materials Article
Design Optimization and Structural Performance Evaluation of Plate Girder Bridge Constructed Using a Turn-Over Process Gi-Ha Eom, Sung Jae Kim, Tae-Hee Lee and Jang-Ho Jay Kim * School of Civil and Environmental Engineering, Yonsei University, Seoul 03722, Korea;
[email protected] (G.-H.E.);
[email protected] (S.J.K.);
[email protected] (T.-H.L.) * Correspondence:
[email protected]; Tel.: +82-2-2123-5802 Academic Editor: Jorge de Brito Received: 4 January 2017; Accepted: 6 March 2017; Published: 13 March 2017
Abstract: A recent trend in bridge construction has been the optimization of the cost-to-performance ratio. The most effective way to optimize the cost-to-performance ratio is to maximize the efficiency of the superstructure. Currently, many bridge engineers and designers favor two- or three- girder plate superstructures, due to their cost advantages. However, research on the performance enhancements of the I-type girder in two- or three- girder plate bridges is lacking. One of the most important performance improvement technologies for the I-type girder is the “preflex” method. In the preflex method, the specimen is inverted during the construction process to apply prestressed cambering to the specimen by using self-weight. However, a problem with the preflex construction method is difficulty with inverting the girder/plate system during the concrete curing process. Therefore, a new inverting system called Turn-Over (TO) wheel was proposed. Using TO wheels, wider variations to the I-type girder design can be achieved. Using this TO construction method, various cross sectional designs of girder plate systems can be considered due to its easiness in inverting the girder/plate system. In this study, the location of concrete confinement sections between the steel I-beams and concrete plates was varied in an I-girder cross-sectional design. Design parameters included effective height, flange thickness, flange width, confining concrete section width, etc. From this study, the optimum cross-sectional design of the I-girder/concrete plate system was achieved. Then, a single 20 m TO girder/plate system and two 20 m TO girder bridges were constructed and tested to evaluate their performance. From the test, failure behavior, load carrying capacity, crack pattern, etc., are obtained. The results are discussed in detail in this paper. Keywords: two- or three- girder plate bridge; precasted girder; turn over construction; preflex method
1. Introduction As urbanization accelerates and city populations rapidly increase, transportation of people and merchandise must become more efficient. Bridge construction plays a vital role in the urban transportation system, in order to improve transport systems and infrastructure. Recently, as bridge construction technologies advance, construction efficiency, sustainable maintenance, and construction cost optimization are becoming important issues in bridge construction. In order to resolve these issues, many studies have been conducted to optimize the cost-to-performance ratio. Among those concerning bridge technologies, the superstructure of a bridge was identified as a critical aspect in maximizing bridge efficiency [1–3]. Generally, the bridge superstructure can be divided into two categories. One type is a closed system and the other is an open system, such as a box-type girder or plate-type girder system, respectively. The box-type girder system is advantageous in torsion and durability, but it is Materials 2017, 10, 283; doi:10.3390/ma10030283
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disadvantageous in terms of construction costs. The plate-type girder system is disadvantageous in Materials 2017, 10, 283 2 of 14 terms of durability and constructability, but it is advantageous in relative construction and maintenance coststerms compared to the other girder systems.but Currently, since the most important issue inand bridge of durability and constructability, it is advantageous in relative construction construction is cost-to-performance efficiency, many bridgeCurrently, engineerssince and the designers favor a plate-type maintenance costs compared to the other girder systems. most important issue in system, bridge construction cost-to-performance efficiency, many bridge engineers designers favor by girder due to theiscost advantages [4–6]. A plate girder bridge is a and bridge constructed a plate-type girder system, due to the cost advantages [4–6]. A plate girder bridge is a bridge placing a concrete plate on steel or concrete I-type girders. Therefore, a plate girder bridge is usually a constructed placing concrete platetime, on steel concrete girders. Therefore, a plate precast-type thatbycan saveaconstruction andorworks byI-type transporting and placing thegirder precasted bridge is usually a precast-type that can save construction time, and works by transporting girders on top of the pre-constructed bridge piers on-site. There are two types of plate girderand bridges. placing the precasted girders on top of the pre-constructed bridge piers on-site. There are two types One type is the multiple girder plate bridge, and the other is the two- or three- girder plate bridge as of plate girder bridges. One type is the multiple girder plate bridge, and the other is the two- or threeshown in Figure 1. girder plate bridge as shown in Figure 1.
Figure 1. Number of I-girders in plate girder bridges.
Figure 1. Number of I-girders in plate girder bridges.
Previously in Korea, multiple girder plate bridges were constructed more frequently, because Korean bridge engineers and designers did not have were sufficient knowledge andfrequently, experiencebecause in Previously in Korea, multiple girder plate bridges constructed more designing twoor threegirder plate bridges. Also, compared to multiple girder plate bridges, twoKorean bridge engineers and designers did not have sufficient knowledge and experience in designing plate bridges tended to be less safe [7,8]. However, due to recent advancements two- or or threethree-girder girder plate bridges. Also, compared to multiple girder plate bridges, two- orinthreebridge technologies, construction materials, and precast construction methods, twoor threegirder plate bridges tended to be less safe [7,8]. However, due to recent advancementsgirder in bridge bridges are becoming more popular. More specifically, two- or three- girder plate bridges have a technologies, construction materials, and precast construction methods, two- or three- girder bridges much simpler structural behavior, better cost-to-performance ratio, and easier structure maintenance, are becoming more popular. More specifically, two- or three- girder plate bridges have a much due to a reduction in the number of girders [8]. simpler structural behavior, better cost-to-performance ratio, and easier structureJapan, maintenance, due to In technologically developed countries, such as France, Germany, Switzerland, and Korea, a reduction in the number of girders [8]. bridge engineers and researchers attempted to maximize the constructability, safety, serviceability, In technologically developed countries, as France, Germany, Switzerland, and Korea, and durability of twoor three- girder platesuch bridges. Jeon et al. conducted research on Japan, life cycle cost (LCC) optimization in the designattempted of main girders to improve constructability and durability of twobridge engineers and researchers to maximize the constructability, safety, serviceability, or three- girder plateorbridges Also,plate Yun et al., Lin et al., and Park et al. triedresearch to improve and cost and durability of twothree-[9]. girder bridges. Jeon et al. conducted onsafety life cycle of two-inorthe threegirder byto focusing on its redundancy [10–13]. In addition,of high (LCC)durability optimization design ofplate mainbridges girders improve constructability and durability two- or performance and high strength steel member developments for twoor threegirder plate bridges three- girder plate bridges [9]. Also, Yun et al., Lin et al., and Park et al. tried to improve safety and have been performed by Coelho et al., Ricles et al., and Yong et al. [14–16]. Even though many durability of two- or three- girder plate bridges by focusing on its redundancy [10–13]. In addition, different types of research have been conducted on two- or three- girder plate bridges, the literature high performance and high strength steel member developments for two- or three- girder plate bridges review shows that studies on enhancements of the I-type girder improvement is lacking. However, a have breakthrough been performed by Coelho al., Ricles et al., Yongby etLipski al. [14–16]. Even in performance foretthe I-type girder wasand proposed [17], called thethough “preflex”many different types of research have been conducted on twoor threegirder plate bridges, the literature method. In the preflex method, pre-deflection is applied to the steel I-type girder using the dead load review shows that plates studies enhancements of thesystem I-typeduring girderthe improvement is lacking. However, of the concrete by on inverting the girder/plate precast construction process as a breakthrough in performance for the I-type girder was proposed by Lipski [17], called the “preflex”
