冲击荷载作用后钢框架结构抗火性能探究

荷载的冲击会导致火灾问题发生,并且火灾与冲击荷载的协同作用下,建筑物会遭到不同程度破坏,致使倒塌问题出现概率增大。通过对建筑物的倒塌以及破坏的分析,认为提升钢框架结构抗火性能势在必行。该文即对冲击荷载作用后钢框架结构抗火性能展开深入分析,结合冲击荷载作用后对钢框架结构抗火承载力影响,从多角度出发,提出提高结构抗火性能的对策,旨在为相关从业者提供参考和借鉴。

冲击荷载作用下穿甲弹风帽的动应力试验研究

用动光弹实验方法研究了冲击荷载作用下穿甲弹风帽模型的应力波的传播过程 ,对其受冲击后的动应力状态进行了分析 ,用应力光学定律得到了模型内的动应力值。并根据应力波理论 ,推导出了风帽受冲击荷载作用时动应力的理论近似解 ,计算结果与实验结果非常一致。另外 ,这种方法还为改进风帽的结构设计提供了有益的建议。

冲击荷载作用下混凝土重力坝破坏特性分析

冲击荷载作用下混凝土重力坝破坏特性较静荷载作用下要复杂得多。采用钢板均匀冲击模拟水下循环冲击波对混凝土重力坝的作用,试验遵循几何和重力相似准则,对模型重力坝进行均匀冲击破坏特性研究,得到模型坝体的动力破坏特性,并对裂缝位置和扩展情况进行定位和追踪。试验结果表明:当坝体遭受循环均匀冲击荷载时,上游坝面坝体最大动应变不再在坝踵处,而是位于坝体中部;坝头部位是抗冲击的薄弱部位,最先出现开裂破坏;坝体破坏模式包括贯穿性断裂、碎裂、层裂和抛掷等。试验结果可为大坝的运行管理、防爆抗振设防及安全评价提供理论依据和技术支持。

冲击荷载作用下饱和软粘土孔压计算模式

在考虑周围压力、冲击能、冲击遍数和冲击次数几个因素相互关系的基础上先建立了一个实用的孔压计算模式,并对试验结果进行了验证分析。对影响孔压发展的诸如土性、固结应力状态、荷载强度等因素进行了简要分析。

变截面构件受冲击荷载作用时的动应力计算

本文根据能量法导出了交截面构件受冲击荷试作用时的动应力计算公式，它对于理论研究及工程实际都具有非常重要的参考价值．

冲击荷载作用下板式橡胶桥梁支座劣化的关联分析

板式橡胶支座是中小跨径桥梁的主要支座型式,是连接桥梁上下部结构的重要构件,劣化是其破坏的主要形式之一。基于灰色关联理论,对冲击荷载作用下的板式橡胶支座劣化进行影响因素分析,可为桥梁支座施工及养护提供一个科学的参考依据。

冲击作用下框架结构的连续性倒塌性能

借助ANSYS/LS-DYNA软件建立了钢筋混凝土框架的有限元模型,研究了钢筋混凝土框架在冲击荷载作用下的连续性倒塌性能,冲击体质量为1000 kg,冲击速度为4 m/s。通过对钢筋混凝土构件冲击试验和框架倒塌过程的验证,保证了数值模拟的有效性。分析结果表明:冲击中柱后结构倒塌过程中,有"拱作用"向"悬索作用"转换的机制,中柱顶部位移先向上后向下,边柱顶部位移先向外后向内;同样冲击作用下,柱轴力越小,则抗冲击能力越强,不同的偏压作用对柱的抗冲击性能的影响不同;加密柱箍筋能够增强钢筋混凝土柱的抗冲击能力,延缓甚至避免钢筋混凝土框架结构的连续性倒塌。

