Papers by Author: Zhi Wu Yu

Abstract: The shear thickening phenomenon was explained in this paper. The characteristics of shear thickening fluids (STFs), including reversibility and liquid to solid transition at critical shear rate were presented. Also, the applications of STFs for protective clothing and equipment were discussed. Since little references can be found which concern the effect of interparticle forces like Van der Waals forces on the performance of cementitious materials subjected to impact loading, understanding the mechanism of STF and knowing how its structure affects the properties, behaviors, and resulting applications is expected to inspire potential designs for building cementitious materials.

Abstract: It’s of great practical significance to improve the durability of steel-concrete composite beam structures.The deterioration of steel-concrete composite beams includes stud rust, reinforcement corrosion, corrosion of the steel beams and concrete performance degradation, which are caused by a number of factors. The corrosion mechanism of composite beams is discussed, and some basic issues remain to be solved in this area are analyzed in the paper. Besides, some research directions in the future are put forward.

Abstract: Time dependency of chloride transport has been studied and an improving model for predicting the apparent chloride diffusion coefficient has been proposed. A probabilistic-based durability analysis to estimate failure probability on the chloride ingress into concrete has been carried out. Results of the analysis demonstrate that the improving model in this paper is appropriate for long term service life prediction of concrete structures exposed to chloride containing environment.

Abstract: In recent years, on the one hand destructive earthquakes frequently occur, and vibration control devices such as dampers and isolation become increasingly application in actual large-scale structures, on the other hand modern structures with complex styles and diversified materials possess significant non-proportional damping characteristics, and traditional methods based on Rayleigh damping assumption no longer meet seismic calculation requirement. According to this situation, firstly multiple degree of freedom modal equation and pseudo excitation method are both utilized to establish a new efficient calculation method system which is suitable for stochastic analysis of non-proportionally damped structure, and the new method can achieve adjustive calculation efficiency and accuracy. Furthermore, advantages and features of established method are analyzed, and guidance suggestions for appropriate method use are also proposed. Finally, numerical study is carried out to verify conclusions proposed by theoretical derivation, and efficiency and accuracy of established method system used in stochastic response calculation of non-proportionally damped structure is confirmed.

Abstract: Based on solving the problems of pre-camber of the prestressed concrete bridge in construction, the calculation principle of the bridge model constructed in each stage is studied, the relation between forward and backward analysis method is illustrated, and the influencing factors related to characteristics of pre-camber and each controlled point are analyzed. Considering the influencing factors such as the establishment of new elements, the stressing of reinforcement, the shrinkage and creep of concrete in construction, the calculation model is established in accordance with the characteristics of prestressed concrete bridge constructed in each stage. The deformation of each construction segment is calculated with the forward and backward analysis method respectively, so that the pre-camber of each cantilever construction segment is gotten,which is the basis of construction control.

Abstract: The behavior of materials under repeated loading has been examined, but extended studies are more and more needed especially for damaged reinforced structures such as bridges, where high-cycle fatigue phenomena and corrosion can be significant. In the present paper, a theoretical model based on fatigue performance of materials and stress analysis for cross-section is proposed in order to analyze the fatigue damage of corroded reinforced concrete beams under repeated loads. Further, fatigue life is predicted by applying this method, and the method is evaluated by test results.

Abstract: The paper discusses the modulus of elasticity of plain concrete for a wide range of compressive strength. A large volume of selected experimental data has been collected from existing literature and then analyzed. Particular emphasis has been given to studying the effects of concrete compressive strength and the type of coarse aggregate on the modulus of elasticity of plain concrete. The adequacy and applicability of the existing models for predicting the modulus of elasticity of high-strength concrete has been critically examined, and a new empirical model is proposed to cover concrete strength up to 125 MPa. The new empirical model seems to perform much better when applied to the published experimental data on normal weight concrete over a wide strength range.

Abstract: The paper examines the effect of the corrosion types of reinforcing steel on the deterioration of shear strength of corroded reinforce concrete (RC) beams. Three possible types of corrosion, i.e., uniform (or general), pitting (or localized) and hybrid corrosion, for RC beams exposed to de-icing salts or sea environments are considered. From the investigation of the present paper, it can be concluded that the corrosion types have great effect on the time-dependent shear strength of a corroded RC beam. Generally, the shear strength degraded fastest for hybrid corrosion among the three corrosion types. When the corrosion rate is relative small, the deterioration of the shear strength for the uniform corrosion is greater than that for pitting corrosion. However, when the corrosion rate becomes larger, the deterioration of the shear strength for the pitting corrosion is greater than that for uniform corrosion as corrosion propagates.

Abstract: The experiments of 26 unbonded prestressed concrete flat beams under fire with elevating the temperature according to the ISO time-temperature standard curve were accomplished in the large structures electrical heating furnace that was manufactured independently. The macroscopical phenomena of water penetration, the lube flowing, the spalling of concrete and the corlor change of aspect were observed. The laws of behaviors such as temperature distribution on section,the deformation characteristic and stress varieties of prestressed tendons were investigated through the tests. The experiments indicated that temperature distribution was not uniform, the dynamic continuous deformation and the complicated varieties of prestressed stress occurred at high temperature. Based on the increment temperature-stress coupling constitutive models and chief deformation compatibility of the unboded prestressed tendons, the nonlinear finite element calculation formula took the unknown nodes displacements and the tensile forces in the unbonded tendons as unsolved column matrix simultaneously. The Increment format of nonlinear finite element method and calculation model for whole process analysis of unbonded prestressed concrete flexural members at high temperature were presented. The solution of nonlinear equilibrium equations for unboded prestressed concrete flexural members at high tempure was proposed, and a FORTRAN program named NAUPCLF was developed also and the results were in good agreement. The conclusions can supply the way and basis for further fire-resistant design and analysis of prestressed concrete structures.

Abstract: The paper presents the results of an experimental study on fatigue performance of corroded reinforced concrete (RC) beams repaired with carbon fiber reinforced polymer (CFRP) sheets. Five beams were constructed. One specimen was strengthened and not corroded; another four specimens were corroded and was strengthened with CFRP sheets. Five specimens were tested in fatigue. The results showed that steel bars corrosion reduced the fatigue life significantly while the CFRP strengthening enhanced the fatigue performance significantly. The effects of reinforcement corrosion on fatigue behavior of the strengthening beam can be attributed to a combination of four factors, including deteriorated bond behavior between reinforcement bras and surrounding concrete, loss of effective cross-section area of reinforcement, the stress concentration on steel bars, and degradation of mechanical properties of steel bars.