极限状态下岩体受拉锚杆锚固承载力的计算

从分析岩体中受拉锚杆的锚固机理及破坏形态出发,研究了承载能力极限状态下受拉锚杆的受力模型,建议在锚杆的锚固承载力计算公式中考虑锚固长度对平均粘结强度的影响,推导了能够反映极限状态下剪力传递机理的受拉锚杆锚固承载力计算公式,并结合岩壁吊车梁受拉锚杆锚固的工程实例与GB 50086公式的计算结果进行了比较、分析和探讨。     

FRP约束木柱轴心抗压性能的弹塑性分析方法

进行了FRP(环向)约束木柱的轴心抗压性能试验,结果表明,FRP约束木柱可提高木柱的抗压承载力,改善木柱的延性,使木柱轴向极限抗压强度提高达15%左右.在Tsai-Wu强度准则的基础上,建立了三向受压木柱的屈服准则及屈服发展方程.根据内力平衡和应变相容的原理,提出了FRP约束木柱在轴心受压时的增量应力-应变计算模型;根据FRP约束木柱受压破坏机理,即达极限应力时,FRP中的拉应变远小于其极限拉应变,提出了FRP约束木柱在极限抗压强度时的应力-应变计算公式,并将之作为计算模型程序运算的结束条件;极限抗压强度之后的FRP约束木柱应力-应变曲线接近水平线,可近似为理想塑性.试验结果表明,所建计算模型精度较好.     

不同石粉含量的机制砂混凝土高温后力学性能

以受火温度、石粉含量为变化参数,设计并制作了210个100 mm×100 mm×100 mm的机制砂混凝土立方体试件,对其进行高温后的物理力学性能试验,获取了试件的质量损失率以及抗压强度和劈裂抗拉强度,建立了机制砂混凝土高温后抗压强度和劈裂强度的劣化模型,同时结合X射线衍射和扫描电子显微镜等技术,揭示了高温后机制砂混凝土力学性能劣化的微观机理。基于最高受火温度和质量损失率,分别提出了高温后机制砂混凝土抗压强度和劈裂抗拉强度评估计算式。结果表明:随着温度的升高,机制砂混凝土试件的表面颜色从灰色变成红褐色,最后呈白色,高温作用使试件表面出现了温度裂缝及剥落现象; 试件的质量损失率随着石粉含量的增加而增大; 混凝土抗压强度和劈裂抗拉强度随着温度的升高显著减小; 随着石粉含量的增加,混凝土抗压强度和劈裂抗拉强度先增大后减小,当石粉含量(质量分数)为10%时,混凝土强度达到最大值; 基于试验结果建立的高温后机制砂混凝土抗压强度和劈裂抗拉强度的劣化模型拟合度较好; 混凝土中掺入适量的石粉能促进体系中钙钒石和氢氧化钙等水化产物数量,当经受700 ℃高温后,水泥水化物脱水分解使混凝土内部裂缝和孔隙增多。     

Section capacity of very high strength (VHS) circular tubes under compression

This paper investigates the section capacity of very high strength (VHS®) circular tubes under compression. Full-section tensile tests were performed to determine the Young's modulus of elasticity, tensile yield stress and ultimate tensile strength. The modulus of elasticity was found around 200,000 MPa, the tensile yield stress (0.2% proof stress) was around 1350 MPa and the ultimate tensile strength was around 1500 MPa. Twelve stub column tests were carried out. The plate element slenderness varies from 86 to 130. It has been demonstrated that the limits on local buckling in most existing design standards are conservative when applied to VHS circular tubes. The reliability of section capacity based on the full effective section model has been verified using a FOSM (first order second moment) approach.     

腐蚀钢绞线预应力混凝土梁受弯承载力评估

考虑腐蚀引起钢筋名义概率强度的降低,采用实用概率极限状态设计表达式中的抗力项进行预应力混凝土梁受弯承载力计算,可以获得基于材料强度平均值、标准值、设计值共3级可靠度水平的受弯承载力评估结果。基于试验结果统计,建立了随腐蚀率变化的腐蚀钢绞线名义抗拉强度与名义条件屈服抗拉强度的平均值、标准值以及设计值计算模型。分析表明：受拉钢绞线的计算极限状态（即条件屈服状态）名义应力低于实际极限状态（即极限受拉状态）名义应力,而其他钢筋的计算极限状态名义应力与实际极限状态名义应力相互吻合。最后结合算例阐述了上述方法的具体应用。图4表4参21     

