Impact of vertical member shortening on the seismic performance of reinforced concrete buildings

Vertical members such as columns and shear walls undergo time-dependent deformations in multi-story buildings due to creep and shrinkage. This causes columns and shear walls to shorten unevenly, especially if their cross-sectional areas, reinforcement ratios, or loading conditions differ. Differential shortening throughout the structure may result from this over time. This can result in unexpected seismic drift, affecting the building’s ability to withstand lateral displacements caused by earthquakes. This study examines the impact of vertical member shortening, caused by creep and shrinkage during construction, on the seismic performance of RC buildings. It also evaluates the suitability of the Static Equivalent Lateral Force (SELF) methods, as outlined in the IBC-2000 (US) and Euro Code 8 (Europe), for RC structures experiencing such shortening under seismic conditions. Two real earthquakes, 1940 EL-Centro and Parkfield, were analyzed across two categories of RC buildings: moment-resisting frames and those with shear walls, designed per ACI 318-19 standards and simulated via Midas Gen’s finite element method. Each category included buildings of six, nine, and twelve stories. The investigation involved two scenarios: SCAT, which accounts for creep and shrinkage, and SCAN, which does not. The results indicate that in the case of momentresisting frame buildings, the maximum column shortening resulting from SCAT exceeds that obtained from SCAN by 68128%, while in the case of shear wall buildings, the maximum vertical member shortening increases by 40-82%. Under the 1940 EL-Centro earthquake, SCAT’s maximum story drift was higher than SCAN’s by 9-15% in multi-story building frames and 38% in shear walls. Also, the limits of the fundamental period of vibration estimated by IBC-2000 and EC-8 are conservative for both cases of SCAN and SCAT. Additionally, the study revealed that IBC-2000’s base shear estimations could be nonconservative for the 1940 EL-Centro earthquake, while EC-8’s predictions were generally conservative for both SCAT and SCAN scenarios.