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。     

基于实测频率的钢筋混凝土柱爆炸损伤快速评估方法

钢筋混凝土柱作为混凝土结构的关键受力构件,在爆炸荷载作用下,其破坏及失效可能进一步引发结构的连续倒塌,加剧灾害的程度.因此,爆炸作用后钢筋混凝土柱的损伤评估对于灾后结构性能评估具有重要意义.但由于灾后爆炸荷载确定困难,爆炸荷载作用下钢筋混凝土柱损伤评估的超压-冲量(P-I)曲线法很难应用于灾后钢筋混凝土构件的爆炸损伤评估.为此,提出了一种基于现场实测频率变化的钢筋混凝土柱爆炸损伤快速评估方法.建立了钢筋混凝土柱模态试验的数值方法,通过数值模态试验提取爆炸前后钢筋混凝土柱的一阶频率,建立钢筋混凝土柱的一阶频率与基于竖向剩余承载力的损伤指标的关系.参数分析结果表明,相同爆炸荷载下,矩形钢筋混凝土柱基于频率变化的损伤指标随配箍率、纵筋配筋率的增大而降低,随长细比的增大而增加.并运用最小二乘曲线拟合方法,得到柱损伤程度与频率变化之间的关系式,从而实现在爆炸现场通过频率测试对矩形钢筋混凝土柱爆炸损伤程度的快速评估.     

基于实测频率的钢筋混凝土柱爆炸损伤快速评估方法

钢筋混凝土柱作为混凝土结构的关键受力构件,在爆炸荷载作用下,其破坏及失效可能进一步引发结构的连续倒塌,加剧灾害的程度.因此,爆炸作用后钢筋混凝土柱的损伤评估对于灾后结构性能评估具有重要意义.但由于灾后爆炸荷载确定困难,爆炸荷载作用下钢筋混凝土柱损伤评估的超压-冲量(P-I)曲线法很难应用于灾后钢筋混凝土构件的爆炸损伤评估.为此,提出了一种基于现场实测频率变化的钢筋混凝土柱爆炸损伤快速评估方法.建立了钢筋混凝土柱模态试验的数值方法,通过数值模态试验提取爆炸前后钢筋混凝土柱的一阶频率,建立钢筋混凝土柱的一阶频率与基于竖向剩余承载力的损伤指标的关系.参数分析结果表明,相同爆炸荷载下,矩形钢筋混凝土柱基于频率变化的损伤指标随配箍率、纵筋配筋率的增大而降低,随长细比的增大而增加.并运用最小二乘曲线拟合方法,得到柱损伤程度与频率变化之间的关系式,从而实现在爆炸现场通过频率测试对矩形钢筋混凝土柱爆炸损伤程度的快速评估.     

弯剪破坏钢筋混凝土柱的荷载-变形关系

在传统的弯曲截面理论分析方法基础上,结合钢筋混凝土弯剪破坏柱的受力特点,对太平洋地震工程研究中心(PEER)钢筋混凝土柱抗震性能试验数据库中的试验数据进行分析,提出了一种确定弯剪破坏钢筋混凝土偏心受压构件荷载-变形关系的实用方法。研究结果表明:采用该方法计算得到的荷载-变形曲线与试验结果吻合良好,可用于确定地震作用下弯剪破坏钢筋混凝土偏心受压构件恢复力模型的骨架曲线。     

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     

受火后钢筋RPC简支梁受力性能试验研究

为了研究受火后活性粉末混凝土(RPC)构件的力学行为及其变形性能,完成5根受火后钢筋RPC简支梁受弯试验,获得了梁的正截面剩余承载力、荷载 跨中位移曲线及裂缝发展规律,考察了配筋率、荷载水平、受火时间等因素对受火后钢筋RPC简支梁受力性能的影响,并将试验结果与常温下受力性能进行对比分析。结果表明：配筋率为220%~5.13%、受火时间135min时,受火后钢筋RPC简支梁均保持为适筋破坏,且配筋率越大,剩余承载力越高,荷载水平越高、受火时间越长,剩余承载力越低;通过简化计算模型得到受火后钢筋RPC简支梁正截面剩余承载力计算值,与试验值吻合较好;受火后配筋率不低于3.94%的各试验梁剩余承载力与常温下相比降低了10%左右,钢筋RPC简支梁受明火作用后的承载力损失较小。     

