Drift-controlled design of reinforced concrete frame structures under distant blast conditions—Part II: Implementation and evaluation

The model for the calculation of an equivalent static force (ESF) and the design procedure with ESF for single-degree-of-freedom (SDOF) systems presented in the first part of the two-part paper are extended into the design for a reinforced concrete (RC) frame structure under distant blast conditions. An empirical formula for the ESF factor involved in the ESF model is presented based on sample points obtained by comparing the nonlinear dynamic responses of frame structures under the blast loading with the corresponding nonlinear pushover analysis of the structure due to an ESF. The use of the method is demonstrated with two six-storey RC frame structures. Numerical verification of the method indicates that the maximum inter-storey drift ratios (MIDR) of the two designed frame structures in comparison to their respective targets are conservative to some extent. The reasons that may lead to the conservative designs are discussed.     

Analysis of RC structures subjected to air-blast loading accounting for strain rate effect of steel reinforcement

A new method to calculate the dynamic strength of reinforced concrete (RC) structures, with emphasis on the embedded response of mild steel reinforcement, subjected to air-blast loading is derived. The proposed method is based on a single-degree-of-freedom (SDOF) system with appropriate modification for strain-rate effect. Approximate formulae are used and explained in detail. A numerical example is presented to show how the derived formulae are used for the analysis of concrete structures subjected to air-blast loading.     

建筑结构倒塌分析的单自由度模型

该文建议了一种能够用于建筑结构倒塌分析的单自由度滞回模型。该模型能够模拟骨架线的强化和峰值点后的退化、滞回捏拢、往复荷载作用下的承载力和刚度退化以及P-Δ效应等。为验证所建议的单自由度滞回模型用于结构倒塌分析的有效性和合理性, 以一座8 层钢筋混凝土框架结构为例, 对原型结构和按照基本模态等效的单自由度模型分别进行了IDA 倒塌易损性分析, 结果表明两者的倒塌易损性曲线吻合较好。     

Numerical derivation of pressure–impulse diagrams for prediction of RC column damage to blast loads

Pressure–impulse (P–I) diagrams are commonly used in the preliminary design or assessment of protective structures to establish safe response limits for given blast-loading scenarios. Current practice in generating the pressure–impulse diagram for structure components is primarily based on the simplified single degree of freedom (SDOF) model. The damage criterion is usually defined in terms of deformation or displacement response. Under blast loads, structures usually respond at their local modes, the equivalent SDOF system derived using the fundamental structure response mode might not be suitable. Moreover, structure is often damaged owing to brittle shear failure. In this case, the deformation-based damage criterion might not be able to give an accurate indication of local damage of a structural component. In this paper, a new damage criterion for RC column is defined based on the residual axial load-carrying capacity. A numerical method to generate pressure–impulse diagram for RC column is proposed. Parametric studies are carried out to investigate the effects of column dimension, concrete strength, longitudinal and transverse reinforcement ratio on the pressure–impulse diagram. Based on the numerical results, analytical formulae to predict the pressure–impulse diagram for RC column are derived. A case study shows that the proposed analytical formulae can be easily used to generate pressure–impulse diagram for RC columns accurately. The results are also compared with those obtained from the SDOF approach. It is shown that the proposed method gives better prediction of pressure–impulse diagram than the SDOF approach.     

考虑面力效应的HFR-LWC梁抗爆理论模型与试验验证

现有的抗爆设计规范通常将面力效应看作一种潜在的安全系数,而对面力作用在爆炸加载过程中的变化规律及其对结构抗力的贡献不做深入探索.该文对近距离爆炸荷载进行适当简化,并考虑面力效应的影响,建立一种基于等效单自由度(SDOF)法的梁式构件抗近距离爆炸分析模型.专门设计了一套面力加载装置,对8根考虑面力效应的混杂纤维轻骨料混凝...     

