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Ultra-high performance concrete (UHPC) is an appropriate material to repair and rehabilitate aged structures due to its excellent properties, such as high compressive strength and durability. Several studies have demonstrated the effectiveness of applying UHPC in old buildings as a rehabilitation or repair material, but the bond between concretes needs more investigation. In this sense, the bond between normal-strength concrete (NSC) and UHPC is currently being studied. Three main parameters are responsible for ensuring a good bond: the surface treatment of the substrate (roughness), the wetting conditions, and the mechanical strength of the substrate. Thus, the present study investigated the bond between concretes experimentally. The concrete of the substrate was carried out in three grades: C25, C45, and C60. The repair concretes were C25, C45, C60, and UHPC. The following parameters were evaluated: wetting conditions, air surface dry (ASD), saturated surface dry (SSD), substrate strength, and repair concrete strength. All models received surface treatment by wire brushing. Slant shear and splitting tensile tests were performed to evaluate the mechanical behavior and the failure modes of the bond between concretes. The bond strength was classified and compared to existing predicting models. The results showed that most expressive strength gains occurred in SSD models with lower strength substrates and UHPC. Furthermore, the influence of surface wetting conditions becomes smaller as the strength of the substrate is reduced.

Perforated beams can bring countless benefits compared to traditional plain-webbed beams. However, steel beams with sequential web openings are more susceptible to instabilities, and special care must be taken in a design concerning the failure modes these structures can present. The study presented herein explicitly dealt with the stability behavior of perforated beams with sinusoidal openings. This type of perforated member features smooth-lined openings constructed from a single thermal cut in conventional plain-webbed steel profiles. A broad study was carried out through numerical simulation using the ABAQUS software, in which perforated profiles manufactured with S600E high-strength stainless steel were studied. The use of high-strength steels in perforated profiles is a little explored topic in the literature, despite having a significant impact on the behavior of these elements. With the study carried out, a broad overview of the stability behavior of these members was obtained, especially concerning global stability. A total of 5940 FE models were developed, considering the application of different types of loads. In these models, linear buckling analysis (LBA) and geometrically and materially nonlinear analysis with imperfections (GMNIA) were performed. The results obtained were compared with international design codes, and it was found that some codes fail to represent the behavior of members that present lateral-distortional buckling (LDB) and interactions between local and global failure modes. This behavior is a significant design concern since the studied members had high yield strength, making them more susceptible to interaction-governed failure modes than usual-yield strength members. Additionally, the study found that some design codes do not accurately represent the behavior of members loaded outside the shear center due to the destabilizing effect of loading on these structures.