Design of FRC tunnel segments considering the ductility requirements of the Model Code 2010

Fibre reinforced concrete (FRC) is used to improve the mechanical response of precast segments for tunnels. The structural use of the material has been regulated by national codes and, recently, by the Model Code 2010 (MC 2010, hereinafter). In this regard, it is necessary to update the philosophy applied to the design of tunnel segments in compliance with the most recent guidelines, evaluating their applicability and repercussion. The objective of this paper is to present a critical analysis of the design of FRC segments according to the ductility requirements from the MC 2010; an alternative approach is proposed that is compatible with the condition found in some tunnels. The repercussions of both approaches are evaluated for the Metro Line 9 from Barcelona using results obtained in an experimental program with full-scale segments. The study suggests that the alternative approach may be applied under certain conditions, leading to a reduction in the fibre consumption.     

地铁盾构隧道衬砌结构变形及破坏探讨

盾构隧道衬砌结构的变形与破坏模式受接头的力学性能控制,但目前国内地铁盾构隧道接头形式多样,不同形式的接头对整环结构受力性能的影响机理还不清晰。基于足尺试验,分别研究单环、多环的国内典型地铁直螺栓接头衬砌结构、弯螺栓接头衬砌结构、快速接头衬砌结构的受力性能,对比分析其正常运营状态的变形、周边扰动下的破坏模式与极限承载力。结果表明：①通缝拼装盾构隧道衬砌结构的性能由纵缝接头性能决定,提高纵缝接头延性可使结构破坏模式从接头处连接件脆性断裂转变为结构整体失稳;②错缝结构性能取决于环间相互作用强弱,随着环间相互作用的增强,结构首个塑性铰位置从纵缝接头向管片本体转移;③可通过环间、环内的协调设计,优化结构正常运营状态基本受力性能,提高结构极限承载力并使结构发生延性破坏。     

Experimental and analytical study of the structural response of segmental tunnel linings based on an in situ loading test.: Part 1: Test configuration and execution

During the last years the use of segmental linings in tunnels bored with tunnel boring machines (TBMs) have increased considerably. Despite this, uncertainties remain on the structural behavior of segmental tunnel linings. To overcome them, a new methodology for an in situ real scale test on this kind of tunnels was developed and applied on an experimental section placed at the new Line 9 (L9) of the metro of Barcelona. The main particularity of this test falls on its performance in the definitive placement of the rings and, therefore, in the real work conditions of the tunnel. The main advantage to previous real scale test experiences was the consideration of the real ground–structure interaction. The experimental section was composed by 15 rings built using steel fibers as a unique reinforcement. Significant loads were applied to the tunnel crown (max 3000 kN) by means of three hydraulic flat jacks embedded at the extrados of the loaded ring. A complete set of internal and external instrumentation was placed on the experimental section to obtain the necessary measurements to characterize the lining behavior. Such measurements were intensively treated and its main results are presented and analyzed in detail in this paper. This in situ test provides significant evidences of the structural response of SFRC segmental tunnel linings in hard ground conditions.     

Experimental investigation of the ultimate bearing capacity of continuously jointed segmental tunnel linings

The serviceability of segmental tunnel linings is attracting more and more attention within the operation of urban rail traffic. Full-scale tests are herein conducted to determine the ultimate bearing capacity of continuously jointed segmental tunnel linings, considering changes of surrounding environment. The design of tested linings and loading schemes are described. The most important results are the evolution of deformations, cracking and opening of joints and forces in bolts. The bearing capacity, role of joint bolts and failure mechanism of the tested linings are analysed. It is found that failure of these linings is caused by the failure of joints. Thus, in order to optimise structural design of tunnel linings, more attention needs to be paid to maximise the joint strength. It is also found that circumferential joint bolts could take action and offer the safety margin in connection with the response of segmental structures. What’s more, a comparison of different experimental loading conditions has shown that segmental lining structures are more vulnerable to lateral unloading than to overload conditions.     

