Innovative Bridge Designs for Rapid Renewal (2014) / Chapter Skim
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From page 70... ...
70 C h a p t e r 3 Overview Sixteen ABC design concepts developed by the R04 team in Phase I have been described with concept sketches and photographs in Chapter 2. They include new concepts, or adaptations of existing concepts, that are proposed as solutions to various ABC problems.
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71 44 Decked stringer system; and 44 Decked trapezoidal box girders. • Segmental superstructure systems 44 Box girders; 44 Segmental slabs; and 44 Segmental voided slabs.
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72 equipment. The deck segment concepts incorporate proven elements and details used by several states.
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73 rapid replacement applications. Omitting the concrete topping and the transverse posttensioning will significantly reduce the on-site time for construction.
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74 Segmental channel SectionS These sections have not been widely used in the United States, or other markets. They are limited in width (typically two lanes)
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75 3. If the deck is to be posttensioned, this operation is then performed.
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76 panels can be designed as either continuous over a series of parallel girders or simply supported over the longitudinal girder. Figure 3.7 depicts an example of precast reinforced concrete panels used by the Utah DOT on the C-437 bridge rehabilitation of the county road over I-80 to Wanship.
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77 thinner than a CIP deck due to the existence of internal tendons in one or both directions. Thinner panels translate into a lighter-weight deck, which could improve the live-load rating of older bridges.
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78 Following installation of the full-depth precast deck panels, the panels were adjusted and leveled for grade and a smooth, flush riding surface. UHPC joint material was transported to the joints by power buggy and then dumped directly into the joints without any vibration, which is an acceptable practice for this material.
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79 Modular superstructure systems are particularly suited to be used as Tier 1 concepts for weekend bridge superstructure replacements or as Tier 2 concepts, when the entire bridge may be scheduled to be replaced within a month using a detour to maintain traffic. DeckeD Stringer SyStemS Prefabricated decked steel stringer systems have been a very popular option for accelerated construction of bridges in this country.
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80 Generally, low carbon content is a prerequisite to good formability in bent plate applications. Steel plates are more readily formed with the bend axis transverse to the rolling direction of the plate.
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81 conceptual DeSign for compoSite Bent plate Box girDer SyStem A preliminary load and resistance factor design (LRFD) was performed for a bent plate box girder system.
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82 AASHTO LRFD Specifications also include limits for the cross-sectional proportions, most of which are based on the thickness of the steel plate. Since the steel plate thickness is fixed at 0.5 in., it is possible to calculate upper-bound values for the depth of the box girder, and also for the upper flange width: • Per AASHTO LRFD 6.11.2.1, maximum depth for the box girder is 75 in.
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83 required further research, testing, and code development. Headed reinforcing bars, as indicated in NEXT D Beams Standards by the Precast/Prestressed Concrete Institute Northeast, also could be used with closure pours.
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84 Connections for Modular Superstructure Systems The ease and speed of construction of a prefabricated bridge system is paramount to its acceptance as a viable system for rapid renewal. Additionally, as discussed, connections between the modular segments can affect the live-load distribution characteristics, seismic performance of the superstructure system, and also the superstructure redundancy.
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85 Two alternates may be considered for passively reinforced joints for modular construction at heavy truck traffic sites: • Full moment connection using ultra-high-performance concrete (UHPC) joints.
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86 • The compressive strength gain behavior of UHPC is an important characteristic of the concrete. UHPC does not have any compressive strength for nearly 1 day after casting.
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87 moDerate-to-light truck traffic SiteS: Shear-only connection By WelDing anD grouting Connections that transfer shear only may be adequate for local roads. This detail has the advantage of reduced construction time, lower cost, and easy adaptability to all types of modular systems.
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88 In-place voided slabs were commonly used during the early period of prestressed concrete bridge development within the span range of 80 to 115 ft and with span-to-depth ratios of up to 20 to 25. Adapting the precasting plant to different deck widths would also be simpler and less expensive.
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From page 89... ...
89 certain projects, such as those in which the bridge is so wide that the individual panels are simply too large to be economically transported to the site and installed using moderately sized equipment, or those that are constructed in stages and require the shifting of traffic from one lane to another during replacement of an existing deck. In many heavily traveled bridge replacement scenarios, a structure is closed during overnight or weekend hours for bridge deck replacement and then reopened to traffic in the morning.
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90 recommendations should be considered for inclusion in future interim specifications: • Guidelines for stress requirement on the panels for stage construction or full construction. It is anticipated that stress requirement for stage construction is higher than that for full construction.
