The following topics in the field of seismic analysis and design of mid-rise (5- and 6-storey) wood-frame buildings are included in this paper: Determination of the building period, linear dynamic analysis of wood-frame structures, deflections of stacked multi-storey shearwalls, diaphragm classification, capacity-based design for woodframe...
Cross-laminated timber (CLT) products are gaining popularity in the North American market and are being used in midrise wood buildings, in particular, in shearwall applications. Shearwalls provide resistance to lateral loads such as wind and earthquake loads, and therefore it is important to gain a better understanding of the behavior of CLT shearwall systems during earthquake events. This paper is focused on the seismic performance of connections between CLT shearwall panels and the foundation. CLT panels are very stiff and energy dissipation is accomplished by the connections. A literature review on previous research work related to damage prediction and assessment for wood frame structures was performed. Furthermore, a test program was conducted to investigate the performance of CLT connections subjected to simulated earthquake loads. Two different brackets in combination with five types of fasteners were tested under monotonic and cyclic loading protocols. In total, 98 connection tests were conducted and the monotonic load-displacement curves and hysteretic loops were obtained. In this paper, an energy-based cumulative damage assessment model was calibrated with the CLT connection test data. Finally, a correlation between the damage index and physical damage is provided.
Wood-frame is the most common construction type for residential buildings in North America. However, there is a limit to the height of the building using a traditional wood-frame structure. Cross-laminated timber (CLT) provides possible solutions to mid-rise and high-rise wood buildings. CLT offers many advantages such as improved dimensional stability, a quicker erection time and good performance in case of fire. In order to introduce the cross-laminated timber products to the North American market, it is important to gain a comprehensive understanding of its structural properties. This paper focuses on the seismic performance of CLT connections. Over the last few years FPInnovations of Canada has conducted a test program to determine the structural properties of CLT panels and its application in shear walls. The test program comprised of more than 100 connection tests which followed the loading procedures of CUREE and ISO test protocols as specified in ASTM Standards ASTM E 2126-09 (2009). These tests were performed parallel and perpendicular to the grain of the outer layer, respectively. The impact of different connections on the seismic performance of CLT walls was investigated in a second phase on full size shearwall. CLT panels are relatively stiff and thus energy dissipation must be accomplished through the ductile behaviour of connections between different shear wall elements and the connections to the story below. A literature review on previous research work related to damage prediction and assessment for wood frame structures was performed. Different approaches for damage indices were compared and discussed. This paper describes how the energy-based cumulative damage assessment model was calibrated to the CLT connection and shear wall test data in order to investigate the damage under monotonic and cyclic loading. Comparison of different wall setup provided a deeper insight into the damage estimation of CLT shear walls and determination of the key parameters in the damage formulation. This represents a first published attempt to apply the damage indices to estimate the seismic behaviour of CLT shear walls.
International Specialty Conference on Behaviour of Steel Structures in Seismic Areas
January 9-11, 2012, Santiago, Chile
A steel-wood hybrid system furnishes not only aesthetically pleasing and sustainable hybrid structures but is superior in seismic applications due to the light weight, high resistance, and adjustable ductility. Such hybrid structural systems are not covered by any material and structural design standards that hinder the general implementation. For light structures, a builder’s guide to hybrid wood and steel connection details already exists in North America. Despite the obvious advantages, however, today’s applications of steel-wood hybrid structures have been limited. Rare hybrid buildings with a concentrically braced frame used for lateral load resistance with a glulam timber floor slab have been built as prototypes. The use of glulam floor slab led to a substantially reduced self-weight, compared with the reinforced concrete slab option. The lighter structure behaves superior in seismic events and has made wind loads the governing design case. The next generation steel-wood hybrid structures should optimally utilize each material. This paper describes a research program of the next generation wood-steel hybrid structures should optimally utilize each material. In detail the following development issues will be addressed: innovative hybrid steel-wood building systems, technical tools to predict structural responses of hybrid systems, design principles underpinning the definition of key code provisions related to strength and serviceability performance of hybrid buildings. It will be highlighted that potential structural problems at the design stage result from material incompatibilities. The constitutive properties of each material, hybrid-material, and joint properties reported in the literature will be used, or supplemented by findings from experimental work.
This study proposes an iterative direct displacement based design method for a novel steel-timber hybrid structure. The hybrid structure incorporates Cross Laminated Timber (CLT) shear panels as an infill in steel moment resisting frames. The proposed design method is applied to design 3-, 6-, and 9-story hybrid buildings with three bays and CLT infilled middle bay. Nonlinear time history analysis, using twenty earthquake ground motion records, is carried out to validate the performance of the design method. The results indicate that the proposed method effectively controls the displacements due to seismic excitation of the hybrid structure.
