Stiffeners are commonly arranged on the web to enhance the local stability of cold-formed thin-walled steel sections. Such web-stiffened cold-formed steels are widely utilized in low-rise buildings, logistics shelving systems, and photovoltaic mounting structures. For pipeline installation purposes, holes are frequently introduced into the webs. However, the combined effects of web stiffeners and web holes on the axial compressive stability of cold-formed steels remain insufficiently investigated. This study combines experiments and nonlinear finite element analyses to examine the influence of various hole parameters on the axial compressive buckling behavior of LQ550 high-strength cold-formed lipped channel sections with stiffened webs. The results indicate that web stiffeners effectively delay the onset of local buckling and enhance the load-bearing capacity. As the hole size and number increase, the load-bearing capacity gradually decreases. The shape, position, and spacing of the holes exhibit a comparatively minor influence. Based on the quantitative influence of different hole parameters, a reduction coefficient formula is proposed for the axial compressive load-bearing capacity of stiffened members due to web holes. This allows designers to efficiently and accurately assess the load-bearing capacity of such members in practice.

In recent years, cold-formed thin-walled steel members have been extensively utilized in prefabricated structures owing to their lightweight and high-strength properties. However, openings in the column web for accommodating water, electricity, heating, and ventilation ducts significantly affect the axial compressive bearing capacity, warranting a comprehensive investigation. This study conducts axial loading tests on LQ550 highstrength cold-formed thin-walled steel channel sections with web openings. The findings indicated that the presence of openings does not significantly affect the buckling mode; however, it intensifies the magnitude of buckling deformation and diminishes the bearing capacity of the columns. Short columns with openings predominantly undergo distortional-local buckling, while long columns exhibit distortional-local-global interactive buckling. The openings affect the location of buckling in the column. Local and distortional buckling in columns with varying heights predominantly occurs in the vicinity of the openings. However, for slender columns, the correlation between the position of maximum global deflection and the opening locations is negligible. The opening size exhibits the most significant impact on bearing capacity, followed by the number of openings, while the opening shape demonstrates the least effect. For the same number of openings, although sections with wide web exhibit a wider range and degree of local buckling around the openings, the reduction in bearing capacity for narrow-web sections is more pronounced. Finally, a conservative recommendation for the reduction coefficient of bearing capacity for the perforated columns is proposed.

The study of high-strength, cold-formed, thin-walled steel predominantly focuses on LQ550 hot-dipped zinccoated rolled channel steel featuring a wall thickness of less than 1.5 mm. These members are characterized by their exceptionally thin thickness and limited cross-sections, which typically lead to buckling failures before the steel's strength is fully utilized. A new lipped channel steel, constructed from cold-bent Q460 steel sheets, is developed in this study to address this issue and improve both the ultimate bearing capacity and the efficiency of material use. This design incorporates a larger cross-section and a lower width-to-thickness ratio for the constitutive plates. Initially, the compression tests are conducted on 12 specimens. Subsequently, the adverse effects of initial geometric imperfections on bearing capacity are considered, employing the validated finite element method, to simulate nearly 300 cold-formed channel columns with varied sectional sizes, lengths, and wall thicknesses. After that, the research evaluates how factors such as column length, web height, flange width, height-to-thickness ratio, aspect ratio, lip width, and wall thickness influence the buckling capacity and buckling mode. The findings revealed that slenderness ratio and flange width significantly impact slender columns prone to global buckling. In contrast, variations in the sectional aspect ratio, lip width, and wall thickness have a more pronounced effect on relatively stubby columns, which are susceptible to distortion-related buckling. Finally, based on comprehensive experimental and finite element analysis data, modified predictive formulas are proposed for L-D-G interactive buckling and global buckling capacities as per the Direct Strength Method outlined in the current code.

The research and application of high-strength cold-formed thin-walled steel are primarily focused on zinc-coated lipped channels with a thickness of less than 1.5 mm. Despite their inherent material strength, these components experience premature buckling failure due to their extremely thin sheet thickness and high width-to-thickness ratio, limiting the utilization of high-yield strength. Therefore, a new cold-formed lipped channel fabricated via the cold bending process of the Q460 hot-rolled steel sheet is proposed. This design features larger crosssectional dimensions and a reduced width-to-thickness ratio of the constitutive plate, enhancing the component's load-carrying capacity and material utilization efficiency. The axial compression loading tests are conducted on 16 simply supported Q460 high-strength cold-formed lipped channel columns with thicknesses of 4 and 6 mm to investigate their load-carrying behavior. Specimens with high slenderness ratios tend to experience overall flexural-torsional buckling. In addition, specimens with medium slenderness ratios and lower aspect ratios are prone to distortional-overall interactive buckling. In contrast, specimens with medium slenderness ratios and higher aspect ratios are susceptible to distortional-local interactive buckling. Lastly, specimens with low slenderness ratios and high web height-to-thickness ratios tend to undergo local buckling. When keeping other dimensions constant, the column's axial load-carrying capacity exhibits a significant decrease with increasing length, an initial increase followed by a subsequent decrease with increasing web height, and a significant rise with increasing flange width and plate thickness. Compared to the loading test results, the predicted buckling capacities from the direct strength method stipulated in current standards generally display conservatism.

