Longitudinal Joints Research Articles

Airtightness Performance Test and Failure Models for Low-to-Vacuum Maglev Train Tunnel Joints

Abstract The airtightness at the joints of segment lining structures is one of the critical problems for low-to-vacuum maglev train tunnels that needs to be addressed. A new apparatus was designed to test the airtightness performance of the gasket-in-groove at longitudinal and circumferential joints. Based on the test results, four mechanical models based on the theory of elastic mechanics were developed to describe the short-term and long-term sealing failure behaviors of longitudinal and circumferential joints, which are subjected to vacuum pressure on one side of the gasket, and the corresponding air-leakage equations for contact interface were also deduced. The test results show (1) a higher initial contact pressure in the gasket-in-groove would result in faster stress relaxation; (2) a greater initial contact pressure would result in better joint sealing; and (3) for the same initial contact pressure, the sealing capacity of longitudinal joints is significantly better than that of circumferential joints. The test results are in good agreement with the models. The developed models can be used to interpret the sealing failure mechanism through the gasket contact pressure path. Moreover, the mechanical models show that the sealing capacity of the circumferential joint gasket is positively correlated with the airtightness coefficient and the gasket equivalent Poisson’s ratio, whereas the sealing capacity of the longitudinal joint gasket is positively correlated with the airtightness coefficient, the gasket equivalent Poisson’s ratio, as well as the tunnel outer diameter, and negatively correlated with the gasket width.

Investigating the impact of thermal stresses on blistering effects in sandwich panels

AbstractLightweight steel constructions made of sandwich panels are an economical solution for wall and roof claddings, especially in industrial construction. The panels consist of two thin sheets of steel and a core with thermal insulating properties. In the mounted state and at high temperatures on the outer face of the panel, damage to the components may occur due to blister formation. In a current research project, the influence of defects in sandwich panels with a PIR‐foam core is examined. This article presents the results of experimental tests regarding the influence of various parameters, such as face temperature, production defects and design of the longitudinal joint on blistering in sandwich wall panels with a PIR‐core. The aim is to identify the necessary conditions for the occurrence of blisters. Using an optical strain measuring method (Digital Image Correlation), the temperature‐induced deformations and strains in the covering nose of sandwich wall panels with hidden fastening are measured and will be analyzed with regard to blistering. First results reveal a significant dependence on the geometry and design of the covering nose.

Vibration wave propagation differences in straight assembled shield tunnels under different deformation conditions

During the implementation of shield tunnel construction, deformation and joint opening may arise as a result of load-induced influences. Recent research has highlighted the crucial role of segment joints in the dynamic analysis of shield tunnels, yet a comprehensive understanding of the influence of joint opening on vibration wave transmission is still lacking. To address this gap, this study established a finite element model of a shield tunnel and investigated the effects of joint opening on the transmission of vibration waves. The findings of this study indicate several important results: (a) The weakening ability of joints to vibration waves within a specific frequency range is closely related to the degree of joint opening. With increasing joint opening, the weakening ability of certain joints towards specific frequency vibration waves can increase by more than 40%; (b) The weakening effect of joints on vibration waves exhibits a significant correlation with the orientation of joint openings. Inward-opening longitudinal joints exhibit a high rate of weakening for vibration waves, while outward-opening longitudinal joints demonstrate limited weakening ability towards the vibration wave; (c) The weakening ability of segment concrete towards vibration waves is significantly weaker compared to that of joints. Hence, the inclusion of segment joints is crucial in the investigation of dynamics of shield tunnels, as they cannot be disregarded.

