Low-rise Shear Walls Research Articles

Behavior of Framed Shearwalls Made of Corrugated Steel under Lateral Load Reversals

Reinforced concrete buildings with shearwalls are very efficient to resist earthquake disturbances. In general, reinforced concrete frames are governed by flexure and low-rise shearwalls are governed by shear. If a structure includes both frames and shearwalls, it is generally governed by shearwalls. However, the ductility of ordinary reinforced concrete framed shearwalls is very limited. The experiments on framed shearwalls made of corrugated steel was recently reported. It was found that the ductility of framed shearwalls can be greatly improved if the thickness of the corrugated steel wall is appropriate to the surrounding reinforced concrete frame. If the thickness of the corrugated steel wall is too large when compared to the surrounding frame, the ductility will be reduced. It is shown in this paper that the fiber-reinforced plastic composites can be used to strengthen the critical regions of the reinforced concrete frames, so that the seismic behavior (including ductility and energy dissipation capability) is greatly improved.

Unified approach to shear analysis and design

The theory of reinforced concrete originated in the late 19th century with the development of the linear theory for bending. As the first rational theory in reinforced concrete behavior, it satisfied Navier's three principles of mechanics of materials: stress equilibrium; strain compatibility; and constitutive law of material. By the 1950s this linear bending theory was generalized to become the Bernoulli compatibility truss model which covered both the linear and non-linear theories for bending, axial load and their combination. For shear and torsion, however, a rational theory that satisfies Navier's principles took the entire 20th century to develop. By the 1990s the theory for shear and torsion contained four truss models: the equilibrium (plasticity) truss model; the Mohr compatibility truss model; the rotating-angle softened-truss model; and the fixed-angle softened-truss model. Together with the strut-and-tie model for local regions and the Bernoulli compatibility truss model for bending and axial load, a unified theory of six rational models for reinforced concrete was established.The two non-linear softened-truss models have capacities for predicting the behavior of reinforced concrete elements subjected to in-plane shear and normal stresses. These two models satisfy the two-dimensional stress equilibrium, Mohr's circular strain compatibility and the softened biaxial constitutive laws of concrete. As a result, they can be used to predict the strength as well as the load-deformation history of a membrane element. The rotating-angle softened-truss model is simple to use and is adequate for situation that does not require the ‘contribution of concrete’ ( V c ), while the fixed-angle softened-truss model is more complex but is capable of predicting V c . The rotating-angle softened-truss model has been used to analyze four types of structures that are subjected predominantly to shear: low-rise shear walls, framed shear walls, deep beams and shear transfer zones. In addition, both softened truss models are used to construct the concrete stiffness matrices used in the finite element analysis. These matrices contain only three moduli in the diagonal elements. The assumption that Poisson ratios are zero in the non-diagonal elements leads to undesirable limitations of applicability. To overcome this weakness, a general model of the stiffness matrix is proposed that includes two additional Poisson ratios. All five material properties in the general matrix are currently being established by new biaxial tests of panels using proportional loading and strain-control procedures.

ASEISMIC CONSTRUCTION AND DESIGN METHOD FOR MULTI-STOREY COMPOSITE STRUCTURES

Using a newly introduced ductile low-rise shear wall with vertical keyways, a seismic resistance design approach for a practical type of composite structure, which consists of a reinforced concrete frame in the bottom floors and masonry structures in the upper floors, has been presented. The purpose of the new design approach is to improve the earthquake resistance of the whole structure by increasing the energy dissipation capacity in the bottom part of the structure. Non-linear analysis shows that, by adopting the newly proposed ductile low-rise shear wall in the bottom of the structure, the lateral deflection of the structure is not much more than that of a structure using conventional solid low-rise shear walls under a small or moderate earthquake excitation, and that even under the attack of a severe earthquake, a stable structural response can be expected for the proposed structure. Thus it is easy for such a structure to achieve the design objective of ‘minor damage in a small earthquake and prevention of collapse in a severe earthquake’ and the design method is of practical value for similar types of composite structures.

Experimental study of Reinforced Concrete framed shearwall with friction damping control devices

In order thoroughly to improve the brittle failure characteristics of conventional lowrise shearwalls, this paper puts forward a new type of ductile lowrise shearwall scheme with friction damping control devices and carries out an experimental study on one piece of conventional framed lowrise shearwall and two pieces of the new type of lowrise shearwall under cyclic reversed loads. Moreover, from the basic assumption, after analysing the edge frame, wall panel and controlling forces, calculation formulae have been derived for the new type of lowrise shearwall. The calculated values given by the formulae show good agreement with the test values.

Softened Truss Model Theory for Shear and Torsion

The softened truss model theory, which has recently been developed for shear and torsion of reinforced concrete members, is summarized in a systematic and unified manner. Eleven equations involving fourteen variables are derived from equilibrium, compatibility, and materials conditions to solve the shear problem. An additional six equations involving six more variables are required to treat the torsion problem. The theory was successfully applied to structures where shear behavior predominates, such as low-rise shearwalls, framed wall panels, deep beams, and shear transfer strengths. It also worked very well for members subjected to torsion. Efficient algorithms are proposed to solve the simultaneous equations for different types of structures. The theoretical predictions are in good agreement with the test results in all cases. The prediction includes not only the shear and torsional strengths, but also the deformations of structures throughout their post-cracking loading history.

Softening of Concrete in Low-Rise Shearwalls

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