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Seismic Applications
Case Study

99. APPLICATION OF ENERGY DISSIPATION TECHNOLOGY FOR RETROFITTING STEEL STRUCTURES WITH VULNERABLE PRE-NORTHRIDGE CONNECTIONS

Prior to the 1994 Northridge earthquake, modern welded moment resisting steel frame structures were regarded as highly resistant to earthquake induced damage and few engineers regarded earthquake induced collapse of such structures as credible. This paradigm changed following the 1994 Northridge, California and 1995 Kobe, Japan earthquakes, creating a new class of potentially hazardous structures. In response to this new information, the Federal Emergency Management Agency retained a consortium of the Structural Engineers Association of California, the Applied Technology Council and the California Universities for Research in Earthquake Engineering, known as the SAC Joint Venture, to research the cause of the unexpected poor performance of these buildings and develop recommended design criteria. The resulting FEAM-351 publication provides performance based design criteria for the evaluation and upgrade of these structures. This paper presents the application of the FEMA-351 criteria to the design of structural upgrades employing energy dissipation technology to an existing 10-story steel structure. The East Bay Municipal Utility District (EBMUD) administration building is nine stories tall, with three below grade basement levels and a rooftop, mechanical penthouse. It was completed in 1991, employing the standard vulnerable moment connections. Alternative upgrade strategies were investigated, including modification of individual connections and application of energy dissipation criteria. The latter approach, using viscous dampers, was selected.
Case Study

98. Seismic Protection System and its Economic Analysis on the Beijing High-Rise Building Pangu Plaza

Pangu Plaza, located at Beijing close to 2008 Olympic main stadium, is a 191 meter, 39-story steel high rise building. It was analyzed under earthquake and wind loads with both Fluid Viscous Dampers (FVD) and Buckling Restrained Braces (BRB or UBB) as the seismic protection system. The complete seismic response on the horizontal and vertical directions showed that the Fluid Viscous Dampers are highly effective to reduce the structural response, as well as the secondary system response. A comparative analysis of structural seismic performance and economic effect was considered, by the traditional method of increasing steel columns and beams size; by using BRB’s and by using FVD’s to absorb the seismic energy. Structural response analysis showed that using FVD’s to absorb the seismic energy made the structure satisfy the Chinese seismic design code for the “rare” earthquake and also greatly improved the seismic performance. Economic analysis showed that FVD’s were the most economic approach for both one-time direct investment and long term maintenance.
White Paper

96. Roof Isolation System to Reduce Seismic Response of Buildings

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.
Uncategorized

95. Optimized Damping Device Configuration Design of a Steel Frame Structure Based on Building Performance Indices

Energy dissipation devices (EDDs) have been accepted as one of the viable strategies for enhancing the seismic performance of building structures. However, current design provisions do not provide guidelines for optimizing the EDD configurations. For many building structures an efficient configuration of EDDs may provide considerable performance improvement. Similarly, an optimized configuration may reduce the number of EDDs required to achieve a target performance objective. In this paper an existing building with added linear viscous dampers is redesigned based on different performance index optimization. The results indicate that the optimal device configurations are highly related to the dynamic properties of the structure and its required performance index. In one instance, where the cost is the major concern and a performance requirement is placed on story drift limitation, the total device damping coefficient can be reduced by 26%.
Technical Brief

94. A Simple Method for the Design of Optimal Damper Configurations in MDOF Structures

Existing methods for the design of optimal configurations of supplemental dampers are usually not simple enough to be used routinely, and typically lead to different damper sizes at virtually every story. This can be avoided with the Sequential Search Algorithm, which lets the designer control the number of different damper sizes. In this paper, a simplification to the Sequential Search Algorithm is developed. This Simplified Sequential Search Algorithm makes it easy for engineers to deal with damper added structures. It was found that the efficiency of damper configurations given by the proposed Simplified Sequential Search Algorithm is comparable to the efficiency of damper configurations given by more sophisticated procedures. The applicability of the method is limited to those cases where the response of the structure with added dampers remains linear.
White Paper

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.
White Paper

92. Energy Dissipation Systems for Seismic Applications

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.
White Paper

91. Coupled Truss Walls with Damped Link Elements

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.
White Paper

89. U.S Code Development of Structures with Damping Systems

Damping devices are being increasingly used in both new and existing buildings in both United States and Japan. This increased popularity has created a demand for design guidance and building codes. This paper provides a summary of the code development activities for the 2003 NEHRP by the Building Seismic Safety Council.
Technical Brief

88. Seismic Performance of Light Framed Wood Structures with Toggle-Braced Fluid Dampers

In recent years, seismic damping systems have been employed in numerous steel and concrete framed buildings. Such systems dissipate a significant portion of the seismic input energy, thereby relieving the energy dissipation demand on the structural framing system and thus reducing damage. As part of a NEESR project to develop a performance based approach to seismic design of multi-story light framed wood structures, the application of damping systems to such structures has been evaluated via seismic shaking table tests and numerical simulations. This paper focuses on the results from shaking table tests of shear walls employing toggle braced fluid dampers. The results demonstrate that toggle braced fluid dampers provide a significant increase in the seismic resistance of the walls, allowing them to achieve high levels of performance when subjected to strong ground motions.

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