Experimental study on the compression-shear performance of a new-type circumferential joint of shield tunnel

To investigate the compression-shear behavior of a new circumferential joint based on the sleeve-straight bolt combination type connection of large-diameter shield tunnels, a series of full-scale joint experiments was carried out. In the process of the experiment, more attention was paid to the specimen displacement, bolt stress and joint damage mode. On the basis of these experiment phenomena, this study discussed the compression-shear bearing process of the new connector, analyzed the damage mode of the joint structure, and finally evaluated the performance of the new connector. It is found that the bearing process of the joint can be divided into four stages: the transitional stage for overcoming the friction of the concrete, the sleeve bearing stage for the sleeve bearing shear loads alone, the combined bearing stage for bearing shear loads by the connector system, and the structural damage stage for structural instability and damage. Generally speaking, affected by connector position and hand hole, the positive compression-shear stiffness of the joint is less than the negative compression-shear stiffness, and the positive shear strength of the joint is greater than the negative shear strength. The increase of longitudinal axial force will improve the compression-shear performance of the joint. The relationship between longitudinal axial force and joint stiffness is a logarithmic function. The use of new type of connector can effectively improve the compression-shear stiffness of joints under low shear loads, but the application of straight bolts will lose part of the strength performance.

Research on the effect of double sealing gaskets arrangement on the mechanical behavior of the segment longitudinal joints with large diameter shield tunnel

The sealing gasket of the traditional double waterproof system of the large diameter shield tunnel consists of two sealing gaskets which are arranged on the outside of the bolt hole(SGOH) or arranged on both sides of the bolt hole(SGBH). The different arrangement of the double sealing gaskets has significant effects on the mechanical behaviors of the longitudinal joints of the segment. In this paper, based on the energy equivalence principle, the actual distribution stress of the compression zone of the segment longitudinal joints was simplified equivalently as rectangular distribution stress. Then, a progressive mechanical model was established for the longitudinal joint, taking into account the effect of double sealing gaskets arrangements. Furthermore, the proposed mechanical model was validated through former experimental results and other analytical models. Finally, the effect of different arrangements of the double sealing gaskets on the mechanical behavior of the longitudinal joints of the segment was compared and analyzed. The results showed that the difference in the arrangement of the double sealing gaskets results in varying effects of the additional bending moment on the joint bending deformation under sagging and hogging moments, leading to the unequal bending stiffness of the joint. The difference in bending stiffness caused by the double sealing gasket arrangements is approximately 100∼150 MN·m/rad. To optimize the mechanical behaviors of the joints, the double sealing gaskets should be arranged on both sides of the bolt hole(SGBH), with the bolt located at the center of both the longitudinal joints and the core compressive zone of the longitudinal joints.

Underwater Explosion Resistance Performance of an Old Gravity Dam without Good Longitudinal-Joint Connection Integrity: Coupled Acoustic-Structural Analysis

A gravity dam monolith bounded by the transverse contraction joints on both sides is usually recognized as an independent element in various dynamic analyses. However, in most cases a gravity dam monolith is actually subdivided by longitudinal joints for mass concrete construction requirements. Previous studies of gravity dams subjected to underwater explosion (UNDEX) shock loadings have not dealt with the longitudinal-joint issue in much detail. In this work, a numerical simulation of the dynamic response of an old gravity dam without good longitudinal-joint connection integrity in an UNDEX event is performed. The coupled acoustic-structural analysis procedure with ABAQUS/Explicit is employed. The reliability of the procedure is validated by numerical simulations of two UNDEX impact tests in the literature. Nine calculation cases are considered to compare different responses of the dam with different connection states between monolith sections and underwater detonation depths. The results of this numerical investigation show that the longitudinal joints play an important role in the UNDEX response of the dam. The longitudinal joints greatly weaken the flexural rigidity of the dam and make the dam damaged in a piecemeal manner. This study adds to the rapidly expanding field of the UNDEX resistance performance evaluation of gravity dams by accounting more for the longitudinal-joint issue.

