Static Nonlinear Analysis of Coupled Shear Wall

Abstract

A Good amount of research and development in analysis and design of high rise structure has increased understanding about their behaviour. In case of tall structure due to height, the lateral sway of building becomes higher and so, considerations of stiffness rather than strength of structural system, control the design. The degree of stiffness depends primarily on the type of structural systems. Coupled shear wall is one of the lateral load resisting systems. It’s in plane stiffness and strength are very high, so it can resist greater amount of forces. Due to its increased ductility compared to solid shear wall, it is more efficient during seismic condition.

Modeling of structural systems is very important for their realistic analysis and design. Finite element modeling and analysis of coupled shear wall building is carried out using ETABS software. Couples shear wall is modeled considering frame and shell element. Parametric study is carried out to understand the seismic behaviour of coupled shear wall in two and three dimensional models considering different geometry. The parameters considered for the study are depth and span of coupling beam, wall length, wall height (or number of storey). Time period of two and three dimensional models is also compared with time period obtained using fourmula of IS: 1893 (Part – I) 2002. The results of dynamic analysis shows that time period, obtained from codal formula is lower than time computed considering two and three dimensional models for building having more than 10 storey.

Different types of support conditions are considered for calculation of time period and base shear of building. The Types of support considered are fixed, hinged and flexible. The Stiffness of spring support is based on coefficient of sub-grade modulus. Time period and base shear are compared for building having different types of support. Time period is also compared when wall is modeled as shall element and frame element.

In case of nonlinear analysis, coupled shear wall is modeled as frame element. Step by step procedure for static nonlinear analysis of coupled shear wall building is discussed. Comparisons of analysis results of two and three dimensional model are also studied. Results of nonlinear analysis shows that in flexure and shear hinge condition capacity curve (Base shear Vs. Roof displacement) are nearly same for two and three dimensional model. A parametric study is carried out by varying wall length, wall height (number of storey), Span and depth of coupling beam. The earthquake loads applied on the coupled shear wall (CSW) building, are calculated as per equivalent static approach as given in IS : 1893:2002. For the load calculation commercial building is considered, whose plan dimensionl is 36 X 20 m. Capacity and Demand Curves are potted for various buildings. Also failure pattern of wall and coupling beam are studied.

In Dynamic as well as pushover analysis orientation of shear wall is very important. Dynamic and inelastic behaviour of centrally located coupled shear wall is good compared to other type of orientation. Compared to solid shear wall, coupled shear wall possess more ductility and it perform well in seismic conditions. The ductility comparison of different buildings, considering core and coupled core shear wall is carried out through static nonlinear (pushover) analysis for same seismic demand. Results shows that coupled core shear wall are more ductile compared core shear wall for same seismic demand.

Failure pattern of building depends on hinge property, which are used in modeling of pushover analysis. ATC 40 based hinge property represents more ductile failure compared to IS 456 based hinge property.

Finally codal provisions of IS 13920, EC 8 and ACI for analysis and design of coupled shear wall and coupling beam are discussed.

In Chapter one, general aspects of nonlinearity and method of nonlinear analysis is discussed. It also includes objectives of study and scope of work. Chapter two presents the literature review on the topics related to nonlinear analysis, static and dynamic behaviour of coupled shear wall and push over analysis. In chapter three, modeling techniques and application of software ETABS (Extended Three Dimensional Analysis of Building Structures) is discussed. Chapter four describes the analysis and parametric study of coupled shear wall building for static and dynamic analysis considering different support condition. Chapter five, deals with the nonlinear behaviour of coupled shear wall building. The different orientations and their effects on dynamic and nonlinear behaviour of coupled shear wall building are discussed in chapter 6. In chapter 7, nonlinear property of hinge based on IS: 456 and limit state is discussed. The seismic design of ductile wall and coupling beam are also compared. The summary of the study, conclusions and future scope of work is given in chapter nine.

A Good amount of research and development in analysis and design of high rise structure has increased understanding about their behaviour. In case of tall structure due to height, the lateral sway of building becomes higher and so, considerations of stiffness rather than strength of structural system, control the design. The degree of stiffness depends primarily on the type of structural systems. Coupled shear wall is one of the lateral load resisting systems. It’s in plane stiffness and strength are very high, so it can resist greater amount of forces. Due to its increased ductility compared to solid shear wall, it is more efficient during seismic condition.

Modeling of structural systems is very important for their realistic analysis and design. Finite element modeling and analysis of coupled shear wall building is carried out using ETABS software. Couples shear wall is modeled considering frame and shell element. Parametric study is carried out to understand the seismic behaviour of coupled shear wall in two and three dimensional models considering different geometry. The parameters considered for the study are depth and span of coupling beam, wall length, wall height (or number of storey). Time period of two and three dimensional models is also compared with time period obtained using fourmula of IS: 1893 (Part – I) 2002. The results of dynamic analysis shows that time period, obtained from codal formula is lower than time computed considering two and three dimensional models for building having more than 10 storey.

Different types of support conditions are considered for calculation of time period and base shear of building. The Types of support considered are fixed, hinged and flexible. The Stiffness of spring support is based on coefficient of sub-grade modulus. Time period and base shear are compared for building having different types of support. Time period is also compared when wall is modeled as shall element and frame element.

In case of nonlinear analysis, coupled shear wall is modeled as frame element. Step by step procedure for static nonlinear analysis of coupled shear wall building is discussed. Comparisons of analysis results of two and three dimensional model are also studied. Results of nonlinear analysis shows that in flexure and shear hinge condition capacity curve (Base shear Vs. Roof displacement) are nearly same for two and three dimensional model. A parametric study is carried out by varying wall length, wall height (number of storey), Span and depth of coupling beam. The earthquake loads applied on the coupled shear wall (CSW) building, are calculated as per equivalent static approach as given in IS : 1893:2002. For the load calculation commercial building is considered, whose plan dimensionl is 36 X 20 m. Capacity and Demand Curves are potted for various buildings. Also failure pattern of wall and coupling beam are studied.

In Dynamic as well as pushover analysis orientation of shear wall is very important. Dynamic and inelastic behaviour of centrally located coupled shear wall is good compared to other type of orientation. Compared to solid shear wall, coupled shear wall possess more ductility and it perform well in seismic conditions. The ductility comparison of different buildings, considering core and coupled core shear wall is carried out through static nonlinear (pushover) analysis for same seismic demand. Results shows that coupled core shear wall are more ductile compared core shear wall for same seismic demand.

Failure pattern of building depends on hinge property, which are used in modeling of pushover analysis. ATC 40 based hinge property represents more ductile failure compared to IS 456 based hinge property.

Finally codal provisions of IS 13920, EC 8 and ACI for analysis and design of coupled shear wall and coupling beam are discussed.

In Chapter one, general aspects of nonlinearity and method of nonlinear analysis is discussed. It also includes objectives of study and scope of work. Chapter two presents the literature review on the topics related to nonlinear analysis, static and dynamic behaviour of coupled shear wall and push over analysis. In chapter three, modeling techniques and application of software ETABS (Extended Three Dimensional Analysis of Building Structures) is discussed. Chapter four describes the analysis and parametric study of coupled shear wall building for static and dynamic analysis considering different support condition. Chapter five, deals with the nonlinear behaviour of coupled shear wall building. The different orientations and their effects on dynamic and nonlinear behaviour of coupled shear wall building are discussed in chapter 6. In chapter 7, nonlinear property of hinge based on IS: 456 and limit state is discussed. The seismic design of ductile wall and coupling beam are also compared. The summary of the study, conclusions and future scope of work is given in chapter nine.