Tong Wang

This article addresses the problem of insufficient bearing capacity and stiffness in laminated timber beams during use and proposes a reinforcement method by increasing the cross-section. Twenty glued laminated timber beams with dimensions of 2850 mm × 120 mm × 50 mm were produced using Pinus sylvestris var. mongolica as the raw material. Douglas fir with good tensile properties and new self-tapping screws were selected as reinforcement materials. Through adhesive bonding and adhesive–nail combination methods, an enlarged section reinforcement beam was formed. The influence of section height, bonding process, and the arrangement of self-tapping screws on the bending performance of three groups of six adhesive-reinforced specimens and three groups of fourteen adhesive–nail reinforced specimens was examined through bending performance tests. The results showed that compared with specimens reinforced with single-layer panels, the ultimate load of specimens reinforced with double-layer panels increased by 22.82 to 29.49%, and bending stiffness increased by 17.26 to 48.17%. Within the same group, the ultimate load of specimens reinforced with standard compressive stress adhesive increased by 3.88 to 5.71% under bending. Compared with adhesive reinforcement specimens, adhesive–nail combined reinforcement specimens showed an 8.91 to 11.36% increase in ultimate load. In specimens with the same screw insertion angle, the ultimate bearing capacity of beams reinforced with longer screws and smaller spacing was actually lower. Moreover, the ultimate load of specimens reinforced with self-tapping screws inserted at 90° was 4.2% higher than that of specimens with screws inserted at 45°.

In this paper, long-term loading tests of ten prestressed glulam beams were carried out for 45 days, using the loading method of three-point hanging heavy objects. We analyzed the influence of prestressed steel wire numbers and total preloading force on parameters such as failure mode of beams, variation of steel wire stress, and long-term deflection of mid-span. When the total prestress was constant and the number of steel wires was 2, 4, and 6, the total stress of steel wires decreased by 33.07%, 37.26%, and 50.04%, respectively, after long-term testing for 45 days. The ratio of mid-span deflection to total deflection was 61.5%, 54.8%, and 40.9% respectively. When the number of steel wires was constant and the values of total prestress were 0, 3.079 kN and 6.158 kN, the total stress decreased by 28.90%, 36.59%, and 36.63%, respectively, after long-term loading. The ratio of long-term deflection of mid-span to total deflection was 60.7%, 54.8%, and 39.3%, respectively. The more steel wires, the greater the value of total prestress and the loss of total stress, the smaller the mid-span long-term deflection. After the test, we analyzed and fitted the test data to obtain the specific numerical of the creep coefficient θ under normal conditions, and the formula for calculating the long-term stiffness of the glulam beams based on the creep effects is proposed.

Purpose: In view of the defects of glued wood beams, a new composite member – reconstituted bamboo board reinforced glued wood beams is proposed to improve the bearing capacity of glued wood beams.Design/methodology/approach: The bending test studied the ordinary glulam beams and the reinforced glulam beams with different layer numbers and different layer thicknesses by comparing with six kinds of glulam beams strengthened with bamboo scrimber and one kind of ordinary glulam beams and used the method of third-point stepwise loading on the glulam beams strengthened with bamboo scrimber.Findings: The bamboo scrimber improved the bending behavior of the ordinary glulam beams. The 10 mm bamboo scrimber layer can meet the requirements of the maximum ultimate bending capacity and minimize the defects. So 10 mm bamboo scrimber layer was the optimal thickness. During the loading process, the strain change of the normal section of the reconstituted bamboo board reinforced glued wood beam basically conforms to the plane section assumption.Originality/value: The bending rigidities of the glulam beams strengthened with bamboo scrimber increased up to 28.25%, 8.53% and 76.67%, and the ultimate bending capacity increased from 83.44% to 99.34% with the increase of the bamboo scrimber plate layers (the replacement rate). The ultimate bending capacities and the bending rigidities of the glulam beams strengthened with bamboo scrimber increased to 52.32%∼60.18% and 90.07%∼99.34% with the changing of the bamboo scrimber thicknesses from 7.1 mm to 25 mm.