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Equivalent Strut Method for the Modelling of Masonry Infill Walls in the Nonlinear Static Analysis of Buildings

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Abstract

In the seismic analysis of a framed building with masonry infill walls, it is necessary to model the effect of the walls on the lateral stiffness, strength and ductility of the building. The equivalent strut method is convenient for modelling the walls in a large building. However, an appropriate axial load versus deformation relationship for the strut is required in a nonlinear static method of seismic analysis, such as the pushover analysis. The present study proposes a nonlinear axial hinge property for the strut, with suitable performance levels. First, the equivalent strut method and the suitability of two approaches available in the literature for modelling the properties of the struts, are briefly discussed. Next, the nonlinear axial load versus deformation relationship is developed based on experimental data compiled from the literature. The parabolic–plastic relationship is idealized as a tri-linear axial hinge property, so that it can be incorporated in commercial software for undertaking pushover analysis. Next, the use of the hinge property is demonstrated in the pushover analyses of two framed reinforced concrete buildings. The pushover curves based on the proposed hinge property shows improved modelling of the inelastic drifts of the buildings. Although the modelling of a wall using a single strut has limitations, the proposed methodology is practical for a pushover analysis of a building.

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Abbreviations

B :

Breadth of section

D :

Depth of section

d :

Length of the equivalent strut, equal to the diagonal length of the infilled panel

f a :

Allowable compressive strength along the diagonal of a wall based on slenderness ratio

\( f_{bs}^{/}\) :

Design bond shear strength between masonry units and mortar

h :

Height of centre-line of beam from top of footing

h / :

Clear height of the wall

l :

Centre-line to centre-line width of bay

l / :

Clear length of the wall

R :

Axial load in the equivalent strut

R c :

Load in the equivalent strut at local crushing of the corners of the infill wall

R s :

Load in the equivalent strut at shear cracking of the infill wall

R dc :

Load in the equivalent strut at diagonal compression failure of the infill wall

R u :

Ultimate strength of the equivalent strut

t :

Thickness of wall

α c :

Coefficient measuring the length of the wall in contact with the column

δ :

Axial deformation of the equivalent strut

ε :

Axial strain in the equivalent strut

ε 0 :

Strain in the equivalent strut when the strength is attained (R/R u attains the value of 1) = 0.0025

ε u :

Strain in the equivalent strut till the strength is retained = 0.004

ε 1, ε 2 :

Strain in the equivalent strut at the diagonal compression failure of a slender infill wall

ϕ :

Diameter of bars

μ :

Coefficient of internal friction between masonry units and mortar

θ :

Angle of inclination of diagonal of the panel, with respect to horizontal

θ eff :

Angle of inclination of strut considering the length of wall in contact with the column

σ c :

Average normal stress on wall in contact with column

τ b :

Average shear stress on wall in contact with beam

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Authors and Affiliations

  1. School of Mechanical and Building Sciences, Vellore Institute of Technology, Vellore, India

    A. Adukadukam

  2. Department of Civil Engineering, Indian Institute of Technology Madras, Chennai, 600036, India

    A. K. Sengupta

Authors
  1. A. Adukadukam
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  2. A. K. Sengupta
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Correspondence to A. K. Sengupta.

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Adukadukam, A., Sengupta, A.K. Equivalent Strut Method for the Modelling of Masonry Infill Walls in the Nonlinear Static Analysis of Buildings. J. Inst. Eng. India Ser. A 94, 99–108 (2013). https://doi.org/10.1007/s40030-013-0042-y

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  • DOI: https://doi.org/10.1007/s40030-013-0042-y

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