Experiments with rock: Remarks on strength and stability issues

In the classical work of Fairhurst and co-workers on machine stiffness, it was shown that the failure response of a rock specimen can be a mixture of material and structural behavior. This is due to the development, around peak stress, of a localized region of microcracking called the intrinsic zone, which may be a property of the rock. The inhomogeneity formed by the intrinsic zone has a fundamental importance for defining the system behavior in terms of material strength and post-peak instability such that size effects appear. In addition, the testing environment, that is, the load frame, with its finite stiffness and load arrangement, has an impact on the overall response. Observations of the intrinsic zone are presented, and the topics of strength and stability are discussed in relation to tensile and compressive testing of rock.     

Predicting the ultimate bending capacity of concrete beams from the “relaxation ratio” analysis of AE signals

This paper presents an alternative approach to the problem, based on “testing” the real structure rather than trying to model it. Experiments on reinforced concrete (RC) beams, representative of bridge beams, are described. The beams were loaded in cycles up to failure whilst recording the acoustic emissions (AE) generated. The analysis of the AE signals was then undertaken based on a proposed new parameter, named the “relaxation ratio”. This quantifies the AE energy recorded during the unloading and loading phases of a cycle test and it showed a clear correlation with the bending failure load of the RC beams. A change in trend was noted when the load reached approximately the 45% of the ultimate bending load. The results appeared to be influenced by factors such as the concrete strength and loading rate and further work is needed to extend the results to full scale testing of bridge beams.     

Structural reliability of concrete bridges including improved chloride-induced corrosion models

A structural deterioration reliability (probabilistic) model has been used herein to calculate probabilities of structural failure. New reinforced concrete corrosion initiation, corrosion rate and time-variant load models are proposed. Three durability design specifications are considered in a lifetime reliability analysis of a RC slab bridge. Time-variant increases in loads are considered also. It was found that the application of de-icing salts causes significant long-term deterioration and reduction in structural safety for poor durability design specifications. A reduced cover or increased water-cement ratio increases failure probabilities. When compared to the case of “no deterioration”, it was observed also that the probability of failure only marginally increased for good durability design specifications. The approaches described herein are relevant to other physical infrastructure also.     

配筋砌块砌体剪力墙抗剪承载力研究

对配筋砌块砌体剪力墙抗剪承载力进行了理论分析和试验研究。在综合分析影响配筋砌块砌体剪力墙抗剪承载力的各种因素的基础上 ,按结构可靠度设计原则 ,提出了配筋砌块砌体剪力墙抗剪承载力的设计计算公式。其计算结果与试验结果吻合较好。     

Evaluation of performance characteristics of the heavy vehicle simulator in Florida

The Florida Department of Transportation (FDOT) Materials Office has recently acquired a heavy vehicle simulator (HVS) and constructed an accelerated pavement testing (APT) facility which uses this HVS. An investigation was conducted to evaluate the operational performance of the HVS, and to determine its most effective test configurations for use in evaluating the rutting performance of pavement materials and/or designs under typical Florida traffic and climate conditions. Five trial runs with the HVS used a super single tire with a load of 4082 kg, tire pressure of 793 kPa and a wheel traveling speed of 12.9 km/h. These five trial runs used different combinations of wheel traveling direction (uni-directional or bi-directional), total wheel wander and wander increments. The uni-directional loading was found to be a more efficient mode for evaluation of rutting performance using the HVS. As compared with the bi-directional loading mode, the uni-directional mode produced substantially higher rut depths for the same number of wheel passes and also for the same testing time duration. When the bi-directional loading with no wander was used, imprints of the tire treads were observed on the wheel track. It was found that using a loading mode with wander smoothened out the imprints of the tire treads considerably. The uni-directional loading mode with 10 cm wander using 2.5 cm increments was selected to be used for evaluation of rutting performance based on consideration of testing efficiency and realistic rutting results.     