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Materials 2017, 10, 283 of 14 method. In the preflex method, pre-deflection is applied to the steel I-type girder using the dead3load of the concrete plates by preflex inverting the girder/plate system during the precast construction process as shown in Figure 2. The method is equivalent to the prestressing method in concrete girders shown in Figure 2. The preflex method is equivalent to the prestressing method in concrete girders shown in Figure The preflex methodisisapplied equivalent to girder the prestressing incarrying concretecapacity girders where the initial 2. cambering deflection to the to increasemethod the load where the initial cambering deflection is applied to the girder to increase the load carrying capacity where the initial cambering deflectionUsing is applied to the girder to increase the load carrying capacity and and plastic deflection serviceability. the preflex method during construction, the I-type girders and plastic deflection serviceability. Using the preflex method during construction, the I-type girders plastic deflection serviceability. Using the preflex method during construction, the I-type girders and and two- or three- girder bridge systems became much safer and more stable, almost equivalent to and two- or three- girder bridge systems became much safer and more stable, almost equivalent to twoor threegirder bridgeHowever, systems became muchtosafer more stable,constructed almost equivalent multiple girder systems. variations the and I-type girders using to themultiple preflex multiple girder systems. However, variations to the I-type girders constructed using the preflex girder systems. However, to the I-type girders constructed usingsystem the preflex method were method were limited duevariations to the difficulty in inverting the girder/plate during the curing method were limited due to the difficulty in inverting the girder/plate system during the curing limited to the difficulty in inverting the girder/plate during the (TO) curing process. Therefore, process.due Therefore, in this study, a new inverting systemsystem called Turn-Over wheel is proposed to process. Therefore, in this study, a new inverting system called Turn-Over (TO) wheel is proposed to in this study, a newgirder inverting system called Turn-Over (TO) wheel is proposed to make the preflex make the preflex construction simpler and quicker. In the TO system, two ends of the make the preflex girder construction simpler and quicker. In the TO system, two ends of the girder construction and quicker. In the ends of the system are girder/plate systemsimpler are initially placed into theTO TOsystem, wheels.two Then, when thegirder/plate concrete plate hardens girder/plate system are initially placed into the TO wheels. Then, when the concrete plate hardens initially placed the TO when concrete plate hardens are sufficiently, theinto wheels arewheels. turned Then, to invert thethe system as shown in Figuresufficiently, 2 (step 3). the It iswheels important sufficiently, the wheels are turned to invert the system as shown in Figure 2 (step 3). It is important turned invert as is shown in Figure 2 (step 3). Itmethod, is important to note that inverting the TO method to notetothat thethe TOsystem method equivalent to the preflex except that the of the to note that the TO method is equivalent to the preflex method, except that the inverting of the is equivalentspecimen to the preflex method, except that thethrough inverting theof girder/plate specimen easier girder/plate is easier in the TO method theofuse the TO wheels. Usingisthe TO girder/plate specimen is easier in the TO method through the use of the TO wheels. Using the TO in the TO method through theI-type use ofgirder the TO wheels. Using the TO system, more variations to the system, more variations to the design can be achieved due to the simplicity of the precast system, more variations to the I-type girder design can be achieved due to the simplicity of the precast I-type girder design can bethe achieved dueperformance to the simplicity of the precast construction. In this study construction. In this study structural and failure behavior of various cross-sectional construction. In this study the structural performance and failure behavior of various cross-sectional the structural performance and failureusing behavior of various cross-sectional designs of I-type girders designs of I-type girders constructed the TO system are evaluated. Specifically, the confining designs of I-type girders constructed using the TO system are evaluated. Specifically, the confining constructed usingbetween the TO the system areflange evaluated. sectionatbetween concrete section upper of theSpecifically, I-type steel.the Theconfining concrete concrete plate is placed the top, concrete section between the upper flange of the I-type steel. The concrete plate is placed at the top, the upperand flange of thesection I-type of steel. concrete is placed at thetotop, middle, the andbest bottom section middle, bottom the The upper flangeplate of the I-type steel determine location of middle, and bottom section of the upper flange of the I-type steel to determine the best location of of upper flange of the as I-type steel determine the best location ofgirder the girder/plate as thethe girder/plate interface, shown in to Figure 3. Then, a single 20 m TO and two 20 interface, m TO girder the girder/plate interface, as shown in Figure 3. Then, a single 20 m TO girder and two 20 m TO girder shown Figure 3. Then, a single mTO TO system girder and twodesigns, 20 m TO test girder bridge areand tested. details bridge in are tested. The details of20 the girder specimens, test The results are bridge are tested. The details of the TO system girder designs, test specimens, and test results are of the TO system discussed in this girder paper. designs, test specimens, and test results are discussed in this paper. discussed in this paper.
Step 1 Step 1 Steel Girder Steel Girder
Step 2 Step 2 Confining Concrete Confining Concrete
Step 3 Step 3 Turn Over Turn Over
Step 4 Step 4 Concrete Plate Concrete Plate
Figure 2. 2. Construction Construction procedure procedure of of steel steel composite composite girder girder applied applied by by Turn-Over Turn-Overprocess process(TO). (TO). Figure Figure 2. Construction procedure of steel composite girder applied by Turn-Over process (TO).
Figure 3. Location of the confining concrete section in the cross section. Figure 3. Location of the confining concrete section in the cross section. Figure 3. Location of the confining concrete section in the cross section.
2. Turn-Over Construction Method 2. Turn-Over Construction Method 2. Turn-Over Construction Method 2.1. Basic Theory 2.1. Basic Basic Theory Theory 2.1. The Turn-Over (TO) method is used to reduce steel section size in a steel I-beam by applying The Turn-Over Turn-Over(TO) (TO)method method is used to reduce steel section size in a I-beam steel I-beam by applying The is used to reduce sizeconcrete in a steel by applying initial deflection using distributed self-weight ofsteel the section confining section and concreteinitial plate initial deflection using distributed self-weight of the confining concrete section and concrete deflection distributed self-weight of the of confining concrete section and concrete plate cast onplate the cast on theusing top flange section. The application the concrete self-weight cambering achieves reduction cast on the top flange section. The application of the concrete self-weight cambering achieves reduction of stress in the member during its service life without any additional treatment, such as thermal of stress in the member during its service life without any additional treatment, such as thermal prestressing, tendon prestressing, etc. [18–25]. prestressing, tendon prestressing, etc. [18–25].
