火灾作用后钢管混凝土构件侧向撞击性能研究

建立火灾作用后钢管混凝土(concrete-filled steel tube,CFST)构件的侧向撞击数值模型以分析构件的抗撞击性能,并对模型的准确性进行了验证。分别对比了不同受火时间后构件的跨中挠度、撞击力和截面弯矩时程曲线,分析了受火后构件的弯矩和剪力分布形态。通过吸能系数和火灾后动态弯矩提高系数对受火后构件的抗撞击性能进行量化分析,并给出构件跨中最大挠度的计算公式。结果表明,受火时间对构件的跨中挠度、撞击时程、撞击力和截面弯矩影响明显。随着受火时间增加,构件的跨中挠度大幅增加,撞击时程变长,且外钢管与混凝土各自承担的动态极限弯矩之比增大。惯性力对构件弯矩和剪力分布的影响主要在峰值阶段,该阶段弯矩和剪力的分布形态明显改变。受火后构件的破坏形式为整体弯曲变形,构件主要通过整体变形耗散落锤的动能。此外,构件的撞击力平台值、截面动态极限弯矩、吸能系数和火灾后动态弯矩提高系数均随着受火时间增加而降低,表明构件抗撞击性能和抗弯能力降低,公式计算的最大挠度与模拟结果吻合良好。     

钢丝网复合砂浆加固混凝土受弯构件非线性分析

对用钢丝网复合砂浆加固的钢筋混凝土梁进行了正截面抗弯试验研究。试验包括16根用钢丝网加固的梁和两根未加固的对比梁,采用U形三面的加固方式(钢丝网复合砂浆包裹了梁的受拉面及两个侧面)。试验中对比了加固与未加固构件的裂缝开展情况、跨中挠度以及极限荷载。试验结果表明,钢丝网复合砂浆薄层可以明显地提高钢筋混凝土梁的抗弯承载力,提高抗裂性能,增强构件的抗弯刚度。理论部分采用非线性的方法得到加固构件的荷载-挠度曲线,与试验结果比较,有较好的吻合。     

CFRP筋体外预应力加固T形截面混凝土梁短期挠度计算方法

通过静力试验和理论分析,研究CFRP筋体外预应力加固T形截面混凝土梁在短期荷载作用下的使用性能,探讨短期挠度计算方法。结果表明,CFRP筋体外预应力加固梁的荷载-跨中挠度曲线呈三折线变化;跨中截面混凝土和CFRP筋的平均应变在梁体开裂之前沿截面高度基本呈线性变化,开裂后,CFRP筋的平均应变明显小于梁底混凝土的应变。基于试验结果,计算开裂刚度折减系数和CFRP筋粘结特征系数,考虑二次效应的影响,运用有效惯性矩法建立了CFRP筋体外预应力加固T形截面混凝土梁的短期挠度计算公式,可供实际工程设计 参考。     

外包不锈钢圆中空夹层钢管混凝土柱抗撞计算方法研究

目前钢筋混凝土和实心钢管混凝土构件已广泛应用于实际工程,在抗冲击性能方面已形成相关设计方法,而针对外包不锈钢圆中空夹层钢管混凝土(CFDST)柱的耐撞性能研究较少。为此,该文在前期试验研究的基础上,采用ABAQUS建立了该类构件在轴力与侧向撞击耦合作用下的有限元模型。分析了轴力-撞击共同作用下该类构件的抗撞机理;重点研究了轴压比、名义含钢率等对构件抗撞性能的影响;给出了该类构件在轴力-撞击耦合作用下撞击力平台值动力放大系数(DIF)的计算公式。结果表明:外钢管的塑性变形是构件耐撞的主要耗能机制;轴压比对构件抗撞性能起削弱作用,且当轴压比大于0.5时,削弱程度更加明显;名义含钢率、外钢管与混凝土强度、撞击速度和截面外径对构件抗撞性能影响较大;建议的计算公式能够较好预测该类构件侧向撞击下的撞击力平台值。     

残余应力对碳纤维增强压弯H型钢弹塑性稳定性的影响研究

建立轴压和弯矩共同作用下碳纤维增强H形截面构件绕强轴失稳时极限荷载的计算公式。通过弹塑性有限元法并结合非线性屈曲理论,进行了压弯荷载共同作用时碳纤维增强钢构件和考虑残余应力影响下钢构件的屈曲分析。当给定弯矩仅在某一范围内时,考虑残余应力的CFRP增强钢构件的极限承载力相比CFRP增强完善条件下的钢构件极限承载力相比要低很多。当给定弯矩超出此范围时,前者要略高于后者。受残余应力影响的碳纤维增强压弯构件极限承载力始终比未增强完善钢构件的限承载力高,表明构件可以通过碳纤维增强来弥补残余应力所导致的构件承载力损失,充分体现了碳纤维良好的增强效果。     

