Abstract
This article introduces an analytical model to compute the monotonic force–displacement response of in-plane loaded unreinforced brick masonry walls accounting for walls failing in shear or flexure. The masonry wall is modelled as elastic in compression with zero tensile strength using a Timoshenko beam element. Its cross-section properties (moment of inertia and area) are continuously updated to capture the non-linearity that results from flexural and shear cracking. For this purpose, diagonal cracking of shear critical walls is represented by one Critical Diagonal Crack. The ultimate drift capacity of the wall is determined based on an approach evaluating a plastic zone at the wall toe. Validation against results of cyclic full-scale tests of unreinforced masonry walls made with vertically perforated clay units shows that the presented formulation is capable of accurately predicting the effective stiffness, the maximum strength and the ultimate drift capacity of the wall. It outperforms current empirical code equations with regard to stiffness and ultimate drift capacity estimates and yields similar results concerning strength prediction.
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Abbreviations
- M :
-
Global bending moment (Nm)
- M e :
-
Bending moment at which decompression in overall cross section occurs (Nm)
- M e,i :
-
Bending moment at which decompression in cross section part i (for i ∈ {1, 2}) occurs (Nm)
- M i :
-
Bending moment in cross section part i (for i ϵ {1, 2}) (Nm)
- N :
-
Global normal force (N)
- N i :
-
Normal force in cross section part i (for i ϵ {1, 2}) (N)
- N 1,2,3 :
-
Normal forces for calculation of residual strength (N)
- V :
-
Global shear force (N)
- V cr :
-
Shear force at which diagonal crack formation starts (N)
- V CP :
-
Shear force triggering failure in flexural walls (N)
- V P :
-
Peak shear resistance (N)
- V R :
-
Residual strength (N)
- V 1,2,3 :
-
Shear forces for calculation of residual strength (N)
- σ 0 :
-
Normal force divided by full cross sectional area of the wall (N/m²)
- σ M :
-
Normal stresses due to global moment (N/m²)
- σ N :
-
Normal stresses due to normal force (N/m²)
- σ T :
-
Normal stresses due to torque moment (N/m²)
- σ xx :
-
Normal stresses in a cross section (N/m²)
- τ xy :
-
Shear stresses in a cross section (N/m²)
- u :
-
Horizontal displacement (m)
- u fl :
-
Horizontal displacements due to flexure (m)
- u sh :
-
Horizontal displacements due to shear (m)
- w :
-
Axial displacement (m)
- δ :
-
Horizontal drift (−)
- δ P :
-
Horizontal drift at peak shear resistance (−)
- δ ult :
-
Ultimate drift (−)
- θ :
-
Rotation (rad)
- θ ult :
-
Rotation at ultimate drift (rad)
- ɛ u :
-
Normal strain masonry is able to sustain at the wall toe (−)
- ɛ xx :
-
Normal strains in cross section (−)
- ɛ 2 :
-
Normal strain in crushed zone dependent on axial loading (−)
- χ :
-
Curvature of a cross section (m−1)
- χ cr :
-
Curvature on bottom crushed zone in shear walls (m−1)
- χ 1,2 :
-
Curvature at ultimate failure in 1st and 2nd bed joint respectively in flexure dominated walls (m−1)
- E :
-
Modulus of elasticity (N/m²)
- G :
-
Shear modulus (N/m²)
- f B,c :
-
Compressive strength of brick (N/m²)
- f B,t :
-
Tensile strength of brick (N/m²)
- f u :
-
Compressive strength of masonry (N/m²)
- μ :
-
Local coefficient of friction (−)
- μ :
-
Global coefficient of friction (−)
- c :
-
Local cohesion (N/m²)
- c :
-
Global cohesion (N/m²)
- A :
-
Cross sectional area of overall cross section (m²)
- H :
-
Height of wall (m)
- H 0 :
-
Shear span of wall (m)
- H crit :
-
Height where the diagonal crack is presumed to commence (m)
- H M :
-
Height where normal stresses due to moment at diagonal crack turn negative (tensile stresses) (m)
- h B :
-
Height of brick (m)
- h cr :
-
Height of crushed zone at wall toe (m)
- h d :
-
Height along which decompression occurs (m)
- I :
-
Moment of inertia of overall cross section (m4)
- I eig,i :
-
Moment of inertia corresponding to centre of gravity of cross section part i (for i ϵ {1, 2}) (m4)
- I eig :
-
Sum of moments of inertia corresponding to respective centres of gravities of parts of cross section (m4)
- I st :
-
Sum of moments of inertia corresponding to parallel axis theorem of parts of cross section (m4)
- L :
-
Length of wall (m)
- L c :
-
Compressed length of overall cross section (m)
- L c,i :
-
Compressed length of cross section part i (for i ϵ {1, 2}) (m)
- L c,v :
-
Virtual compressed length (m)
- L i :
-
Length of wall part i (for i ϵ {1, 2}) (m)
- L i,v :
-
Auxiliary length for computation of shear stress distribution in section part i (for i ϵ {1, 2}) (m)
- L P :
-
Length of plastic normal stress distribution at toe crushing (m)
- l B :
-
Length of brick (m)
- l cr :
-
Length of crushed zone at wall toe (m)
- l cor,i :
-
Length of corner i (for i ϵ {1, 2}) (m)
- T :
-
Thickness of wall (m)
- y CDC :
-
Horizontal distance from wall edge to CDC (m)
- x :
-
Location variable along wall height (m)
- y :
-
Location variable along wall length (m)
- y * :
-
Auxiliary location variable along wall length (m)
- Δl :
-
Discrete step along wall height (m)
- γ :
-
Deformation constraint factor (−)
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Acknowledgements
This study has been supported by the Grant No. 159882 of the Swiss National Science Foundation: “A drift capacity model for unreinforced masonry walls failing in shear”. The authors also gratefully acknowledge the contribution by two anonymous reviewers who provided helpful comments.
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Appendices
Appendix 1: Wall tests used for the validation
The walls and their parameters used in the validation of the model are presented in Tables 2 and 3. The shear modulus G is always taken as ¼ of the elastic modulus E, the tensile strength of a brick (f B,t ) was assumed to be 1.27 MPa for all walls corresponding to the testing campaign by Petry and Beyer (2015a) as values in other reference documents were not provided.
Appendix 2: Comparison of CDC model to wall tests
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Wilding, B.V., Beyer, K. Force–displacement response of in-plane loaded unreinforced brick masonry walls: the Critical Diagonal Crack model. Bull Earthquake Eng 15, 2201–2244 (2017). https://doi.org/10.1007/s10518-016-0049-7
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DOI: https://doi.org/10.1007/s10518-016-0049-7