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The TO method is comprised of four main steps, shown in Figure 2. Step 1 is the overhanging of an asymmetric step, Materials 2017, 10, 283I-section steel member on a frame to start the manufacturing process. In this4 of 14 the initial bottom section, which will ultimately be turned over as a top section of the girder. Step 2 is casting of the confining concrete section at the bottom flange of the overhanging I-section member. top flange The application of the concrete cambering achieves reduction of stress Once the section. confining concrete sufficiently hardens,self-weight the distributed self-weight applies a deflection on inthe theI-section membersteel during its service life without any additional treatment, such as thermal prestressing, member. In step 3, the whole member is turned upside down, where the bottom tendon etc. and [18–25]. sectionprestressing, goes to the top the top section comes down to the bottom. The process is facilitated by The TO method is comprised four main steps, shownover in Figure 2. Step 1 is the overhanging using the turning wheel insteadof of manually turning the member, which reduces the ofconstruction an asymmetric I-section steel member on a frame to start the manufacturing process. this is step, time and effort. Once the member has been turned over, in step 4 a concreteIn plate cast the initial bottom section, which will ultimately be turned over as a top section of the girder. Step 2 on top of the confining concrete section to complete the process. The cambering deflection appliedisto casting of I-beam the confining concrete sectionofatthe the confining bottom flange of the overhanging I-section the steel from the self-weights concrete section is returned back member. to “zero” Once the confining concrete sufficiently hardens, the distributed a deflection on the deflection when the dead load of the bridge is applied. In stepself-weight 4, the best applies composite action between I-section steel member. In step 3, the whole member is turned upside down, where the bottom section the concrete plate and the confining concrete section is selected by determining the optimal location goes to confining the top and the topsection sectionwith comes downtotothe thetop bottom. process is facilitated by using the of the concrete respect flangeThe of the I-section. turning wheel instead of turning over member, which theplate construction time The comparison of manually strain profiles along thethe cross section of thereduces ordinary girder and theand TO effort. Once the member has been turned over, in step 4 a concrete plate is cast on top of the confining girder is shown in Figure 4. In the ordinary steel girder, the addition of stresses from the self-weight concrete section(Figure to complete thethe process. Theplate cambering applied steel I-beam from of the girder 4a) and concrete (Figuredeflection 4b) would resulttointhe summed tensile and the self-weights of the confining concrete section is returned back to “zero” deflection when the dead compressive stresses at the bottom and top of the cross section, respectively, as shown in Figure 4c. load of the bridge applied. step 4,occurring the best composite the concrete plateAs and the Figure 4d–f showsis the stressIn profiles in the TO action girder between before casting of a plate. shown confining section is selected by determining theordinary optimaland location of steel the confining concrete in Figure concrete 4a,d, stresses in the cross section between the the TO girders are similar section with respect to the top flange of the I-section. in magnitude, but compression and tensile stresses are in opposite directions. Therefore, in the TO Thethe comparison of strain profilesare along thecompressive cross section and of the ordinary platerespectively, girder and the TOto girder, bottom and top sections under tensile stresses, due girder is shown in characteristic Figure 4. In the girder, addition of stresses from thethe self-weight the upside-down of ordinary the girdersteel at the initialthe manufacturing process. When confining ofconcrete the girder (Figure 4a) and the concrete plate (Figure 4b) would result in summed tensile and section is placed at the top flange of the TO girder, additional tensile and compressive compressive stresses to at top the bottom and top of cross the cross section, respectively, as shown in Figure 4c. stresses are applied and bottom of the section, respectively. As the TO girder is turned Figure 4d–f shows the stress profiles occurring in the TO girder before casting of a plate. As shown over using the turning wheel, top and bottom section stresses are also turned over and change indirection, Figure 4a,d, stresses the cross section between and the TO steel girders are similar as shown inin Figure 4f. When the plate isthe castordinary above the confined concrete section and the intop magnitude, but compression andadditional tensile stresses are in opposite directions. flange section of the TO girder, compressive and tensile stresses Therefore, are appliedintothe theTO top girder, the bottom and top sections are under compressive and tensile stresses, respectively, due to and bottom flanges, respectively, as shown in Figure 4g. When all of these stresses are added together, the upside-down characteristic of the girder at the initial manufacturing process. When the confining the TO girder has the total tensile and compressive stresses at the bottom and top sections, concrete section is placed at the top the TO girder, additional and compressive stresses respectively shown in Figure 4h.flange It is of important to note that thetensile magnitude of the tensile and are applied to top and bottom of the cross section, respectively. As the TO girder is turned over using compressive stress is much less than that of the ordinary steel girder, which is the reason for the steel the turning wheel, bottom section stresses are upward also turned over and change direction, as shown reduction in the top TO and girder. Also, because of the shifting of the neutral axis due to the inconfining Figure 4f. When the plate is cast above the confined concrete section and the top flange section of concrete and flange sections of the girder, the optimal cross section or the minimal steel design the TO girder, additional compressive and tensile stresses are applied to the top and bottom flanges, can be achieved for the TO girder. Design equations used in Figure 4 are shown in Table 1. respectively, as shown in 4g. When all of these stresses are addedsteel together, TOthe girder has theis The comparison of Figure the amount of steel required for an ordinary girderthe and TO girder total tensile and compressive stresses at the bottom and top sections, respectively shown in Figure tabulated in Table 2. As shown in Table 2, the steel required for the confined section located at 4h. the Itbottom is important the magnitude of the tensile and compressive muchofless flangetoofnote the that TO girder with a confining concrete section widthstress and is height 400than mmthat and of1000 the mm, ordinary steel girder, which the reasondifference for the steel reduction theofTO Also, because respectively, shows no is significant compared to in that an girder. ordinary steel girder. ofHowever, the upward shifting of the neutral axis due to the confining concrete and flange sections of the with respect to the top flange, the required steel for the TO girder is reduced by 85.94% girder, the optimal cross section orsteel the minimal steel design can be achieved forgirder the TO girder. compared to that of an ordinary girder. The reduction in steel in the TO results in Design savings equations used in Figure 4 are shown in Table 1. of material costs and construction time from the precasted construction using the TO method.