Experimental Study on Mechanical Behavior of Gas Transmission Shield Tunnel Segments

To analyze the mechanical behavior of the shield tunnel segment lining of underwater pipelines, based on the prototype segment structure practically applied in a project, a local model test of the combined shield segment considering front and rear ring staggered joints was designed. The internal forces and strains, joint opening and misalignment, and structural deflection change with the axial pressure ratio at different locations of the segment in the range of axial pressure ratio 0.02–0.54 were investigated, and the final failure form of the segment structure was also obtained. The experiment results show that in the assembly segments, the middle segment has the highest stiffness, followed by the side segments. When the segments are damaged, the maximum opening of the longitudinal joint is 1.75 mm. Because the overall damage of the segments is earlier than the joint damage, it is suggested that the development of structural cracks, joint misalignment, and structural deflection be taken as the basis for evaluating the safety of tunnel segments. When the axial compression ratio is loaded above 0.50, top concrete crush damage occurred in the middle segment, while the concrete on both sides happened to incur an oblique 45° shear damage.

Longitudinal joint trajectories of gambling disorder and hypomentalization: A latent class growth analysis among young adults

IntroductionOnly a few studies have investigated the relationship between risk for gambling disorder (GD) and mentalization difficulties. However, these results on positive correlations were all from cross-sectional studies; therefore, it would be important to investigate the longitudinal relationship between the constructs. AimsIt was aimed to identify subgroups of gamblers with different joint growth trajectories of risk for GD and hypomentalization (i.e., uncertainty of understanding own and others' mental states) and to compare the identified latent classes along impulsivity, sensation seeking and depression. MethodsData from waves 1–3 of the Budapest Longitudinal Study were used. The final sample included 219 young adult gamblers who completed the study questionnaire and reported past-year gambling in all three waves (Females: N = 93 [42.29%]; Mean age: 28.36 years [SD = 4.29]). Standardized questionnaires were administered to measure the main constructs. ResultsA four-class model was retained based on latent class growth analysis. Class 1 had consistently moderately high risk for GD and hypomentalization, and Class 4 presented consistently low risk for GD and hypomentalization. Classes 2–3 were characterized by low risk for GD and increasing hypomentalization. Class 1 had significantly higher sensation seeking and depression compared with the other subgroups in multiple cases. Class 4 showed significantly lower impulsivity and sensation seeking than the other classes. ConclusionsElevated hypomentalization was presented among individuals with risk for GD. However, there is little empirical evidence to support that the two constructs have convergently changing trajectories. A cautious interpretation of the results is recommended due to low symptom presence.

Statistical and numerical analysis on characteristics and influence factors of construction cracks of large-diameter underwater shield tunnel: a case study

Tunnel excavation is prone to segment cracks, which may lead to serious safety accidents. This work aims to investigate the type, location and occurrence time of cracks in a large-diameter underwater shield tunnel and also ascertain the causes of the cracks. The correlations between crack characteristics and shield tunneling parameters were analyzed. The effect of jack deflection and poor assembly on cracks were investigated using a refined finite element model of two consecutive rings with consideration of the assembly clearance and the constraint effect of the shield machine. The results confirmed that 93% of the cracks were formed between the current ring and the last ring jacking stage. Positive cracks induced by jack deflection occurred during the current ring jacking stage, while the lengths of the cracks, proportional to the constraint of the boring machine on the segments, remained constant during the subsequent construction process. The cracks caused by poor assembly quality arose during the current and next ring jacking stages. Furthermore, the cracks generated in the current ring jacking stage would propagate during the subsequent construction process. The type, length, and number of cracks were influenced by the assembly clearance. The inverted V-shape longitudinal joints caused more cracks than any other assembly defects. The finding of this study results and conclusions are expected to contribute to the reduction of cracks at the jacking stage of the large-diameter underwater shield tunnels with eccentricity force transfer platforms.

