Earthquake Protection of Colonial Bell Towers in Colima,Mexico with Externally Prestressed FRPs

A methodology for the seismic vulnerability reduction of old masonry towers with external prestressing is presented. It is applied at the Colonial bell-towers of the Cathedral of Colima, Mexico, characterized for being a high seismic area (M>7.5). The 3D FE models are calibrated with experimental data and assessed through nonlinear static approaches including the seismic demand and an accurate validated masonry model. Based on an extensive parametric study on different configurations of old masonry towers, it is selected an optimal prestressing force and device. The Colonial towers are retrofitted with four prestressing devices of FRPs to convert them into a high energy-dissipative reinforced masonry. The external vertical prestressing is included at key points identified in the seismic vulnerability assessment. This technique is in compliance with the demand for architectural conservation and may be located without drilling and unbounded in order to be fully removable. The seismic performance is enhanced by increasing force, displacement, and internal confinement. It is observed an upgrading of 35% and 20% of displacement capacity. With these results it is corroborated that external vertical prestressing allows a substantial increment of ductility for seismic energy dissipation purposes.     

Design and Assessment Spectra for Retrofitting of RC Buildings

This article presents a novel approach for deriving Retrofit Design Spectra (RDS) that are intended for use in preliminary development and assessment of seismic upgrading scenarios of existing structures. The new spectral representation relates the characteristics of the intervention method chosen as the core of the upgrading strategy, with the ductility and strength demand of the retrofitted structure. The methodology utilized for the derivation of the RDS is based on the Capacity Spectrum Method where the capacity curve is described by relationships for global and local intervention methods that are parameterized in terms of fundamental response quantities. The proposed spectra provide direct insight into the complex interrelation between the characteristics of the intervention method and the implications of the upgrading scenario on demand. Alternative retrofit solutions are thus assessed in an efficient way. A case study is used to illustrate practical application of the new approach.     

In-Situ Destructive Testing of Ancient Strengthened Masonry Vaults

ABSTRCT

Developing suitable tools to assess the actual structural performance and designing and executing interventions to improve that performance is a key issue in the field of conservation and enhancement of architectural heritage. This article presents the results of five full-scale destructive tests performed on the Castello di San Pietro in Verona (North-East Italy), a building set on a hill above the city and going back to the 19th century under the Habsburg Empire. It evaluates the behavior of the barrel vaults of 5.6 m span, 1.1 m rise, and 27 cm thickness in the original building. Although experimental work is common in the relevant literature, the testing program described here was not performed on reconstructed vaults but on original elements, which can reveal their real behavior more clearly. Four strengthening solutions were also evaluated, in which organic and inorganic fibers were applied to both types of matrix.     

SEISMIC REHABILITATION OF BEAM-COLUMN JOINTS USING FRP LAMINATES

An innovative and practical technique for the seismic rehabilitation of beam-column joints using fiber reinforced polymers (FRP) is presented. The procedure is to upgrade the shear capacity of the joint and thus allow the ductile ftexural hinge to form in the beam. An experimental study is conducted in order to evaluate the performance of a full-scale reinforced concrete external beam-column joint from a moment resisting frame designed to earlier code then repaired using the proposed technique. The beam-column joint is tested under cyclic loading applied at the free end of the beam and axial column load. The suggested repair procedure was applied to the tested specimen. The composite laminate system proved to be effective in upgrading the shear capacity of the nonductile beam-column joint. Comparison between the behaviour of the specimen before and after the repair is presented. A design methodology for fibre jacketing to upgrade the shear capacity of existing beam-column joints in reinforced concrete moment resisting frames is proposed.     

Experimental Study on Postponing the Deboning of FRP Sheets in Masonry Walls

ABSTRACT

A large number of buildings all around the world are constructed of unreinforced masonry. These structures do not act well during earthquakes because of their vulnerable behavior. In last two decades, fiber-reinforced polymers (FRPs) has been used widely in seismic rehabilitation and strengthening unreinforced concrete and masonry structures. One important issue in using FRP composites for strengthening masonry walls is the inopportune debonding of composites from the wall surface; thus, in this article new methods are proposed to further delay the mentioned debonding issue. For this purpose, 13 masonry panels with 100x870x870 mm dimension are strengthened by using carbon and glass FRPs (CFRPs and GFRPs). A variety of strengthening methods such as surface preparation, boring, grooving, nailing, and plaster are used to mount FRP composites to the walls. For each specimen subjected to diagonal compression test, the loading level along with tensile and compressive diagonal displacements are evaluated. In order to assess the effect of FRP composites, four unreinforced masonry walls are tested as well. The results show 110% increase in ductility index of reinforced specimens compared to the unreinforced ones.     

Numerical Analysis of RC Bridge Piers with Rectangular Hollow Cross-section Retrofitted with FRP Jackets

The research presented in this article deals with the seismic retrofit of bridge piers with rectangular hollow cross-section using fiber-reinforced polymer (FRP) jackets. A two-level numerical approach that combines finite element method (FEM) analyses and fiber modeling is proposed. The FEM is used to study the effect of FRP jackets on the properties of concrete. The analyses show that the existing empirical laws for FRP-confined concrete are not suitable for piers with hollow cross-section, as the effect of confinement is not uniform within the cross-section and the stress–strain curves show softening after peak strength. Fiber modeling is used to study the global behavior of reinforced concrete piers with rectangular hollow cross-section wrapped with FRP jackets. To account for confinement, the properties of the concrete fibers are modified according to the results of the FEM analyses. The proposed method is validated against experimental results and used for an extensive parametric study. It is found that the effectiveness of jacketing is conditioned by the axial load, longitudinal reinforcement, and jacket dimensions. An empirical design equation is formulated on the basis of the numerical analyses.     

Large-Scale Experimental Investigation on Mustafa Pasha Mosque

To evaluate the seismic stability of Mustafa Pasha Mosque in Skopje strengthened by an advanced mixed technology, shaking table tests were carried out on a model in scale 1:6. The investigation was performed within the activities of the Sixth Framework Program PROHITECH – “Earthquake Protection of Historical Buildings by Reversible Mixed Technologies”. To define the effectiveness of the proposed strengthening the testing procedure consisted of two main phases: testing of the original model and testing of the strengthened model. The observed seismic behavior and damage during each phase of the testing program were analyzed on the basis of the obtained experimental results.     

Seismic Behavior of FRP-Retrofitted Reinforced Concrete Frames

Although a significant number of studies have been conducted on the behavior of the reinforced concrete beam-column joints retrofitted with FRP materials, limited investigation considered the overall seismic behavior of the retrofitted frames. In this article, experimental and numerical studies are performed on a scaled-down eight-story and two full scaled low-rise ordinary moment resisting frames (OMRFs) retrofitted with FRP at the joints. Additional, rotational stiffness of the joints is implemented into pushover models to predict seismic performance and behavior factor of the retrofitted frames. Results indicate that FRP retrofitting is more effective than steel braces for low- and medium-rise OMRFs.