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91 To the traveling public, the smoothness of the riding surface is a significant riding comfort issue. This is also an important factor for durability and maintenance, as vibrations from an irregular surface can affect the structural steel components of a bridge.
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92 varies with stress and the age of concrete. The effects of creep on deflections are difficult to estimate.
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93 to diminish the investment and the mobilization and demobilization costs. A support girder for short bridges would have the following: • Simplified self-launching capability.
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94 that existed when they were match cast against each other. This is facilitated by the presence of shear keys on the webs and alignment keys on the slabs, which guide the segment into position.
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95 example illustrating the erection of a segmental solid slab is shown in Figure 3.16. With the span-by-span method, all the segments for a span are positioned before the prestressing tendons are installed and the complete span is lowered onto the bearings.
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96 often used in this case because of the less stringent geometry tolerances. With long-line match casting, two foundation beams support the entire segmental span during construction.
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97 In the case of an integral abutment bridge with a longitudinally posttensioning deck, a cast-in-place closure pour is required to create a monolithic connection to the abutment, which provides for moment transfer. In either of these cases, the need for appropriate curing time of the closure pour can significantly affect the time savings expected in accelerated construction and somewhat retards the purpose of rapid construction.
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From page 98... ...
98 circumstances, this spacing is based on the fatigue capacity of the studs, and not the ultimate capacity. With precast panels it is beneficial, however, to place the shear connector blockouts at the largest spacing possible.
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99 When this method is used, the clear distance between the bottom of the panels and the top of the girders can become very large near the ends of the bridge, making it difficult to level the panels and form the haunch region. • Leveling the full-depth panels with the girder profile a short depth above the girder.
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100 for a typical DOT grade-separation bridge deck, as summarized in Table 3.3. The contractor is assumed to have considerable experience with DOT bridges, but not necessarily with posttensioned deck panels.
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101 longitudinal joint along the centerline, it may be possible to remove half the deck, replace it with precast panels, switch traffic to the new deck, replace the other half the deck with precast panels posttensioned longitudinally, and finally connect the halves with transverse posttensioning. • Long viaduct deck replacement that cannot be completed in a single, continuous concrete placement.
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102 11. Contractors would be more willing to make equipment purchases if bridge construction became more standardized or industrialized, and was based on certain methods of erection to speed the assembly.
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103 Items 4 and 5 There are concerns about the durability of joints and connections in precast elements. There are concerns about seismic performance of precast elements and connections in seismic regions.
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104 certain methods of erection to speed assembly. Repetitive use will allow contractors to amortize equipment costs over several projects, which is an important component to bring overall costs in line with conventional construction.
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105 A number of these important topics are currently under investigation by researchers around the country. These needs can be addressed through a combination of theoretical analysis, numerical analysis, or laboratory testing.
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106 prepared for these systems. Deck bulb tee, deck double tee, and decked steel stringer systems received the highest scores, as these are proven systems for rapid renewal.
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107 is currently envisioned for short spans with no end continuity. Further research and development will be needed to validate a design approach for the negative bending regions.
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108 different perspectives when compared with the other superstructure elements presented in this report. First, full-depth precast concrete deck panels, whether posttensioned or used with a variety of cast-in-place joint materials, are the only elements presented that are truly applicable to both the complete replacement of existing bridges and also in the rapid replacement of a deteriorated bridge deck where the underlying superstructure remains in serviceable condition.
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109 Posttensioning If posttensioning (PT) is used, the following additional recommendations should be considered: • PT force should be applied to only the precast deck to obtain the greatest effective prestressing force in the concrete deck.
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110 • Precast complete pier systems 44 Whole pieces, footing, shaft, cap; and 44 Support options, piles, shafts, spread footing. • Segmental columns and piers 44 Segmental columns; 44 Pier caps; and 44 Footings.
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111 Design Concept Descriptions Precast Modular Abutments Precast modular abutments are composed of separate components fabricated off site, shipped, and then assembled in the field into a complete bridge abutment. Precast modular abutments have been constructed in several states.
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112 reinforcing. Once in place over the wingwall drilled shaft, the wingwall pocket is filled with high early strength concrete.
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113 transportation regulations and erection equipment. Alternatively, the cap length limitation can be avoided by using multiple short caps combined to function as a single pier cap.
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114 additional testing such as seismic response and strength tests of connections are recommended to gain confidence from designers nationwide. Over the next several years, these structures will undergo the scrutiny of maintenance inspections.