锈蚀钢筋截面分布特征及轴向拉伸力学性能

采用半浸泡通电加速锈蚀法获得平均锈蚀率为0%～18%的钢筋,应用三维扫描的实物反求技术获得精确的锈蚀钢筋截面积数据,研究得到了平均锈蚀率与最大截面锈蚀率的关系,统计建立了锈蚀钢筋截面积概率分布模型;通过轴向拉伸试验研究锈蚀钢筋力学性能退化原因,定量分析锈蚀率与钢筋各力学特征值损失率的关系.结果表明:锈蚀钢筋实际材料性能未发生改变,其名义屈服强度、名义极限强度由钢筋最小残余截面积决定;钢筋变形与钢筋残余截面积分布有关,与平均锈蚀率及最大截面锈蚀率的相关程度较低;锈蚀钢筋本构关系仍可采用未锈蚀钢筋的本构关系,并可通过残余截面积概率分布模型来反映锈蚀对钢筋力学性能的影响.     

桥梁拉吊索用不锈钢钢丝腐蚀性能及斜拉索时变可靠度研究

对零应力普通镀锌钢丝和施加0%,20%,30%,40%强度的应力不锈钢钢丝,分7,20,40 d进行中性盐雾试验,研究零应力普通镀锌钢丝和不同应力水平下不锈钢钢丝的质量损失率、强度、延性和断口形貌的变化。通过算例分析了分别采用普通镀锌钢丝和不锈钢钢丝作斜拉桥拉索时可靠指标随时间的变化。结果表明:零应力下普通镀锌钢丝的质量损失率是不锈钢钢丝的30倍以上;不锈钢钢丝的质量损失率随着应力的增加而增加,高应力下的不锈钢钢丝更容易腐蚀;短期腐蚀对钢丝的极限强度影响不大,不锈钢钢丝随着应力的增加延性变差;随着腐蚀的增加,普通镀锌钢丝和不锈钢钢丝的拉伸端口呈现出脆性增加的趋势,普通钢丝的端口形貌由微裂纹向长宽裂纹发展,而不锈钢钢丝由于腐蚀较轻,只是出现了微裂纹;采用普通镀锌钢丝作斜拉桥拉索时可靠指标随时间的下降速度比采用不锈钢钢丝快。     

纳米TiO_2/ZnO/SiO_2在石油沥青聚氨酯防水涂料中的应用研究

研究比较了纳米TiO2、纳米ZnO、纳米SiO2对石油沥青双组分聚氨酯防水涂料性能的影响。结果表明,纳米粒子的添加可显著地改善涂膜的耐候性能、耐酸性能,提高涂膜的硬度、抗张强度和断裂伸长率;对涂膜耐候性改善程度依次为纳米TiO2纳米ZnO纳米SiO2,而对涂膜硬度、抗张强度、断裂伸长率提高程度依次为纳米SiO2纳米ZnO纳米TiO2;纳米粒子较佳的添加量为物料总质量的3%～5%。     

Research on axial loading behaviour of deconstructable bolt spliced square steel tubular columns

为研究采用特殊三角盒装置固定螺母的单边拧紧高强度螺栓的闭口截面方钢管柱-柱拼接节点轴向力学性能，设计制作了5个节点，并对其进行轴向受拉和受压加载试验，得到节点变形、承载力等力学性能，并与按GB 50017—2017《钢结构设计标准》计算的承载力进行对比分析；对部分节点进行承载能力极限状态之后的可拆卸性能分析。在验证有限元模型准确性和有效性的基础上，采用ABAQUS有限元软件对节点的受力性能进行数值模拟分析，研究拼接区高强度螺栓拉力和板件接触面摩擦力的变化规律。结果表明：采用特殊三角盒装置固定螺母的单边拧紧高强度螺栓的闭口截面方钢管柱拼接节点构造简单、安装方便、易于拆卸，抗滑移承载能力和极限承载能力良好；受拉承载能力极限状态后高强度螺栓的拉力与板件间摩擦力损失相对较大；单边拧紧高强度螺栓的闭口截面方钢管柱-柱拼接节点承载力仍可按GB 50017—2017中的承载力计算式进行计算。     

方钢管柱可拆卸螺栓拼接节点轴向力学性能研究

为研究采用特殊三角盒装置固定螺母的单边拧紧高强度螺栓的闭口截面方钢管柱-柱拼接节点轴向力学性能,设计制作了5个节点,并对其进行轴向受拉和受压加载试验,得到节点变形、承载力等力学性能,并与按GB 50017—2017《钢结构设计标准》计算的承载力进行对比分析;对部分节点进行承载能力极限状态之后的可拆卸性能分析。在验证有限元模型准确性和有效性的基础上,采用ABAQUS有限元软件对节点的受力性能进行数值模拟分析,研究拼接区高强度螺栓拉力和板件接触面摩擦力的变化规律。结果表明：采用特殊三角盒装置固定螺母的单边拧紧高强度螺栓的闭口截面方钢管柱拼接节点构造简单、安装方便、易于拆卸,抗滑移承载能力和极限承载能力良好;受拉承载能力极限状态后高强度螺栓的拉力与板件间摩擦力损失相对较大;单边拧紧高强度螺栓的闭口截面方钢管柱-柱拼接节点承载力仍可按GB 50017—2017中的承载力计算式进行计算。     