Experimental and analytical study of the structural response of segmental tunnel linings based on an in situ loading test. Part 2: Numerical simulation

The numerical simulation of the in situ test described in the part 1 of the paper is performed by means of two different approaches: a 2D plane stress model and a 3D shell elements model. A consistent modeling of the tunnel behavior is achieved through the proper simulation of the main phenomena involved on the structural response of the lining: (1) the steel fiber reinforced concrete (SFRC) post-cracking behavior, (2) the detailed behavior of the joints between segments and (3) the ground–structure interaction. The origin and the effects of all these phenomena and the modeling techniques employed to simulate them are carefully described and discussed. Finally, the results obtained are compared with the experimental evidences, showing the excellent accuracy achieved in terms of displacements, joints closures and crack patterns.     

Experimental investigation of the ultimate bearing capacity of deformed segmental tunnel linings strengthened by epoxy-bonded steel plates

In order to develop an effective method to increase the load-bearing capacity of deformed segmental tunnel linings, full-scale tests concerning the ultimate bearing capacity of the linings, strengthened by steel plates, were conducted. The design of the tested linings and the loading scheme are described in this paper. In addition to the bearing capacity, the failure mechanisms of the tested linings were investigated. It was found that bonding of steel plates to the deformed segmental tunnel linings is an effective and practical method for strengthening segmental tunnel linings, thereby enhancing both their ultimate bearing capacity and their overall stiffness. The behaviour of these structures under loading is similar, no matter whether they are strengthened by full-ring or so-called semi-ring steel plates. The failure of the strengthened linings is the consequence of local failure of the bond between the steel plates and the tunnel segment. Therefore, the success of the proposed strengthening method strongly depends on the bonding capacity.     

Experimental investigation of the ultimate bearing capacity of deformed segmental tunnel linings strengthened by epoxy-bonded filament wound profiles

A new strengthening method employing epoxy-bonded filament wound profiles (FWPs) has been applied to shield tunnels subject to large deformation. Full-scale tests were conducted on the ultimate bearing capacity of linings strengthened by the new method. With consideration for secondary loading, the strengthening measures were applied when the lining deformation reached 120 mm (0.02D). The failure phenomena are described, and the main loading process results were obtained, including load-displacement curves, cracking, and joint openings. The failure mechanisms, the key performance points, and bearing capacities of the tested strengthened linings are discussed and analysed. In addition, a comparison was made between two FWP strengthening methods as well as with epoxy-bonded steel plate strengthening methods. The results show that the epoxy-bonded FWP method is effective and practical for strengthening segmental tunnel linings, which can improve both the ultimate bearing capacity and overall stiffness of the structures. The failure of the strengthened linings is primarily caused by bond failure between the FWPs and the concrete lining segments, indicating that the bonding capacity of the adhesive is of great importance when utilising the proposed strengthening method.     

Life-cycle reliability analysis of shield tunnels in coastal regions: emphasis on flexural performance of deteriorating segmental linings

In contrast to reinforced concrete (RC) structures on land, RC shield tunnels in coastal regions deteriorate rapidly after their construction because of the combined effects of multiple mechanical and environmental stressors. In this paper, by considering the coastal hazards associated with chloride and the impacts of hydrostatic pressure, a novel approach is presented to estimate the life-cycle structural performance of a shield tunnel that has undergone deterioration due to chloride-induced steel corrosion. Deterioration processes in segmental linings are investigated via corrosion-accelerated experiments on individual segments, and the combined effects of corrosive agents and loads are emphasized. Monte Carlo simulation is used to estimate the time-variant failure probability of shield tunnels in a marine environment. In an illustrative example, the effects of structural location, hydrostatic pressure and material properties on the life-cycle reliability of shield tunnels are investigated.     

Lining design for the district heating tunnel in Copenhagen with steel fibre reinforced concrete segments

The 3.9 km long district heating tunnel carries heating pipelines from a power plant on the island Amager into the centre of Copenhagen. A shaft on Amager and two shafts in the city centre provide access to the tunnel, which is located within the Copenhagen limestone at a depth between 25 and 38 m below the ground surface. The tunnel is excavated with an earth pressure balance (EPB) shield machine and is lined with steel fibre reinforced concrete (SFRC) segments without any conventional steel bar reinforcement. This represents an advantageous and innovative technical as well as cost-efficient solution. This paper presents the methods applied in the structural and durability design of the SFRC segmental lining for a specified service life of 100 years. Special attention is required due to the temperature increase in the tunnel to approximately 50 °C during operation of the pipelines. The experiences with the SFRC segments during construction of the tunnel are discussed.     

