Seismic performance of functionally graded diagonal braced structures

This paper investigates the usage of functionally graded beam as a bracing member in building-type structures subjected to severe ground motions. Material distribution of functionally graded beam follows power law form along thickness direction. Equivalent stiffness of functionally graded brace (FGBr) is derived and confirmed analytically through applying strain energy equilibrium and appropriate boundary conditions on Euler-Bernoulli beam element for simulation of brace behavior. The seismic response analyses of single and multi-storey shear-type buildings with FGBrs are performed on lumped mass-stiffness models. This modeling technique is validated in terms of fundamental natural periods by continuous and numerical solutions. The effect of varied Young’s modulus and power law exponent on maximum responses such as displacement, storey drift and base shear is evaluated under both harmonic and severe earthquake motions

Preventing seismic pounding of adjacent structures using viscous wall damper device

Today, a number of researchers are broadly studying the effective implementation of supplemental seismic energy dissipation systems to improve seismic behavior of structures during earthquakes. The current article studies the impacts of employing Viscous Wall Damper devices to couple two adjacent structures on seismic response of the new system. An exclusive finite element algorithm capable of modeling and analyzing structures equipped with special damper systems was used in order to perform a nonlinear time history analysis subjected to seismic excitation. Two ten-story RC framed structures are modeled adjacently in 11 different cases, each representing existence or damping coefficient of the Viscous Wall Damper device. A parametric study has been conducted in each case to assess the effectiveness of implementing Viscous Wall Damper devices on improving seismic behavior of the coupled structure. The considered metrics include rotation and displacement amplitude, plastic hinge formation, and induced element forces. It has been proved that the proposed damper system substantially diminishes and dissipates induced seismic response of the system. Also, it is indicated that the extent to which Viscous Wall Damper device contributes in mitigating seismic responses is highly correlated with the damping coefficient

A new simplified method for anti-symmetric mode in-plane vibrations of frame structures with column cracks

This paper is on the natural frequency and mode shape computation of frame structures with column cracks. First, a model of intact frame structures is built to perform vibration analysis. Beam elements are considered as lumped masses and rotational springs at the storey levels of frames. Equivalent model of columns and lumped mass-stiffness effects of beams have been combined to carry out continuous solution for the anti-symmetric mode in-plane vibrations of frames. In addition, frame systems with multiple column cracks are analyzed in terms of anti-symmetric mode vibration characteristics. Cracks are considered as massless rotational springs in compliance with the local flexibility model. Compatibility and continuity conditions are satisfied at crack and storey locations of the equivalent column, modeled using the Euler–Bernoulli beam theory. The proposed method is tested for single-storey single- and multi-bay, H-type and double-storey single-bay frame systems with intact and cracked columns. Results are validated by those given in the current literature and/or obtained by the finite element analyses. © The Author(s) 2016

An optimization study for viscous dampers between adjacent buildings

This paper investigates optimum viscous damper capacity and number for prevention of one-sided structural pounding between two adjacent buildings under earthquake motion. The buildings assumed as shear-type structures are modeled by using lumped mass-stiffness technique. Impact forces due to pounding is simulated by nonlinear elastic spring approximation called Hertz model. A parametric study is conducted by varying storey number and stiffness of buildings in addition to the capacity of the viscous dampers. Pounding force and supplemental damping ratio for each case are presented based upon newly defined nondimensional natural frequency parameter ratio. An optimization procedure for determination of viscous damper capacity is developed based on modified supplemental damping ratio equation. Results are compared with each other to clarify the effect of variation in building parameters on pounding forces and viscous damper capacity. © 2016 Elsevier Lt

Effects of isolator properties on viscous damper capacity of base isolated adjacent buildings

Base isolation technique requires clearance at the base level around the building. The exceedance of clearance during seismic motion leads to pounding with either the moat wall or adjacent building. This paper analyzes two base isolated adjacent buildings in terms of pounding and searches for optimum linear viscous damper capacity as pounding prevention measure. Changing dynamic characteristics of base isolation device has considerable effect on pounding behavior of adjacent buildings since the period of isolator bearing shifts the fundamental period of the superstructure. For multi-storey buildings, as the number of storey increases, the flexibility of isolated building becomes effective on dynamic behavior and the relative displacement between base and top floors increases. In related with this situation, viscous damper linkage for prevention of pounding may be considered as seismic mitigation solution for base isolated multi-storey buildings. The analyses to find out impact forces and damper capacities are carried out for varied isolator characteristics and storey numbers of buildings. The optimization procedure of linear viscous damper capacities for fixed-base adjacent buildings is modified for base isolated buildings. © JVE INTERNATIONAL LTD