高强高性能混凝土极限拉应变性能研究

就C8 0～C10 0高强高性能混凝土的极限拉应变性能进行了初步探讨 ,试验结果表明 :HPC的极限拉应变比高强混凝土、普通混凝土的有明显提高 ,抗拉性能得到了改善 ,脆性有所降低 ,韧性相应提高。同时还提出了HPC极限拉应变与强度间的变化规律 ,给出了计算公式 ,数据回归分析表明用该公式来推定HPC的极限拉应变值精度较高。     

Experimental and theoretical studies on the ultimate bearing capacity of geogrid-reinforced sand

Geosynthetic reinforced soil (GRS) structures have gained popularity in replacing concrete rigid piles as abutments to support medium or small-spanned bridge superstructures in recent years. This study conducted 13 model tests to investigate the ultimate bearing capacity of the GRS mass when sand was used as backfill soil. The GRS mass was constructed and loaded to failure under a plane strain condition. Test results were compared with two analytical solutions available in literature. This study also proposed an analytical model for predicting the ultimate bearing capacity of the GRS mass based on the Mohr-Coulomb failure criterion. The failure surface of the GRS mass was described by the Rankine failure surface. The effects of compaction and reinforcement tension were equivalent to increased confining pressures to account for the reinforcing effects of the geosynthetic reinforcement. The proposed model was verified by the results of the model tests conducted in this study and reported in literature. Results indicated that the proposed model was more capable of predicting the ultimate bearing capacity of the GRS mass than the other two analytical solutions available in literature. The proposed model can be used to predict the ultimate bearing capacity of GRS structures when sand was used as backfill material. In addition, a parametric study was conducted to investigate the effects of friction angle of backfill soil, reinforcement spacing, reinforcement strength, and reinforcement stiffness on the ultimate bearing capacity of the GRS mass calculated with and without compaction effects. Results showed that the ultimate bearing capacity of the GRS mass was significantly affected by the friction angle of backfill soil, reinforcement spacing and strength. Compaction effects resulted in an increase in the ultimate bearing capacity of the GRS mass.     

钢板-超高性能混凝土梁有限元分析研究

为了研究钢板-超高性能混凝土(UHPC)组合梁的抗弯性能,在钢板-UHPC-T组合梁方案下,以钢板厚度、钢板强度等级、UHPC抗拉强度和UHPC极限拉应变为参数,利用ABAQUS软件进行了有限元分析。结果表明:钢板厚度和钢板强度等级的改变对组合梁抗弯承载力的提高作用较为明显;UHPC抗拉强度的提高可以适当提高开裂荷载;UHPC极限拉应变的增加可适当提高梁体的延性。     

配筋率对全珊瑚海水钢筋混凝土梁受弯性能的影响

通过对全珊瑚海水钢筋混凝土梁(CARCB)和普通钢筋混凝土梁(OARCB)进行受弯性能试验,研究了混凝土种类和配筋率对CARCB的变形性能、承载能力的影响。结果表明:随着配筋率的提高,CARCB的开裂弯矩和极限弯矩均逐渐增大,裂缝宽度扩展逐渐减慢,能有效抑制裂缝的发展。同时,可以通过提高配筋率,增大开裂弯矩与极限弯矩的比值,从而延后CARCB的开裂时间。CARCB的裂缝宽度均随着荷载的增长而增大,在加载初期,裂缝宽度增长缓慢,接近极限荷载时,裂缝宽度迅速增大,最终导致梁破坏。此外,综合考虑钢筋锈蚀引起钢筋截面损失和钢筋屈服强度降低的影响,提出了CARCB的极限弯矩、纵向受拉钢筋应力、平均裂缝间距和平均裂缝宽度的计算模型。     

桥梁空心板纸芯模的试验研究

通过对纸芯模材料纵向抗压和抗拉性能试验以及静载试验,提出了纸芯模力学性能的测试方法,得出了纸芯模的弹性模量、泊松比、抗拉极限强度等性能参数。并在试验基础上,分析了在空心板预制中纸芯模的受力状况,建立了有限元力学模型。通过与室内试验结果比较,阐述了纸芯模的变形情况及内力特征,为工程中确定纸芯模参数提供了理论依据。     

