The Elastic-Plastic Analysis of Collinear JointsLoaded by Shearing-Compressive Stresses

In this paper the problem of collinear multi-joint in rockmass loaded by shearing-compressive stresses is simplified as that of a joint in finite rockmass. The basic equations with Mohr-Coulomb criterion are solved by the line field analysis method near the joint line in an elastic-perfectly plastic materials. Through a reasonable boundary condition on the joint surface and matching conditions at the elastic-plastic boundary, the relation between length of the plastic region on the joint line and the shearing-compressive stresses is obtained. The failure laws of the rockmass contained collinear joints are also obtained.     

An Analysis of the Scaling Failure of the Nodular Iron Composite Polls

It is recognized that the scaling failure of nodular iron composite rolls in hot rolling is a problem of fatigue brittle fracture. The temperature field,stress,critical crack size as well as the interior quality of the rolls are presented. The theory of fracture mechanics is used to explain the cause of the scaling failure. At the same time, the way to extend the durability of the rolls is also studied.     

改性竹筋混凝土受弯构件力学性能试验研究

针对竹筋混凝土结构存在的问题,提出了多种对竹筋的改性方法。在此基础上,对12根采用不同配筋和不同改性方法的受弯构件(11根竹筋混凝土梁和1根钢筋混凝土梁)进行了试验研究,分析了不同改性方法和不同配筋率竹筋混凝土受弯构件的力学性能、破坏形态及其影响因素。研究结果表明：竹筋能有效提高混凝土受弯构件的承载能力;经过适当方法改性后的竹筋能确保竹筋和混凝土之间的有效粘结,其正截面强度计算可以采用平截面假定;竹筋混凝土受弯构件的破坏均为脆性破坏,其破坏形态与其截面配筋率有关。     

Near Crack Line Elastoplastic Solution for an Eccentric Cracks Loaded by the Pore Water Pressure

By using near crack line analysis method and Mohr-Coulomb strength criterion,the elastic-plastic solution for near crack line of an eccentric cracks loaded by the pore water pressure under large scale yielding condition is analyzed.The elastic stress fields,the plastic stress field,the unit normal vector of the elastic-plastic boundary near the crack line,the elastic-plastic stress fields near crack line are identified.The change pattern of the length of the plastic zone and the pore water pressure is presented.Besides,the elastic-plastic analytical solution for an eccentric cracks loaded by the pore water pressure is obtained.     

THE MIXED MODE FRACTURE CRITERION OF BRITTLE ROCK UNDER COMPRESSION-SHEAR STRESS STATE

In this paper the test results of mixed mode fracture of three kinds of brittle rock under two kinds of stress paths are reported. The fracture mechanism and failure patterns of brittle lock under different stress paths are discussed. Theory analysis and test results show that the Compression- Shear fracture criterion of brittle rock can be expressed:     

Elastoplastic Analysis of Discrete Jointin Rockmass Loaded by Compress_shear

In this paper the elastoplastic stress fields near joint line in rockmass loaded by compress- shear are analyesd by the line field method in fracture mechanics with Mokr- Coulomb criterion. Through the matching conditions of the elastoplastic fields on their boundary, the relations between the length of plastic zone on the joint line and the compress- shear loads are found, and the fracture criterion of the discrete joint is also obtained     

STABILITY FACTORS OF THREE-POINT BEND ROUND BEAM SPECIMENS FOR FRACTURE TESTING

Crack growth stability is very important for fracture toughness testing of brittle materials. The width of crack for a three-point bend round beam specimen changes continuously during the process of crack extension, so that the analysis of crack growth stability becomes complicated for this kind of specimen. This paper presents a method for calculating its stability factors, and the results of the calculation are compared with those of other specimens.     

Application of Extended Finite Element Method to Fracturing Analysis of Gravity Dam

The extended finite element method(XFEM) presented in recent years is a new and effective method for discontinuity analysis,especially fracture problem analyses.The basic XFEM principle is introduced and the technique for fracture analysis is presented.The fracturing process of a gravity dam is simulated by XFEM,and the rules of stresses and displacements distribution are analyzed.Compared with the classical finite element method,the crack growth in the gravity dam can be modeled by XFEM without making the crack surface associate with the finite element mesh and setting dense mesh near the crack tip as well as remeshing after crack growth.The cumbersome work and disadvantages in conducting fracturing analysis by the finite element method thus can be avoided.The predominance of this method for dam fracturing analysis is displayed.     

BAND DAMAGING CRACK MODEL OF CONCRETE

This paper presents a fracture model of concrete,band damaging crack model (BDCM).The BDCM can be used to analyze mechanical behaviour of concrete effectively and easily.Compared with test results;numerical results calculated by the BDCM are very precise.     

