基于梁-条模型的凝汽器管板强度设计方法

利用美国热交换学会标准推荐的"梁-条"结构力学模型,对管板进行了受力分析,借助结构力学求解器软件,对某型号凝汽器管板进行了强度计算,结果表明该方法合理有效,精度较高,为凝汽器开发设计提供了技术依据。

Analysis model for deformation mechanism of strip foundation of building:Considering shear effect of down-crossing tunnel under excavation

When the tunnel underpasses through the building,it will cause deformation and even damage to the buildings above,and the deformation of building foundation is the key to building safety.Based on the engineering case,the theoretical analysis was employed to evaluate the influence of shield tunnel underpass construction on the stability of the building,and the optimal tunneling parameters in the field construction have been obtained through the verified theoretical model and parameter analysis.First,the strip foundation of the building was simplified to the Timoshenko beam,which was taken into account the shear effect,and then the deformation displacement of the soil at the same place of strip foundation was applied to the simplified Timoshenko beam.Finally,the numerical solution of the displacement of the strip foundation was obtained by using the finite element method and verified its reliability using Euler-Bernoulli beam theoretical model,field monitoring data,and numerical simulation.Parameters analysis for the deformation and internal force of strip foundation under different types of shield machine tunneling parameters showed that the influence of the pressure of shield excavation chamber,thrust of shield,and driving speed played an important role in the deformation of the building’s strip foundation and internal force.

Strengthening of RC T-beams with Shear Deficiencies Using GFRP Strips

The shear performance, modes of failure, and strain analysis of simply supported reinforced concrete （RC） T-beams, externally strengthened in shear using epoxy bonded glass fiber reinforced polymer （GFRP） strips are focused in the present paper. Six RC T-beams of 2.5 m span without shear reinforcement are cast. Three beams are used as control specimens and rest three beams are strengthened in shear with GFRP strips in U-shape, side bonded at 45° and 90° to the longitudinal axis of the beam. All the beams are tested in a Universal Testing Machine. The test results demonstrate the feasibility of using an externally applied, epoxy-bonded GFRP strips to restore or increase the shear strength of RC T-beams. It is also observed that the RC T-beams strengthened by diagonal side strips outperformed those strengthened with vertical side strips.

Natural frequencies analysis of a composite beam consisting of Euler-Bernoulli and Timoshenko beam segments alternately

Present investigation is concerned with the free vibration property of a beam with periodically variable cross-sections.For the special geometry characteristic,the beam was modelled as the combination of long equal-length uniform Euler-Bernoulli beam segments and short equal-length uniform Timoshenko beam segments alternately.By using continuity conditions,the hybrid beam unit(ETE-B) consisting of Euler-Bernoulli beam,Timoshenko beam and Euler-Bernoulli beam in sequence was developed.Classical boundary conditions of pinned-pinned,clamped-clamped and clamped-free were considered to obtain the natural frequencies.Numerical examples of the equal-length composite beam with 1,2 and 3 ETE-B units were presented and compared with the equal-length and equal-cross-section Euler-Bernoulli beam,respectively.The work demonstrates that natural frequencies of the composite beam are larger than those of the Euler-Bernoulli beam,which in practice,is the interpretation that the inner-welded plate can strengthen a hollow beam.In this work,comparisons with the finite element calculation were presented to validate the ETE-B model.

Experimental study on creep of high-performance concretes

In order to investigate the compression creep of two kinds of high-performance concrete mixtures used for prestressed members in a bridge,an experimental test under laboratory conditions was carried out.Based on the experimental results,a power exponent function was used to model the creep degree of these high-performance concretes(HPCs) for structural numerical analysis,and two series parameters of this function for the HPCs were given with the optimum method of evolution program.The experimental data were compared with CEB-FIP 90 and ACI 92 models.Results show that the two code models both overestimate the creep degree of two HPCs,so it is recommended that the power exponent function should be used for the creep analysis of bridge structure.

Lateral static and dynamic characteristics of thin-walled box girder

To analyze the static and dynamic behaviors of the thin-walled box girder in its lateral webs in consideration of shear lag effect and shear deformation, an approach based on the minimum potential principle is introduced in this paper. Both static and dynamic response equations as well as the corresponding natural boundary conditions of the box girder are deduced. Meanwhile, three generalized displacement functions： w （x） , U（x） and O（x） are employed and their differences in the calculus of variation are quantitatively investigated. The comparison of finite shell element results with analytical results of calculation examples validates the feasibility of the proposed approach.

