State-of-the-art on the anchorage performance of rock bolts subjected to shear load

Rock bolts are extensively utilized in underground engineering as a means of offering support and stability to rock masses in tunnels,mines,and other underground structures.In environments of high ground stress,faults or weak zones can frequently arise in rock formations,presenting a significant challenge for engineering and potentially leading to underground engineering collapse.Rock bolts serve as a crucial structural element for the transmission of tensile stress and are capable of withstanding shear loads to prevent sliding of weak zones within rock mass.Therefore,a complete understanding of the behavior of rock bolts subjected to shear loads is essential.This paper presents a state-of-the-art review of the research progress of rock bolts subjected to shear load in three categories:experiment,numerical simulation,and analytical model.The review focuses on the research studies and developments in this area since the 1970s,providing a comprehensive overview of numerous factors that influence the anchorage performance of rock bolts.These factors include the diameter and angle of the rock bolt installation,rock strength,grouting material,bolt material,borehole diameter,rock bolt preload,normal stress,joint surface roughness and joint expansion angle.The paper reviews the improvement of mechanical parameter setting in numerical simulation of rock bolt shear.Furthermore,it delves into the optimization of the analytical model concerning rock bolt shear theory,approached from the perspectives of both Elastic foundation beam theory coupled with Elastoplasticity theory and Structural mechanic methods.The significance of this review lies in its ability to provide insights into the mechanical behavior of rock bolts.The paper also highlights the limitations of current research and guidelines for further research of rock bolts.

Field Load Test Based SHM System Safety Standard Determination for Rigid Frame Bridge

The deteriorated continuous rigid frame bridge is strengthened by external prestressing. Static loading tests wereconducted before and after the bridge rehabilitation to verify the effectiveness of the rehabilitation process. Thestiffness of the repaired bridge is improved, and the maximum deflection of the load test is reduced from 37.9 to27.6 mm. A bridge health monitoring system is installed after the bridge is reinforced. To achieve an easy assessmentof the bridge’s safety status by directly using transferred data, a real-time safety warning system is createdbased on a five-level safety standard. The threshold for each safety level will be determined by theoretical calculationsand the outcomes of static loading tests. The highest risk threshold will be set at the ultimate limit statevalue. The remaining levels, namely middle risk, low risk, and very low risk, will be determined usingreduction coefficients of 0.95, 0.9, and 0.8, respectively.

Analysis of the Application of Static Load Test in Bridge Bearing Capacity Testing

This article uses real engineering projects as examples to analyze how static load test technology is applied in testing the bridge-bearing capacity.The analysis covers aspects such as testing section layout,test load and efficiency coefficient,loading plan,evaluation optimization,test result modification,and result evaluation.The aim is to support the accurate detection and evaluation of bridge-bearing capacity.

Load Testing in Bridge Maintenance

Highway bridges are a crucial component in road transportation networks.These bridges must be maintained according to usage requirements regularly.Test results must be considered before devising a maintenance plan.Load testing is a vital method of assessing the quality and performance of highway bridges.The outcomes of these tests facilitate the formulation of maintenance plans.This article examines the definition of load testing,its significance,and the process of execution,with the goal of providing support for bridge inspection and maintenance.

Load Test Analysis and Research on Long-Span Concrete Continuous Rigid Frame Bridge

Based on the as-built load test of a large bridge,this paper introduces the procedure of the prestressed concrete continuous rigid frame bridge load test.Numerical analysis of the bridge was carried out by simulating and establishing a finite element model,and comparative analysis was carried out with the measured values.The results show that the calculated values were basically consistent with the measured values,which showed that the establishment method of the model was reasonable,and the mechanical performance of the bridge met the service requirements of the designed live load.

Static Load Test Detection of Continuous Rigid- Frame Railway Bridge

The quality of the continuous rigid-frame railway bridge is related to the safety of train operation,so it is necessary to test its stiffness,strength,and other indicators.Static load test is a common technique for bridge inspection.This article summarizes the purpose of the static load test for a continuous rigid-frame railway bridge,including the required equipment,operation methods,etc.,and lists examples to analyze the operation process and precautions of static load test,hoping to provide reference information for relevant personnel.

