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Highway Bridge Maintenance Planning and Scheduling PDF

338 Pages·2016·37.818 MB·English
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HIGHWAY BRIDGE MAINTENANCE PLANNING AND SCHEDULING MARK HURT Bridge Design, Bureau of Structures and Geotechnical Services, Kansas Department of Transportation STEVEN D. SCHROCK Department of Civil, Environmental, and Architectural Engineering, University of Kansas Amsterdam • Boston • Heidelberg • London New York • Oxford • Paris • San Diego San Francisco • Singapore • Sydney • Tokyo Butterworth-Heinemann is an imprint of Elsevier Butterworth-Heinemann is an imprint of Elsevier The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, UK 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, USA Copyright © 2016 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further informa- tion about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www. elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Pub- lisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such informa- tion or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-12-802069-2 For information on all Butterworth-Heinemann publications visit our website at http://www.elsevier.com/ ACKNOWLEDGMENT The authors would like to gratefully acknowledge that figures used in the text are not attributed to specific sources, and which are not their own, but have been graciously provided for use with permission from the Kansas Department of Transportation. ix CHAPTER 1 Introduction “A bridge is to a road as a diamond is to a ring.” – Anonymous Overview The inventory of bridges on public roads in the United States is discussed. The bridge pres- ervation process is introduced. Bridge preservation practices before the establishment of the National Bridge Inspection Standards (NBIS) are examined through the case of such practice in the state of Kansas. The development of the NBIS is presented. The nature of ongoing development in bridge inspection and evaluation practices is illustrated by the case of the I-35W Bridge collapse. The implementation of bridge management systems (BMS) to manage bridge inspection and condition data, and the growth of BMS are dis- cussed. An overview of the layout of the book is provided. 1.1 BRIDGES IN THE UNITED STATES The previous statement may appeal to the vanity of those who work with bridges, but it also reflects a truth: bridges are critical assets that provide important value, but at a cost. Value, in that each highway bridge is a solu- tion to a problem of how to carry traffic across a river or gorge or other obstacle such as conflicting lanes of traffic. Cost, in that the solution comes at a price, each section of a bridge deck costs several times more than an equivalent area of roadway both to construct and to maintain over the life of the bridge. According to the Federal Highway Administration (FHWA), in 2010 the road network of the United States included over 4,083,768 miles of public roads and more than 604,493 bridges [1]. A bridge is defined by the FHWA as, “a structure including supports erected over a depression or an obstruction, such as water, highway, or railway, and having a track or passageway for carrying traffic or other moving loads, and having an opening measured along the center of the roadway of more than 20 feet.” (Figure 1.1) Highway Bridge Maintenance Planning and Scheduling Copyright © 2016 Elsevier Inc. http://dx.doi.org/10.1016/B978-0-12-802069-2.00001-5 All rights reserved. 1 2 Highway Bridge Maintenance Planning and Scheduling Figure 1.1 Bridge Opening. The total length of those bridges is 16,349.5 miles [2], less than 0.5% of the total miles of public road. The amount expended by all levels of government in the United States in 2010 on public roads and bridges was $205.3 billion. Of this, $60 billion was spent on system rehabilitation, which is defined as, “capital improvements on existing roads and bridges that are intended to preserve the existing pavement and bridge infrastructure.” Twenty-eight and half percent, $17.1 billion, of the system rehabilitation expenditures were for bridge-sized structures. This does not include the system rehabilitation funds spent on highway structures with an opening of 20 ft. or less. These small spans and culvert structures are used most often to convey drainage or sometimes to provide a single lane underpass through a roadway berm. These structures are more numerous than bridge-sized struc- tures and are subject to most of the same maintenance issues as the larger structures. The cost of work on structures with an opening of less than 20 ft. conducted under system rehabilitation projects is captured in the $42.9 bil- lion in highway expenditures. Rehabilitating structures for preservation is considerably more expensive than rehabilitating an equal length of roadway. Part of the cost of bridges is also the acceptance of risk. A study of bridge failures in the United States over the period of 1989–2000, by Wardhana and Hadipriono of Ohio State University, found cases of 503 failures [3]. Failure was defined as the incapacity of a bridge or its components to per- form as specified in the design and construction requirements. Conditions of either collapse (total or partial) or distress constitute failure of a bridge and result in its removal from service until either repair