Behavior of steel-concrete composite cantilever beams with web openings under negative moment

The effect of web openings on the mechanical behavior of composite beams under negative moment was studied through monotonically loading tests. Nonlinear finite element method based analysis was also conducted for cantilever composite beams. The test and the finite element analysis results indicated that the initial cracking loads of composite beams with web opening are lower than that without web opening. The first crack initiated from the concrete slab on the top of the opening. The beams with web opening failed due to shear failure of concrete slab upon the opening. It was also found that the load carrying capacity of beam decreases with the increase of the moment-to-shear ratio at the central line of the opening and the mechanical behavior of beam can be improved significantly by applying stiffening steel plates around the opening. To quantify the reduction of load carrying capacity, a method for calculating the load carrying capacity of beams with web openings under negative moment was derived with consideration of the interaction between moment and shear. Good consistency was obtained between the proposed method, the finite element method and the test results.     

带腹板开洞钢梁弹性挠度计算

钢梁腹板上开洞,使得洞口区域不再满足平截面假定,梁的挠度曲线也不能再用梁理论求解,针对目前还没有较好的计算H型钢钢梁腹板开洞的弹性挠曲线的方法,本文推导了计算钢梁腹板开洞的计算公式,该法力学模型简洁清晰,计算结果精度也较高,与有限元软件计算的结果吻合性较好.     

洞口形状对腹板开洞钢-混凝土组合梁的受力性能影响分析

通过研究洞口形状对腹板开洞钢-混凝土组合梁受力的影响,选择合适的洞口形状以降低开洞造成的不利影响;在已有试验基础上,利用ANSYS对洞口设置在弯剪区段且洞口形状不同的组合梁进行力学性能分析,研究了洞口形状对承载力、变形能力以及内力重分布和传力机制的影响。结果表明：钢-混凝土组合梁腹板开洞会导致刚度、极限承载力下降;非正方形洞口组合梁因洞口形状不同,极限变形有不同程度增强;洞口形状会影响洞口处混凝土、钢梁承担的剪力比例,混凝土占总剪力的46%～59%,而钢梁占总剪力的41%～54%;极限变形与洞口处塑性铰的面积大小有关;栓钉会对周围的混凝土产生一定预压力,对混凝土应力重分布有影响,洞口处混凝土的剪力有明显的剪力差,洞口下方钢梁所承受的剪力大于洞口上方钢梁;洞口形状会影响组合梁内部传力机制,长方形、正方形洞口试件在洞口区域以次弯矩传递力,非长方形、正方形洞口试件在洞口区域以主弯矩传递力;在结构设计时应该考虑洞口位置的偏心、主应力方向与洞口边缘的夹角。     

开孔薄壁钢梁-轻骨料混凝土装配式组合楼板受火试验研究

为研究由冷弯卷边H形开孔薄壁钢梁和预制轻骨料混凝土板形成的装配式组合楼板的受火性能,对6个两端简支组合楼板试件开展了高温下试验研究,得到了试件的温度及位移响应。研究结果表明：在等效均布荷载2.0 kN/m²及最高炉温为600℃的烃类火灾作用下,以轻骨料混凝土及腹板开孔薄壁钢梁形成装配式组合楼板具有良好的抗火性能,组合楼板的跨中挠度最大为L/44（L为组合楼板跨度）时,试件仍保持良好的整体性;主钢梁腹板开孔直径与分布形式对组合楼板的整体抗火性能均有显著影响,为减小组合楼板高温下的位移响应,对主钢梁腹板的开孔宜优选孔径大、数量少的分布形式;抗剪键数量对组合楼板抗火性能的响应影响远大于对预制板类型的影响。     

带肋钢板加固腹板开大洞口RC梁的受剪承载力试验研究

设计并制作24根腹板开矩形大洞口钢筋混凝土梁,分别进行外贴钢板和带肋钢板加固,对比分析不同开洞尺寸、开洞位置、多洞口分布和锚栓构造等因素对钢板加固有效性的影响.结果表明:带肋钢板加固能有效改善洞口角部的受力性状,约束钢板不发生平面外屈曲失稳,使得钢板加固梁的洞口上肢整体压溃的脆性破坏模式转变为混凝土局部压碎的延性破坏模...     

