Search

This paper reviews the fundamentals of the durability of structural concrete, and then applies the concepts to the durability design, quality control, performance assessment and maintenance planning of concrete structures in Hong Kong-Zhuhai-Macau (HZM) sea link project with design working life of 120 years. The durability design adopts a multi-level philosophy for different durability risks and uses model-based approach to determine design parameters. The long-term exposure data of 30 years were used to calibrate the chloride ingress model and quantify the modelling uncertainty. The durability quality control was realized through converting the design values to laboratory characterization values, especially for the chloride diffusivity. With the data collected in construction phase, a full-probabilistic assessment is performed on the achieved performance against the chloride ingress, serving as basis for maintenance planning. The open issues related to the durability of concrete infrastructures with long service life are elaborated in the end.

Resilience is an attribute of communities, and is supported by community building sectors (occupancy types) with different functionalities. Evaluating community resilience and functionality requires the establishment of new metrics and their quantification. This study introduces a methodology to consider how the interdependencies in functionality among different building sectors impact community resilience. Four building sectors that provide essential functions to a community, i.e. housing, education, business and public services, are considered. The percentage of people in a community who dislocate following a disaster as a result of the physical damages to buildings is selected as the resilience metric in this conceptual study. A framework is further developed to determine the optimum strategies for retrofitting community building portfolios as a whole in order to achieve an overall community resilience objective expressed in terms of the threshold value of the community resilience metric identified above. Finally, the methodology to quantify community functionality and the associated retrofit optimization algorithm are illustrated using a simplified hypothetical community building portfolio in China exposed to potentially severe earthquakes, in which the objective is to achieve a predetermined functionality level when financial constraints may be present.

Civil structures and infrastructure facilities are susceptible to deterioration posed by the effects of natural hazards and aggressive environmental conditions. These factors may increase the risk of service interruption of infrastructures, and should be taken into account when assessing the structural reliability during an infrastructure's service life. Modeling the resistance deterioration process reasonably is the basis for structural reliability analysis. In this paper, a novel model is developed for describing the deterioration of aging structures. The deterioration is a combination of two stochastic processes: the gradual deterioration posed by environmental effects and the shock deterioration caused by severe load attacks. The dependency of the deterioration magnitude on the load intensity is considered. The Gaussian copula function is employed to help construct the joint distribution of correlated random variables. Semi-analytical methods are developed to assess the structural failure time and the number of significant load events (shocks) to failure. Illustrative examples are presented to demonstrate the applicability of the proposed model in structural reliability analysis. Parametric studies are performed to investigate the role of deterioration-load correlation in structural reliability.

Purpose There are two kinds of thawing temperatures commonly adopted in cancer cryosurgery. We attempted to compare their efficacy differences in this study to optimize the surgical method. Method Forty-five C57BL/6 J mice with GFP-labeled Lewis lung cancer were randomized into three groups ( n = 15 for each): control group, T0 group (thawing temperature 0 °C), and T40 group (thawing temperature 40 °C). Cryoablation was performed using a combined surgical system. When the ice ball reached the border of the tumor, they were rewarmed to 0 °C and 40 °C, respectively, using a single freeze–thaw cycle. After the surgery, weight of these mice, length/width and the fluorescence intensity (FI) of the tumors were recorded. All mice were sacrificed on Day 14 after the procedures and their xenografts were excised and weighed immediately. We also checked for pulmonary metastasis, and examined tumor specimens using HE staining. Results Body weights, tumor volumes and FI in the three groups did not differ significantly at baseline. On Day 14, 39% of the tumors in the T0 group decreased in volume, whereas only 17% in the T40 group did. The average FI in the control group increased by 60%, but declined by 72% in T0 mice and 69% in T40 mice. Tumor inhibition rates were 71.64% in the T0 group and 68.12% in the T40 group. Lung metastases rates and histological changes were compatible between the two intervention groups. Conclusion Using 0 °C as the thawing temperature may have more potential benefits in cryoablation efficacy.

Probabilistic damage evaluation and loss estimation of spatially distributed infrastructure systems (e.g. an electric power system or a building portfolio) under a scenario tropical cyclone must consider the spatial correlation of cyclone wind speeds to estimate their impact on the built environment statistically. Previous studies have seldom considered the impact of this spatial correlation on damage assessments of distributed civil infrastructure. In this paper, a stochastic field model is developed to capture the uncertainty of cyclone wind speeds and their spatial correlation for the North Atlantic region. A series of recorded wind speed fields of historical cyclone events are examined. The bias values between the recorded wind speeds and computed wind speeds based on a widely used cyclonic wind field model are obtained. The statistics of the wind field bias are estimated using geostatistical tools. The effect of wind speed uncertainty and spatial correlation on performance assessment of distributed infrastructure systems is illustrated using an electric power system, where the metrics of performance are damage ratio, outage ratio and outage cost.