Investigation of the Microstructure and Mechanical Properties in Friction Stir Welded Dissimilar Aluminium Alloy Joints via Sampling Direction

This research study investigates the influence of sampling direction on the microstructure and mechanical properties of dissimilar joints formed by friction stir welding (FSW). The specimens were cut in two directions: perpendicular (transverse) and parallel (longitudinal) to the FSW joint. The tests conducted included X-ray diffraction (XRD), macrostructure, microstructure, tensile, microhardness, and fractography analysis. Different phases were noted in the XRD patterns and explained, with the aluminum phase being the dominating one. The results further showed that the transverse dissimilar joint exhibited higher microhardness compared to the longitudinal dissimilar joint, which is consistent with the respective grain sizes. Moreover, the ultimate tensile strength of the longitudinal joint exceeded that of the transverse joints, showing a substantial 47% increase. Similarly, the elongation of the joints followed a similar trend, with the longitudinal joint displaying a significant 41% increase in elongation compared to the transverse joint. Fractographic analysis revealed ductile fracture behaviour in all joints.

Experimental study on the interface bonding characteristic of polyurethane and pavement materials

As a new grouting material, polyurethane has been used in the repair engineering of longitudinal joint distress of semi-rigid base asphalt pavement. It is necessary to study the bonding characteristics of the interface between polyurethane and road materials. In this paper, the interface characteristics of composite materials were considered from the two materials about pavement material and base material. Shear test and split tensile test were carried out on the specimens with different interface roughness and polyurethane density. Based on the test data, the strength models of shear strength and splitting tensile strength with roughness and density were established. The micro-characteristics of the composite interface were analyzed. Polyurethane formed a dense film at the interface, and the film thickness increases with the increase of density. The failure mode of the specimen was affected by the polyurethane film. In addition, the influence of normal stress is considered in the shear test, and the friction angle of the interface was analyzed. The stress-strain curve characteristics of shear test and split tensile test of two kinds of composite materials were summarized. The failure modes were generally three types: failure along the boundary of polyurethane material, failure along the boundary of base material, and joint failure of polyurethane material and base material along the interface. The research results provide a basis for better understanding the influencing factors and failure modes of the bonding characteristic between asphalt mixture, cement stabilized macadam and polyurethane materials.

Performance evaluation of a HMA pavement longitudinal joint containing a void reducing asphalt membrane (VRAM)

Longitudinal joint cracking in Hot Mix Asphalt (HMA) pavements is a major issue that occurs because high density (low air voids) is not easily achieved during construction as compared to the mat away from the joints. High air voids allow water infiltration, which results in moisture-induced damage to the pavement and reduced pavement service life. The use of a Void Reducing Asphalt Membrane (VRAM) has been recommended and used at longitudinal joints of asphalt pavements as a preventative treatment to achieve good performance and increase density/reduce air void content at the longitudinal joint. The Void Reducing Asphalt Membrane material is sprayed on top of a tack coat at the longitudinal joint, 9 inches on each side of the joint below the Hot Mix Asphalt surface overlay, and is expected to migrate upward into the Hot Mix Asphalt overlay, filling 50%–70% of the air voids. This study evaluated and compared the performance of longitudinal joints constructed with Void Reducing Asphalt Membrane to that of a joint without Void Reducing Asphalt Membrane (control). Field cores were collected from 1) a section containing Void Reducing Asphalt Membrane and 2) a section without Void Reducing Asphalt Membrane that was paved for this research. Falling head permeability was carried out to determine the permeability coefficient of the specimen. Disk Compact Tension (DCT) and Semi-Circular Bend (SCB) tests were used to evaluate the cracking performance at low temperatures. A push-pull test was used to evaluate the improvement in adhesion between the top and bottom Hot Mix Asphalt layers at the intermediate temperature. The VRAM-containing samples show high values of fracture energy (Gf) and surface and joint bond energies as compared to the control sections. High surface and joint bond energies indicate that longitudinal cracking at the joints will be delayed as more energy is required to initiate cracks. Additionally, the VRAM-containing samples have a lower permeability coefficient compared to the control section. This indicates that the Void Reducing Asphalt Membrane reduces the possibility of water infiltration. The elastomeric polymer in the Void Reducing Asphalt Membrane increases the cohesion in the mixture, which increases the resistance to deformation and improves the bond strength of the joint Additionally, the Void Reducing Asphalt Membrane enhances the elasticity of the binder, thus increasing the cracking resistance of the joint.