矩形开孔钢筋混凝土伸臂梁受剪性能试验研究

为方便设备管线通过,采用腹部开孔梁可有效降低楼层高度,但开孔会削弱梁的整体刚度,导致孔洞附近的应力及内力重分布十分复杂。为研究腹部矩形开孔的钢筋混凝土伸臂梁的受力性能,以正反弯矩比、孔洞位置、剪跨比及孔侧斜筋作为主要变量,对12根钢筋混凝土开孔伸臂梁和1根钢筋混凝土实腹伸臂梁试件进行了两点加载下的受剪性能试验。研究了各种参数对开孔伸臂梁的裂缝开展及破坏形态、应变分布、变形和受剪承载力等受力性能的影响。试验结果表明：正反弯矩比和孔心剪跨比改变了伸臂梁在孔洞附近的受力状态,导致破坏时孔侧呈现出不同的裂缝形态。配置孔侧斜筋后,孔侧混凝土和箍筋更好地发挥协同抗剪作用,试件的受剪承载力显著提高,裂缝开展和变形均得到有效的控制。利用混凝土开孔简支梁发生孔侧剪压破坏的受剪承载力公式对开孔伸臂梁的受剪承载力进行计算,并和试验数据进行对比可知,按开孔简支梁的算式对开孔伸臂梁的受剪承载力进行计算,计算结果与试验结果的平均比值为0.96,方差为0.07,结果偏于安全。     

Experimental tests and numerical modeling of cellular beams with sinusoidal openings

New type of cellular beams with sinusoidal shape of openings shows a specific behavior in comparison with the standard circular openings. Full scale tests were realized on three beams representing various dimensions of the openings. The aim was to observe the failure modes of these beams and to obtain the ultimate values of strength. The specimens were heavily gauged to clearly identify the local failure modes of the opening zone. Two specific failure modes were observed. For the opening with large height, the failure is reached by the formation of four plastic hinges at the corners of the critical section (Vierendeel bending). This mode is similar to that of the rectangular opening. Whereas with the small opening, failure arises by the local instability of the compressed out stand panel in the sinusoidal parts of the opening. A numerical model is developed and calibrated on the basis of the experimental results. The numerical model is used to analyze with more details the behavior of the critical opening including the stress distribution in its different parts. The experimental results provided useful qualitative and quantitative information to understand the behavior of the cellular beams with sinusoidal openings. The numerical model showed a good accuracy in the prediction of the experimental results. It can be used as a tool to generate complementary results to develop an analytical model.     

负弯矩区腹板开洞钢-混凝土组合梁承载力试验研究与理论分析

通过外挑钢-混凝土组合梁的单调加载试验和有限元分析,研究负弯矩区腹板开洞对其受力性能的影响,并基于弯剪承载力相互作用的准则,提出承载力理论计算方法。结果表明：截面开洞显著降低了组合梁的承载能力和刚度;最终破坏形式为洞口上方混凝土板的剪切破坏;组合梁承载能力随着截面削弱的加大而降低;洞口补强板可减轻洞口区域应力集中,进而提高组合梁的承载力;承载力随着洞口中心线与支座距离减小（即弯剪比的增大）而减小。应用建议的负弯矩区腹板开洞组合梁承载力计算方法得到的承载力计算结果与试验及有限元分析结果吻合较好。     

Elastic rigidity of composite beams with full width slab openings

Openings often exist in the concrete slab of composite floors due to the functional requirements of structures. The strength and rigidity of steel-concrete composite beams are reduced by openings. Based on three tests of steel-concrete composite beams with full openings in the concrete flange, the elastic rigidity of composite beams is analyzed. Finite element analysis (FEA) considering the slip effect between the steel and concrete is conducted to simulate the composite beams with full openings in the concrete slab, and the results show that the FEA method is reliable. The analytical calculation method for the deflection of composite beams with full openings in the concrete slab is also proposed, and the results are verified by tests. The predicted deflections using the analytical method and FEA method both agree well with the test results. It is further verified that openings near the supports have insignificant effects on the deflection at the mid-span and this effect can be thus ignored. The simplified method to calculate the rigidity reduction factor is developed by a regression analysis. The analytical method and FEA method can be used for the serviceability limit state design of steel-concrete composite beams with full openings in the concrete flange.     

