António Sousa Gago

Development of an innovative seismic strengthening technique for traditional load-bearing masonry walls

Traditional non-reinforced masonry walls are particularly prone to failure when subjected to out-of-plane loads and displacements caused by earthquakes. Moreover, singularities such as openings in façades may trigger local collapse, for either in-plane or out-of plane motion. Bearing in mind all the former limitations, STAP, with the scientific support of ICIST and LNEC, has been developing a reduced intrusiveness seismic strengthening methodology for traditional masonry structures. The technique consists in externally applying Glass Fibre Reinforced Polymer (GFRP) composite strips to one or both faces of walls. Connection between GFRP composite strips and masonry substrate is enhanced through specifically detailed anchorages or confinement connectors. This technique has been developed and studied through an extensive series of experimental tests, which are briefly reviewed. This paper focuses more deeply on the latest experimental program, aimed at the characterization of the masonry-GFRP composite interface behaviour. This testing program comprised 29 masonry specimens, strengthened with externally bonded GFRP composite strips with anchorages. The testing variables were the number and spacing of anchorages as well as the loading history type: monotonic or repeated. Results clearly show that the use of anchorages dramatically enhances bond behaviour and that its number and spacing have a significant effect on deformation capacity and a less pronounced effect on strength. Based on experimental evidence, this paper also provides a calculation model and ULS safety assessment procedure for out-of-plane strength of reinforced masonry walls. This calculation model leads to interaction curves on strengthened masonry walls subjected to compression and out-of-plane flexure.

Mechanical Characterization of Masonry Walls With Flat-Jack Tests

The results from an experimental campaign on old masonry buildings from Lisbon are presented and discussed. The tests aim at the evaluation of the masonry deformability properties in compression and the shear strength parameters based on flat-jack testing technique. Tests were carried out in both internal brick masonry walls and external rubble limestone masonry walls. The evaluation of the shear parameters was done according to a new testing technique—shear tests onmasonry walls with flat-jacks—involvingmore than one masonry unit. One of the goals is the calibration and development of this testing technique and to show its first application to the test of rubble stone masonry walls. For that, the experimental technique is fully explained in this paper, and the results of some in situ tests are used to discuss the calibration procedure. Because of the characteristics of the walls, in particular, the great heterogeneity and thickness of the external masonry walls, the application of the flat-jack testing technique involved some uncertainties that are described and debated in this work.

Strengthening of Old Masonry Walls for out-of-Plane Seismic Loading with a CFRP Reinforced Render

This paper presents part of the results of an experimental campaign for the development of a strengthening technique, aimed at retrofitting old buildings by the application of exterior reinforcing render layers to their masonry walls. The experimental campaign comprised tests with out-of-plane loading on both strengthened and non-strengthened masonry walls. The strengthening layer material, hereby designated as CFRP (Carbon Fibre Reinforced Polymer) reinforcing render, is an innovative material for the seismic retrofitting of masonry walls. The reinforcing render material consists of a lime-based mortar reinforced with a carbon fibre mesh, applied on one or both facings of a masonry wall. This solution was developed to provide the masonry wall with improved mechanical properties, while respecting the main principles for a proper rehabilitation of old buildings.

A simplified methodology for the seismic assessment of masonry buildings with RC slabs

Abstract The present paper aims to contribute to the knowledge concerning the seismic assessment of load bearing masonry buildings with reinforced concrete slabs. The final goal of the present research was to propose a simple, yet accurate, methodology to assess the seismic safety of existing masonry buildings. The methodology here presented was based on the so-called ICIST/ACSS methodology with major improvements such as the extension to load bearing masonry wall buildings and the consideration of the effects of one of the most common strengthening solutions for masonry walls, here referred to as reinforced plastering mortar, as well as the possibility of considering four levels of increasing refinement: global, by alignment, by wall panel and by wall element. An extended research was performed on the existing methodologies to evaluate the seismic structural risk of load bearing masonry buildings, briefly describing methodologies similar to the one proposed, namely all of those that have in common the fact that they are based in the physical comparison between the resisting and acting shear forces at all storeys and along the two orthogonal horizontal directions. A case study is presented to check the applicability of the proposed methodology. The case study showed that the proposed methodology is relatively simple to apply and has a sufficiently good accuracy when compared with alternative methodologies. The degree of refinement of the analysis (global, by alignment, by wall panel and by wall element) must be taken into consideration and successively more complex analyses may be required when the results of simpler analyses are inconclusive.

Structural window frame for in-plane seismic strengthening of masonry wall buildings

ABSTRACT This article describes the initial development stages of a structural window frame system for the in-plane seismic strengthening of load-bearing masonry wall buildings. The solution implemented ultimately aims to stiffen (and strengthen) the opening such that the wall would behave as if there were no opening. This is achieved by installing a structural steel window frame composed of a profile forming a closed ring inside the opening, properly tied to the surrounding masonry wall. The strengthening concept was validated by means of a series of tests in which two approximately 1:2 geometric scale physical specimens with a similar central opening were cyclically tested to failure. One of these specimens (UMW) was unreinforced whereas the other (RMW) had a UPN profile internal ring tied at the corners and at mid-length and mid-height of the opening by means of threaded rods with chemical anchors. The material of these walls was common rubble masonry with lime-based mortar and render. The experimental results show that the strengthening technique leads to a significant increase in strength and in-plane deformation capacity, as well as in terms of cumulative dissipated energy at collapse. Nonlinear numerical specimens of the tested walls were also developed and calibrated.