UNDERSTANDING BRITTLE FAILURE OF CONCRETE AGAIN

On the basis of analysing the cause of brittle failure ofconcrete,a conclusion that it is necessary to distinguish brittleness andbrittle failure and a new point of view about evaluating brittleness ofconcrete are proposed.A simple and reliable method about the directtension test of concrete is analysed theoretically.     

ECC/钢筋混凝土叠合梁正截面受弯承载力试验与理论研究

为了探究ECC/高强钢筋混凝土叠合梁的正截面受弯特征,以及ECC层厚度对叠合梁整体受弯性能的影响,做了两组共5根梁试件的正截面受弯试验。发现与高强钢筋混凝土梁相比,叠合梁的承载力更高,相同荷载下的挠度值和最大裂缝宽度较小。在受弯全过程中其截面应变仍符合平截面假定,钢筋与ECC也可以实现协调变形,说明受拉区使用ECC可以使得高强钢筋的应力得到充分发挥。但ECC层厚度过大可能会使叠合梁发生脆性破坏。进一步地,在此研究的基础上,对已有ECC的本构模型进行简化,忽略其应力强化贡献,并运用叠加原理,提出一种用于计算ECC/钢筋混凝土叠合梁正截面受弯承载力的方法,将计算结果与试验结果及诸多文献结果进行比较,发现吻合度较高。     

Simulation on crack growth of drill pipe with XFEM

Crack growth of drill pipe is a typical discontinuous problem. It is difficult to simulate with conventional finite element method and extended finite element method (XFEM) is developed in recent years for the problem. With the introduction of XFEM, the XFEM model of 5 inch drill pipe was proposed with different depth initial cracks under combined action between torque and tension. Based on the simulation, It is found that the smaller cracks is not easy to grow, whilst the crack of depth more than 2mm could grow under relatively lower external load and larger growth surface, eventually leads to pipe fracture failure. Through this simulation on crack growth of drill pipe, it is showed that the XFEM is appropriate in analysis of fracture failure.     

3D Meso scale Failure Simulation of Four phase Composite Concrete

Taking into account the influence of the internal micro cracks on the strength and deformation of concrete, a four phase composite material model was proposed, in which it included mortar, aggregate, interface and random defects. Meso scale unit in concrete was subjected to elastic plastic damage constitutive of increments form in strain space. With the simulation of mesh concrete crack growth by damage elimination, the damage processes of concrete under 3 D uniaxial compression and the elasto plastic damage process of concrete under uniaxial tension with heterogeneous specimen were obtained. It was shown that the proposed four phase model added the simulation of random defects, with which it was more appropriate to the actual situation in concrete forming. The percentage of random defects in volume was the key to determine the weakening degree of macro strength of concrete. The cracks occlusion was obvious for the lower homogeneous uniaxial tension specimen and the fracture was clearer for higher homogeneous specimen. The simulation results was in good agreement with test results.     

Simulation and analysis of mechanics of coal and gas delay outburst

The buried box girders in the mountain city sewage pipeline system would be turned into simple-supported girders because of the removal of the foundation caused by landslide.This change of supporting would result in the failure risk of pipeline structure.The static properties of the buried box girders with small depth-to-span ratio in simple-supported condition are experimentally analyzed.The failure pattern,shear behavior and shear lag effect of the buried box girders in simple-supported condition are studied.The shortages in the present design codes for the calculation of shear capacities of the box girders are also discussed.It is shown that under the vertical uniformly distributed load,the crack distribution of the box girders is uniform,and no major critical diagonal crack is formed,and the box girders lose the bearing capacity in the form of concrete diagonal rod crushing.As the main shear-bearing components,the stirrups devote much to shear capacity of the box girder after concrete cracking.The strains of the longitudinal rebars are affected by those factors such as the redistribution of internal force and cracks,so only few areas of the box girders show the shear lag effect.The change of supporting form leads to the premature cracking of concrete and affects the serviceability of the sewage pipeline.     