钢筋混凝土开洞短梁的受剪试验研究

本文对钢筋混凝土开洞短梁在集中力作用下的受剪性能进行了试验研究,32根试件中包括20根简支开洞短梁和9根两跨连续开洞短梁,另外还有2根简支开洞深梁和1根两跨连续开洞深梁,是为了满足开洞深、短梁研究的连续性。试验结果表明:其破坏形态主要有洞口上下剪切破坏型和弯剪破坏联合型两种,随跨高比、剪跨比的增大,剪切破坏面由斜压破坏向剪压破坏过渡;跨高比、剪跨比、洞口大小和位置、配筋形式及数量是影响开洞短梁的裂缝发展、破坏形态、抗剪承载力、支座反力重分布的主要因素。     

开孔薄壁钢梁-轻骨料混凝土装配式组合楼板受力性能试验研究

为研究开孔薄壁钢梁 轻骨料混凝土组合楼板的受力性能,设计并制作了5块具有不同构造（不同预制板型、抗剪方式及腹板开孔率）的组合楼板试件,进行了简支条件下均布加载受力性能试验研究。结果表明：该组合楼板具有较高的整体刚度和承载能力,当等效均布荷载达到6 kN/m²时,跨中挠度远小于L/500（L为试件跨度）;对于相同的开孔率,薄壁钢梁腹板的开孔应优选孔径小、数量多的开孔形式;采用文中所构造的抗剪键及其布置形式的组合楼板,其抗剪效果明显优于采用结构胶黏结混凝土板和钢梁的;组合效应系数可以较好地反映组合楼板的整体特性及内部损伤。     

Plastic bending behaviour and section moment capacities of mono-symmetric LiteSteel beams with web openings

Recently developed cold-formed LiteSteel beam (LSB) sections have found increasing popularity in residential, industrial and commercial buildings due to their light weight and cost-effectiveness. Currently, there is significant interest in the use of LSB sections as flexural members in floor joist systems, although they can be used as flexural and compression members in a range of building systems. The plastic bending behaviour and section moment capacity of LSB sections with web holes can be assumed to differ from those without, but have yet to be investigated. Hence, no appropriate design rules for determining the section moment capacity of LSB sections with web holes are yet available. This paper presents the results of an investigation of the plastic bending behaviour and section moment capacity of LSB sections with circular web holes. LSB sections with varying circular hole diameters and degrees of spacing were considered. The paper also describes the simplified finite element (FE) modelling technique employed in this study, which incorporates all of the significant behavioural effects that influence the plastic bending behaviour and section moment capacity of these sections. The numerical and experimental test results and associated findings are also presented.     

Experimental behaviour of high‐strength concrete deep beams with web openings

This paper focuses on an experimental study undertaken on high‐strength concrete (HSC) deep beams with various opening sizes and locations on the web. The test covers a wide scope of variables that have not been investigated in previous research. Apart from highlighting the experimental setup, failure loads and typical crack patterns of the test specimens are also reported. Experimental results are then compared with predictions using currently available design methods. The comparison indicates that the predictions using current design methods can overly underestimate or sometimes overestimate the ultimate strength of these HSC deep beams. Further, the reduction of ultimate strengths due to the existence of web openings is not considered adequately in these design methods. To rectify the shortcomings of current design formulae, a new design equation is proposed and compared with the experimental results and those from previous studies on the related topics. The accuracy and reliability of the proposed new equation is subsequently confirmed. With the outcome of this work, more experimental tests with various opening configurations including shape and location of web openings are recommended for future study. Copyright © 2011 John Wiley & Sons, Ltd.     

