Design Guide for Bridges for Service Life (2013) / Chapter Skim
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From page 51... ...
49 2.1 introduction Selecting the proper bridge system and incorporating service life design principles into the planning and design process are critical steps in achieving long-term bridge service life. As it is more cost-effective to address service life at the design stage, the design for service life must be approached in a systematic, coherent manner.
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From page 52... ...
50 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Section 2.5 describes a systematic approach for selecting the most appropriate bridge systems that will accommodate operational requirements and site conditions while achieving the desired target design service life. In addition to primary system selection factors relating to function and initial cost, the necessity of considering service life factors (e.g., importance, potential for obsolescence, element and material durability, element maintenance and possible replacement, and life-cycle cost)
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From page 53... ...
51 Chapter 2. BRiDGE SySTEM SELECTiON 2.2.2 Deck Component 2.2.2.1 Deck Elements Figure 2.2 shows the various elements that make up the deck component, which includes the deck–slab element itself along with other related elements including overlays and wearing surfaces, expansion joints, drainage elements, railings, and curbs and sidewalks.
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From page 54... ...
52 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE members. Proper maintenance of deck drainage elements is essential to avoid clogging and malfunction, and such maintenance requirements must be considered in the design.
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53 Chapter 2. BRiDGE SySTEM SELECTiON Superstructures are often categorized by • Material type.
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From page 56... ...
54 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 2.2.3.1 Steel Superstructures 2.2.3.1.1 Steel Girder Superstructures The most common steel bridge superstructures today are composite multigirder subsystems that use either rolled beams, plate girders, or tub girders. These systems can be single span or multispan and can be either straight or curved.
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From page 57... ...
55 Chapter 2. BRiDGE SySTEM SELECTiON A variation to the typical multigirder system is the girder–substringer system, which has been used as an economical concept for longer spans beyond approximately 275 ft.
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From page 58... ...
56 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE however, do not recommend using such detail. Bottom flanges in compression are typically butted with plates and wedges.
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57 Chapter 2. BRiDGE SySTEM SELECTiON high-performance steel (HPS 70W)
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From page 60... ...
58 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE The maximum span length for this system is currently about 60 ft, and it is limited by the press break length capacity available in the industry. The process of bending the plate to form a girder can take less than an hour.
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From page 61... ...
59 Chapter 2. BRiDGE SySTEM SELECTiON A typical two-lane rural-road bridge would require only three or four prefabricated folded-plate girder units placed side by side and connected longitudinally at the deck, as shown in Figure 2.10.
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From page 62... ...
60 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 2.2.3.2 Concrete Bridge Superstructures Several reinforced concrete bridge systems are commonly used in the United States. The type of system implemented at a particular site is generally dictated by economics and the system's ability to accommodate the required span or geometric requirements such as curvature.
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61 Chapter 2. BRiDGE SySTEM SELECTiON water crossings.
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From page 64... ...
62 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE NCHRP 2009 provides a synthesis of current practice relating to precast adjacent box beam bridges. This superstructure type is the most prevalent box girder system for short- and medium-span bridges, typically 20 to 127 ft, especially on secondary roadways.
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From page 65... ...
63 Chapter 2. BRiDGE SySTEM SELECTiON newer standard AASHTO-PCI bulb-tee shapes are used in 54-, 63-, and 72-in.
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From page 66... ...
64 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE In many instances, precast concrete I-girders are erected as simple spans and then connected over the piers to form continuous for live load systems that eliminate deck joints. A newer alternative to concrete I-girders is the U-beam, or concrete tub girder, first developed in Texas and now used in other states (including Florida and Washington State)
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From page 67... ...
65 Chapter 2. BRiDGE SySTEM SELECTiON Figure 2.14.
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From page 68... ...
66 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE girders, but the deck slab is typically cast as an integral part of a segmental box girder. Spliced girders use bulb-tee, I-beam, U-beam, or box shapes; segmental box girders are typically box shapes.
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From page 69... ...
67 Chapter 2. BRiDGE SySTEM SELECTiON making them particularly suited to curvature.
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From page 70... ...
68 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 2.2.3.2.8 Modular Pretopped Concrete Girders These types of systems use precast beam elements that are fabricated with a portion of the deck in place as a unit and are erected side by side and connected with a CIP closure joint, posttensioning, composite concrete topping, or a combination of these methodologies. The precast elements commonly consist of conventionally reinforced or prestressed sections that include T-beams, double Ts, and deck bulb-tees.
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From page 71... ...
69 Chapter 2. BRiDGE SySTEM SELECTiON and stability of the subsurface geotechnical conditions.
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70 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE supported on one or more columns. The columns are supported by foundations that are typically located at or below the finish grade of the adjacent ground.
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From page 73... ...
71 Chapter 2. BRiDGE SySTEM SELECTiON 2.2.4.2 Abutments Abutments are provided in multiple configurations, but they can be defined in two major categories, as illustrated in Figure 2.22: stub or spill-through abutments and full abutments.
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From page 74... ...
