This study investigated the vibration serviceability of timber structures with dowel-type connections. It addressed the use of such connections in cutting-edge timber structures such as multi-storey buildings and long-span bridges, in which the light weight and flexibility of the structure make it possible that vibration induced by dynamic forces such as wind or footfall may cause discomfort to occupants or users of the structure, or otherwise impair its intended use. The nature of the oscillating force imposed on connections by this form of vibration was defined based on literature review and the use of established mathematical models. This allowed the appropriate cyclic load to be applied in experimental work on the most basic component of a dowel-type connection: a steel dowel embedding into a block of timber. A model for the stiffness of the timber in embedment under this cyclic load was developed based on an elastic stress function, which could then be used as the basis of a model for a complete connector. Nonlinear and time-dependent behaviour was also observed in embedment, and a simple rheological model incorporating elastic, viscoelastic and plastic elements was fitted to the measured response to cyclic load. Observations of the embedment response of the timber were then used to explain features of the behaviour of complete single- and multiple-dowel connections under cyclic load representative of in-service vibration. Complete portal frames and cantilever beams were tested under cyclic load, and a design method was derived for predicting the stiffness of such structures, using analytical equations based on the model for embedment behaviour. In each cyclic load test the energy dissipation in the specimen, which contributes to the damping in a complete structure, was measured. The analytical model was used to predict frictional energy dissipation in embedment, which was shown to make a significant contribution to damping in single-dowel connections. Based on the experimental results and analysis, several defining aspects of the dynamic response of the complete structures, such as a reduction of natural frequency with increased amplitude of applied load, were related to the observed and modelled embedment behaviour of the connections.
Timber building construction has been traditionally utilized to reduce inertial demands in high seismic regions. Applications in the United States however, are often limited to low-rise buildings of light-wood construction with distributed load bearing shear walls. Recent advancements in timber technologies are pushing mass timber systems into larger commercial scale markets where steel and concrete systems dominate the landscape. In high seismic regions, mass timber buildings currently lack code-defined lateral force resisting systems. This paper presents a new lateral force resisting system concept, known as the Heavy Timber Buckling-Restrained Braced Frame. The system is conceived, although not limited, for application in mid and high-rise building timber construction, and is inspired by the unbonded steel brace technology today widely spread throughout Japan and the United States. In order to qualify the system for future implementation in building codes, the paper presents results from proof-of-concept component testing of a brace consisting of a steel core and a mechanically laminated glulam casing acting as the bucklingrestraint mechanism. As well, findings from a study for implementation at the building system level is provided in order to assess overall system performance, constructability, and detailing.
This volume presents a history of heavy timber construction (HTC) in the United States, chronicling nearly two centuries of building history, from inception to a detailed evaluation of one of the best surviving examples of the type, with an emphasis on fire resistance. The book does not limit itself in scope to serving only as a common history. Rather, it provides critical analysis of HTC in terms of construction methods, design, technical specifications, and historical performance under fire conditions. As such, this book provides readers with a truly comprehensive understanding and exploration of heavy timber construction in the United States and its performance under fire conditions.
Although it was found that most of the research foci were on reinforcement of timber connections and flexural members, columns and shear walls play a crucial role in the prevention of structural collapse. Recent trends to build taller timber structures, a demand for structures with larger span, and re-use of existing structures for different purposes have made reinforcement of timber columns and shear walls increasingly important. In addition, repair of damaged timber columns and shear walls so as to prevent further damage to the structures and elongate the life span of existing structures is also important. This paper provides an overview of techniques available to repair and strengthen timber columns and shear walls in both research and practice.
Highly loaded and large span timber beams are often used for halls, public buildings or bridges.
Reinforcement of beams may be required to extend the life of the structure, due to deterioration or damage to the material/product or change of use. The paper summarises methods to repair or enhance the structural performance of timber beams. The main materials/products cross sections and geometries used for timber beam are presented. Furthermore, their general failure modes are described and typical retrofitting and reinforcement techniques are given. The techniques include wood to wood replacements, use of mechanical fasteners and additional strengthening materials/products.
Over the last two decades many constitutive models with different degrees of accuracy have been developed for analysis of sawn timber and engineered wood products. However, most of the existing models for analysis of timber members are not particularly practical to implement, owing to the large number of material properties (and associated testing) required for calibration of the constitutive law. In order to overcome this limitation, this paper presents details of 1D, 2D and 3D non-linear fi nite element (FE) models that take advantage of a quasi-brittle material model, requiring a minimum number of material properties to capture the load-defl ection response and failure load of timber beams under 4-point bending. In order to validate the model, four tapered timber piles with circular cross-section (two plains and two retrofi tted with steel jacket) were tested and analysed with the proposed 3D FE modelling technique; and a good correlation between experimentally observed and numerically captured ultimate load was observed. Consequently, it was concluded that the developed FE models used in conjunction with the quasi-brittle constitutive law were able to adequately capture the failure load and load-defl ection response of the fl exural timber elements.