二次受力下自密实混凝土加固RC梁受弯性能研究

为模拟实际工程中加固构件的真实承载能力,实验在原混凝土构件持续受荷状态下,采用自密实混凝土对构件进行加固、养护。共进行了7根二次受力下自密实混凝土加固钢筋混凝土梁和2根对比梁的受弯性能试验,研究了不同初始受力水平、不同加固厚度及不同界面处理方式对加固钢筋混凝土梁抗弯承载力和截面刚度的影响。试验量测了构件裂缝分布形态、荷载-挠度曲线、钢筋应变发展规律等。结果表明:采用自密实混凝土加固钢筋混凝土梁,能有效地提高钢筋混凝土梁的抗弯承载力、截面刚度等性能;二次受力下自密实混凝土加固梁抗弯承载力随着初始受力水平的增大而降低。在试验结果的基础上,基于平截面假定,提出了二次受力下自密实混凝土加固梁钢筋滞后应变及抗弯承载力计算式,计算结果与试验结果吻合良好。     

基于分形理论的CFRP布增强混凝土梁抗弯性能研究

在实验室模拟酸雨腐蚀环境,完成了普通混凝土梁与CFRP布增强混凝土梁的抗弯试验,得到了各级荷载作用下构件表面裂缝的分布与演化过程,验证了受腐蚀CFRP布增强混凝土梁表面裂缝分布的分形特征。基于分形理论分析了受腐蚀混凝土梁在弯曲荷载作用下的开裂及破坏过程,详细讨论了梁表面裂缝的分形维数与其抗弯性能参数(损伤深度、混凝土强度、一阶频率、极限承载力、跨中挠度、位移延性系数)之间的关系。研究表明裂缝分形维数随着损伤深度的增加而减小,CFRP布增强混凝土梁的分形维数大于普通混凝土梁,其分形维数变化率与构件承载力变化率之间存在线性关系;因此梁表面裂缝分布的分形特征可作为CFRP布增强混凝土受弯构件损伤程度的衡量指标的观点,可为今后对“在役混凝土结构承载力和寿命预测的研究”提供参考。     

复合砂浆钢筋网加固抗弯RC梁的非线性分析

复合砂浆钢筋网薄层加固是一种有效的加固方法,能够显著地提高钢筋混凝土梁的抗弯承载力、变形能力以及抗裂性能。以8根复合砂浆钢筋网加固RC梁的试验研究结果为参考,通过非线性有限元分析广泛地研究了加固梁纵向配筋率、配箍特征值、梁高宽比对极限荷载提高幅度的影响,并初步分析了少筋梁和超筋梁加固后的荷载-跨中挠度曲线的变化规律。根据分析和试验结果,通过等效假定给出了复合砂浆钢筋网加固RC梁的极限承载力计算公式和抗弯刚度计算公式。     

CFRP加固火灾后混凝土短柱抗震性能的试验研究

进行了1根未受火混凝土短柱、1根火灾后混凝土短柱、1根CFRP加固未受火混凝土短柱和3根CFRP加固火灾后混凝土短柱的拟静力试验,考察了CFRP的加固量和加固方式对火灾后混凝土短柱抗震加固效果的影响情况,建议了CFRP加固火灾后混凝土柱抗剪承载力的实用计算方法。研究结果表明:外包CFRP加固可将未受火混凝土短柱的抗剪承载力提高21.8%、可将火灾后混凝土短柱的抗剪承载力提升至未受火试件的111.2%~117.1%、可提高受火前后短柱的极限变形能力和累积滞回耗能。与未受火试件相比,外包CFRP不会提高火灾后加固混凝土短柱的割线刚度。对于相同的加固量,全包CFRP柱的抗剪承载力略优于条带包裹柱。受火前、后和外包CFRP加固前、后混凝土短柱的滞回规则均类似。     

