Shear modulus and stiffness of brickwork masonry: An experimental perspective
Masonry is a composite non-homogeneous structural material, whose mechanical properties depend on the properties of and the interaction between the composite components - brick and mortar, their volume ratio, the properties of their bond, and any cracking in the masonry. The mechanical properties of masonry depend on the orientation of the bed joints and the stress state of the joints, and so the values of the shear modulus, as well as the stiffness of masonry structural elements can depend on various factors. An extensive testing programme in several countries addresses the problem of measurement of the stiffness properties of masonry. These testing programs have provided sufficient data to permit a review of the influence of different testing techniques (mono and bi-axial tests), the variations caused by distinct loading conditions (monotonic and cyclic), the impact of the mortar type, as well as influence of the reinforcement. This review considers the impact of the measurement devices used for determining the shear modulus and stiffness of walls on the results. The results clearly indicate a need to re-assess the values stated in almost all national codes for the shear modulus of the masonry, especially for masonry made with lime mortar, where strong anisotropic behaviour is in the stiffness properties.
Evaluation of the seismic performance of brick masonry walls
Estimating the performance of structural elements requires the assessment of the response of those elements in terms of their response values (i.e. strengths, stresses, drifts, cracks, etc.) against loads and external forces of various kinds. For the seismic performance of masonry structures, until recently this approach was addressed in rather general terms with designers more interested in the survival of the structure in a maximum expected earthquake, with an acceptably low probability of occurrence. This traditional approach to seismic design is being replaced by performance‐based design with the required performance depending on the level of the design seismic forces. This paper provides an overview of some of the methods for the evaluation of the in‐plane resistance of masonry walls, which are already incorporated in national codes. Some results of recent experimental investigations of the shear capacity of in‐plane loaded masonry walls subjected to cyclic loading are also presented with the aim of studying the potential for the application of these new concepts of assessment of seismic performance. The performance of unreinforced masonry walls in relation to the different design performance objectives and performance levels is then discussed. Copyright © 2008 John Wiley & Sons, Ltd.
Seismic analysis of infilled reinforced concrete frames
Abstract This paper presents a numerical method for the analysis of infilled frames subjected to earthquake excitation. The method is based on the concept of equivalent struts used to idealize the infill panels. Properties of the mathematical model are determined using the stiffness matrix method. Dynamic equations of motion are solved numerically in the time domain using the modified step-by-step linear acceleration method known as the Wilson-θ method. The above procedure is implemented into a computer program SAPF (Seismic Analysis of Plane Frames) to be run on an ICL computer. The program has many capabilities such as mesh automatic generation, static, dynamic and spectrum analysis. This program has been used to solve 13 cases of bare and infilled frames in order to assess the effect of different factors such as the presence and continuity of infill panels, the height of the structure, infill material, panel rectangularity ratio and width of the equivalent strut. Results show that infill panels have a great effect on the behavior of such structures. A comparison of this method with existing seismic code formulae showed that the latter overestimate the shear forces in the building due to the fact that they do not consider the effect of infill panels.