ratios and stirrup reinforcement ratios were selected to investigate the seismic behavior (strength, stiffness, energy dissipation capacity, ductility and deformation characteristics) of all the specimens. Two different failure modes were observed during the tests, including the flexural-shear failure for specimens with large shear/span ratio and the shear-diagonal compressive failure for specimens with small shear/span ratio. On the basis of requirement of Chinese seismic code, the deformation performance for all the specimens could not meet the level of ‘three’ fortification goals. Recommendations for improving the structural deformation capacity of T-shaped steel reinforced high strength concrete short-limb shear wall were proposed. Based on the experimental observations, the mechanical analysis models for concrete cracking strength and shear strength were derived using the equivalence principle and superposition theory, respectively. As a result, the proposed method in this paper was verified by the test results, and the experimental results agreed well with the proposed model.

Axial compression ratio limit values for steel reinforced concrete (SRC) special shaped columns

Zongping Chen,Jinjun Xu,Yuliang Chen,Jianyang Xue 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.20 No.2

This paper presents the results of experimental investigation, numerical calculation and theoretical analysis on axial compression ratio limit values for steel reinforced concrete (SRC) special shaped columns. 17 specimens were firstly intensively carried out to investigate the hysteretic behavior of SRC special shaped columns subjected to a constant axial load and cyclic reversed loads. Two theories were used to calculate the limits of axial compression ratio for all the specimens, including the balanced failure theory and superposition theory. It was found that the results of balanced failure theory by numerical integration method cannot conform the reality of test results, while the calculation results by employing the superposition theory can agree well with the test results. On the basis of superposition theory, the design limit values of axial compression ratio under different seismic grades were proposed for SRC special shaped columns.