钢筋混凝土梁式构件抗爆分析的改进等效单自由度方法

爆炸荷载作用下钢筋混凝土梁式构件可能会出现多种破坏模式，主要有弯曲破坏、直剪破坏和弯剪联合破坏等。现有结构构件抗爆分析方法主要考虑爆炸荷载下结构构件的弯曲破坏，对直剪破坏和弯剪联合破坏研究较少，尤其缺少快速准确的抗爆分析方法。基于等效单自由度模型理论，改进了钢筋混凝土梁抗爆分析的直剪单自由度方法，提出了直剪、弯剪联合破坏的判定准则，给出了两种破坏模式下钢筋混凝土梁动态响应的计算方法。进一步考虑爆炸荷载作用下钢筋混凝土梁的弯曲破坏、直剪破坏和弯剪联合破坏，提出钢筋混凝土梁式构件抗爆分析的改进等效单自由度方法，并给出了其分析步骤。该方法可以直接评估爆炸荷载下钢筋混凝土梁式构件的破坏模式，并计算其动态响应。通过有限元软件LS-DYNA数值模拟了不同爆炸工况下钢筋混凝土梁式构件的动态响应和破坏模式，与改进的等效单自由度方法的计算结果进行了对比，验证了提出的改进等效单自由度分析方法的正确性。     

考虑应变率效应的钢筋混凝土动态纤维梁单元模型

为准确描述钢筋混凝土结构的非线性地震灾变过程，建立了一种基于显式算法可考虑地震作用应变率效应的钢筋混凝土动态纤维梁单元模型，并以材料子程序(VUMAT)的形式嵌入ABAQUS有限元分析平台中。对混凝土、钢筋以及钢筋混凝土柱动态加载试验进行了数值模拟，测试并验证该模型用于钢筋混凝土材料及构件动态性能分析的准确性和有效性。研究结果表明，所提出的钢筋混凝土动态纤维梁单元模型计算精度较高，能够准确并实时反映地震作用下应变率对材料及构件动态性能的影响，可为精确计算钢筋混凝土结构在地震作用下的非线性动力反应提供理论基础。     

碳纤维布加固混凝土T形梁试验及有限元分析

在碳纤维布加固桥梁用钢筋混凝土 T 形梁抗弯试验的基础上,应用有限元方法对其进行了力学性能分析,并与试验结果进行了对比,有限元计算结果与试验结果具有较好的一致性,能很好地预测并模拟碳纤维布加固混凝土梁的抗弯性能,为以后的数值研究工作奠定了基础。     

Modelling shear–flexure interaction in equivalent frame models of slender reinforced concrete walls

Quasi‐static cyclic tests on reinforced concrete (RC) walls have shown that shear deformations can constitute a significant ratio of the total deformations when the wall is loaded beyond the elastic regime. For slender RC walls that form a stable flexural mechanism, the ratio of shear to flexural deformations remains approximately constant over the entire range of imposed displacement ductilities. This paper proposes a method for incorporating shear‐flexure interaction effects in equivalent frame models of slender RC walls by coupling the shear force‐shear strain relationship to the curvature and axial strain in the member. The suggested methodology is incorporated in a finite element consisting of two interacting spread inelasticity sub‐elements representing flexural and shear response, respectively. The element is implemented in the general finite element code IDARC and validated against experimental results of RC cantilever walls. In a second step, it is applied in inelastic static and dynamic analyses of tall wall and wall‐frame systems. It is shown that ignoring shear‐flexure interaction may lead to erroneous predictions in particular of local ductility and storey drift demands. Copyright © 2013 John Wiley & Sons, Ltd.     

大气环境条件下钢筋混凝土受弯构件抗力退化分析

混凝土碳化、钢筋锈蚀、保护层胀裂引起混凝土结构性能退化,在试验研究和非线性有限元分析的基础上,建立了锈蚀钢筋混凝土受弯构件正截面和斜截面承载性能分析方法和计算模型,通过实例分析了锈蚀钢筋混凝土受弯构件正截面抗弯、斜截面抗剪性能变化特征和规律。     

Finite difference analysis of simply supported RC slabs for blast loadings

A finite difference procedure that can account for strain-rate effects, both shear and flexural deformations, permits variations in cross-section geometry and strength and loading over the length of a component is proposed to accurately and efficiently analyze the dynamic response of a simply supported structural member under blast loads. A section-based layered analysis model that accommodates varying strain rates across a member’s cross-section is used to derive sectional moment–curvature relationships. A formula is derived to estimate the distribution of strain rate over the depth of a cross-section along the length of the member, and the corresponding strain rate effects are incorporated into the section-based layered analysis model. The Timoshenko beam equations that include both shear deformations and rotational inertia are solved numerically using an explicit finite difference scheme. The accuracy of the proposed finite difference analysis model is part validated using results of blast testing of reinforced concrete slabs with combinations of explosive weights and standoff distances. The results are also compared with those obtained by conventional single-degree-of-freedom (SDOF) analysis and finite element (FE) analysis using solid elements. The finite difference analysis procedure is both fast-running and accurate and most suitable for design office application, combining the speed of SDOF analysis and the detail and accuracy of FE analysis.     

