Experimental investigation on friction and squeezing of roof structure key blocks corner upon long-wall face

The coefficients of friction and squeezing of the key blocks comer in the roof structure of underground coalface are key factors to roof structure stability quantitative analysis. In this paper, through the special test of three-type corner friction and squeez- ing of real rock specimens, and physical simulation test on the roof key blocks of roof structure as well as the finite element calcula- tion of the corner stress distribution and failure mechanism, the characteristics of friction and squeezing of the roof key blocks comer are revealed. It is found that the friction angle of the roof key blocks corner is the residual friction angle, and the frictional angle of the roof key blocks is 22-32° (average 27°), so the friction coefficient is determined as 0.5. It also found the squeezing strength is less than the uniaxial strength, and the squeezing coefficient of the roof blocks corner is determined as 0.4. Based on the results, the ground control theory can be updated from qualitative analysis to quantitative analysis.

Proposal of Stainless Steel Roof Structure and Tiles for Gymnasiums

This work proposed an architectural alternative project of a stainless steel roof structure that uses roof tiles also in stainless steel with emphasis on roofs for multi-sport gymnasiums.In the development of the work,two existing multi-sports gymnasiums are taken as a reference,but with ASTM(American Society for Testing and Materials)A36 steel roof structure.The proposed cover system uses cables and light gauge profiles,in commercial stainless steel,which reduces the weight and of course the final price of the roof structure.A structure that presents technical feasibility is obtained and analyzed by checking its behavior with respect to the efforts and displacements generated by the combinations of the acting loads,following the safety recommendations of the applicable standard.It is verified that using the stainless steel structure proposed in this work would cost 42%of the reference structure if this were in AISI(American Iron and Steel Institute)304 stainless steel.And this cost tends to be minimized due to greater durability and consequent reduction in maintenance costs of this type of steel.

Roof structure theory and support resistance determination of longwall face in shallow seam

This paper presents the structure models founded in shallow seam, the roof asymmetry arch with three articulations in roof first weighting and the step voussoir beam in roof periodic weighting. These structure models are differ from classic theory, it establishes the new roof control theory of instability structure roof, especially in shallow seam. Based on the new roof structure theory, the support working state of "given sliding load" is put forward, and the factor of load transmitting is introduced to determine the load on roof structure. Therefore, the proper and accurate calculating methods of support resistance are established. Based on this, the dynamic structure theory in shallow seam could be predicted.

Lessons from the seismic behavior of a steel grid roof structure heavily damaged in Lushan earthquake

The seismic behavior of a school gymnasium, whose steel grid roof was heavily damaged during the Mw6.6 Lushan earthquake in 2013, is simulated through nonlinear dynamic analysis. The simulated damage is compared with field observations to validate the numerical model, based on which a parametric study was performed to provide insight into the failure process and damage patterns of steel grids. The results suggest that the grid damage is strongly related to roofsubstructure interactions. These include not only the substructure's amplification of the vibration, but the uncoordinated displacement of the substructure's columns which support the grid also play an equally important role. In particular, the latter effect may significantly alter the internal force distribution in the steel grid and lead to unexpected buckling of members that are proportioned as tension-only members. While such interactions are generally not accounted for in the design practice for grid structures in China, similar seismic damage may be expected for other existing grid roofs in future earthquakes. As is also demonstrated in this study, seismic isolation of the roof is a promising solution to protect grid roof structures by mitigating the detrimental effects of roof-substructure interactions.

Experimental Study on Roof Structure Characteristics and Its Failure Pattern in Coal Roadway

Based on the investigation and statistics of logs of 211 bole holes and strata data from 79 roadways in 13 coal mines located in Xishan, Jincheng, Lu’an, Fenxi, and Huozhou in China, the roadways’ roof structures were classified as multi-thin-layer, thin-thick combined layer, integrated thick layer, thick-coal layer, and cracked layer according to the geometric features and spatial strength distribution of surrounding rock. Then eight sub-categories were defined as different situations. And seven simulation modeling tests were carried out. The strata structures of these models were different from each other. At last, the relationship between roof structure and its failure pattern was discussed.

Practical Aspects of the Design and Construction of a Small Cable Roof Structure

Cable roof structures?have?only become widespread in large span structures in the latter part of the twentieth century. However,?they?still represent a relatively new form of roof construction, especially as in the present case of a small span innovative structural solution. The contribution of this text to the structural engineering community lies in the increased interest in building simple cable roof structures. Since its completion in September 1996, this small cable roof structure has been recognized as an interesting architectural and structural example. The text describes aspects of the design and construction of a small cable roof that was designed as a roof for an open-air theater stage for the city of Sao Jose do Rio Pardo, Sao Paulo, Brazil. A cable network, in the shape of a hyperbolic paraboloid surface, is anchored in a reinforced concrete edge ring. The projection of the ring’s axis onto the ground plane is an ellipse. Workers with specialized training were employed in the various stages of the construction, which was completed in September 1996.

