Structural New and Retrofit

Mega Brace seismic dampers for the Torre Mayor project in Mexico City

ABSTRACT

The new 57-story Torre Mayor Building is 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. Dampers are installed in mega-brace elements, up to 20m in length, where a single damper spans up to six floors.

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. A total of one hundred and thirty structures throughout the world utilize Fluid Viscous Dampers for earthquake, hurricane, and typhoon protection.

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Seismic rehabilitation of a historic non-ductile soft story concrete structure using fluid viscous dampers

ABSTRACT

Hotel Woodland is one of the first structures in North America to be seismically retrofitted using viscous dampers (VDs). This 4-story 1927 vintage Historical Landmark reinforced concrete building is located in Woodland, California. Maintaining the historical appearance of the building, the earthquake response performance of the building, and cost were the primary considerations in establishing the retrofit design.

The building is essentially a non-ductile reinforced concrete (RC) frame at the first level, and RC shear wall at levels 2, 3, and 4. Options considered for the retrofit included, both adding conventional shear walls or braces at the first level, and using VDs and steel moment frames at the first level. Adding shear walls or braes at the first level caused 2 ancillary problems: first obscuring the historical appearance of the building and second, limiting commercial development. Both stick and 3D model analyses revealed that installing VDs and moment frames at the first level reduced drifts at all levels (1,2, 3 and 4) to the desired performance. Using VDs proved to be the most cost effective method for seismically retrofitting the building. In addition, using VDs economically facilitated maintaining the historical appearance of the building .

This paper presents detailed results of a case study illustrating the processes and decisions regarding retrofit criteria and design procedure for earthquake demand, building response performance, historical interests, and economic considerations.

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San Francisco’s 1917 Library Transformed into Asian Museum using Seismic Base Isolation

ABSTRACT

The City of San Francisco’s Old Main Library, a 1917 historic building constructed of structural steel and unreinforced brick masonry, was recently renovated and transformed into the New Asian Art Museum. The Museum houses an irreplaceable collection of Asian art and artifacts, including immensely valuable, brittle Ming Dynasty vases, and represents the largest non-property asset in the City of San Francisco with an estimated value of $5 Billion.

Base isolation combined with superstructure reinforcement provided the most reliable protection available to the artifacts stored and displayed in the Museum. Base isolation allowed architectural freedom to manipulate the floor plate in a manner that optimized gallery space and light distribution. The seismic demands imposed on displayed artifacts were reduced to a level for which conventional artifact bracing methods could be effective.

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Viscous damping for base isolated structures

ABSTRACT

Seismic Base Isolation can use elastomeric pads, sliding plates or inverted pendulums. Each method can include an energy dissipation means, but only as some kind of hysteretic damping. Hysteretic damping has imitations in terms of energy absorption and may tend to excite higher modes in some cases.

It’s possible to avoid these problems with viscous dampers. Viscous damping adds energy dissipation through loads that are 90 degree out of phase with bending and shear loads so even with damping levels as high as 40% of critical adverse side effects tend to be minimal.

This paper presents basic theory of viscous damping, and also describes a sample project. Viscous dampers being built for the new San Bernardino Medical Center reduce both deflections and loads by 50% compared with high damping elastomer base isolation bearings by themselves.

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Seismic rehabilitation of historic concrete structure with fluid visco-elastic dampers

ABSTRACT

This paper presents the nonlinear seismic analysis, development and implementation of an innovative seismic retrofit strategy for a six-story nonductile reinforced concrete 145,00-sf (13,470 m²) 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. The analysis indicated that the existing building is 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 desired. Nonlinear fluid viscous dampers were placed at the first story level to reduce the seismic demand and obtain a more uniform response. Visco-elastic fluid viscous dampers are strategically placed at one side of the building to reduce the torsional irregularity of the building. The proposed cost effective, state-of-the-art retrofit will improve the seismic performance of the building.

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Retrofit of a metropolitan midrise to improve torsional response using nonlinear fluid viscous dampers

ABSTRACT

In many metropolitan areas, midrise 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 Dampers (FVD’s) can significantly decrease the torsional excitation, thereby increasing building performance.

The project involves the retrofit of an 18-story steel frame building that exhibits severe torsional response from the “property line” condition the lower two stories. The 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.

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Structural control of high rise building using a tuned mass with integral hermetically sealed, frictionless hydraulic dampers

ABSTRACT

Structural control of large buildings using tuned mass damper systems has gained wide acceptance in North America in recent years. Significant structural performance improvements during wind storms have been realized using both active and passive systems. Disadvantages of employing the of active systems include high engineering and implementation costs, high maintenance costs, unnecessary system complexities, and the requirement ofr 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.

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Development and testing of an improved fluid damper configuration for structures having high rigidity

ABSTRACT

It is generally recognized that structures having high rigidity can be characterized as having relatively small displacements when a shock input occurs. These small deflections are such that the implementation of added damping components has proven to be very difficult. Research was performed combining fluid dampers with a simple mechanical toggle brace assembly that magnifies the small displacement of the structure, while simultaneously producing the required damping force. Test results are provided with the toggle braces and fluid dampers installed on a 32,000 lb. structure, subjected to seismic ground motion transients on a large seismic shake table.

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Seismic protection system and its economic analysis on the beijing high-rise building pangu plaza

ABSTRACT

Pangu Plaza, located at Beijing close to 2008 Olympic main stadium, 191 meter, 39-story steel high-rise

Building, was analyzed under earthquake and wind loads by us, with both Fluid Viscous Dampers (FVD) and Buckling restrained braces (BRB or UBB), as the seismic protection system. A repeated iteration procedure of design and analysis was finished for the optimization. The complete seismic response on the horizontal and vertical directions was shown 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

traditionally increasing steel columns and beams size; increasing seismic braces versus using FVD to absorb the seismic energy. Both structural response and economic analysis results show that using FVD to absorb the seismic energy not only can make the structure satisfied the Chinese seismic design code for the “rare” earthquake, but it greatly improves the resistant capacity of seismic performance and also is the most economic way for both one-time direct investment and a long term maintenance for reducing seismic vibration.

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A living or Smart Building: The Guangzhou Tower

ABSTRACT

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 structural performance of the tower is enhanced and the design greatly improved by making it a Living or Smart building as will be discussed in more detail in the following section. The Key structural elements in this living structural system are Supplemental Taylor Viscous Damping Devices. These devices-dampers are energy dissipating devices that absorb and dissipate the energy going into the structure (by changing/offsetting the characteristics of the tower), and the displacements and floor accelerations (by improving structural integrity). The strength, serviceability and human comfort criteria can then be satisfied with smaller members in the structure.

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

ABSTRACT

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 wood shear walls employing toggle-braced fluid dampers. Within the context of performance-based seismic design, the effect of the fluid dampers on the deformation demand and hysteretic energy dissipation demand is emphasized. 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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