EFFECT OF STIFFNESS MODIFIER ON PREDICTED SEISMIC PERFORMANCE OF RC BUILDINGS

Abstract

In current practices, concrete cracking is considered to reduce the stiffness of the member. Many researchers and codes provide the recommended modified stiffness modifiers for RC Structures. Stiffness modifiers are used in linear analysis to account for the development of concrete cracking and bond-slip of steel reinforcement. Before the inception of the stiffness modifier, designers used the entire stiffness section, which yielded more reinforcement in members, resulting in an uneconomical design and sometimes contradicting the strong column and weak beam concepts. Therefore, the performance of the structure must be verified using newly advanced techniques such as performance-based design based on FEMA. The introduction of stiffness modifiers makes the structure more flexible, increasing the structure's time period and attracting less seismic forces in the member. After using the stiffness modifier, the damage in the structure is reduced during the earthquake while producing more drift in the member. To consider this, a smaller modifier value is provided for the beam compared to the column described in the code. In all the codes worldwide, modifier value is not provided according to the height and shape of the structure. The main objective of the present work is to compare the seismic performance and damage of different heights of structures. Pushover analysis has been carried out for the non-linear static analysis. Fragility analysis was used to check the damage to the structures. It has been observed that the performance point increases after using the stiffness modifier. Also, a percentage change in performance points has been observed as the number of storeys increases. Fragility curve and damage probability matrices have given that, after using the stiffness modifier, the performance of the building improves and experiences lesser damage.