Life-cycle cost analysis of bridges subjected to fatigue damage

Life-cycle cost analysis (LCCA) is a decision-making tool particularly useful for the design of bridges as it predicts lifetime expenses and supports the inspections management and the maintenance activities. LCCA allows to consider uncertainties on loads, resistances, degradation and on the numerical modelling and structural response analysis. It also permits to consider different limit states and different types of damage in a unified framework. Among the types of damages that can occur to steel and steel-concrete composite bridges, fatigue is one of the most dangerous ones, as it may lead to sudden and fragile rupture, even at operational traffic levels. In this context, the present paper proposes a framework for LCCA based on the use of the Pacific Earthquake Engineering Research (PEER) equation which is for the first time utilized for fragility and cost analysis of bridges subjected to fatigue, highlighting the possibility of treating the problem of fatigue damage estimation with an approach similar to the one currently adopted for damage induced by other hazards, like earthquake and wind. To this aim, a damage index computed through the Palmgren-Miner’s rule is adopted as engineering demand parameter. The framework is applied to a composite steel-reinforced concrete multi-span roadway bridge by evaluating the fatigue limit state from different traffic load models, i.e. a Technical Code-based model and a model based on results of Weigh in Motion monitoring system. The evolution over time of the probability of failure and the life-cycle costs due to fatigue damage induced by heavy traffic loads are investigated for different probability distributions of the engineering demand parameter and for different fragility models. The comparison between the fatigue failure probabilities and the life-cycle costs obtained with the two traffic models, encourages the adoption of traffic monitoring systems for a correct damage estimation.

Efficiency of Intensity Measures Considering Near- and Far-Fault Ground Motion Records

This paper focuses on the identification of high-efficiency intensity measures to predict the seismic response of buildings affected by near- and far-fault ground motion records. Near-fault ground motion has received special attention, as it tends to increase the expected damage to civil structures compared to that from ruptures originating further afield. In order to verify this tendency, the nonlinear dynamic response of 3D multi-degree-of-freedom models is estimated by using a subset of records whose distance to the epicenter is lower than 10 Km. In addition, to quantify how much the expected demand may increase because of the proximity to the fault, another subset of records, whose distance to the epicenter is in the range between 10 and 30 Km, has been analyzed. Then, spectral and energy-based intensity measures as well as those obtained from specific computations of the ground motion record are calculated and correlated to several engineering demand parameters. From these analyses, fragility curves are derived and compared for both subsets of records. It has been observed that the subset of records nearer to the fault tends to produce fragility functions with higher probabilities of exceedance than the ones derived for far-fault records. Results also show that the efficiency of the intensity measures is similar for both subsets of records, but it varies depending on the engineering demand parameter to be predicted.

Seismic vulnerability assessment of RC curved bridges piers subjected to bidirectional earthquake

Curved beam bridge is a kind of irregular structure, which has the advantage of adapting to complex terrain, but it is more vulnerable to damage than regular bridge under earthquake. This paper investigates the vulnerability of curved continuous girder bridges under the action of bidirectional earthquake horizontal earthquake, and the difference of vulnerability between side pier and intermediate pier is analyzed. Fragility assessment is performed using an incremental dynamic analysis method subjected to a wide range of as-recorded sequences. A proper engineering demand parameter (EDP) which can result in the most probability of failure at bridges employed in this study is determined. Result indicates that only considering the unidirectional seismic input will underestimate the seismic response and potential damage of the structure, which is not accurate for the seismic performance evaluation of the bridge. Result also shows that the damage probability of the intermediate pier of the curved bridge is higher than that of the side pier, and the more serious the failure, the smaller the difference between the two piers.

A physics-based approach for predicting time-dependent progression length of backward erosion piping

The progression length at various stages of backward erosion piping (BEP) in levee systems can serve as a key engineering demand parameter for reliability and risk assessments. The main goal of this study is to put forward a reliable and computationally efficient technique for predicting the progression length during BEP. Many existing modeling approaches for predicting progression lengths of BEP are either computationally expensive or consider a constant, time-independent amplification factor for the permeability coefficient. In contrast, the model developed here considers the underlying physical phenomena to properly capture the amplification of the permeability coefficient during the progression of BEP. The proposed model is derived considering the rolling threshold condition, which is obtained from the moment equilibrium of erodible particles. This modeling approach with time-varying permeability coefficients has been implemented in FLAC3D, and the derived BEP paths are validated for three flume experiments. The impact of material properties including porosity, tortuosity, and coefficient of uniformity on the amplification factor are investigated. These analyses show that the permeability amplification factor and the progression length increase with low rates at the initial stages of piping. Following the formation of the piping path, they both increase at a generally greater rate over time.

Efficiency of ground motion intensity measures with earthquake-induced earth dam deformations

In a seismic hazard analysis (SHA), the earthquake loading level should be predicted for one or more ground motion intensity measures (IMs) that are expected to relate well with the engineering demand parameters (EDPs) of the site. In this study, the goal was to determine the IMs that best relate to embankment dam deformations based on nonlinear deformation analysis (NDA) results of two embankment dams with a large suite of recorded ground motions. The measure utilized to determine the “best” IM was standard deviation in the engineering demand parameter (e.g., deformation) for a given IM, also termed “efficiency.” Results of the study demonstrated that for the NDA model used, Arias intensity (AI) was found to be the most efficient predictor of embankment dam deformations. In terms of pseudo-spectral acceleration (PSA)-based IMs, the PSA at short periods and then in the general range of the natural period of the dams was seen to be the most efficient IM, but was in almost all cases not as efficient as AI.