Analysis of Joints Patterns in Albian to Santonian Strata on the Eastern Flank of the Abakaliki Anticlinorium: Implications on Paleostress Conditions and Fluid Flow Properties in an Unconventional Petroleum System

An analysis of joint patterns were carried out on multiple exposures in Albian to Turonian strata belonging to the Abakaliki Formation (Asu River Group) and the Eze-Aku Formation (Eze-Aku Group) on the eastern flank of the Abakaliki Anticlinorium of the Southern Benue Trough. The analysis was carried out using FracPaQ a MATLAB based toolbox for quantification of fracture patterns. The tool was used to calculate fracture density, and intensity of the traces; to quantify scaling distributions, and to determine dilation tendencies, slip tendencies, and to quantify connectivity, and fluid flow directions. Analysis show the presence of two major joint systems: A Major Cross-Fold Joint (CF-J) system -orthogonal to the regional fold axes- consisting of the CF-J1 set trending NW/SE (315±5°), and a subordinate Longitudinal Joint System (L-J) -subparallel to the fold axes- consisting of a NE-SW L-j1 set, an ENE-WSW (60°±5°) L-j2 set, and an E-W trending L-j3 set. Fracture patterns show intensity and density ranging from 11.2395- 53.3443 m-1 and 85.2747- 629.5928 m-2 respectively. Joints in the NE-SW show high dilation and low slip tendencies given a NW-SE directed maximum principal horizontal stress σH stress field. The units of the Abakaliki Formation show better connectivity and lower permeability anisotropy as both fracture systems are well developed in those units. These joints, having formed in the period leading up to the Santonian inversion would have been ideal conduits for migration and flow of hydrocarbon and mineral fluids. The Cross-Fold System precedes the folding episode in the Santonian period and is likely a result of overpressure conditions due to disequilibrium compaction in the Albian- Turonian strata in an initial compressive regional tectonic stress field. The Longitudinal System formed later and is related to the outer-arc flexure of the folded units taking advantage of the nascent cleavage structures in the folded shale units.

Investigating UHPC in deck bulb-tee girder connections, part 2: Full-scale experimental testing

Deck bulb-tee girders constitute an excellent precast concrete bridge element system for medium- to longspan bridges. The precast concrete girders are transported to the jobsite, where they are placed adjacent to each other. The girders are connected using field-cast longitudinal joints. When required, a continuity diaphragm over the pier is used to create moment continuity; however, there is a risk of cracking of the field-cast joints and construction can be difficult when adjacent girders have different camber profiles. Given these challenges, adoption of the deck bulb-tee girder systems has been limited. Analytical investigation performed in part 1 of this series of papers indicated that using ultra-high-performance concrete (UHPC) can improve the performance of the field-cast joints and help overcome construction difficulties. This paper describes full-scale experimental testing performed as a follow-up to the analytical investigation. Longitudinal joints grouted with UHPC were tested under a combination of thermal and live load. A continuity diaphragm with partial UHPC was also tested under positive and negative moments over the pier.

Numerical study on mechanical behavior and ultimate bearing capacity of shield segment joints under different load conditions

The lining of a shield tunnel consists of thousands of precast segments that are connected by bolts, resulting in many joints in the shield tunnel structure. The mechanical behaviour of segment joints, which are the most vulnerable part in structures, determine the bearing capacity and deformation characteristic of the overall tunnel structure. Therefore, it is necessary to study the stiffness, bearing capacity and deformation behaviour of joints under different load conditions. However, previous studies have mainly focused on the capacities of longitudinal joints (LJs) against bending moments, and circumferential joints (CJs) against shear forces. Actually, the interaction between segments can be much more complicated, and the joints may suffer other loads, but there have been few relevant studies on this topic. In this study, a series of three-dimensional numerical models were established to investigate the bearing capacity and deformation behaviour of the joints under different kinds of loads. The results showed that when LJs and CJs were subjected to tension or shear forces, the failure was caused by the damage of segment concrete, in other words, the mechanical properties of the concrete determined the ultimate bearing capacity of the joints.