Numerical simulation on seismic retrofitting performance of reinforced concrete columns strengthened with fibre reinforced polymer sheets

This paper evaluates the seismic performance of reinforced concrete columns retrofitted with fibre reinforced polymer (FRP) sheets through numerical simulations of the load–deformation response using two-dimensional finite element analysis (2D-FEA). The relatively rational mesh configuration is verified through comparison of analysis results obtained from the different mesh configurations. The seismic performance of three reinforced concrete (RC) columns strengthened with FRP sheets is assessed through a series of parametric studies, and the applicability of existing crack models and constitutive relationships on crack discontinuity and concrete compressive behaviour are validated. Comparisons of analysis results with tests shows that an equivalent uniaxial strain model and a failure criterion can be used to accurately simulate nonlinear behaviour and the failure of concrete under a biaxial stress state, respectively. Moreover, it is shown that a modified confinement model can be simply adopted to evaluate confined effects from hoop steel and FRP on concrete, which generally operate in three-dimensional confinement. Lastly, the seismic retrofitting performance of RC columns wrapped with FRP sheets is verified by analysing load–deformation responses and the progression of stress–strain at inflection points and bottoms of the columns.     

冲击波和破片联合作用下RC柱的损伤分析

为了研究冲击波和破片联合作用下钢筋混凝土柱的抗爆性能,应用有限元分析软件ANSYS/LS-DYNA对近爆作用下钢筋混凝土柱的损伤过程及破坏机理进行数值模拟分析,同时将冲击波单独作用、破片单独作用、二者联合作用下钢筋混凝土柱的动力响应进行了对比。结果表明:近距离爆炸作用下,冲击波先于破片达到柱子,柱子在冲击波作用下产生一定损伤,在此基础上又受到破片群的侵彻而呈现弯曲破坏;柱位移响应达到最大值的时间主要由破片作用控制;破片群对柱的破坏远大于冲击波对柱的破坏,冲击波与破片联合作用效应大于任一个单独作用效应,且大于二者单独作用时的线性叠加,在抗爆设计中应当考虑破片效应及联合作用。     

爆炸荷载作用下钢筋混凝土柱的动力响应与破坏模式

在爆炸荷载作用下,钢筋混凝土构件和结构的动力响应较之地震荷载和静态荷载作用下要复杂得多。运用有限元显式动力分析软件LS-DYNA,建立了典型钢筋混凝土柱的三维有限元模型,该模型对钢筋混凝土采用分离式建模,并且考虑了材料的应变率效应和钢筋与混凝土间的粘结滑移。在该有限元模型的基础上,通过对爆炸荷载作用下钢筋混凝土柱动态响应的数值模拟,研究了钢筋混凝土柱在爆炸荷载作用下可能的破坏模式及其规律。同时,运用参数化分析方法,研究了截面惯性矩、混凝土轴心抗压强度、纵筋配筋率和配箍率等参数对钢筋混凝土柱在爆炸荷载作用下的动态响应的影响,在数值模拟结果的基础上,分析提出了钢筋混凝土柱抗爆设计时应当注意的问题。研究结果表明:在爆炸荷载作用下,钢筋混凝土柱的破坏模式不仅和自身的特性有关,还取决于爆炸荷载的类型。提高柱截面惯性矩和混凝土轴心抗压强度,能够显著降低钢筋混凝土柱在爆炸荷载作用下的柱中水平位移,从而提高其抗爆性能。增加配箍     

爆炸荷载作用下钢筋混凝土构件动力响应的数值模拟

考虑了高应变率下混凝土和钢筋的动态本构模型,根据已有试验资料对炸药、钢筋混凝土构件和两者之间的空气建立数值模型,使用显式动力有限元软件LS-DYNA模拟了空气中点源炸药爆炸产生的爆轰冲击作用于钢筋混凝土构件和爆炸荷载作用下构件动力响应的全过程。结果表明,钢筋混凝土构件受到爆轰冲击的作用区域主要集中在构件迎爆面,构件背爆面受到的绕射冲击作用相比可以忽略;构件内应力波的传播不规则,同一位置处剪切应力波峰值早于弯曲应力波出现,构件的易损部位和爆轰冲击的主要作用位置有关,构件中部较端部更易发生弯曲破坏,而端部较中部更易发生剪切破坏。数值模拟结果和试验数据具有较好的一致性。成果表明,本文的数值模拟方法可以更准确地模拟爆炸荷载作用下钢筋混凝土构件的破坏机理和研究构件抗爆能力。     

