Soft weak open front (SWOF) buildings often perform poorly in earthquakes. Two examples are buildings with a street facing garage, or commercial facilities with extensive open display windows. The poor performance of SWOF structures can consist of complete loss of use or even total collapse. This paper presents an approach to protecting such structures via the addition of an energy dissipation system (viscous dampers) such that peak inter-story drifts are limited to about 1% under relatively severe seismic events, thus keeping the deformations within the elastic range. With this addition of damping, earthquake survivability of this class of structures increases significantly. A series of seismic analyses are presented herein to demonstrate the potential performance of the damping system. In addition, a variety of damper installation configurations that provide enhanced energy dissipation are discussed.
The well known collapse of Tacoma Narrows Bridge in 1940 clearly identified the importance of aeroelastic effects on long span bridge performance. Extensive research has been carried out since then to better understand the effects of wind on long span bridges, producing various analytical response prediction techniques. An example of the application of such techniques is presented. However, due to challenges related with full scale measurements, these prediction techniques have commonly been validated using only wind tunnel experiments. Recent research has revolved around the conduct of long term full scale measurements on a cable stayed bridge to compare actual bridge performance with those of analytical predictions. In order to ensure the reliability of predicted response, the input parameters, such as wind conditions at the site and modal properties of the bridge are also calibrated using corresponding measured quantities. This paper summarizes some of the preliminary results and outlines their implications.
103. Validation of the 2000 NEHRP Provisions’ Equivalent Lateral Force and Modal Analysis Procedures for Buildings with Damping Systems
Equivalent lateral force and modal analysis procedures for yielding buildings with damping systems were developed, validated, and incorporated in the 2000 NEHRP Provisions. Key to the implementation of the procedures was the validation process that demonstrated the accuracy of the proposed procedures. The procedures for implementing yielding, viscoelastic, linear viscous, and nonlinear viscous dampers were tested using the results of nonlinear response history analysis on sample three- and six story frames and were found to be robust.
Fluid Viscous Devices have been found to be a highly effective protection system for bridges. Introduced to China in 1999, the Taylor Devices damper systems have been successfully installed or will be installed in both large and super large bridges in China for protection from earthquake, wind, vehicle and other vibration. Seventeen different bridge projects include the Sutong Yangtze River Bridge, the longest cable stayed bridge in the world, the Nanjing 3rd Yangtze River Bridge, the fifth longest suspension bridge in the world, and the Xihoumen across Sea Bridge, the second longest suspension bridge in the world. The performance of the bridges and dampers have been reported as “very good” during the May 12, 2008 Wenchuan earthquake. All of the dampers produced have been subjected to rigorous static and dynamic testing, which show the dampers will perform well for the next 50 years and possibly much longer.
Installation of damping devices has been limited to diagonal or chevron brace configurations until the recent development of the toggle brace. This configuration magnifies the effect of damping devices, thus facilitating their use in stiff framing systems. This paper introduces the scissor jack damper system that was developed as a variant of the toggle-brace damper system, with the added advantage of compactness. The effectiveness of the scissor jack configuration is demonstrated through testing of a large scale steel framed model structure on an earthquake simulator. Experiments showed that despite the small size of the damping device considered, the scissor jack system provided a significant amount of damping and substantially reduced the seismic response of the tested structure. Response history and simplified analyses produce results that are consistent with the experimental results.
A roof isolation system is proposed as a means to reduce the detrimental effect of earthquakes in buildings. This roof isolation system entails the insertion of flexible laminated rubber bearings between a building’s roof and the columns that support it and the addition of viscous dampers connected between the roof and the rest of the building. The properties and dimensions of the rubber bearings and viscous dampers are selected in a way that makes the roof, bearings, and dampers form a highly damped vibration absorber. Presented also is a comparative study with a simple five story steel building under a strong earthquake ground motion that is carried out to assess the effectiveness of the proposed system. In this comparative study, it is found that the roof isolation scheme reduces the floor displacements and interstory drifts of the analyzed building by as much as 83 percent. On the basis of these results and in view of its simplicity, it is concluded that the proposed roof isolation system has the potential to become a practical and effective way to reduce earthquake damage in buildings.
93. EXPERIMENTAL STUDY OF RC BUILDING STRUCTURES WITH SUPPLEMENTAL VISCOUS DAMPERS AND LIGHTLY REINFORCED WALLS
This paper describes an experimental evaluation of viscous dampers used to reduce seismic motion in reinforced concrete moment-resisting building structures. Common practice in Taiwan is to use lightly reinforced concrete exterior walls and interior partition walls, which not considered for their contribution of stiffness and strength in the design process. As these additional walls greatly reduce relative story displacement and velocity, it has been suspected that the effectiveness of supplemental dampers would be very limited. However, the test results show that a new displacement multiplying mechanism, the toggle brace damper system, is effective even with a small relative story drift in the seismic response control of the structure. Dampers produce significant force and displacement reduction in the moment-frame structures that were investigated.
This paper presents a summary of current practice and recent developments in the application of passive energy dissipation systems for seismic protection of structures. The emphasis is on the application of passive energy dissipation systems within the framing of building structures. Major topics that are presented include basic principles of energy dissipation systems, descriptions of the mechanical behavior and mathematical modeling of selected passive energy dissipation devices, advantages and disadvantages of these devices,
development of guidelines and design philosophy for analysis and design of structures employing energy dissipation devices, and design considerations that are unique to structures with energy dissipation devices. A selection of recent applications of passive energy dissipation systems is also presented.
A new structural concept is proposed for the seismic design of tall buildings. This system combines the inherent stiffness and strength of a conventional truss system with the energy absorption characteristic of supplemental damping elements. The damping elements are strategically placed to form the linking elements of a coupled vertical truss system. While the force resistance system of the truss wall is in parallel, the damped link beam is in series with the component of the truss stiffness contributed to the coupled wall action. A series of time history dynamic studies gauged the performance of the proposed concept and found the proposed damped link concept superior in performance compared to the conventional approach.
A 1985 steel moment frame was seismically upgraded using passive energy dissipation, without adding stiffness to the system. The design and analysis techniques for sizing the Velocity Braces and their impact on the demand capacity ratios are reviewed in this paper. The original structure was built in the San Francisco Bay Area in compliance with the 1985 Uniform Building Code (UBC). The moment frame contains the classic pre-Northridge nonductile moment connection. Nonlinear time history analysis was used to design a damper system that provides a significant decrease in seismic response.