The Experts below are selected from a list of 180 Experts worldwide ranked by ideXlab platform

C.l. Chow - One of the best experts on this subject based on the ideXlab platform.

  • An analytical solution for fast fatigue assessment under wide-band random loading
    International Journal of Fatigue, 1991
    Co-Authors: C.l. Chow
    Abstract:

    Abstract An analytical solution based on the statistical theory of the peak distribution of a stationary random process and the concept of Equivalent Stress Range is presented for a fast fatigue assessment under wide-band random loading. The fatigue life for structures under wide-band random loading can be predicted by means of this solution and a fatigue damage law based on the constant-amplitude loading. The Equivalent Stress Range can be directly calculated from the spectral parameters of a Stress power spectrum, implying that it is not necessary to reproduce the loading process in the time domain and the count cycle by cycle for fatigue assessment. A comparison between several empirical or semiempirical models and the one proposed has been carried out, from which the relative accuracy and reliability among these models are highlighted.

M. Leitner - One of the best experts on this subject based on the ideXlab platform.

  • Validation of the fatigue strength assessment of HFMI-treated steel joints under variable amplitude loading
    Welding in the World, 2020
    Co-Authors: M. Leitner, M. Stoschka, Z. Barsoum, M. Farajian
    Abstract:

    A recommendation for the application and fatigue assessment of the HFMI post-treatment was published by the IIW in 2016. Recently, the therein recommended HFMI design curves in case of constant amplitude loading (CAL) were validated involving test data with different base material yield strengths, increased plate thicknesses, and elevated load ratios. Continuative to this previous work, this paper focuses on the fatigue assessment of HFMI-treated steel joints under variable amplitude loading (VAL). Four test data sets including randomly distributed VAL and a sufficient amount of tested specimens to ensure a statistically verified assessment are investigated. It is shown that an application of the recommended Equivalent Stress Range approach and a further comparison of the test results to the design curves under CAL lead to a conservative fatigue assessment if the recommended value of the specified damage sum of D  = 0.5 is used. Furthermore, an increased value of D  = 1.0 still maintains a conservative design as presented in the study. Based on this work involving the analysed data sets, it can be concluded that the recommended procedure is well applicable and a conservative fatigue design is facilitated.

  • Fatigue strength of welded and high frequency mechanical impact (HFMI) post-treated steel joints under constant and variable amplitude loading
    Engineering Structures, 2018
    Co-Authors: M. Leitner, Markus Ottersböck, S. Pußwald, Heikki Remes
    Abstract:

    Abstract This study presents fatigue test results of longitudinal stiffener specimens in as-welded and high frequency mechanical impact (HFMI) post-treated condition under both constant amplitude loading (CAL) and variable amplitude loading (VAL). The experiments incorporate mild steel S355 and high-strength steel S700 samples at load Stress ratios of R = 0.1 and R = −1 respectively. VAL tests are performed utilizing a straight-line distribution with a sequence length of 2 ⋅ 105 load-cycles and an omission level of 19% of the maximum Stress Range. The test results reveal a significant benefit of the HFMI-treatment under CAL. On the contrary, the increase in fatigue strength is majorly reduced in case of VAL. X-ray residual Stress measurements for the investigated mild steel S355 specimens demonstrate that even at comparably minor load Stress Ranges, a certain relaxation of the HFMI-treatment induced local compressive residual Stress state at the weld toe occurs. This phenomenon contributes to the decrease of the benefit by the HFMI-treatment under VAL compared to CAL. An evaluation of specified damage sums on the basis of the determination of an Equivalent Stress Range for VAL reveals that damage sums between D = 1.0 and D = 0.5 are well applicable for a conservative fatigue assessment on the basis of the IIW-recommended fatigue design curves. However, facilitating a lightweight component design by considering experimental test results of HFMI-treated joints under CAL, a reduced specified damage sum of D = 0.3, or even of D = 0.2 in case of fluctuating mean Stress states, is suggested for the fatigue assessment to avoid non-conservative results.

  • 3rd International Conference on Material and Component Performance under Variable Amplitude Loading, VAL2015 Fatigue strength of HFMI-treated high-strength steel joints under constant and variable amplitude block loading
    2015
    Co-Authors: M. Leitner, S. Gerstbrein, M. Stoschka
    Abstract:

    Lightweight-design of welded high-strength steel structures in cyclic service necessitates the use of post-treatment methods like the high frequency mechanical impact treatment (HFMI). Service loads during operation mostly consist of variable amplitudes, whereat recommendations are only available for the as-welded condition. Therefore, this paper deals with the effect of variable amplitude block loading on the fatigue strength of HFMI-treated T-joints. An evaluation of the real damage sum exhibits characteristic distinctions to constant amplitude test results in regard to the base material strength. The application of an Equivalent Stress Range method by nominal and effective notch Stress approach is finally presented.