RC beams under blast load: Reliability and sensitivity analysis

The effects of blast loading on structures can be very dangerous: damages and failures are expected with serious threats to structural safety and human life. Materials stresses and strains are often pushed to the limit and the modelling of these phenomena can be very complex. In order to design blast-resistant structures it is very important to determine what are the key parameters of this problem.This paper presents a reliability and parametric analysis of the response of reinforced concrete (RC) beams under blast loads. The main aim is to highlight the key parameters of the problem in order to produce information useful for the design of reliable blast-resistant RC structures.The beam has been idealised as an equivalent SDOF system, in which strain-rate effects are accounted for. This approach is convenient from a computational point of view and it has been validated by a direct comparison with a more sophisticated finite element model and with experimental results found in literature. Then a sensitivity analysis of the parameters involved in beam response under blast load has been developed. Slenderness (which has a direct effect on stiffness) and peak load prove to be the most important parameters, but span length (which has an important influence on the mass) is also a key parameter. Other variables such as concrete strength and reinforcement ratio do not seem to have a strong correlation with the beam response.     

包覆泡沫铝钢梁动态位移的计算及影响因素

为考察运用FSI(流固耦合效应)能否考虑包覆泡沫铝对钢梁在爆炸荷载作用下最大动位移的影响及分析包覆泡沫铝衰减爆炸荷载作用下钢梁最大动位移的影响因素,运用理论及数值模拟方法分析了包覆泡沫铝钢梁在爆炸荷载作用下的动态位移变化情况。在验证理论及数值模拟结果可靠的基础上,对比理论结果与数值模拟计算结果的优缺点,并运用数值模拟分析影响包覆泡沫铝衰减钢梁在爆炸荷载作用下动位移的因素。结果表明:FSI可以考虑包覆材料对爆炸冲击波的衰减作用,但不能反映材料本身变化的影响(如材料厚度、屈服强度等);在计算包覆泡沫铝衰减爆炸荷载作用下钢梁最大动位移时,泡沫铝的厚度、屈服强度均具有最优解;增加刚性面板会放大包覆泡沫铝钢梁在爆炸荷载作用下的最大动位移。     

基于多尺度模型的RC框架撞击倒塌响应数值分析

为了在保证计算精度的同时提高撞击荷载作用下RC框架结构连续倒塌分析的计算效率,本文基于有限元软件LS-DYNA,建立了撞击响应分析的多尺度模型。针对该模型分别采用拆除构件法和撞击全过程分析法分析了撞击荷载下框架结构的连续倒塌动力响应。结果表明：拆除构件法在分析撞击作用下结构的连续倒塌时,由于忽略了撞击力及其对周围结构造成的初始损伤、初始位移和初始速度,低估了结构的动力响应,不能合理反映撞击作用下框架结构的破坏模式;多尺度模型能够准确模拟撞击作用下框架结构的动力响应和破坏模式,同时计算时间仅为精细模型的三分之一,满足整体结构系统撞击倒塌分析的需要。     

Dynamic Deformation of Clamped Circular Plates Subjected to Confined Blast Loading

In this paper, the dynamic deformation of thin metal circular plates subjected to confined blast loading was studied using high‐speed three‐dimensional Digital Image Correlation (3D DIC). A small‐scale confined cylinder vessel was designed for applying blast loading, in which an explosive charge was ignited to generate blast loading acting on a thin metal circular plate clamped on the end of the vessel by a cover flange. The images of the metal plates during the dynamic response were recorded by two high‐speed cameras. The 3D transient displacement fields, velocity fields, strain fields and residual deformation profiles were calculated by using 3D DIC. Some feature deformation parameters including maximum out‐of‐plane displacement, final deflection, maximum principal strain and residual principal strain were extracted, and the result was in good agreement with that simulated by AUTODYN. A dimensionless displacement was introduced to analyse the effects of plate thickness, material types and charge mass on the deflection of metal plates. DIC is also proven to be a powerful technique to measure dynamic deformation under blast loading.     

内爆作用下RC框架结构SAP数值模拟

利用SAP2000软件,在构件拆除法的基础上增加了爆炸冲击荷载对关键失效构件周围其他构件的直接作用,对内爆作用下的RC框架结构进行了动力非线性分析,并将分析结果与仅采用构件拆除法的分析结果进行了对比。通过对比计算结果可以看出,爆炸冲击荷载对失效构件周围其他构件的直接作用会对RC框架结构的损毁程度产生较大影响。与构件拆除法相比,SAP2000分析方法更符合内爆作用下RC框架结构的实际受荷情况。与利用ANSYSLS/DYNA等大型有限元软件进行显示动力分析相比,SAP2000分析方法更易于掌握,节省时间,更便于广大结构设计人员使用。     