Intensity-based demand and capacity factor design: A visual format for safety checking

Quantitative safety checking is an essential part of performance-based design and retrofit of new and existing construction. The intensity-based demand and capacity factor design (DCFD) is a practical closed-form safety-checking format that lends itself quite well to visual interpretation. Adopting the critical demand to capacity ratio as a global damage measure directly, skipping the engineering demand parameter, helps in identifying the onset of the prescribed performance levels. For each intensity level, the contribution to the error in the DCFD format in logarithmic domain is visualized as the distance between the hazard curve and its tangent at median intensity at the onset of the performance level weighted by the probability density of the intensity-based capacity. The latter reaches its maximum value at the median intensity at the onset of the performance level, where the error in hazard is zero, and decays with a rate that depends on the logarithmic standard deviation of fragility. The proposed intensity-based DCFD provides accurate safety-checking estimates that are always on the safe side for concave mono-curvature hazard curves in the logarithmic scale.

Beam-column modeling and seismic fragility analysis of a prestressed segmental concrete tower for wind turbines

As the development of wind energy in earthquake areas advances, the seismic performance of concrete supporting towers has become an important subject. A beam-column model is developed for a prestressed segmental concrete tower supporting a wind turbine considering the properties of dry joints. The proposed model is in good agreement with the solid element model deformation results and the field test modal results. Based on the beam-column model, nonlinear time history analyses considering uncertainties are conducted to evaluate the behavior of the prototype tower under earthquake action. In the process, a new engineering demand parameter, called the average curvature, is defined. The results are compared with those based on a conventional engineering demand parameter. The availability of the prototype tower under earthquake action and the effectiveness of the newly defined engineering demand parameter are validated.

Application of Storm Erosion Index (SEI) to parameterize spatial storm intensity and impacts from Hurricane Michael

Hurricane Michael made landfall as a Category 5 Hurricane on 10 October 2018 between Mexico Beach, Florida and Tyndall Air Force Base in Panama City Beach, Florida causing damages totaling $25 billion (Beven et al. 2019). While damages were caused by both wind and surge, this paper is solely concerned with the surge induced damages which were observed predominantly within 50 km (27 nmi) of the hurricane’s path. Generally, regions to the east of Hurricane Michael’s landfall sustained the most severe damages and appear consistent with the spatial gradient in peak water levels. This gradient was marked; with surge induced damage concentrated in the immediate vicinity of Mexico Beach and attenuating significantly over distances as little as 37 km (20 nmi) to the west in Panama City Beach and east in Port Saint Joe (Kennedy, in review). The gradient in erosion was also pronounced, with Panama City Beach experiencing an average erosion rate of 0.4 m3/m (3.9 cy/ft) while Mexico Beach and Cape San Blas experienced rates approximately three (1.1 m3/m or 11.5 cy/ft) and five (1.7 m3/m or 18.5 cy/ft) times that. For inherent reasons, the pronounced gradient in surge damages and erosion values are of primary interest to coastal researchers and managers. Storm Erosion Index (SEI), developed by Miller and Livermont (2008) combines the three primary drivers of coastal erosion (wave height, total water level, and storm duration) into a physically meaningful form to evaluate storms based on their erosion potential. Here, SEI is applied to explore these spatial variations at seven distinct regions within the Florida Panhandle and are compared to the observed impacts for both erosion and structural damages. These regions include: (west to east) Panama City Beach, Tyndall Air Force Base (AFB), Mexico Beach, Cape San Blas, Port St. Joe, St. Vincent Island, and St. George Island. Empirically, the cumulative SEI relates well with the observed beach erosion; while the Peak Erosion Intensity (PEI) was found to better capture the trends in structural damages. By capturing the spatial variation of the storm intensity, SEI and PEI are therefore proposed as a viable engineering demand parameter with potential applications in community scale fragility curves.

Seismic Response of Plan-Asymmetric Structures with Diaphragm Flexibility

The seismic behavior of asymmetric structures with a flexible diaphragm was studied by conducting inelastic dynamic time-history analyses. Asymmetric structures with different configurations of mass, stiffness, and strength centers, in combination with a wide range of diaphragm flexibility, were evaluated. The behavior of structures was studied by considering three aspects:(1)effect of structural asymmetry on diaphragms deformation;(2)effect of diaphragm flexibility on demands of the lateral load-resisting elements;(3)optimum configuration of mass, stiffness, and strength centers to limit important engineering demand parameters in asymmetric structures with a flexible diaphragm. The results showed that the shear-dominant deformation of diaphragms is sensitive to both structure asymmetry specifications and the degree of diaphragm flexibility; therefore, it can be used for the qualitative classification of the seismic behavior of structures. Also, the center of strength in structures with flexible diaphragm is more important relative to the stiffness center and has a significant effect on engineering demands at all levels of diaphragm flexibility. Moreover, it was found that a suitable configuration of centers in torsionally stiff structures depends on the degree of diaphragm flexibility, in addition to the intensity of earthquakes (structure yield level) and selected engineering demand parameter.