Extreme Loading Events Research Articles

Towards establishing practical multi-hazard bridge design limit states

In the U.S., the current Load and Resistance Factor Design (LRFD) Specifications for highway bridges is a reliability-based formulation that considers failure probabilities of bridge components due to the actions of typical dead load and frequent vehicular loads. Various extreme load effects, such as earthquake and vessel collision, are not considered on the same reliability-based platform. Since these extreme loads are time variables, combining them with frequent, nonextreme loads is a significant challenge. The number of design limit state equations based on these failure probabilities can be unrealistically large and unnecessary from the view point of practical applications. Based on the opinion of AASHTO State Bridge Engineers, many load combinations are insignificant in their states. This paper describes the formulation of a criterion to include only the necessary load combinations to establish the design limit states. This criterion is established by examining the total failure probabilities for all possible time-invariant and time varying load combinations and breaking them down into partial terms. Then, important load combinations can be readily determined quantitatively.

Application of Orthogonal Decomposition Approaches to Long-Term Monitoring of Infrastructure Systems

The long-range monitoring of civil infrastructure systems monitored with dense sensor arrays that are capable of generating voluminous amounts of data from continuous online monitoring requires the implementation of a proper data processing and archiving scheme to maximize the benefits of structural health monitoring operations. This paper focuses on the areas of data management, data quality control, and feature extraction of meaningful parameters to describe the response of large-scale infrastructure systems to ambient excitation in the context of structural health monitoring (SHM). Recordings from the monitoring system installed on the Vincent Thomas Bridge (VTB) in San Pedro, California form the database of the proposed data-management and archiving methodology. The data processing methodology for the VTB is based on the calculation of the sensor array acceleration covariance matrices for every hour of available data and the subsequent orthogonal decomposition of the covariance matrices. The dominant proper orthogonal modes of the bridge are determined, and their statistical variations over an extended observation period covering several months of continuous data are quantified and analyzed. The empirical probability density functions for the mean daily bridge accelerations are computed and used to compare the statistical variations in different periods of operation of the bridge (working days, weekends, holidays). It is shown that the computed statistical distributions of the bridge response can provide a quantitative baseline through which to facilitate the early detection of any anomalies indicative of a possible structural deterioration resulting from fatigue (service loads) or extreme loading events, i.e., earthquakes, artificial hazards, or other natural hazards.

Energy absorption potential of light weight concrete floors

This paper investigates the energy absorption potential offered by light weight concrete (LWC) floors, perhaps when a building is poised to collapse from some extreme loading event. It is assumed here that the failure of LWC structural floor slabs would likely result in both break-up and pulverization of the concrete. To estimate the extent to which crushing of large portions of floor slab material would absorb energy, a series of concrete penetration tests employing patch loading was undertaken on scaled down model slabs. Six specimens had free (unconfined) edges, while the other four were confined along the edges. The test results, together with research findings obtained from the mining and milling industry, indicate that such floor systems would likely play an important role in absorbing energy during global collapse catastrophes.

Lifetime Highway Bridge Traffic Load Effect from a Combination of Traffic States Allowing for Dynamic Amplification

Recent research has shown that the dynamic amplification factor (DAF) to be applied to free-flowing traffic-induced load effect may not be as high as previously thought. Therefore, congested traffic states may govern extreme load effect at lower bridge lengths than currently assumed. Thus, there is a need for a methodology that incorporates both free-flowing and congested traffic states in the calculation of lifetime load effect. It should allow for the relative frequency of occurrence of the different forms of traffic and any form of DAF function that may arise. This paper presents such an approach and also presents a general probabilistic DAF formulation for inclusion. Using measured traffic, the approach is applied to a range of bridge lengths and load effects employing a variety of DAF approaches from the literature, in addition to the new DAF formulation. Using a critical traffic index, it is shown that the governing form of traffic is very sensitive to the dynamic amplification model used. Further, depending on this model, congested traffic can govern short spans, and for other spans, a combination of free- and congested-flow traffic states must be considered.

Behavior of butt-welds and treatments using low-carbon steel under cyclic inelastic strains

The materials and details used to construct sacrificial structural steel components must be evaluated for the full range of inelastic demands imposed by extreme loading events. This study characterizes the cyclic response and low-cycle fatigue life of a plate steel material designed to have a relatively low yield stress and various complete joint penetration butt-weld details considered for use in applications where inelastic behavior is expected. Large amplitude cyclic strain tests were performed on the base material and butt-welded specimens. The welded specimens utilized several different weld treatment details designed to mitigate stress concentrations, reduce tensile residual stresses, and improve weld-toe geometry. Uniaxial material models and a low-cycle fatigue model were used to characterize the cyclic stress–strain response and low-cycle fatigue life of the specimens. A linear damage accumulation model was also applied and found to adequately predict the failure of specimens subjected to more arbitrary strain histories. The presence of butt-welds were found to only slightly decrease the low-cycle fatigue life and the various weld treatments were found to have minimal impact.