内爆作用下RC框架结构SAP数值模拟

利用SAP2000软件,在构件拆除法的基础上增加了爆炸冲击荷载对关键失效构件周围其他构件的直接作用,对内爆作用下的RC框架结构进行了动力非线性分析,并将分析结果与仅采用构件拆除法的分析结果进行了对比。通过对比计算结果可以看出,爆炸冲击荷载对失效构件周围其他构件的直接作用会对RC框架结构的损毁程度产生较大影响。与构件拆除法相比,SAP2000分析方法更符合内爆作用下RC框架结构的实际受荷情况。与利用ANSYS LS/DYNA等大型有限元软件进行显示动力分析相比,SAP2000分析方法更易于掌握,节省时间,更便于广大结构设计人员使用。     

一种简化的R.C框架结构地震位移反应分析方法

采用单自由度体系等效多自由度体系,只考虑第一振型影响,确定结构最大位移反应。该文假定R.C框架结构屈服前刚度与强度相关,屈服位移由结构几何尺寸近似确定。结合我国建筑抗震设计规范,研究不同设计条件下R.C框架结构的超强系数,然后乘以设计地震作用确定结构的实际强度。根据结构屈服位移以及实际强度确定等效结构的有效周期。当有效周期大于特征周期时,结构最大非线性位移反应采用等位移原理确定,当有效周期小于特征周期时,结构最大非线性位移反应采用等能量原理确定。该方法与其它方法相比,避免了复杂的弹塑性动力或静力分析,不需要进行迭代计算,且与我国规范结合紧密,特别适合对既有结构快速评估。     

不同加载制度下RC框架梁抗震性能试验研究

为了研究不同加载制度下RC框架梁的抗震性能,分别采用4种加载制度对RC框架梁试件进行拟静力试验。结果表明：峰值位移（峰值荷载对应的位移）出现的越早,RC框架梁破坏时剪切变形成分越大,试件的最大裂缝宽度越大,塑性铰转角和延性系数越小,但塑性铰高度基本不变;随着循环位移幅值和循环次数的不同,框架梁的刚度、强度退化也有差异,表现为：在滞回曲线软化段,经历较大位移幅值循环（或较多次循环）后的RC框架梁比经历较小位移幅值循环（或较少次循环）后的RC框架梁刚度和强度退化快;同时,不同加载制度下RC框架梁的耗能能力存在差异,峰值位移出现早的框架梁其耗能能力较差。     

爆炸流场与玻璃幕墙动力响应的仿真计算方法

采用ALE有限元法进行了爆炸流场与复杂玻璃幕墙结构相互作用的三维动态仿真。针对数值仿真过程中计算效率过低的问题,根据显式有限元和距离爆炸冲击波试验问题的计算特点,利用高性能计算平台设计并实现了爆炸冲击波与玻璃幕墙动力响应的分步流固耦合仿真计算方法。研究了爆炸冲击波作用下幕墙玻璃的动力响应情况,通过与试验结果相比较,证实了该仿真方法的可行性,为玻璃幕墙结构的抗爆设计与改进提供了参考依据。     

钢筋混凝土异形柱空间框架抗倒塌试验研究

预知结构在偶然荷载作用下的失效机理和提供新荷载路径是异形柱框架结构抗倒塌设计的重要内容。进行1/3比例的两层3×2跨的底层边柱、角柱的突然失效试验及拟静力倒塌试验。分析钢筋混凝土异形柱空间框架的试验现象、裂缝分布、破坏过程及荷载-位移等,进行异形柱空间框架受力过程分析,研究异形柱空间框架结构的受力机制转换过程。研究结果表明：动力效应对异形柱空间框架的影响效果并不显著。试验中没有出现钢筋被拔出现象,裂缝主要集中在竖向构件支座处;异形柱空间框架的边柱、角柱倒塌破坏过程均经历了弹性阶段、弹塑性阶段、塑性阶段和悬链线阶段,边柱表现的悬链线效应远大于角柱的;楼板及梁的钢筋产生的悬链线效应在异形柱空间框架抗倒塌中发挥重要作用。     

