Simplified seismic design procedures mostly recommend the adoption of rigid floor diaphragms when forming a building’s lateral force-resisting structural system. While rigid behavior is compatible with many reinforced concrete or composite steel-concrete floor systems, the intrinsic stiffness properties of wood and ductile timber connections of timber floor slabs typically make reaching a such comparable in-plane response difficult. Codes or standards in North America widely cover wood-frame construction, with provisions given for both rigid and flexible floor diaphragms designs. Instead, research is ongoing for emerging cross-laminated-timber (CLT) and hybrid CLT-based technologies, with seismic design codification still currently limited. This paper deals with a steel-CLT-based hybrid structure built by assembling braced steel frames with CLT-steel composite floors. Preliminary investigation on the performance of a 3-story building under seismic loads is presented, with particular attention to the influence of in-plane timber diaphragms flexibility on the force distribution and lateral deformation at each story. The building complies with the Italian Building Code damage limit state and ultimate limit state design requirements by considering a moderate seismic hazard scenario. Nonlinear static analyses are performed adopting a finite-element model calibrated based on experimental data. The CLT-steel composite floor in-plane deformability shows mitigated effects on the load distribution into the bracing systems compared to the ideal rigid behavior. On the other hand, the lateral deformation always rises at least 17% and 21% on average, independently of the story and load distribution along the building’s height.
Project contact is Cristiano Loss at the University of British Columbia
This research is focused on bridging the current knowledge gap on steel-timber composite floors, where CLT panels are connected to steel beams. Most of the current design codes lack provisions and guidelines for the design of steel-timber composite floors.
Timber-steel hybrid beams have been proposed, tested and analyzed for their use in multi-storey buildings. After the first concepts and tests were presented in the WCTE 2014, two whole testing series are finished and their results globally presented and analyzed. The beams fulfilled all the expectations and therefore can be presented as a reliable possibility for future proposals of timber-based frame multi-storey buildings. The present paper presents a summary of the part regarding hybrid beams inside the research project “Timber based mixed systems for dense construction in urban areas” carried out by the Institute of Structural Design and Timber Engineering of the Vienna University of Technology.
The present contribution deals with the theoretical analysis of a selected geometry of CLT-elements combined with steel trapezoidal cross sections with a subsequent description of test specimens and the results of the conducted four-point-bending test. Used for long span floors this hybrid construction can be adjusted in its bending stiffness as needed. By placing the steel part into the tension zone a ductile failure mode can be achieved as well as notching the trapezoidal cross section is applicable easily. By performing full scale four-point-bending-tests of several test specimens it was possible to confirm the theoretical findings.