水平受荷桩“p-y+M-θ”分析方法

中国近海海上风电机组开发建设中,大直径单桩基础形式使用占比超70%。现行p-y曲线设计方法主要适用于小直径柔性桩,对大直径单桩侧向及桩底受荷描述能力不足,导致其严重低估刚柔性桩和刚性桩(分别常用于中国和欧洲的近海风电工程)的变形和承载能力,过于保守的设计给海上风电降本带来挑战。为此建立了能以统一的方式预测柔性、刚柔性和刚性单桩水平单调受荷响应的“p-y+M-θ”模型,并将该模型推广到循环荷载下单桩的响应分析。通过与相关试验结果比对发现,“p-y+M-θ”模型能较为准确地预测桩基水平加载响应。力图为水平受荷单桩工程设计提供简洁而可行的响应分析方法。

扣件系统横向刚度及抗倾翻试验研究:以WJ-8型扣件为例

为了对扣件系统横向刚度及抗倾翻性能进行研究,首先借鉴等间隔弹性点支承梁模型分析钢轨横向力学行为;然后,考虑钢轨自身截面特性,推导扣件系统横向刚度及抗倾翻系数计算公式;最后,设计并进行1组及3组WJ-8型扣件横向加载试验,验证分析及推导的合理性。试验结果表明:当钢轨整体扭转中心为轨底中心点时,钢轨自身扭转不可忽略,钢轨横向力及扭矩的传递过程都是非线性过程;1组及3组扣件试验得到的位移相对误差不超过6.8%,转角相对误差不超过9.5%;3组扣件试验允许加载范围更大,且更适用于非对称式扣件;WJ-8型扣件钢轨横移过程可按扣件横向反力的组成划分为钢轨滑移、线性变形和非线性变形3个阶段,钢轨倾翻过程可按钢轨轨底与轨下垫板接触形式划分为钢轨脱离和整体倾翻2个阶段。扣件横向刚度及抗倾翻系数可通过横向力-位移曲线、扭矩-转角曲线确定。

部分充填式窄幅钢箱-UHPC组合梁抗剪试验研究

目的为研究部分充填式窄幅钢箱-UHPC组合梁的抗剪性能,方法对4根倒置组合梁试件通过三点加载方式进行了静载试验,通过研究其负弯矩作用下的破坏形态及变形特征,得到了组合梁的荷载-挠度曲线、应变分布、荷载-滑移曲线、最终破坏形态等。结果试验研究结果表明:UHPC翼板显著提升了组合梁的变形能力和极限承载力;相较于试件SUCB-3(NC翼板),试件SUCB-1(1/2UHPC翼板和SUCB-4(全UHPC翼板))的承载力分别提高了18.2%和27.3%,变形能力则分别增强了38.02%和41.2%;钢纤维的添加能有效地抑制翼板裂缝的开展,钢纤维掺量从0提高到2%,试件的最大裂缝宽度从1.06 mm降低到0.92 mm,变形能力增强了23.61%,承载力则提高了4%。结论提出了考虑钢箱、UHPC翼板和充填混凝土贡献的组合梁抗剪承载力计算公式。

窄幅钢箱-UHPC组合梁负弯矩下抗弯性能试验研究

为改善钢-混凝土组合梁负弯矩下的受力性能,提出一种新型窄幅钢箱-超高性能混凝土(UHPC)组合梁。通过6根试验梁的反向静力加载试验,得到试验梁受力全过程跨中荷载-挠度、荷载-应变、荷载-最大裂缝宽度关系曲线、裂缝发生发展及破坏形态等,基于简化塑性理论推导出了组合梁极限抗弯承载力计算公式。结果表明:窄幅钢箱-UHPC组合梁在负弯矩下具有良好的受力性能;提高配筋率、钢纤维掺量和UHPC相对板厚都可在一定程度上改善组合梁延性,提高其极限抗弯承载力;翼板配筋率对承载力影响较大,配筋率由1%增加至2%时,其极限抗弯承载力提高了15%;钢纤维掺量和UHPC相对板厚对初始开裂荷载影响较大,钢纤维掺量从1%增加到2%时,初始开裂荷载提高32%,UHPC相对板厚由0增加到0.5时,初始开裂荷载提高56%;增加钢纤维掺量和UHPC相对板厚可有效控制裂缝宽度,减少结构主裂缝数量,改善组合梁耐久性;组合梁极限抗弯承载力计算公式计算值与试验值吻合较好,表明塑性理论适用于窄幅钢箱-UHPC组合梁的承载力计算。

