体外预应力钢-混凝土组合连续梁的试验研究及有限元分析

与承受正弯矩的简支梁不同,连续梁中支座部分承受负弯矩,组成组合梁的钢板件受压力作用,其力学性能受稳定控制,不考虑稳定影响的规范简化塑性算法会带来不安全的结果.以Ⅱ类、Ⅲ类组合梁和是否配置预应力筋为参数,进行了两组共四根连续组合梁的单调加载对比试验.试验结果表明:无论预应力连续组合梁或是普通连续组合梁,最终破坏特征均为负弯矩区混凝土开裂,钢腹板局部屈曲,整个截面畸变失稳,正弯矩区混凝土板压碎;正弯矩区的承载能力可由简化塑性计算方法计算,而负弯矩区的受力性能由稳定控制,影响其承载能力的主要因素为板件的宽厚比所表征的截面种类,考虑屈曲的承载力计算方法与试验结果吻合.对各组合梁进行了有限元数值分析,分析考虑界面滑移、预应力、稳定等影响,结果和试验吻合较好.     

Experimental study of prestressed steel-concrete composite beams with external tendons for negative moments

Four groups of prestressed steel-concrete composite beams with external tendons in negative moment regions were tested, and the cracking behaviours and the ultimate negative moment resistances of the composite beams were investigated experimentally. It is found that in hogging moment regions, on adding prestressing to the composite beams with external tendons, the cracking resistance of the beams can be effectively increased; however, the incremental internal tendon forces of the prestressed composite beams are rather small, and therefore can be neglected in the evaluation of the negative moment resistance of the beams. In hogging moment regions, the ultimate resistance of a composite beam prestressed with external tendons is governed by either distortional lateral buckling or local buckling, or an interactive mode composed of the two bucklings. For a beam with a compact section, the negative bending moment can reach the plastic moment when the steel section is fully plastic, and for a non-compact section, the negative bending moment is limited to the yield moment at which the compression steel flange initiates yield. The method for evaluating the buckling resistance of the composite beams is discussed, and a tentative design method based on BS5400: Part 3 is proposed to assess the buckling resistances of the prestressed composite beams.     

Numerical investigation of inelastic buckling of steel–concrete composite beams prestressed with external tendons

The ultimate resistance of a continuous composite beam is governed by either distortional lateral buckling or local buckling, or an interactive mode of the two which is sharply different from the torsional buckling mode in a bare steel beam. A finite element model is developed and based on the proposed FE model, inelastic finite element analysis of composite beams in negative bending is investigated, considering the initial geometric imperfection and the residual stress patterns and the FE results are found agree well with the test results. Parametrical analysis is carried out on the prestressed composite beams with external tendons in negative bending. Factors that influence load carrying performance and buckling moment resistance of prestressed composite beams are analyzed, such as initial geometric imperfection, residual stress in steel beams, force ratio, which is defined as the extent of prestressing force and negative reinforcement in the beams, as well as the slenderness ratios of web, flange, and beams. By varying cross-section parameters, 25 groups of composite beams under negative uniform bending with initial geometric imperfection, residual stress as well as different force ratios, 200 beams in total are studied by means of the FE method. The computed buckling moment ratios are drawn against the modified slenderness proposed by the authors and compared with the Chinese Codified steel column design curve. It is demonstrated that the tentative design method based on the Chinese Codified design curve can be used in assessment of buckling strength of composite beams in a term of the modified slenderness defined.     

体外预应力混凝土连续梁的弯矩重分布试验研究

进行了3根体外预应力混凝土两跨连续梁受力全过程试验。试验表明,自加载至受拉区混凝土开裂前,连续梁处于弹性阶段,边支座、中支座反力、跨中截面和中支座截面弯矩的实测值与采用弹性理论计算值接近。受拉区混凝土开裂后至非预应力受拉钢筋屈服,边支座反力及跨中截面弯矩实测值开始向大于弹性理论计算值的方向偏离;而中支座反力及中支座截面弯矩实测值则向小于弹性理论计算值的方向偏离。当梁内受拉非预应力筋屈服后,边支座、中支座反力的实测值以及跨中截面弯矩和中支座截面弯矩实测值与弹性理论计算值的偏差进一步增大,这种偏差在试验梁破坏时达到最大。3根试验梁中支座截面弯矩重分布值分别为12.8%、16.9%及14.6%。试验实测值还与4个不同设计规范的弯矩重分布计算值进行了比较。结果表明:采用美国ACI 318-95规范及中国GB 50010-2010规范计算的中支座截面弯矩重分布值均小于试验实测值;除一根编号为B5的梁外,加拿大A23.3-M84规范的预测值与试验值最为接近;而英国BS8110规范则偏于不安全。实际设计中,可按中国规范公式来计算体外预应力混凝土连续梁的弯矩重分布,但必须合理确定体外预应力筋的极限应力。     