Life cycle cost (LCC) analysis offered a useful framework to think about the efficiency of infrastructures investment. However, the widely accepted algorithm of the LCC doesn’t account for the decision maker's attitude toward the risk of future consequences. The cumulative prospect theory (CPT) can be used to reveal the decision maker's preference under different risk and uncertainty conditions, and has been applied in literature to some design optimization issues. Nevertheless, previous research didn’t consider the fact that people's risk preference may vary with time, i.e., there is a reasonable tendency that people will be more risk-averse to the near future losses than to the far future losses. Recognizing this, this paper adopts the CPT model in the minimum expected cost analysis, and moreover incorporates the time-varying weighting function included in the CPT model to reflect the possible changing of risk preference toward future events. A seismic retrofit optimization of a dam built in strong earthquake-prone area is used to demonstrate the application of the method, and it is found that considering the time-varying of risk preference leads to a low design level compared with that by the CPT model, but a high design level compared with the traditional LCC.

The service life of reinforced concrete (RC) structures in marine environments is mainly influenced by the chloride-induced corrosion of reinforcement, and the development of chloride penetration model is essential for its assessment. The empirical Fick’s second law of diffusion provides a simple way to predict the chloride penetration in practical situations. However, the derivation of parameters of this model is mainly based on the results of laboratory experiments or field exposure trials, and these parameters need to be calibrated with long-term field results of real structures. The filed investigations of seventeen high-pile wharf structures located at the south coast of China were carried out, and the results were compared with the long-term exposure test results in terms of chloride ingress profile. The probability models for surface chloride content and chloride diffusion coefficient were derived according to these results; and finally the effects of different models of chloride ingress parameters, based on exposure trails or based on real structure surveys, on the expected service life of marine structures were investigated.

The intensity and/or frequency of hurricane storms may change due to the impact of potential climate change. This paper presents a probabilistic framework to assess the hurricane damage to residential constructions considering the non-stationarity and correlation in hurricane actions. The framework includes a non-stationary Poisson process of hurricane occurrence, a failure rate function of hurricane damage, and explicit formulas for evaluating the mean and variance of annual hurricane damage. The framework is illustrated using a case study of Miami-Dade County, Florida, where the current probabilistic models of hurricane intensity and occurrence rate were estimated by examining hurricane history in this area. The impacts of time-variant hurricane intensity and time-variant hurricane frequency on building damage are assessed individually using the developed framework. The paper also investigates the effects of correlation in hurricane wind speeds on hurricane damage.

Post-earthquake fire (PEF) is a hazardous secondary disaster following earthquake, and the multi-ignition of PEFs can result in huge economic loss and heavy casualties. The suppression of PEFs depends on the water distribution system (WDS) to provide water. Although a number of studies have been conducted to evaluate the firefighting capacity of WDS, their hydraulic modelling analyses fail to consider the influence of firefighting demand at one node on the water supply capability of other nodes, which may result in an overestimate of the WDS’ capability to suppress multiple simultaneous occurrence of PEFs. In this study, an integrated procedure is developed to evaluate the firefighting capacity of WDS under the effects of both seismic pipeline damage and multi-ignition of PEFs. Under the excitation of earthquakes with different intensities, the spatial distributions of PEFs and pipeline damage are simulated, and the associated uncertainties are included by Monte Carlo simulations. The firefighting capacity of WDS is defined as the probability of providing sufficient water to suppress multiple PEFs, which, combined with the probability distribution of ignition number of PEFs, can achieve the risk assessment of a city to suffer uncontrolled PEFs. The developed method is applied to a WDS currently operating in a Chinese city. Discussions are made on the influences of multiple simultaneous water demands on firefighting capacity evaluation of WDS and the possible applications of the proposed method.

