Abstract. A new remote nondestructive inspection technique, based on thermoelastic temperature measurement by infrared thermography, is developed for detection and evaluation of fatigue cracks propagating from welded joints in steel bridges. Fatigue cracks are detected from localized high thermoelastic temperature change at crack tips due to stress singularity under variable loading from traffics on the bridge. Self- reference lock-in data processing technique is developed for the improvement of signal/noise ratio in the crack detection process. The technique makes it possible to perform correlation processing without an external reference signal. It is very difficult to detect through-deck type fatigue cracks in steel decks by the conventional NDT technique, since they are not open to the inspection. In this paper, self-reference lock-in thermography is applied for detection of through-deck type fatigue cracks. Experiments are carried out to steel deck sample, which simulates an actual steel bridge, during crack propagation test. It is found that significant stress concentration zone can be observed near the crack front, which enabled us to detect through-deck type fatigue cracks and to estimate its size.
Fatigue can result in a local structural discontinuity in welded structural components (1). Fatigue cracks primarily emerge as a result of geometrical complexities, misalignments, and material imperfections, which can progress to cause a fracture in steel structural components. Given the repeated service loads in steel bridges, fatigue failure can jeopardize the health condition and shorten the service life (2). Fatigue-related failures can impose significant costs associated with repair or replacement of structural components. With increasing traffic loads, the prediction of the remaining life of steel bridge components is significant, given that traffic impact related to bridge construction negatively impacts the public. Fatigue condition assessment of welded fatigue- prone details is one of the crucial aspects of long-term management and maintenance programs of steel bridges (3). Fatigue induced fracture in steel truss bridges was firstly reported in Germany, Belgium, and France in the 1930s. In the late 1960s, the current approach for fatigue and fracture in the design and evaluation of steel bridges was first considered in bridge engineering (4).
230 Read more
Shi (1997) addressed the fact that an adequate bracing system for lateral torsional buckling must satisfy both stiffness and strength requirements, therefore special attention must be given to the design of these components of a steel girder bridge. He mentioned that the critical stage for buckling of steel girders takes place during deck pouring, therefore providing intermediate crossframes or diaphragms not only solves this problem, but helps the negative moment region to resist wind load on the girder bottom flange. Usually, crossframes and diaphragms are built stiffer than needed (using the 2% method), leading to a development of larger forces which induce fatigue problems at their locations. The research included the evaluation of the buckling behavior of a simply supported twin girder system with discrete torsional braces by using a FEA. Parameters like skew angle, load type, load height, cross section shape, and brace orientation relative to skew angle were also considered. Finally, Shi (1997) modified previous formulas developed for normal girders to determine both the capacity and the stiffness of the crossframes.
425 Read more
connection plates to the girder tension flanges, due to concern that the strain concentrations from welds would cause fatigue cracks to form. This practice, unfortunately, merely moved the fatigue issue to other locations. Within a given cross section, the girders deflect different amounts, and the relative vertical displacement between the girders produces out-of-plane bending in the web gaps of connection plates that are not welded to the girder flanges (See Figure 1.2). This out-of-plane bending caused fatigue cracks to develop in the web gap areas above the floor beam connection plates in the negative moment regions (NMRs) in several of Iowa FCBs. The confinement of fatigue cracks to the NMRs is explainable when considering the boundary conditions that are imposed on the tension flange throughout the bridge. In the NMRs of a bridge, the concrete deck restrains the tension flange from rotating, whereas in the positive moment regions (PMRs), the tension flange is free to rotate. Because of the difference in rotational restraint, out-of-plane bending in the NMRs is usually larger than that in the PMRs; thus, the likelihood of fatigue crack formation increases. The magnitude of the out-of-plane bending is heavily influenced by the girder spacing and bridge skew. For example, the relative displacement between girders at a cross section will be larger for skewed bridges, which produces larger out-of-plane bending in the web gaps .
154 Read more
A number of large-span steel bridges with orthotropic deck plates have been constructed in the United States, Japan, and China, owing to their relatively light weight, small structural depth, and large load capacity. However, these steel bridge decks were too thin, leading to a large local deformation in the deck pavement; further, fatigue cracks have been recorded in many types of pavement structures within only 1 –2 years [1–3]. Overloading owing to heavy duty vehicles is the main reason behind pavement damage. As steel bridge pavements are often exposed to a large variation in temperature, there is an increased demand for paving materials with considerably higher service temperature requirements. Moreover, there is a lack of design methods and theoretical research in this aspect [4,5]. In recent years, many studies have conducted experiments and theoretical analyses on the mechanical properties and the anti-fatigue performance of asphalt pavements of steel bridge decks, aiming to improve their fatigue reliability [6 –8].
