Case Study To Evaluate Drift Estimation In Non-Ductile Reinforced Concrete Buildings With Foundation Lap-Splices: Numerical Simulation Work
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Past earthquake damage assessments have shown the seismic vulnerability of older non-ductile reinforced concrete buildings. The life safety-risk these buildings pose has motivated researchers to study, develop, and improve modeling techniques to better simulate their behavior with the aim to prioritize retrofits.
This study focuses on the lap splice detailing at the base of the building in columns, shorter than those recommended by modern codes which consider seismic effects. Current modeling efforts in non-ductile reinforced concrete frame structures have considered the connection at the foundation fixed. This study models the influence of the performance of short lap splices on the simulation of response of an instrumented perimeter-frame-non-ductile building located in Van Nuys, California, and to compare results with those of previous studies of the same building.
The methodology consisted of evaluating the response of a non-ductile concrete building subjected to a suite of ground motions through the comparison of three base connections: fixed, pinned, and a rotational spring modeling the short lap splice. Comparison and performance evaluation are done on the basis of drift as the main performance metric. In the building response evaluation flexure and shear forces in frame elements were also compared using the different base conditions.
The models consist of two-dimensional frames in orthogonal direction, including interior and exterior frames, totaling into 4 frames. The dynamic analysis was performed using SAP2000 analysis software. The proposed rotational spring at the base was defined using the Harajli & Mabsout (2002) bond stress – slip relationship and moment – curvature sectional analysis, applied to 24db and 36db lap splices. Deformation considered flexure and slip. Adequacy of shear strength was checked prior to the analysis to verify that shear failure did not occur prior to either reaching first yield of the column reinforcement or splice capacity.
In this study, the response of the frames using the
proposed rotational spring model was found to be between the fixed and pinned
base conditions with regard to roof displacement and interstory drift ratio,
also termed as story drift ratio. The behavior of the frames changed depending
on the yielding of the longitudinal reinforcement, as depicted by the
interstory drift ratio and displacement. The performance of the building frames
also depended on the ground motion. The N-S and E-W direction frame
computational models considered three and four earthquakes, respectively,
totaling to 14 computational models per base condition. Three computational
models out of the 14 with the proposed rotational spring base condition simulated
recorded roof displacement results with accuracy. In the frame simulations
where yielding of most of the column longitudinal bars was not calculated, the
maximum interstory drift occurred in the upper stories, matching column damage
observations during the event. The findings of the study showed that short lap
splice increases the drift and displacement compared to the fixed base supporting
its effect, i.e. the behavior of a non-ductile reinforced concrete case study
building to an earthquake.