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ARTICLE IN PRESS H K Ryu et al Engineering Structures 3 2 2 Fabrication of the prototype The fabrication of the composite girder prototype proceeds as follows Firstly the precast decks manufactured in the factory are transported to the prototype bridge plant Once the girders are positioned the decks are lifted and installed on the girders Atthattime inthecaseoftheprototype theinstallation of the decks was performed on the girders equipped in advance with the shear connectors In such case the assembling may be delicate because of the lack of space due to the presence of the shear connectors and loop joints As a measure to solve this problem the shear connectors can be welded to the girder at the shear pocket locations using a stud welder after installation of the decks on the girder and with the shear connectors not welded to the girders However such methods require suffi cient spacefortheshearpockets andtheprocessmayalsobedelicate when space cannot be secured Especially the enlargement of the shear pockets may generate adverse results in the deck because of the diffi culty to arrange the reinforcing bars which makes it diffi cult to enlarge indefi nitely the space of the shear pockets As another measure shear connectors in the form of screw bolt can be considered On the other hand once the installation of the decks is completed the transverse reinforcement shall be arranged in the overlapping sections of transverse loop joints Fig 2 a and b As illustrated in Fig 2 b six main reinforcements have been arranged at the top and bottom of the overlapping sections of transverse loop joints for the prototype After the arrangement of bars concrete is cast in the shear pockets and transverse joints and curing is performed As shown in Fig 2 a the edge of the shear pockets has been rounded to minimize the effects of stress concentration The fabrication of the two girder continuous composite bridge is completed with the end of curing Fig 2 c 2 3 Loading and measurement locations For all the tests loading was applied at both mid spans Fig 3 a considering the contact surface of the wheel load Fig 3 b A location of loading with respect to the nearest joints was about 600 mm The fi rst loading was applied up to 360 kN and then fatigue loading test proceeded Lastly static loading was applied up to 900 kN The fatigue load of 1 5 Hz cycles was applied using a dynamic actuator with capacity of 500 kN Minimum and maximum load of the test were 3 9 kN and 360 kN respectively The defl ection of the test bridge has been measured by means of LVDT disposed at both loaded mid spans as illustrated in Fig 3 c In the sectional direction defl ections were measured both in the bottom of the girder and in the decks After the development of cracks has been verifi ed using Omega gauges the crack width was measured at the bottom of the decks in the loaded sections and at the top of the decks in the internal support sections Considering that the distribution of relative slip between the girder and the deck occurs anti symmetrically with respect to the center of the internal support measurements were performed only for the span of one girder a Details of transverse joints and shear pocket b Overlap of loops and arrangement of main reinforcement c Completed continuous composite bridge Fig 2 Fabricationofcontinuouscompositebridgewithloopjoint prefabricated slabs at locations SL1 SL6 indicated in Fig 3 c 6 The strain of the girders was measured by sticking strain gauges at mid span and at the web plate and top bottom fl anges of the internal support girder Fig 3 c Furthermore several strain gauges were installed on the top and bottom reinforcements in slabs 2 4 Material properties Table 1 shows mix proportions of concrete Material tests were performed to measure the strength of concrete expansive Please cite this article as Hyung Keun Ryu et al Crack control of a continuous composite two girder bridge with prefabricated slabs under static and fatigue loads Engineering Structures 2006 doi 10 1016 j engstruct 2006 06 021 ARTICLE IN PRESS 4H K Ryu et al Engineering Structures a Loading plan b Simulation of wheel loading of deck c Locations of measurements Fig 3 Loading and measurement locations Table 1 Mix proportions of concrete Strength kgf cm2 Aggregate max size mm Slump mm W CS aAir Proportion by unit weight kgf cm3 WaterCementFine aggregateCoarse aggregate 400251531 741 54 5 1 5165520685973 concrete and non shrinkage mortar listed in Table 2 The precast deck was manufactured in advance using ordinary concrete and exhibited strength at 14 days as shown in Table 2 Since tests started one month after the manufacture of the deck this strength was undoubtedly larger than measured Expansive concrete was cast in the transverse joints between decks so as to minimize the effects due to initial drying shrinkage Non shrinkage mortar was cast as fi lling material in the shear pockets to combine the shear connectors and the deck The strengths of expansive concrete and non shrinkage mortar are listed in Table 2 for the strength measured at the start of the tests that is under loading The plate girder applied for the specimen Please cite this article as Hyung Keun Ryu et al Crack control of a continuous composite two girder bridge with prefabricated slabs under static and fatigue loads Engineering Structures 2006 doi 10 1016 j engstruct 2006 06 021 ARTICLE IN PRESS H K Ryu et al Engineering Structures 5 Table 2 Compressive strength of concrete and mortar MPa StrengthNote Precast concrete deck3614 days Transverse joint expansive concrete 56Loading time at 7 days Filling material of shear pocket non shrinkage mortar 57Loading time at 7 days Table 3 Material properties of steel MPa Yield strengthTensile strength in spec Flange joint surfaces is verifi ed to be larger than the strain developed in the surface of