Seismic behaviour of Confined Masonry Walls

Authors: Miha Tomazevic and Iztok Klemenc

Reference: Earthquake Engg.and Structural Dynamics,Wiley Interscience, March 1997

Summary:

Rational method for modeling of seismic behaviour of CM walls has been carried out based on test results on plain and CM wall with h/l ratio 1.5, made at 1:5 scale. A trrlinear model wherein resistance is calculated as combination of shear resistance of plain masonry and dowel effect of tie-collumn reinforcement. THe method was verified for prototype CM wall with h/l ratio equal to 1.

Conclusion and future Scope:

Monotonic behaviour and actual boundary restraints are assumed in the case of determination of effective stiffness of CM wall panel.  Stiffness degradation has been modelled as a function of effective stiffness of the panel and damage index at characteristic limit states.  Good coorelation between predicted and experimental envelopes has been obtained

Experimental and analytical studies on earthquake resisting behaviour of confined concrete block masonry structures

Authors: Norio Hori, Norio Inoue, Dangol Purushotam, Tetsuya Nishida and Jun Kobayashi (Japan)

Reference:Earthquake Engg. and Structural Dynamics,Wiley Interscience, July,2006

Summary:

Wall specimens made of concrete blocks confined with column ties were tested under cyclic lateral load and simulated by a rigid body spring model that models non-linear behaviour by rigid bodies and boundary springs. Three tests were performed with varying axial stresses and shear span ratio. The results of studies outline the resisting mechanism, indicating that a rigid body spring model is considered appropriate for analysing this type of structures.

Conclusion & Future Scope:

At different axial stresses, shear strength increased with larger axial stress because the shear strength of mortar joint increased. In case different shear span ratio, shear strength  decreased with large shear span ratio: SSR – 0.55 for 2-3 story; 1 – 5-6 story and 1.5 for 7-8 storey building.  Thus, the strength of CM system is primarily controlled by inclined compressive force on a masonry wall and tension strength of tie column reinforcement. In case of large axial stress on tension side due to overturning moment in high reise building, ERD must consider a lower shear resisting capacity of masonry, such as strength and energy dissipating capacity.

Rigid element model for in plane dynamics of masonry walls considering hysteretic behaviour and damage

Authors: Siro Casolo,and Fernando Pena

Reference: Earthquake Engg.and Structural Dynamics,Wiley Interscience, pp 1029-1048, Vol.36 -Feb.2007

Summary:

Specific rigid element approach is propsosed for inplane dynamic analysis of masonry walls whose seismic performance is strongly related to mechanical deterioration and hysteretic energy disssipation. A mechanistic ‘rigid body spring model was adopted which consists of a collection of plane quadrilateral rigid elements connnected to each other by two normal spring and one shear spring at each side.  Separate hysteretic law was assigned for axial and shear deformation between elements. The performance of present approach shown by numerical validation & comparisons with experimental and numerical tests.

Conclusion & Future Scope:

Investigation of complex interaction between strong ground motion and expected damage in relation to the hysteretic and energy dissipation capacity of the material.

Backbone Model for Confined Masonry Walls for Performance Based Seismic Design

Authors: Zahra Riahi, Kenneth J Elwood, S.M. Alcocer (Canada)

Reference: J. Structural Engg., ASCE, June 2009

Summary:

Performance based model is proposed on the basis of both monotonic and reversed cyclic experiements assembled in an database and derived through iterative linerar regression analysis.Specimens with two tie columns, one on either edge of the wall; multiple longitudinal rebar per confining element; no bed joint reinforcement; no openings within confined panel; and a H/L ratio between 0.7-1.2 are considered. Effect of opening on strength characteriestics, capability of exisitng models to predict seismic behaviour for CM walls were studied and validity of predictive equations for specimens with bed joint reinforcement and high axial load were investigated. Models for  cracking shear strength; effect of openings; max.shear strength; crakcing drift capacity; and Ultimate drift capacity were developed.

Conclusion & Future Scope:

The proposed models fails to match recorded response for aspect ratio above 1.2, tie column with one longi.bar, axial stress greater than 0.12fm.  Future tests recommended for CM walls with openings; panel reinforcement; multiple confining elements, or high axial stress.  Tie column transverse reinforcement is one of the design variable that proved insignificant to the ultimate deformation equaiton of this study, hence the factor needs to be studied.  As the current CM codes criteria are mainly rely on conventional force-based equations developed for URM/RM walls, hence the effect of confining element is overlooked, hence incapable of predicting the recorded response with sufficient accuracy.