自攻螺钉双面剪切连接抗剪性能研究

该文通过ABAQUS有限元软件对自攻螺钉双面剪切连接抗剪性能进行了研究,通过已有试验结果验证了有限元模型的准确性,基于此模型讨论了钢材强度等级、钢板厚度、螺钉直径以及不同中间钢板厚度对螺钉双面剪切连接的破坏模式和抗剪承载力的影响。结果表明:螺钉双面剪切连接构件的破坏模式可分成3类,分别为:承压破坏、承压-剪切破坏和剪切破坏。螺钉双面剪切连接抗剪承载力随着钢材强度等级和钢板厚度的增加而提高并趋于稳定;随着螺钉直径的增加,螺钉双面剪切连接抗剪承载力呈线性增加;在一定范围增加中间钢板厚度也可显著提高螺钉双面剪切连接抗剪承载力。将数值模拟结果与中美欧规范计算值进行比较分析得出,当钢板发生承压破坏时,中国、欧洲和AISC规范公式计算值偏于保守,AISI规范计算值较接近有限元值;当螺钉发生剪切破坏时,AISI和中欧规范过于保守。AISC规范公式计算值与有限元值吻合较好,因此,当螺钉发生剪切破坏时,使用AISC规范公式计算具有一定参考价值。     

填充石膏基轻质材料的冷弯型钢复合墙体受剪承载力分析

为研究填充石膏基轻质材料的冷弯型钢复合墙体受剪承载力的计算方法,对2片空腔墙体和9片填充式墙体足尺试件进行低周往复加载试验,研究墙体在水平荷载作用下的破坏模式,结果表明:空腔墙体的破坏模式为墙面板与龙骨之间的螺钉连接破坏,进而导致墙面板蒙皮作用的失效;填充式墙体的失效模式分为两种:填充材料角部的受压破坏和冷弯型钢立柱的弯曲破坏。基于上述破坏模式,考虑墙面板蒙皮作用和填充材料支撑作用的影响,根据极限平衡理论,提出基于叠加法的受剪承载力计算模型,建立受剪承载力计算公式,该模型能反映自攻螺钉连接强度、填充材料强度和冷弯型钢龙骨强度对墙体受剪承载力的影响;理论计算值与试验值的比值在0.947~1.112,结果吻合较好。     

薄壁钢板自冲铆接受剪性能及承载力计算方法研究

为将机械工程领域中效率与自冲化程度高的自冲铆接应用于冷弯薄壁型钢结构，对51组薄壁钢板自冲铆接进行了受剪性能试验。研究了钢板厚度、厚度比及铆钉长度对其受剪性能和破坏机理的影响规律，拟合出了钢板组合厚度与铆钉长度间的经验公式；分析了现有自冲铆接受剪强度计算方法和各国规范中自攻螺钉连接受剪承载力计算方法的适用性；基于试验和分析结果，提出了薄壁钢板自冲铆接受剪承载力计算方法。结果表明:钢板厚度和板厚比分别是影响受剪性能与破坏机理的关键因素，铆钉长度对受剪性能影响较大且存在较优长度，其可通过拟合出的经验公式快速确定；针对不同破坏模式提出的自冲铆接受剪承载力计算方法，与现有方法相比更适用于设计，且其精度更高、稳定性更好。     

冷弯薄壁型钢锁铆连接力学性能及其本构模型研究

为将锁铆连接引入冷弯薄壁型钢结构中构件的连接,对锁铆连接及自攻螺钉连接的试件进行了抗拉、抗剪性能试验,探讨了铆钉端距、基板厚度差、铆钉长度等参数对锁铆连接抗剪性能的影响;基于传染病传播动力学SIR模型建立了铆接本构模型,提出了锁铆连接抗剪承载力设计计算方法。研究结果表明:锁铆连接的主要破坏模式为延性破坏模式,表现为铆钉腿部剥离下层板材并伴随铆钉头部局部脱离上层板材,且刚度、强度和耗能性能均明显优于自攻螺钉连接;所建立的本构模型能够较精确反映锁铆连接荷载-变形曲线的变化趋势,且抗剪承载力的理论值和试验值误差较小;锁铆连接用于冷弯薄壁型钢板间连接时,其组合厚度不宜大于4 mm,厚板与薄板的厚度比不宜大于1.5,锁铆接头的端距应大于2倍铆钉直径。     