钢管再生混凝土抗冲击性能研究

钢管再生混凝土组合结构能够在充分利用钢管和再生混凝土两种材料的优势,还可以有效解决废混凝土堆放导致的环境污染和相关的社会问题。然而,钢管再生混凝土梁柱或桥墩等构件在服役期间可能遭受爆炸的冲击作用或飞机、汽车、船体等移动物体的碰撞,将会影响构件的安全性能,严重时可能导致整个结构的倒塌。因此,要想将钢管再生混凝土构件广泛的应用实际工程中,构件在侧向冲击荷载作用下的工作机理的研究显得尤为重要。本文阐述了钢管再生混凝土构件的抗冲击性能研究现状,并对目前研究存在的主要问题和发前景进行了讨论。

动静荷载联合作用下冲击地压巷道破坏机制大型地质力学模型试验研究

采用静载模拟巷道初始地应力场,TNT爆炸模拟冲击地压,利用大型地质力学模型试验机对巷道在动、静荷载联合作用下的响应规律进行研究。试验中施加了相当于相似材料单轴抗压强度的最大静压力,荷载侧压比为1/3。在模型内部相同位置依次施加10,15和20 g TNT动荷载,在最后一次爆炸荷载作用下,洞室出现抛掷型冲击地压破坏现象。试验结果表明:巷道冲击地压灾害是动、静荷载联合作用的结果;在冲击瞬间作用下,冲击荷载与已存在静荷载叠加,使得巷道围岩压力迅速增加,叠加后作用力大于围岩承载能力时,引发围岩冲击破坏;围岩产生的冲击变形与巷道开挖后产生的初始变形叠加,形变超出围岩的变形能力时,洞壁首先发生破坏。围岩变形和冲击破坏范围与冲击力的大小及地应力水平相关性显著。

沥青路面坑槽几种修补方式的性能特点

0引言公路或城市道路达到其结构寿命年限时就会产生裂缝、拥包、坑槽等病害,从而影响行车的舒适性甚至安全。若不及时修补,路表水很容易淤积在坑槽内,使下面层长期被积水浸泡,出现材料松散、剥落,从而形成更深、更大的坑槽。若积水渗入路面基层,则会使基层材料软化,路面的整体承载能力大幅下降,导致沥青混凝土路面出现严重的结构性破损。而且,沥青混凝土路面一旦出现坑槽破坏,坑槽边缘和底部材料受到骤增的车辆冲击荷载作用,会加速坑槽破损的进一步扩展。所以,

南水北调中线京石段S6标段渠道衬砌UF500纤维素纤维混凝土性能研究

普通混凝土因自身抗拉强度较低、延性差、在拉应力或冲击荷载作用下易发生脆性破坏,抗渗、抗冻融循环、抗收缩、抗冲击及耐磨等耐久性能较差,严重阻碍了混凝土的进一步应用和发展。大量试验研究及工程实践表明,在混凝土中掺纤维可有效改善混凝土离析、泌水,抑制混凝土塑性收缩、干缩、温降收缩及其引起的裂缝,提高混凝土的抗裂、抗渗、抗冻、抗冲击、耐磨等耐久性能。纤维增强混凝土的出现标志着混凝土向高性能化发展。南水北调中线工程是一项跨流域、跨地区的特大型水利工程,对改善我国水资源配置、实现全面建设小康社会宏伟目标具有重要战略意义。中线京石段总干渠是南水北调中线工程的重要组成部分,长227.375km,其中以明渠渠道施工为主,渠道长201.047km,建筑物长26.334km,属典型长距离线性渠道输水工程,渠道过水断面为梯形断面,整个过水断面采用现浇混凝土衬砌。针对京石段S6标段渠道断面尺寸大、薄壁素混凝土结构、对混凝土衬砌板抗裂、防渗、减糙要求高,同时衬砌板底部直接与加强防渗层和保温层接触、衬砌板切缝工艺复杂、嵌缝材料成本高的特点,本文就S6标段渠道衬砌用UF500纤维素纤维混凝土的性能进行室内外研究。

