Project contact is Peter Dusicka at Portland State University
Summary
The urgency in increasing growth in densely populated urban areas, reducing the carbon footprint of new buildings, and targeting rapid return to occupancy following disastrous earthquakes has created a need to reexamine the structural systems of mid- to high-rise buildings. To address these sustainability and seismic resiliency needs, the objective of this research is to enable an all-timber material system in a way that will include architectural as well as structural considerations. Utilization of mass timber is societally important in providing buildings that store, instead of generate, carbon and increase the economic opportunity for depressed timber-producing regions of the country. This research will focus on buildings with core walls because those building types are some of the most common for contemporary urban mid- to high-rise construction. The open floor layout will allow for commercial and mixed-use occupancies, but also will contain significant technical knowledge gaps hindering their implementation with mass timber. The research plan has been formulated to fill these gaps by: (1) developing suitable mid- to high-rise archetypes with input from multiple stakeholders, (2) conducting parametric system-level seismic performance investigations, (3) developing new critical components, (4) validating the performance with large-scale experimentation, and (5) bridging the industry information gaps by incorporating teaching modules within an existing educational and outreach framework. Situated in the heart of a timber-producing region, the multi-disciplinary team will utilize the local design professional community with timber experience and Portland State University's recently implemented Green Building Scholars program to deliver technical outcomes that directly impact the surrounding environment.
Research outcomes will advance knowledge at the system performance level as well as at the critical component level. The investigated building system will incorporate cross laminated timber cores, floors, and glulam structural members. Using mass timber will present challenges in effectively achieving the goal of desirable seismic performance, especially seismic resiliency. These challenges will be addressed at the system level by a unique combination of core rocking combined with beam and floor interaction to achieve non-linear elastic behavior. This system behavior will eliminate the need for post-tensioning to achieve re-centering, but will introduce new parameters that can directly influence the lateral behavior. This research will study the effects of these parameters on the overall building behavior and will develop a methodology in which designers could use these parameters to strategically control the building seismic response. These key parameters will be investigated using parametric numerical analyses as well as large-scale, sub-system experimentation. One of the critical components of the system will be the hold-down, a device that connects the timber core to the foundation and provides hysteretic energy dissipation. Strength requirements and deformation demands in mid- to high-rise buildings, along with integration with mass timber, will necessitate the advancement of knowledge in developing this low-damage component. The investigated hold-down will have large deformation capability with readily replaceable parts. Moreover, the hold-down will have the potential to reduce strength of the component in a controlled and repeatable way at large deformations, while maintaining original strength at low deformations. This component characteristic can reduce the overall system overstrength, which in turn will have beneficial economic implications. Reducing the carbon footprint of new construction, linking rural and urban economies, and increasing the longevity of buildings in seismic zones are all goals that this mass timber research will advance and will be critical to the sustainable development of cities moving forward.
The advantages of the two different building construction materials, timber and concrete, can be used effectively in adhesive-bonded timber-concrete composite constructions. The long-term behavior was investigated experimentally on small-scale shear and bond specimens under artificial, alternating climatic conditions and on fullscale specimens under natural climatic conditions for an application in construction practice. The development of the shear strength and the deformation behavior under permanent loads were studied, focusing on the different material behavior of wood and concrete regarding changes in temperature and moisture. The general applicability of adhesivebonded timber-concrete composites in construction practice was proved in the investigations.
We model the dynamic behavior of laminated curved beams on the assumption that the different layers of such structures are perfectly bonded at the interface and can show different flexural rotations from one another. We formulate a mechanical theory and a finite element model accounting for bending, shear, warping and extensional deformation modes, as well as radial, tangential and rotary inertias. The main novelty of the proposed theory consists of a generalization of layer-wise displacement approaches available in literature to the dynamics of beams with finite curvature. The work includes some numerical results related to the free vibration of laminated arches and showing different support conditions and aspect ratios to establish comparisons with different theories in the literature. We observe that an accurate mechanical modeling of curved laminated beams is crucial for correct estimation of the eigenfrequencies and eigenmodes of such structures within a 1D framework.
This paper discusses the impact of the natural frequency of multi-storey timber structures, focusing on force-based seismic design. Simplified approaches to determine the frequency of light-frame and cross-laminated timber structures are investigated. How stiffness parameters for simple two-dimensional analysis models can be derived from the different contributions of deformation...
A research study was undertaken to investigate the mechanical performance of glulam beams reinforced by CFRP or bamboo. Local reinforcement is proposed in order to improve the flexural strength of glulam beams. The glulam beam is strengthened in tension and along its sides with the carbon fiber-reinforced polymer CFRP or bamboo. A series of CFRP reinforced glulam beams and bamboo reinforced glulam beams were tested to determine their load-deformation characteristics. Experimental work for evaluating the reinforcing technique is reported here. According to experiment results, the CFRP and bamboo reinforcements led to a higher glulam beam performance. By using CFRP and bamboo reinforcements several improvements in strength may be obtained.
In the presented paper, results of theoretical and experimental investigation of timber-concrete composite members with adhesive connection are described. For the timber part of composite beams Cross Laminated Timber and for concrete part lightweight concrete was used. For the composite connection special adhesive to bounding wet concrete and timber was applied. For experimental investigation two types of composite beams with different dimensions was used. Due to the shrinkage of lightweight concrete small precamber of timber beams during concrete hardening was applied. CLT panels combined with concrete slab dispose of higher load-carrying capacity, lower deformation and vibration. In case of theoretical analysis, simplified analytical -method was used to consider shear flexibility of the CLT cross layer. Results of presented experimental and theoretical analysis provide wider scope for further research and application of adhesively bonded CLT-concrete composite members.
With the introduction of 5 and 6-storey wood structures into the National Building Code of Canada 2015, it is important that guidance be provided to engineers to ensure that a reasonable design approach can be sought in the design of taller wood structures. The purpose of this technical paper is to compare various methods for calculating building deformations for wood-platform framed structures, which range from simply assuming each storey acts independent of the adjacent storey to a purely mechanics-based approach considering all 6 storeys acting as a continuous wall in order to compare the differences in drifts, stiffness, building period, base shear, and force distribution based on relative stiffness. General guidance is provided on which method to use.
