The present study deals with the innovation and the possibilities of improving the design solution of a frame connection for two selected types of fasteners. All specimens were made of glued laminated timber. Dowel-type mechanical fasteners, a combination of bolts and dowels, and full-threaded screws were used for the connection. The main goal of this research was to replace the typical solution (common dowel-type fasteners) with a more modern, faster, and easier solution in order to improve the load-carrying capacity, ductility, and deformation capacity of this type of frame connection. This article also aimed to provide a detailed evaluation of the mechanical properties of the used glued laminated timber and fasteners in order to comprehensively evaluate the research task. For the design solution, a frame connection created from a system of two struts and a partition was chosen as the basis of the experimental program. Dowel-type mechanical fasteners, as well as combinations of bolts and dowels, were used for the connection; however, in addition to these standardly used mechanical fasteners, full-threaded screws were used. The article describes the use of static destructive testing to determine the ductility of the connection, considering different variations in the strengthening of the individual segments of the mentioned connection means. In the first variation, the individual components of the frame were not reinforced in any way. In the second, the crossbar was reinforced with two full-threaded bolts. In the third, the webs and the crossbar were reinforced with two full-threaded bolts. In the article, these ductility values were compared with each other and the procedure was set by the currently valid standard.
The post-tensioned frame is one of the recently emerged structural systems for multi-story timber buildings. It is characterized by a high level of prefabrication and quick erection on the construction site. The post-tensioned frame developed at ETH Zurich is based on post-tensioned beam–column connections with hardwood reinforcement of the column in the connection region and column base connections with glued-in steel rods. Such a construction system is suitable for low- and mid-rise buildings that are located in regions characterized by low to moderate seismicity.
This paper presents a series of hybrid simulations of the response of a two-story two-bay post-tensioned timber frame subjected to ground motion excitation. Nonlinear numerical models of both beam–column and column base connections to be used for design purposes are validated based on the experiments.
A new timber frame structural system consisting of continuous columns, prefabricated hollow box timber decks and beam-to-column moment-resisting connections is investigated. The hollow box timber decks allow long spans with competitive floor height and efficient material consumption. To achieve long spans, semi-rigid connections at the corners of deck elements are used to join the columns to the deck elements. In the present paper, experimental investigations of a semi-rigid moment-resisting connection and a mock-up frame assembly are presented. The semi-rigid connection consists of inclined screwed-in threaded rods and steel coupling parts, connected with friction bolts. Full-scale moment-resisting timber connections were tested under monotonic and cyclic loading to quantify rotational stiffness, energy dissipation and moment resistance. The mock-up frame assembly was tested under cyclic lateral loading and with experimental modal analysis. The lateral stiffness, energy dissipation, rotational stiffness of the connections and the eigen frequencies of the mock-up frame assembly were quantified based on the experimental tests in combination with a Finite Element model, i.e., the model was validated with experimental results from the rotational stiffness tests of the beam-to-column connections. Finally, the structural damping measured with experimental modal analysis was evaluated and compared with FE model using the material damping of timber parts and equivalent viscous damping of the moment-resisting connections.
This study involves the application of timber-based bracings elements. For this purpose, seismic analyses are performed on special portal steel frames without the brace and diagonally braced with Glued Laminated Timber (glulam) and Timber-Steel Buckling Restrained Brace (TS-BRB), and the results are compared with the same configuration using steel Hollow Structural Sections (HSS) bracing, using OpenSees structural analyzer. First, to verify the accuracy of the modeling, the numerical results are compared with experimental measurements on several types of elements: (a) diagonally braced frame with steel Hollow Structural Sections with a concentrically steel braced frame which was tested by the quasi-static method under cyclic loading protocol by previous researchers, (b) diagonally glulam braced frame with results of shake table tests on single-story timber braced frames, and (c) Timber-Steel Buckling Restrained Brace (TS-BRB) frame with experimental results of Heavy Timber Buckling-Restrained Braced Frame (HT-BRB). In the second step, the aforementioned timber base bracing alternatives (glulam, TS-BRB) are applied in the special portal steel frame, then the seismic performance of the frame is investigated under pushover, cyclic, time history, and incremental dynamic analysis (IDA), and then the results are compared with the behavior of similar portal frame in two conditions without the brace and diagonally braced with the steel-HSS brace. Results showed that steel-HSS, glulam, and timber-steel buckling restrained braces have significant roles in energy dissipation, increasing shear capacity, decreasing interstory drift, and decreasing weight and cost of estimation of the structure.