连续梁中无粘结预应力筋极限应力增量

无粘结筋极限应力增量的合理计算,是较准确计算无粘结预应力混凝土梁正截面承载力和极限荷载的基础。采用弯矩-曲率非线性分析法编制了可考察预应力混凝土梁中无粘结筋极限应力增量的计算程序,通过与16根两跨预应力混凝土连续梁中无粘结筋极限应力实测值的比较,验证了该方法的精确性。最后基于仿真分析结果,得到了预应力筋配筋指标、非预应力筋配筋指标、跨高比、加载形式等参数对承载能力极限状态下连续梁中无粘结筋应力增长的影响规律;建立了无粘结部分预应力混凝土连续梁中无粘结筋极限应力增量的计算公式。     

对预装体外钢筋的钢-混凝土组合梁弹塑性屈曲的数值分析

连续组合梁的极限承载力由侧向畸变屈曲、局部屈曲,或者由两者的相互作用决定,这一点与纯钢梁的扭转屈曲破坏模式完全不同。利用有限元模型对负弯矩区的组合梁进行了弹塑性有限元分析,其中考虑了初始几何缺陷和残余应力,最终发现有限元分析结果与试验结果吻合良好。另外,对负弯矩区的预装体外钢筋的组合梁进行了参数研究。分析了影响组合梁承载能力和屈曲弯矩抗力的因子,如初始几何缺陷、钢梁的残余应力、力比值、预应力范围、负力矩钢筋、板、翼缘和梁的宽厚比。利用有限元法对负弯矩作用下的25组共200根具有不同截面参数、初始几何缺陷、残余应力和不同力比值的组合梁进行了分析。将计算出的屈曲弯矩率与改进宽厚比的曲线与中国规范中钢柱设计曲线进行了对比。结果证实:对于改进了的宽厚比值,本文依据中国规范的设计曲线推导出来的设计方法可以用于对组合梁屈曲强度的评估。     

体外预应力钢-混凝土组合梁负弯矩区的承载力研究

通过体外预应力组合梁的承载力试验,研究了负弯矩作用下体外预应力组合梁的开裂和极限承载力。研究结果表明:对负弯矩区组合梁施加体外预应力后,可有效提高截面的开裂弯矩。负弯矩作用下体外预应力组合梁的预应力增量很小,可忽略。一般情况下,对负弯矩截面施加体外预应力,不会提高截面的屈服承载弯矩。负弯矩作用下体外预应力组合梁的极限承载力受失稳控制。把预应力作用作为等效荷载,探讨组合梁失稳承载力的计算方法,采用BS5400:Part3方法计算了预应力组合梁的失稳临界弯矩。     

钢-混凝土组合梁抗裂性能的试验研究

为研究钢-混凝土连续组合梁的受力性能,特别是体外预应力对抗裂性能和刚度的影响,完成3根反向加载的简支组合梁和3根2跨连续组合梁的静力加载试验,其中包括2根在钢梁和混凝土板内折线布筋的体外预应力组合梁。试验表明:非预应力组合梁在负弯矩作用下的开裂荷载较低,连续梁在较低荷载下就会由于混凝土开裂而发生明显的内力重分布,且横向钢筋间距对裂缝间距具有一定影响;折线布筋的体外预应力组合梁开裂荷载增大,裂缝间距和裂缝宽度明显减小,且相同荷载下的挠度下降,说明体外预应力可有效改善组合梁的综合受力性能。此外,预应力作用对组合梁的滑移分布有较明显影响。     

体外预应力混凝土连续梁弯曲性能试验研究

为了研究体外预应力混凝土连续梁的弯曲性能、极限受力状态及内力重分布规律,以施工方法和体内外预应力筋配比为参数,对1根整体式(体内外配筋)和2根节段式(体内外配筋和全体外配筋)体外预应力混凝土连续梁进行了模型试验。通过试验数据分析,得到了模型梁挠度、混凝土应变、体外预应力筋应力与有效高度随荷载变化规律,以及混凝土裂缝发展与分布情况。结果表明:整体式梁的混凝土极限压应变和挠度最大、延性较好但体外预应力筋有效高度减少最大,节段式体内外预应力梁的体外预应力筋极限应力最大,节段式全体外预应力梁的混凝土极限压应变和挠度最小、延性较差、体外预应力筋极限应力及有效高度减少也最小。节段式梁的裂缝主要集中在接缝位置、无斜裂缝,接缝位置的塑性变形使内力重分布更充分。整体式梁内力重分布的区域集中而节段式全体外预应力梁的范围较大,各梁控制截面弯矩增、减幅值不超过10%。     