索承式桥梁吊索钢丝腐蚀疲劳寿命评估

根据吊索镀锌钢丝腐蚀疲劳破坏特点,把镀锌钢丝腐蚀疲劳纹形成和扩展过程分解成镀锌层腐蚀失效、蚀坑萌生、蚀坑形成、短裂纹扩展、长裂纹扩展和断裂破坏等阶段,建立各阶段时间表达式,得到镀锌钢丝疲劳寿命表达式,提出基于断裂力学的吊索钢丝腐蚀疲劳寿命评估研究结果方法。通过算例分析复杂运营条件下腐蚀环境和应力幅等因素对吊索钢丝腐蚀疲劳寿命的影响,研究结果表明：吊索钢丝腐蚀疲劳寿命主要由钢丝镀锌层腐蚀、蚀坑发展和短裂纹扩展等3个阶段组成,为了准确地评估吊索腐蚀疲劳寿命,需要掌握大桥的运营环境和交通荷载。     

Experimental Analysis of Shear Performance of Wet-bonding Interface between FRP Plate and Concrete

By adopting seven kinds of adhesive resins, the mechanical properties of the interface between pultruded Basalt fiber reinforced polymer plates and cast-in-place concrete is studied according to two groups of stretching double-shear test. And it is compared with the dry-bonding interface between BFRP plates and the precast concrete. Further study is conducted by comparing the damage features, load-displacement curves, effective bond length, bond slip relationship and interface fracture energy between the two interfaces. It is found that the effective bond length of the two interfaces are similar, but the bond strength of the wet-bonding is about half of the dry-bonding. Finally, the shear stress-slip model is proposed for the wet-bonding interface based on the experimental data.     

Study of Cracks on Rubber Concrete Beams Based on Fractal Theory

The flexural performances of a rubber concrete beam and a ordinary concrete beam are studied under concentrated load through the experiment. The influences of the content of the rubber powder in the rubber concrete beam on the bearing capacity and the crack width of beams are analyzed. The experimental results show that the crack distributions on two beam surfaces possess the characteristics of self-similar in statistical sense. The maximum crack width of the rubber concrete beam is less than that of the ordinary concrete beam under the same load level. The performance of anti-crack of the concrete beam is improved by adding the crumb rubber. Using the fractal theory, the fractal dimension values of the surface crack of the beams under different load grades are calculated and the relationship between the fractal dimension and the maximum crack width of the surface cracks is established.     

T形板肋对预制带肋底板混凝土叠合板弯曲疲劳性能的影响

为研究T形板肋对预制带肋底板混凝土叠合板弯曲疲劳性能的影响,对3块T形肋底板叠合板和1块整浇板进行弯曲疲劳性能对比试验,主要考察T形板肋与疲劳荷载幅值对试件疲劳破坏形态及疲劳损伤程度的影响,得到了在不同疲劳循环加载次数下的跨中动位移、混凝土应变、预应力筋应变、残余变形等,分析了在不同疲劳循环加载次数下的刚度退化情况、荷载-应变分布规律、裂缝分布规律及剩余承载力等。研究结果表明,经历200万次疲劳循环加载后,T形肋底板叠合板无明显的刚度和强度退化,增设T形板肋的叠合板能达到与整浇板相同的弯曲疲劳性能;T形肋底板叠合板正截面弯曲疲劳强度计算可采用普通预应力混凝土受弯构件正截面疲劳应力验算的4个假定,最终以此建立了其正截面弯曲疲劳强度验算方法。     

Concrete with a Crack Treated by Silane Soakage

If a crack appears in marine or concrete structures due to chloride corrosion, it will be a convenient channel for the chloride to penetrate into the concrete and easily corrode the steel bars and damage the concrete. A concrete specimen with a 0.2mm wide crack was prepared. After the specimen was soaked in a silane solution, emulsion and gel, a chloride ion corrosion test was carried out. The analysis of two dimensional chloride content shows that the silane soakage treatment of cracked concrete seals the crack and prevents further corrosion.     

Experimental and Numerical Analysis on Rupture of Rock Bridge with Non-Coplanar Intermittent Joints Under Direct Shear

By using servo control shear loading system, specimens with non-coplanar rock-like intermittent joints were tested by the way of forward and reverse direct shear, rupture mechanism and shearing law for rock bridge with non-coplanar intermittent joints were studied under direct shear. The experimental studies showed that five apparent stages are presented in the process of rock bridge rupture under direct shear, which are linear elastic stage, initiation and extension of crack, fracture and transfixion of rock bridge, climbing and occlusion of shear plane and residual friction. Rock bridge presented profile fracture plane under forward direct shear. While under reverse direct shear, band form fracture plane is showed which penetrated along with the direction of forward shear, and the shear strength of initiation and peak shear strength under reverse direct shear are bigger than that under forward shear. Crack angle, normal stress and lap proportion among adjacent joint are the main factors that influence the initiation strength and peak shear strength. The FLAC 3D simulation for the process of non-coplanar intermittent joints rock bridge rupture and formation of shear rupture surface under forward and reverse direct shear was conducted. The results of numerical simulation agreed well with those of experiment. The simulation results revealed tension crack failure of non-coplanar intermittent joints rock bridge and shear yielding mechanism of fracture plane.