  • Fatigue Strength of HFMI-treated High-strength Steel Joints under Constant and Variable Amplitude Block Loading
    Procedia Engineering, 2015
    Co-Authors: M. Leitner, S. Gerstbrein, Markus Ottersböck, M. Stoschka
    Abstract:

    Abstract Lightweight-design of welded high-strength steel structures in cyclic service necessitates the use of post-treatment methods like the high frequency mechanical impact treatment (HFMI). Service loads during operation mostly consist of variable amplitudes, whereat recommendations are only available for the as-welded condition. Therefore, this paper deals with the effect of variable amplitude block loading on the fatigue strength of HFMI-treated T-joints. An evaluation of the real damage sum exhibits characteristic distinctions to constant amplitude test results in regard to the base material strength. The application of an Equivalent Stress Range method by nominal and effective notch Stress approach is finally presented.

M. Stoschka - One of the best experts on this subject based on the ideXlab platform.

  • Validation of the fatigue strength assessment of HFMI-treated steel joints under variable amplitude loading
    Welding in the World, 2020
    Co-Authors: M. Leitner, M. Stoschka, Z. Barsoum, M. Farajian
    Abstract:

    A recommendation for the application and fatigue assessment of the HFMI post-treatment was published by the IIW in 2016. Recently, the therein recommended HFMI design curves in case of constant amplitude loading (CAL) were validated involving test data with different base material yield strengths, increased plate thicknesses, and elevated load ratios. Continuative to this previous work, this paper focuses on the fatigue assessment of HFMI-treated steel joints under variable amplitude loading (VAL). Four test data sets including randomly distributed VAL and a sufficient amount of tested specimens to ensure a statistically verified assessment are investigated. It is shown that an application of the recommended Equivalent Stress Range approach and a further comparison of the test results to the design curves under CAL lead to a conservative fatigue assessment if the recommended value of the specified damage sum of D  = 0.5 is used. Furthermore, an increased value of D  = 1.0 still maintains a conservative design as presented in the study. Based on this work involving the analysed data sets, it can be concluded that the recommended procedure is well applicable and a conservative fatigue design is facilitated.

  • 3rd International Conference on Material and Component Performance under Variable Amplitude Loading, VAL2015 Fatigue strength of HFMI-treated high-strength steel joints under constant and variable amplitude block loading
    2015
    Co-Authors: M. Leitner, S. Gerstbrein, M. Stoschka
    Abstract:

    Lightweight-design of welded high-strength steel structures in cyclic service necessitates the use of post-treatment methods like the high frequency mechanical impact treatment (HFMI). Service loads during operation mostly consist of variable amplitudes, whereat recommendations are only available for the as-welded condition. Therefore, this paper deals with the effect of variable amplitude block loading on the fatigue strength of HFMI-treated T-joints. An evaluation of the real damage sum exhibits characteristic distinctions to constant amplitude test results in regard to the base material strength. The application of an Equivalent Stress Range method by nominal and effective notch Stress approach is finally presented.

  • Fatigue Strength of HFMI-treated High-strength Steel Joints under Constant and Variable Amplitude Block Loading
    Procedia Engineering, 2015
    Co-Authors: M. Leitner, S. Gerstbrein, Markus Ottersböck, M. Stoschka
    Abstract:

    Abstract Lightweight-design of welded high-strength steel structures in cyclic service necessitates the use of post-treatment methods like the high frequency mechanical impact treatment (HFMI). Service loads during operation mostly consist of variable amplitudes, whereat recommendations are only available for the as-welded condition. Therefore, this paper deals with the effect of variable amplitude block loading on the fatigue strength of HFMI-treated T-joints. An evaluation of the real damage sum exhibits characteristic distinctions to constant amplitude test results in regard to the base material strength. The application of an Equivalent Stress Range method by nominal and effective notch Stress approach is finally presented.

Dan M Frangopol - One of the best experts on this subject based on the ideXlab platform.