Finite element modelling of anisotropic elasto-plastic timber composite beams with openings

In this paper, constitutive equations to model anisotropic elasto-plastic timber composite beams with openings were formulated and implemented into the finite element (FE) package ABAQUS, via a user-defined subroutine. The Tsai–Hill criterion was applied to judge failure of Oriented Strand Board (OSB) and timber in tension. Both OSB and timber in tension were modelled as linear orthotropic elastic materials, and in compression as orthotropic elasto-plastic materials. Good correlation has been obtained between the experimental results and the FE simulations. The user subroutine was used to check and remove critical elements, through which crack growth was simulated. In addition, interactions between two openings were modelled, which gave the corresponding critical distance.     

Shear capacity of steel plate girders with large web openings, Part II: Design guidelines

The present design procedure for the shear capacity of steel girders with large web openings is based on the shear buckling capacity of webs, as given by Eurocode 3, modified to account for the effect of the openings by means of reduction factors determined on the basis of numerical simulations. Guidelines are given for the use of the design procedure in practical design. Equations for determination of the secondary effects are presented, as well as some cut-off factors which limit the shear capacity for certain opening configurations. Requirements for design of welds are also given. Further, the paper presents equations for shear and primary moment interaction. Finally, two design examples illustrate the features of the guidelines in practical design of girders with openings.     

Experimental studies of the shear behaviour and strength of lipped channel beams with web openings

Cold-formed steel members are increasingly used as primary structural elements in the building industries around the world due to the availability of thin and high strength steels and advanced cold-forming technologies. Cold-formed lipped channel beams (LCB) are commonly used as flexural members such as floor joists and bearers. However, their shear capacities are determined based on conservative design rules. Current practice in flooring systems is to include openings in the web element of floor joists or bearers so that building services can be located within them. Shear behaviour of LCBs with web openings is more complicated while their shear strengths are considerably reduced by the presence of web openings. However, limited research has been undertaken on the shear behaviour and strength of LCBs with web openings. Hence a detailed experimental study involving 40 shear tests was undertaken to investigate the shear behaviour and strength of LCBs with web openings. Simply supported test specimens of LCBs with aspect ratios of 1.0 and 1.5 were loaded at mid-span until failure. This paper presents the details of this experimental study and the results of their shear capacities and behavioural characteristics. Experimental results showed that the current design rules in cold-formed steel structures design codes are very conservative for the shear design of LCBs with web openings. Improved design equations have been proposed for the shear strength of LCBs with web openings based on the experimental results from this study.     

混凝土翼板开洞钢-混凝土组合梁的试验研究及刚度分析

对9根混凝土翼板开洞的钢-混凝土组合梁进行了试验研究,试件变化的参数主要为洞口的大小及位置。试验表明,根据不同的荷载工况和洞口位置,翼板开洞组合梁有两种不同的破坏形式。针对不同的洞口特征参数,对多种荷载工况下组合梁的刚度进行了研究,得到了考虑滑移效应的混凝土翼板开洞钢-混凝土组合梁的刚度计算公式,计算结果与实测值吻合良好,该方法可供设计参考。     

带肋钢板加固腹板开洞RC梁受力性能模拟分析

为改善腹板开洞RC梁的受力性能,利用Abaqus有限元分析软件,在低周反复荷载作用下,对26根腹板开洞RC梁进行不同洞口长度、洞口高度、洞口偏移、钢板厚度参数数值模拟分析。模拟分析结果表明,带肋钢板加固腹板开洞梁相比未加固试件有良好的受力性能、耗能能力,变形能力增强,刚度退化减缓。有限元数值模拟分析为合理确定带肋钢板加固开洞梁参数提供了理论依据。     

蝴蝶腹板梁的设计和施工

日本正在建造一种叫做蝴蝶腹板桥的新型桥梁,即田久保川桥。该桥是一座高速公路桥,共10跨,其中最大跨度为87.5m。蝴蝶腹板结构是在箱梁腹板处使用厚度为150mm的蝴蝶型的预制板。腹板的组成材料是强度为80MPa的混凝土,拉应力区用单根的预应力筋加强。另外,这个150mm厚的腹板内没有用钢筋而是用钢纤维加强。该桥使用自由悬臂法施工。蝴蝶型腹板是在混凝土厂预制,重3.3t。这使得主梁的施工重量比普通混凝土腹板的箱梁轻。因此,悬臂施工的速度比传统的现场浇筑法快约50%。