Figure4.4.Cont. Cont. Figure
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Figure 4. Strain profiles along the cross section height of the ordinary plate girder and TO girder. Figure plate girder girder and and TO TO girder. girder. Figure 4. 4. Strain Strain profiles profiles along along the the cross cross section section height height of of the the ordinary ordinary plate Figure Figure 4. Strain profiles along the cross section height of the ordinary plate girder and TO girder. Figure 4. 4. Strain Strain profiles profiles along along the the cross cross section section height height of of the the ordinary ordinary plate plate girder girder and and TO TO girder. girder. Table 1. Stresses induced in the I-beam from Turn-Over (TO) method. Table 1. Stresses induced in the I-beam from Turn-Over (TO) method. Table 1. Stresses induced in induced the I-beam from Turn-Over (TO) method. method. Table 1. from Turn-Over Table 1. Stresses induced in the I-beam from Turn-Over (TO) Table 1. Stresses Stresses induced in in the the I-beam I-beam from Turn-Over (TO) (TO) method. method. Step-Title Manufacturing Step Top Flange Stress Bottom Flange Stress
Step-Title
Manufacturing Step Top Flange Stress Manufacturing Step Flange Stress Manufacturing Step TopTop Flange Stress Manufacturing Top Flange Stress Manufacturing Step Step Top Flange Stress
Step-Title Step-Title Step-Title Step-Title
Steel I-beam Steel I-beam self-weight Steel I-beam Steel Steel I-beam I-beam self-weight Steel I-beamself-weight self-weight self-weight self-weight Confined concrete Confined Confined Confined Confined self-weight concrete Confined concrete concrete concrete concrete self-weight self-weight self-weight self-weight self-weight
Msteel Ssteeltop
f steelbottom =
Msteel Ssteelbottom
f steeltop =
Mcon S(s+c)top
f steelbottom =
Mcon S(s+c)bottom
2
2+con steel2 2 f steeltop = 2M S(s+c)top
Msteel Ssteeltop + 2Msteel+con − 2 S(s+c)top
f steeltop =
Upright position Upright position
f steeltop =
2
Turn-Over process Turn-Over Turn-Over Turn-Over Turn-Over Turn-Over process process process process process
Upright position Upright Upright Upright position position position
Bottom Flange Stress Bottom Flange Stress Bottom Flange Bottom Flange BottomStress Flange Stress Stress
2
Mcon
S(s+c)top
22 2
2
f steelbttom =
22Msteel+con222 S(s+c)bottom
Msteel f steelbttom = − Ssteelbottom − Mcon S(s+c)bottom
+
2Msteel+con S(s+c)bottom
2
2 22 2
The comparison of the amount of steel required for an ordinary steel girder and the TO girder Table 2. Comparison of the amount of steel required for ordinary and TO girder. is tabulated in Table 2. As shown in Table 2, the steel required for the confined section located at the Table 2. Comparison of amount of required for ordinary and TO girder. Girder TO (TO) Table Comparison of the amount of steel required for ordinary and TO girder. Table 2. with Comparison of the the amount of steel steel required forGirder ordinary andof TO400 girder. 2. TO Comparison ofOrdinary thea amount of(OG) steel required for ordinary and TO girder. bottom flangeTable of the girder2. confining concrete section width and height mmArea andRatio Cross-Section Width Height Area Width Ordinary Height Area Girder (OG) TO Girder (TO) (TO/OG, %) Ordinary Girder (OG) TO Girder 1000 mm, respectively, shows noGirder significant difference to that of an(TO) ordinary Ordinary Girder (OG) TO Girder (TO) Area Ratio (mm) (mm) (mm2)steel girder. (mm) (mm) (mm2)compared Ordinary (OG) TO Girder (TO) Area Area Ratio Ratio Cross-Section Width Height Area Width Height Area Area Ratio Cross-Section Width Height Area Width Height Area Cross-Section Width Height Area Width Height Area (TO/OG, However, withTop respect top the for(mm) the TO girder is reduced flange 800 flange,(mm) 40 32,000 300 15 Area 45002) by 85.94% 14.06 %) Cross-Section Width Height Widthto theHeight Arearequired (TO/OG, %) 2steel (TO/OG, %) ) (mm) (mm (mm) (mm 22) (TO/OG, %) (mm) (mm) (mm (mm) (mm) (mm (mm) (mm) 2 (mm ) (mm) (mm) 2 (mm22)) Web 26steel girder. 3153 81,978 26 (mm) 3146 81,796 99.8 ) (mm) (mm ) (mm) (mm) (mm compared to that of an ordinary The reduction in steel in the TO girder results in savings Top flange 800 40 32,000 300 15 4500 14.06 Top flange 800 40 32,000 300 15 4500 14.06 Top flange 800 40 32,000 300 15 4500 14.06 Bottom flange 800 57 45,600 800 64 Top flange 800 40 32,000 300 15 using 4500TO51,200 14.06 112.3 Web 26 3153 81,978 26 3146 81,796 99.8 of material costs and the precasted the method. Web 3153 81,978 3146 81,796 99.8 Webconstruction 26 time from 3153 81,978 construction 26 3146 81,796 99.8 Total -26 159,578 -26 137,496 86.2 Web 26 3153 81,978 26 3146 81,796 99.8 Bottom flange 800 57 45,600 800 64 51,200 Bottom 800 57 45,600 800 64 51,200 Bottom flange flange 800 57 45,600 800 64 51,200 Bottom flange 800 57 45,600 800 112.3 Total --159,578 -- 64 -- 51,200 137,496 Total 159,578 137,496 Total 159,578 137,496 2. -Comparison of the amount for ordinary and 137,496 TO girder. The Optimum Cross- Section Determination Total 2.2.Table 159,578of steel required 86.2
112.3 112.3 112.3 86.2 86.2 86.2
2.2. Optimum Cross Section Determination 2.2. The The Optimum Cross Section Determination In order to obtain the optimal cross section design for the(TO) TO girder, the following construction Ordinary Girder (OG) TO Girder 2.2. The Optimum Cross Section Determination Area parameters have been considered: (1) Confining the concrete section (2)Ratio Cross-section In order to obtain the optimal cross section design for the girder, the construction Cross-Section Height Area Widthdesign Height Area location; In Width order to obtain the optimal cross section for the TO TO girder, the following following construction (TO/OG, %) 2 2 weight and steel ratios; (3) Span-to-depth ratio. (mm) (mm) (mm ) (mm) (mm) (mm ) In order to obtain the optimal cross section design for the TO girder, the following construction parameters have been considered: (1) Confining the concrete section location; (2) Cross-section parameters have been considered: (1) Confining the concrete section location; (2) Cross-section and ratios; Span-to-depth ratio. parameters have been considered: Confining the300 concrete section location; Top flangeweight 800 steel 40 (3) 32,000 15 4500 (2) Cross-section 14.06 weight and steel ratios; (3)(1) Span-to-depth ratio. Concrete Section 26 (3) the 3153 81,978 3146 81,796 99.8 weightWeb and2.2.1. steel Confining ratios; Span-to-depth ratio.Location26 Bottom flange 800 57 45,600 800 64 51,200 112.3 2.2.1. the Location 2.2.1.InConfining Confining the Concrete Concrete Section Locationorder to determine theSection optimal action between the confining concrete and plate Total 159,578 composite 137,496 86.2 2.2.1. Confining the Concrete Section Location sections, the location of the confining concrete section in the cross section is varied, as shown in Figure 3. In order to determine the optimal composite action between the confining concrete plate In order to determine the optimal composite action between the confining concrete and and plate The effective height of the bridge cross section is maintained at 3200 mm for all three cases shown in sections, the location of the confining concrete section in the cross section is varied, as shown in Figure sections, the Section location of the confining concrete section in the cross section is varied, as shown in Figure 3. 3. In order to determine theDetermination optimal composite action between the confining concrete and plate 2.2. The Optimum Cross Figure 3. The cross section dimensions of the confining concrete section are 1000 mm in height and The effective height of the bridge cross section is maintained at 3200 mm for all three cases shown in The effective height of the bridge cross section is maintained at 3200 mm for all three cases shown in sections, the location of the confining concrete section in the cross section is varied, as shown in Figure 3. In order tomm obtain thecross optimal cross sectionconsidered design for thethe TOconfining girder, the following construction 400 width. The three locations for concrete section are as Figure 3. The section of concrete section are 1000 in height Figure 3.inof The section dimensions of the the confining confining concrete section are 1000 mm in follows. height and The effective height thecross bridge crossdimensions section is maintained at 3200 mm for all three casesmm shown in and parameters have been considered: (1) Confining the concrete section location; (2) Cross-section weight 400 mm in width. The three locations considered for the confining concrete section are as follows. 400cross mm section in width. The three locations considered for the section confining section are as and follows. Figure 3. The dimensions of the confining concrete areconcrete 1000 mm in height and steel ratios; (3) Span-to-depth ratio. 400 mm in width. The three locations considered for the confining concrete section are as follows.
