Experimental investigation on the low cycle fatigue life of piles

et al.;IABMAS, International Association for Bridge Maintenance and Safety;Monash University;RMIT University;Swinburne University of Technology;VicRoads9th International Conference on Bridge Maintenance, Safety and Management, IABMAS 2018 -- 9 July 2018 through 13 July 2018 -- -- 226219In this study, the low cycle fatigue tests are conducted to investigate the fatigue life of steel H-piles subjected to thermal induced cyclic strains/displacements. Review of literature revealed that there are few experimental research data on the low cycle fatigue performance of integral bridge steel H-piles. For this purpose, experimental studies on full scale steel H-pile specimens are conducted to simulate cyclic behavior of steel H-piles under thermal effects in integral bridges by considering the effect of axial load combined with large amplitude strain cycles with various amplitude levels. Using experimental test results, the effect of axial load level is investigated on the low cycle fatigue performance of integral bridge steel H–piles. It is observed that the effect of axial load on the low cycle fatigue performance of integral bridge steel H-piles are so important to reduce the bending stresses in the steel H-piles and also increase the low-cycle fatigue performance of steel H-piles at the abutments of integral bridges at the moderate strain amplitudes. Moreover, it is observed that at large strain amplitudes the effect of local buckling should be considered more than the effect of axial load on the low cycle fatigue life of steel H piles at the abutments of integral bridges. © 2018 Taylor & Francis Group, London

Fatigue in jointless bridge H-piles under axial load and thermal movements

The seasonal and short-term temperature variations produce cyclic horizontal displacements in the continuous superstructure of jointless bridges and hence in the abutment piles. Thorough study of the available field measurement data for jointless bridges showed that the thermal-induced cyclic flexural strains in steel H-piles (SHPs) at the abutments are composed of large, primary small and secondary small flexural strain cycles. While the SHPs at the abutments of jointless bridges laterally deform and experience these cyclic flexural strains due to thermal effects, they also carry axial loads transferred from the superstructure through the abutments. Review of the literature revealed that there is no specific study on the combined effects of axial load and thermal-induced/flexural strain cycles with various amplitudes on the low cycle fatigue (LCF) performance of jointless bridge SHPs. For this purpose, parametric experimental studies on full scale SHP specimens are conducted to simulate the cyclic behavior of SHPs under thermal effects in jointless bridges by considering the effect of axial load combined with large and small flexural strain cycles with various amplitudes. It is observed that at large flexural strain amplitudes, local buckling of the pile due to the effect of axial load adversely affects the LCF life of SHPs at the abutments of jointless bridges. Furthermore, it is observed that the effect of small flexural strain cycles on the LCF life of uncompact SHPs depends on the amplitude of large flexural strains and the amplitude ratio of the small and large flexural strains. © 2017 Elsevier Lt

Importance of simulation in the design of experimental tests

et al.;IABMAS, International Association for Bridge Maintenance and Safety;Monash University;RMIT University;Swinburne University of Technology;VicRoads9th International Conference on Bridge Maintenance, Safety and Management, IABMAS 2018 -- 9 July 2018 through 13 July 2018 -- -- 226219Linear and Nonlinear finite element (FE) models of the steel H-pile specimens used in the experimental test set up are developed using the computer program ANSYS to identify potential problems that may be encountered during testing and to improve the test apparatus. First, linear FE models of the steel Hpile specimens are built to determine maximum stress concentrations occurring in the HP sections and the steel base fixture used for fixing the pile to the testing frame. From these linear analyses results; the locations of stress concentrations in the HP sections are identified. Using these results, the test set up is modified to decrease the stress concentrations. Then, nonlinear FE analyses of the steel H-pile specimens are repeated on the modified specimen model to observe the distribution of stresses and strains in the steel HP sections and the steel base fixture. Then, low cycle fatigue tests are conducted to investigate the fatigue life of steel H-piles subjected to thermal induced cyclic strains/displacements. In the experimental part, HP220x57 pile specimens are tested to estimate the low cycle fatigue life of steel H-piles as a function of large flexural strain cycles with various amplitudes. Using the FEM, comparisons between FE model predictions and experimental test results are made in terms of fatigue life in the steel H-pile specimens. Consequently, it is shown that nonlinear FEMs of the steel H-pile used in the experimental part should be used to identify potential problems that may be encountered during testing and to improve the test apparatus if necessary. © 2018 Taylor & Francis Group, London

