Hybrid cross laminated timber (HCLT) was fabricated using lumber (Spruce-pine-fir,SPF) and laminated veneer lumber (LVL), the bending and shear performances of which were evaluated. Three types of CLT panels, one generic CLT (used as control) and two types HCLT, were fabricated. The failure modes of CLT and HCLT were visually examined and recorded. The mechanical properties measured included the bending properties (in the major direction) and shear properties (in both major and minor directions). It was found that the planar shear failure of cross layer was the key and primary failure mode of CLT and HCLT under bending. Lumber and LVL had different direction of crack propagation in planar shear, and LVL had lower planar shear properties than SPF lumber. The weak zones in the radial-tangential (RT) section of wood including earlywood/laterwood boundary and wood ray were easy to occur shear failure. The HCLT having LVL as the outer layer had the highest bending and shear strengths. The modulus of elasticity (MOE) of the HCLT having LVL as the outer layer and lumber as the cross layer was 17.6% higher than that of generic CLT. However, the HCLT having lumber as the outer layer and LVL as the cross layer had the lowest mechanical properties.
The Italian building heritage is aged and inadequate to the high-performance levels required nowadays in terms of energy efficiency and seismic response. Innovative techniques are generating a strong interest, especially in terms of multi-level approaches and solution optimizations. Among these, Nested Buildings, an integrated intervention approach which preserves the external existing structure and provides a new structural system inside, aim at improving both energy and structural performances. The research presented hereinafter focuses on the strengthening of unreinforced masonry (URM) buildings with cross-laminated timber (CLT) panels, thanks to their lightweight, high stiffness, and good hygrothermal characteristics. The improvement of the hygrothermal performance was investigated through a 2D-model analyzed in the dynamic regime, which showed a general decreasing in the overall thermal transmittance for the retrofitted configurations. Then, to evaluate the seismic behavior of the coupled system, a parametric linear static analysis was implemented for both in-plane and out-of-plane directions, considering various masonry types and connector spacings. Results showed the efficiency of the intervention to improve the in-plane response of walls, thus validating possible applications to existing URM buildings, where local overturning mechanisms are prevented by either sufficient construction details or specific solutions. View Full-Text
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.
This paper discusses the state-of-the-art of displacement-based seismic design (DBD) methods and their applications to timber buildings. First, an in-depth review of the DBD methods is presented, focusing in particular on the direct, modal and N2 methods. Then, paper presents DBD application on a wide range of construction systems, including both traditional light-frame structures as well as the emerging sector of tall and hybrid timber buildings. Finally, potentials of using these DBD methods for seismic design as well as possible implications of including DBD within the next generation of building codes are discussed.