PSI - Issue 18

Bilal L. Khan et al. / Procedia Structural Integrity 18 (2019) 108–118 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

110

3

In this paper, state space approach is being used in MATLAB to analyze an eight storey building with vertical irregularity (weak storey). A comparative study of dynamic performance of three types of passive base isolators is presented, namely High Damping Rubber bearing (HDRB), Low Damping Rubber Bearing (LDRB) and Lead Core Rubber Bearing (LCRB). Parameters like Building displacement, inter-storey drifts, transmissibility of acceleration are compared for isolated building with responses of non-isolated building under near and far field earthquake excitations. Generally the research is carried out focusing on investigating the response of structures with soft storey and factors influencing it and a little research is carried out in investigating the dynamic response of a structure with vertical irregularity, especially the effect of weak storey located at top of the structure. This research focuses on the investigation of performance of three passive base isolation systems under near and far field earthquakes for an eight storey structure having a weak storey at its top. The variation in their behavior under near and far field earthquakes provide a good indication about their limitations and advantages over one another to control the response of vertically irregular structure. The study also serves as the guideline for the structural designers on how to analyze the behavior of the new and already constructed structures with various base isolated systems under various earthquake excitations for an efficient design. The focus should be on all the three parameters (global drift, inter storey drift and transmissibility ratio) as each base isolation system is better in controlling one or two parameters and lacks in controlling the remaining ones. 2. System Description An eight storey building system is under study as shown in figure 1. This building system and its modal parameters are taken from a 2016 research study by Pozo et al. titled “Vibration control of hysteretic base -isolated structures: an LMI approach” and is similar to existing building in Los Angeles, California (Pozo, Pujol, & Acho, 2016). Dynamic model of the system is composed of two coupled subsystems, mainly the super structure and a base isolator. The dynamics parameters of the structure mass, stiffness and damping are presented in Table 1. Mass, stiffness and damping are usually estimated through system identification. However, they can also be calculated using the material properties and structural specifications. Mass of the structure is usually the tributary weight of the slab, stiffness is calculated through Euler’s formula (12 EI/L3), however, damping ratio cannot be calculated therefore it is assumed as an average for design and analysis of concrete structures, for example 5% for concrete, 5% – 10% for masonry and 2% for steel structures. 1.1. Research Significance

Table 1. Model parameters of the structure (Pozo et al., 2016). Storey Mass (kg)

Stiffness (N/m)

Damping (Ns/m)

1st Floor 2nd Floor 3rd Floor 4th Floor 5th Floor 6th Floor 7th Floor 8th Floor

2580 2247 2057 2051 2051 2051 2051 2051

12913000 10431000 7928600 5743900 3292800 1674400

11363 10213

8904 7578 5738 4092 2228

496420

49620 704 Table 1 shows the model parameters of eight storey building. At the base level of structure parameters (mass, stiffness & damping) would be decided based on passive base isolator and isolation layer (Ground Floor Slab). Percentage change in masses from 1st floor to 4th floor with respect to each other are 12.9%, 8.45% and 0.29% decrease. From 4th floor to 8th floor 0% decrease in mass. Percentage change in stiffness from 1st floor to 4th floor