The low-cycle seismic performance of typical screws used in timber structures is analysed by performing monotonic and fully reversed cyclic bending tests on the threaded length of the shank. Tests considered partially threaded screws made of carbon steel with diameter varying between 6 and 10 mm. Results of the monotonic bending tests are used to assess the compliance of the screws with the requirement of ductility prescribed by EN 14592 and to define the average yielding moment of the shank. Cyclic bending tests are carried out afterwards by assuming three classes of low cycle seismic performance (S1 - low ductility class, S2 - medium ductility class and S3 - high ductility class). Results of the cyclic tests are used to evaluate the residual moment of the shank, which is then compared to the average yielding moment from monotonic tests. The outcomes of the testing programmes highlight that screws with a diameter equal to 6 mm can be assigned to a low-cycle seismic class S2, while screws with a diameter greater than or equal to 8 mm are capable of ensuring a higher seismic performance and can be assigned to a seismic class S3.
Different methods, including bending tests and small and medium size shear tests, were used to assess the skin to stringer glue line shear strength of Radiata Pine Cross-Laminated Timber Derived Stressed-Skin Panels (CLT SSP). Bending test shear strengths were estimated using the mechanically jointed beam theory (gamma method) for CrossLaminated Timber (CLT) panels with modifications in the layers’ effective widths, and then compared with results from the small and medium size shear tests. Small and medium size shear tests proved to be possible methods for assessing bonding strength for factory production control. The small shear tests provided lower strength values and higher scatter results than those gathered from the medium size tests. The mean shear strength results obtained from bending tests were inferior to the values obtained from the small and medium size specimens. The bending tests proved necessary for assessing the mechanical behaviour of CLT SSP.
Inspection, Testing, and Monitoring of Buildings and Bridges
Depending on the severity, fire damage can compromise the structural integrity of wood structures such as buildings or residences. Fire damage of wood structures can incorporate several models that address (1) the type, cause, and spread of the fire, (2) the thermal gradients and fire-resistance ratings, and (3) the residual load capacity.
The investigator should employ engineering judgment to identify those in-service members that are to be replaced, repaired, or can remain in-service as they are. Suchjudgment will likely be based on the visual inspection of damaged members, connections, and any protective membranes.
One of the challenges in mass timber construction is the design of efficient floor systems. This thesis focuses on studying composite T-beams, connecting Spruce-Pine-Fir Cross Laminated Timber (CLT) panels and Douglas-Fir Glued-Laminated timber (glulam) beams. In this study, three different types of self-tapping wood screws (ASSY SK, ASSY Ecofast, and ASSY VG), inserted at different angles, were investigated. Firstly, small-scale experimental tests were performed to investigate the strength and stiffness of the screws when submitted to lateral shear loads. It was found that the most promising fastener was the ASSY VG and that changing the angle of installation of the screws from 90° to the wood grain, to 45°, increased the strength and the stiffness of the studied connection. Secondly, full-scale composite beams experimental tests were completed to validate mechanistic-based and computational methods used to predict the effective bending stiffness of the composite T-beam. A degree of composite action achieved for the experimental T-beams was calculated through the studied methods. It was found that the studied T-beam achieved a moderately high percentage of composite action. Moreover, the methods were compared in terms of prediction accuracy, computational difficulty, required number of parameters, and versatility. Finally, parametric analyses were completed to gain insight into the structural performance of the composite beam when varying the number of CLT plies, the width of the CLT panel and of the glulam beams, as well as the length of the T-beam. Results indicate, conservatively, that the proposed connection, with a 3-ply CLT panel and a 130x190mm glulam beam, can be used to span 6m, maintaining a flange width of 2.8m. The results also suggest that with a 5-ply CLT panel and a 365x190mm glulam beam, it is possible to manufacture a 10m long T-beam that spans 3m laterally and supports live loads compatible with office use and occupancy.
