负弯矩区部分充填式窄幅钢箱-UHPC-NC组合梁抗剪承载力研究

Study on the shear capacity of partially filled narrow steel box-UHPC-NC composite beams in negative moment regions

为研究部分充填式窄幅钢箱-UHPC-NC组合梁负弯矩区受剪性能,开展3根部分充填式窄幅钢箱组合梁加载试验,研究组合梁的破坏模式、变形及裂缝分布规律。基于ABAQUS软件建立组合梁有限元模型,通过试验结果验证模型的准确性,并分析充填混凝土强度fcu、充填混凝土高度hf、UHPC层厚度hu和剪跨比λ对组合梁抗剪承载力的影响。研究结果表明:3根组合梁钢箱上箱室均发生剪切破坏,翼板跨中出现弯曲主裂缝,加载点与支座间产生剪切斜裂缝。在弹性阶段,UHPC和NC、钢箱与翼板协同工作性能良好,NC翼板组合梁端部表现出明显的剪切破坏;UHPC翼板组合梁的开裂荷载、屈服荷载及极限荷载较NC翼板组合梁分别提高55%、37.5%和12.5%,最大裂缝宽度从1.48 mm降至0.82 mm。有限元模型计算与试验结果吻合良好,可用于组合梁受力性能参数分析。组合梁抗剪承载力随hu的增加基本呈线性关系,当hu从0增加至100 mm时,组合梁抗剪承载力提高12.5%;当hf达到0.3后、提高fcu对组合梁抗剪承载力的影响并不显著,hf应控制在0.3左右且fcu不宜过高;组合梁抗剪承载力随着λ的增加基本呈线性关系递减,λ=2.8为组合梁弯剪破坏和受弯破坏界限剪跨比。提出考虑钢箱、充填混凝土和翼板贡献的组合梁抗剪承载力计算公式,并与试验和数值模拟结果进行验证分析,结果吻合良好且偏于安全。

To analyze the shear behavior of partially filled narrow steel box-UHPC-NC composite beams in negative moment regions,loading tests were conducted on three partially filled narrow steel box composite beams to study their failure modes,deformation,and crack distribution.A finite element model of the composite beams was established using ABAQUS,and its accuracy was verified against the experimental results.The influences of the infilled concrete strength(fcu),infilled concrete height(hf),UHPC layer thickness(hu),and shear�span ratio(λ)on the shear capacity were analyzed.The results show that shear failure occurred in the upper chamber of the steel box of all three composite beams.Main bending induced cracks appeared in the middle span of the flange,and multiple shearing induced oblique cracks emerged between the loading point and the support.At the elastic stage,both UHPC and NC,as well as the steel box and flange,worked well in coordination.The ends of the NC flange composite beam exhibited obvious shear failure.The cracking load,yield load,and ultimate load of the UHPC flange composite beams were 55%,37.5%,and 12.5%higher than those of the NC flange composite beam,respectively.Additionally,the maximum crack width decreased from 1.48 mm to 0.82 mm.The finite element model calculations are in good agreement with the experimental results,indicating its applicability for analyzing the mechanical performance parameters of the composite beams.The shear capacity of the composite beams increased linearly with increasing hu.When hu increased from 0 to 100 mm,the shear capacity of the composite beams increased by 12.5%.When hf reached 0.3,increasing fcu had no significant effect on the shear capacity of the composite beams,suggesting that hf should be controlled at around 0.3 and that fcu should not be excessively high.The shear capacity of the composite beams decreased linearly with increasingλ,andλ=2.8 is identified as the limiting shear-span ratio for the transition between bending-shear and bending failure of the composite beam.A calculation formula for the shear capacity of the composite beams was proposed,considering the contributions of the steel box,infilled concrete,and flange.The calculated results are in good agreement with both the experimental and numerical findings and tend to be conservative.