| Promoting bamboo and wood structures is an important means to achieve energy saving and emission reduction,to achieve sustainable development,and to help achieve carbon peaking before 2030 and carbon neutrality before 2060 goals proposed by China,based on the background of vigorously developing prefabricated building.Because of its many advantages such as good seismic performance,quick construction and easy repair,light wood frame structure has been widely used in foreign civil buildings and gradually applied in projects such as homestay in natural scenic spots,infrastructure of forest traffic engineering and new rural construction in China.China’s " Standard for Design of Timber Structures "(GB 50005-2017)states that light wood frame structure buildings are suitable for civil buildings with three floors and less than three floors,which largely limits the application of the structure and is not suitable for China’s national conditions of large population and small land area.With the maturity of related wood structure technology in Europe and the United States,the applicable height of light wood frame structure buildings has gradually increased.Ministry of Housing and Urban-Rural Development(MOHURD)of people’s republic of China approved and issued the Technical Standard for Multi-Story and High-Rise Timber Buildings(GB/T 51226-2017)in2017,which stipulates that a maximum of 6 floors can be built for light wood frame structures in a pure wood structure system,and a maximum of 7 floors can be built for light wood frame structures in the upper part of a wood-concrete structure system.The more stories a building has,the higher the lateral resistance is required,so it is necessary to improve the lateral resistance of light wood frame structures.As the main lateral force resisting member in light wood frame structures,light wood frame shear walls directly determine the ability of the structure to resist lateral loads.The failure of traditional light wood frame shear walls under horizontal load is mainly concentrated in the bottom corner,wall composition material strength cannot be fully utilized and the fastened connection damage is serious.And the limited working conditions of traditional light wood frame shear walls specified in Chinese design standards affect the scope of its application.In response to the above problems,this paper proposed a new type of bamboo scrimber(BS)panel strengthened light wood frame shear wall,replaced the top and bottom of the traditional light wood frame shear wall where the Oriented strand board(OSB panels)are more severely damaged with BS panels with better material properties,and applied common self-tapping screws with better mechanical properties to the BS panels.Applied special anti-cracking cuttail knurled self-tapping screws for wood structure at the framing-to-framing connection,and set bracing at the joints of BS panels and OSB panel.The aim was to improve the lateral resistance of conventional light wood frame shear walls by enhancing the strength of fastened connection in key bearing areas of the wall and the integrity of the wall.The specific research work in this paper is as follows:(1)Monotonic and cyclic loading tests were conducted on sheathing-to-framing connections and framing-to-framing connections comprising the new BS panel strengthened light wood frame shear walls,and the test results showed that increasing the length of selftapping screws effectively improved the ultimate load capacity of the connections.In sheathing-to-framing connections,the use of 40 mm and 50 mm long screws increased the ultimate load capacity by 80% and 129%,respectively,compared to the use of 30 mm long screws.In framing-to-framing connections,the use of 140 mm long screws increased the ultimate load capacity by 28% to 47% compared to the use of 100 mm long screws.(2)Based on the results of the BS panel embedding,self-tapping screw bending and withdrawal tests,the material strengths that meet the target reliability indexes were determined according to the standard GB 50005-2017 and the Uniform Standard for Reliability Design of Building Structures(GB 50068-2018).Since the design values of shear bearing capacity of BS panels-screw connections calculated according to the standard GB 50005-2017 were on the conservative side,reference to the European Design of timber structures(Eurocode 5)suggested considering the contribution of rope effect when calculating the design values of shear bearing capacity of BS-screw connections.Using the first order second moment method to obtain the shear bearing capacity reference design value adjustment factor under different load combinations,the ratio of the standard value of the variable load to the standard value of the permanent load and the coefficient of variation,which meet the target reliability index of3.7,to provide basic data for the improvement of design methods and revision of specifications related to BS-screw connections.(3)Monotonic and cyclic loading tests were conducted on BS panel strengthened light wood frame shear walls to obtain the effects of Hold-down,framing screws and bracing on the lateral resistance performance of the shear walls.The test results show that: all walls occurred for the sheathing-to-framing connection failure damage,which also set Hold-down and bracing wall occurred wall stud splitting damage.Compared with traditional walls,the setting of BS panels increased the ultimate load and shear modulus by 17% to 36% and 37% to 49%,respectively.Setting Hold-down increased the ultimate bearing capacity of the wall by27%～117% and reduced the stiffness and strength degradation.Meanwhile,setting framing screws and bracing enhanced the shear modulus and ductility of the wall.(4)The ultimate bearing capacity of the wall under different BS panel heights,sheathing screw lengths,framing screw setting conditions and wall lengths was obtained by finite element analysis software,and a reasonable BS panel height of 350 mm was given for the project.A theoretical analysis model that can effectively predict the ultimate load of the new wall was established based on the test results.The reference design value of shear bearing capacity based on displacement was given in accordance with the standard GB 50005-2017.Through the reliability analysis,all the working conditions designed by this method except for the walls without any anti-overturning elements met the target reliability index requirements.The design method based on the target reliability index was given in the reference specification Eurocode 5,and the average reliability index of this method was calculated to be between 3.72 and 4.59 at each wall length by the reliability verification. |
PDF Full Text Request