Software Practicalization for Analysis of Wind-Induced Vibrations of Large Span Roof Structures

Wind loads are key considerations in the structural design of large-span structures since wind loads can be more important than earthquake loads, especially for large flexible structures. The analysis of wind loads on large span roof structures (LSRS) requires large amounts of calculations. Due to the com- bined effects of horizontal and vertical winds, the wind-induced vibrations of LSRS are analyzed in this pa- per with the frequency domain method as the first application of method for the analysis of the wind re- sponse of LSRS. A program is developed to analyze the wind-induced vibrations due to a combination of wind vibration modes. The program, which predicts the wind vibration coefficient and the wind pressure act- ing on the LSRS, interfaces with other finite element software to facilitate analysis of wind loads in the de- sign of LSRS. The effectiveness and accuracy of the frequency domain method have been verified by nu- merical analyses of practical projects.

Analysis of solar radiation changes in Chinese solar greenhouses with different roof structures based on a solar radiation model

Chinese solar greenhouses(CSGs)are important agricultural production facilities.Under non-artificial heating conditions,solar radiation is the only CSGs energy source.It is highly important to optimally obtain solar energy in greenhouse construction and production.In this study,a solar radiation model for solar greenhouses was adopted to explore the quantities of solar radiation in greenhouses considering different front roof forms and angles.Herein,the solar radiation amounts corresponding to five roof forms,namely,double-section arc,parabolic,oval,arc,and linear roofs,are compared and analyzed during the four solar periods(beginning of spring,vernal equinox,beginning of winter,and winter solstice).It was found that the solar radiation of oval roof greenhouses on the ground was the largest and was 4.44%-23.68%higher than that of parabolic roofs.In addition,the cumulative sum of light on the linear roof greenhouse wall is also the largest and was 6.02%to 12.08%higher than the parabolic roof greenhouse in the four solar terms.Moreover,the solar radiation in CSGs was compared with front roof angles of 25°,30°,and 35°.It was observed that the solar radiation amount gradually increases with increasing angles.Notably,the variation at an angle of 35°influences the solar radiation of the paraboloidal CSGs ground and elliptical CSGs north wall to the greatest extent,which increased by 8.23%and 12.74%,respectively.This study confirms the role of front roof form and inclination angle in enhancing the greenhouse solar radiation level.

Mode of overlying rock roofing structure in large mining height coal face and analysis of support resistance

The mining space of large mining height coal face is large,the range of movement and caving of rock strata is large and the stability of supports at coal face is low and damage rate of supports is high,which significantly affects the safe and efficient production of coal mines.By similar simulation experiment and theoretical analysis,the mode of fractured roofing structure of large mining height coal face and the method of determination of reasonable support resistance of the support was evaluated.Analysis shows that the structural mode of "combined cantilever beam – non-hinged roofing – hinged roofing" of the large mining height coal face appears at the roofing of large mining height coal face.The supporting factor of caved gangue at the gob is introduced,the calculating equations of the fractured step distance of roofing were derived and conventional calculating method of caved height of roofing was corrected and the method of determination of the length and height of each structural area of the roofing was provided.With reference to the excavating conditions at Jinhuagong coal mine in Datong minefield,the dimensions of structural areas of the roofing of the coal face were determined and analyzed,and reasonable support resistance of the height coal face was acquired.By selecting Model ZZ13000/28/60 support and with procedures of advanced pre-cracking blasting,the safe production of large mining height coal face was assured.

Using of Key Stratum Theory to Study the Structural Development of Roof Aquifer

During the underground mining of coal resources,overlying rocks on the roof of excavated tunnels will be destroyed due to ground pressure,and as a result,part of them will break and fall into the tunnels.How to determine the distribution of fractured areas and fissures presents a major problem for preserving the overlying aquifer.

Effect of a single weak lithological structure on the height of a collapsing roof in a deep soft rock roadway

Besides the cross sections of roadways and the tendency and obliquity of roadway axes, the major controlling factors affecting the height of a collapsing roof include the weak lithological structure of surrounding rocks. This thesis analyzes the effect of two single and weak lithological structures of both sides and the roof on the height of a collapsing roof in a deep soft rock road-way. Using the two-dimensional UDEC3.1 software, a numerical simulation was carried out on the models of weak lithological structures of both sides of a roadway and of two weak lithological structures of roof of different depths. We reconstruct the overall processes from a break-away layer, bending, subsidence and the cracking of a collapsing roof. We also illustrate the distribution characteristics of displacement fields in the surrounding rock after the roof collapse in a deep soft rock roadway. The results of our numerical simulations indicate that the form of a roof collapse is side-expanding when the roadway is a weak structure at both sides. The height of the roof collapse is related to the lithological combination of the roof when the roadway is a weak structure of the roof.