Reinforced concrete (RC) structures are among the most prevalent in the construction industry. However, various in-service conditions such as loading, environmental exposure, and construction practices can lead to the formation of concrete cracks. In extreme cases, these cracks may propagate through the cross-section of structural members, creating section pre-cracks. This study examines the influence of section pre-cracks on the shear failure behavior of RC deep beams (with a shear span-to-depth ratio of 1.57) through three-point bend-loading tests and 3D RBSM analysis. The primary experimental variables include the number of pre-cracks (one or two) and their width (0.5 mm or 1.0 mm). The findings reveal that pre-cracks significantly reduce the initial stiffness and shear strength of deep beams, primarily by disrupting the transmission of axial compressive stress in the concrete, thereby diminishing the contribution of arch action to shear strength. Furthermore, it is observed that the greater the total width and number of pre-cracks, the more significant the reduction in shear strength. In addition, combining both experimental tests and numerical simulations, a total of 48 deep beams were subjected to shear failure tests. Based on the shear strength data, two degradation models for shear strength (one representing the average trend and the other a conservative lower-bound envelope model) were developed in relation to the total crack width.

Since the column in precipitator casing mainly presents buckling failure,the stability strengthening method for column was investigated so as to improve its buckling capacity and optimize the structural design of precipitator equipment.For the structure system composed of stiffened wallboard and H-Shaped steel column in precipitator casing,in consideration of initial imperfection,the buckling mechanism of column was investigated by non-linear finite element method first.Since being influenced by the wall stressed skin effect,the buckling of column occurs on the high compressive stress region adjacent to the column top.The column presents the interactive buckling that the overall flexural-torsional buckling occurs on the front half section composed of the front flange and the web and the local buckling occurs simultaneously on the web.Based on the buckling characteristics,the strengthening configuration measurement for enhancing column buckling capacity was proposed,that is,the strengthening steel plates would be welded on both sides of the front flange of the column in top region,and its upper and lower sides would be welded with the L-shaped diaphragms.The influences of several configuration parameters on the column buckling capacity were investigated,including the width,thickness and the locating range of the strengthening steel plates and the L-shaped diaphragm thickness.Consequently,a rational design method of the strengthening configuration for enhancing column buckling capacity was proposed.The buckling capacity of the column can be increased significantly by employing the strengthening configuration measurement.

With rapid urbanization and development, high-strength cold-formed thin-walled steel structures are gaining significant attention in China's low-rise construction industry. For the same cross-sectional area, varying section profile sizes result in distinct buckling modes and divergent load-carrying capacities. The cold-formed thinwalled lipped channel column is prone to local web buckling due to the large width-to-thickness ratio. A Vshaped stiffener is set in the middle of the web to enhance local stability. Hence, investigating the section with higher load-carrying capacity is critical for optimizing the design. In this study, a program was first developed to identify several candidate sections with higher load-carrying capacity based on theoretical calculations. Then, finite element analyses and loading tests were conducted to determine the optimal section. It was found that the stiffener significantly improved load-carrying capacity. The results from theoretical calculations, finite element simulations, and loading tests exhibited the consistent variation trend of load-carrying capacities of columns with different cross-sections. The short columns with the optimal section underwent distortional buckling, while the long columns with the optimal section exhibited both distortional and overall flexural buckling. A relatively high axial load-carrying capacity is achieved when the ratio of the web height to the sum of the flange and lip width is between 1 and 2. For the commonly used 180 mm wide sheet, the optimal section features a web height of 67 mm, a flange width of 38 mm, and a lip width of 12 mm.