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2.2.1. Confining the Concrete Section Location In order to determine the optimal composite action between the confining concrete and plate sections, the location of the confining concrete section in the cross section is varied, as shown in Figure 3. The effective height of the bridge cross section is maintained at 3200 mm for all three cases shown in Figure 3. The cross section dimensions of the confining concrete section are 1000 mm in height and 400 mm in width. The three locations considered for the confining concrete section are as follows. 1. 2. 3.
The confining concrete section is located between the bottom surface of the plate and the top flange section surface of the I-steel member. The top flange of I-steel member is embedded in the confining concrete section and the confining concrete section is attached to the bottom surface of the plate. The confining section is attached to the bottom surface of the top flange section of the I-steel member with the top flange section embedded in the plate.
With the confining concrete section location parameter as the top surface, center, and bottom surface of the top flange section of the I-steel member, this study focuses on the stress and steel ratios of a TO girder bridge. When the confining concrete section is located at the top surface of the top flange of I-steel member, the compressive forces acting on the confining concrete section is large enough to require a larger width of the confining section. The calculated amount of steel needed for this setup is approximately 50 t. When the top flange section is embedded in the confining concrete section, inverting of the system becomes easier and the required amount of steel is 50.2 t. Finally, when the confining concrete section is placed at the bottom surface of the top flange section of the steel I-beam, the compressive force acting on the confining concrete section is increased due to the effective height reduction of the cross section and the required steel amount is approximately 51.0 t. Also, in order to implement this setup, dowel studs and complex formwork are required, making the construction much more difficult. Also, since the effective height of the girder bridge is increased, the required steel amount is increased. However, since the difference in the required steel amount for all three cases is nearly equal, the case with the top flange section embedded in the confining concrete section is selected for its construction simplicity, better structural stability, smoother force transfer, better embedment connection of the steel I-beam, etc. 2.2.2. Required Steel and Stress Ratios for Various Cross-Sectional Parameters Once the confining concrete section location is selected, the required amount of steel and concrete section area are calculated based on 9 different cross-sectional parameters as follows: the effective height (H), the top and bottom flange thicknesses and widths (Tft, Tfb, Wst, and Wsb), the confining concrete section thickness and width (Tc and Wc), and the distance between confining concrete and top flange upper surfaces (Hc) as shown in Table 3. In Table 3, the upper and lower values for all of the parameters are tabulated, obtained from design equation calculations of required strength. Based on these upper and lower values, the design of the TO girder cross-section is performed. Materials 2017, 10, 283
of 14 Table 3. Dimensional parameters of the cross 7section (unit: mm).
Table 3. Dimensional parameters of the cross section (unit: mm).
Wst
WsbTft Tfb
Wst
Tfb
Tft
Lower value Lower
800 300 value
40800 15
Upper Upper value
value 1000
400
100025 60
300 400
40 60
15 25
Parameter Parameter Wsb
Tw
Tw
H
Wc
Tc H Hc
Wc
Tc
Hc
26
26 30
3000
1500
300 3000150
4000
2500
400 4000250
1500 2500
300 400
150 250
30
The total number of possible parametric variables cases are 29 = 512. However, if the Determination of Experiment (DOE) method is used, then the parametric variable cases can be
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reduced to one eighth of 512, i.e., 64 cases. Also, in Korea a 50 (unit: m span girder, a general steel Table 3. Dimensional parameters of the crossfor section mm). weight per unit area is less than 200 kg/m2 and the allowable stress limit is 90% of the actual stress. Therefore, these values are used as the criteria in the analysis.Wsb From the analysis Parameter Wst Tfb results, Tft the required steel weight, steel stress and concrete stress were plotted, as shown in Figure 5. Depending on the Lower value 800 300the parameter’s 40 15 sensitivity to slope of the curve between the upper and lower values of the parameter, the cross-sectional design can be observed. In Figure 5, the dotted lines indicate the average values Upper value 1000 400 60 25 of required steel weight, steel stress, and concrete stress. From the parametric study, the order of parameter importance in required steel amount isTw as follows: H the effective (H) Wc height Tc Hc > the bottom flange thickness (Tfb) > the web thickness (Tw). With respect to the steel stress, the order is as follows: 26 (Tfb) > the 3000bottom 1500flange 300 width 150(Wsb). Finally, the effective height (H) > the bottom flange thickness with respect to the parameter effect on stress applied to concrete section, the importance of order is as 30 4000 2500 250 follows: the effective height (H) > the confining concrete section width (Wc).400
Figure 5. Steel weight, steel and concrete stress by cross section area. Figure 5. Steel weight, steel and concrete stress by cross section area.
In conclusion, the effective height most significantly affects the required steel weight as well as In conclusion, the effective significantly affects thenumber requiredcases steel weight as well as the the steel and concrete stressesheight on themost cross section. Since the from nine different steel and concrete stresses the cross the number cases from nine different parameters parameters turns out to be on 64 cases, thesection. differentSince parameter combinations give slightly different result turns out to be 64in cases, the of different parameter combinations giveweight slightly trends. Therefore, the case Hc parameter, the required unit steel atdifferent the upperresult valuetrends. is less Therefore, in thevalue, case of Hctoparameter, the required steel weight at the upper value is less than the than the lower due the nonlinear trend in unit the analysis result. lower value, due to the nonlinear trend in the analysis result.
