EXPERIMENTAL RESEARCH ON SPLICING JOINT OF WIDENING HOLLOW SLAB BRIDGE

10th International Conference on Short and Medium Span Bridges Quebec City, Quebec, Canada, July 31 – August 3, 2018 EXPERIMENTAL RESEARCH ON SPLICING JOINT OF WIDENING HOLLOW SLAB BRIDGE Wang, Qu1, Wu, Qing-xiong2,4 and Chen, Kang-ming3 College of Civil Engineering, Fuzhou University, Fuzhou, P.R China College of Civil Engineering, Fuzhou University, Fuzhou, P.R China College of Civil Engineering, Fuzhou University, Fuzhou, P.R China wuqingx@fzu.edu.cn Abstract: In order to save construction cost and shorten the construction period, and keep the capacity of road in process of construction, it is an effective way to widen the existing bridges The holistic resistant behavior of widening bridge under various factors has been researched deeply in China recently, although the splicing joint has already been widely used, there was also lake of systematic theoretical and experimental research This paper summarizes the principles of widening bridge reconstruction, and describes the connection structure and method of widening bridge, such as cast-in-situ concrete rigid wet joint and cast-in-situ concrete hinge joint Based on widening hollow slab bridges with splicing joint, a fullscale model of widening hollow slab bridge made up of two new plates and two old plates with the span of 8m is designed and made The failure modes of the splicing joint under vehicle loads are discussed, such as the failure type, failure position and cracking load The results show that the failure type of splicing joint is longitudinal tensile failure, its cracking load is larger than main hollow slab It proved that the splicing structure is reasonable and effective Before cracking of the widening bridge splicing joint, deflection of hollow slab girder and splicing joint changes synchronous, the new bridge and the old bridge worked together approximately; The transverse distribution of deflections change up to a point, and the ability of load lateral transmission decrease after cracking of splicing joint Keywords：Widening bridge, Hollow slab, Splicing joint, Failure mode, Experiment INTRODUCTION By the end of 2016, China has completed 60.12 million km of second-class highway or above, with a total of 13.1 million km of expressways and 71.49 million short and medium span bridges, ranking first in the world However, it is still not enough to meet the increasing capacity demand and it costs too much if new roads are built Therefore, it is an effective way to expand the existing roads and improve their capacity and service level This involves the expansion of a large number of existing Bridges, which face the problem of splicing joint between new and old bridge It is proved that reasonable and effective splicing techniques and measures are important to expand the existing bridge (Xu 2011) At present, most of old bridges are built by the old code, while the expansion is followed the new code In the progress of the research in mechanical behavior of widening bridge, Meng and Teng (2004) considered that the load standard of bridge should be high, it should be noted that the old bridge can meet the new specification design load requirements at the same time Zhang et al.(2006), Liang et al (2007), Xie(2009) calculated and analyzed stress and deformation of old bridge It is considered that the 19-1 carrying capacity of old bridge can be improved after the expansion Wu et al (2013) calculated stress of old bridge, and found that the combination of pre-stressed reinforced concrete hollow slab and ordinary reinforced concrete hollow slab can uninstall partial internal force and structural deformation of old bridge However, the pre-stressed concrete hollow slab will share the larger external load, due to its larger rigidity It should be focused during the design In the progress of the research in mechanical behavior of splicing joint, Lian et al (2007) suggested that the transverse partition should meet the rigidity requirements and the splicing joint can cause connection damage which is not strong enough What is more, the difference of the stiffness between new and old girder may cause the deflection is different Wang et al (2013) analyzed the influence of the stiffness of load transverse distribution for widening hollow slab bridge and through that the increase of splicing joint stiffness can be to enhance the performance of whole bridge, reduce bearing capacity of bridge In addition, it is suggested that the suitable thickness of splicing joint should be applied to the connection design According to an 1:4 