Class Of Bridges Research Articles

Structural calculation of existing masonry arch bridges

AbstractFor masonry bridges with small spans built before 1900, there are often no documents available since such bridges were often built from experience. Surveying is often restricted to the visible parts of the structure. Geometrical assistance in the form of drilling cores is only ever at points, which inevitably have to be interpolated. Large parts of these structures are in the ground (abutments, foundations) and are largely inaccessible for adequate geometrical recording. The constitutive laws for the existing masonry can only be described with reasonable effort through minimum values from regulations. The article describes a procedure with additions to the missing documents from experience to obtain statements about the load‐bearing capacity based on approximate models, which permit categorisation into decisive bridge classes based on the regulations for the structural analysis of existing road bridges and also enable usable results for the comparison between the result of categorisation and special load cases for heavy transport.

Estimation of cables’ tension of cable-stayed footbridge using measured natural frequencies

This paper presents analysis of cables’ tension of steel cable-stayed footbridge using their field-test natural frequencies. A vibration method is usually used for the measured cable tension during the construction of cable systems stiffened with inclined cables. Practical formulas for the vibration method applied herein, mainly based on cable-sag and vertical angle effects (a survey measurement), have been verified on the one-tower steel cable-stayed bridge. The bridge is situated in Sieradz (Poland) and it was the structure with the longest span concerning all the cable-stayed bridges in Poland until 1999. The obtained cable axial forces for estimated natural frequencies of low- and high-order modes are verified using FEM models. The final conclusions drawn on the basis of conducted studies can be useful for technical diagnosis, monitoring programs and repair works of similar class of cable-stayed bridges.

Genome Instability as a Consequence of Defects in the Resolution of Recombination Intermediates.

The efficient processing of homologous recombination (HR) intermediates, which often contain four-way structures known as Holliday junctions (HJs), is required for proper chromosome segregation at mitosis. Eukaryotic cells possess three distinct pathways of resolution: (i) HJ dissolution mediated by BLM-topoisomerase IIIα-RMI1-RMI2 (BTR) complex, and HJ resolution catalyzed by either (ii) SLX1-SLX4-MUS81-EME1-XPF-ERCC1 (SMX complex) or (iii) GEN1. The BTR pathway acts at all times throughout the cell cycle, whereas the actions of SMX and GEN1 are restrained in S phase and become elevated late in the cell cycle to ensure the resolution of persistent recombination intermediates before mitotic division. By developing a "resolvase-deficient" model system in which the activities of MUS81 and GEN1 are compromised, we have explored the fate of unresolved recombination intermediates. We find that covalently linked sister chromatids promote the formation of a new class of ultrafine bridges at anaphase that we term HR-UFBs. These bridges are broken at cell division, leading to activation of the DNA damage checkpoint and repair by nonhomologous end joining (NHEJ) in the next cell cycle. As a consequence, high levels of gross chromosomal rearrangements and aberrations are observed, together with frequent cell death. These results show that the HJ resolvases provide essential functions for the resolution of recombination intermediates, even in cells that remain proficient for BTR-mediated HJ dissolution.

Shaping tolerant attitudes towards immigrants: The role of welfare state expenditures

This article contributes to the ongoing discussion on how tolerance may be fostered in Western European countries and to the question of how contextual factors such as welfare state expenditures may contribute to this formation. Tolerance is understood as a basic democratic principle that helps civil societies cope with rising levels of diversity stemming from increased immigration and individualism. Within the tolerance literature, it is commonly agreed upon that a comprehensive welfare state is capable of bridging class divides and overcoming social categorization. However, over the past decades, European welfare states experienced an ongoing influx of immigrants, challenging their general purpose and increasing notions of ‘welfare chauvinism’. Drawing on insights from both tolerance and welfare state solidarity literature, we implement hierarchical analyses based on Eurobarometer data to assess the potential influence of welfare state universalism on political and social tolerance in 15 Western European countries. Moreover, we demonstrate that this relationship is highly conditional on the degree of ethnic heterogeneity within a country.

