Strength and Serviceability Performances of Southern Yellow Pine Cross-Laminated Timber (CLT) and CLT-Glulam Composite Beam

Cross-Laminated Timber (CLT) is a relatively new engineered mass timber construction material in the North America. While CLT was invented roughly three decades ago in Europe, it was not popular in the North America until recent years, in which there has been a surging demand for mass timber construction in the North American market. The advantages from the material itself and the level of pre-fabrication offers a flexible system suitable for large and tall wood buildings. However, the design provisions for CLT have not been developed for the building codes of the United States (US). Thus, the use of CLT is limited to custom projects. There were two phases in this research. During the inception of this research, there was no commercial production of structural grade CLT panels in the US using local wood species. The first phase of the research investigated the manufacturing process of CLT panels in a pilot scale using Southern Yellow Pine (SYP), a group of tree species native to the Southeast US. Tests were conducted to evaluate the adhesive and structural performances of CLT panels in flexural and shear. The test results showed that SYP can be used to produce CLT panels that meet and exceed the product standard requirements for CLT in the North America. The results generated from the pilot study were used in the second phase of the research to design, fabricate and test a full-scale 5 ft. wide and 40 ft. long CLT-Glulam composite floor system designed for long span applications. The proposed CLT-Glulam composite section is analogous to a typical precast concrete box girder, which is designed to improve the material efficiency. The CLT panels and Glulam beams in the composite floor system were fastened by screws installed at an incline angle. To investigate the feasibility of using the CLT-Glulam composite section for floor system in residential/office construction, a non-destructive vibration (modal) test was conducted to evaluate the serviceability behavior and destructive structural tests were performed to evaluate the flexure and shear strengths. The modal test utilized an instrumented heel-drop excitation to simulate the impact from human footsteps and accelerometers to record the vibration responses. The vibration test results revealed that the composite floor could produce vibration sensitive to building occupants. The results of the destructive tests verified that the composite floor system could safely carry the design load in terms of bending and shear strengths. Based on the findings of the experimental study, it was found that the design of the CLT-Glulam composite system is governed by serviceability and not ultimate strengths. It is recommended that, in addition to designing for the ultimate strengths, the serviceability criteria be considered with equal important as the strength design for improved occupant comfort