the deck This reveals that cracks concentrate at the cast interface in the joint section The initial crack spacing of the loop joint precast decks at the internal supports is assumed as the distance from the cast interface at the transverse joint to the cast interface at the transverse joint in the opposite direction Since the initial crack spacing was wider than in general RC slabs without joints it is estimated that the crack width will be scaled up to an extent larger than generally proposed in the provisions 7 The experimental curve plotted in Fig 13 could be drawn from the relationship between the crack width O 1 or O 2 and reinforcement strain measured in the joint cast interface Also the curves shown in Fig 13 have been drawn using the formulae proposed in foreign specifi cations 1 4 in order to control the experimental results and crack widths As expected the crack width O 1 or O 2 experimentally observed appears to have been scaled up The strain on the reinforcement of the loop overlapping joints has been measured by sticking reinforcement gauges oriented longitudinally Fig 14 J7 8 Fig 14 compares the values of the strain of the loop joint reinforcement J7 8 with the ones of the reinforcement located in the deck joint interface L81 Comparison revealed that the reinforcement strain L81 near the joint interface is signifi cantly larger than that J7 8 in the overlapping section This is due to the doubling of the steel ratio in the loop joint section where reinforcement overlaps while concrete crack concentrates in the joint cast interface without overlapping of reinforcement Accordingly the section to which particular attention shall be paid for the control of crack width should be the joint cast interface Through the experiments moment curvature relationship of the composite bridge was evaluated as shown in Fig 15 In this fi gure moment was calculated assuming uncracked section and curvature was recorded using girder strains measured in the test Moment curvature relationship of the composite bridge can be evaluated according to Eurocode 4 2 4 and compared with the test results In spite of cracking of the bottom slabs at loading points the stiffness of the maximum positive moment section was nearly that of uncracked section Also the stiffness of the maximum negative moment section was also nearly that of uncracked section It is considered that initial enlargement of crack width at transverse joints O 1 and O 2 slightly infl uenced the stiffness of the composite section Up to the initial static load 360 kN before design cracking load estimated by Eurocode 4 2 insignifi cant cracking was observed except for enlargement of transverse joints of slabs on the interior support Please cite this article as Hyung Keun Ryu et al Crack control of a continuous composite two girder bridge with prefabricated slabs under static and fatigue loads Engineering Structures 2006 doi 10 1016 j engstruct 2006 06 021 Please cite this article as Hyung Keun Ryu et al Crack control of a continuous composite two girder bridge with prefabricated slabs under static and fatigue H K Ryu et al Engineering Structures Fig 14 Strain developed in the reinforcements of loop overlapping and joint interface Fig 15 Moment curvature curve ARTICLE IN PRESS H K Ryu et al Engineering Structures 11 a Repeated cycles crack width relationship O 1 O 2 b Repeated cycles crack width relationship O 3 O 4 c Repeated cycles crack width relationship O 5 O 6 Fig 17 Repeated cycles crack width relationships remained below 0 2 mm until 670 kN Fig 22 a This load is 2 7 times the design rear wheel load considering impact 9 Thus it is considered that in negative moment regions control of crack widths within 0 2 mm can be done for composite bridges with prefabricated slabs under service loads O 1 and O 3 did not exceed 0 3 mm under 900 kN while O 4 exhibited a Repeated loading cycle relative slip curves b Longitudinal distribution of relative slip Fig 18 Relative slip between deck and girder sudden increase of crack width at the proximity of 700 kN to exceed 0 3 mm near 900 kN On the other hand the presence of residual crack widths made O 6 to exceed 0 3 mm at 300 kN to reach an extremely large crack width of 0 8 mm at 900 kN Fig 23 presents the curves expressing the relationship between the crack width O 1 or O 2 measured in the deck joint cast interface at internal support and the reinforcement stresscalculatedfromthestrainofthereinforcement Comparison is also done with the crack widths proposed in ACI code Gergely Lutz equation CEB FIP code and Eurocode to control crack width 1 4 It is seen that crack width occurring in the joint cast interface is initially larger than the ones calculated according to foreign codes With increasing steel stress crack widths of the test girder O 1 and O 2 became less than that evaluated by Eurocode 2 It is considered that propagation of crack width was mitigated because some cracks were developed in different parts of slabs near the interior support Accordingly it is considered that the appropriate crack width control initially at transverse joints is more important Load relative slip curves were also measured experimen tally through the static loading test performed up to 900 kN after the repeated loading test Fig 24 The increase of rela tive slip provokes the increase of defl ection and the occurrence Please cite this article as Hyung Keun Ryu et al Crack control of a continuous composite two girder bridge with prefabricated slabs under static and fatigue loads Engineering Structures 2006 doi 10 1016 j engstruct 2006 06 021 ARTICLE IN PRESS 12H K Ryu et al Engineering Structures a Displacement b Crack width c Relative slip Fig 19 The ratio of increase displacement crack width and slip after fatigue test of cracks in the concrete deck at the internal support may also affect the increase of defl ection Also the difference of long