72 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE thin layers of compacted fill and geosynthetic reinforcement sheets that combine to form a reinforced soil mass foundation that directly supports the bridge superstructure without the need for piles. The geosynthetic reinforcement is connected into layers of precast facing blocks that are placed with the reinforcement and soil backfill.
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73 Chapter 2. BRiDGE SySTEM SELECTiON analysis is continued until the basic events or lowest levels of resolution are reached and discussed.
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From page 76... ...
74 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE existing bridges from being widened. Increased corridor traffic can also require replacement of overpass bridges to accommodate widened roadways and increased span requirements below.
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75 Chapter 2. BRiDGE SySTEM SELECTiON steel elements, it is more predominant in steel elements.
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From page 78... ...
76 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Because overload occurs on many bridges, the risk of overload should be considered on certain vehicular routes when planning new bridges. It may also be necessary to consider special owner-specified loads to avoid or mitigate this risk.
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From page 79... ...
77 Chapter 2. BRiDGE SySTEM SELECTiON 2.3.1.3.1 Thermal Climate Deicing salts corrosion.
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From page 80... ...
78 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 2.3.1.3.2 Coastal Climate Salt water and spray corrosion. Coastal saltwater environments also have severe effects on bridge service life as a result of wetting and chloride penetration causing corrosion of unprotected reinforcing and unprotected structural steel.
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From page 81... ...
79 Chapter 2. BRiDGE SySTEM SELECTiON Alkali-carbonate reactivity (ACR)
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From page 82... ...
80 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE more energy than calm water to lift and carry sediment downriver. A hole is created adjacent to the pier or abutment when material is washed away from the river bottom, exposing or undermining footings, a situation which can compromise the integrity of the structure and lead to failure.
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From page 83... ...
81 Chapter 2. BRiDGE SySTEM SELECTiON Bridges crossing water bodies or waterways are subject to ships colliding with either piers or superstructure.
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From page 84... ...
82 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE are caused by accidents with tanker trucks or railroad tanker cars carrying large quantities of highly flammable fuels or chemicals. The temperature of a recent fire below a bridge that was caused by a railroad tanker car collision loaded with 30,000 gallons of methyl alcohol was estimated to be approximately 3,000°F (Stoddard 2002)
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From page 85... ...
83 Chapter 2. BRiDGE SySTEM SELECTiON In cases in which damage to steel bridges sustained during a fire is not obvious (i.e., no clear signs of distress, such as sagging or buckling)
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84 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE and discoloration and then tested for changes in material properties after cooling. The results showed that up to steel surface temperatures of 1,200°F, the fire-exposed material after cooling still satisfied AASHTO material specifications.
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85 Chapter 2. BRiDGE SySTEM SELECTiON 2.3.1.3.6c Blast The possibility of terrorism against our nation's bridges is an ever-increasing threat.
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From page 88... ...
86 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE localized spherical shock wave striking the structure to produce a nonuniform load and impulse-dominated response. A plane wave blast is far enough away to produce essentially planar shock waves and a uniform load on the structure.
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87 Chapter 2.
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88 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE as shown in Figure 2.32. This arrangement allows larger portions of the pier column (two plastic hinges versus one for single curvature)
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From page 91... ...
89 Chapter 2. BRiDGE SySTEM SELECTiON In the capacity design approach, protected elements are designed for the largest possible force effects they might experience; the design considers the overstrength that may exist because of higher actual material strength than that specified in design.
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From page 92... ...
90 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE • Close proximity to fault rupture. Such proximity results in ground motions having high horizontal and vertical ground accelerations and large-velocity pulses.
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From page 93... ...
91 Chapter 2. BRiDGE SySTEM SELECTiON 2.3.1.4 Reduced Service Life Resulting from Production or Operation Defects Decisions made for the production of a bridge and activities during its operation can have a significant influence on overall bridge service life.
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From page 94... ...
92 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 2.3.1.4.1 Design and Detailing Decisions made during the system selection, design, and detailing phase of a bridge project can significantly affect the service life of the bridge. It is incumbent on designers to understand the implications of these decisions in order to help in making rational choices that will improve service life.
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From page 95... ...
93 Chapter 2. BRiDGE SySTEM SELECTiON 2.3.1.4.3 Construction Defects or damage in construction can reduce service life in steel or concrete bridge elements.
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From page 96... ...
94 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Bridge railings are affected by wet chloride environments that cause corrosion of reinforcing steel and concrete cracking and spalling in concrete railings. This condition is exacerbated at cold joints between the concrete barrier and the top of the slab, where salt moisture can easily penetrate and cause reinforcing corrosion.
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From page 97... ...
95 Chapter 2. BRiDGE SySTEM SELECTiON 2.3.3.1.2 Deficiency Caused by Natural or Man-Made Hazards: Corrosion Corrosion, the result of exposure to oxygen and moisture, is a fundamental limitation of steel as a construction material.
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From page 98... ...
96 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE • Load-induced influences – Traffic causing vibration, impact, or wear; and – Restrained thermal movement causing internal stress and cracking. • Natural or man-made hazards – Environmental influences, including effects from moisture and freezing and thawing, and reinforcing corrosion caused by chloride exposure; and – Chemical influences, including exposure sulfates, carbon dioxide, alkalis, and various acids.
