Shear-strengthening of RC continuous T-beams with spliced CFRP U-strips around bars against flange top

Chaoyang Zhou,Da Ren,Xiaonian Cheng 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.64 No.1

To upgrade shear performance of reinforced concrete (RC) beams, and particularly of the segments under negative moment within continuous T-section beams, a series of original schemes has been proposed using carbon fibre-reinforced polymer (CFRP) U-shaped strips for shear-strengthening. The current work focuses on one of them, in which CFRP U-strips are wound around steel bars against the top of the flange of a T-beam and then spliced on its bottom face in addition to being bonded onto its sides. The test results showed that the proposed scheme successfully provided reliable anchorage for U-strips and prevented premature onset of shear failure due to FRP debonding. The governing shear mode of failure changed from peeling of CFRP to its fracture or crushing of concrete. The strengthened specimens displayed an average increase of about 60% in shear capacity over the unstrengthened control one. The specimen with a relatively high ratio and uniform distribution of CFRP reinforcement had a maximum increase of nearly 75% in strength as well as significantly improved ductility. The formulas by various codes or guidelines exhibited different accuracy in estimating FRP contribution to shear resistance of the segments that are subjected to negative moment and strengthened with well-anchored FRP U-strips within continuous T-beams. Further investigation is necessary to find a suitable approach to predicting load-carrying capacity of continuous beams shear strengthened in this way.

Experimental study on RC beams externally bonded by CFRP sheets with and without end self-locking

Chaoyang Zhou,Yanan Yu,Chengfeng Zhou,Xuejun He,Yi Wang 국제구조공학회 2023 Steel and Composite Structures, An International J Vol.48 No.5

To avoid debonding failure, a novel type of hybrid anchorage (HA) is proposed in this study that uses a slotted plate to lock the ends of the fiber-reinforced polymer (FRP) sheet in addition to the usual bonding over the substrate of the strengthened member. An experimental investigation was performed on three groups of RC beams, which differed from one another in either concrete strength or steel reinforcement ratio. The test results indicate that the end self-locking of the CFRP sheet can improve the failure ductility, ultimate capacity of the beams and its utilization ratio. Although intermediate debonding occurred in all the strengthened beams, it was not a fatal mode of failure for the three specimens with end anchorage. Among them, FRP rupture occurred in the beam with higher concrete strength and lower steel reinforcement ratio, whereas the other two failed by concrete crushing. The beam strengthened by HA obtained a relatively high percentage of increase in ultimate capacity when the rebar ratio or concrete strength decreased. The expressions in the literature were inspected to calculate the critical loads at intermediate debonding, FRP rupturing and concrete crushing after debonding for the strengthened beam. Then, the necessity of further research is addressed.

Prediction of Surface Settlement with Ultra-shallow-burial and Large Rectangular Cross-section Urban Underpass

Chaoyang Heng,Song Sun,Zhi Zhou,Jiantao Zhang 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.11

Based on the actual measured surface settlement of two super-shallow buried large rectangular-section urban underpass, a settlement fitting function is established. The superposition curve used the reduction of settlement trough. By comparing the results of fitting analysis with Peck formula result, settlement characteristics and simple prediction method for super-shallow and large rectangular section urban underpass are proposed, including: 1) The settlement trough is a superposition of three normal distribution curves, with the maximum surface settlement appeared above the central line of each single passage; 2) The depth and width of the middle passage settlement trough should be uniformly reduced. The reduction coefficient is calculated based on the ratio of the middle passage width to the side passage; 3) The loss rate of the side passage is 0.7% − 1.0%, while it is 0.4% − 0.6% for the middle passage, 4) If the underpass is excavated in staggered sequence, the peck formula can be used to calculate the surface settlement. The surface settlement of a single passage is calculated firstly, and then the surface settlement of three passages is superimposed to obtain the final settlement.