黄土区楔形桩-网复合地基承载特性

[目的]针对黄土地区中楔形桩-网复合地基的承载性能进行探究.[方法]开展以几何相似常数为第一基本量、重度相似常数为第二基本量的土工模型试验,研究了不同受荷区域基桩承载能力,并通过有限元计算方法进一步分析其承载特性.比较模型试验结果与有限元计算结果,揭示了黄土区楔形桩-网复合地基的荷载沉降、桩身轴力、侧摩阻力、桩土应力比及荷载分担比等分布与变化规律.[结果]复合地基沉降变化总体趋于均匀,荷载-沉降曲线为缓变型;不同受荷区域基桩的桩身轴力、侧摩阻力呈现明显差异性;楔形桩-土相互作用与荷载和深度呈现正相关关系,但存在一定上限;复合地基中楔形桩随荷载增大能有效分散桩身应力,并将荷载由桩体向桩周土传递、由地基中心向外围扩散.[结论]楔形桩-网复合地基表现出良好的承载能力,直接受荷区桩能更高效地发挥楔形桩承载特性,楔形桩在复合地基中很好地实现桩-网-土协同作用.

钢-UHPC轻型组合结构短栓钉抗剪性能试验研究

通过6个钢-超高性能混凝土(ultra-high performance concrete,UHPC)轻型组合结构短栓钉推出试验,对其抗剪承载力、破坏形态、栓钉应变及荷载-滑移曲线进行了研究,探讨了栓钉直径、长度、数量以及界面黏结对短栓钉抗剪性能的影响规律.结果表明:所有试件均为栓钉根部剪切破坏,UHPC板除栓钉根部沿承压方向部分UHPC压碎外,其余部分保持完好,UHPC可以抵抗栓钉传递的高压应力;栓钉根部截面屈服后应力强化阶段明显,栓钉发生剪切破坏时,栓钉根部上侧应变超过3500με;长径比为2.0的短栓钉在UHPC中也能发挥全部强度;所有试件的荷载-滑移曲线分为弹性、弹塑性和塑性3个阶段,所有短栓钉的最大滑移量均小于4 mm,工程应用时应按照弹性剪力连接件进行设计;栓钉直径对栓钉抗剪性能提高最显著,直径16 mm的栓钉比直径13 mm的栓钉的抗剪承载力和极限滑移分别提高了46.4%和11%,弹性刚度和塑性刚度分别提高了35.8%和59.1%,增加栓钉长度和界面黏结能有效提高栓钉的剪切刚度,长径比为3.0的栓钉比长径比为2.5的栓钉的弹性刚度提高了12.3%,界面有黏结试件比界面无黏结试件的弹性刚度提高了17.4%;相同间距内,合理增加更多栓钉有利于提高整体抗剪强度,但会降低延性变形能力.最后,结合实验数据和国内外UHPC中栓钉推出试验结果,建立了UHPC中栓钉荷载-滑移曲线和抗剪承载力预测表达式,计算值与试验值吻合良好.

常泰长江大桥组合索塔锚固结构钢-混传剪构造足尺模型试验研究

常泰长江大桥索塔锚固结构采用钢箱-核芯混凝土组合结构,为研究该新型组合索塔锚固结构钢-混传剪构造的受力特性,进行钢-混传剪构造足尺模型试验研究。制作2个锚固结构足尺节段试验模型,通过压剪试验研究锚固结构的荷载~滑移曲线及应力、应变分布等受力特性,并通过有限元模型分析锚固结构的传力机理和各组件的内力分配比例,推导剪力钉剪力计算方法。结果表明:在2.14倍单索最大索力荷载作用下,锚固结构保持弹性状态,钢壁板未产生明显滑移,钢-混界面最大滑移不超过0.25 mm,该锚固结构中钢-混传剪构造至少具有2.14倍的安全系数;荷载作用下,剪力钉剪力从上至下逐渐增大,锚腹板附近底部3排剪力钉剪力较大,钢-混传剪构造至少存在剪力钉和界面摩擦力2种传剪机制,钢-混传剪构造的承载能力显著提高;钢-混传剪构造受力过程分为粘结力传力阶段和局部滑移阶段,剪力钉剪力分布不仅与沿剪切方向长度分布有关,也与荷载的大小线性相关。

