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1、lnnovations Explonatony Analysis Elesenving Pnognarns Highway Program The Rehabilitation of Steel Bridge Girders Using Advanced Gomposite Materials Final Report for NCHRP-IDEA Project 51 Dennis R. Mertz, John W. Gillespie, Jr., Michael J. Chajes, and Scott A. Sabol, University of Delaware Fehruary 2
2、OO2 TRRI.ISPoRTATIoI.I RESEAncH BoARD o NATIoNAL ResenRcH CoUNcIL INNOVATIONS DESERVING EXPLORATORY ANALYSIS (IDEA) PROGRAMS MANAGED BY THE TRANSPORTATION RESEARCH BOARD (TRB) This NCHRP-IDEA investigation was completed as part of the National Cooperative Highway Research Program (NCHRP). The NCHRP-
3、IDEA program is one of the four IDEA programs managed by the Transportation Research Board (TRB) to foster innovations in highway and intermodal surface transportation systems. The other three IDEA program areas are Transit-IDEA, which focuses on products and results for transit practice, in support
4、 of the Transit Cooperative Research Program (TCRP), Safety-IDEA, which focuses on motor carrier safety practice, in support of the Federal Motor Carrier Safety Administration and Federal Railroad Administration, and High Speed Rail-IDEA (HSR), which focuses on products and results for high speed ra
5、il practice, in support of the Federal Railroad Administration. The four IDEA program areas are integrated to promote the development and testing of nontraditional and innovative concepts, methods, and technologies for surface transportation systems. For information on the IDEA Program contact IDEA
6、Program, Transportation Research Board, 500 5th Street, N.W., Washington, D.C. 20001 (phone: 202/334-1461, fax: 202/334-3471, http:/www.nationalacademies.org/trb/idea) The project that is the subject of this contractor-authored report was a part of the Innovations Deserving Exploratory Analysis (IDE
7、A) Programs, which are managed by the Transportation Research Board (TRB) with the approval of the Governing Board of the National Research Council. The members of the oversight committee that monitored the project and reviewed the report were chosen for their special competencies and with regard fo
8、r appropriate balance. The views expressed in this report are those of the contractor who conducted the investigation documented in this report and do not necessarily reflect those of the Transportation Research Board, the National Research Council, or the sponsors of the IDEA Programs. This documen
9、t has not been edited by TRB. The Transportation Research Board of the National Academies, the National Research Council, and the organizations that sponsor the IDEA Programs do not endorse products or manufacturers. Trade or manufacturers names appear herein solely because they are considered essen
10、tial to the object of the investigation. ACKNOryLEDGEMENTS The researchers gratefully acknowledge the support of the National Research Council through the National Cooperative Highway Research Program IDEA program. The authors would also like to acknowledge Nouredine Ammar, John Demitz, and William
11、Edberg for their contributions during the initial research. In addition, the authors would like to thank the Delaware Department of Transportation, especially Dennis OShea and Bill Thatcher, for their help in coordinating the bridge field tests. i j Table of Contents Force Transfer Length for CFRP P
12、lates Bonded To Steel. -4 Application of Test Data to thel0 Bridge Rehabilitation . l0 Conclusions: Force Transfer Length for CFRP Plates Bonded to Steel l0 Application of Fatigue Test Results to the 704 Bridge Girder Rehabilitation . l8 EXECTIVE STJMMARY The rehabilitation of steel bridges using ad
13、vanced composite materials offers many advantages to bridge owners who are looking for feasible and cost-effective solutions for an increasing number of deficient bridges. A previous IDEA (Type l) effort investigated the use of advanced composite materials to strengthen and stiffen steel bridges (NC
14、HRP-93-ID0l l). This project resulted in the development of a selection process for adhesives that demonstrate durability under a variety of anticipated freld conditions and the demonstration of repair schemes on steel girders taken out of service in Pennsylvania due to excessive corrosion. The reha
15、bilitated beams were tested in the laboratory under service-load conditions. The tests showed that signif,rcant increases in strength and stiffness were realized with the composite repair. The Phase 2 effort described in this report focused on applying advanced composites to steel-bridge retrofittin
16、g in the field. The major issues investigated were fatigue resistance and envionmental durability. An existing steel bridge girder on Delaware Bridge l-704 was rehabilitated using carbon-fiber-reinforced polymer (CFRP) plates. It was shown that a small crew could quickly and easily perform the rehab
17、ilitation without the need for special tools, experience, or training. Load tests performed prior to and after the rehabilitation indicate a reduction in tension flange strains of ll%o. Monitoring will continue for an indefinite period of time to enable the durability of the CFRP/steel bond to be as