国际期刊导读

1蜂窝结构的抗冲击参数数值模拟与试验研究 采用有限元方法和试验对铝制六角蜂窝结构在冲击荷载作用下的抗冲击参数进行研究。为了验证有限元模型的正确性，将数值计算结果与试验数据及文献中已知的理论结果进行对比。在蜂窝结构的数值模拟中，需要考虑平面外荷载，因为铝箔厚度、单元侧面大小、单元扩展角度、冲击速度和质量多种多样，同时动力特性和抗冲击参数需要检验。研究发现，数值分析、试验结论与理论结果相符。数值模拟结果显示抗冲击参数与单元的大小和蜂窝结构铝箔的厚度有关，与冲击质量和速率关系不大。

在元古代黏土中采用超前支护的导坑的稳定性

俄罗斯圣彼得堡地质条件和城市建设特点，制约着深埋于元古代黏土中的地铁区间隧道和车站的施工。 上元古代黏土的主要特性为干燥、坚硬和致密。它本身渗水能力很小，透水性只取决于裂隙的发育程度，天然含水率为12％～14％。这种土壤很容易切削，在冲击荷载作用下表现脆性破坏。

路面模量反算中土基模量预估方法的研究

落锤式弯沉仪（FWD）是目前国内外应用最为广泛的无损式路面弯沉检测设备，应用FWD测定路面弯沉具有省时、省力、测定结果精度高的优点。通过FWD测定的各测点在冲击荷载作用下的动态弯沉峰值和弯沉盆数据，可以反算路面各结构层的模量，从而对道路施工质量和使用情况做出评价，这是其它弯沉测定方法所无法比拟的。

Mitigation of blast loadings on structures by an anti-blast plastic water wall

Seven in-situ tests were carried out in far field to study the blast mitigation effect of a kind of water filled plastic wall. Test results show that the mitigation effect of water filled plastic wall is remarkable. The maximum reduction of peak reflected overpressure reaches up to 94.53%, as well as 36.3% of the minimum peak reflected overpressure reduction in the scaled distance ranging from 1.71 m/kg1/3 to 3.42 m/kg1/3. Parametric studies were also carried out. The effects of the scaled gauge height, water/charge scaled distance(the distance between the explosive charge and the water wall), water wall scaled height and water/structure scaled distance(the distance between the water wall and the structure) were systematically investigated and compared with the usual rigid anti-blast wall. It is concluded that these parameters affect the mitigation effects of plastic water wall on blast loadings significantly, which is basically consistent to the trend of usual rigid anti-blast wall. Some formulae are also derived based on the numerical and test results, providing a simple but reliable prediction model to evaluate the peak overpressure of mitigated blast loadings on the structures.

Effects of thermal treatment on physical and mechanical characteristics of coal rock

To study the physical and mechanical properties of coal rock after treatment at different temperatures under impact loading, dynamic compression experiments were conducted by using a split Hopkinson pressure bar(SHPB). The stress–strain curves of specimens under impact loading were obtained, and then four indexes affected by temperature were analyzed in the experiment: the longitudinal wave velocity, elastic modulus, peak stress and peak strain. Among these indexes, the elastic modulus was utilized to express the specimens' damage characteristics. The results show that the stress–strain curves under impact loading lack the stage of micro-fissure closure and the slope of the elastic deformation stage is higher than that under static loading. Due to the dynamic loading effect, the peak stress increases while peak strain decreases. The dynamic mechanical properties of coal rock show obvious temperature effects. The longitudinal wave velocity, elastic modulus and peak stress all decrease to different extents with increasing temperature, while the peak strain increases continuously. During the whole heating process, the thermal damage value continues to increase linearly, which indicates that the internal structure of coal rock is gradually damaged by high temperature.