Multiple-Hazard Fragility and Restoration Models of Highway Bridges for Regional Risk and Resilience Assessment in the United States: State-of-the-Art Review

AbstractHighway bridges are one of the most vulnerable constituents of transportation networks when exposed to one or more natural hazards, such as earthquakes, hurricanes, tsunamis, and riverine floods. To facilitate and enhance prehazard and posthazard event mitigation and emergency response strategies of transportation systems and entire communities, probabilistic risk and resilience assessment methodologies have attracted increased attention recently. In this context, fragility and restoration models for highway bridges subjected to a range of hazards are essential tools for efficient and accurate quantification of risk and resilience. This paper provides a comprehensive review of state-of-the-art fragility and restoration models for typical highway bridge classes that are applicable for implementation in multihazard risk and resilience analyses of regional portfolios or transportation networks in the United States. An overview of key gaps in the literature is also presented to guide future research.

Experimental study of an in-service spread slab beam bridge

A new class of spread slab beam bridges has recently been developed and implemented in Texas. Due to the absence of appropriate design guidelines, moment and shear design actions have been based on those used for spread box beam bridges; however, their applicability remains in question. To develop new criteria, the load distribution behavior of this new bridge system is investigated. Comprehensive static and dynamic tests are performed on an in-service spread slab beam bridge located on US 69 in the city of Denison, Texas. Various experimental methods are used to infer the moments and shears resisted by individual beams that arise from a heavily loaded truck. Experimentally derived load distribution factors (LDFs) are compared with refined finite element model predictions. Satisfactory agreement is obtained. The experimental test results indicate that the existence of a sidewalk and guardrail markedly stiffens the structure leading to higher than expected moment values. The observed bridge responses under moving dynamic loads exceed the present design specifications impact factor of 33%. Thus, for service load design it is recommended the allowable tensile stress be slightly reduced.

I-5 Skagit River Bridge Collapse Review

AbstractOn May 23, 2013, a truck-tractor with a flatbed semitrailer hauling an oversized container was traveling south on Interstate 5 (I-5) near Mount Vernon, Washington. While crossing the Skagit River, the oversized container struck portions of the through-truss bridge, which resulted in a 49-m (160-ft) simple-span section of the 339-m (1,112-ft) bridge collapsing into the river. This collapse occurred even though the oversized container had a permit authorizing the travel route and was being escorted by a pilot vehicle. This paper (1) identifies some key transportation issues related to this scenario, e.g., permitting, route databases, signage, buffer between posted and actual clearance, insurance coverage, and pilot car requirements/operation; and (2) presents a structural analysis of the impact that provides insight into the truss design, damage sequence, failure mode, and potential techniques to increase the robustness of this class of bridge.

ANCOVA-based grouping of bridge classes for seismic fragility assessment

Fragility curves that can be applicable for vulnerability modeling of various configurations of structures, such as bridges, are required to facilitate regional seismic risk assessment. However, it is cumbersome and time-consuming to develop unique fragility curves for each structure across a regional portfolio. One strategy that has been adopted to address this challenge is to group bridges into classes with similar design or structural performance. Traditionally, this grouping has been performed based on a relatively subjective identification of sub-classes. However, such an identification leads to a number of bridge classes with unwarranted grouping. To overcome this limitation, a new grouping technique based on an analysis of covariance on probabilistic seismic demand models is suggested in this paper. The proposed analysis of covariance based grouping helps to identify important attribute-related parameters and to create distinct bridge sub-classes. The effectiveness of the proposed approach is demonstrated in this paper through case studies of four concrete box-girder bridges in California. This is the first systematic approach to sub-binning bridge classes for the regional risk assessment. The results suggest that the proposed grouping method significantly reduces bridge sub-classes from all possible sub-class combinations. The proposed method is relevant and can be applicable to other bridge types.