or replacement. A distressed bridge is one with one or more components in such condition that the facility is rendered unserviceable. An example would be excessive deflections in the superstructure resulting in a dip in the bridge deck that would render the bridge unusable for traffic. Almost all of the failures with identified conditions were either partial or total collapse. The consequences of the collapse of a bridge can be quite severe and, in the worst case, result in fatalities. In the cases studied, there were 76 fatalities and 161 people injured. Introduction 3 To characterize a bridge as having failed in the study, it was not only implied that it became unserviceable, but that it became unserviceable sud- denly and unexpectedly. Of the 503 bridge failures studied by Wardhana and Hadipriono, 266 failed due to high-water events, 103 failed due to either overloading or vehicular impacts, and 45 failed due to other events such as fire or earthquakes. The failures of only 48 bridges were attributed to either deterioration or fatigue. The most common way for a bridge to fail was to be subjected to an extreme event. A far more common end to the life of a bridge is deterioration that accumulates and results in a progressively less serviceable structure. Under the wear of traffic loads and exposure to the weather and to agents such as salts used to melt snow and ice on roadways, steel corrodes, and con- crete cracks and spalls. The wearing surface of the bridge deck may become rough enough to require slowing traffic. The supporting members of the structure may lose enough material that their ability to bear load is reduced, requiring the restriction of heavy trucks from the bridge. Thankfully, slow deterioration rarely results in a sudden failure with the attending risk of injury to bridge users; however, it may still result in significant economic impact by disrupting traffic. This is particularly true for the movement of commercial freight by heavy trucks. The cost of bridges makes them a significant investment for owners and operators of highways. The risks and consequences of bridge failure require owners and operators to act to maintain their bridges in good repair. In the United States, these actions have come to be classified as bridge preservation. The FHWA defines bridge preservation “as actions or strategies that prevent, delay or reduce deterioration of bridges or bridge elements, restore the function of existing bridges, keep bridges in good condition and extend their life” [4]. Bridge preservation has become increasingly important to the owners and operators of highway bridges in the United States due the age and numbers of bridges in their inventories. According to data from the National Bridge Inventory (NBI) maintained by the FHWA, as of 2013 the average age of bridges carrying traffic on public roads in the United States was 43 years [5]. This is due to the rapid expansion of the highway system and public roads in general after World War II. Figure 1.2 shows the decade of construction for bridges on public roads in the United States constructed between 1910 and 2010. For bridges constructed in the post-World War II period and prior to adaption of the American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Design Specification, the anticipated service life was 50 years. 4 Highway Bridge Maintenance Planning and Scheduling Figure 1.2 Bridges by Decade of Construction. Over 11% of the bridges on the NBI in 2013 are categorized as structur- ally deficient [6]. A bridge is categorized as structurally deficient when one of its major components – the deck, superstructure, or substructure – is rated as poor during a bridge inspection, or when it is evaluated to be inadequate either for load-carrying capacity or for its waterway opening. Structural deficiency does not automatically imply an imminent danger to the travel- ing public using the bridge. It does imply impairment to the operation of the bridge in that some heavy truck traffic will not be allowed to use the bridge. And it also implies that work is required to restore the condition of the bridge. The poor rating of one or more bridge components is almost always due to deterioration. Deterioration comes about as a function of en- vironmental exposure and use over time. The average age of a bridge rated structurally deficient was 65 years old. By 2023, one in four of the existing bridges in the inventory will be 65 years or older if left in service [7]. For these bridges, preservation actions will be required to maintain them in full service. A bridge on the NBI may be also considered deficient if it is function- ally obsolete [6]. A bridge is categorized as functionally obsolete if either the geometry of its deck, the clearance for roadways under the bridge, or the width of the roadway at the approaches to the bridge deck are inadequate. It may also be considered functionally obsolete if either its load-carrying ca- pacity or waterway opening is inadequate, but not to the degree to be con- sidered structurally deficient. If a bridge qualifies as structurally deficient, it is not also considered functionally obsolete. Almost 13% of bridges on the Introduction 5 2010 NBI were functionally obsolete. The total number of deficient bridges in the 2010 NBI was 146,636, over 24% of the total inventory. 