Partial collapses experienced for a steel space truss roof structure induced by ice ponds

This paper presents investigations on the steel space truss roof of an industrial plant collapsed partially after exceptional snowfalls. This low sloped light weight roof structure supported on steel columns of 16.3 m height and covering totally 26,080 m² closed area in plan was constructed as Mero type double layer grid steel space truss system having a height of 2 m. Also, parapets of 90 cm height were placed along the perimeter of the building and siphonic system was used for roof drainage. To find out the main reasons of the partial collapse of the roof structure, a site investigation was conducted and findings were collected, then conformity of the structural members were checked with respect to the current Turkish steel building design codes. The material properties of the primary load carrying members of the roof were scrutinized by performing tensile tests. Finally, it was understood that two unexpected catastrophic collapses were experienced as a consequence of ice ponds that occurred on the edge regions of the roof due to discontinuously heated roof parts by the radiant heaters mounted on the roof structure and the freezing of the siphonic system.     

Collapse of Katowice Fair Building

The Katowice Fair Building in Poland collapsed on 28 January 2006. It was a steel building having dimensions 96.360 × 102.875 m in the general plan. The roof was constructed from truss elements, supported on 6 internal and 66 external columns situated along external walls. The results of engineering investigations on the reasons of total collapse of Katowice Fair Building structure has presented herein. Generally the collapse occurred as a consequences of: incorrect arrangement of the structure, unsufficient strength and rigidity of main structural elements, and finally of the overloading action of thick ice – snow layer. The following parameters have been estimated: the reliability model of the structure system, arrangement of bracings, construction of main columns, main girders and supporting, field connections of elements and shaping of the roof surface.     

Strengthening of Garudchatti bridge after failure of Chauras bridge

Two continuous lattice steel truss bridges spanning 190 m with subdivided top chord members were constructed on the same design across river Alaknanda at Dugadda and Srinagar, respectively, in Uttarakhand, India. Both bridges were similar in design and geometry having middle span of 110.0 m and two end spans of 40.0 m. Garudchatti bridge at Dugadda was constructed first and opened to traffic, but excessive vibrations and lifting of end supports under live load condition were observed. Construction of Chauras bridge at Srinagar started later, but it collapsed during casting of the deck slab due to buckling of one of its top chord compression members. Failure of Chauras bridge led to the serious concerns in the minds of people and technocrats about the safety of Garudchatti bridge also, because it was constructed using the same design of Chauras bridge. Therefore, it was decided to strengthen and carry out load testing of Garudchatti bridge before reopening to the traffic.In the present work analyses of Garudchatti bridge are presented to identify structurally unsafe members for most severe live loads given in IRC:6-2010 code, and recommendations for strengthening of the critical members. Finite element space frame analyses of the bridge were carried out using STAAD Pro. v8i software to find excessively stressed members beyond their permissible stress limit. The critical compression members were strengthened by welding additional channel sections. RCC anchor blocks were constructed to restrict lifting of end supports under live load. After strengthening, load testing of the bridge was performed to ensure the safety of the bridge. The bridge is now reopened for traffic.In the past a number of bridges have collapsed during load testing. In case of any shortcoming in the design or overloading during load testing, compression members of the truss may suddenly buckle and cause collapse of the bridge. Therefore, it is not advisable to load test steel truss bridges which do not have adequate margin beyond the service load condition.     

粘滞阻尼器对空间桁架结构减震作用研究

为研究粘滞阻尼器对大跨空间桁架结构减震控制作用,在某体育馆屋盖不同部位设置粘滞阻尼器,输入三向地震波进行时程分析。以屋盖结构水平向位移、加速度及构件内力为减震控制目标,计算分析表明,设置粘滞阻尼器能有效抑制结构在地震作用下响应;屋盖结构均匀布置阻尼器较集中布置减震效果好;结构减震效果不随阻尼系数的增大而线性提高,且存在较优值范围;不同地震烈度下粘滞阻尼器对空间桁架结构减震控制均有明显效果;粘滞阻尼器在不同地震波输入时滞回曲线均较饱满,呈现典型速度相关型阻尼器特征。研究结果对粘滞阻尼器用于大跨空间结构减震控制具有一定参考价值。     