高强钢绞线网-聚合物砂浆加固RC梁的有限元分析

高强钢绞线网-聚合物砂浆加固技术（SMPM）是一种先进的新型加固技术。本文利用通用有限元软件ANSYS对该加固技术加固RC梁进行了数值模拟分析,包括对抗弯及抗剪加固梁的挠度、应变、应力等的分析,并与相关试验结果进行比较,发现分析结果与试验结果吻合较好,为该加固方法提供了有效的理论依据。     

A simplified approach for predicting temperature in reinforced concrete members exposed to standard fire

For evaluating fire resistance of a reinforced concrete member, temperature profile in the cross section of the member is required. Current simplified approaches and design graphs do not yield reliable temperature predictions in rebar and concrete. In this paper, a simplified approach is proposed for evaluating cross-sectional temperatures in fire-exposed reinforced concrete members. The approach is derived through statistical nonlinear regression analysis, utilizing data generated from finite element analysis. The parameters that were varied in the finite element analysis include sectional geometry, concrete characteristics and fire exposure conditions. The validity of the approach for different types of concrete is established by comparing predictions from the proposed equation with data from fire tests and finite element analysis. Through these comparisons it is shown that the proposed equation gives better predictions of temperatures in reinforced concrete members. The applicability of the proposed approach in design situations is illustrated though a numerical example. The simplicity of the proposed method makes it attractive for use in design situations and for incorporation in design standards.     

施工期钢筋混凝土受弯构件承载性能研究

研究施工期钢筋混凝土受弯构件的受力特征并建立承载力计算模型,为分析施工期钢筋混凝土结构的承载性能提供可靠的理论依据,对钢筋混凝土结构施工期的安全性分析与控制以及钢筋混凝土结构全寿命分析具有重要的理论意义和实际价值。选取14,180 d两个混凝土龄期,对4根钢筋混凝土梁进行承载力试验,观测试件的破坏形态及变形特点,对比两个龄期极限弯矩值的大小,分析跨中挠度、跨中混凝土应变分布、钢筋自由端滑移等变量随荷载的变化规律。通过对施工期钢筋混凝土受弯构件的数值模拟,分析施工期钢筋混凝土受弯构件主要的受力特征。运用极限平衡理论,建立施工期钢筋混凝土受弯构件正截面承载力的计算模型,分析施工期钢筋混凝土受弯构件承载力随龄期而变化的规律。     

Seismic fragility of short period reinforced concrete structural walls under near-source ground motions

The Bayesian parameter estimation technique is used to develop probabilistic displacement and strength capacity and demand models for reinforced concrete structural walls. Experimental data are used to develop the capacity models, and nonlinear dynamic analysis is employed to develop the demand models. Both flexural and shear failures are accounted for. These models are used to assess the seismic fragility of an example RC structural wall. As a new measure of the ground motion intensity, the significant peak ground acceleration is defined and incorporated in the probabilistic demand models and fragility assessment. It is shown that, for short period structures, this measure better correlates with the inelastic response than the elastic response spectrum.     

Analytical models for the nonlinear seismic analysis of reinforced concrete structures

This paper discusses the analytical techniques for nonlinear dynamic analysis of reinforced concrete structures. The paper reviews the strain-rate effect, damping, and the hysteretic behaviour of structural members. Three classifications of analytical models of RC structures are reviewed, and their applications to the different types of structural systems discussed. The three groups are: (1), simple models; (2), line element models; (3), finite element models. A large portion of this paper discusses different hysteresis and analytical line element models of RC members and their application to structural systems.     

基于空间等效桁架单元方法的钢筋混凝土结构非线性分析

针对传统有限元分析的复杂性以及裂缝描述不准确等缺点,从空间应力单元出发,结合平面等效桁架单元的研究方法,提出了一种空间等效桁架单元;基于空间等效桁架单元和空间应力单元刚度等效的原则,推导了等效后的单元刚度矩阵、杆件截面面积和杆件轴力计算公式,探讨了空间等效桁架单元应用于钢筋混凝土结构非线性分析的相关问题;借助ANSYS10.0采用该方法对一桥墩结构进行计算分析,并与采用平面等效桁架单元方法和试验方法所得结果进行了对比。结果表明:采用该方法对钢筋混凝土结构进行分析能够满足工程精度要求,并且能够准确描述裂缝的开展。     