Calculation Method of Underground Passage Excavation on Interactive Effects among Pipe-Roof, Steel Bracing and Foundation Soil

Chaoyang Heng,Song Sun,Jiantao Zhang,Zhi Zhou 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.1

The ultra-shallow buried excavation technology, utilizing pipe-roof steel arches as main supporting structure, has broad application prospects. Current mainstream pipe-roof design schemes often adopt simple beam theory or engineering analogy methods, which do not take into account the cumulative deformation and have high engineering disaster risk. Based on the beam Winkler model of elastic foundation, this paper studies the method on interactive effects among pipe-roof, steel bracing and foundation soil. The calculation model of the ultra-shallow buried pipe-roof and steel bracing is established with theoretical derivation. And a new supporting design method of ultra-shallow buried excavation under interactive effects is proposed. Firstly, an optimal method for determining the elasticity coefficient of steel arch and foundation soil is put forward on interactive effects among pipe-roof, steel bracing and foundation. Secondly, considering the enhancement effect of concrete wall, a procedure of determining the elasticity coefficient of fulcrum is described. That is, the first steel arch, which is adjacent to underground passage tunnel face, returns to the 1.5H (H is the height of the hole) range as an enhanced transition section, and the elasticity coefficient of fulcrum varies linearly with its position. Furthermore, the key issue is the deformation of the inlet section increases to a stable level in a certain range, while the ground settlement does not exceed the threshold. The selection of pipe-roof is controlled by calculated deformation. If the deformation meets the requirements, the internal force will be far enough to meet the requirements. Only two sections need to be considered when calculating the ultra-shallow buried underground passage, the entrances 2.0H and the central across section. Finally, the accuracy of the interactive effects calculated method is validated by using the measured data of a practical example.

DFT study of the adsorption of 2, 3, 7, 8-tetrachlorodibenzofuran (TCDF) on vacancy-defected graphene doped with Mn and Fe

Qingxiao Zhou,Yongliang Yong,Weiwei Ju,Xiangying Su,Xiaohong Li,Chaoyang Wang,Zhibing Fu 한국물리학회 2018 Current Applied Physics Vol.18 No.1

Dioxins are highly toxic to humans and environment, and developing the effective methods to control and detect the organic pollutant is particular important. Here we performed a density functional theory (DFT) study on the adsorption of 2, 3, 7, 8-tetrachlorodibenzofuran (TCDF) molecules on the modified graphene substrates. The results indicated that the introducing of vacancy-defect and dopants (Mn and Fe) significantly improves the sensitivity toward TCDF molecules. The impurity played a crucial role for interacting with TCDF molecules. Furthermore, the adsorption of TCDF induced band-gap open in defected graphene substrates, which could be seen as electric signal to detect TCDF pollutant. The present study is expected to be useful to explore effective materials to detect and remove dioxin pollutants based on graphene.

Research on Support Technology of a Soil-Rock Combination Deep Excavation in Qingdao

Weilong Zhang,Chaoyang Heng,Chunbo Xu,Zhi Zhou,Liqin Mao 대한토목학회 2024 KSCE Journal of Civil Engineering Vol.28 No.8

Based on a deep excavation engineering in Qingdao, which is one of the largest or deepestsoil-rock combination excavations in China, the design parameters and calculation results aregiven for excavation retaining and protection. The excavation on-site test data are provided,including the anchor axial force and pile top displacement, and a comprehensive analysis iscarried out. Using numerical simulation, the distribution of anchor axial force is analyzedunder different working conditions, as same as pile body deformation and slope bodydisplacement are analyzed. Retaining and protection structure can be calculated in four stagesby the elastic foundation beam method. Results: when the lower rock mass is calculated assoil by equivalent internal friction angle, the retaining and protection structure designparameters deviate from the actual needs with working conditions. The ratio of tested anddesigned axial force of anchor in soil layer is generally greater than the ratio in rock layer. Whether above the soil-rock interface or the pit base, the measured horizontal compositeforce of anchors is between the calculated active earth pressure and the static earth pressure. Anchorage section length is recommended 2.0 m in the medium or slightly weathered rock.