The use of the finite element method in the design of reinforced concrete slabs and beams has bec... more The use of the finite element method in the design of reinforced concrete slabs and beams has become a generally accepted practice in recent times and when designing structural members, both ultimate and serviceability limit states are required to be considered in the consequent analyses. This paper presents a simplified method to the nonlinear analysis of reinforced concrete slabs and beams for serviceability and ultimate limit states. The method allows for the use of simple design equations familiar to all structural engineers undertaking reinforced concrete designs. Using the finite element method, plate elements and simplified constitutive properties, a nonlinear algorithm is developed which results in the accurate estimation of the displacements during loading as well as a design ultimate loading. The proposed model and nonlinear algorithm is validated and verified against three experimental case studies which show the accuracy and relevance of the given nonlinear solution. The...
The aim of this investigation is the development of a passive vibration isolator with high-static... more The aim of this investigation is the development of a passive vibration isolator with high-static stiffness to bear static load while limiting the static displacement and providing lower-even-zero dynamic stiffness required to reduce the basic natural frequency resulting in an increased frequency range over which attenuation can be achieved. A passive vibration isolator integrated a dynamic vibration absorber with a negative stiffness spring is proposed. The dynamic behavior of the new isolator supporting a lumped mass is investigated using force and displacement transmissibility equations. The force and displacement transmissibility equations are derived by modelling the dynamic system as a two-degree-of-freedom system rather than a single-degree-of freedom system as that of a traditional passive vibration isolator. A unique constraint on the negative stiffness ratio $$\alpha$$ for the isolator’s stable operation is developed. The design of such an isolator is further demonstrated ...
The paper proposes a simple method which optimises the design of plane, rigid no sway frame struc... more The paper proposes a simple method which optimises the design of plane, rigid no sway frame structures based on the system buckling load. It is centred on either maximising the buckling load or minimising the weight of the structure, or both; and to have all stories buckling at the same time. The approach to calculate the system buckling load is derived and also presented. The optimisation method is applied to various frames examples and the results are compared to that obtained from a system buckling analysis performed with ANSYS finite element analysis (FEA) software. The proposed optimisation procedure proved successful for no sway multi-story rigid frames, as validated by the acceptable percentage differences of below 5% from the FEA analysis.
International Journal of Engineering and Technology, 2016
Presented in this paper is an experimental investigation on the load capacity of a scaffolding fr... more Presented in this paper is an experimental investigation on the load capacity of a scaffolding frame. Effects on load carrying capacity of base jacks, bracing and using of buckled pipes are investigated. Especially, bracing a scaffolding frame with steel wire strand is experimentally studied and the results are compared with that of a frame braced with pipes.
Journal of Computational and Nonlinear Dynamics, 2009
Based on the high precision direct (HPD) integration scheme for linear systems, a high precision ... more Based on the high precision direct (HPD) integration scheme for linear systems, a high precision direct integration scheme for nonlinear (HPD-NL) dynamic systems is developed. The method retains all the advantages of the standard HPD scheme (high precision with large time-steps and computational efficiency) while allowing nonlinearities to be introduced with little additional computational effort. In addition, limitations on minimum time step resulting from the approximation that load varies linearly between time-steps are reduced by introducing a polynomial approximation of the load. This means that, in situations where a rapidly varying or transient dynamic load occurs, a larger time-step can still be used while maintaining a good approximation of the forcing function and, hence, the accuracy of the solution. Numerical examples of the HPD-NL scheme compared with Newmark’s method and the fourth-order Runge–Kutta (Kutta 4) method are presented. The examples demonstrate the high accu...
This paper presents a simple, practical method of modelling non-destructive impacts macroscopical... more This paper presents a simple, practical method of modelling non-destructive impacts macroscopically, where the impact force and post-impact motion of the impacting bodies are of primary concern. The main focus is use of the model for simulating the dynamics of impact dampers used to control the response complex structures. A spring-damper pair is used to model the contact surface between the damper mass and the structure. The key to such a model is the ability to define the contact surface spring stiffness and damping parameters, which does not relate to simple mechanical properties under high-rate loading. A method is developed to derive these parameters by making use of experimentally measured coefficient of restitution and contact time of an impact. The model is able to represent contact force and elastic deformation during an impact process. A simple structure, controlled by an impact damper, is used to compare theoretical and experimental results and demonstrate the validity of the resulting spring-damper model. The results demonstrate that the spring-damper model can be effectively used in situations where the impulse-momentum model fails.