两层单跨缩尺RC框架结构外爆炸试验数值模拟

基于已有1/4缩尺钢筋混凝土(RC)框架结构爆炸试验,采用有限元软件LS-DYNA建立了精细化有限元模型,系统全面地分析了爆炸荷载作用下开口框架、带填充墙框架、带部分开洞填充墙框架、车库4种结构形式的动态响应行为,对爆炸冲击波超压、冲量、结构局部及整体响应情况进行了数值模拟,并与试验结果进行对比分析。结果表明:当空气、炸药网格尺寸为50 mm×50 mm时,有限元模型可以较好地预测爆炸冲击波的传播过程和结构响应情况; 框架中柱的正面反射超压模拟值呈上小下大的梯度分布; 框架中柱的冲量模拟值和试验值较为吻合,正面冲量呈上小下大的梯度分布,背面冲量在楼层位置和填充墙附近明显增大; 底层框架中柱的损伤破坏与试验接近,跨中位移模拟值和试验值相对误差小于5%; 填充墙能够阻止爆炸冲击波在结构内部传播,但显著增加中柱位置的冲击荷载和底层楼板上下表面压力差; 通过对比模拟结果与试验结果验证了数值模拟方法、网格尺寸、材料模型与参数取值的正确性与适用性,可为原型RC框架结构抗爆响应和破坏倒塌分析提供有益的参考。     

A simplified approach for predicting temperatures in insulated RC members exposed to standard fire

Fire resistance of concrete structural members can be enhanced through the application of external fire insulation on the surfaces of concrete member. For evaluating fire resistance of such insulated RC members, temperatures in concrete and steel reinforcement are to be known. This paper develops a simplified approach for predicting cross-sectional temperatures in an insulated RC structural member exposed to standard fire. The approach is derived by replacing the insulation layer into an equivalent concrete thickness layer and then undertaking statistical regression analysis on temperature data of modified concrete section. The effect of critical parameters, including geometry of concrete member and insulation, thermal properties of concrete and fire insulation, and duration of fire exposure is accounted for in temperature equations. The validity of the approach is established by comparing predictions from the proposed equation with data generated from fire tests and finite element analysis. These comparisons show the proposed equation gives reasonable prediction of temperatures, within a range of ±10%, in insulated concrete members. The applicability of the proposed approach in design situations is illustrated though a numerical example. The simplicity of the proposed method makes it attractive for use in design situations and for incorporation in design manuals.     

爆炸荷载作用下钢筋混凝土板破坏评定方法

压力-冲量(P-I)曲线是结构构件在爆炸荷载作用下的初始设计及在爆炸荷载作用后的破坏评定的有效工具。目前,确定结构构件的P-I曲线采用的方法均是基于单自由度结构体系假定的,并且多以结构构件的中点位移作为破坏指标。然而在爆炸荷载作用下,结构构件大多因高阶响应而发生局部破坏,且可能发生弯剪破坏。因此,通过将结构构件简化为单自由度体系模型并且选择结构构件中点位移为单一破坏指标获得的结构构件的P-I曲线,不能准确评定其破坏程度。利用LS-DYNA有限元动力分析软件,建立了典型钢筋混凝土板在爆炸荷载作用下响应和破坏的分析方法,提出了基于钢筋混凝土板跨中截面受弯剩余承载力的破坏指标以及利用数值方法确定钢筋混凝土板跨中截面受弯剩余承载力的步骤。同时,综合分析数值模拟结果,拟合了钢筋混凝土板P-I曲线的数学表达式,提出了一种简化了的确定钢筋混凝土板P-I曲线的方法,采用该方法确定的P-I曲线可用来对任意爆炸荷载作用后钢筋混凝土板的破坏进行评定。     

Progressive collapse performance analysis of precast reinforced concrete structures

In this paper, the progressive collapse performance analysis of precast reinforced concrete (RC) structures is performed. A numerical simulation framework for precast RC structures is developed on the basis of the OpenSEES software, where the fiber frame element is used for beam and column type members and Joint2D element is used for the beam‐to‐column connections. The conjugated material models are then introduced, and a min–max failure criterion is imposed on the original models to reflect the steel fracture and concrete crushing when the structure is undergoing progressive collapse. In addition, to overcome the computational difficulties arisen from progressive collapse behavior, two enhanced nonlinear solutions , that is, the consistent quasi‐Newton algorithm and the explicit KR‐α algorithm, are employed, respectively, for static and dynamic analysis. A 10‐storey prototype precast RC structures is designed to verify the developed numerical framework, and the progressive collapse resisting mechanism of the structures is investigated through both static pushdown analysis and dynamic column‐removal analysis. Finally, influences of some typical parameters in precast RC structures on their progressive collapse performance are studied.