Cyclic testing of unreinforced masonry walls in two‐way bending

Abstract

An experimental programme was conducted in which eight full-scale unreinforced masonry walls were subjected to cyclic face loading using a system of airbags. Of the eight walls, six contained a window opening and four were subjected to vertical pre-compression. Combined supports at the vertical and horizontal edges ensured that under face loading the walls underwent two-way bending. The test walls were found to possess good post-peak strength and displacement capacity as well as reasonable energy dissipation characteristics. Significant strength and stiffness degradation and non-symmetry of strength in the positive and negative displacement directions were also evident. Discussion of the causes of the aforementioned trends and their implications towards the seismic response of masonry walls is provided. and limited displacement capacity perpendicular to the wall face, slender masonry walls (heightto-thickness greater than 10) are especially prone to out-of-plane failure which has been identified as one of the most dominant modes of failure in masonry construction during seismic loading [1].As part of a long-term goal to reduce the seismic risk posed by URM construction, research is currently underway to develop suitable design and assessment procedures to protect against this type of failure. Research into the out-of-plane seismic response of vertically spanning URM panels [10] has led to the development of a simplified displacement-based (DB) design procedure. DB methods have gained popularity in recent years for the seismic design and assessment of ductile structural systems including multi-storey buildings [11,12], continuous concrete bridges [13] and in-plane masonry walls [14]. The overall aim of the current research is to develop a DB design procedure for two-way spanning masonry walls, which include any class of walls supported on at least one vertical edge and one horizontal edge. However, the development of such a method requires the load-displacement behaviour of two-way walls to be properly understood and characterized through experimental tests under the application of cyclic loading.While a significant amount of experimental research has been conducted into the static strength of URM walls in out-of-plane flexure (e.g. [15-18]), published literature reporting quasi-static cyclic tests or dynamic tests on such wall panels is limited. Most of the out-of-plane cyclic load tests on masonry panels have been performed on one-way spanning walls supported at their top and bottom edges and include tests using standard URM [19-21], as well as URM strengthened by various means including fibre reinforced polymer (FRP) strips [22], expansive epoxy [23] and timber backup framing [24, 25]. Benedetti et al.[26] conducted a study of dynamic shaking table tests on 24 half-scale two-storey masonry buildings which focused on the overall building response with limited attention given to the two-way out-of-plane flexural response of component walls. Cyclic tests on two-way spanning walls in bending are especially rare, bu...

Experimental characterization of the out-of-plane performance of regular stone masonry walls, including test setups and axial load influence

“…Following the same trend, with the second axial pre-compression increment of 114.2 kPa (level 2 to level 3), there was an average increase of 70 and 83 % in M max and M min(hMu) , respectively. The improvement of peak and post-peak capacity of masonry walls with the application of vertical pre-compression is a well-known phenomenon which has been observed and discussed in several past works (for example in Griffith et al (2007)). Moreover, the increase of the maximum overturning moment is strongly affected by the static equilibrium due to the increase of stabilization forces.…”

“…Among the various examples that could be cited here, a highlight for the recent experimental laboratory campaign presented by Restrepo-Vélez et al (2014) and Vaculik et al (2014), wherein a series of static 1:5 scale tests were performed on stone masonry walls with the aim of verifying existing analytical expressions for the computation of their horizontal resistance, and for the late in situ work of Costa et al (2012b) in which a traditional two-storey masonry building was tested by means of the application of quasi-static loads at the building top level in the out-of-plane direction. Some further examples of relevant works were recently published in this field namely by Costa et al (2013a, b), D'Ayala and Shi (2011) and Griffith et al (2007). Nevertheless, the effective knowledge about the out-of-plane behaviour of masonry walls under earthquake action is still limited and the currently available experimental techniques are not completely stabilized and validated.…”

Empirical-Based Infill Model Accounting for in-Plane/Out-of-Plane Interaction Applied for the Seismic Assessment of Ec8-Designed Rc Frames

“…Experimental tests aimed at assessing the OOP behaviour of URM infills and the effects of IP displacement demand on the OOP capacity were performed by different authors ( [7][8][9][10][11][12][13][14][15], among others). In a companion paper [21], the Authors of this study collected in a database the values of secant stiffness and lateral force registered for the above test specimens at first macro-cracking and peak load, as well as the value, if provided, of their ultimate OOP displacement.…”

“…Based on experimental evidences (Angel et al [8], Guidi et al [14], Calvi and Bolognini [13], Griffith and Vaculik [12]), a plastic post-peak behaviour is assumed and the collapse OOP displacement is assumed equal to 3.7 times the predicted displacement at peak load.…”

“…OOP acceleration can produce infills' collapse by their overturning, which is a great risk for life safety as well as an obstacle to escape/rescue operations during seismic emergency [2]: in this sense, the OOP collapse of infill walls is associable to the attainment of the Life Safety Limit State (LS). A great number of experimental and analytical works concerning the IP behaviour of URM infills is available in literature ( [3][4][5][6], among many others) and some analytical and experimental works have been proposed about their OOP behaviour, especially in recent years ( [7][8][9][10][11][12][13][14][15], among others), and concerning the IP-OOP interaction phenomena, i.e., the effects of IP actions on the OOP behaviour and vice versa. For instance, several authors showed through analytical and experimental studies how the IP displacement demand affects the OOP response of infills in terms of capacity and demand acting on them.…”