角钢塔K形节点初始转动刚度计算模型

运用组件法建立了输电塔中角钢塔K形节点初始转动刚度的计算模型,考虑了主角钢受剪、螺栓受剪、孔壁变形对节点转动刚度的影响。将主角钢受剪肢视为以剪切变形为主的短柱,采用叠加原理计算受剪肢的剪切变形,进而得到其转动刚度;将螺栓视为铁摩辛柯梁,采用虚功原理和单位荷载法求解其抗剪刚度。并结合5组足尺试验进行了修正,结果表明:该力学模型具有较好的适用性。通过参数分析可知,螺栓个数和螺栓间距是影响该类节点初始刚度最重要的因素,其他如主角钢肢宽和肢厚、螺栓直径、节点板厚度对初始刚度也有一定的 影响。     

梁柱端板连接节点初始转动刚度计算模型

应用组件法建立了端板连接节点初始转动刚度计算模型,考虑了端板受弯、柱翼缘受弯、螺栓受拉、柱子腹板受剪、柱子腹板受压和柱子腹板受拉变形对连接节点转动刚度的影响。基于板壳理论计算端板和柱子翼缘的弯曲变形,给出了不同加劲肋设置情况下的刚度计算公式;根据有限元分析结果,把柱子腹板受压刚度计算采用的有效宽度和EC3建议的承载力计算有效宽度统一;在计算螺栓刚度时,考虑了因螺栓预拉所挤紧的周围板件对螺栓变形的影响。该文模型和试验结果及已有模型进行对比,表明该计算模型不仅能精确计算节点的转动刚度,且相对于现有的分析模型更为简便、准确,便于实际工程中应用。     

竖向缝螺栓连接全装配式联肢复合墙抗震性能试验研究EI北大核心CSCD

课题组前期提出一种竖向缝采用螺栓连接的全装配式联肢复合墙,为进一步明确此类连接方式对墙体抗震性能的影响规律,以连接钢板厚度为变参设计了3榀联肢复合墙试件(PCW-B),通过拟静力试验对比研究各试件的破坏模式、裂缝发展、抗震性能,以及竖向缝在受力过程中的变形规律。试验结果表明:竖缝连接钢板厚度对试件破坏形态无明显影响;提升竖缝板厚可显著增强试件的初始刚度、承载力,但会降低试件延性;当板厚超过6 mm可显著提升试件耗能性能;分析并提出竖缝受剪承载力主要取决于连接件的抗剪和界面摩擦力抗剪两项,其中连接件抗剪贡献因素包括:连接钢板强度、高强螺栓和预埋件处箍筋作用力,并基于此提出竖向接缝受剪承载力计算公式。此公式亦可为其它墙体结构提供理论参考。     

自钻自攻螺钉与不同基材连接节点抗拉拔承载力试验与理论研究

螺钉与基材连接节点的力学性能是大跨金属屋面研究的关键问题之一,可靠的连接节点是确保屋面抗风安全的重要组件之一。开展了碳钢螺钉与铝基材(CSA节点)、不锈钢复合螺钉与铝基材(SSA节点)、不锈钢复合螺钉与钢基材(SSS节点)三类节点共360组样本试验研究,分析了三类节点的损伤失效模式,揭示了抗拉拔承载力的参数影响规律,建立了节点承载力设计计算公式。结果表明：两种钻入方式下三类节点均呈现螺钉与基材共同承载、到二者咬合处产生损伤变形行为、再到螺钉被拔出基材的失效模式,节点抗拉拔能力依次为SSS节点、CSA节点、SSA节点;基材厚度、螺钉直径和螺距均对节点承载力产生影响,尤以基材厚度和螺距最为显著,同等条件下改变螺距对三类节点承载力的影响最高达94.54%;所提三类节点承载力设计计算公式与试验结果吻合度良好。     

考虑开孔钢板厚度的PBL剪力键力学性能研究

钢-混凝土组合结构中PBL剪力键的力学性能受到多种参数的影响.为了解开孔钢板厚度对PBL剪力键力学性能的影响,进行了6 组24 个PBL 键试件的推出试验,研究PBL 键的静力性能及影响因素;从荷载-滑移曲线出发对PBL 键的传力机理进行分析;研究PBL 键的破坏机理和开孔钢板厚度对破坏模式的影响.试验研究结果表明:开孔钢板的厚度对PBL 键的设计承载力、抗剪刚度和极限承载力都有显著影响;荷载较小时PBL 键的承载能力由混凝土榫抗剪提供,混凝土榫抗剪失效后转由贯穿钢筋抗剪承载;受开孔钢板厚度的影响,PBL 键的破坏形式有贯穿钢筋的弯剪破坏、剪切破坏或开孔钢板的剪切破坏.结合国内典型推出试验的结果,推导了考虑开孔钢板厚度的PBL键承载力计算公式,公式与试验结果吻合良好.     