粘结层和预应力对CFRP板加固损伤钢梁抗弯性能的影响

为了对比粘结层和预应力对碳纤维增强聚合物复合材料(CFRP)板加固损伤钢梁抗弯性能的影响,进行了5根H型损伤钢梁的抗弯试验,分析了特征荷载、荷载-挠度曲线、CFRP板应变及其强度利用率的变化。试验结果表明:有粘结和无粘结CFRP板具有相近的加固效果,特征荷载差值小于2%;非预应力CFRP板在正常使用阶段的加固效果很小,而预应力CFRP板加固钢梁的特征荷载比非预应力CFRP板提高了近30%。平截面假定适用于有粘结CFRP板-钢梁复合截面,而不适用于无粘结CFRP板-钢梁复合截面。相比于非预应力CFRP板,对CFRP板施加预应力可以显著提高CFRP板的强度利用率。建立的有限元模型可以较好地预测试件的抗弯性能,增加CFRP板的预应力、厚度和弹性模量可以提高损伤钢梁的抗弯加固效果。      

Deflection behaviour of FRP reinforced concrete beams and slabs: An experimental investigation

The flexural response of FRP RC elements is investigated through load–deflection tests on 24 RC beams and slabs with glass FRP (GFRP) and carbon FRP (CFRP) reinforcement covering a wide range of reinforcement ratios. Rebar and concrete strains around a crack inducer are used to establish moment–curvature relationships and evaluate the shear and flexural components of mid-span deflections. It is concluded that the contribution of shear and bond induced deformations can be of major significance in FRP RC elements having moderate to high reinforcement ratios. Existing equations to calculate short-term deflection of FRP RC elements are discussed and compared to experimental values.     

Analytical approach for the flexural analysis of RC beams strengthened with prestressed CFRP

The objective of this paper is to propose a simplified analytical approach to predict the flexural behavior of simply supported reinforced-concrete (RC) beams flexurally strengthened with prestressed carbon fiber reinforced polymer (CFRP) reinforcements using either externally bonded reinforcing (EBR) or near surface mounted (NSM) techniques. This design methodology also considers the ultimate flexural capacity of NSM CFRP strengthened beams when concrete cover delamination is the governing failure mode. A moment–curvature (M–χ) relationship formed by three linear branches corresponding to the precracking, postcracking, and postyielding stages is established by considering the four critical M–χ points that characterize the flexural behavior of CFRP strengthened beams. Two additional M–χ points, namely, concrete decompression and steel decompression, are also defined to assess the initial effects of the prestress force applied by the FRP reinforcement. The mid-span deflection of the beams is predicted based on the curvature approach, assuming a linear curvature variation between the critical points along the beam length. The good predictive performance of the analytical model is appraised by simulating the force–deflection response registered in experimental programs composed of RC beams strengthened with prestressed NSM CFRP reinforcements.     

Tests of continuous concrete slabs reinforced with carbon fibre reinforced polymer bars

Although several research studies have been conducted on simply supported concrete elements reinforced with fibre reinforced polymer (FRP) bars, there is little reported work on the behaviour of continuous elements. This paper reports the testing of four continuously supported concrete slabs reinforced with carbon fibre reinforced polymer (CFRP) bars. Different arrangements of CFRP reinforcement at mid-span and over the middle support were considered. Two simply supported concrete slabs reinforced with under and over CFRP reinforcement and a continuous concrete slab reinforced with steel bars were also tested for comparison purposes. All continuous CFRP reinforced concrete slabs exhibited a combined shear–flexure failure mode. It was also shown that increasing the bottom mid-span CFRP reinforcement of continuous slabs is more effective than the top over middle support CFRP reinforcement in improving the load capacity and reducing mid-span deflections. The ACI 440.1R–06 formulas overestimated the experimental moment at failure but better predicted the load capacity of continuous CFRP reinforced concrete slabs tested. The ACI 440.1R–06, ISIS–M03–07 and CSA S806-06 design code equations reasonably predicted the deflections of the CFRP continuously supported slabs having under reinforcement at the bottom layer but underestimated deflections of continuous slabs with over-reinforcement at the bottom layer.     

Flexural performance of FRP reinforced concrete beams

A numerical method for estimating the curvature, deflection and moment capacity of FRP reinforced concrete beams is developed. Force equilibrium and strain compatibility equations for a beam section divided into a number of segments are numerically solved due to the non-linear behaviour of concrete. The deflection is then obtained from the flexural rigidity at mid-span section using the deflection formula for various load cases. A proposed modification to the mid-span flexural rigidity is also introduced to account for the experimentally observed wide cracks over the intermediate support of continuous FRP reinforced concrete beams.     