控制爆破技术在连拱隧道掘进应用的研究

九江至瑞昌高速公路A2标新合连拱隧道,穿越地层复杂,施工要求高。为保证工期和施工质量、安全,针对岩体特征及浅埋偏压段的实际,进行合理的超前支护;采用隧道光面爆破技术,经现场试验,对连拱隧道开挖爆破参数、装药结构和起爆网路进行优化设计;对钻爆、施工管理,提出了合理的质量要求和安全措施,实现了改善爆破效果、降低施工成本的目的。对类似隧道开挖施工具有一定的参考价值。     

桁架结构厂房房顶聚能切割爆破拆除

根据钢筋混凝土桁架结构厂房房顶的结构特点,在保证行车轨道等设施不被破坏的条件下,利用聚能切割技术对其关键部位实施切割爆破。施工中采用了双侧对称爆破切割方案,使房顶结构失稳并一次性塌落。本文介绍了线型聚能切割器参数设计、零炸高试验、起爆网路及安全防护措施,讨论了聚能切割爆破的设计和实施中应注意的问题。同时,简述了利用聚能切割技术拆除大型桁架式构筑物的效果和体会。     

Practical design optimization of truss structures using the genetic algorithms

Truss structures are widely employed in the industrialized world. They appear as bridges, towers, pylons, roof supports, building exoskeletons or high technology light space structures. This paper investigates the simultaneous size, geometry and topology optimization of real life large truss structures using genetic algorithms (GAs) as optimizer and finite element method as analyzer. In general, the large truss structures are constructed for practical reasons from the duplication of some basic structures called bays. Thus, the final optimum design may be reached by optimizing the characteristics of the basic bays instead of optimizing the whole structure. Both single and multiobjective functions based on the mass of the structure and the maximum nodal displacement have been considered as the cost functions. In order to obtain realistic optimal designs, the cross-sectional areas have been extracted from the standard profiles according to AISC codes and practical conditions are imposed on the bays. The design optimization problem is also constrained by the maximum stress, maximum slenderness ratio and the maximum and minimum cross-sectional area of the truss members. To accommodate all these constraints, two different penalty functions are considered. The first penalty function considers the normalization of violated constraints with respect to the allowable stress or slenderness ratio. The second penalty function is a constant function which is used to penalize the violations of the slenderness ratio. Three illustrative examples of realistic planar and space truss structures have been optimized to demonstrate the effectiveness of the proposed methodology. However, other criteria such as cost and/or manufacturability could be quantified and included in the optimization formulation.     

Forensic assessment of a bridge downfall using Bayesian networks

Bayesian networks proved to be a useful tool in many technical fields as well as in forensic sciences. The present paper proposes a novel application of Bayesian networks in forensic engineering, focusing on the analysis of technical causes of a catastrophic bridge downfall. During repair a road bridge over important railway lines suddenly slipped down from temporary supports. Incidentally at the same time an intercity train approached the location and crashed into the collapsed bridge at a high speed. The accident resulted in great societal and economic consequences. Forensic investigation concerning causes of the bridge collapse was complicated due to the additional damage caused by the train. Moreover, the remaining structural elements of the collapsed bridge and temporary supports were shortly after the accident removed to renew railway traffic. Background materials of the investigation and additional detailed structural analyses did not reveal any convincing evidence of the initiation cause. Critical consideration of all possible causes including aerodynamic effects supplemented by a causal (Bayesian) network finally resulted in identification of the most significant causes including insufficient foundation and overall stiffness of temporary supports.     

加载速率对点阵铝力学行为及吸能特性的影响

目的研究基体材料和加载速率对点阵铝力学性能和吸能特性的影响规律。方法针对工业纯铝、6063铝合金为基体的点阵铝在3种不同的加载速率下进行压缩力学试验。结果加载速率从2mm/min增加到250 mm/min时,点阵纯铝的屈服强度增加了2 MPa,点阵6063铝合金的屈服强度增加了7.6 MPa;加载速率从250 mm/min增加到500 mm/min时,点阵纯铝的屈服强度变化不大,而点阵6063铝合金的屈服强度增加了8.2 MPa;当加载速率一定时,点阵6063铝合金的屈服强度要大于点阵纯铝。结论点阵6063铝合金的力学性能和单位体积吸能随着加载速率的增大而增大,并且点阵6063铝合金的力学性能和吸能特性要大于点阵纯铝。     

Mechanical behaviour of CFRP sandwich structures with tetrahedral lattice truss cores

A method of manufacturing carbon fibre reinforced polymer (CFRP) tetrahedral lattice truss core sandwich structure by thermal expansion silicon rubber mould was developed. The sandwich structure was manufactured integrally without secondary bonding and the silicon rubber mould can be made mass-production with low cost in this approach. The intrinsic property of the CFRP was fully exploited because of carbon fibres aligned in the axial orientation of the truss member. The mechanical properties of CFRP tetrahedral lattice truss core sandwich structures were investigated by flatwise compression and shear test. The experimental results indicate that CFRP tetrahedral lattice truss core sandwich structures have higher weight-specific compressive strength than some metal truss cores, and are competitive with conventional honeycombs.     