ECC-混凝土叠合梁弯曲试验及裂缝发展的分形表征

为明确ECC(工程纤维增强型水泥基复合材料)-混凝土叠合梁抗弯性能及影响参数,并定性表征裂缝发展情况,设计、制作11根不同材料强度等级、配筋率、ECC层厚度、PVA纤维体积掺量的ECC-混凝土叠合梁及3根不同混凝土强度等级的混凝土梁进行四点弯曲试验,研究承载力、延性及裂缝发展等情况,并基于分形理论及数字图像处理技术,采用分形维数对不同影响参数下的叠合梁裂缝发展规律进行表征。结果表明:ECC-混凝土叠合梁较相同材料强度和配筋率的混凝土梁极限承载力和抗裂性能明显更优;材料强度等级提高,模型梁承载力及延性均提高;适筋范围内,配筋率越小模型梁延性越好;ECC层厚度对模型梁的承载力及延性影响不大;PVA纤维体积掺量为2.0%时,裂缝整体分布更均衡。计算分形维数得到的叠合梁表面裂缝分布具有自相似性;加载过程中叠合梁的分形维数小于混凝土梁,与试验结果相符,梁表面裂缝分形维数在一定范围内随着材料强度等级、配筋率、ECC层厚度、PVA纤维体积掺量的增加而降低,分形理论结合数字图像技术求得的裂缝分形维数可作为叠合梁裂缝分布及受弯损伤程度的定性表征指标。

Influence of volume compression on the unloading deformation behavior of red sandstone under damage-controlled cyclic triaxial loading

A reasonable evaluation of unloading deformation characteristics is of great significance for the effective analysis of deformation and stability of surrounding rocks after underground excavation.In this study,the damage-controlled cyclic triaxial loading tests were conducted to investigate the pore compaction mechanism and its influences on the unloading deformation behavior of red sandstone,including Young’s modulus,Poisson’s ratio,volumetric strain,and irreversible strain.The experimental results show that the increases of volumetric and irreversible strains of rocks can be attributed to the compaction mechanism,which almost dominates the entire pre-peak deformation process.The unloading deformation consists of the reversible linear and nonlinear strains,and the irreversible strain under the influence of the porous grain structure.The pre-peak Young’s modulus tends to increase and then decrease due to the influence of the unloading irreversible strain.However,it hardly changes with the increasing volumetric strain compaction under the influence of reversible nonlinear strain.Instead,the initial unloading tangent modulus is highly related to the volumetric strain,and clearly reflects the compaction state of red sandstone.Furthermore,both the reversible nonlinear and irreversible unloading deformations are independent of confining pressure.This study is beneficial for the theoretical modeling and prediction of cyclic unloading deformation behavior of red sandstone.

Model tests on XCC-piled embankment under dynamic train load of high-speed railways

Piled embankments,which offer many advantages,are increasingly popular in construction of high-speed railways in China.Although the performance of piled embankment under static loading is well-known,the behavior under the dynamic train load of a high-speed railway is not yet understood.In light of this,a heavily instrumented piled embankment model was set up,and a model test was carried out,in which a servo-hydraulic actuator outputting M-shaped waves was adopted to simulate the process of a running train.Earth pressure,settlement,strain in the geogrid and pile and excess pore water pressure were measured.The results show that the soil arching height under the dynamic train load of a high-speed railway is shorter than under static loading.The growth trend for accumulated settlement slowed down after long-term vibration although there was still a tendency for it to increase.Accumulated geogrid strain has an increasing tendency after long-term vibration.The closer the embankment edge,the greater the geogrid strain over the subsoil.Strains in the pile were smaller under dynamic train loads,and their distribution was different from that under static loading.At the same elevation,excess pore water pressure under the track slab was greater than that under the embankment shoulder.