马道静载试验与有限元分析

本文以某大剧院多功能厅钢桁架结构马道为背景,对该马道进行了静载试验研究。由于是新建结构,对其正常使用存在不确定性,所以用单调加载静力试验来研究其承载力和稳定性。通过静载试验得到马道最大跨主要受力杆件的应变大小以及最大跨挠度大小等重要数据,然后使用有限元软件ABAQUS进行了建模分析,由此也进一步的验证出检测数据的可靠性。有了这一分析过程也将为现实工程结构静载试验检测鉴定提供参考。     

深部矿区煤岩体强度测试与分析

 基于钻孔触探法原理,开发出小孔径井下煤岩体强度测定装置。在实验室对34个煤岩样品进行试验：在煤岩块上钻取标准试件,测量单轴抗压强度;在留下的钻孔中,用煤岩体强度测定装置测定探针临界载荷,分析探针破坏钻孔壁煤岩的形态;然后确定煤岩块单轴抗压强度与探针临界载荷的关系。试验表明,探针破坏钻孔壁煤岩的形状、深度及范围与煤岩性质密切相关。煤岩体强度越高,破坏范围、侵入深度越小,破坏形状越规则。结合井下实测数据,回归得出描述探针临界载荷与煤岩体单轴抗压强度关系的公式。同时,分析临界载荷的离散性及控制措施,讨论结构面对煤岩体强度的影响及测试分析方法,并在典型的深部矿区——新汶矿区进行井下原位测试。新汶矿区巷道顶板不同岩性的岩层强度相差很大,不同矿井的岩层强度也存在明显差别。煤层强度由于煤帮出现破碎区、煤层性质不均匀、煤层结构面分布不均匀等原因变化较大,出现明显的波动。基于井下煤岩体强度实测数据的巷道支护设计,符合井下环境中的煤岩体条件,设计的合理性与可靠性显著提高,巷道围岩稳定性与支护状况得到明显改善。最后分析钻孔触探法存在的问题,并提出改进建议。     

Optimisation of shell buckling using lower bound capacities

In the context of aerospace and marine applications there are considerable incentives for designers to adopt thin shells, whose performances are enhanced by appropriately chosen rib stiffeners or using high-performance composite materials. Imperfection-sensitive buckling in these circumstances is controlled by extremely high numbers of independent material and geometric parameters. As a basis for design, traditional reliance upon scatter of test results is suggested to be untenable and the increasing tendency to replace this approach by use of nonlinear finite elements is argued to bring with it all sorts of other quite considerable practical problems.This paper describes how the long established and very simple “reduced stiffness method” (RSM) is able to provide an alternative design strategy. It shows how a very straightforward extension of classical critical load analysis allows the definition of lower bounds to the potential imperfection sensitivity in each mode and consequently the delineation of the mode and load likely to provide the controlling influence on design. Reliability of its predictions is briefly demonstrated through comparisons with extensive test programmes and confirmation through carefully controlled nonlinear numerical studies. Use of the RSM is shown to offer scope for identifying material and geometric parameters that result in improved and even “optimum” buckling loads. Case studies from past and a current programme of research looking at the buckling of composite shells are used to illustrate this design potential.     

Numerical simulation of structural behaviour of transmission towers

Transmission towers are a vital component and management needs to assess the reliability and safety of these towers to minimise the risk of disruption to power supply that may result from in-service tower failure. Latticed transmission towers are constructed using angle section members which are eccentrically connected. Factors such as fabrication errors, inadequate joint details and variation of material properties are difficult to quantify. Consequently, proof-loading or full-scale testing of towers has traditionally formed an integral part of the tower design. The paper describes a nonlinear analytical technique to simulate and assess the ultimate structural response of latticed transmission towers. The technique may be used to verify new tower design and reduce or eliminate the need for full-scale tower testing. The method can also be used to assess the strength of existing towers, or to upgrade old and aging towers. The method has been calibrated with results from full-scale tower tests with good accuracy both in terms of the failure load and the failure mode. The method has been employed by electricity utilities in Australia and other countries to: (a) verify new tower design; (b) strengthen existing towers, and (c) upgrade old and aging towers.     

Reliability-based calibration of load duration factors for timber structures

The load bearing capacity of timber structures decrease with time depending on the type of load and timber. Based on representative limit states and stochastic models for timber structures, load duration factors are calibrated using probabilistic methods. Load duration effects are estimated on basis of simulation of realizations of wind, snow and imposed loads in accordance with the load models in the Danish structural codes. Three damage accumulation models are considered, namely Gerhards model, Barrett and Foschi’s model and Foschi and Yao’s model. The parameters in these models are fitted by the Maximum Likelihood Method using data relevant for Danish structural timber and the statistical uncertainty is quantified. The reliability is evaluated using representative short- and long-term limit states, and the load duration factor k_mod is estimated using the probabilistic model such that equivalent reliability levels are obtained using short- and long-term design equations. Time variant reliability aspect is considered using a simple, representative limit state with time variant strength and simulation of the whole life time load processes.     

