Dr. Núñez-Castellanos, Eduardo

In this research an experimental study to assess the cyclic behavior of bolted moment connection in racks structures is performed. The effect of bolt pretension in the response is evaluated. Sixteen full-scale steel rack joint configurations were subjected to cyclic load according to the protocol established in AISC Seismic provisions. The cyclic performance was evaluated in terms of hysteretic response, failure mechanism, energy dissipation, stiffness, and rotation on the components. Two different configurations were studied. The results showed that the steel rack connections using a 70 % of bolt pretension can accommodate a 0.8 My at 0.04 rad of drift angle, while the joints without bolt pretension reached values below 0.7 My at 4 % of rotation. The failure mechanism was controlled by weld fracture at 4 % of the rotation. A high dispersion in the energy dissipation pattern was obtained and a drop in energy dissipation of up to 4 times in all specimens tested for a 4 % rotation was developed. This phenomenon is due to the welding rupture between the beam and the L-connector. A degradation of the secant stiffness reached up to 60 % for 2 % rotation. Finally, the most important effect of bolt pretension on the cyclic response of steel rack connections was achieved in the increase of flexural resistance and rotation developed.

Concrete strength assessment is an important topic in evaluating existing structures. Formerly, only destructive tests were employed, limiting the number of tests due to their complexity and cost. Nowadays, the application of non-destructive tests has been booming to determine material strength, offering a more accessible and cheaper strategy than its counterpart. Non-destructive strategies are based on two steps: (1) the identification of the correlation between the concrete strength and another parameter that is easy to measure in situ, and (2) the use of this easy-to-measure parameter to infer the concrete strength in any desired element of the structure. The most common parameter adopted for this purpose is the Ultrasonic Pulse Velocity (UPV). However, the correlation between concrete strength and UPV must be determined via destructive experiments. From the research perspective, attention has focused on determining the correlation coefficient and the range of credibility for estimating the inferred concrete strength. Despite it, this strategy has remained elusive in the fundamental understanding and accounting of the joint dispersion of the concrete strength and the UPV. The present work addresses this knowledge gap by proposing a new correlation method based on probability interpretations to infer the compressive concrete strength from in-situ UPV measurements and including the dispersion evidenced in UPV measurements in both steps mentioned. The results demonstrated that it is possible to determine the confidence interval for the concrete compressive strength given a certain percentile of the UPV measured in situ. Finally, the application of the proposed method is illustrated through a case study, which is representative of different building pathologies. This novel proposal is a foundation to deal with the uncertainties involved in non-destructive tests, inspiring future advances in this field.

In this research the seismic performance of eccentrically braced frames (EBF) with short links using Chilean earthquakes is studied. The study includes nonlinear static and dynamic analyses, calibration of numerical link models with experimental studies, and over 15,000 models analyzed. Results show that higher ductility and deformation are obtained in most archetypes, while models with 8 stories exhibit more stiffness and less ductile behavior. Furthermore, the strength capacity and ductility increase with the increment of the seismic zone and soft type of soil. Moreover, the research provides a table with the seismic design parameters for each archetype group comparing these values with Chilean seismic specifications. Finally, the study concludes that structures designed with more strength and stiffness have a lower collapse probability under extreme events. This research provides valuable information for structural design and includes fragility curves and a discussion of results that can be applied to structural design.