Status and prospect of the development of liquid lithium limiters for stellarotor TJ-II

Stellarator concept is considered as a promising approach for power fusion reactor development because it basically free from disruptions and other extreme thermal load events. However, the potential problem of impurity accumulation in stellarator plasma should be taken into account. Very promising results in density control, plasma reproducibility and confinement characteristics have been obtained with application of “lithiation” technology. The next step in the improvement of TJ-II Heliac plasma performance is the development and creation of two poloidal liquid lithium limiters (LL). Experimental possibilities, design, structural materials and main parameters of LL based on capillary-pore structure (CPS) filled with liquid lithium are considered. Understanding in hydrogen isotope interaction with liquid lithium surface is an important aspect of lithium technology development for fusion reactor application. Therefore study of deuterium sorption/desorption process on a lithium surface of LL is stipulated. The development of lithium CPS based devices decreasing intensity of plasma–wall interaction on a central “groove” of TJ-II vacuum camera is proposed as the further step in plasma performance improvement owing to decrease in impurity flux from the wall.

SMA in Mitigation of Extreme Loads in Civil Engineering: Study of their Application in a Realistic Steel Portico

Guaranteeing the use of Shape Memory Alloys (SMA) in mitigation of extreme load effects requires a deep study of the SMA behavior according to the specific requirements of the applications in damping. The damper was defined according the expected requirements (length of SMA and number of SMA wires). It is applied to two types of alloys (CuAlBe and NiTi) in the diagonals of a realistic steel portico (2.47 m x 4.10 m). The measurements establish that the used SMA reduces the oscillation amplitude to a less than a half.

SMA in Mitigation of Extreme Loads in Civil Engineering: Damping Actions in Stayed Cables

Reliable use of Shape Memory Alloys (SMA) in mitigation of extreme load effects requires a deep study of the SMA behavior according to the necessities of the application. Damping the oscillations induced by one storm of three or four days with a strong wind and/or rain usually requires more than one million of working cycles. A SMA damper is checked in to two realistic cables of ELSA and of IFSTTAR. The measurements establish that the SMA damping device reduces drastically the oscillation amplitude. Technical suggestions for the preparation of the dampers built by several SMA wires of NiTi with 2.46 mm of diameter are included. The choice of appropriate length and the choice of the number of required SMA wires are suggested. Moreover, a suitable simulation by proprietary SMA routine inside ANSYS is included.

2D numerical simulations of ice rubble formation process against an inclined structure

Abstract This paper examines ice sheet failure and rubble pile formation process against a wide inclined structure by simulating the process with a two dimensional combined finite–discrete element method. In particular, rubble pile formation and deformation, as well as extreme ice load events are addressed. In the method used, the level ice sheet and its fracture are modeled by using a finite element scheme, while the contact forces between the colliding ice blocks are calculated by using the discrete element method. A total of 28 peak load cases are analyzed in detail and the phenomena during these peak load events are described. Peak loads are noticed to occur in the cases of ice ride-up, formation of a sail in front or away from the structure, and loading through a rubble pile. The common phenomenon in these four peak load situations was the loading of the rubble pile in a manner that a part of the pile is pushed upwards.

Optical FBG Sensors for Static Structural Health Monitoring

In this paper, the monitoring of an adobe structure with optical fiber sensors is reported. Static measurements were made during a destructive test on a full-scale wall, in which an in-plane cyclic force was imposed by a hydraulic jack until its collapse. The recorded data with these sensors and the force applied evolution allows to identify the two instants when the major diagonal cracks occur in the wall. Initially, before the cracking, a linear elastic response was observed, corresponding to a deformation at each monitoring point proportional to the applied lateral force, being quantified the relation between the external force and the deformation at each point. This structural test allows demonstrating the feasibility of applying static optical FBG sensors to study the behavior and performance of civil engineering infrastructures even for extreme loading events.

Design audit of the Phu My cable-stayed bridge, Vietnam

Details of selected analyses and design checks conducted in connection with the design audit of Phu My cable-stayed bridge in Vietnam are presented. The project is briefly introduced with regard to the contractual set up and the principal design standards. Techniques used for the analyses are discussed with reference to the provisions of the governing design standards. Details of the advanced finite-element analyses conducted in order to facilitate the design checks of the permanent works under temporary as well as in-service conditions are then presented. It is shown how the scope of the analyses was integrated to interface non-linear staged construction analysis, incorporating time-dependent effects, with the analysis for extreme load events under US design codes. Details are provided in particular for staged construction analysis, ship impact analysis, dynamic response spectrum analysis and cable stay fracture analysis. In addition, cable stay fatigue, cable stay replacement and vehicular live load effects are also discussed. A brief description of wind analysis, particularly with regard to construction stage wind buffeting, is also presented together with the considerations taken on board for other environmental factors such as temperature and humidity. The importance of appropriate engineering experience in the management and validation of large analytical models is also discussed before presenting selective elements of the structural design checks. The paper is concluded with some thoughts on the role of advanced analyses in prospectively investigating the long-term sustainability of the structure through its life cycle.