冻融循环作用后变形钢筋与混凝土粘结性能退化研究

冻融循环作用后,混凝土内部发生损伤,混凝土的质量损失增加,超声波速、抗压强度和劈裂抗拉强度下降;而随着冻融循环作用次数的增加,钢筋与混凝土的粘结强度下降,钢筋自由端的峰值滑移量则增大;通过对3种直径螺纹钢筋与混凝土冻融后的粘结性能的试验研究得出:冻融循环作用后钢筋与混凝土粘结性能下降,特别是极限粘结强度随着冻融循环作用次数增加而下降,根本原因是由于冻融作用损伤混凝土造成混凝土的强度下降所致。     

Model for post-yield tension stiffening and rebar rupture in concrete members

A tension stiffening model is presented which enables the calculation of average tensile stresses in concrete, after yielding of reinforcement, in reinforced concrete elements subjected to uniaxial tension, shear or flexure. To determine the average tensile stress-strain relationship for concrete, a crack analysis approach is employed taking into account the bond mechanism between concrete and deformed reinforcing bars, and numerical analyses are conducted to determine the tensile behavior of reinforced concrete members including post-yield response. Analytical parametric studies are conducted to determine the influence of various parameters including concrete compressive strength and reinforcement yield strength, ultimate strength, hardening stress, and hardening strain. Analysis results obtained from the proposed model, when compared to experimental results for uniaxial members, indicate good agreement for structural behavior after yielding of reinforcement. The proposed model makes it possible to accurately calculate reinforcement stresses at crack locations and, thus, average strain conditions which result in rupture of reinforcement. This leads to more realistic predictions of the uniaxial, flexural, and shear ductility of reinforced concrete members.     

预应力纤维布加固混凝土圆形截面短柱轴压性能试验

为研究环向预应力纤维布加固混凝土圆形截面短柱的轴心受压性能,制作25个试件并进行轴心受压试验。试验考虑的影响因素包括：试件的混凝土强度等级、截面尺寸、箍筋间距、既有损伤及表面处理情况、纤维布种类、层数和预应力大小。试验得到了各个试件的破坏形态和应力 应变关系,进而分析了各影响因素对加固效果的影响。结果表明：与非加固试件相比,环向预应力纤维布加固试件的轴心受压承载力和延性均有明显提高;对纤维布施加预应力能避免纤维布的应力滞后,更好地发挥纤维布的高强性能;当环向预应力与纤维布的抗拉强度的比值在0～0.20范围内,试件的承载力和延性随预应力的增大而增大;当环向预应力达到纤维布抗拉强度的0.25倍时加固效果会降低,因此在工程应用中环向纤维布的预应力宜控制在纤维布抗拉强度的0～0.20倍之间。     

高轴压比钢骨混凝土剪力墙抗震性能试验研究

为研究高轴压比钢骨混凝土剪力墙的抗震性能,完成了6片剪跨比为2.43、轴压比试验值为0.33~0.35的钢筋、钢骨和钢管混凝土剪力墙试件的往复水平力加载试验。试验表明:试件的纵筋和钢骨(钢管)受压屈服先于受拉屈服。试件的破坏形态为底部混凝土压碎剥落,约束边缘构件内的纵筋和钢骨(钢管)压曲,试件丧失竖向承载力。钢骨和钢管提高了试件的正截面承载力,且随位移增大试件能稳定地保持最大承载力。配置工字钢、槽钢和方钢管的试件的极限位移角为1/73~1/59,与钢筋混凝土试件基本相同;配置圆钢管的试件的极限位移角达1/44,墙端约束边缘构件配置圆钢管对提高高轴压比剪力墙的变形能力有显著作用。根据试验结果,提出了高轴压比钢骨混凝土剪力墙屈服、承载力极限状态和变形极限状态的截面应变、应力分布,建立了正截面承载力的计算式和顶点水平位移计算式,计算结果与试验结果符合较好。     

Tensile strength and abutment relaxation as failure control mechanisms in underground excavations

Classical assessment of instability potential in underground excavations are normally based on yield and rupture criteria for stress driven failure and on limit equilibrium analysis of structurally controlled failure. While it is true that ultimate failure and falls of ground can be an eventual consequence of stress fracturing and unfavourable structure within the rock mass, the timing of such failure is often controlled by the presence of residual tensile capacity, in the form of rock bridges separating joint segments and fractures and by the mechanisms of clamping and relaxation. Using crack and rock-bridge analogues in conjunction with an updated voussoir beam model, this paper explores the influence of residual tensile strength and boundary parallel relaxation on the failure process. The impact on support design is also examined. In underground hard rock mines with complex geometries and interacting openings, relaxation is identified as a key controlling factor in groundfall occurrence. Empirical stability assessment techniques for underground tunnels and for mining stopes are updated to account for relaxation.