Estimation of optimum isolator parameters for effective mitigation of seismic risk for bridges

In this study, closed form equations as functions of the isolator, bridge and ground motion properties are formulated to calculate the optimum characteristic strength, Q(d) and post-elastic stiffness, k(d), of the isolator to minimize the maximum isolator displacement (MID) and force (MIF) for seismic isolated bridges (SIBs). This formulation required more than 13000 nonlinear time history analyses of simplified SIB models. The analyses results revealed that the optimum Qd and kd are highly dependent on the site soil conditions and peak ground acceleration of the ground motion

Effect of thermal induced flexural strain cycles on the low cycle fatigue performance of integral bridge steel H-piles

Close examination of the field measurement data for integral bridges revealed that the measured cyclic flexural strains in steel H-piles at the abutments due to thermal fluctuations consist of large amplitude, primary small amplitude and secondary small amplitude cycles. The effect of the small amplitude strain cycles on the low cycle fatigue life of these steel H-piles has not been extensively studied yet. Accordingly, to investigate the effect of the small amplitude strain cycles on the low cycle fatigue life of steel H piles at the abutments, first a new cycle counting method is developed specifically to facilitate the counting of thermal induced strain cycles in the steel H-piles. Then, using the field measurement data of several integral bridges in North America, and the developed cycle counting method, an equation is formulated to estimate the fatigue life of integral bridge steel H-piles. It is observed that secondary small amplitude flexural strain cycles do not have a significant effect on the low cycle fatigue life of steel H-piles. Experimental studies on full scale compact steel H-pile specimens are conducted to verify the analytical results and a close match between the experimental and analytical results is observed. © 2016 Elsevier Lt

AN ENERGY APPROACH TO SLIDING OF SINGLE-SPAN SIMPLY SUPPORTED SLAB-ON-GIRDER STEEL HIGHWAY BRIDGES WITH DAMAGED BEARINGS

This paper investigates the non-linear inelastic seismic response of existing single-span simply supported bridges having bearings which can remain stable and slide after their anchor bolts are ruptured. A simplified equivalent model is developed for the inelastic analysis of these single-span simply supported bridges. Non-linear inelastic time-history analyses are conducted for various acceleration inputs. It is found that narrower bridges with longer spans may have considerable sliding displacements and fall off their supports if adequate seat width is not provided. It is also found that for the same ratio of friction coefficient to peak ground acceleration, the sliding displacement of a structural system is linearly proportional to the amplitude of the peak ground acceleration beyond a certain threshold value. This is also demonstrated analytically from an energy approach point of view. The distribution of the energy content of an earthquake, which is related to its velocity time history, can be an indication of the propensity of an earthquake to cause high sliding displacement Ground motions with high frequency content or high A(p)/V-p ratio may produce smaller sliding displacements than ground motions with relatively lower A(p)/V-p ratios

Development of a new cycle counting method for cyclic thermal strains in integral bridge piles

In this study, a new cycle counting method is developed to determine the number and amplitude of large and small displacement/strain cycles. A new equation is obtained to determine a displacement/strain cycle amplitude representative of a number of small amplitude cycles existing in a typical temperature induced displacement/strain history in steel H-piles of integral bridges. The effect of primary and secondary small cycles are investigated for different integral bridge

FATIGUE-BASED METHODOLOGY FOR MANAGING IMPACT OF HEAVY-PERMIT TRUCKS ON STEEL HIGHWAY BRIDGES

Currently, in many areas of North America, special permits are issued to extra heavy vehicles without a detailed evaluation of individual components, considering only the ultimate capacity of the bridge inventory as a whole. Based on this, a large number of special permits have been issued to extra heavy vehicles. In this perspective, the ultimate and cumulative effect of such overloads on steel bridge components is studied. It is found that steel bridge members have adequate ultimate capacity to accommodate such overloads; however, they may suffer fatigue damage due to the cumulative effect of these overloads. Accordingly, a fatigue-based methodology is developed to assess the reduction in service life of bridges due to heavy-permit trucks. It is found that a reasonably large number of special permits can be issued at small reductions in fatigue life, but because stress ranges in excess of the constant-amplitude fatigue limit significantly alter the shape of the S-N curve, it is essential to appreciate that the concept of infinite fatigue life cannot be relied upon anymore