压缩载荷下复合材料整体加筋板渐进损伤非线性数值分析

建立了考虑脱粘的复合材料整体加筋板渐进损伤有限元分析模型。该模型采用界面单元模拟筋条与壁板之间的连接界面, 连接界面和复合材料层板分别采用Quads准则和Hashin准则作为失效判据, 基于ABAQUS软件, 建立了含连续损伤状态变量的材料刚度退化方案。基于该模型, 采用非线性有限元方法研究了压缩载荷下复合材料整体加筋壁板在考虑初始几何缺陷时的破坏过程, 分析了结构相应失效模式的细观损伤机制; 详细讨论了轴向刚度比对结构承载能力及破坏模式的影响。结果表明: 考虑脱粘损伤的有限元模型能有效模拟加筋板的破坏过程; 在加筋板铺层设计合理的情况下, 增加筋条与壁板刚度比能有效提高加筋板截面单位面积的承载能力。      

Combined effect of strength & sheet thickness on fatigue behaviour of resistance spot welded joint

Fatigue performance of spot welded lap shear joint is primarily dependent on weld nugget size, sheet thickness and corresponding joint stiffness. Two automotive steel sheets having higher strength lower thickness and lower strength higher thickness are resistance spot welded with established optimum welding condition. The tensile‐shear strength and fatigue strength of lap shear joint of the two automotive steel sheets are determined and compared. Experimental fatigue life of spot welded lap shear joint of each steel are compared with predicted fatigue lives using different stress intensity factor solutions for kinked crack and spot weld available in literature. Micrographs of fatigue fractured surfaces are examined to understand fracture micro‐mechanisms.     

基于厚度和应变映射方法的成形和抗凹性能联合仿真

为提升汽车板抗凹性能仿真精度,开展了成形和抗凹性能仿真研究。首先,利用模具将HC180BD+Z板料冲压成两种应变量的试样,然后利用半球形钢制压头以10 mm/min速度对试样进行加载,获得试样初始刚度和失稳凹陷载荷;其次,利用Ls-dyna进行成形和抗凹性能仿真,不考虑成形因素的影响下,初始刚度和失稳凹陷载荷仿真误差<10%,通过采用厚度和应变映射方法后,初始刚度和失稳凹陷载荷仿真误差<5%;最后,对比分析了厚度和应变映射对初始刚度和失稳凹陷载荷仿真结果的影响。研究表明：初始刚度与材料厚度相关,而失稳凹陷载荷与材料厚度和屈服强度相关;通过采用厚度和应变映射方法,能有效提升抗凹性能仿真分析精度;各向同性硬化模型高估了失稳凹陷载荷,采用各向同性和随动混合硬化模型能获得更好的仿真结果。     

含双槽钢截面可更换耗能梁段的高强钢框筒结构滞回性能研究

为了研究含双槽钢截面可更换耗能梁段的高强钢框筒结构(HSS-FTS-RDSL)的滞回性能,利用ABAQUS有限元分析软件建立了2/3比例的单层单跨HSS-FTS-RDSL子结构试件的有限元模型,对耗能梁段所用钢材进行循环加载试验得到其循环本构,验证了有限元模型的准确性和适用性。建立了16个足尺子结构有限元模型,分析耗能梁段长度比、裙梁净跨高比、耗能梁段腹板加劲肋间距、连接处螺栓直径和加固板厚度对结构滞回性能的影响规律。研究结果表明:HSS-FTS-RDSL子结构主要通过双槽钢截面耗能梁段进入塑性耗散地震能量,其余构件基本处于弹性状态或者轻微发展塑性;随着耗能梁段长度比的增加,结构承载力、刚度和耗能能力逐渐降低,耗能梁段超强系数减小,建议耗能梁段长度比取0.84~1.40;双槽钢截面可更换耗能梁段可较好地应用于净跨高比不超过4.6的裙梁中;改变耗能梁段加劲肋间距对结构承载力、刚度和耗能能力影响较小;减小螺栓直径会使连接区域螺栓滑移提前,对结构刚度和承载力影响较小;减小加固板厚度会增加连接变形,降低耗能梁段的塑性变形程度。     

