Seismic retrofit of steel tall buildings with bilinear oil dampers

This paper presents retrofit solutions for existing tall buildings by utilizing supplemental damping devices, namely oil dampers with relief valve (bilinear oil dampers). To this end, multiple retrofit schemes are presented for a benchmark 40-story steel moment-resisting frame building designed in 1970s in North America. This building has a high collapse risk based on the regional seismic hazard and rigorous nonlinear response history analyses that were conducted with state-of-the-art nonlinear building model representations. Nine retrofit schemes are designed based on three damping levels and three vertical damping distribution methods (i.e. effective, direct and balanced shear force proportional damping distributions). The oil dampers are designed with the aid of a multi-degree of freedom (MDF) performance curves tool. A balanced distribution method is proposed to provide an alternative vertical damping distribution method for frames that exhibit yielding. To assess the proposed retrofit schemes, rigorous nonlinear response history analysis of the retrofitted schemes are carried out in accordance to ASCE 41-13 recommendations. The results suggest that supplemental damping can significantly reduce the collapse risk and control the drift distribution along the building height. The effectiveness of the vertical damping distribution methods is strongly influenced by the extent of frame inelasticity, which in turn depends on the supplemental damping level. Although damper velocity demands may exceed the expected values in a low probability of occurrence seismic event, the corresponding damper forces remain relatively constant. In addition, a large amount of linear supplemental damping is provided at low and moderate ground shaking intensities

Adaptive numerical method algorithms for nonlinear viscous and bilinear oil damper models subjected to dynamic loading

Adaptive numerical method algorithms are presented for the numerical simulation of the hysteretic behaviour of nonlinear viscous and bilinear oil dampers within a finite element program for nonlinear dynamic analysis of frame structures under earthquake excitations. The adaptive algorithms are applicable for computing high-precision solutions for nonlinear viscous and bilinear oil dampers with valve relief that are typically represented mathematically with a nonlinear Maxwell model. The algorithms presented possess excellent convergence characteristics for viscous dampers with a wide range of velocity exponents and axial stiffness properties. The algorithms are implemented in an open source finite element software, and their applicability and computational efficiency is demonstrated through a number of validation examples with data that involve component experimentation as well as the utilization of full-scale shake table tests of a 5-story steel building equipped with nonlinear viscous and bilinear oil dampers

Seismic Assessment and Retrofit of Pre-Northridge High Rise Steel Moment Resisting Frame Buildings with Bilinear Oil Dampers

This paper presents quantitative information on the effectiveness of seismic retrofit solutions using bilinear oil dampers for seismically deficient existing tall steel buildings. For this purpose, a benchmark 40-story steel space moment-resisting frame building is studied that represents 1970s design practice in North America. Rigorous seismic performance assessment based on ASCE 41 recommendations reveals a high collapse risk for the existing building. The local engineering demand parameters are comprehensively assessed to quantify the impact of seismic retrofit on steel columns and column splices, which are particularly vulnerable due to the time of construction. Multiple retrofit schemes are explored with numerous damping levels and vertical damping distribution methods. The dampers are designed via a recently developed multi-degree-of-freedom performance curves method. A new balanced vertical damping method is proposed to account for the effects of frame inelasticity. This strongly depends on the supplemental damping level, and it determines the effectiveness of the employed vertical damping distribution method. The results indicate that the proposed retrofit strategies can minimize the collapse risk of the tall building. It is shown that the balanced vertical damping distribution method provides the most uniform drift distribution along the building height. Despite the reduction in story drift ratios, the axial force demand in exterior columns remains relatively high in the bottom stories regardless of the seismic retrofit solution. On the other hand, bilinear oil dampers produce relative constant forces despite exhibiting higher velocity demands than expected.</jats:p

A practical method for seismic retrofit of tall buildings with supplemental damping

Current simplified design methods for buildings with supplemental damping devices are mainly based on single-degreefreedom (SDF) shear-models. Common errors of such methods are attributed to the linearization of nonlinear damping and stiffness, higher building vibration modes and flexural deformations that may be ignored in the damper design phase. In tall buildings, dampers are typically placed at certain levels only, leading to an irregular vertical damping distribution along the building height. To overcome the above-mentioned challenges, a practical multi-degree-of-freedom (MDF) performance curve tool is developed for the design of tall buildings with dampers. The method first utilizes the SDF performance curve method to design and distribute dampers along the building height for a broad range of design parameters. Then, it conducts an intermediate evaluation through response history analysis based on simplified MDF models. The emphasis is placed on the use of bilinear oil dampers for seismic retrofit applications. Dampers are represented mathematically with a Maxwell model, which accounts for the stiffness characteristics of a bilinear oil damper. Guidance is provided on the development of the MDF performance curves with simplified flexural-shear beam models. A parametric study is carried out based on a broad range of damping properties and vertical damping distribution methods. An existing 40-story steel building representing typical 1970s construction in North America is used as a benchmark in this case. It is shown that the proposed tool allows for a reliable computation of story-based engineering demand parameters for a range of available seismic retrofit design solutions

Seismic Assessment and Retrofit of Pre-Northridge High Rise Steel Moment Resisting Frame Buildings with Bilinear Oil Dampers

