Nicola Tarque

Structural Behaviour and Retrofitting of Adobe Masonry Buildings

Earth is one of the most widely used building materials in the World. Different types of adobe dwellings are made to assure protection and wellbeing of the population according to the diverse zones needs. Therefore, it is important to study the structural behaviour of the adobe masonry constructions, analysing their seismic vulnerability, which may help in preventing social, cultural and economic losses. In the present chapter, an explanation of the seismic behaviour of adobe buildings, a summary of recent research outputs from experimental tests conducted on adobe masonry components and from numerical modelling of full-scale representative adobe constructions are reported. In addition, different rehabilitation and strengthening solutions are presented and results from the testing of retrofitted adobe constructions and components are discussed.

Displacement-Based Fragility Curves for Seismic Assessment of Adobe Buildings in Cusco, Peru

The seismic vulnerability of single-story adobe dwellings located in Cusco, Peru, is studied based on a mechanics-based procedure, which considers the analysis of in-plane and out-of-plane failure mechanisms of walls. The capacity of each dwelling is expressed as a function of its displacement capacity and period of vibration and is evaluated for different limit states to damage. The seismic demand has been obtained from several displacement response spectral shapes. From the comparison of the capacity with the demand, probabilities of limit state exceedance have been obtained for different PGA values. The results indicate that fragility curves in terms of PGA are strongly influenced by the response spectrum shape; however, this is not the case for the derivation of fragility curves in terms of limit state spectral displacement. Finally, fragility curves for dwellings located in Pisco, Peru, were computed and the probabilities of limit state exceedance were compared with the data obtained from the 2007 Peruvian earthquake.

Development of a Fragility Model for the Residential Building Stock in South America

South America—in particular, the Andean countries—are exposed to high levels of seismic hazard, which, when combined with the elevated concentration of population and properties, has led to an alarming potential for human and economic losses. Although several fragility models have been developed in recent decades for South America, and occasionally used in probabilistic risk analysis, these models have been developed using distinct methodologies and assumptions, which renders any direct comparison of the results across countries questionable, and thus application at a regional level unreliable. This publication aims at obtaining a uniform fragility model for the most representative building classes in the Andean region, for large-scale risk analysis. To this end, sets of single-degree-of-freedom oscillators were created and subjected to a series of ground motion records using nonlinear time history analyses, and the resulting damage distributions were used to derive sets of fragility functions.

Nonlinear Dynamic Analysis of a Full-Scale Unreinforced Adobe Model

This paper describes the results of a numerical study of a full-scale adobe building model tested on a shaking table. Material properties of adobe masonry were calibrated to represent the wall in-plane seismic behavior, based on a prior numerical analysis of an adobe wall carried out by the authors. The inelastic part of the constitutive model was represented by a softening curve in tension and by a hardening/softening behavior in compression; thus, the fracture energy is a key issue in the modeling process. A finite element model that relies on a homogenous continuum approach was developed in Abaqus/Explicit software. The damage evolution in the numerical simulation represented fairly well the experimental crack pattern, for in-plane and out-of-plane seismic effects. Overall, the calibrated material properties and the explicit solution scheme proved to be appropriate for simulating the seismic behavior and predicting capacity of unreinforced adobe structures subjected to seismic loading.

Evaluation of a Rope Mesh Reinforcement System for Adobe Dwellings in Seismic Areas

Throughout the world millions of people are at unacceptable risk because they live in unreinforced earthen dwellings, which have consistently shown extremely poor structural behavior during earthquakes. This article presents a design procedure for the structural reinforcement system for one-story earthen constructions located in seismic areas. The proposed reinforcement consists of a mesh made of nylon ropes which envelopes completely all the earthen walls and maintains structural integrity even after the walls have been significantly damaged. It is thought that its use has the potential to protect the lives of millions of families which are currently are at risk, and the integrity of invaluable earthen historical monuments.