CLT panels have been investigated for reinforcement of existing masonry-infilled RC framed buildings through the increase of the overall lateral stiffness of the structure, thus reducing the story drift demand. The contribution of CLT panels depends on the connection to the RC frame elements. This paper evaluates the role of connectors by which CLT is attached to RC frames for capacity, ductility, and energy dissipation of the structure and its elements separately using different kinds of RC-CLT connections, and ultimately finds and compares the optimum number and arrangement of connectors. The results show that the geometry of connections plays a greater seismic role in RC frames than their mechanical properties. Regarding masonry infills, they allow a higher strength capacity but reduce the efficacy of CLT strengthening. However, strong connectors decrease the ability of infills in dissipation. Finally, in the optimum arrangement of connectors, they are distributed equally along the upper and lower beams at equal spacing, where CLT is added, starting in the middle of the beams and moving to the frame corners.
Behaviour and capacity of cross-laminated timber (CLT) infills built inside steel frames have been given increasing research attention in recent years. It is widely accepted that when the CLT wall panel is built in tight contact with the bounding steel frame to participate in the load sharing, its inherently large in-plane stiffness will attract additional forces to the frame area and change the behaviour of the hybrid system. If not designed properly, the structural integrity of both the infill and the frame will be compromised. It is thus crucial to accurately evaluate the contribution of the infill CLT wall panel to the stiffness and strength of the hybrid system. To that end, a finite element study was performed to investigate the frame-wall interaction effect on the behaviour of hybrid systems. The lateral stiffness, lateral load capacities and hysteretic characteristics of the hybrid systems with frictional and connected interfaces were investigated. The load-sharing effect between the CLT wall and the steel frame was studied. The numerical results showed that the connected models were very effective as the infill absorbed a substantial part of the lateral load, during the initial stages of loading.
This paper presents a direct displacement-based design (DDBD) approach for the buckling restrained braces (BRBs) braced glue-laminated timber (glulam) frame (BRBGF) structures. First, the critical design parameters of the DDBD approach were derived for BRBGFs. Then, using experimentally verified numerical models, pushover analyses and nonlinear time-history analyses (NLTHAs) were conducted on a series of one-storey BRBGFs to calibrate the stiffness adjustment factor for BRB-timber connections and the spectral displacement reduction factor . Finally, the DDBD approach was verified as a prospective approach for the seismic design of multi-storey BRBGF buildings by NLTHAs of the case study buildings.
The need to lower the embodied carbon impact of the built environment and sequester carbon over the life of buildings has spurred the growth of mass timber building construction, leading to the introduction of new building types (Types IV-A, B, and C) in the 2021 International Building Code (IBC). The achievement of sustainability goals has been hindered by the perceived first cost assessment of mass timber systems. Optimizing cost is an urgent prerequisite to embodied carbon reduction. Due to a high level of prefabrication and reduction in field labor, the mass timber material volume constitutes a larger portion of total project cost when compared to buildings with traditional materials. In this study, the dollar cost, carbon emitted, and carbon sequestered of mass timber beam–column gravity system solutions with different design configurations was studied. Design parameters studied in this sensitivity analysis included viable building types, column grid dimension, and building height. A scenario study was conducted to estimate the economic viability of tall wood buildings with respect to land costs. It is concluded that, while Type III building designations are the most economical for lower building heights, the newly introduced Type IV subcategories remain competitive for taller structures while providing a potentially significant embodied carbon benefit.
This InfoNote briefly introduces the promising mass timber seismic force resisting systems, and the corresponding analytical and finite element models to support their adoptions in structural design offices.
Mass timber (MT) products, such as Glued Laminated Timber (GLT), Cross Laminated Timber (CLT), Laminated Veneer Lumber (LVL), Nail Laminated Timber (NLT), Dowel Laminated Timber (DLT), Laminated Strand Lumber (LSL), Parallel Strand Lumber (PSL), Mass Plywood Panels (MPP) and others, provide options for developing efficient structural systems to resist gravity and lateral loads. Such systems can be competitive alternatives to their steel and concrete counterparts. This InfoNote briefly introduces the MT Seismic Force Resisting Systems (SFRSs) that will be implemented in the 2020 National Building Code (NBC) of Canada, their height limits, and the main design requirements according to Canadian Standard for Engineering Design in Wood CSA O86-19. Differences among height limits for MT gravity and lateral load resisting systems are also discussed.