In this paper a precise model is established for deflection prediction of mechanically jointed beams with partial composite action. High accuracy of the proposed method is demonstrated through comparison with a comprehensive finite element (FE) modelling for a timber-concrete partial composite beam. Next, the obtained numerical results are compared with gamma-method, a well-known simplified solution for timber engineers according to the Eurocode 5. Validity and accuracy level of the gamma-method are investigated for various boundary conditions as well as different values of beam length-to-depth ratio, and discussed in details.
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.
Cross-Laminated Timber (CLT) is a renewable, sustainable, and cost-efficient building element that has been growing in popularity in recent years. To improve one of its weaknesses, suboptimal noise and vibration isolation performance, computationally efficient, accessible, and extensible CLT vibro-acoustic models are required. An effective approach for such models is the homogenisation of layered materials. This paper presents a validated homogenisation method based on First-Order Shear Deformation Theory (FSDT) that obtains the frequency-independent elastic material properties. It is applicable to arbitrary stacking sequences and orientations. The homogenised material properties are utilised with FSDT Equivalent Single Layer (ESL) models that are readily implemented with many finite element method codes to calculate the vibro-acoustic behaviour of CLT elements, even including thickness resonance effects when applied with an appropriate model. The presented homogenisation method for CLT is validated in a numerical study by comparing the mechanical mobilities of ESL models against layerwise dynamic models. The numerical study is conducted based on a validated 5-ply model, for 2- to 7-ply CLT plates with proportionally increasing thicknesses and three idealised boundary conditions. The frequency-independent material properties allow for graphical exploration of the anisotropic nature of CLT and the calculation universal anisotropic index of the considered CLT plates. The flexibility of the homogenisation method, combined with its ready implementation in already widely implemented FSDT models can have an application and impact beyond the vibro-acoustic considerations of CLT, into the general mechanical modelling of CLT as it is implemented in ever more advanced applications.
Cross-laminated timber makes timber buildings with an increasing number of storeys achievable. With more storeys, structural robustness needs more attention to make a building survive unforeseen events (e.g. accidents, terrorism) and save lives. For steel and concrete buildings, design methods for robustness focus on connection details. The assessment of joints in cross-laminated timber buildings regarding robustness is rather limited in the literature. The objective of this paper is to conduct an initial assessment of the connectors after the removal of a wall in a platform cross-laminated timber building. We used the finite element method and the component method for the analysis of a case building. The results indicate that the wall-to-wall and the floor-to-floor connectors may fail at low deflection levels leading to high shear loads in the floor panel above the removed wall, which might induce cracking. The removal analysis was only partially completed, but we identified an indication of the deformation behaviour of the case building. Testing and refined modelling of the connections is needed in the future to verify the results. This study may facilitate future investigations regarding robustness of multi-storey cross-laminated timber buildings.
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.