Fabrication and crushing behavior of low density carbon fiber composite pyramidal truss structures

A new method for fabricating carbon fiber composite pyramidal truss cores was developed based on the molding hot-press technique. In this method, all the continuous fibers of composite are aligned in the direction of struts and thus, the truss structure can fully exploit the intrinsic strength of the fiber reinforced composite. The microstructure and organizations of fibers of fabricated composite structures were examined using scanning electron microscope. The crushing response of the truss cores was also investigated and the corresponding failure modes were studied and complemented with an analytic model of the core crushing response. Our results show that the fabricated low-density truss cores have superior compressive strength and thus, could be used in development of novel lightweight multifunctional structures.     

提高地铁车站结构抗震能力的理论及数值分析

1995年阪神地震中,地铁车站等地下结构遭受了严重的破坏,其中大开地铁车站破坏尤为严重,一半以上的中柱发生坍塌,为了提高地铁车站结构的抗震能力,本文基于第二类拉格朗日方程首先建立了地震荷载和轴力联合作用下柔性动边界梁动力响应的分析方法,并讨论了轴力和弹簧刚度与阻尼系数对动力响应的影响特点与规律,然后利用ABAQUS软件对阪神地震荷载作用下大开地铁车站在有无设置隔震器时进行了三维非线性动力分析。研究结果表明：)     

A statically determinate truss model for thin shells: One-surface analysis (membrane hypothesis)

This paper presents the modelling of open shells, such as those used in roof construction, by means of a single-layered, pin-jointed truss. The latter exhibits several advantages over existing framework models, such as, for example, statical determinacy and the capacity to cope with arbitrary material constants. In the present article, the truss model is developed for and applied to the numerical analysis of shells subject to the membrane hypothesis. However, the same statically determinate model forms the basis for a computational scheme for analysing shells according to the more formal, statically indeterminate bending theory; the latter application of the truss model will be presented in a subsequent paper.     

基于ANSYS的离心复合校准装置桁架结构分析

在离心复合校准装置极限载荷工况下,为确定桁架强度满足离心复合校准应用需求,对桁架结构进行有限元分析和试验验证。利用ANSYS有限元分析软件,设计仿真过程,完成对该种离心转臂式桁架结构,从结构组成、模型建立、网格划分、载荷约束设置等程序描述整个分析过程。通过分析结果云图,确定桁架受力结果符合机械结构要求。经线加速度计校准试验测试对结构分析结果进行验证,结果表明：桁架的结构强度满足使用要求,变形量与实测值接近,结构分析结果与实际应用测试值相符合,分析结果可靠。此桁架分析过程和验证方式可为类似桁架分析提供参考。     

Lateral buckling failure of steel cantilever roof of a tribune due to snow loads

This paper presents lateral buckling failures of laterally unrestrained steel cantilever roof of a tribune with slender cross section under snow load. A structure located in eastern part of Turkey, and collapsed on October 25, 2015 is considered as a case study. This mild sloped roof structure was built from a variable I beam, and supported on steel columns of 5.5 m height covering totally 240 m² closed area in plan. The roof of the tribune collapsed completely during first snowfall after construction without any indication. The meteorological records and observations of local people are combined together to estimate the intensity of snow load in the region, and it is compared with the values specified by the code. Also, the wide/thickness and height/thickness ratios for flange and body are evaluated according to the design codes. Three dimensional finite element model of the existing steel tribune roof is generated by ANSYS commercially available software, considering the project drawings and site investigations to determine the buckling modes and related buckling loads. The analytical solutions of the cantilever beam are carried out and buckling load are obtained as q = 22.236 kN/m². To validate the analytical solution using finite element analyses, one cantilever beam is modelled separately with roof slope. At the end of the analyses, the buckling loads are obtained as q = 22.440 kN/m². It is seen that there is a good agreement between the results and maximum difference is attained as 0.91%. After the finite element analyses considering full system, the buckling load is obtained as q = 31.00 kN/m². The failure mechanism using buckling mode shapes is very similar to site investigation. The obtained results are lower than the derived snow load considering field investigation. These results can be evaluated as the evidence to explain the reason of failures. The experimental, numerical and analytical works conducted in this study indicate that the snow could be trigger of the collapse, but not alone the main reason for this situation, with the combination of inadequate section properties, faulty design and workmanship errors during construction.     