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From page 99... ...
97 Chapter 2. BRiDGE SySTEM SELECTiON failed near midspan and fell to the highway below, as shown in Figure 2.38.
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From page 100... ...
98 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 2.3.4 factors Affecting Service Life of Substructure Component The numerous causes of substructure deterioration can be categorized in three areas: • Improper detailing and improper consideration of appropriate forces resulting from applied mean recurrence-level event forces, such as scour, vessel collision, and earthquake; • Deterioration caused by corrosion and section loss, primarily from chloride intrusion; and • Seized bearings and unintended movement restraint. 2.3.4.1 Mean Recurrence-Level Event Forces As bridge service life increases, bridges are subjected to environmental conditions for a longer period of time.
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From page 101... ...
99 Chapter 2. BRiDGE SySTEM SELECTiON • Multiple catastrophic vessel and bridge accidents around the world from the 1960s to the mid 1980s (Knott and Larsen 1990)
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From page 102... ...
100 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE their long-term effectiveness and expected life are not verifiable with historic data. Some of the more promising techniques include • Cathodic protection with embedded sacrificial anodes; • Pile jacketing, as shown in Figure 2.41; • Metalized coatings; • Crystalline admixtures for crack sealing; • Repassivation through the removal of chloride ions; and • Various combinations of these techniques.
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From page 103... ...
101 Chapter 2. BRiDGE SySTEM SELECTiON States and its coastal waters, and empirical projections suggest that many of these impacts will grow in severity in the future (U.S.
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102 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Although there is still debate on the level of severity that will be experienced over the next decades because of climate change, it is important to consider this factor when planning for new bridges or retrofitting existing bridges located in areas that could be affected. Currently there are no organized, formal plans for considering the possible effects of climate changes on existing and new bridges located in coastal areas.
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From page 105... ...
103 Chapter 2. BRiDGE SySTEM SELECTiON the intended design.
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From page 106... ...
104 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 2.4.1.2.2 Maximum Length Limits for Continuity Using the procedure specified in Chapter 8, establish the maximum lengths for continuity to minimize the number of joints in long, multispan viaducts. Length in the following types of structures should be considered: • Superstructure with integral abutments and no joints.
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From page 107... ...
105 Chapter 2. BRiDGE SySTEM SELECTiON is usually acceptable for minimum height bridges and balances thermal movements at adjacent piers and abutments as much as practicable.
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From page 108... ...
106 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE 2.4.2 Deck Component options For options related to deck components, see Chapter 4. For options related to joint elements, see Chapter 9 on expansion joints.
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From page 109... ...
107 Chapter 2. BRiDGE SySTEM SELECTiON premature reflective cracks in the wearing surface on the bridges built in the late 1980s and early 1990s.
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From page 110... ...
108 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE large number of posttensioning operations, and the excessive traffic control required for replacement projects. Moreover, posttensioned diaphragms depend on the shear keys to achieve the desired continuity.
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From page 111... ...
109 Chapter 2. BRiDGE SySTEM SELECTiON Hansen et al.
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From page 112... ...
110 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE • Element material deterioration due to thermal, coastal, or chemical climate and reactive materials. Strategies for mitigating these effects are discussed in – Chapter 3 on materials, – Chapter 5 on corrosion protection of reinforced concrete, and – Chapter 6 on corrosion protection of steel bridges.
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From page 113... ...
111 Chapter 2. BRiDGE SySTEM SELECTiON venting all bays will reduce the effects of buoyancy forces on a structure.
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From page 114... ...
112 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Providing bridge systems with enhanced service life requires a complete understanding of the potential deterioration mechanisms, or factors affecting service life. These mechanisms, described in Section 2.3, are associated with load-induced conditions, local environmental hazards, production-created deficiencies, and lack of effective operational procedures.
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113 Chapter 2.
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114 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Does factor apply?
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115 Chapter 2.
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From page 118... ...
116 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE tABLE 2.2. SyStem SeLection ProceSS For oPerAtionAL And Service LiFe reQuirementS Stage and Major Steps Process Preliminary Planning or Type, Size, and Location Stage 1.
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From page 119... ...
117 Chapter 2. BRiDGE SySTEM SELECTiON Stage and Major Steps Process 1.
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From page 120... ...
118 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Stage and Major Steps Process 4. Select optimal alternative Compare operational advantages and disadvantages of bridge system alternatives: • Identify local preferences for structure types and construction; • Compare estimated life-cycle costs; and • Select optimal cost-effective system considering operational and service life requirements and cost–benefit analysis.
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From page 121... ...
119 Chapter 2.
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From page 122... ...
120 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE Block 5. After all factors are considered, the identified strategies are summarized and integrated into the bridge system to develop a draft final configuration.
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121 Chapter 2. BRiDGE SySTEM SELECTiON system alternative.
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From page 124... ...
122 DESiGN GUiDE FOR BRiDGES FOR SERviCE LiFE to the bridge owner just before opening the bridge to traffic. The bridge Owner's Manual is similar to the design calculation document that is usually provided to the bridge owner.
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