体外索钢箱-混凝土组合连续梁非线性结构性能试验研究

钢箱-混凝土组合连续梁负弯矩区混凝土的开裂问题影响了这类组合结构向更大跨度的发展。针对这一问题,提出在钢箱-混凝土组合连续梁中施加体外索的新技术,研究施加体外索对增强钢箱-混凝土组合连续梁负弯矩区混凝土的抗裂能力,提高钢箱-混凝土组合连续梁弹塑性结构性能的有利作用。经对比试验表明,施加体外索后,钢箱-混凝土组合连续梁负弯矩区混凝土的开裂荷载提高2.8倍,组合连续梁的弹塑性抗弯刚度提高29.35%,承载力提高34.67%,结构性能显著提高。在试验研究基础上,分析钢箱-混凝土组合连续梁负弯矩区局部力学性能与整体非线性结构性能的关系,揭示体外索提高钢箱-混凝土组合连续梁弹塑性结构性能的力学实质,给出承载力计算建议。研究结果可作为体外索钢箱-混凝土组合连续梁工程应用和理论分析的参考。     

Behavior of composite beams prestressed with external tendons: Experimental study

The paper deals with the failure mechanisms and behavior of composite steel-concrete beams prestressed with external tendons and subjected to positive bending. Experimental tests were carried out on beams with straight and draped tendons as well as on a non-prestressed beam. Six simply supported beams subjected to a positive static bending moment were tested up to failure. The influence of shear connection flexibility was taken into account and slip was measured along the beam axis. Concurrently, push-out specimens were made and tested to determine shear force vs. slip curves. It was found that at the same eccentricity of tendons (draped or straight without saddle points) the tendon shape has no significant effect on the behavior and ultimate resistance of composite steel-concrete beams. It is also shown that steel-concrete bond cohesion can significantly influence the behavior of the shear connection in composite beams. This influence is comparable with the design shear resistance of a single stud connector.     

Load carrying capacity of composite beams prestressed with external tendons under positive moment

Tests have been carried out to study the ultimate moment and incremental tendon stress of steel-concrete composite beams prestressed with external tendons under positive moment. It appears that adding prestressing by external tendons of the composite beams can significantly increase the yield load and the ultimate resistance of the beams. The deflection at the serviceability state is also reduced. However, a substantial incremental stress will develop in the tendons at the ultimate state. On the basis of the compatibility of the tendons and the composite beam at the anchorage section, and equilibrium of the internal force, the neutral axis equation of the composite beam section at the ultimate state is derived. The simplified expressions for the ultimate incremental tendon stress related to the ultimate span/deflection value for four typical external tendon cases are developed. The results compare well with the test results and the finite element analysis. A simplified method for predicting the ultimate incremental tendon force and the load carrying capacity of the composite beams prestressed with external tendons is proposed.     

无粘结预应力连续梁塑性设计试验研究

基于16根两跨无粘结预应力混凝土连续梁试验结果,考察分析了试验梁塑性内力重分布性能,建立了以中支座相对塑性转角为自变量的弯矩调幅系数计算公式,为无粘结预应力混凝土连续梁按塑性方法设计及相关标准的修订提供了试验依据。     

钢－混凝土连续组合梁负弯矩区的局部失稳

本文提出截面曲率延性Ｋ１、Ｋ２和Ｋ３的概念，来描述二类截面局部失稳对连续组合梁内力重分布的影响，采用非线性增量迭代法，分析了３６组二跨连续组合梁承受均布荷载时弯矩重分布的情况。研究表明：二类截面连续组合梁的局部失稳，可采用对中间支承处弯矩调幅３０％来等效。本文提出的设计方法，可避免复杂的弹塑性稳定计算。     