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3. Performance Evaluations by TO Girder Static Testing 3. Performance Evaluations by TO Girder Static Testing
In order to evaluate the performance of the girder built by the TO method, a 20 m TO girder In order to evaluate the performance of the girder built by the TO method, a 20 m TO girder specimen andand a two-main TOTO girder specimenwith with a plate section tested. The cross specimen a two-main girderplate platebridge bridge specimen a plate section are are tested. The cross section dimensions two specimens inFigure Figure6a,b. 6a,b. Materials 2017, 10,of 283these 8 of 14 section dimensions of these two specimensare are shown shown in 3. Performance Evaluations by TO Girder Static Testing In order to evaluate the performance of the girder built by the TO method, a 20 m TO girder specimen and a two-main TO girder plate bridge specimen with a plate section are tested. The cross section dimensions of these two specimens are shown in Figure 6a,b.
(a) Girder specimen
(b) Bridge specimen
Figure 6. Cross section dimensions. (a) Girder specimen; (b) Bridge specimen. (Unit: mm).
Figure 6. Cross section dimensions. (a) Girder specimen; (b) Bridge specimen. (Unit: mm).
3.1. Expeimental Details (a) Girder specimen 3.1. Expeimental Details
(b) Bridge specimen
The TO girder and bridge specimens with a central location for a confining concrete section were Figure 6. Cross section dimensions. (a) Girder (b) Bridge specimen. (Unit: mm).of statically toand evaluate their load carrying capacity. As shown in Figure the width the girder The TO tested girder bridge specimens with a specimen; central location for a6,confining concrete section the plate were 1.0 and 1.5 m,load respectively. HSB-600 reinforcements and 506,MPa 28 dayof the wereand statically tested to evaluate their carrying capacity. As shown in Figure the width 3.1. Expeimental Details compressive strength concrete were to design the specimens. However, due toand the testing girder and the plate were 1.0 and 1.5 used m, respectively. HSB-600 reinforcements 50 MPasite 28 day The TO girder andlimitations, bridge specimens with×a 200 central location for a confining concrete section 28 were and casting condition the 100 mm cylindrical concrete specimen’s day compressive strength concrete were used to design the specimens. However, due to the testing site and statically tested to evaluate loadand carrying capacity. shown in Figure 6, the of the concrete girder compressive strength data attheir 30 MPa 27 MPa were As only available to cast thewidth confining casting and condition limitations, the 100 × 200 mm cylindrical concrete specimen’s 28 day28compressive the plate were 1.0 and 1.5 m, respectively. HSB-600 reinforcements and 50 MPa day is and the plate sections, respectively. As shown in Figure 6b, the top flange of the I-steel member strength data at 30 MPa and 27 MPa were only available to cast the confining concrete and the plate compressive strength concrete were used to design the specimens. However, due to the testing site embedded in the confining concrete section and approximately 30 mm of the confining concrete and casting condition limitations, the 100 × 200 mm cylindrical concrete specimen’s 28 day sections, respectively. As shown in Figure 6b, the top flange of the I-steel member is embedded section is embedded in the plate section. Also, the two-main girder/plate were connected by ain the compressive strength data atapproximately 30 MPa and 27 MPa wereofonly available to cast the confining concrete confining concrete section and 30specimens mm the confining section is embedded stiffener connection using bolt attachments. The were tested inconcrete a simply supported setup and the plate sections, respectively. As shown in Figure 6b, the top flange of the I-steel member is in thewith plate section. Also, theFor two-main girder/plate wereUTM connected by a kN stiffener connection three-point loading. the application of the load, with 10,000 capacity was used.using embedded in the confining concrete section and approximately 30 mm of the confining concrete In order to firmly setspecimens the specimen on the supports, the loadsupported was appliedsetup up to with 300 kN with a 100 kN bolt attachments. The were tested in a simply three-point loading. section is embedded in the plate section. Also, the two-main girder/plate were connected by a force loading increment beforeUTM a displacement controlled loadingwas was used. appliedInatorder a rate of 0.1 mm/s. For the application of the load, with 10,000 kN capacity to firmly stiffener connection using bolt attachments. The specimens were tested in a simply supported setup set the The schematic drawings of the specimen setupofare in Figure A center span deflection was specimen onthree-point the supports, the load applied up toload, 300UTM kN with a10,000 100 kN loading increment with loading. For thewas application theshown with7. kN force capacity was used. measured using a 250 mm LVDT. The top and bottom flange surface strains and mid-height web order to firmly controlled set the specimen on the supports, theat load was of applied up to 300 kNschematic with a 100 kN before aIndisplacement loading was applied a rate 0.1 mm/s. The drawings strains were measured using strain gauges. Embedded strain was gauges were also placed in the force loading increment before a displacement controlled loading applied at a rate of 0.1 mm/s. of the specimen setup are shown in Figure 7. A center span deflection was measured using a 250 mm confining concrete section and onspecimen reinforcement surfaces plate7.section. The schematic drawings of the setup are shownofinthe Figure A center span deflection was
LVDT. The top and bottom flange surface strains and mid-height web strains were measured using measured using a 250 mm LVDT. The top and bottom flange surface strains and mid-height web strain gauges. Embedded strain gauges were also placed in the confining concrete section and on strains were measured using strain gauges. Embedded strain gauges were also placed in the reinforcement surfaces the plate section. confining concreteof section and on reinforcement surfaces of the plate section.
(a) Side view Figure 7. Cont.
(a) Side view Figure 7. Cont.
Figure 7. Cont.