On the relationship between platform topology, topside weight and structural reliability under storm overload

The relationship between platform configuration and structural reliability is investigated by comparing the collapse behaviour of simple jacket, jack-up and monopod topologies under storm loading in moderately shallow North West Shelf (NWS) waters. Two different pushover analysis methods are used to find the ultimate strength, which give quite different reserve strength ratio (RSR) results for certain structures. The effect on the structural reliability of varying topside weight is also assessed. It is found that the reliability trends are strongly dependent on structural topology — an effect that is not included in current Codes of practice. It is also shown that a single set of partial load factors for dead and environmental loads cannot achieve uniform reliability across different platform configurations in the same environment. Furthermore, in some cases, a working stress design format gives more consistent reliability results than the load and resistance design factor approach.     

结构运营模态测-辨相和理论

运营模态是表征实际工程结构动力特性的重要参数。从结构动力学基本理论出发,阐释了振动测试与模态识别的动力学互馈本质,指出传统模态测试精度不高的根本原因在于两者的割裂操作,提出“振动测试正向服务模态辨识、模态辨识逆向指导振动测试”的动力学统一范畴,建立了结构运营模态测 辨相和理论,给出由响应强度、识别误差和重构精度三大系列评价准则构成的理论体系框架,以健康监测基准模型模拟数据和某大跨径桥梁实测数据为例,共同印证该理论可有效解决以往振动测试的盲目性和模态识别的被动性。文末,总结并展望了结构运营模态测 辨相和理论的发展趋势。     

“Objective” low informative priors for Bayesian inference from totally censored Gaussian data

Consider structural elements with random strength that after a suitable transformation has normal distribution with unknown mean μ and known or unknown standard deviation σ. By proof testing of n of these structural elements to a given load level it is observed that none of the elements fail. Given solely this test information the problem is that in order to state anything about either the value of μ when σ is known or about the values of μ and σ when both parameters are unknown, it is necessary to introduce some more information in the form of a suitable prior distribution of the parameters, that is, to use a Bayesian procedure with an informative prior. The paper considers the problem of defining such a prior in an axiomatic (“objective”) way without extending the information represented by the test results by more than very little extra information based on common physical sense. The solution suggested in the paper implies that the posterior distribution of the mean shifts towards larger values when the sample size n increases. However, convergence to a specific value is not obtained as long as no failures are observed among the tests. Moreover it turns out that the posterior distribution of the standard deviation is invariant to the sample size n, that is, no updating of the standard deviation is obtained as long as there are no failures among the tests.     

Reliability analysis of reinforced concrete columns exposed to fire

A reliability analysis is conducted on reinforced concrete columns subjected to fire load. From an evaluation of load frequency of occurrence, load random variables are taken to be dead load, sustained live load, and fire temperature. Resistance is developed for axial capacity, with random variables taken as steel yield strength, concrete compressive strength, placement of reinforcement, and section width and height. A rational interaction model based on the Rankine approach is used to estimate column capacity as a function of fire exposure time. Various factors were considered in the analysis such as fire type, load ratio, reinforcement ratio, cover, concrete strength, load eccentricity, and other parameters. Reliability was computed from 0 to 4 h of fire exposure using Monte Carlo simulation. It was found that reliability decreased nonlinearly as a function of time, while the most significant parameters were fire type, load ratio, eccentricity, and reinforcement ratio.     

圆CFRP-钢管混凝土的剪切性能试验研究

研发了结构用杆件在剪切力作用下的试验装置和方法。以混凝土强度和横向CFRP层数为主要参数,分别进行了9个圆CFRP-钢管混凝土试件和3个圆钢管混凝土试件的剪切静力试验研究。试验结果表明,试件的剪力-剪切位移曲线可以划分为弹性阶段、增强阶段和软化阶段。提高混凝土强度和增加横向CFRP层数都可以提高试件的抗剪承载力。钢管和CFRP可以协同工作,纵向应变和横向应变均为拉应变,而45?方向应变为压应变。应用有限元软件ABAQUS模拟了试件的剪力-剪切位移曲线,模拟结果与试验结果吻合良好。     

静载检测技术在房屋改造工程中的应用

随着结构加固施工技术不断发展改进,如何验证加固施工效果成为工程技术人员研究和探索的课题。结合北京京广中心装修改造工程加固施工,详细介绍了胶栓粘钢加固梁静载检测技术原理、工艺流程、操作要点、加载方式。通过静载检测技术在改造工程中的应用,为同类工程提供借鉴意义。     