巷道吸能支护的减震防冲效应分析

冲击地压是煤矿开采的主要动力灾害，巷道吸能支护是防御冲击地压灾害的新型支护方式和有效手段。吸能支护是在刚性支护基础上附加阻尼耗能构件形成的巷道支护，基于巷道顶板与支护相互作用的动力学模型，分析了在巷道刚性支护与吸能支护作用下的顶板-支护系统动力响应，同时就阻尼构件在吸能支护上的分布特征对减震防冲效应的影响进行了分析，研究了阻尼构件在支护中的串联、并联、混联3种分布特征下的支护吸能减震防冲效应。结果表明：相比于刚性支护，吸能支护不仅能有效抑制顶板的冲击响应，还对支护体的冲击响应具有自保护能力；串联吸能支护模式与混联吸能支护模式对顶板冲击位移的控制及支护体加速度的抑制作用相当，且均优于并联吸能支护模式，其中，在串联吸能支护模式下，顶板冲击位移可下降约89%，支护体加速度可下降约55%。进一步优化串联吸能支护模式可知，当采用支护体上端串联布置吸能构件时，构件吸能效果发挥的最好，并且支护体的变形、应力、等效塑性应变变化平稳且幅值较小，同时相比于在下端以及两端串联吸能构件时支护等效塑性应变分别下降约77%和96%。该研究为冲击地压动力灾害的防冲吸能支护动力可靠性设计提供思路。     

浦东国际机场钢屋架上弦主梁的残余应力测定与分析

利用X射线应力测定技术对浦东国际机场钢屋架上弦主梁的残余应力进行现场测定。简要阐明了造成不同焊缝应力分布的原因及火工校弯成形工艺对构件残余应力分布的影响。     

Hybrid carbon fiber composite lattice truss structures

Carbon fiber reinforced polymer (CFRP) composite sandwich panels with hybrid foam filled CFRP pyramidal lattice cores have been assembled from linear carbon fiber braids and Divinycell H250 polymer foam trapezoids. These have been stitched to 3D woven carbon fiber face sheets and infused with an epoxy resin using a vacuum assisted resin transfer molding process. Sandwich panels with carbon fiber composite truss volumes of 1.5–17.5% of the core volume have been fabricated, and the through-thickness compressive strength and modulus measured, and compared with micromechanical models that establish the relationships between the mechanical properties of the core, its topology and the mechanical properties of the truss and foam. The through thickness modulus and strength of the hybrid cores is found to increase with increasing truss core volume fraction. However, the lattice strength saturates at high CFRP truss volume fraction as the proportion of the truss material contained in the nodes increases. The use of linear carbon fiber braids is shown to facilitate the simpler fabrication of hybrid CFRP structures compared to previously described approaches. Their specific strength, moduli and energy absorption is found to be comparable to those made by alternative approaches.     

大跨桁架体系的连续性倒塌分析与机理研究

在突发事件的直接影响下,结构的局部构件可能首先发生初始破坏并进一步导致结构的连续性倒塌。与框架结构或承重墙体系相比,大型公共建筑中普遍采用的桁架体系具有冗余度较低的特点,为提高其结构鲁棒性,必须在详细分析基础上采用不同的设计策略。该文以钢屋架体系为例,通过连续性倒塌过程的数值分析,研究了内力重分布过程、动力效应和主要破坏模式等问题;根据局部杆件失效后的结构特性,归纳出转动铰机制、滑移面机制和长压杆机制等三种基本的局部内力重分布机制;结合简化数学模型的理论分析,阐述了敏感构件和关键构件的概念,为该类结构的安全性评价提供了一种简便的尺度。     

Statistical features of mechanical properties of current Japanese steels

As part of the work of RILEM T/C83-CUS, a statistical survey on mechanical properties of recent Japanese steels was performed on the basis of mill sheet data collected from six major mill makers of Japan. As a major result, wide scatter bands of yield point strength were found; this caused higher yield ratios of supplied steels than those based on the specified lower limits of yield strength and tensile strength. A high yield ratio is not preferable for ductility design of steel yield strength and tensile strength. A high yield ratio is not preferable for ductility design of steel structures. Thus, the upper limit of yield strength or yield ratio should be specified for such design use.