scaled model box girder bridges with two spans test, Zong et al (2009) analyzed the static and dynamic behavior of two different connection style: rigid connection and hinged connection, and though rigid connection is better than hinged connection for box girder bridges Zhao and Zhang (2013) calculated a simplified T beam bridge with different splicing joint, and though that bearing capacity of old bridge can be improved by the higher stiffness of splicing joint In the progress of the research in structural influencing factors of widening hollow slab bridge, He et al (2008) and Ferretti et al (2013) through larger girder stiffness of new bridge can reduce the stress of the old bridge by calculation analysis; Kwan and Ng (2006) through additional internal force of girder was caused by uneven settlement, which can affect local performance of spline joint; Wen and Ye (2007), Fang et al (2013) and Chen et al (2016) through the stress redistribution was occurred both new and old beams by the addition of the shrinkage and creep In summary, some researchers have obtained some results on the overall mechanical behavior of bridge and various factors of splicing joint However, the study on local mechanical property and failure mode of splicing joint is less, and lack of reliable and efficient connection mode What is more, guideline of key technologies has not yet been formed This paper summarizes the principles of widening bridge reconstruction, and describes the connection structure and method of widening bridge Based on widening hollow slab bridges with splicing joint, a full-scale model of widening hollow slab bridge made up of two new plates and two old plates with the span of 8m is designed and made The failure modes of the splicing joint under vehicle loads are discussed, such as the failure type, failure position and cracking load SPLICING JOINT STRUCTURE OF WIDENING BRIDGE Hollow slab bridge is widely adopted and has already become the main bridge type in expressway in China At present, cast-in-situ concrete rigid wet joint and cast-in-situ concrete hinge wet joint are widely used in the joint in the widening bridge, as shown in Figure1 Rigid joint is a kind of connection that can transmit moment and shear force, also known as the strong connection Hinge joint is a kind of connection that mainly transmit shear force, also known as weak connection Due to the large stiffness of rigid joint, the foundation settlement of new bridge has an unfavorable influence on the old bridge Under the condition of soft soil foundation, the difference of settlement deformation between old and new Bridges is obvious, which will bring great uncertainty to safety of widening bridge (Deng et al 2009; Zhang 2012) In addition, the diameter of bar in two kinds of joints is same, but double layer mesh is used in the structure of rigid joint Rigid joint with new cast-in-situ concrete diaphragm is mainly adopts in widening box girder bridge, as shown in Figure3 Hinge joint also used in widening box girder bridge Cast-in-situ concrete is used in flange of bridge and saw kerf is used in bottom edge, as shown in Figure4 The box girder splicing structure recommended in the widening bridges opinion instruction by U S is similar to hinge joint shown in Figure4, the main difference is that the bottom edge is not cut and rigidity is larger (Wu et al 2009; Hua et al 2006) 19-2 Figure 1: Rigid joint in widening hollow slab bridge Figure 2: Hinge joint in widening hollow slab bridge Figure 3: Rigid joint in widening box girder bridge Figure4: Hinge joint in widening box girder bridge The separation between new widening bridge and old bridge is also common approach According to the design requirements of lateral broaden by structure separation, longitudinal expansion device can meet the transverse and vertical deformation requirements of the old and new bridge, ensure the smooth surface of bridge, and able to withstand the repeated rolling of vehicle without damage Yinchuan Yellow River Bridge (12×30 m + 60 m + 5×90 m + 60 m) reserved 20 mm wide gap along the longitudinal in the superstructure between the old bridge and new widening bridge, and longitudinal extension devices were used There are three kinds of expansion devices: elastic-plastic body non-shrinkage expansion device, EMR resin elastic concrete expansion device and JFC damping anti-slip expansion device, as shown in Figure5 The separation scheme is simple, but also disadvantage is clear The separation between new widening bridge and old bridge still exist mutual dynamic function cannot control the deformation