1.2 BRIDGE PRESERVATION PROCESS The term bridge preservation should not be taken to focus solely on the particular maintenance actions to keep a bridge in good condition. These are actions such as sealing open cracks on a bridge deck. Implementing these actions and developing effective strategies for their deployment re- quires owners and operators to assess the condition of the components of the bridge and to know the relevance of any defects found. Bridge pres- ervation may be defined as a process consisting of three general activities: inspection, evaluation, and maintenance (Figure 1.3). The cornerstone of the bridge preservation process is inspection. In- spection provides information as to the physical condition of bridge com- ponents. An initial inspection provides a baseline for review throughout the life of the structure. Subsequent inspections alert the owner to changes in condition and to any current needs. Maintaining records of bridge inspec- tions allows an owner to track deterioration. Combining the information available from the records of an inventory of bridges over time allows the owner to intelligently predict rates of deterioration and anticipate future needs. Inspection procedures and the intervals at which inspections are con- ducted are determined by policies adopted by the bridge owner. For bridges on the NBI, those policies are set forth in the NBIS. Evaluation is an assessment of a bridge’s ability to safely carry traffic. Bridge inspectors evaluate the condition of bridge elements during the inspection process. The evaluation step in the bridge preservation process Figure 1.3 Bridge Preservation Process. 6 Highway Bridge Maintenance Planning and Scheduling is an assessment of the bridge as a whole. Bridge owners must determine whether a bridge is safe to remain open after experiencing an extreme event, such as a large flood or a fire. Although if a significant amount of damage is apparent it may be obvious that a bridge needs to be removed from service, often an engineering analysis is required to determine the de- gree of impairment suffered by the structure. An engineering analysis may also be required to assess the effect of a change in site conditions, such as experienced from stream degradation. A structural analysis conducted to determine the load-carrying capacity of the existing bridge components in their current condition, noting any loss in capacity due to deterioration or damage, is a load rating. Older bridges may have lower load-carrying capacity than desired for the highway route they ser- vice not only due to the effects of deterioration, but the loading used for their initial design may have been significantly less than current standards require. The current AASHTO LRFD design truck is the HL-93, a 72,000 pound truck with a maximum axle load of 32,000 pounds. Its load effects are com- bined concurrently with those of a uniform load of 640 pounds per ft. per lane. It was not until 1944 that the design specifications of the predecessor to AASHTO, the American Association of State Highway Officials (AASHO), recommended a minimum design truck load for highways with heavy truck traffic, the H15-S12. The H15-S12 loading consisted of checking for the effects of either a 54,000 pound truck or a 480 pound per ft. lane load with a 13,500 pound concentrated load. This was still considerably heavier than the first weight limits for trucks on public roads in the United States. These were enacted by four states in 1913: 18,000 pounds gross vehicular weight (GVW) in Maine; 24,000 pounds GVW in Pennsylvania and Washington; and 28,000 pounds GVW in Massachusetts [8] (Figures 1.4 and 1.5). All bridges on the NBI are required by the NBIS to be load rated for the HL-93 truck configuration, note that the concurrent lane loading is not used [9]. The HL-93 truck configuration is known as HS20-44 truck con- figuration in previous design specifications. Two load ratings are reported to the FHWA: operating and inventory ratings. The operating rating is the maximum permissible weight of truck in the chosen load configuration to which the bridge may be subjected. The inventory rating is the maxi- mum permissible weight of truck in the chosen load configuration, which may safely utilize the bridge for an indefinite period of time. For example, an inventory rating of 39 tons for the HL-93 truck configuration would imply that a truck weighing 39 tons with axles spaced and apportioned similar to the HL-93 should be able to use the bridge indefinitely without Introduction 7 Figure 1.4 HL-93 Design Truck. (Adapted from AASHTO LRFD [10]). causing undue distress on the structure. A HL-93 design truck has a front axle weight of 8,000 pounds and two rear axles each with 32,000 pounds. A 39 ton (78,000 pound) truck in the same configuration would have a front axle of 8,666 pounds (78/72 × 8) and two rear axles of 34,667 pounds. Maintenance consists of those actions to sustain a bridge in operation despite onslaughts by both deterioration and damage. A broad spectrum of actions will fall into this activity, from actions as simple as cleaning the bridge wearing surface, to as involved as the removal and reconstruction of bridge decks. Bridge maintenance actions can be generally categorized as preventative or substantial. Figure 1.5 H15-S12 Design Truck. (Adapted from 1941 AASHO Design Manual [11]).

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