Characteristic Dynamic Increment for extreme traffic loading events on short and medium span highway bridges

More accurate assessment of safety can prevent unnecessary repair or replacement of existing bridges which in turn can result in great cost savings at network level. The allowance for dynamics is a significant component of traffic loading in many bridges and is often unnecessarily conservative. Critical traffic loading scenarios are considered in this paper with a model that allows for vehicle–bridge interaction and takes into account the road surface condition. Characteristic dynamic allowance values are presented for the assessment of mid-span bending moment in a wide range of short to medium span bridges for bidirectional traffic.

Role of Insulation Effectiveness on Fire Resistance of Steel Structures under Extreme Loading Events

Fire performance of steel structures is highly dependent on the effectiveness of applied fire insulation. However, insulation materials are susceptible to damage under extreme loading events. A state-of-the-art review on the role of insulation damage on fire resistance of steel structures is presented. Parametric studies on a six-story steel-framed building were carried out to illustrate the effect of insulation damage on fire response of a steel structure. In the analysis, realistic fire scenarios, loading, and failure criteria were taken into consideration. Analysis results indicate that the fire resistance of a steel-framed structure is significantly influenced by the extent of insulation loss, type of fire scenario, and level of lateral load. Insulation damage causes faster deterioration in the structural response of framed buildings under the combined effect of fire and lateral loading. The need for accounting for any insulation damage, arising under extreme loading events, in fire design of steel-framed structures is highlighted, and a performance-based design strategy incorporating fire resistance analysis is discussed.

Multiscale modelling in real-time flood forecasting systems: From sand grain to dike failure and inundation

Abstract Severe events around the globe have highlighted the threat to life, infrastructure and the environment posed by flooding. Flood forecasting systems are a vital component of broader flood risk management activities. These systems are becoming increasingly more sophisticated as their importance in reducing life loss and economic damages is realized. Part of this increase in complexity is focused on the ability to predict and warn of failures in dykes, levees and embankments. A new European ICT project, UrbanFlood for Environmental Services and Climate Change Adaptation, has recently been commissioned and is introduced in this presentation. The primary objective of the Urban Flood project is to develop early warning systems that will monitor flood protection systems in real-time, identify vulnerable locations, model the failure and predict dike collapse and subsequent inundation. In combination with the damage assessment, Urban Flood will serve as an advanced decision support system, mitigating the impact of seasonal and catastrophic floods. Modeling is one of the key tasks in the project. The models will be required to simulate the behavior of the material properties of the layered dikes (sand, clay, peat, grass or concrete cover, metal frame, dam gates, etc.), during extreme hydraulic loading events. In earthen dikes, extra challenge is posed by the non-linear elastic plastic properties of the deformable clay. A realistic simulation of the dike will model the free-surface water dynamics; convective and diffusive transfer of water inside the porous materials; dynamic response of clay to the water pressure; structural mechanics, deformation and actual dike breakdown and flood. The models shall cover a wide range of scales from a sand grain to a flooded city. The time scales will range from seconds (for water penetrating the soil) to hours (for dike collapse dynamics and ocean tides). Eventually, the models will predict the influence of seasonal and global changes on the stability of flood defense systems. Full 3D transient simulation of dike failure with subsequent inundation will require significant computing resources. The project started three months ago, and we will present the plan for developing the modeling cascade for the system. This work is supported by the UrbanFlood European Union project N 248767, theme ICT-2009.6.4

Enabling framework for structural health monitoring using smart sensors

Structural health monitoring (SHM) is an important tool for the ongoing maintenance of aging infrastructure. The ultimate goals of implementing an SHM system are to improve infrastructure maintenance, increase public safety, and minimize the economic impact of an extreme loading event by streamlining repair and retrofit measures. Networks of wireless smart sensors offer tremendous promise for accurate and continuous structural monitoring using a dense array of inexpensive sensors; however, hurdles still remain. Although smart sensors have been commercially available for nearly a decade, full-scale implementation for civil infrastructure has been lacking, with the exception of a few short-term demonstration projects. This slow progress is due in part to the fact that programming smart sensors is extremely complex, putting the use of these devices for all but the simplest tasks out of the reach of most engineers. This article presents an enabling, open-source framework for SHM using networks of wireless smart sensors. The framework is based on a service-oriented architecture that is modular, reusable, and extensible, thus allowing engineers to more readily realize the potential of smart sensing technology. To demonstrate the efficacy of the proposed framework, an example SHM application is provided. Copyright © 2010 John Wiley & Sons, Ltd.