difference between old and new structure effectively It causes the crack of deck pavement and the safety accident of high speed driving (Caltrans 1991; Wu et al 2015) Rigid joint with new cast-in-situ concrete diaphragm is mainly adopts in widening T-beam bridge, as shown in Figure In a word, hollow slab bridge, T-beam bridge and box girder bridge have been widened and rich engineering experience has been obtained between the new widening bridge and old bridge But different expressway adopts different widening structure form The unified structure form, construction methods and measures of widening structure form is necessary for future engineering 19-3 a) Elastic-plastic body non-shrinkage b) EMR resin elastic concrete c) JFC damping anti-slip Figure 5: Expansion Device in Yinchuan Yellow River Bridge Figure 6: Rigid joint of widening T-beam bridge FULL SCALE MODEL TEST 3.1 Design of experimental model In this paper, a full-scale model of widening hollow slab bridge with the span of m is designed and made The test model was made by new hollow slab, old hollow slab and splicing joint The hollow slab was equal section The width of old hollow slab is 1.24 m and 1.245 m, the plate is 0.4 m high The width of new hollow slab is 1.24 m and 1.31 m wide, the plate is 0.45 m high The old hollow slab has been reinforced by concrete pavement with a thickness of 0.22 m, and the pavement layer of new widening hollow slab is 0.12 m thickness The cross section of widening hollow slab is shown in Figure Figure 7: Cross section of widening hollow slab (Unit: m) As shown in Figure 8, splicing joint of test model and actual bridge was completely identical The cast-insitu concrete splicing joint was 0.30 m × 0.37 m between new widening bridge and old bridge (including the pavement layer thickness) Firstly, part of old bridge and concrete of pavement layer were cut Secondly, horizontal bar of old bridge was kept and welded to pavement bar of new widening bridge; at the same time, bar was inserted into the outside edge of old bridge in the place from the bottom and welded to embedded bar of new widening bridge; then three bars in the bottom and two bars in the top were arranged along longitudinal direction and closed stirrup was layout Thirdly, concrete construction of splicing joint, integration pavement layer and reserved pavement of new widening bridge were done at the same time supports was used for each side of one main beam The completed experiment test model is shown in Figure 19-4 a) Cross section b：Structural drawing of bar Figure 8: Structural Drawing of Splicing Joint (Units: m) Figure 9: Scene of Experiment Test Model 3.2 Test condition of experimental model According to provision in General Specification for Highway Bridge and Culvert Design (JTG D60-2015): vehicle load is used for the calculation of local loading, culvert, abutment and lateral earth pressure of retaining wall Because the study object is the splicing joint, the vehicle load is used to calculate According to finite element analysis, rear axle load was used in the test, as shown in Figure10 The wheel load weight of rear axle is 70 kN in standard vehicle of Road-I level load, what is more, in order to simulate the vehicle load in the test accurately, the rear axle load was conversed to the uniformly distributed load The resultant point of rear axle force is placed in the L/2 section The landing area was simulated by rubber cushion block, as shown in Figure 11 1Jack was used for loading The test adopted a hierarchical loading method, and load level is kN Figure 10: Schematic diagram of standard car (Unit: m; kN) 19-5 a) Longitudinal direction b) Transversed direction Figure 11: Schematic diagram of loading position 3.3 Measuring points of experimental model The deflection and strain measurement points of hollow slab and splicing joint were arranged in the midspan section Each hollow slab has a deflection measuring point Each one deflection and longitudinal concrete strain measurement points were arranged in the middle of splicing joint and edge of the hollow slab The arrangement diagram of displacement transducers and strain gauges is shown in Figure 12 Figure 12: Arrangement diagram of displacement transducers and strain gauges 3.4 Analysis of test results 3.4.1 Full process description In the early stage of loading, splicing joint and hollow slab were all in elastic working state The load of each slab was linear and the change rate was basically same Firstly, when the single-point test load reaches 190 kN, cracks were found in No.1 slab, and the overall stiffness of model decreased