爆炸荷载下盾构管片的动力响应分析

在综合国内外有关隧道抗爆理论和方法的基础上,忽略管片的变形,将管片假设为刚体,提出了一种爆炸荷载作用下管片结构动力分析的简化计算方法,该方法能模拟管片与管片之间、管片与螺栓间以及地基与结构间的相互作用。随后利用该方法对南京地铁进行了抗爆动力响应分析,得到了隧道的位移和速度时程曲线,研究了管片参数变化对结构动力响应的影响。计算结果表明,简化计算方法能准确反映隧道管片结构在爆炸荷载作用下的动力响应,是一个简便实用的计算方法,所得结果可为管片结构抗爆设计提供具有一定的参考价值。     

Dynamic response of walls and slabs by single-degree-of-freedom analysis—a critical review and revision

Single-degree-of-freedom (SDOF) methods for dynamic analysis of reinforced concrete flexural members subjected to blast or ground-shock loading are reviewed. It is concluded that the Equivalent single-degree-of-freedom method is an appropriate approximate method of analysis, but that the widely published parameters in common usage for two-way spanning members such as slabs and walls are inaccurate by up to almost 50% for some coefficients, due to inappropriate assumptions and approximations being used in their original derivation. Revised values of SDOF parameters are presented for two-way spanning members, based on modern finite element and yield-line calculations.     

爆炸荷载下钢筋混凝土柱动态响应分析的宏观模型

目前常用于爆炸荷载下钢筋混凝土柱动态响应分析的精细化模型,建模复杂、计算效率低,难以在大规模计算中应用。该文研究了纤维模型在模拟爆炸荷载下钢筋混凝土柱动态响应和破坏的缺陷,针对该缺陷在纤维模型的基础上引入弹簧单元,建立了爆炸荷载下钢筋混凝土柱动态响应分析的宏观模型,并给出了模型参数的确定方法。最后以某典型钢筋混凝土柱为例,分别通过精细化模型和宏观模型对其在不同爆炸工况下的动态响应和破坏进行对比分析,结果表明,提出的宏观模型在计算效率高的同时,能够明显弥补纤维模型的缺陷,达到和精细化模型相近的分析结果。     

爆炸荷载作用下钢筋混凝土结构的动态响应与破坏模式的数值分析

在爆炸荷载(尤其是脉冲荷载)作用下,除了常见的弯曲破坏形态之外,钢筋混凝土结构还可能发生直剪破坏和弯剪破坏。如何准确地预测爆炸荷载作用下的钢筋混凝土结构动态响应和破坏特征是当前抗爆结构领域十分关注的课题之一。该文介绍作者近年来在这方面的一些研究成果,主要有:将三参数形式的应变速率型材料模型推广应用于二维状态下的混凝土本构关系,建立了弹粘塑性混凝土结构有限元分析方法;基于Timoshenko梁理论和弹粘塑性理论,分别采用有限差分法和有限元法,建立了土中浅埋钢筋混凝土结构动力响应和破坏模式的有限差分和有限元分析方法。对爆炸荷载作用下的典型钢筋混凝土结构计算结果表明:基于Timoshenko梁理论的有限差分分析方法和有限元分析方法能较好地模拟梁的动态响应和弯曲、弯剪以及直剪的破坏模式,而二维弹粘塑性混凝土结构有限元分析方法只能较好地模拟梁的弯曲破坏模式。     

FRC框架结构基于等效单自由度模型的抗地震倒塌能力评估

为了快速评估建筑结构的抗地震倒塌能力,该文基于Adam等提出的等效单自由度模型,首先用Pushover分析方法对纤维增强混凝土(FRC)结构进行静力弹塑性分析,获得其基底剪力-顶点位移曲线,据此确定其力-变形关系;然后根据力-变形关系以及侧向位移形状函数,确定相应的等效单自由度模型的相关参数;按等效单自由度模型计算结构的抗地震倒塌能力。分别对某8层钢筋混凝土框架结构和FRC框架结构进行分析。结果表明:用与多自由度结构相应的等效单自由度模型评估FRC框架结构的整体抗地震倒塌能力是可行和偏于保守的;采用抛物线加载模式比倒三角加载模式得到更接近由IDA分析所得的结构抗地震倒塌能力中位值;在其他条件相同时,FRC框架结构比普通混凝土框架结构具有更高的抗地震倒塌能力。