Physical Modeling of Influence of Rock Mass Structure on Roof Stability

Based on the developing degree of structure planes in coal roof, whole, blocky and heavily fractured structure models are built up. Through simulation test of similar materials, the distribution of deformation, failure and underground pressure induced by coal mining in coal roof with different rock mass structures are analyzed. The test results indicate that the distances of first and periodic weighting of main roof and the height of caving and fracture zone decrease with the increment of fractures in roof rock mass. From whole to blocky and heavily fractured structures, abutment pressure ahead of working face reduces and the peak value of abutment pressure migrates to inside of roof rock mass.

Basic Structural Forms of Main Roof

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基于力学模型构建的留巷切顶高度确定与围岩控制技术

以顺和煤矿2401运输巷道沿空留巷为工程背景,分析巷道围岩结构特征,基于巷道局部空间结构稳定性,分别构建了沿空留巷未切顶与切顶力学结构模型,并以巷道不同切顶高度进行物理相似模拟试验。结果表明:巷旁采空区切落的矸石增加对关键块的支撑力,同时弱化关键块对直接顶悬壁端部挤压,巷旁支护阻力减少35.78%;随着切顶高度增加,巷道顶板采空区侧端部悬臂由F型缓慢过渡到大I型,同时大保护结构具有向上平移趋势,相比于未切顶1巷,4 cm切顶2巷、8 cm切顶3巷与16 cm切顶4巷叠加应力峰值分别下降9.38%,28.13%,25.00%。结合巷道顶板岩性,最终确定切顶高度为8.2 m,留巷段采用三列单体液压支柱作巷旁支护,长短锚索超前补强,巷道围岩稳定,较好满足使用要求。

大倾角煤层开采顶板主应力方向分布特征及力学分析

为了分析大倾角煤层开采顶板最大主应力方向旋转对顶板变形破坏的影响,以新疆焦煤集团2130矿25221工作面为背景,采用物理相似模拟实验、FLAC^(3D)数值模拟方法对大倾角煤层开采过程中顶板破坏及岩层结构演化特征、最大主应力方向等值线分布及其对顶板破坏影响进行分析,在此基础上建立顶板力学模型,讨论了顶板挠度分布特征。结果表明:随工作面推进,顶板破坏包络线上方承载拱拱体范围逐渐增大,拱顶逐渐向岩层中上部延伸;顶板的最大主应力方向等值线分布形态由“m”逐渐向“n”型演化(采空区中、上部区域顶板最大主应力方向偏转程度较大),在主应力方向偏转和最优扩展裂隙角协同作用下,促使顶板中上部发生破坏并逐步向高位岩层迁移;建立顶板力学模型,通过Python编程将顶板数据代入计算可得,在顶板岩层倾向4/5处出现挠度峰值。

绿色屋顶降雨径流特性及其结构参数优选试验研究

为研究北方半湿润区绿色屋顶降雨径流特性,探究结构参数变化对其雨水蓄滞效应的影响,为海绵城市绿色新基建提供数据支撑及引导。建立绿色屋顶(坡度0°)、普通屋顶(坡度0°)、坡面屋顶(坡度5°)3种类型屋顶的对照试验,以及基于基质层厚度、基质层、排水层和排水方式结构参数调整的五组绿色屋顶试验,基于实测降雨径流开展监测。研究表明:监测期内,绿色屋顶、普通屋顶、坡面屋顶综合降雨量的平均径流系数分别为0.27、0.50、0.77,绿色屋顶降雨径流削减效应明显。随着降雨强度增大,绿色屋顶产流概率呈逐渐增大趋势,径流总量控制率呈逐渐较小趋势,绿色屋顶对小雨~大雨级别场次降雨蓄滞效应显著。监测期内降雨事件中,绿色屋顶降雨径流系数与降雨总量显著正相关,与前期降雨间隔天数和前期降雨量为弱负相关;绿色屋顶降雨径流控制效率显著降低对应降雨强度临界值为30 mm。绿色屋顶雨水蓄滞效应影响因素显著程度由大到小依次为基质层(超轻量基质层)、排水方式(距底部5 cm排水)、基质层厚度(20 cm)、排水层(陶粒层)。绿色屋顶降雨径流特性及雨水蓄滞效应受到内、外因多因素影响,后续应基于长序列降雨监测期,进一步研究不同结构、不同尺度的绿色屋顶的海绵城市生态效应。