Flexural retrofitting of RC buildings using GFRP/CFRP – A comparative study

The effectiveness of fibre reinforced polymers (FRPs) in retrofitting/repairing of the reinforced concrete (RC) components has been studied in the past to great detail. However, the seismic performance of RC structures retrofitted using FRP composites is yet to be scrutinised in terms of lateral resistance, ductility, and failure mechanism. This is of high importance if the retrofitted structures are to withstand higher seismic ground motions than they were designed for and/or pulse-type ground motions. In a comparative study, this paper reports on the results of an investigation into the flexural strengthening of RC buildings using glass/carbon fibre reinforced polymers (GFRP/CFRP). An 8-storey code-compliant RC building was considered as the case study to represent the medium-rise structures. With a slight intervention in the lateral displacement ductility and provision of the weak-beam strong-column design philosophy, the strengthening design strategy is aimed at increasing the lateral resistance. For this purpose, composite sheets are designed to be applied at the two end regions of all beams and columns on a practical flange-bonded scheme. The nonlinear pushover analysis with lumped plasticity approach was implemented in order to compare the seismic response of the original structure with the GFRP/CFRP retrofitted structures. Following validation of the adopted models, the force–deformation curves of the nonlinear plastic hinges are determined in a rigorous approach considering the material inelastic behaviour, reinforcement details, and dimensions of the members. While the nonlinear results confirm a significant increase in the lateral load carrying capacity using both composite materials, the CFRP improvement was as much as twice of the GFRP. However, the latter provides higher ductility.     

智能CFRP加固RC梁荷载效应的实时模拟与测评

制备了4 根炭纤维复合材料(CFRP) 加固钢筋混凝土(RC) 实验梁, 并在梁内钢筋、混凝土及加固CFRP中预置了布拉格光栅光纤传感器(FBG) 和电阻应变片两种传感器。根据钢筋混凝土理论和ANSYS 有限元软件编制了实验梁受弯荷载效应模拟计算程序。实验表明, 实验梁在受弯承载过程中, 布拉格光栅光纤传感器与传统应变片有完全一致的线性关系; 模拟计算出的实验梁受拉钢筋、压区混凝土应变值及挠度与荷载的关系与CFRP 中FBG的实测值吻合较好。由于对既成RC 结构不能在内部装置传感器(会破坏结构降低抗力) , 采用智能CFRP 加固RC 结构可实现加固和实时健康测评双重功能。      

高强型钢超高性能混凝土梁受弯性能试验研究及有限元分析

为研究高强型钢超高性能混凝土梁的受弯性能,以配钢率、型钢位置和钢纤维体积分数为变化参数,设计了6个试件,并对其进行了静力加载试验,获得了试件的破坏形态和荷载-跨中挠度曲线,分析了试件的承载能力和变形能力,以及型钢、纵向钢筋和超高性能混凝土的应变变化规律。基于试验研究,建立了高强型钢超高性能混凝土梁受弯性能的有限元分析模型,计算结果与试验结果吻合较好,进而进行了参数分析。结果表明：所有试件均发生的是适筋破坏,纵向受拉钢筋和型钢下翼缘率先屈服,然后受压区超高性能混凝土被压碎;在试件的破坏阶段,所承担的荷载会依次经历陡降、波动、缓慢上升和缓慢下降四个阶段;试件的变形能力系数超过5,呈现出较强的变形能力;试件开裂前,超高性能混凝土的应变符合平截面假定,但开裂后,只有受压区和受拉区在中和轴附近的一小部分超高性能混凝土应变呈线性分布;配钢率和型钢强度增大,试件的承载能力和变形能力均提高;超高性能混凝土抗压强度增大及型钢从截面居中位置下移,试件的承载能力提高,但变形能力下降;钢纤维体积分数增加,试件的抗裂能力和变形能力均提高,但承载能力变化不显著。     

冲击作用下钢筋混凝土深梁动力性能试验研究

为了探讨在冲击荷载作用下钢筋混凝土深梁的动力性能,利用大型落锤试验机对两组具有不同静载破坏特性的简支钢筋混凝土深梁进行了不同冲击速度下的动力性能试验研究,并考虑了二次冲击的影响。通过对高速摄像机所记录的各试件在冲击过程中裂缝的发生、发展直至试件破坏的全过程进行分析和不同荷载下裂缝形态差异的对比分析,表明不同的冲击速度下试件裂缝的发生、发展过程及裂缝形态表现出明显的差异,二次冲击下的主要裂缝基本遵循一次冲击产生的裂缝路径发展。详细分析了冲击力和跨中位移时程曲线以及冲击力-跨中位移曲线的特征,发现冲击力峰值与冲击速度、最大跨中位移和跨中残余位移与冲击速度在不发生严重剪切破坏时均满足近似线性关系。分析还表明,具有较好延性的深梁具有更好的抗冲击性能。最后,通过对比分析冲击力、支座反力和惯性力时程曲线,得出采用冲击力峰值和支座反力峰值作为深梁的抗冲击承载力均不准确的结论。