Nonlinear finite element modeling of concrete deep beams with openings strengthened with externally-bonded composites

This paper aims to develop 3D nonlinear finite element (FE) models for reinforced concrete (RC) deep beams containing web openings and strengthened in shear with carbon fiber reinforced polymer (CFRP) composite sheets. The web openings interrupted the natural load path either fully or partially. The FE models adopted realistic materials constitutive laws that account for the nonlinear behavior of materials. In the FE models, solid elements for concrete, multi-layer shell elements for CFRP and link elements for steel reinforcement were used to simulate the physical models. Special interface elements were implemented in the FE models to simulate the interfacial bond behavior between the concrete and CFRP composites. A comparison between the FE results and experimental data published in the literature demonstrated the validity of the computational models in capturing the structural response for both unstrengthened and CFRP-strengthened deep beams with openings. The developed FE models can serve as a numerical platform for performance prediction of RC deep beams with openings strengthened in shear with CFRP composites.     

Influence of initial shear stress on the vibration behavior of single-layered graphene sheets embedded in an elastic medium based on Reddy's higher-order shear deformation plate theory

In this article, the small-scale effect on the vibration behavior of orthotropic single-layered graphene sheets is studied based on the nonlocal Reddy's plate theory embedded in elastic medium considering initial shear stress. Elastic theory of the graphene sheets is reformulated using the nonlocal differential constitutive relations of Eringen. To simulate the interaction between the graphene sheet and surrounding elastic medium we used both Winkler-type and Pasternak-type foundation models. The effects of initial shear stress and surrounding elastic medium and boundary conditions on the vibration analysis of orthotropic single-layered graphene sheets are studied considering five different boundary conditions. Numerical approach of the obtained equation is derived by differential quadrature method. Effects of shear stress, nonlocal parameter, size of the graphene sheets, stiffness of surrounding elastic medium, and boundary conditions on vibration frequency rate are investigated. The results reveal that as the stiffness of the surrounding elastic medium increases, the nonlocal effect decreases. Further, the nonlocal effect increases as the size of the graphene sheet is decreased. It is also found that the frequency ratios decrease with an increase in vibration modes.     

Failure mode of laser welds in lap‐shear specimens of high strength low alloy (HSLA) steel sheets

In this paper, the failure mode of laser welds in lap‐shear specimens of non‐galvanized SAE J2340 300Y high strength low alloy steel sheets under quasi‐static loading conditions is examined based on experimental observations and finite element analyses. Laser welded lap‐shear specimens with reduced cross sections were made. Optical micrographs of the cross sections of the welds in the specimens before and after tests are examined to understand the microstructure and failure mode of the welds. Micro‐hardness tests were also conducted to provide an assessment of the mechanical properties in the base metal, heat‐affected and fusion zones. The micrographs indicate that the weld failure appears to be initiated from the base metal near the boundary of the base metal and the heat‐affected zone at a distance away from the pre‐existing crack tip, and the specimens fail due to the necking/shear of the lower left load carrying sheets. Finite element analyses based on non‐homogenous multi‐zone material models were conducted to model the ductile necking/shear failure and to obtain the J integral solutions for the pre‐existing cracks. The results of the finite element analyses are used to explain the ductile failure initiation sites and the necking/shear of the lower left load carrying sheets. The J integral solutions obtained from the finite element analyses based on the 3‐zone finite element model indicate that the J integral for the pre‐existing cracks at the failure loads are low compared to the fracture toughness and the specimens should fail in a plastic collapse or necking/shear mode. The effects of the sheet thickness on the failure mode were then investigated for laser welds with a fixed ratio of the weld width to the thickness. For the given non‐homogenous material model, the J integral solutions appear to be scaled by the sheet thickness. With consideration of the plastic collapse failure mode and fracture initiation failure mode, a critical thickness can be obtained for the transition of the plastic collapse or necking/shear failure mode to the fracture initiation failure mode. Finally, the failure load is expressed as a function of the sheet thickness according to the governing equations based on the two failure modes. The results demonstrate that the failure mode of welds of thin sheets depends on the sheet thickness, ductility of the base metal and fracture toughness of the heat‐affected zone. Therefore, failure criteria based on either the plastic collapse failure mode or the fracture initiation failure mode should be used cautiously for welds of thin sheets.