Quanwang Li

Time-dependent reliability of ageing structures: an approximate approach

Abstract Concrete structures may deteriorate over time due to aggressive service environments, leading to a reduction in their strengths, stiffnesses and reliabilities. In general, the assessment of time-dependent reliability of ageing structures must consider uncertainties in structural deterioration as well as non-stationarities in the structural load processes. This paper develops an approximate method for assessing the impact of structural deterioration and non-stationary live loads on structures, which requires only low-dimensional integration and reduces the cost of assessing time-dependent reliability over a service life extending to 50 years significantly. This approximate method is demonstrated through several examples. The importance of non-stationarities in the resistance and load processes on time-dependent reliability is illustrated and the accuracy of the method is confirmed in several cases utilising Monte Carlo simulation.

Structural response and damage assessment by enhanced uncoupled modal response history analysis

The Uncoupled Modal Response History Analysis (UMRHA) method developed by Chopra et al. is modified in this paper to estimate damage to welded moment-resisting connections in a steel frame (MRSF) subjected to earthquake ground motions. The behaviour of these connections is modelled by a moment-rotation relationship that accounts for the cracking of the beam flange-to-column flange groove weld. The behaviour of the frame is approximated by a sequence of single-degree-of-freedom (SDOF) models for the first three modes to allow for the contribution of higher modes of vibration. The dynamic properties of these SDOF systems are determined by nonlinear static pushover analyses of the building frame. Because of the significant drop in connection strength caused by beam-to-column weld cracking, the pushover procedure uses a changing rather than invariant distribution of horizontal loads, while the structural responses are calculated from shapes that are based on the displaced shape of the frame after damage occurs. The accuracy of the method is demonstrated by a comparison with the results of a nonlinear time history analysis of the frame. This method can be used for rapid assessment of seismic damage or damage potential and to identify buildings requiring more detailed investigation.

Reliability assessment of aging structures subjected to gradual and shock deteriorations

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 infrastructures 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.

Durability Design of the Hong Kong–Zhuhai–Macau Sea-Link Project: Principle and Procedure

AbstractThis paper introduces the durability design of concrete structures in the Hong Kong–Zhuhai–Macau project for a working life of 120 years. The environmental actions are analyzed and the deterioration processes for the structural concrete are identified. The durability design is performed through material composition control and a performance-based procedure. The target design lives and durability limit states are attributed to concrete elements according to their structural importance and maintenanceability. Given the prescriptive requirements on material compositions, the carbonation-induced and chloride-induced corrosions of reinforcement steel are considered as the most critical processes and subject to model-based design. The thickness and quality of concrete covers are determined from carbonation and chloride penetration models using a partial factor scheme. For chloride ingress, the partial factors are calibrated from a full probabilistic approach for a target reliability β=1.3. The statistic...

Assessing hurricane damage costs in the presence of vulnerability model uncertainty

Probability-based assessment of hurricane damage costs for coastal communities is vital for policy-makers and insurers. The uncertainties associated with hurricane damage costs include both the inherent uncertainty due to the random nature of hurricane process and the model uncertainty of the mathematical representation of hurricane damage (vulnerability model). The hurricane vulnerability model has traditionally been modeled as a deterministic function of hurricane wind speed in the literature, without considering the effect of vulnerability model uncertainty on hurricane damage assessment. This paper develops two methods to assess the hurricane damage costs in the presence of vulnerability model uncertainty. To account for the non-stationarity in hurricane actions due to the potential impact of climate change, the hurricane occurrence process is modeled as a non-stationary Poisson process and the hurricane intensity is assumed to vary in time with time-variant statistical parameters of hurricane wind speed. A case study of Miami-Dade County, Florida, is conducted to illustrate the proposed methods and to investigate the impact of vulnerability model uncertainty on hurricane damage costs.

Modeling the Temporal Correlation in Hurricane Frequency for Damage Assessment of Residential Structures Subjected to Climate Change

AbstractSevere hurricanes in coastal areas have caused enormous human and economic losses. Furthermore, the intensity and frequency of future hurricanes may increase due to the potential impact of ...

Maintenance Design and Optimization of Long Service Life Port Structures Considering Crack Control Levels

This paper investigates the maintenance design for reinforced concrete (RC) elements in a marine port with service life of 100 years. The dominant deterioration process is the chloride-induced corrosion of reinforcement steel bars in RC elements, and the durability limit state (DLS) is defined as the corrosion initiation. The impact of concrete crack on steel corrosion is described by the acceleration effect of the micro-damaged zones in concrete besides crack opening. Then the maintenance cost model is established considering both operation and users costs. The Monte-Carlo simulation technique is used to evaluate the intervention times of maintenance operations. In particular, the influence of crack control width on maintenance costs is investigated. The results show that: (1) the necessary maintenance achieves always the optimized cost, and (2) the crack width of 0.3 mm is the turning point for flexural elements in terms of maintenance costs.

Moment-based evaluation of structural reliability

Abstract Reliability analysis is a widely-used tool to measure a structure’s ability of fulfilling safety and serviceability requirements. Existing methods for reliability assessment have, for the most part, been developed based on using the probability distribution functions of input random variables accounting for the uncertainties arising from both structural properties (e.g., material strength, geometry) and external loads. This paper develops a moment-based method for reliability assessment, which relies on the moment information of input variables rather than the probability distribution functions. It is shown that the proposed method is useful in solving multi-dimensional reliability assessment problems with improved efficiency compared with Monte Carlo simulation. The implementation, validity and efficiency of the proposed method are demonstrated through illustrative examples.

Time-dependent reliability assessment of aging series systems subjected to non-stationary loads

Civil infrastructure systems provide physical supports to a community’s functionalities and are expected to achieve acceptable safety levels subjected to extreme load effects. However, these systems may deteriorate with time as a result of aggressive environmental or operating conditions in service, implying that the system reliability may decline beyond the baseline as assumed for design. Moreover, the increasing trend of the external loads may also contribute to the reduction of the system reliability. In this paper, a semi-analytical method is proposed for assessing the reliability of aging systems subjected to non-stationary loads. The series system is considered, where the system failure is defined as the failure of any single component (structure) among the system. The application of the proposed method is illustrated using a representative series bridge network with several individual bridges. The role of parameters such as the variations in the load intensity, resistance correlation and number of components under attack in the system reliability are investigated.

A simplified method for stability analysis of multi-story frames considering vertical interactions between stories:

Effective length method is still widely used in engineering practice to evaluate the stability of compression members in frame structures. However, the conventional effective length method can be inaccurate in many cases as it considers columns in isolation from the stories above and below. This article proposes an improved method for simplified frame stability analysis that accounts for the vertical interaction effects of columns. The idealized sub-assemblage model includes the columns of all stories and their restraining beams. The stability matrix for a single-story unit is first derived, and then the system stability matrix is obtained by considering the compatibility of the story units. The governing equation for the elastic buckling load of the sub-assemblage is derived. The method is applicable to both sway-permitted and sway-prevented frames. The applicability and accuracy of the proposed method are demonstrated using a series of examples with a wide variation of parameters including numbers of story, boundary conditions, stiffness of beam-to-column connections, column length and stiffness, and axial force level.