The application of cross-laminated timber (CLT) as floor panels is limited by excessive deflection and vibration. A composite system combining CLT and ultra high-performance fibre-reinforced concrete (UHPFRC) was developed to extend span limits. Push-off tests were conducted on different connectors, and a glued-in rod connector was chosen and further refined for the proposed system. Static bending tests and free vibration tests were conducted on bare CLT panels and two composite specimens. By comparing the results, it is concluded that the proposed system considerably extend the span limits of CLT panels.
This book contains experiences and results of computer simulations in the field of research on glued laminated timber. Literature and references to the corresponding methodical approach are given to facilitate the access to the elementary basics. It also contains constructive explanations and critical annotations on modelling glued laminated timber for bending, tension and compression tests. Finally, the relevance of the simulation results for practical issues is discussed.
In this contribution bending and shear tests of cross laminated timber (CLT) plates under concentrated loads are presented. The so loaded structural members can fail either due to punching along a critical perimeter line in the vicinity of the concentrated load or in bending. Two test configurations were developed and investigated by linear elastic models. The obtained test results and observed failures as well as their correlation with the mechanical modeling are shown in this paper. The established numerical model was a 3D solid model with different material behavior for all acting stresses. The material behavior was implemented in a user subroutine for the FE program ABAQUS. By comparison of measured and computed load displacement curves numerical models could be discussed regarding their reliability and conclusions about missing input for an increasing accuracy of the model could be drawn.
Laminated veneer lumber (LVL) is an engineered wood product manufactured from specially selected veneers with varying strength and stiffness properties. LVL products are often specified where a certain span, strength and/or stiffness is required. As such, LVL products are generally designed for and used in applications where they will be highly stressed under design loads. For this reason, field modifications, such as notching, tapering, or drilling should be avoided and never done without a thorough understanding of the effects on the structural capacities of the LVL. Nonetheless, it is not uncommon for the designer and contractor to find a need to cut holes through LVL members for plumbing pipes, electrical conduits, or air ducts. Therefore, it is usually necessary to determine the residual structural capacities of the LVL member when holes are cut. The objective of this paper is to examine the effect of round holes on the structural capacities of LVL, including bending moment, shear, and bending stiffness. Full-scale LVL bending and shear tests were conducted to provide data for characterization of the hole effect. Based on the test data, design equations that account for single and multiple holes up to 2/3 of the LVL member depth and a clear distance of 15% or more of the LVL depth from the edge of the hole to either tension and compression edge of the LVL member have been developed. To ensure safe implementation of such design recommendations in practice, prescriptive limitations, such as the minimum clear distance between the face of a support and the edge of a hole, and the minimum clear distance between adjacent holes, are also prescribed.
The performance of timber-concrete composite bridge constructions crucially depends on the design of the joint between concrete deck and timber main girders. In research studies at the Bauhaus-University Weimar, innovative joining techniques based on grouting with highly-filled, tolerance-compensating polymer glue mortars have been developed to improve the shear capacity of this joint significantly. By applying a thin layer of polymer mortar on the top of the wooden main girder a continuous, slip-free connection to the timber can be realized. This layer can be utilized for the embedding of steel plates with welded-on shear studs (stud connectors), so that the joint to the concrete side is ensured by a standardised connection. The steel plates are rigidly anchored in the polymer mortar by adhesive bond and form closure. As an alternative, a slip-free grout-glued connection between concrete and timber can be realized by the glue mortar itself, so that also a continuous connection to the concrete is accessible, whereby manufacturing tolerances can easily be compensated due to the high degree of mineral filling of the polymer mortar. The paper focuses on experimental results of shear and bending tests for the new composite joint configurations.
Massive timber panels (MTPs) has shown a great potential in construction of tall buildings. Evaluation of the face-bond strength of MTPs is of an interest to use of this kind of products. This study was aimed at developing an appropriate test procedure for evaluating the adhesive bond strength of cross-laminated laminated strand lumber (LSL). Short span bending tests were conducted on two-layer asymmetric cross-laminated LSL specimens, which were adhesively bonded using two-component polyurethane (PUR) and polyvinyl acetate (PVAc). For comparison, block shear specimens were tested as well. It was found that the 2-layer asymmetric cross-laminated specimen assembly under the short span bending could be used to differentiate between good and poor bond quality.