20 Read more
Dynamic behavior of long span box girder bridges subjected to moving loads are validated experimentally and numerically (using four node Langrangian and Hermits finite elements) for various position of moving loads and results are in good agreements 20 . Using sampling method, partial rank correlation coefficient, standardized rank regression coefficient are examined to quantity the sensitivity of the outputs of each input variables and to obtain a method of uncertainty analysis and sensitivity analysis of effects of the creep and shrinkage in presstressed box girder bridges to reduce the uncertainties of prediction of time dependant effects due to creep and shrinkage and to improve long-term serviceability 21 .
13 Read more
The steel used in the present experimental study was a high tensile structural steel suitable for welded, bolted and riveted structures and for all general engineering purposes . Table 1 gives the chemical composition of the material and the specified values of various constituents as per IS 2062. Tension testing was done as per ASTM E 8M - 13a  to find the mechanical properties of the material. Table 2 gives the mechanical properties of the steel and it satisfies the requirement of Gr. E 300 of IS 2062.
12 Read more
A serious result of this pilot experiment is the fact documented no only by the fractographic observation, but mainly by the AE records that the fatigue service life of this material is high if it its not stressed by tension approximating the yield point R e . However, such stress is not common in practical use of tools made of damask steel and thus under common bending stress an exceptionally long service life of tools made of this type of material is demonstrable. The fact that damask steel behaves like a homogeneous material is mainly conﬁ rmed by the records of the AE signal at lower values of stress a. When stressed by higher amplitudes of tension a damask responds in AE records similarly
11 Read more
Fatigue testing has been conducted by numerous researchers on similar metal laser welded lap joints7071. There are two main types of stress life fatigue data that can be produced to assess a joint’s fatigue properties. These are high stress-low cycle fatigue and low stress-high cycle fatigue. The selection of the type of testing required depends on the level of stress the joint will be subjected to in service. However, if time (test frequency at resolvable load) and money are critical factors, high stress-low cycle fatigue can be conducted to produce a series of results that can be extrapolated to give an indication of the joint fatigue properties at lower stress and higher cycles. In some situations this may be feasible, as the scatter of cycles to failure increases at higher fatigue lives, but, obviously, there is no substitute for conducting the tests and generating the results at these lower load levels and higher cycles.
372 Read more
Reinforced concrete is used in bridge substructures due to its durability, strength, and bulk properties. There are many factors that contribute to concrete deterioration. Corrosion of reinforcing steel is considered a major cause of concrete deterioration. Typically, the alkalinity of cement paste protects the steel from corrosion. However, with improper mix designs the alkali film around the reinforcing steel is reduced. With sufficient moisture and oxygen the steel corrodes, and the rust significantly increases in volume. This causes loss of steel-concrete bond, reduction of reinforcement cross section, and cracking and spalling of concrete (Mindess et al. 2003). Alkali aggregate reaction is another cause of deterioration in concrete piles. Poor quality aggregate reacts with alkali cement expanding the aggregate and cracking the concrete (U.S. Army Corps of Engineering et al. 2001). Frost action also contributes to damaging concrete piles. Freezing of water in the cement pores causes difference in ion concentrations, which withdraws water from capillary voids. This causes the cement paste to crack and accelerates pile deterioration. Additional factors such as abrasion wear, overloading, and shrinkage contribute to concrete pile deterioration (Mindess et al. 2003).
296 Read more
The use of carbon textile reinforced mortar (CTRM) offers an innovative alternative for strengthening measures by combining the advantages of light glued CFRP-stripes and the better bond characteristics of an additional concrete layer. Two possible fields of application were investigated and described in the paper: A considerable increase of the shear fatigue strength can be obtained by strengthening the web with CTRM. Furthermore, the static shear capacity also increases considerably due to the CTRM-strengthening, which could also be shown for bridge deck slabs that are CTRM-strengthened in the tension zone. Within the scope of further experimental investigations, the strengthening method is to be optimized. In addition to experimental investigations, a more detailed investigation is required regarding the actual design checks of beams and slabs strengthened with CTRM.
15 Read more
The live load distribution factor equations have been modified during the past ten years but the new, more complex distribution factors are seldom used by county engineers who use the more conservative “s-over” equations. From the 1998 AASHTO Standard Specifications for Highway Bridges, the distribution factors for a bridge with a concrete deck on steel I-girder girders are S/7.0 and S/5.5 for one and two traffic lanes, respectively. Using the bottom flange strains, the percent distributions were calculated as the ratio of the individual girder strain to the sum of all six girder strains. With each of the three load increments producing slightly different load distribution percentages, the maximum values, summarized in Table 3.5, were selected for each of the three lanes. Note that the values are the maximum percentage values of the three load cases and therefore do not sum to 100%. As may be seen, the maximum distribution percentages occurred in the exterior girders when directly loaded. Girders 3 and 4 had distribution percentages very close to each other for Lane 2 loading further displaying the bridge symmetry observed in the bottom flange strain profile shown in Figure 3.17.