This paper presents the durability design of concrete structures in the Hong Kong–Zhuhai–Macau (HZM) sea link project for a design service life of 120 years. Among all the durability issues, this paper focuses on the model-based durability design of concrete structures in the project subject to the action of marine chlorides. The mechanism and modeling of chloride penetration into concrete are reviewed in depth and the applicability of models for durability design is evaluated. On the basis of long-term exposure tests and in-place structural investigations during the past 30 years in South-eastern China, the design model for concrete structures in the HZM project is established. The statistical properties of model parameters are analyzed in details and compared to other chloride ingress models. Using the established HZM model for chloride ingress and specified durability limit state (DLS), the design parameters are first evaluated through a fully probabilistic analysis in terms of service lives (50 years, 120 years) and target reliability levels ( β = 1.3, 1.5, 1.8). The partial factor format for durability design is then established and the partial factors are calibrated from the first order reliability method (FORM) from specified service life and specified reliability level. The design results from the partial factor design equation are given for different exposure zones, and the achieved reliability index is verified for each design through the full probabilistic method. Finally remarks are given on the HZM model and its application in durability design of RC elements.

Civil infrastructure performance and reliability may be affected by deterioration in strength or stiffness caused by service or environmental conditions or by systemic changes in load beyond the baseline conditions assumed for design. These changes should be considered when assessing a structure for its continued future reliability in service. This paper presents an improved method for evaluating time-dependent reliability of structures taking these factors into account. The method enables the impact on safety and serviceability of non-stationarity in the load and resistance deterioration processes to be assessed quantitatively. Parametric analyses show that the reliability is sensitive to the load intensity at the end of the service period, moderately sensitive to the initial and final mean occurrence rates of load events and the nature of these increases in time, and relatively insensitive to the nature of the increase in mean load intensity. A realistic time-dependent model of structural resistance is proposed and the role played by the auto-covariance in the resistance degradation process is investigated. The auto-covariance in stochastic resistance plays a significant role in time-dependent reliability assessment. Assuming that the time-dependent resistance is ‘fully correlated’ generally gives a reasonable estimation of structural reliability, while assuming that the resistances are statistically independent at two points in time may cause the failure probability to be overestimated.

Presently, elderly and advanced lung cancer patients have very limited treatment options. With no promising therapy, treatment of these patients is challenging. We have reviewed 119 primary lung cancer patients who received a combined percutaneous cryoablation and traditional Chinese medicine therapy (Cryo-TCM therapy) between 2005 and 2013. Out of 119 patients, 84.1% patients were elderly or advanced lung cancer when receiving cryoablation. Overall Survival time from the time of Diagnosis (DOS) and Cryoablation (COS) was 19 and 10 months respectively, which were longer than data previously published. Patients who accepted only Cryo-TCM therapy got similar DOS as those who were treated with Cryo-TCM and other classic anticancer therapies. Thus, Cryo-TCM therapy can prolong the survival time and can be used as the main therapy for the elderly or advanced lung cancer patients in China both in quality of life and cost effectiveness.

This paper investigates vibration characteristics of footbridge induced by crowd random walking, and presents the application of multiple tuned mass dampers (MTMD) in suppressing crowd-induced vibration. A single foot force model for the vertical component of walking-induced force is developed, avoiding the phase angle inaccessibility of the continuous walking force. Based on the single foot force model, the crowd–footbridge random vibration model, in which pedestrians are modeled as a crowd flow characterized with the average time headway, is developed to consider the worst vibration state of footbridge. In this random vibration model, an analytic formulation is developed to calculate the acceleration power spectral density in arbitrary position of footbridge with arbitrary span layout. Resonant effect is observed as the footbridge natural frequencies fall within the frequency bandwidth of crowd excitation. To suppress the excessive acceleration for human normal walking comfort, a MTMD system is used to improve the footbridge dynamic characteristics. According to the random vibration model, an optimization procedure, based on the minimization of maximum root-mean-square (rms) acceleration of footbridge, is introduced to determine the optimal design parameters of MTMD system. Numerical analysis shows that the proposed MTMD designed by random optimization procedure, is more effective than traditional MTMD design methodology in reducing dynamic response during crowd–footbridge resonance, and that the proper frequency spacing enlargement will effectively reduce the off-tuning effect of MTMD.

The Northridge earthquake caused a number of steel moment-resisting frame (SMRF) buildings to suffer brittle fractures in their beam-to-column welded connections, which raised the concern that similar (undetected) damage may have occurred in other SMRF buildings during past earthquakes in the region. Several issues may arise in decisions to rehabilitate or upgrade older buildings. One is the extent of building to inspect for possible weld fractures. A second is whether fractured connections identified in inspection should be repaired before permitting long-term occupancy. A third is the connection repair cost. This paper proposes an efficient method for selecting connections to be inspected in an existing SMRF for purposes of condition and seismic fragility assessment. The efficiency of this selection method is illustrated by modeling the partial inspection process of two steel frame buildings. Finally, a vulnerability analysis of these buildings is performed as a basis for evaluating repair costs.