Sample-specific linearization in reliability analysis of off-shore structures

The reliability analysis of off-shore structures under dynamic non-Gaussian wave, wind and water current loading is considered using an outcrossing approach and directional simulation in the space of the load processes. To circumvent the non-Gaussianity of the load processes for which results for mean outcrossing rate are not generally available, the “sample-specific linearization method” is proposed. This method is based on well-known results for Gaussian processes and uses the functional relationships between the non-Gaussian wave, wind and water current loads and the corresponding velocities. The proposed method is applied to a simple model off-shore structure. The structure is analyzed also to obtain probability of failure by means of Monte Carlo simulation and using time domain simulation of the load processes. This was found to be extremely expensive of computer time. The results were found to compare very favourably with those obtained by the proposed method, both in terms of accuracy and computation required.     

沈阳文化艺术中心单层折板空间网格结构整体模型试验研究

沈阳文化艺术中心主体结构采用不规则单层折板空间网格结构,此结构面内、面外刚度受结构折板构型影响较大,内力分布与整体稳定性对折板构型的变化敏感。因此,对该结构进行了整体模型试验,以考察结构设计的安全性。针对试验模型构型复杂、加载难度大等特点,设计了基于“并联弹簧拉索按刚度分配荷载”的顶面网格加载系统和基于“使用定滑轮实现荷载转向”的侧面网格加载系统,完成对模型竖向恒载、活载与水平风载工况的有效模拟。试验结果表明,在设计荷载范围内,随着荷载的增大,结构位移与内力响应基本呈线性发展,模型竖向荷载向基础的传递主要依靠竖向主构件实现,环向主构件起拉结作用。同时,对模型结构进行了有限元分析,分析结果与试验结果吻合较好,验证了有限元分析模型的合理性与分析结果的准确性。在此基础上,进行了原型结构的稳定承载力分析和出现局部破坏时的抗连续性倒塌分析,证实该结构在设计荷载下具有足够的稳定承载能力和抗倒塌性能。     

Reliability assessment of cable-stayed bridges based on structural health monitoring techniques

This paper presents the reliability analysis approach of long-span cable-stayed bridges based on structural health monitoring (SHM) technology. First, the framework of structural reliability analysis is recognised based on SHM. The modelling approach of vehicle loads and environmental actions and the extreme value of responses based on SHM are proposed, and then models of vehicle and environmental actions and the extreme value of inner force are statistically obtained using the monitored data of a cable-stayed bridge. For the components without FBG strain sensors, the effects and models (extreme values) of dead load, unit temperature load, and wind load of the bridge can be calculated by the updated finite element model and monitored load models. The bearing capacity of a deteriorated structure can be obtained by the updated finite element model or durability analysis. The reliability index of the bridge's critical components (stiffening girder in this study) can be estimated by using a reliability analysis method, e.g. first order reliability method (FORM) based on the models of extreme value of response and ultimate capacity of the structure. Finally, the proposed approach is validated by a practical long-span cable-stayed bridge with the SHM system. In the example, reliability indices of the bridge's stiffening girder at the stage after repair and replacement after 18 years of operation, and the damaged stage are evaluated.     

The design of perforated cold-formed steel sections subject to axial load and bending

The uprights in a typical pallet rack are typically singly-symmetrical cold-formed sections subject to axial load together with bending about both axes. They usually contain arrays of holes in order to enable beams to be clipped into position at heights that are not pre-determined prior to manufacture. Their slenderness is such that their behaviour may be influenced by the three generic forms of buckling, namely local, distortional and global (lateral torsional). In practice, these members have generally been designed on the basis of expensive test programmes. This paper addresses the problem of how they might be designed analytically. The basis of the investigation is a comprehensive set of test results on upright sections in compression which embraces both stub column tests, in which the load position was varied along the axis of symmetry, and longer columns. The test results were analysed using both finite elements and a version of “Generalized Beam Theory” (GBT) which incorporated systematic imperfections. Consideration was also given to the design procedures proposed by the “Federation Europeene de la Manutention” (FEM) and recent research into the influence of perforations on the performance of cold formed steel sections. It is shown that GBT can be modified to take account of perforations so that the lower bound results give a sufficiently accurate column design curve, which takes account of local, distortional and global buckling, thus making extensive testing unnecessary.