在箱式钢结构中起主要承载作用的侧面墙板-立柱结构体系中,受墙板蒙皮支撑作用的高强钢立柱,其残余应力分布受与墙板焊接连接过程影响,与独立工作焊接H形截面构件有较大差异.为研究Q235钢墙板—Q460高强钢立柱结构体系的残余应力分布规律,采用盲孔法对6个结构体系试件和2个独立Q460高强钢焊接H形截面试件进行了试验研究.基于测量数据,得到了所有试件的全截面残余应力分布,分析了墙板与立柱焊接连接、截面尺寸等因素对残余应力分布的影响,并研究了截面各板件间残余应力的相互影响及自平衡性.结果表明:立柱与墙板的焊接在一定程度上降低了立柱后翼缘中部的最大残余拉应力,减小了后翼缘残余压应力的分布范围,对前翼缘和腹板无明显影响;残余拉应力幅值与截面尺寸无直接关系,残余压应力随着板件宽厚比的增大而减小;各板件间残余应力存在相互影响作用,前翼缘、腹板以及后翼缘与墙板组合板件这3部分分别满足自平衡.提出了适用于Q235钢墙板-Q460高强钢立柱结构体系的较为准确和安全的残余应力分布数学模型,为后续研究受墙板蒙皮支撑的高强钢立柱稳定性奠定基础.

In practice, web openings are usually drilled in reinforced concrete (RC) beams to accommodate pipes and cable installations. But introducing web openings always causes shear degradation of RC beams. This study aims to establish a rational position design of multiple small web openings, which can improve the shear behavior of RC beams, by controlling the path of critical diagonal crack. Three-point bending tests on four RC beams without and with web openings (shear span depth ratio: 2.59 and 3.56) were firstly carried out to evaluate the strengthening effect attributed to the proposed placement of web openings. Besides, the Three Dimensional Rigid-Body-Spring Method (3D RBSM), a discrete numerical methodology, was applied to simulate the test process, and the strengthening effect due to the placement of web openings was parametrically investigated. Finally, the decoupling of shear components (beam and arch actions) was conducted to comprehensively understand the shear strengthening mechanism due to drilling web openings, by using RBSM-based methodology. The test and numerical results confirmed that the proposed position design of web openings could evidently improve the shear strength and deformation ability of RC beams, because the multiple web openings could increase the angle of critical diagonal crack, by predetermining it propagation path. Moreover, it was clarified that the strengthening mechanism of shear behavior owing to web opening setting was dependent on the more dramatic development of arch action with the increasing angle of critical diagonal crack. The present paper provided a rational design to solve the problem of shear degradation caused by small web openings in the field of concrete member design, and proved a possibility to strengthen the shear behavior of existing concrete beams by drilling web openings.

选取典型的钢筋混凝土(RC)深梁受剪试验,开发并运用三维刚体弹簧元法(3D RBSM)模拟了大尺寸截面深梁的受剪破坏过程,以及箍筋对深梁抗剪性能的影响。结果表明,3D RBSM不仅能够较准确地计算RC深梁的开裂荷载、名义抗剪强度以及箍筋的增强作用,而且能够模拟裂缝的开展以及构件的破坏。相比于有限元法,3D RBSM具有以下优势:大幅度提高了名义抗剪强度的计算精度,实现了散布裂缝模拟的可视化以及混凝土裂缝宽度的直观、定量评价; 能够更好地捕捉峰值荷载后的软化行为。因此,3D RBSM为大尺寸截面深梁的受剪破坏模拟、明晰抗剪性能尺寸效应机理和完善大尺寸RC构件设计提供了有效研究手段。

在重要结构的抗震设计与分析中,常需要输入拟合设计反应谱的地震动时程.该研究提出一种基于数字滤波技术调整天然地震动记录拟合规范反应谱的方法,以设计谱频率控制点为中心确定频带数目与范围,针对各个频带利用无限冲激响应数字滤波器对强震动记录时程开展带通滤波,并以滤波所得频带分量为基函数重构地震动时程;以重构时程为种子时程,引入影响矩阵方法开展迭代计算逐步调整频带分量的幅值向量,直至时程反应谱与目标谱的拟合精度满足要求为止.选取3个不同类型设计谱为目标谱分别开展拟合计算,结果表明:该方法分解并重构的地震动时程与天然强震动记录在时域和频域的重合度均较高;可与不同设计谱实现高精度拟合,时程反应谱迭代收敛性好,且能较好地保留时程非平稳性,可为工程结构抗震设计与分析提供合适的地震输入.

