Fatigue Evaluation of Structural Composite Lumber (SCL) T-Beam Bridge Girders

• Other Authors: Enam, Muhammad Badre (authoraut)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Civil engineering; Environmental engineering
• Online Access: http://purl.flvc.org/fsu/fd/FSU_migr_etd-0565

Recent innovation in the engineered wood industry has produced Structural Composite Lumber (SCL) that tends to achieve maximum strength, stiffness and efficient use of wood. Product variations of SCL such as Laminated Veneer Lumber (LVL) and Parallel Strand Lumber (PSL), are currently being used in the transportation sector to produce bridge girders, decks etc. for rural and other low traffic volume roads. Although, the elastic and shear properties of SCL materials are clearly understood, no attempt has been made to estimate fatigue performance of these bridge girders. With their increasing use, they are repeatedly being subjected to numerous cycles of wheel load that raises concern about their behavior under fatigue. The current research tested 12 newly procured and 2 old and weathered pre-built SCL T-beam bridge girders for flexural fatigue under a stress controlled test setup. The girders were of 20 ft span and having variation in their constituent material types and applied preservatives. Loading was applied according to the AASHTO LRFD specifications for bridge design. The number of load application cycles was consistent with expected traffic volume for a sixty year time span. In a regular bridge structure comprised of pre-built SCL T-beam girders, transverse post-tension is applied to adjacent girders to form a stress laminated deck. This effect had been simulated on the girders and the effect of fatigue loading on the loss of post-tension force was observed. Results from the study indicated that the SCL Tbeam bridge girders were capable of withstanding the repetitive loads coming from the heavy truck traffic. Most of the beams did not suffer any physical damage. A few of them had severe de-lamination at the SCL-epoxy interface. The girders without any damage due to fatigue were loaded statically up to failure. This result was compared to the ultimate flexural strength of fresh beams of similar material type, to investigate their residual strengths after fatigue loading. Some weathered girders were also fatigued under the same experimental setup for comparison purposes. This provided a comparison of the fatigue performance of fresh and weathered SCL T-beam bridge girders. Comparably high strength fatigue loading was applied to two additional girders. The fatigue lives for these girders were less and compared well with those of clear wood at the same stress level. A rudimentary fatigue curve was proposed based on the data. A finite element model was developed, using layered shell elements, to simulate the structural behavior of these girders. Subsequent analyses of this model produced results that were highly representative of the data obtained in experimental testing of SCL T-beam girders. === A Dissertation submitted to Department of Civil and Environmental Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. === Degree Awarded: Spring, 2008. === Date of Defense: December 19, 2007. === SCL, Structural Composite, Lumber, LVL, PSL, Fatigue Re === Includes bibliographical references. === Primus V. Mtenga, Professor Directing Dissertation; Kamal S. Tawfiq, Professor Directing Dissertation; Lisa Spainhour, Committee Member; Peter N. Kalu, Outside Committee Member.