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.
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.
85. SHOCK DESIGN FOR MK-49 ISOLATION
The Sperry Marine MK 49 Ship’s Inertial Navigation System (SINS) is now in production for marine surface and subsurface applications. This system has been selected as the standard NATO SINS equipment and is the only marine inertial navigator which utilizes ring laser gyros. In order to serve the NATO community, the system must withstand a variety of shock stimuli (STANAG 4141, STANAG 4142, BR3021, etc.). Sperry Marine has shock hardened the system enclosures and developed a shock isolation system for the Inertial Measurement Unit (IMU) using tension compression liquid spring/dampers in a hexapod configuration. This isolator assembly provides the shock attenuation and precision angular alignment return ability that is needed to meet the above specifications. This paper addresses the design process to shock harden the IMU and presents experimental results.
80. A LIVING OR SMART BUILDING: THE GUANGZHOU TOWER
This paper presents the evolution of the structural design of one of the tallest structures in the world. The architectural design was developed by Mehrdad Yazdani at Cannon Design Group. The basic architectural vision of the Guangzhou Tower is three twisting interconnected legs. The architectural plan at each level of the tower rotates and twists. The basic structural vision here is of a Living Structure that can be adapted and improved from a structural engineering perspective as new high-tech products become available, as our understanding of the forces of nature improves using ground and aerial instrumentation and as we improve the accuracy of our structural modeling to estimate structural response to wind and earthquake loading.
75. STRUCTURAL CONTROL USING HYBRID SPRING-DAMPER ISOLATOR WITH INTEGRAL GAPPING FUNCTION
The spring-damper isolators described in this paper were used on the world’s largest cable stayed bridge – the Sutong Bridge over China’s Yangtze River, completed in 2008. The Sutong Bridge is located north of Shanghai in China’s Jiangsu Province at a site where catastrophic earthquakes, typhoons, and ship impact are key design issues. The total length of the bridge is 4.7 miles, with a .67 mile long center span. The tall support towers of this bridge and the long support cables create long period motions along the primary axis of the bridge. The need to accommodate thermal expansion and contraction of the deck axially means that extensive motion can occur in this direction. The configuration of the bridge permits large axial motion of the suspended deck during earthquakes, typhoons, and synchronized truck/car braking loads such as would occur during a mass vehicular accident on the bridge. During dynamic earthquake loading, the long period of the suspended deck provides inherent isolation, albeit essentially undamped. Analysis indicated that added viscous damping would reduce deck motions substantially. During other events like typhoons and vehicle loading, analysis determined that the most cost-effective solution was to incorporate a snubbing type spring element that would only engage (become active) when the damper was approaching its end of travel in either extension or compression. The spring-dampers on this bridge have only damping forces for roughly 85% of the available displacement from the neutral (center of travel) position. Beyond this travel the spring element engage and a combined response of spring plus damper forces results. Essentially, the spring elements are “gapped” through all but approximately the last 15% of the damper stroke in either direction.
72. MODULAR TUNED MASS DAMPER UNITS FOR THE SPRING MOUNTAIN ROAD PEDESTRIAN BRIDGE
Modern pedestrian bridges tend to be long and slender, usually causing relatively low frequency primary modes of vibration. This type of structure can be excited to resonance by synchronized crowd footfall. Added damping is often required to prevent excessive structural motions and loadings. This paper describes the Modular Tuned Mass Dampers used to provide the required added damping for the three Spring Mountain footbridges in Las Vegas.
70. SEISMIC REHABILITATION OF HISTORIC CONCRETE STRUCTURE WITH FLUID VISCO-ELASTIC DAMPERS
This paper presents the nonlinear seismic analysis, development, and implementation of an innovative seismic retrofit strategy for a six story nonductile reinforced concrete 145,000 square foot historic building. Dynamic and nonlinear static analytical results verified that the building had a weak soft story with inadequate post yield capacity and large torsional response. Hotel Stockton, in Stockton, CA, is also torsionally irregular. The analysis indicated that the existing building was not seismically adequate to withstand anticipated lateral forces generated by earthquake excitations at the site. A “collapse prevention” performance upgrade for a 475-year return event was developed. Nonlinear fluid viscous dampers were placed at the first story level to reduce the seismic demand and obtain a more uniform response. Viscoelastic fluid viscous dampers were strategically placed at one side of the building to reduce the torsional irregularity of the building. This cost effective retrofit significantly improved the seismic performance of the building.
67. U.S. DESIGN OF STRUCTURES WITH DAMPING SYSTEMS
This paper presents an earthquake design procedure and a case study of the Vacaville Police Headquarters. The design goal for this essential facility was to provide immediate occupancy after a 475-year return seismic event. The project also required construction cost within typical code conforming buildings. A combination of Special Moment Resisting Frames (SMRF) and Fluid Viscous Dampers (FVDs) was used as the lateral force resistance system. This system, as described by Gimmel, Lindorfer, and Miyamoto, (2002) results in cost efficiency and superior seismic performance. The 2000 NEHRP (FEMA, 2000) guideline was used to design the project, since it is considered to be a state-of-art procedure for seismic damping devices. This project was the first structure in the United States to use this advanced procedure.
66. DAMPER RETROFIT OF THE LONDON MILLENNIUM FOOTBRIDGE
The Millennium Footbridge was opened to the public on June 10, 2000 – the first new bridge across the River Thames in historic London in more than a century. Nearly 100,000 people used the new bridge in its first day of operation. On June 12, 2000, the Millennium Bridge was ordered closed, due to hazardous deck motions. Seemingly random pedestrian footfalls were causing resonance of the bridge deck, with lateral accelerations measuring up to 0.25 g. The selected method of retrofit was to add fluid damping to the bridge. This paper describes how this was done, including testing of the bridge with groups of up to 2,000 people.
64. VIRTUAL BASE ISOLATION BY BUILDING SOFTENING WITH DRIFT CONTROL PROVIDED BY FLUID VISCOUS DAMPERS
In many metropolitan areas, mid rise buildings are constructed adjacent to existing buildings, and incorporate concrete shear walls to act as a barrier between the two buildings. The orientation of these shear walls often causes severe torsional response within the building. The addition of a few well placed nonlinear Fluid Viscous Dampers (FVD’s) can significantly decrease the torsional excitation, thereby increasing building performance. This paper describes the retrofit of an 18-story steel frame building that exhibits severe torsional response from the “property line” condition at the lower two stories. FVD’s significantly reduce the displacement and acceleration of the second and third floors of the building, where sensitive telecommunications equipment is being housed. They reduce the demand and drift on the stories above with no additional construction required on these floors. FVD’s offer a very economical and effective means of mitigating undesirable building response due to torsional irregularities. Their use would be effective in the retrofit of many existing buildings with similar “property line” conditions.