  • fatigue assessment and service life prediction of existing steel bridges by integrating shm into a probabilistic bilinear s n approach
    Journal of Structural Engineering-asce, 2013
    Co-Authors: Mohamed Soliman, Dan M Frangopol, Kihyon Kown
    Abstract:

    AbstractFatigue assessment of several steel bridge details, having Equivalent Stress Range below the constant amplitude fatigue threshold (CAFT), showed that many of these details are free of cracks, although the remaining life calculations predicted that they should have already been suffering from cracks. This shows that the current methods for predicting the fatigue remaining life of steel bridges can be conservative and may lead to unnecessary retrofit and rehabilitation actions. For a better fatigue life prediction, a bilinear S-N approach has been proposed. In this approach, the bilinear S-N lines have different slopes above and below the CAFT. This paper addresses fatigue assessment and service life prediction of existing fatigue-prone steel bridges by integrating structural health monitoring (SHM) data into a probabilistic bilinear S-N approach. The effect of changing the value of the slope of the AASHTO S-N lines below the CAFT on the fatigue life is investigated through a parametric study. In ad...

  • probabilistic fatigue life estimation of steel bridges by using a bilinear s n approach
    Journal of Bridge Engineering, 2012
    Co-Authors: Kihyon Kwon, Dan M Frangopol, Mohamed Soliman
    Abstract:

    This paper focuses on estimating the fatigue life below the constant amplitude fatigue threshold (CAFT) of steel bridges by using a probabilistic approach on the basis of a bilinear Stress life (i.e., the S-N approach). The current AASHTO S-N approach uses a single S-N line for predicting the fatigue life. However, because of the variation of actual applied live-load Stress cycles, this approach very often results in a severe underestimation of the useful life of structures. It implies that fatigue damage in respective structural steel details may be overestimated. To improve fatigue life estimation, a bilinear S-N approach is integrated into a probabilistic framework that can model the uncertainties associated with the fatigue deterioration process. In this approach, the Equivalent Stress Range is computed by using two S-N slopes and several probability density functions associated with Stress Ranges. These probabilistic functions are determined on the basis of Stress-Range bin histograms from long-term ...

  • bridge fatigue reliability assessment using probability density functions of Equivalent Stress Range based on field monitoring data
    International Journal of Fatigue, 2010
    Co-Authors: Kihyon Kwon, Dan M Frangopol
    Abstract:

    This paper focuses on fatigue reliability assessment of steel bridges by using probability density functions of Equivalent Stress Range based on field monitoring data. To date, existing steel bridges have experienced fatigue cracks initiated and propagated. As a result, bridge structural integrity may not be preserved safely up to its anticipated service life. For this reason, it is necessary to assess and predict bridge fatigue reliability. The AASHTO Specifications can be used to estimate capacity of structural details in the fatigue reliability assessment, whereas long-term monitoring data can be used to provide efficient information for fatigue in terms of Equivalent Stress Range and cumulative number of Stress cycles. Under uncertainties, an approach using probabilistic distributions associated with Stress Ranges is proposed to effectively predict Equivalent Stress Ranges for bridge fatigue reliability assessment. The fatigue detail coefficient, A, and the Equivalent Stress Range, Sre, are both treated as random variables in the proposed fatigue reliability approach. This approach is illustrated on two existing bridges which are expected to experience finite or infinite fatigue life.

Dongming Feng - One of the best experts on this subject based on the ideXlab platform.

  • Fatigue reliability assessment for orthotropic steel decks based on long-term strain monitoring
    Sensors (Switzerland), 2018
    Co-Authors: Yang Deng, Aiqun Li, Dongming Feng
    Abstract:

    A time-dependent fatigue reliability assessment approach is proposed for welded details of orthotropic steel decks (OSDs) using long-term strain monitoring data. The fatigue reliability limit function of the welded details is established based on the Eurocode specifications. Depending on the distribution characteristics of the measured daily Equivalent Stress Range, either the lognormal distribution or Gaussian mixture model (GMM) is selected to quantify its uncertainty. Subsequently, the fatigue reliability can be calculated using either an explicit formula or the Monte Carlo method. This proposed approach is applied for the fatigue reliability evaluation of two rib-to-deck and two rib-to-rib welded fatigue details of an in-service suspension bridge. The results show that the reliability indices decrease significantly with bridge’s service life. Except for a rib-to-deck detail, all other three welded details cannot meet the target fatigue reliability during this bridge’s 100-year service life. The proposed approach can help bridge owners and operators make informed decisions regarding maintenance and repair of potential fatigue cracks.