地铁盾构隧道纵向接缝承载能力试验研究与解析分析

当前地铁运营实践和研究表明管片接缝是盾构隧道衬砌结构的薄弱环节,接缝的受力性能直接决定了隧道结构的承载能力。依托于整环试验研究结论,以盾构隧道管片纵缝接缝为研究对象,对不同运营工况下管片接缝的承载性能进行了足尺试验研究,获得不同工况下构件挠度、接缝转角等变化规律,得到转角刚度。分析得到了纵缝接缝的破坏链条,推导了可模拟接缝受力全过程的解析模型分析了纵缝接缝的全过程受力性能及其极限承载力。并借此模型对接缝截面与全截面受力变形进行对比分析,通过试验数据与解析模型数据的对比分析验证解析模型的合理性。     

An asset-management model for use in the evaluation and regulation of public-lighting systems

In this paper, an asset-management model is proposed to address challenges facing regulators, managers, and operators of public-lighting systems and suggest optimal performance strategies. A new method is presented to estimate the failure rate of lamps based on the normal distribution function. The impact of technology improvement in lamp manufacturing as well as the growth and extension of lighting systems on the failure rate are investigated. In order to achieve satisfaction of customers and risk reduction, a method for establishing a performance standard for lamp failure rates is presented. Considering technical and economic issues, a procedure for selecting the best lamp in the market and then estimating costs associated with system operation is described. Finally, a methodology is proposed for evaluating performance in public-lighting systems. Results of a case study for the public-lighting system of the newly constructed suburb of the city of Isfahan, Iran, show the efficacy of the proposed method.     

Effect of embedment length of untreated natural fibres on the bond behaviour in cement mortar

The present investigation is focused on studying the effects of various matrices with 1:3, 1:4 and 1:5 mortars and fibre types of sisal and coir on the bond behavior at various ages of curing, i.e., 24 h, 3 d, 7 d and 28 d. The other parameters included in the investigation are water/cement (w/c) ratio, sand gradation and embedment length of fibres. In addition, the type of failure of sisal and coir fibres for different mixes of mortars at various curing ages is also reported. From the results, it is seen that the bond strength is improving with respect to age of curing in case of sisal fibres, but decreases in case of coir fibres. The failure of fibres due to fibre fracture is observed in sisal fibres and fibre pullout is observed in coir fibres. The other varying parameters such as mortar mixes, sand gradation, w/c ratio and embedded length also showed significant effect on bond behaviour of sisal and coir fibre with the cement mortar mixes.     

An approach in architectural design of energy-efficient timber buildings with a focus on the optimal glazing size in the south-oriented façade

The current research presents an architectural design approach to determine an optimal proportion of the glazing areas in regard to energy-efficiency of prefabricated timber-frame buildings, with a special focus on the south-oriented glazing surfaces. A parametric analysis is performed on the variation of the glazing-to-wall area ratio (AGAW) from 0% to 80% for six different exterior wall elements with different thermal properties. Modifications are performed for the main cardinal directions, while a detailed analysis is carried out only for the south façade. The impact of the presented variable parameters on the energy demand for heating and cooling is analysed with the use of the PHPP software. A basic theoretical contribution of the present research is transformation of a complex energy related problem to only one single independent variable - that of thermal transmittance of the wall elements (U_wall-value), with a view to determining the optimal glazing area size (AGAW_opt) for all contemporary prefabricated timber construction systems. The main aim of the current study is to offer architects a simple and useful shortcut to energy-efficient design of prefabricated timber-frame buildings. The use of mathematical linear interpolation is therefore presented as a simple method for predicting an approximate energy demand with respect to AGAW and U_wall-values.     