针对泥水盾构长距离穿越粉质黏土地层时产生的大量高黏粒含量泥浆难以快速脱水的问题,开展PAM类有机絮凝剂与泥浆混合后的絮凝沉降试验,研究泥浆中颗粒沉降速率的变化,通过颗粒粒径、上清液浊度和Zeta电位等性质变化分析絮凝沉降效果的差异,并通过比阻试验评价其脱水性能.结果表明:1)阳离子型聚丙烯酰胺(CPAM)添加量为0.12％～0.15％、阴离子型聚丙烯酰胺(APAM)添加量为0.06％～0.09％时絮凝沉降效果较好,可在2 h之内降低泥浆约10％的水分;2)非离子型聚丙烯酰胺(NPAM)无法有效降低泥浆含水率;3)PAM类絮凝剂通过团聚泥浆中黏土颗粒形成大尺寸的絮团,是实现泥浆快速絮凝沉降的关键因素,APAM对泥浆Zeta电位影响较小,CPAM添加量的增加使Zeta电位逐渐减小;4)PAM类絮凝剂可加快泥浆的前期排水速率,使泥浆比阻值降低至1013 cm/g数量级.

In the side supporting structure of a precipitator casing, the skeleton column is sometimes designed as a composite section composed of double H-shaped steel limbs and connecting wallboard. Column buckling is characterized by its special section and the stressed skin effect from wallboard. The influence of initial imperfections and structural parameters on column stability was investigated using the nonlinear finite element method. The residual stress has a slight adverse effect on column stability. The buckling modes can be categorized into two types: 1) buckling of connecting wallboard; 2) simultaneous buckling of connecting wallboard and flexural-torsional buckling of H-shaped limbs in top segment. Column stability significantly increases with increasing connecting wallboard thickness, decreasing connecting wallboard width, and decreasing distance between the connecting wallboard and the rear flange of H-shaped limbs. The structural parameters of the wallboard, angle steel stiffeners, and transverse brace interval have no noticeable effect. Column stability slightly increases with a decrease in the width-to-thickness ratio of flange, the height-to-thickness ratio of web, and torsional slenderness ratio. Based on the simulation results, a buckling capacity calculation recommendation was developed for an axial compressive double-limb column, which is important for the design of heavily stressed double-limb columns in box-type structures.

For the wallboard -column structural system on the side of box-type steel structures, the residual stress distri-bution of the high-strength steel (HSS) column supported by stressed skin wallboards is affected by the welding between columns and wallboards, making it significantly different from an independent welded H-section member. To investigate and model the residual stress in Q235 steel wallboard -Q460 HSS column structural system, to which little attention has been paid, an experimental study was conducted using both the hole-drilling method and sectioning method. The residual stress magnitude and distribution were obtained. Comparison of the two measurement methods indicates that the maximum tensile residual stresses near the welds measured using the hole-drilling method are much greater than those obtained from the sectioning method. The welding between column and wallboards reduces the maximum tensile residual stress in the middle of column rear flange as well as the compressive stress distribution range in the rear flange. The magnitudes of compressive residual stresses decrease with increasing width-to-thickness ratio and component plate thickness, while no significant correlation with geometries was observed for the tensile stresses. The residual stresses in the combination of the rear flange and wallboards, front flange, and web can be regarded as being in self-equilibrium respectively. In addition, a simplified distribution model is proposed and compared with the experimental results. The new stress distri-bution model can provide a foundation for investigating the buckling behavior of HSS columns supported by stressed wallboards.

In the seismic design and analysis of important structures, ground motion time histories are generally required as the input for the conduction of seismic response history analysis. Taking a selected spectrum as the target, the approaches for generating spectral compatible time histories based on artificial or synthetic ground motion and real recorded earthquake ground motion, respectively, are commonly used and discussed in this review. The pure artificial approaches have relative higher effectiveness and computational efficiency, while the approaches by adjusting the real records could simulate the nonstationary in both time domain and frequency domain.

For the RC members under cyclic loading, flexural cracks commonly propagate in two opposite transverse directions at the zone under high bending moment and possibly form the cracks penetrating through the entire cross sections (precrack), which is considered as a crucial factor for flexure-shear failure of member. This paper clarified the influence of imitation pre-crack on the shear failure behavior of RC slender beams by three point bending test. Shear span depth ratio (a/d=3.14, 4.69) and location and thickness of pre-crack were set as main variables. As the important findings, it was revealed that the influence of pre-crack on the shear strength of RC slender beams is relatively small because it does not affect the formation of the critical diagonal crack and the mode of diagonal tension failure. It was also noted that the pre-crack at 2d (the section of pre-crack is 512 mm, which is twice of the effective depth d, far away from the loading plate center) leads to a reduction of shear strength with increasing pre-crack width, and the maximum reduction is 21.4%. Based on the detailed analysis of crack propagation, it was clarified that pre-crack may result in two patterns of critical diagonal crack, and in the condition that the pre-crack plane vertically intersects with the lateral splitting part of diagonal crack, the lateral splitting part becomes more severe and thereby reduces the shear strength and deformation ability.