弹−塑性基础边界两侧采空(留煤柱)基本顶板结构初次破断特征

为了研究两侧采空留煤柱工程条件下基本顶板结构的断裂位态及工程指导意义,构建考虑实体煤弹塑性变形与两侧煤柱宽度及支撑能力弱化的基本顶板结构双塑化基础边界力学模型,基于有限差分算法与主弯矩破断准则系统计算了在非对称煤柱区和长边实体煤区的断裂线形态、区位属性及整体位态特征,并从7个层面、横纵向4对区域与传统模型对比,阐明新模型所得新结论及工程意义。结论如下:(1)两侧非对称煤柱参数对长边实体煤区域的基本顶主弯矩及破断位置影响小,但分别显著影响煤柱区的主弯矩大小、位置及断裂形态。两侧煤柱区(较强/宽煤柱区+较弱/窄煤柱区)基本顶断裂线形态有3类演化模式,随基本顶厚度及弹模增大而煤柱宽度、支撑能力及悬顶跨度减小,其变化规律为:非对称的“连续单弧形+连续单弧形”→“连续单弧形+开口间断双短弧形”→非对称的“开口间断双短弧形+开口间断双短弧形”。(2)长边实体煤区基本顶的断裂线主要有3类区位属性,随基本顶厚度及弹模增大而实体煤的塑性区宽度、塑化程度及悬顶跨度减小,其演变规律为:断裂线在塑性煤体区(C-S式)→弹塑性煤体分界区(C-TS式)→弹性煤体区(C-T式);(3)考虑断裂线区位属性,随基本顶厚度和弹模增大而煤柱宽度、支撑能力及悬顶跨度减小的基本顶全区域破断模式及演变规律为:C-S式的■→C-TS式的■→C-T式的■→C-T式的■→C-T式的■。针对研究两侧采空(煤柱)基本顶板结构破断的3类力学模型,从7个层面对比了3类模型的重要区别,从横向4个区域(开采区域的前方与后方、两侧煤柱区)与纵向4个区域(非对称遗留煤柱下伏、下伏开采空间出/进煤柱/体)阐明了其重要工程作用。

底板动压巷道压裂弱结构体应力转移控制技术

为了满足煤矿安全生产的需要,许多巷道都会布置在煤层底板中,如部分运输大巷、排水巷道、瓦斯抽采巷道等。采动应力容易造成底板巷道围岩应力升高,加剧底板巷道围岩变形,造成支护永久失效、顶板下沉、巷道底鼓、两帮收敛等破坏。针对此,提出了在应力传递路径上实施水力压裂,在指定的区域制造出一定空间形态的水压裂缝网,形成压裂弱结构体,实现区域范围内的应力转移,从而降低巷道区域范围内的应力,控制巷道的围岩稳定性的控制技术,并通过理论分析及现场工程验证等方式,揭示了底板动压巷道压裂弱结构体应力转移的力学机制,建立了相应的力学模型,对压裂弱结构体的合理位置、范围等影响因素进行了求解。得出:(1)压裂弱结构体使局部应力场发生明显变化,出现应力升高区和应力降低区,应力降低区主要分布在弱结构体与采动应力连线的方向上,主要集中在一个拱形的范围内;由于膨胀效应,在与应力来源垂直的方向上产生应力集中,出现应力升高区。(2)最大主应力变化幅度与压裂弱结构体的长轴长L、短轴长H、到巷道的距离P、与巷道连线的水平夹角β、压裂层的强度C及内摩擦角α、压裂的损伤变量D等有关。其中到巷道的距离P对卸压效果影响最大,损伤变量D对卸压效果影响最小。(3)采用提出的计算方法设计了淮北矿业集团袁店一矿的103运输集中巷的卸压方案,工程应用结果表明,底板动压巷道变形速率明显减缓,验证了底板强动压巷道压裂弱结构体应力转移模型的合理性。

重庆江北机场T3B航站楼大厅屋盖钢结构提升施工技术

重庆江北机场T3B航站楼大厅屋盖钢结构为异形三维曲面造型焊接球网架。由于周边飞机不停航,且由于构造复杂、结构高差大、跨度大、杆件数量多,给屋盖钢结构施工带来很大挑战。基于方案探讨和专家论证,提出一种优化施工方案:大厅钢屋盖划为7个提升分区,每个分区在楼面拼装为提升小分块,通过二次及多次累积提升进行施工。施工前运用BIM技术进行工序预演,并采用3D3S,MIDAS Gen软件进行数值模拟分析,为施工的准确性和安全性提供有力支撑。