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115 piers are constructed by posttensioning the precast cap to the precast column. Additionally, precast caps on cast-in-place columns and complete segmental piers have been used and have proven to be successful on many projects.
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116 Shear along the joint surface of the column is adequately resisted in most instances by shear friction. Shear keys can be used to enhance the shear resistance of the column at the joint location.
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117 As is the case with precast modular abutments, the designer should always consider state and local shipping size regulations, as well as erection load limits for typical cranes when designing precast complete pier components. If necessary, consideration should also be given to the pavement capacity of local streets.
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118 These details include the grouted splice sleeves, but other connection methods are available. The designer should refer to FHWA's Connection Details for Prefabricated Bridge Elements and Systems (Culmo, 2009)
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119 This research project, as well as those in the future, will begin the standardization process, and standardization will lead to repeatable, cost-effective, and constructible projects. The cost-effectiveness will give the owners the unassisted financial incentive they need to pursue precast substructures for their projects.
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120 to price that risk. The contractor is in business to make a profit.
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121 Connection Type I An important aspect of project acceleration is expediting the construction of bridge foundations and substructures. In traditional foundation construction, driven piles are frequently embedded in a cast-in-place footing.
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122 No literature could be identified that documented previously completed testing of these details. It is anticipated, however, that these details will perform just as well as cast-inplace footings.
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123 Seismic performance of grouted sleeve couplers is a research area that needs to be further explored before the couplers' use in high seismic zones can gain acceptance. The use of these connectors is common in the precast building market and is being increasingly promoted for bridge construction using precast elements as well.
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124 with that of the CIP control specimen. Many connection types were tested, including the grouted duct connection and the cap pocket connection.
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125 strength degradation and exhibiting extensive plastic hinging of the column, limited joint distress, and essentially elastic behavior of the bent cap. Additionally, the report found that the emulative performance is concluded on the basis of closely matching overall behavior to the CIP control specimen, including lateral force–displacement response; plastic hinging; joint shear stiffness; level of joint distress; pattern of joint cracking; strain patterns of bent cap and joint reinforcement; integral behavior between the bedding layer, column, ducts, and bent cap; and minor bar slip.
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126 recommends that additional testing be conducted for foundation-to-column connections. It also recommends that the grouted splice sleeve connection be further studied and tested for use in high seismic regions.
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127 testing various foundation-to-column connections for high seismic regions is also needed. The acceptance of precast elements, such as prestressed concrete girders, by state DOTs has been well established for more than 50 years.
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128 designs or ABC Designs similar to those presented in this report. Costs associated with investment in these technologies will not be addressed nor will they be evaluated at this time, as the intrinsic soft costs driving the need for accelerated or specialized construction equipment and techniques may outweigh the additional project hard costs.
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129 fully preassembled structures is not practical (although it is possible on a very small scale)
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130 Figure 3.38. Alternate drilled shaft–to–footing connection.
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131 Figure 3.39. Alternate column-to-foundation connection -- Option 1.
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132 Figure 3.40. Alternate column-to-foundation connection -- Option 2.
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133 Figure 3.41. Alternate column-to-foundation connection -- Option 3.
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134 Figure 3.42. Alternate drilled shaft to integrated precast abutment cap and backwall connection -- Option 1.
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135 2. Bridge Designs built with conventional construction a.
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136 more innovative construction equipment and structural systems are available to provide more rapid renewal and less disruptive construction. The key for owners and their engineering consultants is to define the goals of a renewal project, survey the limits and constraints that could affect the design and construction of the project, evaluate the impact of those limits and constraints, and finally develop a list of design criteria that will be used to prepare plans and specifications for construction.
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137 44 The matrix would factor in the site and traffic variables and constraints. 44 The matrix would factor in the surrounding environment.
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138 moving loads. An example of ADDC equipment is shown in Figure 3.46.
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139 Figure 3.48. Modified ADDC concept used for widening the inside edges of a set of existing twin bridge structures.
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140 shown in Figure 3.50. Once the modified LTTB has bridged the new span, it would be stabilized and supported at each pier or abutment substructure unit.
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141 segments can be delivered and preassembled at the site and then delivered as one unit over the span. • Allows work to proceed on multiple fronts (i.e., where multiple-span LTTBs are used, girders can be set while the next girder is delivered)
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143 As illustrated by the examples below, both launching and lateral shifting technologies involve the use of specialized equipment. To launch a bridge structure, a contractor would potentially require a launching nose, a method of movement (jacks, tuggers, push/pull rams)
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144 • Minimizes disruption of environmentally sensitive areas under the bridge. • Reduces crane size requirements by pre-erecting the new structure behind the abutment.
