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Ductile concentrically braced frames (CBFs) are commonly used seismic force-resisting systems in seismic regions. The capacity design approach described in the state-of-the-art seismic codes of the US, Canada, and Turkey defines a design procedure for columns and girders via two structural analyses that intend to capture the nonlinear behavior of CBFs while assuming braces in different stories undergo yielding or buckling, simultaneously. It would be, therefore, befitting to question the validity of the anticipated mechanism controlling CBF design considering limited studies in the literature. In addition to chevron and two-story Xbraced frame configurations, an alternative design approach is proposed without changing the current habits in the industry. The present study aims to investigate whether or not the capacity design approach adopted by the leading seismic codes is consistent with the nonlinear behavior of CBFs via pushover analyses and time-history analysis. For the proto-type CBFs, peak and residual inter-story drift ratios were compared as well as ductility demands of braces. In conclusion, it is found that mechanism scenarios stimulated in current seismic codes are unlikely to occur under an earthquake event and the proposed balanced design approach provided significant reductions on seismic demands, only with an 8% increase in weight. [ABSTRACT FROM AUTHOR]

This study examines the seismic behaviour of steel multi-tiered concentrically braced frames (MT-CBFs) of the conventional construction category (Type CC) in moderate seismic regions of eastern Canada and proposes a new seismic design method for such structures. A total of 32 prototype MT-CBFs part of a single-storey building are selected and designed in accordance with the 2019 Canadian steel design standard (CSA S16-19) provisions for Type CC structures, excluding the design requirements prescribed for frames taller than 15 m, namely the amplification of seismic forces varying by the frame height and the amplification of the column factored seismic force. Nonlinear response history analyses are then performed to examine their seismic response. The results confirmed that tiers experience limited lateral deformation, intermediate horizontal struts are required between tiers, and columns are subjected to combined axial force and bi-axial bending, which in some cases led to column buckling. The results are used to propose a new seismic design method in the framework of CSA S16. [ABSTRACT FROM AUTHOR]

• Combined out-of-plane bending and compression is an inevitable loading condition for CLT walls. • The experimental program consisted of 36 CLT panel specimens. • The damage was caused by the local buckling near the mid-height of the outer layer on the compression side. • Signs of shear failure of cross layers were evident almost simultaneously with the outer layer failure. • The interaction equations specified in the Canadian design standard are appropriate for the CLT panels under small load eccentricities. Combined out-of-plane bending and compression is an inevitable loading condition for cross-laminated timber (CLT) walls due to the out of plumbness, initial panel curvature and load eccentricity. Because of the weaker cross layers, the mechanical performance and failure mode of the CLT panels under such loading significantly differ from those of the other wood members, such as sawn timber and glulam. This experimental study focuses on investigating the behavior of CLT panels under the stated loading scenario. The experimental program consisted of 36 specimens, including 12 five-layer CLT panels provided by two Canadian manufacturers, as well as 12 three-layer and 12 five-layer CLT panels provided by a Chinese manufacturer. All the specimens were tested in Canada and China, respectively, using the same test setup. It was found that in the majority of the specimens, the damage was caused by the local buckling near the mid-height of the outer layer on the concave compression side at about 45%–60% of the ultimate failure load and 25%–35% of the ultimate deflection. The dominant failure mode was characterized as the crushing yield of the outer layer on the concave side (fibers in compression) near the mid-height after the local buckling progressed. Signs of shear failure of cross layers were evident almost simultaneously with the outer layer failure. Hence, although the dominant failure mode was likely triggered by the fracture in the cross layers due to rolling shear, the load-carrying capacity of the CLT panels under the combined out-of-plane bending and compression is governed by the compression failure of the longitudinal outer layers. It was found that a cross-layered panel can maintain its integrity before failure. It was also noted that the interaction equations specified in the Canadian design standard are appropriate for the CLT panels under small load eccentricity, while for panels that have large load eccentricity, the appropriateness of the interaction equation is questionable. Based on the test results obtained, the validity of the interaction equation for the prediction of the load-carrying capacity of CLT columns, specified in the CSA O86-19, is confirmed for cases in which P f / P r > 0.5 and M f / M r < 0.3. For the cases of P f / P r < 0.5 and M f / M r > 0.3 , modification of the equation is needed. [ABSTRACT FROM AUTHOR]