To improve the seismic performance of mid-rise heavy timber moment-resisting frames, a hybrid timbersteel moment-resisting connection was developed that incorporates specially detailed replaceable steel yielding link elements fastened to timber beams and columns using self-tapping screws (STS). Performance of the connection was verified using four 2/3 scale experimental tests. The connection reached a moment of 142 kN m at the column face while reaching a storey drift angle of 0.05 rad. Two specimens utilizing a dogbone detail in the steel link avoided fracture of the link, while two specimens absent of the dogbone detail underwent brittle failure at 0.05 rad drift. All four test specimens met the acceptance criteria in the AISC 341-10 provisions for steel moment frames. The STS connections exhibited high strength and stiffness, and all timber members and self-tapping screw connections remained elastic. The results of the experimental program indicated that this hybrid connection is capable of achieving a ductility factor similar to that of a steel-only moment-resisting connection. This research suggests that the use of high ductility factors in the design of timber systems that use the proposed hybrid connection would be appropriate, thus lowering seismic design base shears and increasing structure economy.
This article presents the seismic performance of a timber frame with three-dimensional (3D) rigid connections. The connections were made with self-tapping screws and hardwood blocks were used to support the beams. The frame was designed to resist high seismic excitations with the goal of controlling the drift. The moment-rotation characteristics of the connections were measured in the laboratory by applying static cyclic loads. The frame made of laminated wood beams and columns, and cross-laminated lumber deck, was subjected to seismic, white noise, snapback, and sinusoidal sweep excitations. The synthetic seismic excitation was designed to contain a considerable amount of energy close to the frame’s first natural frequency. The structure showed no significant damage up to a peak ground acceleration of 1.25g. Failure of the frame occurred due to shearing of the columns with a peak ground acceleration of 1.5g. The designed structure fulfilled with current serviceability limits up to 0.8g.
The performance of heavy-timber structures in earthquakes depends strongly on the inelastic behavior of the mechanical connections. Nevertheless, the nonlinear behavior of timber structures is only considered in the design phase indirectly through the use of an R-factor or a q-factor, which reduces the seismic elastic response spectrum. To improve the estimation of this, the seismic performance of a three-story building designed with ring-doweled moment resisting connections is analyzed here. Connections and members were designed to fulfill the seismic detailing requirements present in Eurocode 5 and Eurocode 8 for high ductility class structures. The performance of the structure is evaluated through a probabilistic approach, which accounts for uncertainties in mechanical properties of members and connections. Nonlinear static analyses and multi-record incremental dynamic analyses were performed to characterize the q-factor and develop fragility curves for different damage levels. The results indicate that the detailing requirements of Eurocode 5 and Eurocode 8 are sufficient to achieve the required performance, even though they also indicate that these requirements may be optimized to achieve more cost-effective connections and members. From the obtained fragility curves, it was verified that neglecting modeling uncertainties may lead to overestimation of the collapse capacity.
A study on the static and dynamic properties of sawn timber beams reinforced with glass fiber-reinforced polymer (GFRP) is reported in this paper. The experimental program is focused on the behavior of unidirectional wooden slabs, and the main objective is to fulfill the service state limit upon vibrations using GFRP when an architectonical retrofitting project is necessary. Two different typologies of reinforcement were evaluated on pine wood beams: one applied the composite only on the lower side of the beams, while the other also covered half of the beams depth. For the dynamic characterization, the natural frequency, damping ratio, and dynamic elastic modulus were measured using two different techniques: experimental modal analysis upon the whole beams; and bandwidth method using smaller samples of the same material. The static characterization consisted on four point bending tests, where elastic modulus, bending strength and ductility were assessed. The lower composite had better ductility and bending strength. On the other hand, the U-shaped laminate showed higher stiffness but also at a higher material cost. However, it allowed some ductility, i.e. compressive plasticity, even in the presence of hidden knots. Both dynamic techniques gave similar results and were capable of measuring the structure stiffness, even if short samples were used. Finally, the changes on dynamic properties because of the GFRP did not jeopardize the dynamic performance of the reinforced timber beams.