The Equivalent Viscous Damping (EVD) parameter is used to simplify the dynamic problem, passing from a non-linear solution of the system to a simple linear-elastic one. In the case of Direct Displacement-Based seismic Design (DDBD) methods, the EVD value allows direct design of structures, without an iterative computational process. This paper proposes a rational analytical formula to evaluate the EVD value of timber structures with dowel-type metal fastener connections. The EVD model is developed at the ultimate limit state, as a solution of the equilibrium problem related to an inelastic configuration. For a specific joint configuration, the EVD predicted via an analytical model was compared to experimental results. The proposed EVD model was validated using non-linear dynamic analysis on a portal frame, built with dowel-type fasteners arranged in two concentric crowns.
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 study assesses the seismic performance of a new hybrid timber-steel moment-resisting connection for mid-rise heavy timber structures. This system consists predominantly of timber members, but utilizes a steel yielding link at the beam-column joint that improves seismic performance by replacing connection components that are susceptible to brittle failure with ductile steel elements. The steel-to-timber connection was made using self-tapping screws. By localizing all inelastic behaviour to a single ductile component, design with high seismic force reduction factors becomes justifiable. Four connections were tested; a majority of the plastic rotation was localized to the link, high levels of ductility were achieved, and the steel-to-timber connections remained undamaged. A numerical study was performed on a hybrid frame using the proposed connection, and an equivalent steel-only frame. Results showed that drifts and accelerations remained within allowable limits, indicating that well-detailed hybrid connections can result in seismic performance similar to steel-only frames.
The outcomes of an experimental study aimed to investigate the structural behaviour of wood-steel-wood glulam frame moment-resisting connections that were subjected to static bending are presented in this paper. Each frame test assembly was consisted of two glulam beams simply supported at their far ends and were connected to an inverselyloaded glulam column in the centre using two steel T-stub connectors. Two test variables including bolt’s end distance and number of bolt rows were investigated in eight full-size glulam beam-column assemblies. Test results revealed that increasing the number of bolt rows from two to three, with each row included two bolts, significantly increased the connection moment capacity with much greater increments compared to those added by increasing the bolt’s end distance from four- to five-times bolt diameter. However, brittle failure modes were found to be more pronounced in the connections with three rows compared to the connections with two rows of bolts.
The seismic performance of a post-tensioned (PT) energy dissipating beam-to-column joint for glulam heavy timber structure is investigated in this paper. Such connection incorporates post-tensioned high-strength strand to provide self-centering capacity along with energy dissipating produced by a special steel cap, which is attached with the timber beam and also to prevent the end bearing failure of wood. The moment-rotation behaviour of the proposed posttensioned timber joint was investigated through a series of cyclic loading tests. The timber joint was loaded at the end of the beams to produce a moment at the joint, and the tests were conducted with three different post-tension forces in the steel strand. The hysteretic behaviour and self-centering capacity of the joint are evaluated based on the results from cyclic loading tests. The failure mechanism of the joint was illustrated through test observations, and the momentresisting capacity and energy dissipation of the joint were analysed with regard to various drift level. This research aims to provide possible solutions to minimize the residual deformation of heavy timber structure made of glulam in China.
This paper presents a research study about timber connections in moment resisting frames, with materials commercially available in Costa Rica. With new developments in engineered timber, the Costa Rican Seismic Code included a chapter on timber structures, defining moment resisting timber frames with several values of structural global ductility, depending on the local ductility of the connections. A research study was then carried out, with the objective of determining the structural behaviour and static ductility factor of a beam to column connection. Twelve specimens were constructed and tested, varying the geometric characteristics, wood species and type of bolts. The specimens consisted of a glulam beam and column segment connected with a different bolt pattern. The beam segment was loaded at its free end to induce a moment in the connection, and the ends of the column segment were simply supported. The rotation of the connection was measured by placing two LVDTs in the beam and two LVDTs in the column. It was found that the ductility factors achieved by the test specimens ranged from 2.0 to 2.7 in average. The moment capacity of the connections can be safely estimated using the nominal values of bending yield strength of the bolts and the dowel bearing stresses. These results are an important input for the Costa Rican Seismic Code and for the development of engineered timber in Costa Rica.
Glulam members which are manufactured with Japanese cedar plantation timber are constructed into a box type of portal frames to investigate the moment-resisting performance when subjected to a lateral load. The joints of the frame are connected using aluminium connectors and self-tapping screw fasteners, and the placement of fasteners on the connection are arranged into three patterns. The loading protocol is applied laterally in seven cyclic stages for the racking test. The maximum lateral load of 51.4 kN is attained for the portal frame fastened using self-tapping screws arranged in square pattern, followed by single circular pattern and double circular pattern. Resulted dissipated energy obtained from the portal frame with square pattern placement is 1224.2 kNmm during the cyclic loading stages, higher than the other fastener arrangement by 20%. The allowable shear strength of the box-type portal frame is decided by the load corresponding to the shear deformation of 1/120 radian.
Over the last decades, the increasing urbanization and environmental challenges have created a demand for mid-rise and high-rise timber buildings in modern cities. The major challenge for mid-rise and high-rise timber buildings typically is the fulfillment of the serviceability requirements, especially limitation with respect to the wind-induced displacements and accelerations. The purpose of the present paper is to evaluate the feasibility and the limitations of moment-resisting timber frames under service load according to the present regulations. The parametric analyses investigate the effects of the rotational stiffness of beam-to-column and column-to-foundation connections, storey number and height, number and length of bays, column cross-section dimensions and spacing between frames on the overall serviceability performance of the frames. Elastic and modal analysis were carried out for a total of 17,800 planar moment-resisting timber frames with different parameters by use of Abaqus Finite Element (abbr. FE) software. Finally, the obtained results were used to derive simple expressions for the lateral displacement, maximum inter-story drift, fundamental eigen-frequency, mode shapes and acceleration.
Glulam-based post-tensioned moment-resisting portal frames were developed by a producer from British Columbia in collaboration with ASPECT Structural Engineers. These modular frames, manufactured from appearance-grade glulam, can be viable solutions for substitution of steel moment frames in predominantly wood-framed buildings. This paper presents an experimental study on the structural performance of post-tensioned glulam moment-resisting portal frames under in-plane lateral loads. A total of twelve frame specimens in four different configurations were tested under static or reversed cyclic loads. The test results show that the behaviour of post-tensioned moment-resisting portal frames was relatively similar under static and cyclic loading, in which non-linear elastic behaviour was observed due to the post-tensioning. The peak lateral loads applied to the tested post-tensioned frames was in a range of 34.1 kN to 61.7 kN and the lateral stiffness ranged from 0.53 kN/mm to 2.65 kN/mm, respectively. Depending of the frame configuration, typical failure modes identified during the testing consisted of a combination of either (i) compression perpendicular to grain failure at the columns on the side in contact with the beam; or (ii) compression perpendicular to grain failure at the beam on the side in contact with the columns; and (iii) screw failure in the column-to-base joints (if present). The tests give a valuable insight into the seismic performance of post-tensioned glulam moment-resisting portal frames.