193 Read more
Any additional research to follow this project should keep one main objective. It is imperative that the reinforcing and timber act as a composite member under load. As shown in the results of this thesis the stiffness (EI) which is an integral parameter fell outside the range of Main Roads requirements and therefore the girder must be made to be less rigid. With this additional deflection the timber must stay bonded to the steel or the girder will fail as the timber cracks away from the reinforcing.
55 Read more
where is fictitious stress amplitude corrected for influence of mean stress, is ultimate strength at test temperature, and is the cyclic yield strength at test temperature. In this test, the cyclic stress-strain curve closes to the monotonic tensile curve in test temperature. It isn’t important to consider cyclic stress-strain response in estimating the effect of mean stress on fatigue life. may approximate by 0.2% percent offset yield strength at test temperature. Compared the design fatigue curve with curve, for which ultimate tensile strength is greater than 793MPa, in ASME Code Sec. Division 2
Commercial pressure and changes of design have resulted in lighting columns more closely matched to their design loadings without the additional strength that may have been present in earlier designs [4, 5]. In common with many industrial sectors, design envelopes are being pushed in terms of operating conditions and manufacturing costs. It is not unusual when this happens that previously unforeseen failure mechanisms manifest themselves. This has been the case with lighting columns as designs push the maximum 18/20m height limit permitted in Codes of Practice. Modern designs often have fewer swage joints with fewer changes in section. This results in more mass further from the base and greater wind sensitivity. In some cases, the swage joint above the door is more abrupt than previous designs, resulting in poorer fatigue detail as a consequence. These changes are no doubt driven by a requirement to minimise manufacturing costs.
20 Read more
The increase of vibration problems in modern footbridges shows that footbridges should no longer be designed for static loads only. But fulfilling the natural frequency requirements that are given in many codes restricts footbridge design: very slender, lightweight structures, such as stress ribbon bridges and suspension bridges may not satisfy these requirements. Moreover not only natural frequencies but also damping properties, bridge mass and pedestrian loading altogether determine the dynamic response. Design tools should consider all of these factors. Provided that the vibration behavior due to expected pedestrian traffic is checked with dynamic calculations and satisfies the required comfort, any type of footbridge can be designed and constructed. If the vibration behavior does not satisfy some comfort criteria, changes in the design or damping devices could be considered. The need for construction of Foot Bridges is: Structural steel has been the natural solution for long span bridges since 1890; Steel is indeed suitable for most span ranges, but particularly for longer spans. So, to overcome all these problems Seismic Resistant Foot Bridges need to be constructed.
14 Read more
Guo et al .  established an intrinsic energy dissipation model, based on the double exponential regression for one-dimensional distribution of specimen surface temperature variations. According to the authors, this energy method takes intrinsic dissipation as the fatigue damage indicator, eliminating the interference of internal friction on fatigue life evaluations. The analysis indicates that in high-cycle fatigue, processed under constant stress amplitude, the microstructure evolution is characterized by a stable intrinsic energy dissipation rate. They established that fatigue failure would occur after part of this intrinsic dissipation, due to microplastic deformation, has accumulated a threshold value, which would be a material constant independent of the loading history.
15 Read more
S-N curve is very important parameter in fatigue analysis because in case of bridges, deck slab directly sustains repeated moving wheel loads; it is one of the major bridge components susceptible to fatigue failure.After sample testing at various stress ranges, number of cycles causing failure is arrived. Based on that, S-N curve is plotted. The results are plotted as an S-N diagram usually on semi-log or on log-log paper, depicting the life in number of cycles tested as a function of the stress amplitude. The output of fatigue analysis is fatigue life.
K.B.Parikh, N.S.Patel, 2016, Analytical study carried out by different author using FEM based software they found ultimate capacity of beam increased noticeably. Analytical investigation of reinforced concrete (RC) beam with FRP were carried out by number of investigator they all studied on different aspect, some of those worked on single layer or double layer of FRP , some of those worked on different pattern and thickness of FRP and then compared stress, strain and deflection with control specimen. For precise result by finite element method use fine mashing and appropriate material property. Bond behaviour between steel-concrete and concrete-FRP sheets/plate must be specify for accurate and realistic results.
Conventional construction, the superstructure typically consists of a series of simply supported spans separated by expansion joints and resting on bearings at the abutments and intermediate piers. The main reason for their popularity is that these structures are simple to design and execute. The sub-structural design is also greatly simplified because of the determinate nature of the structure. In conventional bridges, girders sit on bearings that largely transfers only vertical load to the bridge abutments and thermal expansion and contraction of the bridge is accommodated by expansion joints. Unfortunately, deterioration of these expansion joints, due to seasonal weathering (ice, road salts, and rain), traffic wear, jamming with debris, and other damage mechanisms, leads to corrosion in the bearings; girder ends, and even substructure elements of jointed bridges. Joints and bearings are expensive to buy, install, maintain and repair and more costly to replace