Date of Graduation
Statler College of Engineering and Mineral Resources
Civil and Environmental Engineering
Hota V.S. GangaRao
Roger H.L. Chen
Roger H.L. Chen
In 2013, the California Bay Area (CBA) passed a set of ordinances to ensure that their 10,000 plus timber soft-story buildings were prepared for seismic events, through nondestructive evaluation methods. Many property owners are searching for an affordable retrofitting system that will also meet CBA’s new laws focusing on installations by the mandated deadlines in 2020. Over the past three to four decades, Fiber Reinforced Polymer (FRP) composites have found their way into the civil infrastructure sector for rehabilitation. The objective of this study is to evaluate the bending behavior retrofitted mortise and tenon timber joints reinforced with engineered wood filler-modules and FRP composite gussets. In addition failure modes with filler-modules and/or gussets are evaluated for future studies to develop design methodologies. The above efforts are focused on a West Virginia University (WVU) patented joint performance enhancement system.
A total of ten specimens with varying retrofitting schemes were studied by using a static bending test. A 6” by 6” timber post joining system with a mortise and tenon connection style were used throughout this study. These bending tests are conducted and reported herein to determine the predominate failure modes based off of the inclusion of filler-modules and gussets. The increase in load capacity and energy absorption after retrofitting the joints subjected to bending and shear, and also the limit states on deflections and deformations of timber joints after incorporating the proposed retrofit schemes, are evaluated from the test data and reported herein.
The results from the tests indicate that a joint with filler-modules and a FRP gusset with an enhanced stiffness will perform better than a conventional joint system. The control specimens, i.e. without retrofit schemes, averaged a maximum load of ~2,900 lbs. A retrofitted specimen was able to reach a maximum load of ~16,000 lbs. Conventional beam-column mortise and tenon joints made of 6” x 6” size could only deflect 0.29” at the peak load with a 18” bending span, while a retrofitted joint with filler-modules and gussets was able to reach 0.96” at peak load. Joints retrofit with the proposed scheme also show up to 500% increase in energy absorption.
Mortise and tenon joints have a shear failure on tenon when the dowel is made of a harder wood than the beam and column but will have a dowel bending/shear failure if it is softer than the bearing material. Joints retrofitted with filler-modules were able to prevent the tenon failure but failed once the filler-module on the tension side would debond. To delay the debond, FRP gussets were installed which resulted in FRP rupture failure at the tip of the joint area or beam-column interface.
The retrofit system proposed in this paper displayed an increase in strength, ductility, and energy absorption by factors of about 3 to 5. The data herein proves that the filler-module and gusset combination is an effective retrofitting scheme. The system is an easy to learn installation process which can be implemented cost-effectively in a short amount of time and would save millions, in both the rehabilitation and retrofit costs.
Pacifico, Andrew Robert, "Bending Response of Timber Mortise and Tenon Joints Reinforced with Filler-Modules and FRP Gussets" (2019). Graduate Theses, Dissertations, and Problem Reports. 4125.