Geometric parameters affecting seismic fragilities of curved multi-frame concrete box-girder bridges with integral abutments

The current study presents the effect of geometric parameters such as horizontal curvature, abutment skew, and column height on the seismic response and fragility of curved multi-frame concrete box-girder bridges with in-span hinges. For this purpose, two as-built bridges with integral abutments (two- and three-frame) with typical configurations of this class of bridges in California are selected to create a detailed three-dimensional inelastic model for each bridge. The model is used to perform a set of nonlinear time history analyses for a ground motion suite to compute the fragility function of components and system. Moreover, multiple levels of each geometric parameter are determined to identify the effect of geometry. As-built bridge models are modified by varying one of each parameter and the modified models are repeatedly simulated for the seismic fragility assessment. Outcomes are used to examine the above parameters affecting seismic demands and fragility curves for this class of bridges. It is observed that most geometric parameters significantly affect fragilities for some components, but not all system fragilities; the column height is the most influence parameter affecting the system fragility while the horizontal curvature and abutment skew have a relatively minimal influence on the system fragility of this class of bridges.

Seismic fragility curves of as-built single-span masonry arch bridges

Masonry arch bridges are crucial elements in the railway transportation network throughout Europe. Although significant advances in seismic risk assessment of various bridge types have been made by developing fragility curves of generalized classes of structures, there are no comparable tools for masonry arch structures. In this context, this paper presents the construction of seismic fragility curves of single-span masonry bridges according to the limit analysis method. An iterative procedure is implemented to define the capacity curve of the equivalent single degree of freedom system through non-linear kinematic analysis. The process involves determination of the collapse mechanism, calculation of the limit load multiplier, and definition of the thrust line. The intrinsic variability of the seismic action is incorporated with the use of different sets of elastic spectra compatible with EC 8 Type-1 spectrum for various types of soil, with peak ground acceleration varying over the range 0.05–1.5 g. The fragility curves of the generalized classes of single-span masonry bridges are finally obtained from the effective ranges of the main geometric and material parameters affecting arch bridge capacity.

Improvements to field and remote sensing methods for mapping discontinuity persistence and intact rock bridges in rock slopes

Discontinuity persistence and intact rock bridges are critical factors that influence the stability of rock slopes. Persistence influences the extent of pre-existing potential failure surfaces, and intact rock bridges can add cohesion and tensile strength to an incipient failure surface, which must be destroyed before slope failure can occur. Despite continued research and improvements in mapping technology, computing power, and numerical modelling codes, there is no standard recommended methodology for field characterisation of intact rock bridges, or their incorporation into stability analysis. We use observations from remote sensing and field mapping investigations at three open pit mines and one natural rock slope to recommend improvements to field and remote sensing methods for mapping discontinuity persistence and intact rock bridges in rock slopes.We apply a fracture network engineering approach to discontinuity trace mapping, using new intensity factors to describe intact rock bridge trace intensity R21, and blast-induced fracture intensity B21. We emphasize the importance of multi-scale characterisation of discontinuity persistence and rock bridges in rock slopes, and we distinguish between different classes of intact rock bridges based on scale and geometry, with particular attention given to the distinction between laboratory sample scale intact rock bridges on incipient discontinuities, and larger rock mass bridges, which represent metre or larger scale intervals of fractured rock mass that may exist between very high persistence joints and faults.

Le Fort 1 osteotomy and calvarial bone grafting for severely resorbed maxillae.

Long standing maxillary edentulism leads to alveolar ridge resorption which prevent implant placement and causes prosthetic malocclusion. The aim of the study was to assess vertical and transversal bone increase following Le Fort 1 osteotomy associated with calvarial bone grafting. 66 patients who presented severely atrophic maxillae were treated with Le Fort 1 osteotomy with bone grafting from 2003 to 2014. Vertical and transversal bone level was measured preoperatively and 6 months post-operatively to calculate the alveolar ridge augmentation. Follow up ranged from 10 months to 11 years. The mean increase of bone height was 9.3mm and the mean increase of bone width was 6mm 417 endosseous implants were placed in the grafted maxilla. Mean endosseous implant length was of 10.7mm at the first molar site (range: 8-16mm). A total of 25 implants failed, the overall implant survival rate is of 94%. The definitive prosthetis was fixed in 65% of the patients and removable in 35% of the patients. Le Fort 1 osteotomy associated with calvarial bone grafting is the main treatment option able to offer fixed bridge and perfect class 1 occlusion in cases of severe maxillary atrophy.

