Research Outputs
Monotonic response of exposed base plates of columns: Numerical study and a new design method
This paper describes a numerical study of the behavior of exposed base plates of columns under the action of axial and bending loads. The aim of this research is to evaluate numerically the failure mechanisms on stiffened and non-stiffened base plates and propose a new design method. The effects of base plate thickness, location of anchor rods, location of stiffeners and tensile strength of anchor rods were considered in the analysis. Sixteen finite elements simulations were performed considering different combinations of the above mentioned parameters. The results show a fragile response in the base plates when high resistance anchor rods are used. The anchor rods worked as fuse elements in base plates with a large thickness or many stiffeners. Additionally, the models with anchor bars located outside of the column flanges showed lower flexural strength and rotational stiffness compared to the models with anchor rods located between column flanges. The simulations showed that the base plate strength was determined by the simultaneous failure mechanisms of two or more components, different to what is stated in current design guides. Finally, the new method is suitable to design base plates with stiffened and not stiffened configurations, which unlike traditional design methods, show a good adjustment with numerical models.
A nonlinear model for multilayered rubber isolators based on a co-rotational formulation
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.
Damping assessment of lightweight timber floors under human walking excitations
Vibrations on timber floors are among the most common serviceability problems in social housing projects. The presence of low damping levels on these floors could cause excessive vibrations in a range of frequency and amplitude that generate discomfort in users. This study focuses on the influence of the damping ratio in the dynamic serviceability of social housing timber floors due to walking excitations. More than 60 human-walking vibration tests were conducted on both laboratory and in-situ timber floors. The floors were instrumented with accelerometers, and fundamental modal damping ratios were estimated by applying Enhanced Frequency Decomposition Domain (EFDD) and Subspace Stochastic Identification (SSI) methods. The vibration dose value (VDV) was used to estimate the dynamic serviceability of floors. The results indicated that timber floors had an impulsive-type vibration response, with fundamental damping ratios between 1.9% and 14.8%, depending on their constructive characteristics. The in-situ floors had damping ratios between two to three times greater than the laboratory floors due to the presence of non-structural elements. Finally, it was possible to demonstrate that the floors with the highest damping ratios reached lower vibration dose values and, therefore, a better dynamic serviceability performance.
Damage assessment of the May 31st, 2019, Talcahuano tornado, Chile
On May 31st, 2019, a tornado hit the city of Talcahuano, Chile, generating significant damage to structures and leaving one person dead. The objective of the present paper is to report on damage to structures in Talcahuano. A preliminary survey was performed by the Municipality of Talcahuano and covered the entire affected area with a cellphone web application used to report the severity and distribution of damage. A more comprehensive damage survey was conducted in the Brisa del Sol neighborhood in the Medio Camino area by the UCSC team to assess the damage distribution within an area with well-defined and homogeneous building typologies. The results of the field surveys showed that the tornado behaved as a skipping tornado and that most damage to houses consisted of wall opening damage, roof sheathing failure, and wall cover removal (EF0), followed by partial roof removal(EF1). It was noticeable that self-built systems (house additions) were more damaged than original houses, which may be explained by the fact that such structures do not always meet minimum building standards. It is recommended that field surveys conducted by municipalities and the Ministry of Social Development considertypical damage types rather than just categories such as minor, moderate, or major. Finally, it is recommendedthat the feasibility of implementing mitigation measures such as stricter wind load provisions and dual-objective tornado design philosophy in the Concepci´on-Talcahuano area be analyzed.
Non-Destructive assessment of the elastic properties of Low-Grade CLT panels
The use of cross-laminated timber panels (CLT) made of low-grade structural timber has steadily increased in developing countries. These panels usually present several natural defects, which can cause a high local variation of their orthotropic elastic properties, generating future structural serviceability problems. Our work aims to estimate the local variability of the elastic properties in low-grade CLT panels by combining nondestructive transverse vibration testing, numerical simulations, and regional sensitivity analysis (RSA). Four three-layer Radiata pine CLT panels were subjected to transverse vibration tests with supports at four points. Besides, a series of numerical simulations of the panels, considering the local variability of the elastic properties of the panels in eight zones, were carried out using the finite element method. Then, RSA analysis was performed to study in which ranges of values the panels’ elastic properties generated lower differences between the measured versus simulated dynamic properties. Finally, a structural quality control indicator was proposed for the CLT panels based on keeping low the probability that the elastic properties in the central zones do not exceed minimum acceptable values. The results obtained suggest that the proposed methodology is suitable for segregating CLT panels with high concentrations of defects such as pith presence.
Damage assessment of squat, thin and lightly-reinforced concrete walls by the Park & Ang damage index
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.
Damage identification of unreinforced masonry panels using Vibration-Based Techniques
Several damage indicators based on changes in modal properties validated for homogeneous materials were applied to detect damage in an unreinforced masonry cantilever panel. Damage was created by a “clean diagonal cut” at the center of the specimen which length was progressively extended towards the specimen’s corners. Numerical simulations were employed to determine the modal response at several damage states and this data was used to calculate the damage indicators. Those indicators presenting a good performance were then applied to identify damage on a physical specimen tested in the laboratory. The outcomes of this study demonstrated that vibration-based damage detection in unreinforced masonry structures can be satisfactorily performed.However, the identification of the damage spatial distribution using vibration-based methods in unreinforced masonry structures is still difficult. To improve the prediction of damage distribution, a large number of measurement points need to be considered to obtain an acceptable level of resolution.
Seismic and coastal vulnerability assessment model for buildings in Chile
This article proposes a vulnerability assessment model for evaluating buildings’ expected seismic performance, as well as their vulnerability to tsunamis. The objective of this assessment is to provide appropriate information for decision makers regarding the need of repairs and reinforcement of buildings or other mitigation measures that need to be applied in a territory. A procedure for assessing seismic vulnerability and another methodology for evaluating tsunami vulnerability faced by coastal structures is presented. Finally, a method that integrates both procedures is proposed, providing a combined index of vulnerability. The assessment model was applied to the central area of the city of Talcahuano, Chile, which was affected by the 2010 Maule earthquake and tsunami.
Variation in the modal response of retrofitted unreinforced masonry walls at different levels of damage
This article presents the results of an experimental campaign conducted on a set of four unreinforced masonry walls at full scale. The purpose of this study is to assess, using non-destructive methods, the impact of retrofitting and damage on the modal response of masonry wall systems. Each wall underwent a sequence of increasing cyclic displacements applied by an actuator at the upper end of the specimen. Modal tests based on vibrations were performed both before and after rehabilitation, as well as during the sequence of increasing displacements. It was demonstrated that frequencies can identify progressive damage when the maximum crack is about to occur, as well as the effect of wall retrofitting when mass contribution is considerable. However, the modal assurance criterion indicator (MAC) fails to properly identify a trend of decreasing correlations as progressive damage increases; instead, it is sensitive to detecting maximum crack and instability conditions. Furthermore, it was determined that the coordinated modal assurance criterion indicator (COMAC) does not identify the damage distribution as expected. However, the cumulative COMAC provides a useful tool for quick visualization and interpretation of COMAC behavior. Finally, a novel damage indicator was tested, MACVF, which improves the trend and successfully identifies the most damage-sensitive mode, especially when the maximum level of damage is reached, giving MAC values below 80%. In addition, frequency variations ranged from 70% to 110% when TRM and WWM retrofitting techniques were applied.
The physical and mechanical consequences of incorporating industrial residues into mortar and concrete mixtures for eco-friendly marine constructions
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.