78. EXPERIENCE AND PRACTICAL CONSIDERATIONS IN THE DESIGN OF VISCOUS DAMPING
This paper describes how viscous dampers work, and how they significantly reduce seismic excitation in structures.
77. ENERGY MANAGEMENT UTILIZING THE HYDRAULIC SHOCK ABSORBER
The advent of high speed equipment and machinery has brought with it numerous problems associated with slowing and stopping masses of various forms. The hydraulic shock absorber has proven to be one of the most satisfactory means of solving these problems, yet the shock absorber still remains as one of the least understood fluid power components. This paper presents design constraints, design parameters and a description of how to use shock absorbers into a system for the purpose of dissipating kinetic energy. Information is presented in both qualitative and functional equation format to enable the reader to grasp the subjective aspects of shock absorber usage which go beyond normal mathematical constraints.
74. INTRODUCTION TO SHOCK AND VIBRATION ISOLATION AND DAMPING SYSTEMS
This paper presents an introduction to shock and vibration isolation of complex structures and mechanisms. It provides an outline of various ways to provide isolation, shock absorbing and damping within a wide array of dynamic systems and structures. This paper presents key definitions that are widely used within the shock and vibration community. Additionally, useful formulae are presented that provide the user with an approach to typical problems. Finally, a comparison of different types of shock isolators, shock absorbers and dampers compares their advantages and disadvantages for use in the commercial, military, and aerospace sectors.
71. SEISMIC PROTECTION WITH FLUID VISCOUS DAMPERS FOR THE TORRE MAYOR, A 57-STORY OFFICE TOWER IN MEXICO CITY, MEXICO
The new 57 story Torre Mayor Building is the now the dominant structure in the Mexico City skyline. It is also the first tall building to utilize large Fluid Viscous Dampers as a primary means of seismic energy dissipation. A total of 98 dampers are used, including 24 large dampers, each rated at 570 tonnes of output force, located in the long walls of the building. The short walls utilize 74 smaller dampers, each rated at 280 tonnes of output force. The damping technology successfully implemented for Torre Mayor is now being used on five other tall buildings, including three in the USA, and two in Japan.
69. ANALYSIS, OPTIMIZATION, AND DEVELOPMENT OF A SPECIALIZED PASSIVE SHOCK ISOLATION SYSTEM FOR HIGH SPEED PLANING BOAT SEATS
The Mk V Special Operations Craft (SOC) is used to carry Special Operations Forces (SOF) into and out of combat operations. During operation, particularly during extended training missions, the passengers and crew have reported numerous cases of musculoskeletal injuries from operation in high sea states. This paper describes the analysis, development and operational testing of a highly specialized, non-linear, passive shock isolated seat for this craft. Initial sea trial testing of the isolation system resulted in positive operator feedback that correlated well with earlier field measurements and also validated the analytical predictions.
65. VISCOUS DAMPER DEVELOPMENT AND FUTURE TRENDS
Viscous dampers can protect structures against wind excitation, blast and earthquakes. Viscous damper technology originated with military and aerospace applications. Approximately 20 years ago it was found that the same fluid viscous dampers that protect missiles against nuclear attack and guard submarines against near miss underwater explosions could also protect buildings, bridges and other structures from destructive shock and vibration. This paper describes fluid damper technology, analysis considerations, installation methods and development work in progress.
63. VIRTUAL BASE ISOLATION BY BUILDING SOFTENING WITH DRIFT CONTROL PROVIDED BY FLUID VISCOUS DAMPERS
The paper describes “virtual isolation” for buildings with one or more soft stories. Using the 1999 SEAOC Blue Book (SEAOC, 1999) recommendations for passive energy dissipation, the building’s Lateral Force Resisting System (LFRS) is designed for strength requirements only, resulting in a relatively flexible LFRS, while Fluid Viscous Dampers (FVD) are incorporated to limit story drifts to acceptable levels. There are many benefits to this “virtual isolation” system. With the elimination of the maximum drift requirements, the moment frames are substantially lighter than a traditionally framed building, thus lowering the structural steel cost of the LFRS. The long period structure also produces significantly reduced forces in the foundation elements. Velocity and displacement are reduced significantly through the use of the FVDs, which protects the sensitive contents of the building. These benefits lead to a reduced response resulting in an enhanced performance level during a major seismic event.
62. STRUCTURAL CONTROL OF HIGH RISE BUILDING USING A TUNED MASS WITH INTEGRAL HERMETICALLY SEALED, FRICTIONLESS HYDRAULIC DAMPERS
Structural control of large buildings using tuned mass damper systems has gained wide acceptance in recent years. Significant structural performance improvements during wind storms have been realized using both active and passive systems. Disadvantages of employing active systems include high engineering and implementation costs, high maintenance costs, unnecessary system complexities, and the requirement for a continuous and non-interrupted power supply. A design for a passive tuned mass damper system is presented with analytical simulations and component test results. These demonstrate the effectiveness of using a tuned mass in conjunction with a maintenance free, hydraulic damper, having frictionless flexural seals to successfully attenuate the response of a high rise building subject to severe wind inputs.
61. A NUMERICAL INVESTIGATION OF COMBINED SHOCK AND VIBRATION ISOLATION THROUGH THE SEMI-ACTIVE CONTROL OF MAGNETORHEOLOGICAL FLUID DAMPER IN PARALLEL WITH AN AIR SPRING
Combining shock and vibration isolation into a single isolation mount is investigated numerically through the use of the Bouc-Wen model of a magnetorheological fluid damper in parallel with an air spring. The stability and dissipative capabilities of the Bouc-Wen model are proven mathematically. The response characteristic of this hybrid isolator to shock and vibration inputs is explored. The advantages of combining shock and vibration isolation into a single package is discussed. It is possible, using this technique, for a single device to perform equally well as a shock and a vibration isolator.
60. FLUID LOCK-UP DEVICES
Fluid Lock-up Devices have recently become popular for passive control of large structures subjected to earthquake or wind storm effects. The Lock-up Device, a variation of the Fluid Viscous Damper, allows unrestricted motion at low translational speeds. When a transient event occurs the Lock-up Device activates and forms a rigid connection. After the transient event the Lock-up Device reverts to low force output, permitting structural sections to thermally expand or contract without added stress. The operation of the device is completely passive. It enables multi-mass structures to be dynamically braced without resorting to the cost and complexity of an active actuator system..