Replacement of Flexural and Shear Reinforcement of Double-Column Bridge Bent with CFRP under Combined loadings

The bridge bent is the most critical structural component of short span bridge that highly affected by different types of loadings. The bent failure has been observed due to in plane and out of plane loadings. Strengthening techniques are utilized for existing bridges. However, a replacement technique can be used for the new bridges to avoid bent failure. Moreover, the effect of combined loading on bent performance need to be evaluated. Therefore, this study assessed the performance of bridge bent under in plane, out of plane and combined loadings. Furthermore, replace the traditional flexural and shear steel reinforcement of the columns with CFRP bars. The performance of bent is assessed numerically by finite element analysis. For this purpose, six numerical bent models are developed. The first three models with traditional steel bars and the remaining models with CFRP rebars. The results demonstrated that out of plane loadings has more impact on the bent structural performance than other loading cases. Flexural and shear failures are observed in the columns for models with steel rebars. The failure started from lower side of the column for both in plane and out of plane loadings showing low resistance. The steel rebars yielded in early stage of loading indicating limited stiffness. However, the bent performance has been enhanced by replacing rebars with CFRP. The bent stiffness has slightly improved by replacing with less diameter of CFRP rods and stirrups. In addition, the CFRP bars showed considerable resistance and hardly showed plasticity during apply loading indicating that the CFRP is suitable material to replace steel reinforcement.

Near-component testing of materials for cylinder heads to determine thermomechanical fatigue under superimposed high-frequency mechanical loads

Due to higher combustion chamber temperatures and pressures in efficient combustion engines, both the high-cycle and thermomechanical fatigue loads on service life-critical components, such as the cylinder head, are increasing. Material comparisons and analysis of damage behavior are very expensive and time-consuming using component tests. This study therefore develops a test method for cylinder head materials that takes into account the combined loading conditions from the above-mentioned loads and allows realistic temperature transients and gradients on near-component samples. The near-component cylinder head sample represents the failure-critical exhaust valve crosspiece and is tested in a test rig specially designed with the aid of conjugate heat transfer simulations. In the test rig, the sample is subjected to thermal stress by a hot gas burner and to mechanical stress by a high-frequency pulsator. Optical crack detection allows permanent observation of fatigue crack growth and crack closure during the test. Fractographic and metallo-graphic examinations of the fracture areas as well as analyses of the damage patterns show that loads close to engine operation can be set in this way and their influences on the damage can be monitored.