Safety Evaluation of Concrete Structures Based on a Novel Energy Criterion

In this article,the post-peak softening stage of the constitutive relation and the elastic stiffness degradation of concrete are investigated,and a highly reasonable constitutive relation curve is proposed.At the material level,the energy change in the concrete failure process is studied based on the different stress-strain curves of concrete under uniaxial tension and compression.The concrete failure criterion based on elastic strain energy density is deemed suitable and consistent with the experimental phenomena.The hysteresis phenomenon(lags behind the peak strength)is also discussed.At the structure level,the strength reduction method is employed for the stability analysis,the energy change in the failure process of the Long Xi-Kou Dam is examined,and the results show that the dam failure criterion based on elastic strain energy shows a greater significance in practical applications compared with other conventional structural failure criteria in engineering.This criterion is objective and can avoid subjective arbitrariness.

A laser synthesis of vanadium oxide bonded graphene for high-rate supercapacitors

Graphene is a type of promising electrode material for high-energy and high-power density supercapacitors,but its electrochemical performance is greatly limited by the restacking problem.In this work,we reported a facile approach to synthesis graphene with chemically bonded vanadium oxide(VOx)nanoparticles and demonstrated that chemically-bonded VOxnanoparticles can effectively prevent the graphene sheets from restacking and hence improve the electrochemical performance.The capacitance of VOxbonded graphene increases to 272 F/g compared to 183 F/g of pristine graphene in 1 M H3PO4 aqueous electrolyte at 2 A/g.The VOx-bonded graphene also showed improved rate capability in both H3PO4 and ionic liquid electrolytes.The capacitance retention increases to 54.5%from 28.5%at 100 A/g(compare to2 A/g)in H3PO4 and increases to 65.1%from 46.3%at 2 A/g(compare to 0.2 A/g)in neat ionic liquid.A high energy density of 84.4 Wh/kg is obtained within the voltage window of 4 V in ionic liquid.Even at a high-power density of 1000 W/kg,the VOx-bonded graphene shows a high energy density of 47.3 Wh/kg.

Comprehensive safety evaluation method of surrounding rock during underground cavern construction

The deformation instability of surrounding rock and the collapse of rock blocks are two common failure modes observed during the construction of underground caverns.Therefore,a comprehensive safety evaluation method(CSEM)of surrounding rock for application during underground cavern construction is presented in this paper.The method can be used to evaluate the deformation stability of surrounding rock and predict the collapse of rock blocks,rapidly.First,a deformation stability prediction and evaluation method(DSPEM)for rock mass is established.It combines the safety evaluation method based on a deformation statistical analysis and an inverse deformation prediction method using measured deformation data of surrounding rock.This approach possesses the unique characteristics of complementary and mutual verification.In addition,a comprehensive early-warning index system(CWIS)for assessing the deformation stability of surrounding rock is presented.It consists of three types of warning indicators and three levels of warning values.The earlywarning values can be adjusted reasonably by the prediction correction method according to the measured displacements.For the collapse of rock blocks controlled by structural surfaces,a rapid prediction method of rock block collapse(RPMBC)based on the block theory is then presented.Finally,combining the DSPEM,RPMBC,and CWIS,the CSEM of surrounding rock for assessing the safety of cavern construction is established.It can provide technical support for decision making on the safety of surrounding rock during the construction of underground caverns.