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(b) Cross-sectional view of girder specimen
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(c) Cross-sectional view of bridge specimen
Figure 7. Schematic drawings of the bending test setup, (a) Side view; (b) Cross-sectional view of
Figure girder 7. Schematic drawings of the bending test setup, (a) Side view; (b) Cross-sectional view of specimen and (c) Cross-sectional view of bridge specimen. girder specimen and (c) Cross-sectional view of bridge specimen. 3.2. Results and Discussion
3.2. Results and Discussion
3.2.1. Load-Deflection Relationship
3.2.1. Load-Deflection Relationship The load-deflection relationships measured at the center of the span for the girder and bridge specimens are shown in Figure 8a,b respectively. The girder and bridge specimens initially cracked
The relationships measured the center of the span fordeflection the girder and bridge at load-deflection loads of 886 kN and 1248 kN, respectively, withatthe corresponding center span of 111.1 specimens in Figure 8a,b The girder bridge specimens initially cracked at and are 145.5shown mm, respectively. Theserespectively. initial cracking loads wereand approximately 1.3 to 1.6 times greater cracking of 665 kN and 750 the kN for the girder and bridge respectively. loads ofthan 886the kNdesign and 1248 kN,load respectively, with corresponding centerspecimens, span deflection of 111.1 and After initial cracking of theinitial specimens, stiffness reduction occurred in both specimens maximum 145.5 mm, respectively. These cracking loads were approximately 1.3 to 1.6 at times greater than loads of 1276.8 kN and 2128.7 kN with the corresponding center deflections of 170.4 and 220.4 mm the design cracking load of 665 kN and 750 kN for the girder and bridge specimens, respectively. After for the girder and bridge specimens as shown in Figure 8a,b respectively. In Figure 8b the load cycles initial cracking of the specimens, stiffness reduction occurred in both specimens at maximum loads show were conducted as follows. The load was applied until initial cracks formed, then the specimen of 1276.8 kN and 2128.7 kN the corresponding center 170.4 and 220.4 was unloaded. Then, thewith specimen was reloaded until the deflections load reached of approximately twicemm the for the girder and bridge as shown in Figure 8a,b respectively. Figure was 8b the load cycles design load, specimens at which point, the specimen was unloaded. Finally, theIn specimen reloaded until show significant as macro-damage occurred, which can be considered as an ultimate load. This load was were conducted follows. The load was applied until initial cracks formed, then thecycle specimen was used to clearly understand the specimen failure behavior at initial cracking stage, service stage, and unloaded. Then, the specimen was reloaded until the load reached approximately twice the design ultimate failure stage. load, at which point, the specimen was unloaded. Finally, the specimen was reloaded until significant Since the load-deflection data obtained from both the girder and bridge specimens are similar, macro-damage occurred, which can be considered as an ultimate load. This load cycle was used to it is safe to conclude that the stress distributions in the bridge specimens are even and symmetrical. clearly understand specimen failure behavior at initial service stage, and ultimate In both girderthe and bridge specimens, both buckling andcracking interfacialstage, cracking failures occurred. failure stage. However, only in a bridge specimen was there bearing failure (e.g., concrete spalling above the support), as shown in Figure 9. Because of from the buckling andgirder interfacial failures, the ultimate Since the load-deflection data obtained both the andcracking bridge specimens are similar, it is loads could not be measured. However, since the maximum applied load was approximately 1.9 to In both safe to conclude that the stress distributions in the bridge specimens are even and symmetrical. 2.8 times greater than the design load, it is safe to conclude that the load carrying capacity of the TO girder and bridge specimens, both buckling and interfacial cracking failures occurred. However, only girder and TO girder bridge is sufficient for practical applications. in a bridge specimen was there bearing failure (e.g., concrete spalling above the support), as shown in Figure 9. Because of the buckling and interfacial cracking failures, the ultimate loads could not be measured. However, since the maximum applied load was approximately 1.9 to 2.8 times greater than the design load, it is safe to conclude that the load carrying capacity of the TO girder and TO girder bridge is sufficient for practical applications.
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(a) Girder specimen
(a) Girder specimen
(b) Bridge specimen Figure 8. Load-deflection relationships measured the center of the span, (a) Girder specimen and (b) Bridge at specimen Figure 8. Load-deflection relationships measured at the center of the span, (a) Girder specimen and (b) Bridge specimen. 8. Load-deflection relationships measured at the center of the span, (a) Girder specimen and (b) BridgeFigure specimen. (b) Bridge specimen.
(a) Girder/plate specimen Figure 9. Cont.
Figure 9. Cont. (a) Girder/plate specimen Figure 9. Cont.
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(b) Bridge specimen Figure 9. Failure pattern of girder and bridge test specimens, (a) Girder/plate specimen and
Figure 9. (b)Failure pattern of girder and bridge test specimens, (a) Girder/plate specimen and Bridge specimen. (b) Bridge specimen. 3.2.2. Load-Strain Relationship
(b) Bridge specimen
3.2.2. Load-Strain Relationship The load-strain relations at the center span of the girder and bridge specimens are shown in Figure 9. Failure pattern of girder and bridge test specimens, (a) Girder/plate specimen and Figure 10a,b respectively. For the girder specimen, the initial cracking at the confining concrete section (b) Bridge specimen. The load-strain relationsatata load the center span the the girder and load-strain bridge specimens occurred approximately of 900 kN, afterof which non-linear relationship are was shown in observed. At this cracking the confining concrete section cracking cracked, and propagated as Figure 10a,b respectively. For theload, girder specimen, the initial atthe thecracks confining concrete section 3.2.2. the Load-Strain Relationship strain of the steel also Figure 9a shows a load-strain photo of local buckling occurred approximately atgirder a load ofcorrespondingly 900 kN, afterincreased. which the non-linear relationship was failure, which occurred slightly the confining concrete section bridge cracked, indicating are that the relations theafter center span of the girder in observed.The At load-strain this cracking load, at the confining concrete sectionand cracked, specimens and the cracksshown propagated interfacial cracking caused this local buckling. Additionally, the interface failure of confining concrete Figure 10a,b respectively. For the girder specimen, the initial cracking at the confining concrete section as the strain steel girder also increased. Figure a photo and of the the I-steel girder is likely duecorrespondingly to the compressive strength of concrete used9a to shows manufacture the of local occurred approximately at a load of 900 kN, after which the non-linear load-strain relationship was specimens, which was lower than the required design compressive strength. However, the load-strain buckling failure, which occurred slightly after the confining concrete section cracked, indicating that observed. At this obtained cracking from load,the thetests confining concrete section cracked, the andbottom the cracks propagated as relationships that the tensile strain of flange section the interfacial cracking caused this localshowed buckling. Additionally, the interface failure of confining the strain of the steel girder also correspondingly increased. Figure 9a shows a photo of local buckling exceeded 2500 με and the top flange had approximately 50% of the strain measured at the bottom flange. concrete and the I-steel girderslightly is likely duethe to the compressive strength oftoconcrete used to manufacture failure, occurred after concrete section indicating that the Thewhich relatively small compressive strain in confining the steel member is likely due cracked, the confining concrete the specimens, which was lower than theto required strength. However, interfacial cracking caused thissection. local buckling. the compressive interface of capacity confining concrete the section cast at the top flange Due theAdditionally, increaseddesign compressive stress failure resistance of the section above the neutral axis, afrom smaller compressive force needed be resisted by the steel load-strain relationships obtained the tests showed that the tensile strain thesection bottomthe flange and the I-steel girder is likely due to the compressive strength oftoconcrete used toof manufacture above the neutral axis, thereby reducing the size ofapproximately thecompressive top steel flange section for the girder. specimens, which was lower thantop the flange required design strength. However, the load-strainat the section exceeded 2500 µε and the had 50% ofneeded the strain measured relationships obtained from the tests showed that strain the tensile strain the bottom bottom flange. The relatively small compressive in the steelof member is flange likely section due to the exceeded 2500 με and the top flange had approximately 50% of the strain measured at the bottom flange. confining concrete section cast at the top flange section. Due to the increased compressive stress The relatively small compressive strain in the steel member is likely due to the confining concrete resistance capacity of the section above the neutral axis, a smaller compressive force needed to be section cast at the top flange section. Due to the increased compressive stress resistance capacity of the resisted by the steel section above the neutral axis, thereby reducing the size of the top steel flange section above the neutral axis, a smaller compressive force needed to be resisted by the steel section section needed for theaxis, girder. above the neutral thereby reducing the size of the top steel flange section needed for the girder.
(a) Girder specimen Figure 10. Cont.
(a) Girder specimen Figure 10. Cont.
Figure 10. Cont.