Importance of the Tail in Truck Weight Modeling for Bridge Assessment

To predict characteristic extreme traffic load effects, simulations are sometimes performed of bridge loading events. To generalize the truck weight data, statistical distributions are fitted to histograms of weight measurements. This paper is based on extensive weight-in-motion measurements from two European sites and shows the sensitivity of the characteristic traffic load effects to the fitting process. A semiparametric fitting procedure is proposed: direct use of the measured histogram where there are sufficient data for this to be reliable and parametric fitting to a statistical distribution in the tail region where there are less data. Calculated characteristic load effects are shown to be highly sensitive to the fit in the tail region of the histogram.

Inelastic response of structures due to large impact and blast loadings

This article provides a broad overview of the contributions that relatively simple methods of analysis can make to the design of structural systems for the protection of the public and the security of industrial plant against extreme dynamic loading events which involve explosive blast pressures or impact loadings from fragments and projectiles. It is possible, by careful design, to absorb the external dynamic energies through large inelastic deformations of the structural members and specially designed energy-absorbing and cladding systems. Experimental studies are important because the large impact loadings produce inelastic strains and highly non-linear structural responses. The dynamic properties of ductile materials, including inelastic failure, the impact response of pipelines, and the scaling laws required for predicting the behaviour of full-scale prototypes from experiments on small-scale structures, are also discussed. Some phenomena are emphasized that are important for numerical finite element schemes as well as theoretical methods of analysis.

Design of Dynamically Wind-Loaded Helical Piers for Small Wind Turbines

The expansion of alternative energy has created a demand for sustainable alternatives for wind turbine foundation design. This study investigates the proposed application of helical piers as foundations for guyed cables of small (1–10-kW) wind towers. Before the foundation system can be implemented, pier response to typical working loads and extreme environmental conditions must be determined. Field conditions were determined by equipping an existing wind tower with accelerometers and load cells while monitoring wind speed to determine tower response. A full-scale testing program was conducted, which simulated dynamic loading conditions based on the tower response. The testing program varied between typical working conditions and extreme load events to determine the critical loading case and creep potential from long-term loading. This paper discusses the effects of dynamic loading on helical pier performance and compares the results to that of uplift prediction methods typically used in helical pier design.

Dynamic Crack Propagations in Prestressed Concrete Sleepers in Railway Track Systems Subjected to Severe Impact Loads

Prestressed concrete sleepers (or railroad ties) are the crosstie beam support in railway track systems. They are designed and constructed under flexural constraints in order to carry and transfer the dynamic wheel loads from the rails to the ground. Under perfect wheel and rail conditions, the dynamic loading on railway tracks could be treated as a quasi-static load using a dynamic impact factor. The current design method for the prestressed concrete sleepers taking into account the quasi-static effect is based on allowable stress where crack initiation is not permitted. In reality, the impact events are often detected due to the uncertainties of wheel or rail abnormalities such as flat wheels, dipped rails, etc. These loads are of very high magnitude but short duration. Over the design life span of the prestressed concrete sleepers, there exists the feasibility of extreme and repeated impact loading events. These have led to two proposed limit states for the consideration of structural engineers: ultimate limit states and fatigue limit states. Prestressing techniques have been long used to maintain the high endurance of the sleepers under repeated impact cycles. In spite of the most common use of the prestressed concrete sleepers, their impact behavior and capacity under the repetitions of severe impact loads are unclear. This paper presents the experimental investigation aimed at understanding the dynamic crack propagations in prestressed concrete sleepers in railway track structures under repeated impact loading. The impact forces have been correlated against the probabilistic track force distribution obtained from an Australian heavy haul rail network. The effects of track environment including soft and hard tracks are highlighted in this paper.

Estimation of Probabilistic Extreme Wind Load Effects: Combination of Aerodynamic and Wind Climate Data

A refined full-order method is presented for estimating the extreme wind load effects of rigid structures with given mean recurrence intervals (MRIs) by combining the distributions of annual maximum wind speed and extreme load coefficients. This refined method is capable of dealing with any type of asymptotic extreme value distribution. With this full-order method, the predictions of wind load effects by using distributions of annual maximum wind velocity pressure and wind speed are compared that provide information on the sensitivity of predictions to the upper tail of wind speed distribution. The efficacy of the first-order method is examined. The influences of the type of distributions and the variations of annual maximum wind speed and extreme load coefficient on the predictions are quantified. Finally, the first- and full-order methods are extended to wind load effects of dynamically sensitive structures which facilitate a comprehensive probabilistic analysis as compared to the Monte Carlo simulation...