Acoustic emission characteristics of rock under impact loading

Acoustic emission tests were performed using a split Hopkinson pressure bar system(SHPB) on 50-mm-diameter bars of granite, limestone, sandstone and skarn. The results show that the amplitude distribution of hits is not well centralized around 50 d B, and that some hits with large amplitudes, usually larger than 70 d B, occur in the early stages of each test, which is different from the findings from static and low-loading-rate tests. Furthermore, the dominant frequency range of the recorded acoustic emission waveforms is between 300 k Hz and 500 k Hz, and frequency components higher than 500 k Hz are not significant. The hit with the largest values of amplitude, counts, signal strength, and absolute energy in each test, displays a waveform with similar frequency characteristics and greater correlation with the waveform obtained from the elastic input bar of the split Hopkinson pressure bar system compared with the waveforms of the other hits. This indicates that the hit with the largest values of amplitude, counts, signal strength, and absolute energy is generated by elastic wave propagation instead of fracture within the rock specimen.

Dynamic rupture and crushing of an extruded tube using artificial neural network(ANN)approximation method

A numerical study of the crushing of thin-walled circular aluminum tubes has been carried out to investigate the crashworthiness behaviors under axial impact loading. These kinds of tubes are usually used in automobile and train structures to absorb the impact energy. Previous researches show that thin-walled circular tube has the highest energy absorption under axial impact amongst different structures. In this work, the crushing between two rigid flat plates and the tube rupture by 4 and 6 blades cutting tools is modeled with the help of ductile failure criterion using the numerical method. The tube material is aluminum EN AW-7108 T6 and its length and diameter are 300 mm and 50 ram, respectively. Using the artificial neural network （ANN）, the most important surfaces of energy absorption parameters, including the maximum displacement of the striker, the maximum axial force, the specific energy absorption and the crushing force efficiency in terms of impact velocity and tube thickness are obtained and compared to each other. The analyses show that the tube rupture by the 6 blades cutting tool has more energy absorption in comparison with others. Furthermore, the results demonstrate that tube cutting with the help of multi-blades cutting tools is more stable, controllable and predictable than tube folding.

Study and application of a new type of foamed concrete wall in coal mines

A new type of airtight wall with the combination of foamed concrete and pier support was designed in this study. Based on the theories and models related to the foamed concrete and blasting shock load, using the numerical analysis method, this study obtains the new material＇s mechanical and destruction laws through analyzing its reaction to different conditions of load （mining and shock waves）, airtight wall thickness （1.2, 1.5, 1.8, 2.1 m） and steel pipe diameters （400, 450, 500 and 600 mm）. The results show that： ①foamed concrete can have very good suspension, and the pier column support is the main carrier of roof pressure; ② the damaged area of foamed concrete decreases as the foamed concrete thickness increases. Under impact loading, the thickness of the foamed concrete wall plays a more obvious role in retaining its integrity; ③under the same mining pressure, the damage area increases as the steel pipe diameter increases; ④ with additional mining stress increase, under whether static load or impact load, the stress on the foamed concrete and steel pipe will also increase gradually, therefore the actual airtight wall design will need to be based on specific circumstances in steel stress.

Strength Evaluation of Normal Strength and Self-compacting Reinforced Concrete Beams under the Effect of Impact Loading

This paper is devoted to investigate experimentally the strength evaluation of normal strength and self-compacting reinforced concrete beams under the effect of impact. The experimental work includes investigating of eight （180×250×1,200 ram） beam specimens. Three variables are adopted in this paper： tensile reinforcement ratio, type of concrete （NSC （normal strength concrete） or SCC （self-compacting concrete）） and height of falling （dropped） ball （1 m or 2 m）. The experimental results indicated that the number of blows increased with increasing of tensile reinforcement ratio and compressive strength by about 35% and 123%, respectively. Maximum mid-span deflection was increased with increasing falling height and decreased with increasing reinforcement ration and concrete compressive strength. The increasing of concrete compressive strength is more effective than increasing of the reinforcement ratio, it appeared that the percentage of increasing exceeds 50%. The ultimate strength is decreased with increasing the falling height for about 34%-44%.