SUMMARYThe paper is concerned with the seismic design of steel-braced frames in which the braces are conÿgured in a chevron pattern. According to EuroCode 8 (EC8), the behaviour factor q, which allows for the tradeo between the strength and ductility, is set at 2.5 for chevron-braced frames, while 6.5 is assigned for most ductile steel moment-resisting frames. Strength deterioration in post-buckling regime varies with the brace's slenderness, but EC8 adopts a unique q value irrespective of the brace slenderness. The study focuses on reevaluation of the q value adequate for the seismic design of chevron-braced frames. The present EC8 method for the calculation of brace strength supplies signiÿcantly di erent elastic sti nesses and actual strengths for di erent values of brace slenderness. A new method to estimate the strength of a chevron brace pair is proposed, in which the yield strength (for the brace in tension) and the post-buckling strength (for the brace in compression) are considered. The new method ensures an identical elastic sti ness and a similar strength regardless of the brace slenderness. The advantage of the proposed method over the conventional EC8 method is demonstrated for the capacity of the proposed method to control the maximum inter-storey drift. The q values adequate for the chevron-braced frames are examined in reference to the maximum inter-storey drifts sustained by most ductile moment-resisting frames. When the proposed method is employed for strength calculation, the q value of 3.5 is found to be reasonable. It is notable that the proposed method does not require larger cross-sections for the braces compared to the cross-sections required for the present EC8 method.

In seismic European countries most of the residential building stock is highly energy-intensive and earthquake-prone because it was built before the enforcement of the most recent energy and seismic codes. Furthermore, this stock often shows a low architectural quality due to poor maintenance and/or construction and design deficiencies: for all these reasons, it needs deep renovation, but the use of common energy and seismic upgrading techniques is often unsustainable in terms of costs, work duration, and occupants’ disturbance. Therefore, new integrated, affordable, fast, and low-disruptive renovation actions are strongly needed. This study proposes an innovative energy, seismic, and architectural renovation solution for reinforced concrete (RC) framed buildings, based on the addition of cross-laminated timber (CLT) panels to the outer walls, in combination with wooden-framed panels. The two panels integrate insulation and cladding materials in order to improve the energy performance and the architectural image of the renovated building. Moreover, the CLT panels are connected to the existing RC frame through innovative seismic energy dissipation devices. In case of an earthquake, these devices in combination with the CLT panels reduce the drift demand of the building, preventing or reducing structural damages and consequent repair costs. In particular, this paper investigates the technical feasibility, the energy efficiency, and the architectural enhancement of the proposed retrofitting system. To this purpose, dynamic thermal simulations were conducted on a typical multi-story residential building from the 1960s, located in Catania, Italy. The results indicated that this retrofitting technique considerably improved the energy performance of the selected building, with a reduction of the global energy demand up to nearly 60%. The presented study is part of a larger research project aimed at also investigating, in a further stage, the seismic performance achievable by the above-mentioned renovation solution.

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SUMMARY Eurocode 8 (EC8) stipulates design methods for frames with diagonal braces and for chevron braced frames, which differ as regards the numerical model adopted, the value of the behavior factor q and the estimation of the lateral strength provided by braces. Instead, in this paper, the use of the same design method is suggested for both types of concentrically braced frames. The design method is a generalization of the one proposed for chevron braced frames in a previous study. A numerical investigation is conducted to assess the reliability of this design method. A set of concentrically braced frames is designed according to the EC8 and proposed design methods. The seismic response of these frames is determined by nonlinear dynamic analysis. Finally, it is demonstrated that the proposed design method is equivalent to those provided by EC8, because it can ensure the same level of structural safety which would be expected when using EC8. Copyright © 2013 John Wiley & Sons, Ltd.