Chevron Bracing Research Articles

Semi‐active friction system with amplifying braces for control of MDOF structures

AbstractThe development and applications of a semi‐active friction damping system with amplifying braces is studied. A system of dampers and braces, defined as the friction damping system with amplifying braces (FDSAB) is considered. Active control theory with velocity and acceleration feedback is used to obtain the control forces in the proposed system. The system can be used efficiently to enhance the damping of a structure and improving its response. The efficiency of the proposed system is demonstrated by the numerical simulation of a seven storey building subjected to earthquakes. The simulation shows that the behaviour of the damped structure with the FDSAB is significantly improved. The required control forces are much less compared with a control system with semi‐active friction dampers connected either to chevron or diagonal braces. Copyright © 2001 John Wiley & Sons, Ltd.

Toggle-Brace-Damper Seismic Energy Dissipation Systems

Energy dissipation systems are being increasingly employed in the United States to provide enhanced seismic protection for new and retrofit building and bridge construction. The hardware utilized includes yielding steel devices, friction devices, viscoelastic solid devices, and mostly, so far, fluid viscous devices. This hardware has been used in either diagonal or chevron brace configurations. This paper presents three new configurations that utilize toggle-brace mechanisms to substantially magnify the effect of damping devices so that they can be utilized effectively in applications of small structural drift. Shake table testing of a large scale steel model structure and analysis are used to demonstrate the utility of these configurations. The experimental results demonstrate substantial increases in the damping ratio despite the use of small size damping devices, and, accordingly, significant attenuation of the seismic response of the tested stiff structure is observed. Moreover, the experimental results are found to be consistent with analytical predictions based on either simplified methods or response history analysis. Applications of the new configurations are briefly described.

Seismic design of low- and medium-rise chevron braced steel frames

This paper presents two different seismic design approaches for multistorey chevron (inverted V) steel braced frames. The first method complies with current Canadian code provisions in which the beams in the bracing bents must be designed to sustain the forces expected to develop up to buckling of the bracing members. In the second approach, the beams must also resist the gravity loads together with a fraction of the brace loads that are induced after buckling of the braces. This second approach aims at minimizing the degradation in storey shear resistance typically exhibited by chevron bracing subjected to strong ground motions, and it is proposed that such braced frames with reinforced beams be designed for reduced seismic loads. Both design procedures are applied to typical multistorey braced frames to examine their economical impacts. Three different beam strength levels were considered for the second design method. The results show that the saving expected from reducing the seismic loads in the second design approach is generally offset by the increase in beam sizes required by this method. However, the braced frames with stronger beams exhibit a much higher storey shear resistance after buckling of the bracing members has occurred.Key words: earthquakes, seismic, design, steel, structures, braced frames, bracing members, beams, columns, connections.

Aluminium shear-links for enhanced seismic resistance

SUMMARY An aluminium beam shear-link is developed for earthquake-resistant structures. The aluminium beam is designed to yield in shear mode to limit the maximum lateral force which is transmitted to primary structural members and to provide significant energy dissipation potential. Aluminium was chosen because of its low yield strength, which enables the use of thicker webs, reducing the problems of web buckling. Cyclic load tests on medium scale (1 : 4) models were conducted to study the hysteretic behaviour and energy dissipation potential of shear-links made of two alloys of aluminium (3003-O and 6061-O). The links were also tested at faster rates (cycling frequencies of 5, 10 and 17 Hz) to determine the e⁄ect of strain rate. The links exhibited very ductile shear yielding and excellent energy dissipation capacity. Unpinched and full hysteresis loops were observed until 10 per cent shear strain, and a relatively small influence of strain rates was observed on the link’s performance. Simple design equations are developed to proportion these shear-links, using data from the cyclic load tests. In chevron-type braced systems, the shear-link is sandwiched between the tops of diagonal braces and a girder from the floor above, resulting in yielding at a lateral force less than that required to buckle the compression brace. A Shear-Link Braced Frame (SLBF) system was designed and its seismic performance was compared to that of an Ordinary Concentric Braced Frame (OCBF) with chevron braces. The SLBF system demonstrated more uniform distribution of storey drifts, reduced base shear, and a larger energy dissipation capacity per unit drift. ( 1998 John Wiley & Sons, Ltd.

Technology Transfer in Building Construction—Case of Seismic Design

Many construction innovations incorporate technologies that have been transferred from one geographical area or discipline to another and subsequently modified for the new conditions. This paper analyzes an example of this technology transfer on a sample project: chevron bracing was first used in the structural system of a tall building located in a high seismic zone. This paper describes current technologies for structural systems and the evolution of the unique structural design used for this project. This paper discusses three types of barriers to technology transfer in the U.S. construction industry: building codes, conservatism, and organizational barriers. The focus of this paper is on examining how the project team overcame those barriers. This paper concludes that the teamwork should be based on a reciprocal relationship. Each team member must possess technical competency. It is also vital for each team member to expend efforts to understand not only the technical aspects of the project but the needs and concerns expressed by the other team members. This paper provides insights about the reciprocal relationship and the qualifications of the participants required to surmount barriers to technology transfer in the U.S. construction industry.

Seismic Testing of Steel Plate Energy Dissipation Devices

In a research program, co-sponsored by Bechtel Power Corporation and CounterQuake Corporation, the seismic performance of steel plate added damping and stiffness (ADAS) elements was investigated through a series of sub-assemblage experiments and by the earthquake simulator testing of a three story ductile moment resisting space frame (DMRSF) upgraded with ADAS elements. The sub-assemblage testing of the ADAS elements demonstrated their stable hysteresis for a large number of yielding cycles. The addition of the ADAS system (ADAS elements and chevron braces) to the DMRSF limited the frame's response to acceptable levels during severe earthquake simulation. The research program clearly demonstrated that ADAS elements can be used to effectively upgrade moment resisting frames (MRFs) and concentrically braced frames (CBFs) to achieve a moderately stiff building with extremely good energy dissipation characteristics. The implications of the research results for the design and upgrade of buildings using ADAS elements, and potential uses for ADAS elements, are presented in the latter part of the paper.

Small‐Scale Model Tests of Structural Steel Assemblies

Replica models of three beam‐column assemblies and a six‐story braced frame specimen were constructed at a scale of 1:12.5. These models were then tested using the same displacement histories as corresponding prototype tests. A comparison of the model and prototype test results indicates that small‐scale models can be used to predict global elastic and inelastic behavior of structures very well. Localized failure modes were simulated with less accuracy, with the model specimens generally exhibiting slower deterioration in strength and stiffness than the prototype. General conclusions about the behavior of dual steel structural systems with chevron braces are given. Conclusions are drawn on the feasibilities and limitations of small‐scale testing in earthquake engineering.