An impact damper is a freely moving mass, constrained by stops, located on the structural system ... more An impact damper is a freely moving mass, constrained by stops, located on the structural system to be controlled. As the system is excited dynamically, the impact mass moves relative to the structure, resulting in impacts between the mass and the stops, dissipating energy as heat, noise and high frequency vibrations. Whilst the use of impact dampers for single-degree-of-freedom (SDOF) systems has received a significant amount of attention, investigations into their interaction with multiple-degree-of-freedom (MDOF) systems is rare. This paper presents results of a series of experimental investigations into the effect of an impact damper on a MDOF primary system. The effects of the size of the impact mass, clearance between the impact mass and the stops, excitation type and excitation location are considered. The results in some instances do not correspond with those found for control of SDOF systems1 in particular, increased size of impact mass does not necessarily lead to an increase in damping for all modes. Also, the effect of clearance is unpredictable, particularly for higher modes. The paper raises these and other issues which require consideration if impact dampers are to be used to control the dynamic response of MDOF systems.
With the intension of developing a simple method for system buckling analysis for engineering pra... more With the intension of developing a simple method for system buckling analysis for engineering practice, a story buckling method for evaluating the system buckling load of a plane rigid frame is suggested. The method is developed based on the idea that at lower modes a plane sway frame buckles in story and story stiffness is getting to zero as the system getting close to the corresponding mode of buckling at that story. The stiffness of any story of a plane sway frame can be found with the stiffness without loading and then modified by a negative stiffness which represents the effect of vertical loads on the horizontal stiffness. P-∆ effect is first considered independently by letting the modified stiffness equal to zero and the system buckling load by first order analysis is obtained. To take P-δ effect into account, the buckling load from the first order analysis is modified with a modification factor and an estimation of buckling load of the whole system is obtained. Application examples are presented and the results are compared with those from FEA of the whole system. The simplicity and accuracy of the suggested method are demonstrated. The restraints of the method for application are discussed.
The use of the finite element method in the design of reinforced concrete slabs and beams has bec... more The use of the finite element method in the design of reinforced concrete slabs and beams has become a generally accepted practice in recent times and when designing structural members, both ultimate and serviceability limit states are required to be considered in the consequent analyses. This paper presents a simplified method to the nonlinear analysis of reinforced concrete slabs and beams for serviceability and ultimate limit states. The method allows for the use of simple design equations familiar to all structural engineers undertaking reinforced concrete designs. Using the finite element method, plate elements and simplified constitutive properties, a nonlinear algorithm is developed which results in the accurate estimation of the displacements during loading as well as a design ultimate loading. The proposed model and nonlinear algorithm is validated and verified against three experimental case studies which show the accuracy and relevance of the given nonlinear solution. The...
The aim of this investigation is the development of a passive vibration isolator with high-static... more The aim of this investigation is the development of a passive vibration isolator with high-static stiffness to bear static load while limiting the static displacement and providing lower-even-zero dynamic stiffness required to reduce the basic natural frequency resulting in an increased frequency range over which attenuation can be achieved. A passive vibration isolator integrated a dynamic vibration absorber with a negative stiffness spring is proposed. The dynamic behavior of the new isolator supporting a lumped mass is investigated using force and displacement transmissibility equations. The force and displacement transmissibility equations are derived by modelling the dynamic system as a two-degree-of-freedom system rather than a single-degree-of freedom system as that of a traditional passive vibration isolator. A unique constraint on the negative stiffness ratio $$\alpha$$ for the isolator’s stable operation is developed. The design of such an isolator is further demonstrated ...
The paper proposes a simple method which optimises the design of plane, rigid no sway frame struc... more The paper proposes a simple method which optimises the design of plane, rigid no sway frame structures based on the system buckling load. It is centred on either maximising the buckling load or minimising the weight of the structure, or both; and to have all stories buckling at the same time. The approach to calculate the system buckling load is derived and also presented. The optimisation method is applied to various frames examples and the results are compared to that obtained from a system buckling analysis performed with ANSYS finite element analysis (FEA) software. The proposed optimisation procedure proved successful for no sway multi-story rigid frames, as validated by the acceptable percentage differences of below 5% from the FEA analysis.