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145 Figure 3.59. Secondary road over mainline–rural (single or twin)
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146 for ABC Construction Technologies and the matrix directs the user to a new matrix.
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147 that due to the ability to adjust the traffic flows, ABC Construction Technologies may not be required for the project. The Bridge Widening matrix focuses on the traffic control, the number of bridges, and the type of widening proposed for the project.
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148 • Is there space adjacent to the proposed bridge location to preassemble the new structure?
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149 As a result of completing the matrix, owners and engineers will know whether the site and traffic constraints minimize, restrict, or promote the need for ABC Construction Technologies. If ABC Construction Technologies are promoted, they will be categorized in the following set of opportunities: exterior eDgeS • Launching or the use of ADDCs or LTTBs, or explore the use of SPMTs.
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150 Recommendations for Further Development of ABC Construction Technologies This section focused on the following: • Developing a matrix of questions for owners and their consultants to assist with the proper selection of a construction technology; • Developing a checklist of items that owners and their consultants must address during the design and construction phases of a project; and • Developing of a set of standard conceptual details that owners and their consultants could use as a guide for visualizing the possibilities and defining the limits of the four specified ABC Construction Technologies. Future development of ABC Construction Technologies could evolve around the demonstration of which technologies work best with the ABC Designs (both substructure and superstructure)
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From page 151... ...
151 and conceptual details in Phase III are presented under the following headings: • Precast modular abutment systems 44 Integral abutments; 44 Semi-integral abutments; and 44 Precast approach slabs. • Precast complete pier systems 44 Conventional pier bents; and 44 Straddle pier bents.
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152 Washington State, have already developed extensive sets of pre-engineered bridges for precast construction or rapid renewal. These serve as the team's starting point.
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153 finish. Testing of the UHPC material for abrasion resistance was completed at Iowa State University in February and March 2011.
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154 abrasion resistance than did cut surfaces because of the steel fibers present in the UHPC. At the formed surface, the steel fibers were aligned preferentially, parallel with the surface.
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155 Joint Intersection Detail Recommendations Final inspection of the specimen upon removal from the forms allowed for additional observations and recommendations. The proposed stay-in-place acrylic bulkhead successfully allowed for sequential placement of the UHPC, but also created a possible infiltration plane where water and chemicals could access the embedded steel joint reinforcement.
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156 interface that was suggested in the strain gauge data, as shown in Figure 3.68. Later, inspection during fatigue testing further confirmed the interfacial debonding and opening occurring below service-level conditions.
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157 as shown in Figure 3.70, was devised to posttension the deck in this region and minimize tensile stresses in the concrete through Service Level II moments without compromising the accelerated construction aspect of the project. The transverse module-to-module connection detail was modified to include high-strength steel rods mounted just under the deck surface to posttension the entire joint region.
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158 Figure 3.69. Row 1, top-of-deck embedded strain gauges (static)
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159 By contrast, applying 70 kips posttensioning force in each of the rods minimized or negated the tensile strain across the interface entirely when loaded to Service Level I All surfacemounted strain gauges spanning the interface registered below the HPC cracking strain until after the Service Level I conditions were exceeded, as shown in Figure 3.71.
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160 fractures of multiple hairpin reinforcement bars acted as the ultimate mode of failure for the transverse connection. UHPC Testing Conclusions The durability of full-depth deck joints between prefabricated panels has been a major concern for many years.
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From page 161... ...
161 strain level relative to regular concrete proved useful for application in this ABC project. While the UHPC displayed several superior material characteristics with respect to the strength of the deck joints themselves, the direct tensile bond strength between the UHPC and the precast HPC deck observed during the strength and serviceability testing raised a durability concern.
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162 proposed. The bridge was originally designed in-house to be constructed with a planned 13-mi detour (ADT = 4,000)
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163 Demonstration Project Construction The construction letting for the project was held on February 15, 2011. A total of seven fully responsive bids were received on the Keg Creek Bridge project, with a low bid of $2.65 million submitted by Godbersen–Smith Construction (G-S)
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From page 164... ...
164 represented state DOTs, the FHWA, designers, and contractors who shared an interest in accelerated bridge construction. The showcase agenda included presentations from a variety of viewpoints.
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