Research and Application of Seismic Retrofit Technologies in Canada Mark M. Lumbay MSST-06

Earthquakes along the Pacific ring, such as India, Japan, Taiwan, and U.S.A. in the last decade, demonstrated the power of nature and the catastrophic impact of such power upon urban cities. Casualties and damage associated with older buildings, which were designed and constructed using codes that are now known to provide inadequate seismic safety, are far worse than that for newer buildings which have been designed and built in accordance with more stringent code requirements. Satisfactory performance of retrofitted buildings in the latest earthquakes indicates that upgrading older and deficient buildings is the most effective and efficient seismic hazard mitigation measure. Abstract

Relatively speaking, seismic retrofitting of buildings is still a new activity for most structural engineers. During the past several years, Public Works and Government Services Canada, or PWGSC, has been conducing research and development for innovative seismic retrofit technologies and has demonstrated the successful applications of some of these innovative technologies in a number of seismic retrofit projects on federal buildings. This paper gives an overview of PWGSC’s research and application activities on seismic retrofit technologies for buildings. Abstract Cont..

Friction Damper: Research The principle of the work of these dampers is based on energy dissipation by friction. The friction dampers consist of a series of steel plates that are specially treated to develop the largest amount of friction. These plates are clamped together with high-strength steel bolts. During severe seismic excitations, friction dampers slip at a predetermined optimum load before yielding occurs in other structural members and dissipate a major portion of the seismic energy.

Friction Damper: Application X-braced friction damper in Harry Stevens Building

Friction Damper : Application Cont.. Friction damper at the top of a chevron brace (Justice Building).

Friction Damper : Application Cont.. Friction dampers in Pump House Building

Carbon Fiber Reinforced Plastic: Research Advanced composite materials such as carbon fiber reinforced plastic (CFRP) is much stronger and lighter than steel. The terms fiber composites, advanced composite materials, or fiber reinforced plastic (FRP) materials, are generally applied to synthetic fiber materials such as fiberglass, carbon fibers, and aramids embedded in a resin matrix (epoxy or ester). The primary load-carrying element within a composite is the fiber. The resin provides a mechanism for the transfer of load among the fibers. It also protects the fibers from abrasion and other environmental and chemical attacks. The fibers can be oriented in a single direction (unidirectional) or several directions to optimize the performance of the composite.

Reinforced concrete shear walls strengthened with CFRP

Test set-up for shear wall specimens

Anchoring system for the carbon fiber sheets at the base of the wall specimen

Application of CFRP sheets onto the column Retrofitted column with minimal interruption to business

External Pre-stressing: Research Most common deficiencies, i.e. failure, found in older reinforced concrete columns are due to lack of confinement, insufficient lateral reinforcement and inadequate reinforcement splicing. Providing steel or concrete jacketing to deficient columns not only improves the strength but also increases the stiffness of the column. Increasing the columns’ stiffness is not desirable as the stiffened columns now attract, or are subjected to, higher seismic loads. One alternative would be wrapping the column with CFRP sheets. A second alternative would be wrapping the column with individual cable strands, which are pre-stressed to exert active pressure against the column section.

Extensive experimental investigations on seismic retrofit of reinforced concrete columns using external pre-stressing have been conducted at the University of Ottawa [Yalcin 1997; Mes 1999; Beausejour, 2000; Saatcioglu, 2000]. As a result of these investigations, a new retrofitting technique was developed. This technique consists of external pre-stressing, which provides active and passive lateral pressure to overcome lateral expansion in concrete under compression. It also provides a clamping force in reinforcement splice locations to improve bond between the steel and concrete. In shear dominant columns, transverse pre-stressing counteracts diagonal tension caused by shear, thereby improving column shear resistance. The pre-stressing is achieved by means of high-strength seven-wire steel strands, individually pre- stressed by a small hydraulic jack, connected by specially designed anchors. External Pre-stressing: Research Cont..

Circular column strengthened with external pre-stressing Square column strengthened with external pre-stressing

Plan view of square column with external pre-stressing

External Pre-stressing: Application Application of external pre-stressing technology is very promising for the retrofit of building columns. It is efficient and can be more economical than steel jacketing. Installation of such a system can be less disturbing to the building occupants. This technique was developed during the last four years and its potential application on buildings has yet to be realized. Results of planned research will provide needed information on the technology’s applicability and effectiveness on rectangular columns. It is expected that the technology’s first application on buildings can take place within the next couple of years.

Stone Masonry Structures: Research In Canada, many government and heritage buildings, such as the Parliament Buildings and Provincial Legislature Buildings, are of stone masonry structures. While guidelines and standards are available for the seismic evaluation of buildings constructed with brick and block masonry, concrete and steel, comparable documents are lacking for stone masonry structures in Canada and the U.S. Even lesser research has been done on the seismic upgrading of stone masonry structures. The assessment document presents technical information on past performance, material and engineering properties, modeling and evaluation procedure and assessment criteria for stone masonry structures. Based on research in past seismic performance of stone masonry structures, a structural checklist has been compiled to identify potential inadequacy in the seismic capacity of stone-masonry bearing wall buildings with stiff diaphragms. Procedure and sample application of the procedure for the seismic evaluation of stone masonry structures are also given.

Reinforced injection for multi-wythe stone masonry wall (conventional)

Isolator for exterior wall (innovative)

Research and Application of Seismic Retrofit Technologies: Non-Structural Shake Table Testing LAN rack on seismic isolation platform LAN rack on rollers

LAN rack on caster cups Light fixture with restraint

A modern office work station on raised floor

Close-up view of personal environment systems for a raised floor system

Summary During the past few years, PWGSC has been rather active in conducting and supporting research and development on seismic retrofit technologies for both structural and nonstructural components. PWGSC’s research activities into various technologies all have one thing in common: eventual transfer of the technologies into construction industry. PWGSC’s research initiative on non- structural building components can be considered as ground breaking. The initiative led to the development of the PWGSSC guideline for office buildings and of the new national guideline for most occupancies covered by the National Building Code of Canada. In parallel with its leading research activities in seismic retrofit technologies, PWGSC has also been very proactive in demonstrating the application of innovative technologies in a number of seismic upgrading projects on federal buildings. The proper use of these emerging technologies in building retrofit projects can lead to lower construction cost and client satisfaction in terms of minimal business interruption and avoidance of tenant relocation. Heritage conservation can also be achieved through the use of innovative strategies and technologies.