Second European Conference on Earthquake Engineering and Seismology
August 25-29, 2014, Istanbul, Turkey
Cross-laminated timber (CLT) as a structural system has not been fully introduced in European or North American building codes. One of the most important issues for designers of CLT structures in earthquake prone regions when equivalent static design procedure is used, are the values for the force modification factors (R-factors) for this structural system. Consequently, the objective of this study was to derive suitable ductility-based force modification factors (Rd-factors) for seismic design of CLT buildings for the National Building Code of Canada (NBCC). For that purpose, the six-storey NEESWood Capstone wood-frame building was redesigned as a CLT structure and was used as a reference symmetrical structure for the analyses. The same floor plan was used to develop models for ten and fifteen storey buildings. Non-linear analytical models of the buildings designed with different Rd-factors were developed using the SAPWood computer program. CLT walls were modelled using the output from mechanics models developed in Matlab that were verified against CLT wall tests conducted at FPInnovations. Two design methodologies for determining the CLT wall design resistance (to include and exclude the influence of the hold-downs), were used. To study the effects of fastener behaviour on the R-factors, three different fasteners (16d nails, 4x70mm and 5x90mm screws) used to connect the CLT walls, were used in the analyses. Each of the 3-D building models was subjected to a series of 22 bi-axial input earthquake motions suggested in the FEMA P-695 procedure. Based on the results, the fragility curves were developed for the analysed buildings. Results showed that an Rd-factor of 2.0 is appropriate conservative estimate for the symmetrical CLT buildings studied, for the chosen level of seismic performance.
Nail-Laminated Timber (NLT) and box beam are efficient and economical engineered wood products. Although NLT has been used in North America for more than a century, only in recent years it has gained renewed interests as they have been seen as the most economical panel products used in mass timber buildings. Box beams, on the other hand, are lightweight and generally possess higher strength and stiffness than comparable-sized solid timber and are more efficient than solid timber large spans and loads.
In this report, existing design provisions and their limitations for the design and construction of NLT in box beam in Canadian standards are reviewed. For NLT, there is a general lack of information related to manufacturing, design and construction to ensure consistent manufacturing and installation practices. Therefore, it is difficult to research and document with confidence the full range of performance that can be achieved with NLT. It is therefore recommended that a North American product standard and design information on structural performance, floor vibration, fire resistance, acoustic performance, and construction risk mitigation measures (e.g. moisture and fire) be developed.
In CSA 086, design methods are limited to box beams with flanges and webs bonded with glue. As the flanges and webs of a box beam can be assembled by either glue or mechanical fasteners, it is recommended that design provisions for box beam with mechanical joints be also developed. With the information in Eurocode 5 and relevant supporting research papers, it is ready to be implemented.
Due to the awareness of the importance of reducing environmental footprint and the rising costs of construction, timber structures have been increasingly attracting attention and, subsequently, adoption for being built taller and larger. Computer modelling plays a crucial role in the analysis and design of large and tall timber structures, and in the development of wood-based products, connections, and systems. A survey by FPInnovations showed that practising engineers are typically unfamiliar with timber structure modelling, and researchers generally lack resources for advanced modelling of timber systems. Therefore, in 2020, FPInnovations initiated a project to develop a guide that would support the application of numerical modelling on the analysis and design of timber structures, and the development and optimisation of wood-based products and systems. The Modelling Guide for Timber Structures is the result of a global effort involving over 100 collaborators, including experts from research institutes, consulting firms, manufacturers, software companies, government entities, and associations.
This guide brings together the experience gained from recently built timber projects, and the latest research development in the modelling of timber structures. It includes a wide range of practical and advanced modelling topics, such as key modelling principles, methods, and techniques specific to timber structures; modelling approaches and considerations for wood-based components, connections, and assemblies; and analytical approaches and considerations for timber structures during progressive collapse, wind, and earthquake events. It also presents the differences in the modelling approaches to timber, steel, and concrete structures.
The information presented in this guide is intended to assist practising engineers to apply computer modelling to timber structures, enrich researchers’ resources for advanced computer modelling of timber systems, and assist software companies in identifying knowledge gaps so that they may upgrade programs accordingly to accommodate the advanced computer modelling of timber structures.
European experience shows that besides single family housing, Cross-Laminated Timber (CLT) can be competitive in mid-rise and high-rise buildings. Although this system has not been used to the same extent so far in North America, it can be viable wood structural solution for the shift towards sustainable densification of urban and suburban centres. FPInnovations has undertaken a multidisciplinary project on determining the structural properties of a typical CLT construction, including quantifying the seismic resistance and force modification factors of CLT buildings. In this paper, some of the results from a series of quasi-static tests on CLT wall panels are presented as well as preliminary estimates for the force modification factors (R-factors) for seismic design of CLT structures. CLT wall panels with various configurations and connection details were tested. Wall configurations included single panels without openings with three different aspect ratios, panels with openings, as well as multi-panel walls with step joints and fasteners between them. Connections for securing the walls to the foundation included off-the-shelf steel brackets with annular ring nails, spiral nails, and screws; a combination of steel brackets and hold-downs; and custom made brackets with timber rivets. Results from two storey configurations that include two walls and a CLT slab in between are presented and discussed. Finally preliminary estimates and recommendations for the force modification factors (R-factors) for seismic design of CLT structures according to National Building Code of Canada (NBCC) are also made.
A survey was conducted under the "Renessaince in Wood Construction" project that was funded by Natural Resources Canada (NRCan) under the Transformative Technologies Program to see information about numerical modelling on mass timber buildings. A questionnaire was sent to designers and researchers covering different performance attributes. The compiled information includes the available software packages and resources of empirical equations that are used by the designers and researchers for predicting the structural, fire, acoustic, and building envelope (energy and durability) performance of mass timber buildings, and the challenges that they are facing in using those tools. This report summarizes the input obtained from practicing designers and researchers who responded to this survey.