18、sessed. The research demonstrated that this rehabilitation approach is a feasible and potentially cost-effective repair solution for deteriorated steel bridges. IDEA PRODUCT The product developed under this project is a method for rehabilitating structurally deficient steel bridge girders using adva
19、nced composite materials. Several laboratory studies conducted at the University of Delaware had previously shown that CFRP plates can be used to effectively strengthen steel bridge girders. This project was aimed at demonstrating the acceptability of this concept for deployment into mainstream brid
20、ge retrof,rt practice through laboratory and field experimentation. The project resulted in demonstration of this technology on a bridge on Interstate 95 in Newark, Delaware (Bridge l-7 O4). CONCEPT AND INNOVATION The Federal Highway Administration (FIWA) had a total of 587,550 bridges in the Nation
21、al Bridge Inventory (NBI) as of Septemberof 2000(/). Of thesenearly600,000bridges,roughly l5%oareclassifiedasstructurallydeficient. Of the structurally deficient bridges, 56Vo have steel superstructures. Because of the substantial cost associated with replacing all of these deficient bridges, owners
22、 are searching for novel yet viable and cost-effective rehabilitation techniques. The application of advanced composite materials for bridge rehabilitation represents one such innovative solution. Previous research at the University of Delaware established the effectiveness of bonding CFRP plates to
23、 the tension flange of steel bridge girders to increase strength and stiffness. Researchers have also verified the durability of the CFRP/steel bond under varying environmental conditions (2) and examined the durability of the CFRP/steel bond subjected to cyclic and sustained loads as well as force
24、transfer issues applicable to CFRP plate joints (3). With this groundwork set, the next step was to apply this rehabilitation system to an existing bridge. This report presents the full- scale rehabilitation ofan existing steel bridge girder. Such an effort offers two significant opportunities. Firs
25、t is the opportunity to demonstrate the rehabilitation technique under actual field conditions. The application procedure is presented, highlighting the relative ease and speed with which a minimal crew can complete the procedure, thereby minimizing the traffic disruption associated with bridge repa
26、ir. A field demonstration of the rehabilitation technique also provides an opportunity to address typical construction issues that arise during the application process and the steps used to deal with them. Second, full-scale field rehabilitation provides the opportunity to monitor the in-service dur
27、ability of the retrofit when exposed to a combination of detrimental conditions. The issues of fatigue durability, environmental durability, and force transfer are now imposed concurrently. Long-term monitoring of this system provides important information on the effectiveness and longevity of this
28、rehabilitation system. INVESTIGATION INTRODUCTION The project was performed in two stages. The first stage of involved selecting a steel bridge in collaboration with ?lDoT and developing site-specific design, installation, and moniroring requiremenrs for retrohfting in-service girders, followed by p
29、erformance of laboratory-scale preparatory tests representng site-specific conditions. The n“*t ,p *u, establishment of the adequacy of the installation process and the test procedures for in-service testing of the systemn the actual steel bridge selected. Finally, the preliminary results *“r“ .eu“*
30、“d by a regional expert panel, and, bsed on this review and the recommendations made, a detailed field testing plan was develped ior eualuting in-service performance. The second stage was field installation and monitoring of the performance and durability of the composite retrofrt system under actua
31、l highway traffic and environmental conditions, followed by review of the sults and prparation oi u guidance report for applying the system to steel bridge members. In addition, a long-term monitoring pog.u* was put into place in collaboration with the Delaware Department of Transportation (DelDOT C
32、ANDIDATE BRIDGE DOWNSELECTTON Bridges considered for rehabilitation were chosen from the DeIDOT bridge inventory. Several criteria were used in narrowing the inventory to potential candidates. The first selection criterion was ttt“ tyi“ of steel bridge. Slab-on-girder bridges were selected for consi
33、deration in this demonstration. Bridges with high uuLrug“ daily truck trafhc (ADTT) would be beneficial with respect to assessing fatigue durability of tne Cpl.plsteei bond. Sliluriy, exposure to adverse environmental factors such as de-icing agents or moisture from underlying water sources would be