GL-Net: Semantic segmentation for point clouds of shield tunnel via global feature learning and local feature discriminative aggregation

has gradually become the first choice of modern urban public transportation due to its advantages of safety and high-efficiency. Shield tunnel is an important type of subway tunnel, and its structural stability and safety play an important role in subway operation. The shield tunnels are prone to problems such as water leakage and tunnel collapse, which affect the safe operation of subways. Efficient monitoring methods are required to detect the status of subway tunnels. The data collection and accurate segmentation of key components of shield tunnels are the basis and key to the automatic monitoring of subway tunnels. This research presents a novel semantic segmentation method of three-dimensional (3-D) point clouds of typical structural elements (e.g., longitudinal joint, circumferential joints, bolt hole and grouting hole) in shield tunnel based on deep learning. In this method, we focus on how to make the network learn robust global features and complex local distribution patterns. Further, we propose a global and local feature encoding block (namely GL-block) to discriminatively aggregate local features while learning global representation. After multiple encodings by the GL-block, we design a global correlation modeling (GCM) module to establish a global awareness of each point. Finally, a weighted cross-entropy loss function is designed to solve the problem of unbalanced number of samples in each category of shield tunnel. In the experiments, we make a dataset of shield tunnel point clouds with a length of about 1,000 m collected by CNU-TS-1 (DU et al., 2018) mobile tunnel monitoring system, and use the dataset to train and test the segmentation ability of our method on the typical structural elements of shield tunnels. Experiments verify the effectiveness of our method by comparing with the other state-of-the-art 3-D point cloud semantic segmentation methods, and our method has an mIoU score of 73.02 %, which is at least 14.54 % higher than the other compared state-of-the-art networks. Also, we further verify the adaptability of our method to different tunnels and different laser scanning equipment, such as FARO, Leica and Z + F, and achieve very advanced performance.

Failure mechanism of underwater shield tunnel: An experimental and theoretical study

This study proposes a plastic hinge-based approach to investigate the failure mechanism of underwater shield tunnel lining structures. Joint plastic hinge and segmental plastic hinge are defined based on the observed failure patterns. The rotational demands of the plastic hinges are obtained through theoretical and numerical methods, and the locations of potential plastic hinges are determined based on the displacement requirement of the structure. A damage index model is used to evaluate the damage of the plastic hinges. Full-scale tests are conducted on two types of shield tunnel lining structures: straight-joint assembly structure (STRJS) and staggered-joint assembly structure (STGJS) under high-water pressure loading conditions. The test results indicate that the assembly method is found to significantly affect the failure pattern, with STRJS and STGJS failing through longitudinal joints and concrete segments, respectively. Furthermore, the STRJS and STGJS exhibit comparable load-bearing capacities, with ultimate loads of 2912 kN and 2867 kN, respectively. The plastic hinge approach is used to compare the failure mechanisms of STRJS and STGJS, revealing that STGJS has fewer joint plastic hinges than STRJS at the ultimate state of the shield tunnel lining structure. The failure of STRJS and STGJS is caused by the joint and segmental plastic hinges exceeding their rotation capacity, respectively. The study highlights the importance of considering the assembly method and the type of plastic hinge in the design of underwater shield tunnel lining structures.