An Extensive Survey of the Historic Center of Cusco for Its Seismic Vulnerability Assessment

This paper presents the main important typological data collected during an extensive survey carried out on the buildings of the historic center of Cusco, Peru. These data will represent the basis for a future analysis devoted to large scale seismic vulnerability assessment, to develop, in a structured and efficient manner, policies and measures for the seismic risk mitigation. Starting from the collection of available data and from the historical analysis of the urban development of the center, also accounting for earthquakes of the past, the most representative architectural typologies are identified. Moreover, statistical analyses are carried out, in order to detect the most recurrent structural details. On these bases, the main potential fragilities are identified, giving a preliminary idea of the structural behavior of the considered buildings under seismic forces.

Bell Towers of Lima’s Cathedral: An Architectural-Engineering Combined Seismic Study

This paper focuses on the seismic evaluation of the Bell Towers of Lima’s Cathedral. The church, which dates back to 1535, has been modified and reconstructed several times over the centuries, changing its structural assembly in terms of lightening and strengthening. Focusing on the massive 45 m tall towers, linear kinematic analyses have been performed in order to evaluate their vulnerability. The results show how its actual performance is far below the safety requirements of the Peruvian code. Such code, however, lacks of regulations aimed at increasing structural safety of existing buildings and, thus, it does not provide any reference on the minimum safety level to reach on a monumental construction such as the Cathedral. A simple intervention using steel ties has been proposed in order to increase such performance on nearly all the considered collapse mechanisms, however the reference value of structural safety, due to absence of other prescription, has been set as the ultimate limit state for new constructions.

Non-linear Modelling of a Geomesh-Reinforced Earthen Wall Subjected to Dynamic Loading

Earthen structures externally reinforced with geogrid mesh are becoming a viable alternative for improving the seismic vulnerability of adobe dwellings. The ductile properties of the geogrid provide the necessary deformability to the overall structure so that it may resist a moderate earthquake with certain damage and prevent loss of life. This practice has been studied thoroughly, on an experimental basis, in countries like Peru, but an adequate numerical model that simulates the combined cyclic and non-linear behavior of the adobe and the geogrid reinforcement is still a work in progress. This research aims to improve a previous model of a geomesh-reinforced adobe wall where the geogrid was idealized as a linear-elastic material with an equivalent initial elastic modulus. Now, the new constitutive law for the geogrid reproduces a non-linear elasto-plastic stress-strain relationship which aims to simulate the hysteretic cycles of a real cyclic pushover test of an geomesh-reinforced adobe wall. Lastly, the calibrated numerical model is subjected to dynamic base loadings with the aim of simulating earthquakes of varying magnitudes. These results will be useful for future studies to evaluate the seismic performance of reinforced earthen structures.

Development of Fragility Curves for Confined Masonry Buildings in Lima, Peru

This paper aims at investigating the seismic fragility of confined masonry (CM) structures in Lima, Peru, which can be used to perform earthquake scenarios at urban scale. A database describing the geometric properties (walls density, building area, height) of this type of structure was developed using data from field surveys. This information was complemented with results from experimental tests to compute a large set of capacity curves using a mechanical procedure. These models were tested against a set of ground motion records using the displacement-based earthquake loss assessment (DBELA) procedure, and the structural responses were used to derive fragility functions for four building classes. The resulting fragility curves were convoluted with seismic hazard curves to evaluate the annualized expected loss ratio and annual collapse probability.

Evaluation of the Ground Motion Amplification at Poggio Picenze (Italy)

The study presented here evaluates the ground motion amplification effects at the site of San Felice Martire church, a historical construction located at Poggio Picenze (L’Aquila, Italy). To characterize the soil profile at the site of investigation field geological observations, boreholes and geophysical tests from previous campaigns were gathered. Dynamic soil properties of the identified soil profile were obtained by the test results from selected literature. Then, the amplification effects at San Felice church’s site was estimated using fully 1D stochastic site response analyses and for the object motion seven real records compatible to the Italian code-based spectrum referred to 475-year return period. The set of real records was downloaded from SEISM-HOME web portal. The stochastic analyses allowed to simulate 1,000 different soil profiles and to run 1,000 simulations, taking into account the inherent variability and uncertainty in the soil profile and on the seismic demand.