Modified capacity design rule for columns in tall steel MRFs with linear viscous dampers within the framework of Eurocode 8

Abstract

Seismic design codes enforce a set of capacity design rules for steel moment-resisting frames (MRFs) to promote a ductile sway plastic mechanism that involves plastic hinges in beams and column bases. Previous research showed that these capacity design rules may not be effective for tall steel MRFs with viscous dampers under strong earthquakes due to high axial forces in columns. To address this issue, steel MRFs with linear viscous dampers of different stories are designed according to Eurocode 8 along with using a slightly modified conservative capacity design rule. According to this rule, the axial force for the capacity design of a column in the force path of viscous dampers is calculated as the envelope of the axial force from the peak drift state, and, the axial force from the peak velocity state times a scale factor. This envelope axial force value along with the bending moment and shear force from the peak drift state are used to carry out the capacity design of the column by using the formulae of Eurocode 8, i.e. in the same way with a column of a steel MRF without dampers. Incremental dynamic analyses for 44 earthquake ground motions show that the modified conservative capacity design rule results in steel MRFs with viscous dampers that have plastic mechanisms similar to those of steel MRFs without dampers. Moreover, the proposed capacity design rule becomes stricter for buildings with more than 10 stories to address that available analysis methods for structures with dampers underestimate the peak damper forces in the lower stories of yielding tall steel MRFs. More work is needed to extend the findings of this work to the case of steel MRFs with nonlinear viscous dampers.

Modal properties and seismic behaviour of buildings equipped with external dissipative pinned rocking braced frames

“…( 16 ), the time-history of the base rotation is known, and the vector of nodal displacements of the MDOF system is determined via Eqn. ( 14 ). The corresponding circular vibration frequency and added damping ratio due to the dampers located at the tower's base are:…”

“…[5]- [11]), presents some disadvantages, particularly when employed for retrofitting existing buildings. Usually, the addition of dissipative diagonal in existing frames provides an increment of axial forces in the columns and this may lead to premature local failures, as observed numerically in the case of moment resisting frames equipped with nonlinear hysteretic dampers [12], [13] as well as with linear viscous dampers [14]. In order to avoid this, column strengthening may be required, in the case of existing frames [12], or application of specific capacity design rules, in the case of newly designed moment resisting frames [14].…”

Building Back Better: The Case Study of the Fazzini College

“…devices installed within the building frame, in diagonal configurations or V-shaped braces connecting adjacent floors). Such disadvantages concern the increasing of tensile and compressive forces in the columns that can leads to fragile ruptures [12], [13], and the eventual need of localized strengthening of beam-column joints or foundations. Furthermore, the demolition and reconstruction of internal partition walls, the installation of bracings, and the possible structural reinforcement works, may cause downtime of buildings and related indirect costs for the temporary relocation of the activities.…”

The Seismic Retrofit by External Dissipative Systems: A Case Study

“…This type of configuration is widely studied and tested [6]- [10], but it has some disadvantages especially in the case of existing buildings. Generally, tensile and compressive forces increase in the columns leading to fragile ruptures [11], [12] and localized strengthening of beam-column joints or foundations may be necessary. Moreover, in the case of existing buildings the demolition and reconstruction of internal partition walls, the installation of bracings and possible structural reinforcement works, cause downtime of buildings and related indirect costs for the temporary relocation of the activities.…”