钢与混凝土组合梁板结构在沉井顶板中的应用

在借鉴钢与混凝土组合梁原理的基础上,结合沉井施工工艺,研究了钢梁作为钢模板结构和作为组合梁顶板结构一部分的全过程受力机理,提出了钢与混凝土组合梁板结构在沉井顶板结构中应用的技术方案,并以内净空跨度6 m的顶板结构为例,开展了组合梁板结构的优化设计。结果表明,与现浇结构相比,组合梁板结构的施工工期短,但在设计时应考虑防水、结构耐久性等问题;组合梁中钢梁的横向布置间距可从l0/3处开始优化分析。     

我国砌体结构抗震的经验与展望

砌体结构抗震历来颇受人们争议,但面对我国国情,量大面广的砌体结构房屋还将继续在各地建造,面临的抗震问题将无法回避。在经过几代人的努力下认真总结出的系统、宝贵的经验,为指导我国砌体结构抗震指明了方向,并在此基础上采取的一系列对策作为我国技术法规的依据,被证明是合理的和有效的。总结的十项主要震害规律和六项技术对策,既是个人感受也是参与我国建筑抗震设计规范数十年来的切身经历和体会,抛砖引玉,愿与业内同行共同为提高我国砌体结构的抗震水平而努力。     

Optimization of open cross section of the thin-walled beam with flat web and circular flange

This paper is devoted to cold-formed thin-walled beams with open cross section. The beam cross section is optimized for a fixed cross section area under strength and stability constraints. Optimal geometrical parameters of the cross section are determined with regard to maximal and safe bending moment. The strength condition is a classical condition applied to the theory of beams for assumed allowable stress. The stability condition serves also as a classical condition for lateral buckling, taking the warping torsion into account. Moreover, the thin-walled beams have been analyzed, for which the shear center, i.e. the main pole, is located in the centroid of the cross section. Results of the numerical analysis are given. Figures present examples of optimal cross sections of the thin-walled beams.     

Formation of bromoform in irradiated titanium dioxide suspensions with varying photocatalyst, dissolved organic carbon and bromide concentrations

We report the formation of bromoform in TiO₂ suspensions (P25) under simulated solar UV irradiation at different concentrations of photocatalyst (0.5-1.5 g L⁻¹) as well as initial concentrations of bromide ions (1-3 mg L⁻¹) and 2,4-dihydroxybenzoic acid (2-10 mg L⁻¹). The extent of bromoform formation (3-17 μg L⁻¹) was most strongly affected by the amount of photocatalyst present and by the initial bromide concentration, increasing either of which leads to increased bromoform formation. Important interaction effects were observed when simultaneously increasing the concentrations of TiO₂ and bromide as well as of bromide and DHBA. The time it takes for bromoform to appear in measurable concentrations in the irradiated TiO₂ suspensions was between 10 and 90 min and most strongly depended on the initial concentration of dissolved organic carbon present in the suspensions, along with the amount of photocatalyst, also in interaction with the initial bromide concentration.     

探讨深圳CBD规划建设的经验教训

本文对深圳CBD规划建设30年以来的经验和教训作了阶段性总结和探讨,重点阐述深圳CBD超前规划、预留土地实现金融产业、轴线景观一脉相承、留足市政设施容量、采用仿真规划精品、完整保存档案等历史经验;也分析了机非分流未实施、中轴线滞后实施、管理机构短暂运行8年影响规划实施的质量和效率等教训,为未来CBD规划建设提供借鉴。     

建筑模型在建筑设计教学中的运用

在建筑设计教学中应重视运用模型手段来加强学生设计思想的表达,激发学生的学习兴趣,把空间模型作为方案设计中一个重要的环节来对待,促进学生设计水平和空间思维能力的均衡发展。     

论吉祥纹样在现代室内设计中的运用

中国传统吉祥图案是中华民族传统文化重要的组成部分,是表现民族历史完整的艺术形式,在艺术研究领域里具有重要的意义.本文从中国传统吉祥纹样入手,归纳总结出现代室内设计继承传统的许多方法.