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(b) Bridge specimen
(b) Bridge specimen Figure 10. Load-strain relations at the center span of the girder and bridge specimens, (a) Girder Figure 10. Load-strain relations at the center span of the girder and bridge specimens, (a) Girder Figure 10. and Load-strain relations at the center span of the girder and bridge specimens, (a) Girder specimen (b) Bridge specimen. specimen and (b) Bridge specimen. specimen and (b) Bridge specimen.
In the specimen, initial ataaload loadofofapproximately approximately 1300 which Inbridge the bridge specimen, initialcracking crackingoccurred occurred at 1300 kN, kN, afterafter which In the bridge specimen, initial cracking at a load offrom approximately 1300 kN, section, aftersection, which a non-linear behavior was observed. Dueto tooccurred the confining confining effect thethe confining concrete a non-linear behavior was observed. Due the effect from confining concrete a very strain of 580 με wasobserved observed atthe theconfining web and sections of the I-steel member aa non-linear behavior was Due toat effect from the confining concrete section, very low low strain of 580 μεobserved. was the web andtop topflange flange sections of the I-steel member with high strain values. awith veryhigh low strain strain values. of 580 µε was observed at the web and top flange sections of the I-steel member with Overall specimen showedductile ductile behavior behavior of section. As shown in high Overall strain values. the the specimen showed of the thebottom bottomflange flange section. As shown in Figure 11, both the top and bottom flange sections showed compressive stresses in the bridge Overall the specimen showed ductile behavior of the bottom flange section. As shown in Figure 11, both the top and bottom flange sections showed compressive stresses in the bridge specimen. The load-strain relationship measured from the plate section of the bridge specimen is Figure 11, both top and bottom flangemeasured sections showed compressive stresses in the bridge specimen. specimen. The the load-strain relationship from the plate section of the bridge specimen is shown in Figure 11. Both the top and bottom surfaces of the plate section showed compressive The load-strain relationship measured frombottom the platesurfaces section of the bridge specimen is showncompressive in Figure 11. shown in Figure 11. Both the top and of the plate section showed stresses, indicating that large compressive stresses occurred in the top section of the specimen. The Both the andindicate bottom surfaces ofgirder the plate section showed compressive stresses,behavior that large stresses, indicating thatthat large stresses occurred ina the section ofindicating the specimen. The test top results thecompressive TO bridge specimen shows goodtop composite between compressive stresses occurred in the top section of the specimen. The test results indicate that the test results indicate that the TO girder bridge specimen shows a good composite behavior between the plate and the girder, having a low effective height with strong compressive stress resisting TO girder bridge shows a good behavior between the andorthe girder, having a low capacity of the the specimen. This indicates the overall steel usagestrong forplate the compressive twothreemain girder the plate andspecimen girder, having a composite low that effective height with stress resisting plateheight canstrong be significantly reduced by using the TOusage girders, effective with compressive stress resisting capacity of the specimen. This indicates that capacity ofbridges the specimen. This indicates that the overall steel for proving the two-itsoradvantages threemainforgirder construction reductions in costs time. main the overall steelcan usage the two- and orreduced threegirder the plate bridges canproving be significantly reduced for by plate bridges be for significantly by using TO girders, its advantages using the TO girders, proving its advantages for construction reductions in costs and time. construction reductions in costs and time.
Figure 11. Load-strain relationship measured from the plate section of the bridge specimen.
Figure 11. Load-strain relationship measured from the plate section of the bridge specimen. Figure 11. Load-strain relationship measured from the plate section of the bridge specimen.
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4. Conclusions In this study, a modified precast construction method called Turn Over (TO) was proposed for construction efficiency improvement for turning over an I-section steel girder. A full-scale 20 m single girder specimen and a full-scale 20 m two-girder plate bridge specimen were used to investigate the optimum cross section design and the confining concrete section location, and to evaluate the structural performance. Based on the study results, the following conclusions were drawn.
•
•
•
•
•
The ordinary I-section steel girder and proposed TO girder with a confining concrete section and a height of 3250 mm were compared. With respect to saving steel in the I-beam, the required steel area for the TO girder was reduced by over 13.8% than that of ordinary steel girders. Also, due to the simplicity of precast inverting construction using the TO method, the savings on manufacturing costs are significant. Therefore, there are significant economic benefits in using a TO girder over an ordinary steel girder. In order to investigate the optimal cross section for a TO girder, parametric studies of the confining concrete section location, cross-section weight, and stress ratios were carried out. The optimal location of the confining concrete section was selected as the flange of the I-beam. It was embedded in the section for its benefits in performance enhancements and construction simplicity. The sensitivity of the parameters with respect to steel weight and applied stresses are in the order of height, bottom flange thickness, and top flange thickness. A full-scale 20 m TO girder and bridge system were tested. From the static test results, initial crack of the TO girder and bridge system behaved elastically and occurred after reaching the design loads. Since the maximum applied load was approximately 1.9 to 2.8 times greater than the design load, the steel I-beam and concrete plate girder system constructed using the TO method can be assumed to have sufficient safety and load carrying capacity. From the TO manufacturing, the steel I-beam showed well distributed deflection from the application of self-weight of the confining concrete section. Since the failure load of the TO girder system increased by implementing the confining concrete section, the efficient composite behavior between the I-section steel girder, confining concrete, and concrete plate can be assumed. Analysis of the study results showed that the proposed TO method can be applied to practical designs as an improved precast construction method. However, additional experiments with other parametric variations of the TO girder need to be carried out. (i.e., buckling, interface bonding, etc.)
Acknowledgments: This study was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2016R1A2B3009444) and the Nuclear Safety Research Program through the Korea Foundation of Nuclear Safety (KOFONS), granted financial resource from the Nuclear Safety and Security Commission (NSSC), Republic of Korea (No. 1403010). Author Contributions: Gi-Ha Eom is a person who performed most of test and analysis works; a main writer of the paper. Jang-Ho Jay Kim is a PI of the research project, who provided the main idea of the study. Tae-Hee Lee is a person who assisted the research and writing the paper. Sung Jae Kim is a consultant to the research work and writing of the paper. Conflicts of Interest: The authors declare no conflict of interest.
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Park, S.Y.; Kim, B.S. State-of-the-art of ultra-high performance concrete bridges. Mag. Korea Concr. Inst. 2016, 28, 31–35. Kim, Y.J.; Kim, H.S. Construction technology of super long span bridge. Rev. Arch. Build. Sci. 2016, 60, 43–47. You, Y.J.; Kim, J.H.J.; Park, Y.H.; Choi, J.H. Fatigue performance of bridge deck reinforced with cost-to-performance optimized GFRP rebar with 900 MPa guaranteed tensile strength. J. Adv. Concr. Technol. 2015, 13, 252–262. [CrossRef] Jung, K.H.; Yi, J.W.; Lee, S.H.; Ha, J.H.; Kim, J.H.J. Fatigue capacity of a new connection system for a prestressed concrete hybrid truss web girder. Mag. Concr. Res. 2012, 64, 665–672. [CrossRef]
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