International Journal of Engineering and Technology, 2016
Presented in this paper is an experimental investigation on the load capacity of a scaffolding fr... more Presented in this paper is an experimental investigation on the load capacity of a scaffolding frame. Effects on load carrying capacity of base jacks, bracing and using of buckled pipes are investigated. Especially, bracing a scaffolding frame with steel wire strand is experimentally studied and the results are compared with that of a frame braced with pipes.
Journal of Computational and Nonlinear Dynamics, 2009
Based on the high precision direct (HPD) integration scheme for linear systems, a high precision ... more Based on the high precision direct (HPD) integration scheme for linear systems, a high precision direct integration scheme for nonlinear (HPD-NL) dynamic systems is developed. The method retains all the advantages of the standard HPD scheme (high precision with large time-steps and computational efficiency) while allowing nonlinearities to be introduced with little additional computational effort. In addition, limitations on minimum time step resulting from the approximation that load varies linearly between time-steps are reduced by introducing a polynomial approximation of the load. This means that, in situations where a rapidly varying or transient dynamic load occurs, a larger time-step can still be used while maintaining a good approximation of the forcing function and, hence, the accuracy of the solution. Numerical examples of the HPD-NL scheme compared with Newmark’s method and the fourth-order Runge–Kutta (Kutta 4) method are presented. The examples demonstrate the high accu...
This paper presents a simple, practical method of modelling non-destructive impacts macroscopical... more This paper presents a simple, practical method of modelling non-destructive impacts macroscopically, where the impact force and post-impact motion of the impacting bodies are of primary concern. The main focus is use of the model for simulating the dynamics of impact dampers used to control the response complex structures. A spring-damper pair is used to model the contact surface between the damper mass and the structure. The key to such a model is the ability to define the contact surface spring stiffness and damping parameters, which does not relate to simple mechanical properties under high-rate loading. A method is developed to derive these parameters by making use of experimentally measured coefficient of restitution and contact time of an impact. The model is able to represent contact force and elastic deformation during an impact process. A simple structure, controlled by an impact damper, is used to compare theoretical and experimental results and demonstrate the validity of the resulting spring-damper model. The results demonstrate that the spring-damper model can be effectively used in situations where the impulse-momentum model fails.
An impact damper is a freely moving mass, constrained by stops, located on the structural system ... more An impact damper is a freely moving mass, constrained by stops, located on the structural system to be controlled. As the system is excited dynamically, the impact mass moves relative to the structure, resulting in impacts between the mass and the stops, dissipating energy as heat, noise and high frequency vibrations. Whilst the use of impact dampers for single-degree-of-freedom (SDOF) systems has received a significant amount of attention, investigations into their interaction with multiple-degree-of-freedom (MDOF) systems is rare. This paper presents results of a series of experimental investigations into the effect of an impact damper on a MDOF primary system. The effects of the size of the impact mass, clearance between the impact mass and the stops, excitation type and excitation location are considered. The results in some instances do not correspond with those found for control of SDOF systems1 in particular, increased size of impact mass does not necessarily lead to an increase in damping for all modes. Also, the effect of clearance is unpredictable, particularly for higher modes. The paper raises these and other issues which require consideration if impact dampers are to be used to control the dynamic response of MDOF systems.
With the intension of developing a simple method for system buckling analysis for engineering pra... more With the intension of developing a simple method for system buckling analysis for engineering practice, a story buckling method for evaluating the system buckling load of a plane rigid frame is suggested. The method is developed based on the idea that at lower modes a plane sway frame buckles in story and story stiffness is getting to zero as the system getting close to the corresponding mode of buckling at that story. The stiffness of any story of a plane sway frame can be found with the stiffness without loading and then modified by a negative stiffness which represents the effect of vertical loads on the horizontal stiffness. P-∆ effect is first considered independently by letting the modified stiffness equal to zero and the system buckling load by first order analysis is obtained. To take P-δ effect into account, the buckling load from the first order analysis is modified with a modification factor and an estimation of buckling load of the whole system is obtained. Application examples are presented and the results are compared with those from FEA of the whole system. The simplicity and accuracy of the suggested method are demonstrated. The restraints of the method for application are discussed.
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