This paper presents an experimental campaign conducted on the beam-to-column glulam joints combing glued-in rods and steel brackets (BCGS glulam joints) aiming to investigate the mechanical behaviour of these glulam joints under low cyclic loading. Three types of steel brackets were designed for connecting the beam and column combing with glued-in rods and to work as energy dissipaters. In each group of specimens (except for group MJ4), two specimens were tested under monotonic loading and the others were subjected to low cyclic loading. The test results were summarized comprehensively in terms of failure modes, joint stiffness, hysteresis loops, ductility and energy dissipation ability. Generally, the difference of load capacity between BCGS glulam joints and the beam-to-column glulam joints only with glued-in rods (BCG glulam joints) was not significant. The joint stiffness of BCG glulam joints was higher than that of the BCGS glulam joints, while the stiffness degradation of the later is slower than the former. The hysteresis loops of the BCGS glulam joints exhibited less pinching effect obviously compared with the BCG glulam joints, which indicated that the energy dissipation ability of the glulam joints with glued-in rods could be improved significantly by using the steel brackets as energy dissipaters. Moreover, it should be noted that the hysteresis loops of groups CJ1 showed slipping effect obviously during testing. This might due to the insufficient shear resistance of these two groups, so that further investigations on BCG glulam joints with shear-resisting components are urgently needed.
An experimental study of four full-scale cruciform sub-assemblages of beam-to-column steel-timber composite joints with extended end plates was conducted to simulate the behaviour of an internal joint in a semi-rigid steel-timber frame. In this system, the Cross-Laminated Timber (CLT) panels were attached compositely to the steel beam using coach screws to achieve the shear connection and the steel-CLT composite beams were connected to the steel columns by bolted extended end plates. In addition, one specimen without a CLT slab was constructed and tested as a control with which to assess the influence of the CLT panels on the performance of the joint. The structural behaviour of this type of joint which requires the connection of the two juxtaposed CLT panels subjected to tension near the column was explored. The test results show that these novel composite joints have credible rotation and moment capacities and provide a viable alternative to their steel-concrete counterparts within a paradigm of reduced carbonemissions in the construction sector.
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.
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.
In this study, five full-scale bolted glulam beam-to-beam connections with slotted-in steel plates were conducted under a third-point loading, and a three-dimensional finite element method based model was also established to investigate the failure modes and moment resistance of such connections. A material model based on the Continuum Damage Mechanics (CDM) theory was developed to predict damage evolution of wood. Different damage variables were used to consider the ductile and brittle failure modes of wood, respectively. The test results indicated that splitting and shear plug failures were the main failure modes. The numerical analysis model prediction achieved fair agreements with the test results. The research could provide the guide for the design of bolted beam-to-column connections in heavy timber structures.
This paper presents the results of an on-going program of the mechanical behaviour of bolted glulam beamto-column connections. The program included testing and modelling of connections of various bolt size, edge distance and lamina alignment patterns. This paper presents part of the obtained results, including monotonic and reversed cyclic loading test results of 10 full-scale beam-to-column connections and the corresponding modelling results. The test results indicated that the perpendicular-to-grain properties of glulam and the localized contact between the bolts and surrounding glulam had significant influence on the stiffness and the maximum moment of the connections. A finite element method based model, which can be easily incorporated in commercial available software packages, was developed and verified based on the test results. Good agreement was achieved. Parametric study results indicated that the tolerance of the bolt holes can significantly affect the mechanical behaviour of the bolted beam-to-column connections.
International Journal of Advanced Structural Engineering
Summary
This paper presents analytical and numerical models for semirigid timber frame with Lagscrewbolt (LSB) connections. A series of static and reverse cyclic experimental tests were carried out for different beam sizes (400, 500, and 600 mm depth) and column–base connections with different numbers of LSBs (4, 5, 8). For the beam–column connections, with increase in beam depth, moment resistance and stiffness values increased, and ductility factor reduced. For the column–base connection, with increase in the number of LSBs, the strength, stiffness, and ductility values increased. A material model available in OpenSees, Pinching4 hysteretic model, was calibrated for all connection test results. Finally, analytical model of the portal frame was developed and compared with the experimental test results. Overall, there was good agreement with the experimental test results, and the Pinching4 hysteretic model can readily be used for full-scale structural model.
Post-tensioned rocking structures are known to perform well under seismic action, but as with most other structural systems, there is concern about possible damage to floor diaphragms. This is due to displacement incompatibilities, especially if frame elongation occurs due to gap opening at the beam-column-joints. This paper describes the experimental behaviour of an engineered timber floor connected to a post-tensioned timber frame subjected to horizontal seismic loading.
A full scale two-bay post-tensioned frame was loaded with lateral loads, which were applied through a strip of floor diaphragm spanning perpendicular to the beams. Several different connection configurations between the floor portions on either side of the central column were tested. The diaphragm deformation demand adjacent to the beam-columnjoint gap opening was accommodated through two mechanisms: a concentrated floor gap opening at the column or a combination of panel elongation and small gap openings over a number of floor elements. In all the tests, only elastic deformations were observed and the diaphragm behaviour of the floor elements was fully maintained throughout the testing.
The results showed that design to allow flexibility of timber elements combined with proper connection detailing can prevent damage at high level of drift to the floor diaphragms in post-tensioned timber frame buildings.
The Softwood Lumber Board, Arup, MyTiCon and DR Johnson have partnered to complete three full-scale fire tests for glulam beam to column connectors. The fire tests have been completed for “off-the-shelf” connectors for glulam beams, testing the connector to meet a minimum of a 1hr fire resistance rating (FRR).
To assist the construction industry, three different configurations of glulam beam to column connections were fire tested at an approved fire testing facility. The fire tests were carried out to meet ASTM E119-16a “Standard Test Methods for Fire Tests of Building Construction and Materials”, hence meeting Chapter 7 of the IBC.
The completed fire tests and supporting reports allow engineers and architects to specify these tested connection assemblies and satisfy the requirements of the IBC. Approval by an authority having jurisdiction (AHJ) will therefore be easier for future building projects.