This paper presents quantitative information on the effectiveness of seismic retrofit solutions using bilinear oil dampers for seismically deficient existing tall steel buildings. For this purpose, a benchmark 40-story steel space moment-resisting frame building is studied that represents 1970s design practice in North America. Rigorous seismic performance assessment based on ASCE 41 recommendations reveals a high collapse risk for the existing building. The local engineering demand parameters are comprehensively assessed to quantify the impact of seismic retrofit on steel columns and column splices, which are particularly vulnerable due to the time of construction. Multiple retrofit schemes are explored with numerous damping levels and vertical damping distribution methods. The dampers are designed via a recently developed multi-degree-of-freedom performance curves method. A new balanced vertical damping method is proposed to account for the effects of frame inelasticity. This strongly depends on the supplemental damping level, and it determines the effectiveness of the employed vertical damping distribution method. The results indicate that the proposed retrofit strategies can minimize the collapse risk of the tall building. It is shown that the balanced vertical damping distribution method provides the most uniform drift distribution along the building height. Despite the reduction in story drift ratios, the axial force demand in exterior columns remains relatively high in the bottom stories regardless of the seismic retrofit solution. On the other hand, bilinear oil dampers produce relative constant forces despite exhibiting higher velocity demands than expected.RESSLA

Seismic Assessment and Retrofit of Pre-Northridge High Rise Steel Moment Resisting Frame Buildings with Bilinear Oil Dampers

This paper presents quantitative information on the effectiveness of seismic retrofit solutions using bilinear oil dampers for seismically deficient existing tall steel buildings. For this purpose, a benchmark 40-story steel space moment-resisting frame building is studied that represents 1970s design practice in North America. Rigorous seismic performance assessment based on ASCE 41 recommendations reveals a high collapse risk for the existing building. The local engineering demand parameters are comprehensively assessed to quantify the impact of seismic retrofit on steel columns and column splices, which are particularly vulnerable due to the time of construction. Multiple retrofit schemes are explored with numerous damping levels and vertical damping distribution methods. The dampers are designed via a recently developed multi-degree-of-freedom performance curves method. A new balanced vertical damping method is proposed to account for the effects of frame inelasticity. This strongly depends on the supplemental damping level, and it determines the effectiveness of the employed vertical damping distribution method. The results indicate that the proposed retrofit strategies can minimize the collapse risk of the tall building. It is shown that the balanced vertical damping distribution method provides the most uniform drift distribution along the building height. Despite the reduction in story drift ratios, the axial force demand in exterior columns remains relatively high in the bottom stories regardless of the seismic retrofit solution. On the other hand, bilinear oil dampers produce relative constant forces despite exhibiting higher velocity demands than expected

Rate-dependent model for simulating the hysteretic behavior of low-yield stress buckling-restrained braces under dynamic excitations

Buckling-restrained braces (BRBs) are often idealized with rate-independent simulation models. However, under dynamic loading, BRBs featuring low-yield point steel exhibit rate-dependency that may lead to appreciable amplifications of the BRB forces. This paper proposes a new rate dependent model for simulating a BRB's response under dynamic excitations. The proposed model consists of a displacement-dependent asymmetric Menegotto-Pinto material law and a velocity-dependent bilinear oil damper model. The calibration process of the proposed model is also presented. Two approaches are demonstrated in which the proposed model can be utilized within a nonlinear frame analysis program. A comparative study based on test data from full-scale shake table tests of a five-story steel building equipped with BRBs underscores that if their rate-dependency is neglected then the BRB local force demands may be significantly underestimated. This may also lead to erroneous predictions of lateral story drift demands as well as absolute floor accelerations during earthquake shaking

Seismic Assessment and Retrofit of Pre-Northridge High Rise Steel Moment Resisting Frame Buildings with Bilinear Oil Dampers

This paper presents quantitative information on the effectiveness of seismic retrofit solutions using bilinear oil dampers for seismically deficient existing tall steel buildings. For this purpose, a benchmark 40-story steel space moment-resisting frame building is studied that represents 1970s design practice in North America. Rigorous seismic performance assessment based on ASCE 41 recommendations reveals a high collapse risk for the existing building. The local engineering demand parameters are comprehensively assessed to quantify the impact of seismic retrofit on steel columns and column splices, which are particularly vulnerable due to the time of construction. Multiple retrofit schemes are explored with numerous damping levels and vertical damping distribution methods. The dampers are designed via a recently developed multi-degree-of-freedom performance curves method. A new balanced vertical damping method is proposed to account for the effects of frame inelasticity. This strongly depends on the supplemental damping level, and it determines the effectiveness of the employed vertical damping distribution method. The results indicate that the proposed retrofit strategies can minimize the collapse risk of the tall building. It is shown that the balanced vertical damping distribution method provides the most uniform drift distribution along the building height. Despite the reduction in story drift ratios, the axial force demand in exterior columns remains relatively high in the bottom stories regardless of the seismic retrofit solution. On the other hand, bilinear oil dampers produce relative constant forces despite exhibiting higher velocity demands than expected.Fonds de recherche du Quebec Nature et technologies [2013-NC-166845]; Natural Sciences and Engineering Research Council of Canada (NSERC); Ecole Polytechnique Federale de Lausanne (EPFL); Individual Research Fund of Kadir Has UniversityThis research was supported by Fonds de recherche du Quebec Nature et technologies (Grant No. 2013-NC-166845), Natural Sciences and Engineering Research Council of Canada (NSERC), Individual Research Fund of Kadir Has University, and internal funding from Ecole Polytechnique Federale de Lausanne (EPFL). The findings in this paper are those of the authors and do not necessarily reflect the view of the sponsors