Finite element model updating of existing steel bridge based on structural health monitoring

Based on the physical meaning of sensitivity,a new finite element(FE) model updating method was proposed. In this method,a three-dimensional FE model of the Nanjing Yangtze River Bridge(NYRB) with ANSYS program was established and updated by modifying some design parameters. To further validate the updated FE model,the analytical stress-time histories responses of main members induced by a moving train were compared with the measured ones. The results show that the relative error of maximum stress is 2.49% and the minimum relative coefficient of analytical stress-time histories responses is 0.793. The updated model has a good agreement between the calculated data and the tested data,and provides a current baseline FE model for long-term health monitoring and condition assessment of the NYRB. At the same time,the model is validated by stress-time histories responses to be feasible and practical for railway steel bridge model updating.

Instability characteristics of the cracked roof rock beam under shallow mining conditions

To establish the movement relationship for the roof breaking under shallow mining conditions, the mechanical model of the roof rock beam was built, then the structure instability process of the roof rock beam was analyzed. The changing criterion of the vertical displacement was established and the relationship between the deflection and the rotary motion of roof block was determined. Regarding a mining face in Shangwan Mine, the responsing laws of the deflection and horizontal thrust of the roof rock beam were obtained through FLAC3D numerical analysis. The results show that the structure instability of the cracked roof rock beam depends on the interaction between the vertical load and the horizontal thrust.For the roof rock beam, when the vertical load keeps constant, the horizontal thrust fluctuating rises with increasing deflection. The horizontal thrust increases constantly with the deeper buried depth and the smaller span.

Reinforcement and numerical analysis on the corbel of a halfthrough arch bridge

Corbels support the crossbeams of half-through arch bridges. They are prone to cracking easily due to their characteristics and complicated loading conditions. Based on a practical diagnosis of a bridge crossbeam, we bonded steel plates onto bridge corbels to strengthen them. We carried out a numerical analysis on the effectiveness of the reinforcement by using the commercial sof^are ANSYS. The numerical analysis shows that the stresses near the section break increased slightly, but the variation amplitude was small and all the stresses were within an allowable range. The loading test indicates that it is feasible to strengthen the corbel with vertical bonded steel plates. Therefore, the reinforcement is effective and economical. This reinforcement method is suitable for this type of corbel and can be applied in similar cases.

Variational Approach of Timoshenko Beams with Internal Elastic Restraints

An exact approach for free transverse vibrations of a Timoshenko beam with ends elastically restrained against rotation and translation and arbitrarily located internal restraints is presented. The calculus of variations is used to obtain the equations of motion, the boundary conditions and the transitions conditions which correspond to the described mechanical system. The derived differential equations are solved individually for each segment of the beam with the corresponding boundary and transitions conditions. The derived mathematical formulation generates as particular cases, and several mathematical models are used to simulate the presence of cracks. Some cases available in the literature and the presence of some errors are discussed. New results are presented for different end conditions and restraint conditions in the intermediate elastic constraints with their corresponding modal shapes.

Scaled boundary isogeometric analysis for 2D elastostatics

A new numerical method,scaled boundary isogeometric analysis(SBIGA)combining the concept of the scaled boundary finite element method(SBFEM)and the isogeometric analysis(IGA),is proposed in this study for 2D elastostatic problems with both homogenous and inhomogeneous essential boundary conditions.Scaled boundary isogeometric transformation is established at a specified scaling center with boundary isogeometric representation identical to the design model imported from CAD system,which can be automatically refined without communication with the original system and keeping geometry invariability.The field variable,that is,displacement,is constructed by the same basis as boundary isogeometric description keeping analytical features in radial direction.A Lagrange multiplier scheme is suggested to impose the inhomogeneous essential boundary conditions.The new proposed method holds the semi-analytical feature inherited from SBFEM,that is,discretization only on boundaries rather than the entire domain,and isogeometric boundary geometry from IGA,which further increases the accuracy of the solution.Numerical examples,including circular cavity in full plane,Timoshenko beam with inhomogenous boundary conditions and infinite plate with circular hole subjected to remotely tension,demonstrate that SBIGA can be applied efficiently to elastostatic problems with various boundary conditions,and powerful in accuracy of solution and less degrees of freedom(DOF)can be achieved in SBIGA than other methods.

Regular Global Attractors of Type Ⅲ Thermoelastic Extensible Beams

For β∈ R,the authors consider the evolution system in the unknown variables u and ααttu+αxxxxu+αxxtα-(β+αxu L22)αxxu=f,αttα-αxxα-αxxtα-αxxtu=0 describing the dynamics of type III thermoelastic extensible beams,where the dissipation is entirely contributed by the second equation ruling the evolution of the thermal displacement α.Under natural boundary conditions,the existence of the global attractor of optimal regularity for the related dynamical system acting on the phase space of weak energy solutions is established.