爆炸荷载作用下外贴FRP加固钢筋混凝土双向板试验研究

通过集团装药隔土爆炸荷载作用下4块外贴FRP条带加固钢筋混凝土双向板和1块普通板的对比试验,考察了裂缝的产生、开展过程及分布形状,分析了FRP加固板的荷载、位移、加速度、钢筋和混凝土以及FRP应变动力响应时程,研究了FRP加固板的抗爆破坏特征。研究结果表明：外贴FRP条带加固能有效延缓混凝土的开裂,限制裂缝的开展,改善钢筋混凝土板的抗爆性能;外贴FRP条带加固后,RC双向板的跨中位移响应、混凝土和钢筋应变响应明显降低,结构的抗爆炸冲击波能力得到明显提高;外贴FRP条带加固双向板在爆炸冲击荷载作用下的破坏形态有受弯破坏和弯曲屈服后的剪切破坏,外贴FRP条带在极限状态时发生了剥离及断裂破坏。图12表6参10     

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。     

钢筋混凝土柱弯剪破坏恢复力模型骨架曲线

为研究弯剪破坏柱的抗震性能,进行了不同设计参数的24根钢筋混凝土（RC）柱的拟静力试验,分析了剪跨比、轴压比及配箍率（箍筋间距）对柱破坏模式及其抗震性能的影响,给出了确定弯剪破坏柱开裂、屈服和破坏时对应荷载及位移的计算方法,并提出了建立弯剪破坏柱恢复力模型骨架曲线的简化方法。研究结果表明：发生弯剪破坏的柱,其变形在2Δy～4Δy前弯曲作用明显,滞回曲线饱满,但之后由于抗剪能力不足会突然丧失承载力;利用弯剪破坏柱的3个特征点（开裂点、屈服点、剪切破坏点）建立其恢复力模型骨架曲线的方法,简化了RC柱的受力分析,可用于计算地震作用下弯剪破坏RC柱的荷载-变形全曲线。建立的恢复力模型骨架曲线与试验曲线吻合较好。     

爆炸荷载作用下框架结构的薄弱部位分析

采用通用有限元软件SAP2000模拟钢筋混凝土框架在不同部位受到爆炸荷载作用的动力响应过程,并对荷载作用相应部位梁柱节点的位移进行对比分析。分析结果表明,荷载作用于角柱所在边跨引起的梁柱节点位移均大于荷载作用于中跨的梁柱节点位移。说明爆炸荷载对框架结构的影响与荷载作用部位密切相关,边跨动力响应大于中跨,而边跨中的角柱更是结构抗爆设计关键构件。     

Probabilistic response evaluation for RC flexural members subjected to blast loadings

The probabilistic responses of the maximum displacement and displacement ductility factor for a reinforced concrete (RC) flexural member against potential blast loadings are evaluated through a nonlinear dynamic analysis of its equivalent single-degree-of-freedom (SDOF) system. Monte-Carlo simulation is used in the analysis. Some differences are observed between the actual responses of the RC member and those of the equivalent SDOF system due to the complex behaviours of reinforced concrete structural members under blast conditions. Two non-dimensional indices are defined to quantify the differences and their expressions are generated through a large amount of numerical and statistical analyses. The approach of utilizing the indices into a probabilistic response assessment of RC flexural members accounting for different kinds of uncertainties is illustrated via four numerical examples which are verified through nonlinear dynamic finite element analysis. It is concluded that the probabilistic response of RC flexural members obtained from the developed approach have a similar distribution with those from probabilistic nonlinear finite element analysis.     

多层框架结构在其地下室内部爆炸冲击下的连续倒塌机理研究

为了研究框架结构在地下室内部爆炸时的连续倒塌特性,运用有限元显式动力分析软件LS-DYNA建立了一个含有1层地下室、4层地上结构的钢筋混凝土框架结构分离式模型;考虑钢筋和混凝土共节点的连接方式,采用三阶段模拟法将不同炸药作用位置时结构的连续倒塌模式进行对比,分析梁、板、柱等主要受力构件的具体破坏方式;阐释结构在地下室内部爆炸后的不同倒塌破坏模式。结果表明:地下室内部爆炸发生后地上一层破坏严重,在地下结构柱附近爆炸使得结构节点处破坏严重,从而导致结构的连续倒塌。     

A methodology for evaluating dynamic responses of steel columns subjected to blast load under different situations

In recent studies, the uniform simplified distribution blast load and numerical simulation have proven to be prevalent in the use of investigating structural components dynamic behaviour during blast events, whilst neglecting the negative phase pressure. This study compares the steel column's response during the total pressure period to that of its response during only the positive stage. Moreover, the real blast pressure has varying values depending on the point distance and explosion incident angle. The real blast load curve was derived by using a specialised program to calculate pressure at different points on the steel column vertical line; and the results were used to compare its impact with the uniform and concentrated cases. Also ABAQUS finite element code was used to check the validity of the single-degree-of-freedom (SDOF) analysis method when the column is subjected to axial and transverse blast loads. The obtained results show the SDOF inability through dynamic reaction calculations. In addition, SDOF has limitations in dealing with dynamic steel response when the axial load ratio was greater than 0.5. Damage prediction methods and equations were introduced through different concepts and the ductility ratio was used to estimate the damage level of 100 kg TNT at 4.5 m stand-off distance. The strain rate effects were included in the material with different scenarios based on the dynamic increase factor.     

