Dr. Oyarzo-Vera, Claudio

This article proposes a geometrically nonlinear co-rotational model aimed to characterize the mechanical behavior of elastomeric seismic isolators. The model is able to capture the axial and lateral coupling in both axial directions, i.e. compression and tension of the isolator. Also reproduces the instability the loads in tension as well as in compression, and provides theoretical evidence of the non-symmetric behavior of the isolator in these two directions. To validate model results, a quasistatic analysis was performed on a typical isolator with many different shape factors. From the parametric analysis performed, it is observed that buckling loads are higher in tension than in compression. However, as the shape factor of the isolator increases, the behavior in compression and tension becomes symmetric. It becomes apparent that significant differences in normal stresses and strains under tensile and compressives loads are observed for axial loads smaller than 10% of the nominal buckling load. The example presented shows that lateral displacements of about ±25% of isolator radius and tension forces up to 10% of the buckling load are possible without inducing cavitation in the rubber. Accuracy of the model was also tested against finite element model results and experimental data showing satisfactory results. Furthermore, a response-history analysis of an isolated structure is presented and compared for two isolator models: the two-spring model and the model proposed herein. Finally, material nonlinearity was introduced in the dynamic analysis using a Bouc-Wen type element in parallel with the isolator. The responses are similar between models; however, significant differences occur locally in the isolator for high axial loads and/or large lateral displacements.

Damage progression indexes are widely used to evaluate the performance of structural elements in buildings and bridges subjected to seismic actions. Although the Park & Ang damage index is currently implemented in several computational tools, the index has not been calibrated for squat and thin reinforced concrete (RC) elements controlled by shear deformations. It has been observed that the equations originally proposed for the Park & Ang damage index are unsuited for these types of structural elements, which are characterized by a failure mode dominated by shear instead of flexural deformations. The index was evaluated in this study for squat, thin and lightly-reinforced concrete walls using experimental data from a program comprising monotonic and reversedcyclic load testing of 25 RC squat cantilever walls. The experimental program included walls, with and without openings, having height-to-length ratios equal to 0.5, 1.0 and 2.0. Full-scale wall thickness and clear height were 100 mm and 2.4 m, respectively. The specimens were built using three different types of concrete (normal-weight, light-weight and self-consolidating) with nominal compressive strength of 15 MPa. A novel formulation for the parameter β included in the Park & Ang damage index was proposed in this study using key variables of the wall specimens such as web reinforcement ratio and cumulative ductility. Comparison between the computed damage index and crack pattern evolution observed in wall specimens at different damage states demonstrated the ability of the model to numerically assess the damage of the wall specimens. Hence, this new formulation proposed for parameter β leads to a better estimation of damage for this particular type of elements when applying the broadly used Park & Ang damage index.

In pursuit of a more sustainable construction material with the potential to improve bioreceptivity in marine environments, this study investigates the feasibility of incorporating three industrial residues—steel sludge (“Conox”), mytilid mussel shells, and wheat straw fibers—as partial substitutes for cement and sand. The research focuses on evaluating the physical and mechanical properties of mortar and concrete mixtures containing these residues, both individually and in combination. Additionally, it assesses the metal leaching potential of concrete incorporating Conox sludges into the environment. The results show that mixture containing 10% Conox sludges as a sand substitute exhibit the highest mechanical strength but also increased porosity, water absorption, and chloride ion diffusion. The addition of mussel shells and straw fibers generally reduced mechanical properties and increased porosity in mortars, though a 20% mussel shell substitution maintained mechanical strength and chloride ion diffusion in the concrete. The combination of mussel shells with Conox sludges allowed the concrete to retain its mechanical properties, although it also increased porosity and chloride ion penetration, which may limit its use where impermeability is key. However, this increased porosity could benefit coastal erosion control structures like breakwaters and revetments, and sea walls. Moreover, metal leaching from concrete incorporating Conox sludges remained within established safety limits. Despite these challenges, the materials show promise for non-structural applications or projects where sustainability is prioritized. Our research lays the foundation and opens new possibilities for future investigations that innovate in the combination of industrial wastes, aiming to create more sustainable construction materials with a reduced impact on biodiversity.

Non-destructive vibration-based damage identification techniques are especially attractive for assessing damage in structures of high historical and architectural value. So far, most studies have focused on slender structures built using relatively homogeneous materials. In this study, global damage identification methods based on vibration response parameters were applied for identifying damage in an unreinforced masonry full-scale house model (non-homogeneous material and non-slender structure). The house model was dynamically loaded using an eccentric-mass shaker. Structural damage to the walls was initiated by increasing the amplitude of the applied load. At each damage state, a modal test was performed by impacting the walls with a calibrated hammer. Statistically significant variations of modal frequencies and the modal assurance criteria were considered as suitable parameters to identify damage. It was concluded that different sets of modes can be found for different states of damage because of material degradation, change in the support and connectivity conditions, and breaks in the members continuity generated by damage. All these changes are reflected in variations of modal frequencies and modal assurance criteria. It was also established that prior to identifying the damage distribution on the entire building, it was necessary to determine how the modal frequencies were related to each wall.

Base isolation is an efficient strategy for protecting structures, especially in countries with high seismic risk, such as Chile. This paper presents the conceptual model, mathematical model, experimental validation and numerical analysis of a roller type base isolation device that aims to solve problems of limited tensile strength (compared to its compressive strength) and lateral instability of all types of rubber bearing isolators when faced with elevated axial load. The conceptual model describes the device’s components and operation. The mathematical model establishes its constitutive law based on the equilibrium equations formulated considering large lateral displacements. Experimental tests were run on a shake-table with a load frame to simulate the isolator’s interaction with the superstructure, considering a combination of the device’s design parameters, in order to identify their effect. In the numerical analysis, six simple frame buildings were modelled and subjected to a seismic record using the proposed roller isolator. Error parameters were obtained between the numerical predictions and the experimental results in each loading and unloading cycle, varying between 1.6% and 5.1% for dissipated energy and 4.0% to 17.7% for the magnitude of force. The proposed device worked as a seismic isolator, reducing the structure’s response in a magnitude order in relation to the building fixed on its base.