34、 useful in verifying the durability of the bond over an extended exposure period. Also considered in the selection of a demonstration brigJwas the ease and safety with which the span could be reached for the application and inspection of the CFRp plates. DEMONSTRATION BRIDGE The bridge selected for
35、rehabilitation using CFRP plates was Bridge l-704, which carries southbound I-95 traffic over Chistina Creek just outside Newark, Delaware (Figure l). l“ -l FIGURE I Location of CFRP demonstration bridge (l-704. This specific bridge was selected because it satisfied the criteria discussed in the pre
36、vious section. Carrying I-95 traffic, the bridge has a reasonably high ADTT (estimated by DeIDOT to be approximately 5,920). The bridge also spans Christin Creek, resulting in increased moisture in the area of the bond. The lack of traffic under the bridge provides a relatively safe work environment
37、 during the rehabilitation and inspection Processes. ln addition, the girders of the northern approach span are easily accessible, eliminating the need for extensive scaffolding during both of these operations. The bridge comprises three simple spans with a total length of I 15 ft. and a skew angle
38、of 13 degrees (Figure 2). The main rp* it 62.5 ft. long with two approach spans measuring24.S ft. The original construction on the northern approach span consisted of four W24x84 steel girders spaced at 7 ft. ll in. Two W36xl50 fascia girders at the same spcing were also used. Two separate road wide
39、nings added three W36xl50 girders to each side of the bridge. Figure 2 Demonstration bridge (1-704). GIRDER SELECTION FOR RETIABILITATION One bridge girder was chosen to undergo rehabilitation using the CFRP plates. The use of a single test girder provides an adequateiemonstration of the rehabilitat
40、ion technique as well as sufficient data on long-term durability. In-service peak strains were recorded for four girders under the primary driving lanes to determine which girder is subjected to the largest stress range. The monitoring system consisted of a strain transducer, data-acquisition system
41、, and power supply. The strain transducer was attached to the bottom flange of the girder being tested. Since the entire system runs off battery power, strain data could be taken continuously without supervision. Peak strains recorded for several girders for approximately L2-14 hours indicated that
42、girder G5 is subjected to the largest liveload stress range. This is due to the position of girder G5 between the first two driving lanes, which contains the majority of truck traffic. Subsequent l4-day strain-time histories were monitored on girder G5 to determine hourly and daily variations in liv
43、e-load strains. A trigger threshold of 75 n was used for this particular test; therefore, peak strains below 75 ts are not shown. The extended test indicates typical stress ranges for the heaviest trucks between 2 and 3 ksi, with roughly 757o of the stresses between 2.25 and 2.5 ksi (only stresses a
44、bove2.25 ksi were recorded) and an averageof2-4ksi Ifoneconsideredallstresses(thoseaboveandbelow2.25ksi),theaveragestressduetotruckswould be less than the 2.4 ksi. FORCE TRANSFER LENGTH FOR CFRP PLATES BONDED TO STEEL Background The use of a single joint or series of joints is advantageous in the pr
45、actical application of this rehabilitation technique. Short lengths of the CFRP plates allow for easier transportation to the bridge sit“; uut perhaps more importantly, ony a limited number of workers are needed to install the shorter plate sections. When conside.ing a joint, ai proposed here, force
46、 transfer between the steel flange and CFRP plates beomes a primary focus. This wrk address“i ttri, issue by examining the force development along the CFRP plates through smll-scale specimens and an analytical model. The transfer distance becomes particularly important when using staggered joints to
47、 connect plate sectioni. The principle is similar to development lengths considered for reinforcement splices in concrete members. When a single CFRp ptate is severed, the load carried in the plate must shed back through the steel substrate and into the a jacent p-lates. A specifrc distance is requi
48、red for the plates to fully develop this additional force and then transfer it back to the steel flang when that strip is severed. Variations in the amount of adhesive applied during the rehabilitation, clamping pressure, and bonding surface affect the amount and location of adhesive squeezed betwee
49、n plates. Force transfene thiugh the adhesive interface between consecutive or adjacent plates is not considered here. Test Overview The purpose of this test program is to analyze the force transfer length for a steel specimen doubly reinforced with CFRp plates Six 36-in. specimens wete placed under tensile loading to etermine the rate of force transfer between the steel substrate material and CFRP reinforcement. Eighteen foil strain gages were placed along the length of each specimen to captue the longitudinal strain distribution in the CFRP plates. T