Study On Pull-out Strength And Behavior Of Glulam Glued-in Rods

Glued laminated timber structure is applicable for large span and scale construction. Todevelop our country glued laminated structure, the domestic wood species glulam manufactureand connections are researched with a lot of experimental and theoretical analysis. Glued-inrods connection is a reliable connection method in glued laminated structure to resist bendingmoment. This connection method has great strength and stiffness and can effective transferload which present good aesthetical and fire prevention. In our country, glued-in rodconnection in glued laminated timber research reports are few; therefore there is importantsignificance and good application of researching this high strength connection.This paper is about using SPF and masson pine (Pinus massoniana Lamb.) wood tomanufacture glulam and study the glulam properties. Glued-in rods specimens adhesive istwo-component epoxy. The steel rods with metric threads have different diameter and lengthcorrespond to quality8.8. The glued-in rods test include double-ended glued-in rod parallel tothe grain and single-ended glued-in rod parallel to the grain and single-ended glued-in rodperpendicular to the grain and glued-in multiple rods. The research analysis the edge distance,distance between rods, bond line thickness, anchoring length, rod diameter factor influence onglued-in rod connection strength and failure mode. The main results are as follows:1. The masson pine mechanical properties are similar to SPF. However, the masson pineglulam properties are low than SPF glulam. The MOR and MOE of SPF glulam are58.40-68.45MPa and16.23-19.46GPa. The MOR and MOE of masson pine glulam are24.49-52.12MPa and9.72-12.69GPa. Masson pine glulam bending properties can reachJapanese structural glulam standard E135-F345grade.2. Double-ended glued-in rod parallel to the grain testing to test edge distance bond linethickness, anchoring length, rod diameter factor influence on glued-in rod connection strengthand failure mode. The edge distance testing results show that the failure is mainly affected and the edge distance is too small will cause the wood splitting in pull-out test. This study suggeststhe edge distance greater than or equal4d to avoid the error in the drilling process and notvertical to the axial in glued-in rod process to occur the wood splitting failure mode. The bondline thickness testing results show that with bond line thickness increasing, the failure loadpresents no obvious change, but the wood/adhesive shear strength decreased linearly, thecorrelation coefficient is0.89-0.91. With the slenderness ratio increases, the failure increasesand wood/adhesive shear strength decreased. The relationship between slenderness ratio andfailure load is polynomial linear and the correlation coefficient was0.95-0.99. The failuremodes of double-ended glued-in rod parallel to the grain are rod pull-out failure and rodyielding failure.3. The load capacity of single-ended glued-in rod parallel to the grain and single-endedglued-in rod perpendicular to the grain in SPF and masson pine glulam are similar. The massonpine glulam tension property glued-in rod perpendicular to the grain is better than SPF. Insingle-ended glued-in rod parallel to the grain, the failure load increases with the slendernessratio increasing. The nominal shear strength is decreased with slenderness ratio increasing. Thenominal shear strength can be quantified by a power function of λ with exponent of-0.35~-0.38. The failure modes in single-ended glued-in rod parallel to the grain are rodpull-out failure and rod yielding failure. The failure modes in single-ended glued-in rodperpendicular to the grain are rod pull-out failure and rod yielding failure and timber collapsefailure.4. The pull-out property of glued-in multiple rods has been developed. The failure mode iscomplicated. The wood block failure mode occurs when the distance between rods smaller than3d. The recommended distance between rods is4d. In the same distance between rods, the rodnumber more, the every rod average tensile load capacity is low.5. The glued-in rod mean failure load empirical prediction models of SPF glulam andmasson pine glulam are established with the slenderness ratio and threaded rods diameter. Thedesign value equations of failure are given. Based on the Volkersen model, the theoreticalpredicting models are derived by linear elastic shear stiffness approach of glud-in rods under Pull-pull and Pull-compression loading modes. Theoretical predicting models have moreapplicability compare with empirical prediction models.