Application of bi-directional static loading test to deep foundations

Bi-directional static loading test adopting load cells is widely used around the world at present, with increase in diameter and length of deep foundations. In this paper, a new simple conversion method to predict the equivalent pile head load-settlement curve considering elastic shortening of deep foundation was put forward according to the load transfer mechanism. The proposed conversion method was applied to root caisson foundation in a bridge and to large diameter pipe piles in a sea wind power plant. Some new load cells, test procedure, and construction technology were adopted based on the applications to different deep foundations, which could enlarge the application scopes of bi-directional loading test. A new type of bi-directional loading test for pipe pile was conducted, in which the load cell was installed and loaded after the pipe pile with special connector has been set up. Unlike the conventional bi-directional loading test, the load cell can be reused and shows an evident economic benefit.

Technical Analysis of Highway Bridge Static Load Test

Highway bridges are an important part of the transportation industry and can promote social economic construction and development.In actual operation,highway bridges are often damaged due to overload and natural factors,which tend to affect the safety and shorten the service life of these bridges.Assessing the overall state and performance of highway bridges is therefore a key element.Static load test,which is a type of sustainable detection experiment,has many advantages,including low cost,high efficiency,and high accuracy.In this paper,the bridge structure is analyzed through the application of theoretical calculations and relevant comparisons,so as to judge the operating state of the bridge.

Test and numerical investigations on static and dynamic characteristics of extra-wide concrete self-anchored suspension bridge under vehicle loads

The present work is aimed at studying the mechanic properties of the extra-wide concrete self-anchored suspension bridge under static and dynamic vehicle loads. Based on the field test using 12 heavy trucks and finite element simulations, the static deformations of different components, stress increments and distributions of the girder, as well as the vibration characteristics and damping ratio of the Hunan Road Bridge were analyzed, which is the widest self-anchored suspension bridge in China at present. The dynamic responses were calculated using the Newmark-β integration method assisted by the simulation models of bridge and vehicles, the influences on the dynamic impact coefficient(DIC) brought by the vehicle parameters, girder width, eccentricity travel and deck flatness were also researched. The spatial effect of the girder is obvious due to the extra width, which performs as the stress increments distribute unevenly along the transverse direction, and the girder deflections and stress increments of the upper plate change as a "V" and "M" shape respectively under the symmetrical vehicle loads affected by the shear lag effect, cross slope and local effect of the wheels, the maximum of stress increments are located in the junctions with the inner webs. The obvious girder torsional deformation and the apparent unevenness of the hanger forces between the two cable planes under the eccentric vehicle loads, together with the mode shapes such as the girder transverse bending and torsion which appear relatively earlier, all reflect the weakened torsional rigidity of the extra-wide girder. The transverse displacements of towers are more obvious than the longitudinal ones. As for the influences on the DIC, the static effect of the heavier vehicles plays a major role when pass through with a higher speed and the changes of vehicle suspension stiffness generate greater impacts than the suspension damp. The values of DIC in the vehicle-running side during the eccentric travel, affected by the restricts from the static effects of the eccentric moving trucks, are significantly smaller than the vehicle-free side, the increase in the road roughness is the most sensitive one among the above influential factors. The results could provide references for the design, static and dynamic response analysis of the similar extra-wide suspension bridges.

Mechanical Properties of Deep-buried Marble Material Under Loading and Unloading Tests

The mechanical properties are essentially different when rock material is subjected to loading or unloading conditions. In this study, loading and unloading tests with various confining pressures are conducted to investigate the mechanical properties of marble material samples taken from the deep diversion tunnels of Jinping II Hydropower Station. The stress-strain relationship, failure characteristics and strength criterion are compared and analyzed based on the experiment results. The results show： in the loading and unloading test, peak strength, lateral strain, axial strain and plastic deformation increase significantly as the confining pressure increases. Lateral strain increased significantly and obvious lateral dilatancy can be observed to the change of confining pressure; The fracture mode is mainly the single shear fracture for the triaxial compression test and post-peak test, angle between the failure surface and the ends of the rock material becomes smaller as the confining pressure increases. Hock-Brown strength criterion reflects the strength characteristics of marble material under two different unloading conditions, and has some supplementary effects to the rock material of mechanical field.