Secondly, the other slabs were cracked as the load increased Thirdly, when the test load increased to about 290 kN, a transverse crack was found in mid-span section of bottom edge of splicing joint A typically transverse crack is shown in Figure 13 When the test load reaches 300 kN, the load was stopped 19-6 Figure 13: Transverse crack 3.4.2 Splicing joint The load-deflection curve and load-strain curve of splicing joint in the mid-span section is shown in Figure 14 and Figure 15 In the whole loading process, the deflection and strain of splicing joint shows linear behavior with the increase of load The deflection and strain in the middle of splicing joint and edge of the hollow slab were basically the same, and the splicing joint can effectively transfer the load When the load is 290 kN (4.1 times highway-I), a transverse crack was found in mid-span section of bottom edge of splicing joint At this time, cracks have been found in each slab So cracks of slab were found early than that of splicing joint, the splicing joint is safe, reasonable and reliable When the load reaches 290 kN (4.1 times highway-I), the load-deflection curve and load-strain curve took a certain turn in the position of splicing joint, and lateral transmission capacity had been reduced Figure 14: Load-deflection curve at mid-span of splicing joint 19-7 Figure 15: Load-strain curve at mid-span of splicing joint 3.4.3 Hollow slab The load-deflection curve of hollow slab in the mid-span section is shown in Figure 16 In the early stage of loading, hollow slab was in elastic working state, the deflection of splicing joint shows linear behavior with the increase of load When the load reaches 190 kN, cracks were found in No slab, and the overall stiffness of model decreased Cracks were found in other slab after that, cracks were found in No slab, No slab and No slab with the load from 220 kN to 260 kN When the load is larger than 260 kN, the curve presented a distinct nonlinear relation, and the slope became smaller obviously, which means that the deflection of each slab increased faster when unit load increased Figure 16: Load-deflection curve at mid-span of slab CONCLUSIONS This paper presents a summary of the experimental investigation on splicing joints for widening existing hollow slab bridges Based on the experimental findings, the following conclusions are drawn (1) At present, cast-in-situ concrete rigid wet joint and cast-in-situ concrete hinge wet joint are widely used in the joint in the widening bridge (2) Experiment analysis on a full-scale hollow slab bridge with span of m was carried out (3) When the test load increased to about 290 kN, a transverse crack was found in mid-span section of bottom edge of splicing joint At this time, cracks have been found in each slab So cracks of slab were found early than that of splicing joint, the splicing joint is safe, reasonable and reliable (4) The deflection and strain in the middle of splicing joint and edge of the hollow slab were basically the same before cracks were found The overall stiffness of model decreased and lateral transmission capacity had been reduced after cracks were found Since the fatigue issue with the welded bars is not clear, the research should be going on Some ideas to be done in the future work can be listed as follows In the future (1) The average daily traffic of this kind bridge should be investigated 19-8 (2) Durability test of bar should be carried on Acknowledgement The research described in this paper was financially supported by the National Natural Science Foundation of China (Grant No 51678154) and and those from the Fuzhou University under the research project “GXRC-17041” References Xu, Q 2011 Splicing Technical for Bridges and Culverts in Expressway Reconstruction and Extension China Communications Press (in Chinese) Meng, G.W and Teng, J.J 2004 Study on Design Standard of the Highway Old Bridge with Opening Wide Communications Standardization, 7: 17-20 (in Chinese) Zhang, L F., Guo, T., Wu, W.Q and et al 2006 Analysis of the Influence of Connecting Method on Old Bridge Performance in Widening Bridge Journal of Highway and Transportation 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Rigid joint in widening hollow slab bridge Figure 2: Hinge joint in widening hollow slab bridge Figure 3: Rigid joint in widening box girder bridge Figure4: Hinge joint in widening box girder bridge. .. model of widening hollow slab bridge with the span of m is designed and made The test model was made by new hollow slab, old hollow slab and splicing joint The hollow slab was equal section The