Braced frames, usually steel, are among the most common and cost-effective primary retrofit systems. Compared to reinforced concrete walls they are light-weight and have less impact upon views from windows and natural light. Figure 12.14 shows rather unusually configured, yet fully triangulated braced frames. Most load transfer is through tension forces in the slender diagonal members as their buckling capacity is limited. Eccentrically braced frames inserted into a 1960s three-storey reinforced concrete building provide a new line of seismic resisting structure (Fig. 12.15). Strong
connections at diaphragms transfer forces into the new frames. Braced frames incorporating buckling-restrained braces are increasingly an alternative to eccentric braced frames (Chapter 14).
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