Seismic Fragility Assessment of Skewed MSSS-I Girder Concrete Bridges with Unequal Height Columns

Multi Span Simply Supported Bridges (MSSS) are categorized among the most vulnerable bridge classes and their vulnerability increases when different sources of irregularities such as skewness as well as columns height differences are included. Different sources of irregularities make the irregular bridge more complicated in case of dynamic response than regular bridges, and therefore a comprehensive study should be implemented to explore the effect of different irregularities on seismic performance of bridges individually and jointly. This paper explores the effect of skewness and unequal height columns on the seismic response of MSSS-I girder concrete bridges commonly constructed in Central and Southeastern United States (CSUS). The scope of the study is limited to tree spans which are the most prevalent spans in this class of bridges. The results show that the component fragilities become more sensitive to column height ratio with increase in the bridge skew angle particularly in longitudinal direction. The study of the combined effects of skewness and column height ratio on the bridge system fragility also reveals that the column height ratio has negative effect on the fragility of bridge system in all damage states and different skew angles but this effect increases by increasing the skewness as well as damage state of interest.

Creation of Third Space in a Bridge Class: "Dwelling In and Stretching Out"

Creation of Third Space in a Bridge Class: "Dwelling In and Stretching Out"

Seismic Reliability Analysis of Deteriorating Representative U.S. West Coast Bridge Transportation Networks

AbstractFor optimal functioning of societies and economies, understanding how networks of lifeline infrastructure, e.g., bridge networks, perform after a hazard is essential. Such hazard resilience can be quantified by considering the reliability of the network against disconnection or blocked network flow; however, a major challenge associated with such analysis is making sure that the component models are realistic while keeping the analysis accurate. For this reason, a methodology has been developed for realistic bridge network modeling using the following components: representative bridge classes identified by clustering a database, cutting-edge time-variant fragility models of bridges, and a multiscale network reliability analysis method, which accounts for the impact of bridge structural deterioration on network-level performance. Using the proposed methodology, the broader effects of various deterioration scenarios are investigated as well as the impacts of spatial correlation and the use of subjun...

Improved Charge Pump Power Factor Correction Electronic Ballast Based on Class DE Inverter

This paper proposes fluorescent electronic ballast with high power factor and low line input current harmonics. The system performance can be improved by a charged pump circuit. Details of design and circuit operation are described. The proposed electronic ballast is modified from single-stage half bridge class D electronic ballast by adding capacitor parallel with each power switch and setting the circuit parameter to operate under class DE inverter condition. By using this proposed method the DC bus voltage can be reduced around by 50% compare with conventional class D inverter circuit. Because the power switches are operated at zero voltage switching condition and low dv/dt of class DE switching. The experimental results show that the proper frequency of the prototype is around 50 kHz with input power factor of 0.982, <TEX>$THD_i$</TEX> 10.2% at full load and efficiency of more than 90%.

Temporal evolution of seismic fragility curves for concrete box-girder bridges in California

Fragility analyses is a powerful tool for the seismic risk assessment of highway bridges. Multispan continuous concrete box-girder bridges account for the bulk of the California bridge inventory. Although several studies have looked at the seismic response and fragility of individual box-girder bridges, very little research has explored the fragility of the box-girder bridge class holistically. Exacerbating this situation is the lack of considerations of design details unique to the era in which the bridges were designed and constructed, in their fragility development. This paper addresses this gap by investigating the influence of evolution of seismic design principles and details on the seismic performance of multispan continuous concrete box-girder bridge class, as well as the failure probability through the development of fragility curves across three design eras demarcated by the 1971 San Fernando and 1989 Loma Prieta earthquakes. Detailed nonlinear analytical models capturing the bridge characteristics within a design era are developed and nonlinear time history analysis is employed to develop analytical fragility curves. Significant improvement in performance is seen in modern bridges designed according to capacity design principles.

