Study of the compressive strength of concrete block prisms: stack and running bond

Estudo da resistência à compressão de prismas de blocos de concreto: juntas sobrepostas e amarradas

Study of the compressive strength of concrete block prisms – stack and running bond

Estudo da resistência à compressão de prismas de blocos de concreto - juntas sobrepostas e amarradas

G. Mohamad^I; P.B. Lourenço^II; H. R. Roman^III

^IUniversidade Federal do Pampa, Curso de Engenharia Civil, Av. Tiarajú, 810, Alegrete, RS, Brasil. [e-mail]

^IIUniversidade do Minho, Departamento de Engenharia Civil, 4800-058 Guimarães, Portugal. [e-mail]

^IIIUniversidade Federal de Santa Catarina, Departamento de Engenharia Civil. 88040-900, Florianópolis, SC, Brasil [e-mail]

ABSTRACT

The main goal of this work is to investigate the nonlinear behavior of concrete block masonry prisms under compression, with an emphasis in the prism deformability and the failure modes. A total of 18 stack-bonded prisms have been tested, using hollow blocks of a single geometry and two different mortar types. To investigate the effect of vertical joints, the bond pattern – stack and running bond – in the prism was varied, by using half units. Finite element analysis of hollow masonry prisms was done utilizing a commercial non-linear finite element code DIANA. The numerical simulation were carried out using non-linear two dimensional 8-node elements and the biaxial stress state material was modeled by a combination of the yield conditions of Rankine and Drucker-Prager. The numerical and experimental results were compared to validate the ability to predict deformation and peak load. The results show that an analytical model cannot be formulated without understanding the interaction between block and mortar. It was observed that: the non-linearities of the masonry correspond to an increase in the lateral strain due to extensive cracking of the material and a progressive increase in the ratio between lateral and axial strains.; the cracks in the three block stacked prisms constructed with a stronger mortar were vertical on both sides; the prisms constructed with a weaker mortar had, as a consequence of localized crushing, also vertical cracks due to stress concentration at some points; the presence of a vertical joint in the prism led to the appearance of separation cracks between the middle block and the vertical mortar joint.

Keywords: concrete blocks, structural masonry, failure mode, compression behavior.

RESUMO

O principal objetivo deste trabalho é investigar o comportamento não linear de prismas de blocos de concreto a compressão, com ênfase na deformabilidade e modo de ruptura. Um total de dezoito (18) prismas com blocos sobrepostos foram testados, usando blocos vazados com uma única geometria e dois traços de argamassa. Para investigar o efeito da junta vertical utilizaram-se dois meios blocos na junta intermediária dos prismas. Utilizou-se o programa comercial DIANA para simular em elementos finitos o comportamento da alvenaria estrutural. As simulações numéricas foram realizadas usando um elemento bidimensional de oito (8) nós e o estado biaxial de tensões do material foi modelado pela combinação das condições de Rankine e Drucker-Prager. Foram comparados os resultados numéricos e experimentais para validar a capacidade de prever as deformações e a carga última do conjunto. Pode se perceber pelos resultados que um modelo analítico não pode ser formulado sem um entendimento das interações entre o bloco e argamassa. Foi observado que a não linearidade da alvenaria correspondeu a um aumento nas deformações laterais devido à extensiva fissuração do material e a um progressivo aumento nas proporções entre a deformação lateral e axial; as fissuras nos prismas de três blocos construídas com argamassa forte foram verticais em ambos os lados; os prismas construídos com argamassa mais fraca tiveram um modo de ruptura por esmagamento e, também, fissuras verticais devido à concentração de tensões em alguns pontos; a presença da junta vertical nos prismas levou a uma fissura de separação entre o bloco do meio e a junta vertical de argamassa.

Palavras-chave: blocos de concreto, alvenaria estrutural, modo de ruptura, comportamento à compressão.

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Received: 13 Aug 2010

Accepted: 14 Apr 2011

Available Online: 19 Aug 2011

Publication Dates

• Publication in this collection
  19 Aug 2014
• Date of issue
  Aug 2011

History

• Accepted
  14 Apr 2011
• Received
  13 Aug 2010