Disproportionate collapse analysis of mid-rise cross-laminated timber buildings

This paper investigates the structural behaviour of a twelve-storey Cross-Laminated Timber (CLT) building subjected to sudden removal of internal and external ground floor loadbearing walls, and computes the probability of disproportionate collapse. Analyses are carried out at three different structural idealisations, accounting for feasibility and complexity of finite elements models to understand their performance at: i) the global, ii) the component, and iii) the connection level. Focus is devoted on force and deformation-demands obtained from nonlinear dynamic analyses of the building. The demands are compared against the supply from common CLT panel sizes and the rotational stiffness (k) of the joints, detailed with off-the-shelf angle brackets and self-tapping screws. The study demonstrates that the applied forces and deformations required to develop resistance mechanisms are too large to be supplied by the proposed element and connection designs, if an internal ground floor wall is removed. The considered building has a probability of failure as high as 32% if designed without considerations of the complexities associated with disproportionate collapse. Consequently, to resist the effects of internal wall removal, the floors need to be redesigned and improved structural detailing with sufficient strength, stiffness, and ductility is necessary to trigger collapse resistance mechanisms

Disproportionate Collapse Prevention of CLT Platform-Type Buildings

Without additional design considerations, such as structural robustness, the failure of a building’s structural element can develop into a progressive and/or disproportionate collapse. The existing requirements given in international guidelines for preventing disproportionate collapse are generally not practical and uneconomic when applied to multi-storey cross-laminated timber (CLT) buildings in platform-type construction. This paper summarises recent research and improved approaches developed to meet structural robustness for such buildings. To ensure alternative load-paths using simplified linear elastic analytical procedures, an improved method using engineering mechanics was derived for CLT buildings in platform-type construction to aid in quantifying connection tie forces between structural components. Using advanced nonlinear dynamic analyses, the behaviour of two case-study buildings under element removal scenarios are studied: i) 12-storey with CLT floor and wall system; and ii) 9-storey flat-plate CLT floor system point-supported on glulam columns. Finally, in a nonlinear pushdown analysis of a platform CLT bay to characterise the resistance mechanism of the floor and wall panels, four different alternative load-paths are evaluated. The presented findings can support the design of multi-storey CLT buildings in platform-type construction to ensure structural robustness.Godkänd;2021;Nivå 0;2021-05-28 (alebob)</p

Disproportionate Collapse Prevention of CLT Platform-Type Buildings

Without additional design considerations, such as structural robustness, the failure of a building’s structural element can develop into a progressive and/or disproportionate collapse. The existing requirements given in international guidelines for preventing disproportionate collapse are generally not practical and uneconomic when applied to multi-storey cross-laminated timber (CLT) buildings in platform-type construction. This paper summarises recent research and improved approaches developed to meet structural robustness for such buildings. To ensure alternative load-paths using simplified linear elastic analytical procedures, an improved method using engineering mechanics was derived for CLT buildings in platform-type construction to aid in quantifying connection tie forces between structural components. Using advanced nonlinear dynamic analyses, the behaviour of two case-study buildings under element removal scenarios are studied: i) 12-storey with CLT floor and wall system; and ii) 9-storey flat-plate CLT floor system point-supported on glulam columns. Finally, in a nonlinear pushdown analysis of a platform CLT bay to characterise the resistance mechanism of the floor and wall panels, four different alternative load-paths are evaluated. The presented findings can support the design of multi-storey CLT buildings in platform-type construction to ensure structural robustness.Godkänd;2021;Nivå 0;2021-05-28 (alebob)</p