Computation of bridge seismic fragility by large‐scale simulation for probabilistic resilience analysis

SummarySeismic resilience of structures and infrastructure systems is a fast developing concept in the field of disaster management, promoting communities that are resistant and quickly recoverable in case of an extreme event. In this contest, probabilistic seismic demand and fragility analyses are two key elements of the seismic resilience assessment in the majority of the proposed methodologies. Several techniques are available to calculate fragility curves for different types of structures. In particular, to assess the seismic performance of the regional transportation infrastructure, methods for the fragility curve estimation for entire classes of bridges are required. These methods usually rely on a set of assumptions, partially because of the limited information. Other assumptions were introduced at the time when computational resources were inadequate for a purely numerical approach and closed‐form solutions were a convenient alternative. For instance, some of these popular assumptions are aimed at simplifying the model of the engineering demand. In this paper, a simulation‐based methodology is proposed, to take advantage of the computational resources widely available today and avoid such assumptions on the demand. The resulting increase in accuracy is estimated on a typical class of bridges (multi‐span simply supported). Most importantly, the quantitative impact of the assumptions is assessed in the context of a life‐cycle loss estimation analysis and resilience analysis. The results show that some assumptions preserve an acceptable level of accuracy, but others introduce a considerable error in the fragility curves and, in turn, in the expected resilience and life‐cycle losses of the structure. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Seismic Response Analysis of Continuous Multispan Bridges with Partial Isolation

Partially isolated bridges are a particular class of bridges in which isolation bearings are placed only between the piers top and the deck whereas seismic stoppers restrain the transverse motion of the deck at the abutments. This paper proposes an analytical formulation for the seismic analysis of these bridges, modelled as beams with intermediate viscoelastic restraints whose properties describe the pier-isolator behaviour. Different techniques are developed for solving the seismic problem. The first technique employs the complex mode superposition method and provides an exact benchmark solution to the problem at hand. The two other simplified techniques are based on an approximation of the displacement field and are useful for preliminary assessment and design purposes. A realistic bridge is considered as case study and its seismic response under a set of ground motion records is analyzed. First, the complex mode superposition method is applied to study the characteristic features of the dynamic and seismic response of the system. A parametric analysis is carried out to evaluate the influence of support stiffness and damping on the seismic performance. Then, a comparison is made between the exact solution and the approximate solutions in order to evaluate the accuracy and suitability of the simplified analysis techniques for evaluating the seismic response of partially isolated bridges.

Seismic fragility analysis of skewed bridges in the central southeastern United States

Skewed bridges are often encountered in the highway bridge system when the geometry cannot accommodate straight (unskewed) bridges. The objective of this study is to investigate the influence of skew angle on the seismic response of bridges using nonlinear time-history analysis and probabilistic seismic assessments. Six types of skewed and straight bridges (including multi-span simply supported, multi-span continuous, and single-span skewed bridges with steel or concrete girders together with non-integral abutments) commonly used in the central and southeastern United States (CSEUS) are considered for establishing three-dimensional numerical bridge models. The six bridge types are further categorized as: (1) non-seismically designed (NSD) bridges, (2) bridges with seismically designed (SD) columns, (3) bridges retrofitted by (i) column jackets, (ii) isolator bearings (IBs) and keeper plates (KPs), (iii) restrainer cables (RCs) and shear keys (SKs), or (iv) seat extenders (SEs) and shear keys (SKs). Probabilistic seismic demand models incorporating geometric and material uncertainty parameters for the bridges under a suite of ground motions are established to develop corresponding sets of fragility curves in terms of vulnerable bridge components. System fragility curves are further developed through a combination of the component fragility curves in the bridges. Comparisons of the fragility curves between the straight and skewed bridges indicate that the larger the skew angle, the more vulnerable the bridges, regardless of NSD bridges, bridges with SD columns, and retrofitted bridges. Formulas that consider effect of skew on the values of fragility parameters in the fragility curves are derived for each bridge class, component type, and limit state. Finally, the retrofit of columns and seismically designed columns can reduce column damage probabilities without significantly increasing demands to the other bridge component types, leading to a lower bridge system risk than that for the NSD bridges. However, although the other three retrofits (IB&KP, RC&SK, and SE&SK) can reduce transverse and/or longitudinal demands on the bearings, the column demands remain a similar or worse damage level than that for the NSD bridges, resulting in a similar or higher risk for the three retrofitted bridge systems.