To explore the application feasibility of high-strength steel in skeleton columns of precipitator casing structures, the bearing behavior of axially compressed H-section high-strength steel columns was investigated by the nonlinear finite element method by considering the stressed-skin effect of wallboard. When the column yield strength does not exceed 460 MPa, the column undergoes elasto-plastic interactive buckling, which means the steel strength can be fully utilized. For the column strength of 550 MPa or 690 MPa, the wallboard yield failure occurs, owing to excessive loading of the relatively weak wallboard, and column stress magnitude is usually in the elastic range without the full utilization of steel strength, whereas if the wallboard is stiff enough, columns will still undergo buckling failure. A welding residual stress measuring test was conducted to validate the residual stress generation simulation via the thermal-mechanical coupling finite element method. Concerning the geometrical imperfections and residual stresses, it was found that their influence becomes less severe when the column steel strength increases. The bearing capacity can be improved by increasing the wallboard thickness and stiffener stiffness, or reducing the wallboard width, the stiffener spacing, the width-to-thickness ratio of column flange, the height-to-thickness ratio of column web, and column torsional slenderness ratio. Column material can be fully utilized when column steel strength does not exceed 460 MPa. Hence, employing high-strength steel is reasonable. When the column steel strength is equal to or higher than 550 MPa, wallboard strength should be sufficient to ensure that the column failure occurs before wallboard failure. In such cases, high-strength steel should be used carefully.

This paper evaluated the improvement effect of multiple small circular transverse openings (diameter is 1/10 of member height) on the shear performance of RC beams without shear reinforcement and explained the shear resistance mechanism, using three dimensional Rigid-Body-Spring-Method (3D RBSM). First, 3D RBSM was employed to reproduce the shear loading test on the RC beams with multiple small circular transverse openings, and the contributions of beam and arch actions to the shear resistance at each loading stage was evaluated. The analytical load-deflection relationship and cracking behavior were in good consistent with the experiment, and it was noted that the connecting line of the opening centers (line of openings) could control the path of critical diagonal crack, and transfer the failure mode of one of the beams from the diagonal tension pattern to the shear compression pattern. Moreover, the shear strength and ultimate deflection of this beam with openings were significantly improved due to the increase in the shear resistance contribution of arch action. Furthermore, the analysis of additional cases with three transverse openings at each shear span were conducted aiming to explore the possibility that a proper setting of openings can reliably improve the shear performance of RC beams. The line of openings was on a straight line and passed through the loading point at the same side, and the main parameter was set as the angle of the line of openings to beam axis (25°-50°). As a result, the role of the transverse openings in improving the shear performance was confirmed and the corresponding mechanism was explained based on the investigation on the beam and arch actions and crack behaviors.

为了研究刚体弹簧元法对钢筋混凝土构件在循环往复荷载作用下剪切性能尺寸效应研究的适用性与准确性,在平面二维刚体弹簧元模型的基础上,将其发展至三维,并应用于钢筋混凝土悬臂梁尺寸效应研究中.通过对比试验结果与数值模拟结果,分析了钢筋混凝土悬臂梁在循环往复荷载下的滞回性能、开裂变形等特征.结果表明:三维刚体弹簧元法能够较好地模拟不同尺寸的钢筋混凝土悬臂梁在循环往复荷载下的剪切性能,模拟得到的承载力、延性变形等和已有文献试验结果基本相符;循环往复荷载作用下的钢筋混凝土悬臂梁表现出明显的尺寸效应.

为了研究钢筋混凝土短柱在循环荷载作用下受剪性能尺寸效应产生的机理,应用三维刚体弹簧元法,基于梁-拱模型,对3个不同截面尺寸的钢筋混凝土短柱抗剪作用进行分解,结果表明:应用三维刚体弹簧元法能较好地模拟不同截面尺寸钢筋混凝土短柱在循环荷载下的受剪性能;当达到极限荷载时,随着截面尺寸的增加,以名义剪应力为评判标准的抗剪强度逐渐减小,相比于单调荷载,一次循环后的尺寸效应变化较小,而两次循环(短柱临近破坏)后尺寸效应更加明显,这主要是由于拱模型的抗剪作用急剧下降导致的.