非线性阶段预应力次弯矩概念及其在弯矩调幅中的应用

非线性阶段次弯矩的演化,以及承载力极限状态下是否考虑次弯矩的问题一直存在争议。为解决这一问题,拓展了预应力次弯矩的概念,使其能够适用于非线性阶段。运用变刚度法数值模拟了初始次弯矩(M₂)与弹性最大荷载弯矩(M_e)之比为0.15~0.36的15根有黏结预应力混凝土两跨连续梁。基于拓展后的次弯矩概念,提出了以混凝土受压区相对高度、初始次弯矩与弹性最大荷载弯矩之比为影响参数的有黏结预应力混凝土连续梁弯矩调幅公式。采用已有文献中受压区相对高度为0.35的试验梁比较了所提公式和现有的弯矩调幅公式。设计制作受压区相对高度为0.18的两跨预应力混凝土连续梁,获取单调加载下支座反力数据,检验了内力重分布程度较大时所提公式的效果。结果表明,给出的弯矩调幅公式的计算结果偏于安全,且更接近试验结果。     

负弯矩作用下钢-混凝土组合梁受力性能试验研究

通过8根跨度为3.0m和4.2m的钢-混凝土组合梁在负弯矩作用下的受力性能试验,研究了端部弯矩、跨度、H形钢的腹板高厚比、抗剪连接栓钉数量、设置横向加劲肋等因素对组合梁失稳破坏模式、受弯承载力及转动能力的影响。试验结果表明：对两端部作用数值相等的负弯矩工况,组合梁发生畸变失稳,其受弯承载力小于组合梁全截面塑性弯矩,转动能力偏小,而对其他接近实际结构的负弯矩工况,组合梁发生局部失稳或局部与畸变耦合失稳,其受弯承载力大于组合梁全截面塑性弯矩,转动能力较大;随着腹板高厚比减小或者在腹板上设置横向加劲肋,组合梁的受弯承载力和转动能力都有明显提高。     

钢-部分预应力混凝土连续组合梁内力重分布研究

本文报道了10榀钢-部分预应力混凝土连续组合梁和1榀钢-普通混凝土连续组合梁的极限承载力试验结果。试件为两跨连续梁,主要试验参数为负弯矩区部分预应力比PPR、综合力比Rp及栓钉连接程度。试验采用跨中单调一次加载。试验发现,在负弯矩区施加预应力的钢-部分预应力混凝土连续组合梁可产生较充分的内力重分布,其主要影响因素为截面相对受压区高度ξu和负弯矩区综合力比Rp。本文通过试验研究和理论分析,提出了钢-部分预应力混凝土连续组合梁满足承载力要求的弯矩调幅限值犤β犦的计算公式,其计算结果与试验结果吻合较好。     

钢-砼连续组合梁塑性铰特性及内力重分布研究

本文在两根3.6m长单跨倒置组合梁和两根7.6m长双跨连续梁试验及电算分析的基础上,着重对连续组合梁塑性铰特性及内力重分布现象进行了研究。结果表明:力比R是影响塑性转动能力及弯矩重分布程度的一个重要参数。负塑性铰的极限塑性转动能力在力比R≤O.3时,由钢筋极限拉应变ε_tu=0.O1控制;在力比R>0.3时,由钢粱极限压屈应变ε_Bu控制,ε_Bu可用公式ε_Bu=(-1.153+3.421/R)×10~(-3)近似计算。为了保证35％的弯矩调幅,负弯矩截面的力比R应不大于O.5。     

Design of semi-continuous composite steel-concrete beams at the fire limit state

A two-dimensional temperature analysis procedure based on the finite element method (FEM) is described and applied to steel-concrete composite beams. A computer program developed for the analysis is detailed. A strategy is also proposed for incorporating the influence of the partial resistance of the composite connections in reducing the sagging moment at central regions of the beam spans when the beam is calculated as semi-continuous. Finally, an example problem is discussed, comparing the design uniformly distributed loads that can be supported by a composite beam calculated as semi-continuous and with simply supported spans. The temperature distribution due to fire at the central region of the spans is taken as in the simplified procedure proposed in European Prestandard ENV 1994-1-2 [ENV 1994-1-2. Eurocode 4, Design of composite steel and concrete structures — Structural fire design. Brussels: European Committee for Standardization (CEN); 1994] and then obtained with the more rigorous calculation using the described numerical algorithm. It will be assumed that no ultimate limit state will occur due to shear force (web buckling) or due to bending moment at the hogging moment regions of the beam (web and bottom flange buckling or distortional lateral buckling).     

连续组合梁的局部失稳与弯矩重分布

研究了负弯矩区截面未完全塑性时出现局部失稳的连续组合梁的稳定。研究结果表明 :对于第三类截面的连续组合梁局部稳定设计 ,中间支座负弯矩可调幅 2 0 %