Impact of Rumble Strips on Longitudinal Joint Pavement Performance

Milled centerline rumble strips are commonly used to reduce lane departure crashes. Safety benefits of installing rumble strips are viewed as a higher priority than the potential impacts to longitudinal joint performance, often leading to a reduced pavement life. There are several different approaches to minimize the impact that rumble strips may have on joint performance, such as careful selection of pavement candidates for installation of rumble strips, using a sealant on top of the rumble strip (top-down) or using a joint sealer (bottom-up). The objective of this study was to assess the impact of using a void reducing asphalt membrane (VRAM) as a joint sealer on longitudinal joint performance with and without the addition of rumble strips. Laboratory testing was completed on plant mix lab compacted specimens and field cores sampled along the centerline joint of two different roadways. Testing consisted of low and intermediate temperature cracking tests and permeability testing. Results from this study showed that VRAM was effective in mitigating increased permeability concerns with the addition of rumble strips into the pavement surface. In relation to laboratory cracking results, there was no significant difference observed between cracking tolerance index (CT-Index) values with and without rumble strips for cores sampled from one project location, while the second project location showed that CT-Index increased with the presence of the VRAM. Continued monitoring of field sections included in this study and future trial sections will be beneficial in understanding the link between laboratory testing, field performance, and variability associated with centerline joint performance.

Longitudinal joint modeling for assessing parallel interactive development of latent ability and processing speed using responses and response times.

To measure the parallel interactive development of latent ability and processing speed using longitudinal item response accuracy (RA) and longitudinal response time (RT) data, we proposed three longitudinal joint modeling approaches from the structural equation modeling perspective, namely unstructured-covariance-matrix-based longitudinal joint modeling, latent growth curve-based longitudinal joint modeling, and autoregressive cross-lagged longitudinal joint modeling. The proposed modeling approaches can not only provide the developmental trajectories of latent ability and processing speed individually, but also exploit the relationship between the change in latent ability and processing speed through the across-time relationships of these two constructs. The results of two empirical studies indicate that (1) all three models are practically applicable and have highly consistent conclusions in terms of the changes in ability and speed in the analysis of the same data set, and (2) additional analysis of the RT data and acquisition of individual processing speed measurements can reveal the parallel interactive development phenomena that are difficult to detect using RA data alone. Furthermore, the results of our simulation study demonstrate that the proposed Bayesian Markov chain Monte Carlo estimation algorithm can ensure accurate model parameter recovery for all three proposed longitudinal joint models. Finally, the implications of our findings are discussed from the research and practice perspectives.

Evaluation of the Performance of Expanded Polystyrene Block on the Reduction of the Deck Cracking in Wide Integral Abutment Bridge

Longitudinal joints are thought to provide relief from expansion and contraction of the bridge deck owing to temperature change, shrinkage, and live loads, especially for a wide bridge. Historically, however, these joints have been known to leak, allowing chloride-laden water to reach the bottom of the deck overhang and even the exterior girders. Research conducted by Phares et al. indicated that the development of cracking in bridge decks seems less dependent on the total width of the deck and more so on internal restraint of the abutment to temperature changes and, in particular, gradients. Based on the finite element method (FEM) results, an effective solution to reduce cracking in the deck might be to place an isolation pad between the soil and the back side of the abutment. The primary objective of this paper is to investigate the effectiveness of an isolation foam block at the back of an integral abutment in reducing the stress-induced strain and the deck end longitudinal and diagonal cracking near the end of the deck with an integral abutment. To achieve this objective, a highway bridge (Viking Road Bridge) in Iowa, US, designed with a width of 228 ft, was selected for the study. The bridge deck has no longitudinal joints but, based on the previous research results, it was equipped with thermal isolation pads behind the abutment. The newly constructed bridge was monitored for over two years, and this was followed by multiple bridge inspections. An analytical study was conducted to investigate the efficiency of the isolation foam on the bridge deck end structural behavior. The results indicated that the thermal isolation foam is effective in reducing the temperature gradient through the abutment thickness, especially on extremely cold days. By reducing the temperature difference between the abutment and the deck, a thermal isolation block is effective at reducing the deck end strain and resisting deck end cracking. The FEM results indicated that the maximum deck stress-induced strain was 46% greater without the effects of the thermal isolation block and greater than the concrete cracking strain. This indicated that, without the thermal isolation pad, the Viking Road Bridge could crack at the end of its deck.