Experimental investigation of small-scale clay blocks masonry walls with chases under compression

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Abstract

The clay block structural masonry is the most common building system in Brazil, being used even in buildings with ten or more floors. Sometimes, when the buildings are already in use and the total load is fully completed, the dwellings users need to change hydraulic, gas or electrical installation position in masonry walls, cutting the structural elements. This is the most critical problem for building masonry safety because it was not originally predicted during design. The aim of this study was to evaluate the influence of chases on the mechanical behavior of structural masonry walls under compression using clay blocks small-scale models with proportions of 1:5. Three chase positions and depth were tested, as follows: horizontal, vertical and inclined chases, with depths of 20%, 30% and 50% in relation to masonry thickness. Also, concentric and eccentric loads were considered during tests. From experimental results, it was possible to conclude that the presence of horizontal and inclined chase changed the failure mode characteristics of masonry. For masonry with mid-height horizontal chase, it was found to have a significant drop on the residual strength. From experimental tests, it was possible to obtain a relationship between the strength reduction and the chase depth and load conditions. The strength reduction due to the second-order effects induced by the horizontal chases can be successfully evaluated by normative models, specially EN 1996-1-1.

Introduction

Structural masonry building is one of the most important construction systems because of its economical, modular and feasible solution for social interest dwellings. Masonry is a complex material built from different units and mortar that induce an anisotropic behavior for the composite. Because of this, when the structural masonry is subjected to vertical loading, it is important for designers that the stress-strain relationship achieves the ultimate compressive strength and the elastic modulus, in order to preview the load capacity and in-plane displacement of masonry. Sometimes, when the buildings are already in use and the total load is fully completed, the dwellings users need to change hydraulic, gas or electrical installation position in masonry walls. This is indeed the most critical problem for safety on masonry buildings. Actually, stands out a lack of knowledge on the mechanical properties of composite elements like masonry with chases, which is important to evaluate the building global security factor and the local instability of the structural elements. Mojsilovic [1] stated that the amount of research work in this area is rather modest, only with tests on typical masonry elements with vertical and horizontal chases. So far, studies of masonry chases are a quite recent matter, with limited works regarding out-of-plane displacements and the chase directions, if horizontal, vertical and inclined.

The execution of chases can affect considerably the mechanical behavior of masonry walls, although at the present, a complete understanding of the mechanisms involved in the deformation, failure and the strength reduction is not fully explained. It is believed that the development of a theoretical model of universal application is a rather hard task. Thus, the present study evaluates the influence of chases on the mechanical behavior of masonry walls subjected to vertical load. Because of this, the main goal of this article is to evaluate comparatively the effects of chases presence on the mechanical behavior of structural masonry under compression using small-scale models (1:5). The research evaluated the strength reduction, in-plane and out-of-plane displacement of chased masonry produced by the variation of cuts depth, the eccentricity of loads, and the chase position, when horizontal, vertical and inclined. The results allow to propose a practical relation between the compressive strength reduction and the chases depth.

Section snippets

Scale effect on masonry

To evaluate the chase effect on masonry walls it was developed small-scale units to reproduce comparatively the strength reduction for different chase directions. Due to this, one of the greatest challenges is how to develop reliable models using small-scale to represent the behavior of structures in a full-scale. The size effect studies are important for structural and geotechnical engineer problems for large elements to be tested systematically [2]. This intrinsic concept of physically

Masonry chases

Standards and buildings codes establish two methods to determine the load-bearing capacity of masonry [13], [14], [15], [16], [17], [18], [19]. One of the methods consists of testing specimens like prisms, wallets or walls and then correlate them with the compressive strength of masonry demanded from the project, considering the slenderness coefficient of reduction, cross section area of the wall and the total load applied. The other method consists of using an empirical formula and graphs to

Materials and experimental program

It was performed in a series of mechanical tests on small-scale masonry using reduction proportion of 1:5. The first step of this research was producing the clay blocks units, prisms and wallets to determine the relations between strength and deformation of masonry components in small and full-scale. It used a common geometry of clay blocks found in Brazil, with specific modular dimensions in full-scale of 140 mm × 190 mm × 290 mm (thickness × height × length). The units presented solid

Experimental results of tests

Except for full-scale masonry walls, the experimental results of masonry components on small and full-scale are presented in Table 4. As expected from experimental results, it was found that there were differences on the compressive strength of small-scale masonry in relation to the full-scale components. Where, the strength relations between small-scale and full-scale depend on each type of component. For example, the fwallet/fprism strength ratio had an increase of 35% between full to small

Strength reduction

The residual strength relation due to a net area reduction were plotted in Fig. 13. It was possible to conclude from experimental results that the chase depth had influenced the masonry residual strength. The residual strength is the load bearing capacity that remains after the object was damaged or, in other words, how much load capacity the masonry can still support, without failing. The residual strength drop was more accentuated for mid-height horizontal chase, as presented in Fig. 14. The

Conclusions

This work was an experimental analysis of the chase influence on structural masonry behavior using small-scale models. The main conclusions to be highlighted are:

  • The presence of horizontal and inclined chases had changed the masonry failure mode in relation to the masonry reference, although for vertical chase it was not observed differences in strength or failure behavior.

  • When it was compared the masonry chase with the same depth of cuts (H30C and H30E) but changing the load conditions

CRediT authorship contribution statement

Alisson Simonetti Milani: Conceptualization, Methodology, Investigation, Writing - original draft. André Lübeck: Validation, Writing - review & editing. Gihad Mohamad: Conceptualization, Supervision. Almir Barros da Silva Santos Neto: Conceptualization, Supervision. Jaelson Budny: Resources, Investigation.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References (40)

  • H.G. Harris et al.

    Structural Modeling and Experimental Techniques

    (1999)
  • A. Quinonez et al.

    Small-scale models for testing masonry structures

    Adv. Mater. Res.

    (2010)
  • S. Petry et al.

    Testing unreinforced masonry structures at reduced scale

    15° World Conference on Earthquake Engineering Lisbon, 2012, Lisbon, Portugal. Proceedings of 15 WCEE

    (2012)
  • D.M. Herbert et al.

    Uniform lateral load capacity of small-scale masonry wall panels

    Mater. Struct.

    (2014)
  • L. Long et al.

    Small-scale modelling of concrete masonry using ½-scale units: a preliminary study

    10th Canadian Masonry Symposium, Banff, Alberta

    (2005)
  • N. Sathiparan et al.

    The scale effect on small-scale modelling of cement block masonry

    Mater. Struct.

    (2016)
  • J.S. Camacho et al.

    Structural masonry: application of small-scale modeling (in Portuguese)

    Technical Boletim of USP Polytechnic School, BT/PMI, São Paulo

    (1997)
  • ABNT. Brazilian Association of Technical Standards. NBR 16868-1: Structural masonry Part 1: Design. Rio de Janeiro,...
  • ABNT. Brazilian Association of Technical Standards. NBR 15961-1: Structural masonry - Concrete blocks Part 1: Design....
  • MSJC. Masonry Standards Joint Committee. TMS 402-08/ACI 530-08/ASCE 5-08: Building Code Requirements and Specification...
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      Citation Excerpt :

      Studies developed before using small-scale models proved to be feasible [1–3]. Authors like Abboud et al. [4], Dhanasekar et al. [5], Quinonez et al. [6], Sandoval et al. [7], Herbert et al. [8], Thamboo and Dhanasekar [9] and Milani et al. [49] pointed out that the small-scale analysis could be representative of the masonry behavior in a general way like failure and strength. Allowing us to conclude that more research is needed to advance in this field, following the evolution of block industry development capabilities.

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