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This paper presents an experimental study on the determination of the mechanical behaviors of Grade 8.8 and 10.9 high-strength bolts at elevated temperatures. Strength reduction coefficients are obtained based on test results at temperatures ranging from 20°C to 900°C, for both yield and ultimate stresses. Simplified expressions are presented to identify the strength reduction factors at considered temperatures. At 400°C, the yield and ultimate strengths of bolts decrease by 30%–35% for both grades compared to those in ambient temperature. Yield strengths are 30% and 20% of yield strengths of Grade 8.8 and 10.9 bolts at ambient temperature, respectively, when the temperature exceeds 500°C. The ultimate strength decreases slightly slower than the yield strength at high temperatures. Although the decrease in ultimate strength follows the decrease in yield strength at elevated temperatures, it is slightly slower. About 3%–6% of yield and ultimate strengths at ambient temperature remain for both grades at 700°C. Moreover, a series of expressions are provided to obtain the full range stress–strain curve of high-strength bolts at elevated temperatures. Comprehensive literature studies are taken into consideration to propose a more generalized description of the stress–strain curves. The proposed model can be fully drawn by only using elastic modulus, yield, and ultimate stresses at ambient temperature. It is shown that the proposed model has enough efficiency to describe the general material behavior at elevated temperatures. [ABSTRACT FROM AUTHOR]

The determination of the dynamic performance of a high-speed (HS) railway bridge is an ever-increasingly topical matter in public transportation networks owing to the broad establishment of ongoing HS railway transportation networks and the implementation of conventional networks for superior operational vehicle velocities. This paper examines the fatigue performance of a welded gusset plate connection of a composite steel I-girder railway bridge under trains moving within a certain range of velocities. The global three-dimensional finite element models (FEMs) are applied to examine the dynamic response of the I-girder composite steel-concrete railway bridge. The natural frequencies of the numerical model of bridge are verified using ambient vibration test results. A local three-dimensional FEM is generated in accordance with critical welded gusset plate connection using the ABAQUS platform. The local submodel is generated congruent with displacement field interpolation. The fatigue performance of a welded joint zone considering critical stress accumulation regions is determined by the hot-spot stress method under resonance conditions due to train passage with varying velocities. Stress cycles are extracted by taking real traffic spectra into account. Fatigue damage is calculated by using Palmgren-Miner's rule and the rain-flow counting method. The outcomes demonstrate that the bridge is not vulnerable to the forthcoming fatigue failure mode. [ABSTRACT FROM AUTHOR]

The determination of the dynamic performance of a high-speed (HS) railway bridge is an ever-increasingly topical matter in public transportation networks owing to the broad establishment of ongoing HS railway transportation networks and the implementation of conventional networks for superior operational vehicle velocities. This paper examines the fatigue performance of a welded gusset plate connection of a composite steel I-girder railway bridge under trains moving within a certain range of velocities. The global three-dimensional finite element models (FEMs) are applied to examine the dynamic response of the I-girder composite steel-concrete railway bridge. The natural frequencies of the numerical model of bridge are verified using ambient vibration test results. A local three-dimensional FEM is generated in accordance with critical welded gusset plate connection using the ABAQUS platform. The local submodel is generated congruent with displacement field interpolation. The fatigue performance of a welded joint zone considering critical stress accumulation regions is determined by the hot-spot stress method under resonance conditions due to train passage with varying velocities. Stress cycles are extracted by taking real traffic spectra into account. Fatigue damage is calculated by using Palmgren-Miner's rule and the rain-flow counting method. The outcomes demonstrate that the bridge is not vulnerable to the forthcoming fatigue failure mode. [ABSTRACT FROM AUTHOR]