Development of dimensionless P-I diagram for curved SCS sandwich shell subjected to uniformly distributed blast pressure

The curved steel-concrete-steel (SCS) sandwich shell was recently proposed to resist blast loading and it showed better blast resistant performance as compared to flat SCS sandwich shell via developing compressive force along the shell. In this paper, a dimensionless Pressure-Impulse (P-I) diagram was constructed as a convenient tool to predict the damage level of curved SCS sandwich shell subjected to uniformly distributed blast loading. The curved SCS sandwich shell was equivalent to a single-degree-of-freedom (SDOF) system and the equation of motion was established by employing the Lagrange’s equation. To construct the dimensionless P-I diagram, the energy balance method was utilized to yield the pressure and impulse asymptotes and the responses in the dynamic response regime were obtained via employing the SDOF method. Then, the finite element method was employed to validate the developed dimensionless P-I diagram. Finally, the procedures of using the constructed dimensionless P-I diagram to quickly conduct the blast resistant design of curved SCS sandwich shell were presented.     

利用塑性铰线理论求解墙体抗爆能力

有限元软件模拟结果发现,燃气爆炸荷载作用下四边约束墙体的破坏模式与双向（RC）板非常相似,故尝试使用塑性铰线法对墙体的抗爆能力进行试算。以传统的双向固支RC板塑性铰线理论为基础,结合砌块墙体的特点,推导出了四边约束墙体的极限抗爆能力机动法计算公式,通过可信的有限元计算结果反推出极限弯矩的取值,并回归出计算公式;重新计算的理论值与有限元模拟结果非常接近。表明完全可以参照普通RC双向板的塑性铰线理论对四边约束墙体进行极限抗爆能力的计算。     

Survivability of steel frame structures subject to blast and fire

The lesson learned from the terrorist attacks on buildings is the need to assure structures’ ability to sustain local damage without total collapse. Some of the terrorist attacks take the form of blast followed by fire which may cause catastrophic failure of the structure. This paper presents a numerical model for analyzing steel frame structures subject to localized damage caused by blast load and subsequently investigating their survivability under fire attack. The proposed numerical method adopts a mixed-element approach for modeling large-scale framework and it is proven to be sufficiently accurate for capturing the detailed behaviour of member and frame instability associated with the effects of high-strain rate and fire temperature. Design implications related to the use of various numerical models for separate assessment of blast and fire resistance of steel structures and their components are discussed. Fire–blast interaction diagrams are generated to determine the fire resistance of columns considering the initial damage caused by the blast loads. A multi-storey steel building frame is analyzed so that the complex interaction effects of blast and fire can be understood and quantified. The frame is found to be vulnerable, as it possesses little fire resistance due to the deformation of key structural elements caused by the high blast load.     

溪洛渡电站地下厂房爆破损伤范围及判据研究

通过现场爆破振动测试和数值模拟方法研究地下厂房爆破损伤范围及判据;在应用FLAC3D数值模拟软件中,损伤变量D被引入弹塑性本构模型,同时将简化的三角形荷载作为爆破冲击荷载施加在炮孔孔壁上,并根据岩石中有效应力确定爆破损伤范围。调整同时起爆炮孔数目,改变单段起爆药量,研究爆破损伤范围与单段药量的关系,结果表明:损伤深度和损伤水平半径均随单段药量的增加而增大,损伤范围随着炮孔深度增加而减小,爆破损伤最大水平半径出现在炮孔顶部面上。根据爆破近区质点速度衰减规律,并通过数据拟合得到对应于不同单段起爆药量的最大损伤水平半径和相应部位爆破质点临界损伤振动速度的关系,临界损伤振动速度可作为爆破损伤安全判据。研究成果有效地应用到实践中,对类似开挖爆破工程具有一定指导意义。     

反复荷载作用下混凝土异形柱结构累积损伤分析及试验研究

反复荷载作用下混凝土结构的累积损伤将加重其力学性能的劣化,实用的结构累积损伤评价模型,可以定量确定结构的剩余刚度和强度,为结构安全评估和修复加固提供理论依据。本文以结构在理想无损伤状态下外力所作的功为初始标量,依据能量耗散原理,提出反复荷载作用下结构累积损伤评价模型。应用该损伤模型结合试验数据分别对L形截面柱、异形柱框架节点和异形柱框架结构进行了累积损伤分析,所得到的损伤评价指标,能较好地反映在反复荷载作用下钢筋混凝土结构的累计损伤状态。