| The industrialization development of construction in China puts forward new requirements for building technology.Improving the industrialization level of residential buildings is an important way to realize green architecture and green construction.As a new structure system,cold-formed steel(CFS)structures have been widely used in lower-rise residential buildings in the USA,Japan,Australia,and Europe because of their light weight,high strength,environmental characteristics and easy installation,which satisfy the requirements of building industrialization.However,the system is still in the primary development phase in our country.Because of large population,the shortage of land resource,the development of mid-rise CFS structure is more consistent with Chinese national conditions.For this purpose,a mid-rise CFS structure system was proposed by Prof.Ye et al.,for which the requirements of vertical bearing capacity,lateral resistance and fire prevention can be satisfied simultaneously,and the main lateral load-bearing structural components are CFS shear walls with continuous concrete-filled rectangular steel tube columns as end studs.In this thesis,a systematically experimental and theoretical investigation was carried out on the key problems of such system in shear,including real mechanical performance of beam-column joints,shear behavior and numerical simulitation method of sigle-story and mid-rise CFS shear walls under cyclic load,simplified calculation method of the walls.The main contents and conclusions of this thesis are summarized as follows:1.In order to accurately obtain the actual response of mid-rise CFS structure,the real mechanical performance of joints should be considered during the analysis and design of the whole structure.Two new-type beam-column joints specific to the system were innovatively designed first,an experimental investigation of seven CFS joints under cyclic load was conducted to study the mechanical performance of the two new-type joints comparasively.On this basis,the prediction model together with finite element analysis model of the moment-rotation relationship was established.The main conclusions are as follows:?During cyclic loading,both beam and column of the joints connected with ring plate had no damage,while elastic bending failure of the beam section occurred in the joint connected with reinforced blocks,means the latter has a certain bending moment transmission capacity.?The moment-rotation curves of the two kinds of joints undergone elastic stage,nonlinear stage and final failure stage;compared with the joint connected with ring plate,the mechanical performance of the joint connected with reinforced blocks is better and more in line with the requirements of mid-rise CFS structures.?For the joint connected with reinforced blocks,the ultimate buckling capacity of beam flange can be used as the critical point of its elastic stage;the flexural strength of beam end is determined by the elastic flexural capacity of beam section.?The improved Richard-Abbott model can fit the mr-?r curve of the joint connected with reinforced blocks well,which can be used to predict the moment-rotation relationship of the joints with different beam sizes;the non-linear finite element model of beam-columm joints based on OpenSees can reflect the real mechanical performance of the joint connected with reinforced blocks.2.An experimental investigation of nine full-scale CFS shear walls with reinforced end studs under cyclic load was described in this thesis.Factors such as sheathing material,stud type and openings were considered.The results show that:?With cyclic load,the failure modes of those walls include the invalidation of screw connections,steel frame deformation and sheathing failure;screws on the reinforced end studs were less able to tilt due to the concrete core,resulting those screws being sheared off w hen the wall damaged.?Screw connection plays a dominate role in the shear performance of the walls,and the load-displacement hysteretic curves have the same pinching characteristic as the that of traditional shear wall with coupled C section end studs.?Both the shear strength and shear stiffness of CFS shear wall with reinforced end studs can be enhanced more than 30%compared with the traditional shear wall with coupled C section end studs;the walls' ductility may be improved by increasing stud thickness,but no meaningful difference in shear strength was observed when the interior stud section's type was replaced with a coupled C section.?Autoclaved lightweight concrete(ALC)slabs have lower strength,compared to a wall that was individually sheathed with ALC slabs on the external side,the shear strength could be increased by approximately 58.1%due to the addition of supplementary bolihian magnesium boards,which would be installed under the condition of an identical sheathing setup on the inner side.?The wall's shear capacity would be decreased due to an increase in the opening's size,and this shear capacity would also be impacted by the opening's position.The comparison between test and calculated results indicate that,for perforated shear walls with reinforced end studs,the empirical equations described in AISI are not suitable for predicting their shear capacity.Therefore,based on a bearing mechanism analysis of CFS shear walls with reinforced end studs,a simplified method for predicting the perforated walls'shear capacity w as proposed,and the differences between the calculated and experimental results were within 8%.3.The first experimental research on the lateral performance of mid-rise CFS shear wall at home was finished in this thesis.Cyclic tests on seven different mid-rise CFS shear wall specimens were conducted,by which the lateral performance of mid-rise CFS shear wall were revealed intuitively.Factors such as stud type,stud section and interlayer action were considered.The results show that:?With horizontal load,fthe failure modes of those specimens,which mainly occurred in the underlying wall,did not differ significantly from that observed in the single-story shear wall tests;specimens will have shear type failure if their aspect ratios are less than 2.0 and bending-failure if their aspect ratios are larger than 3.0.?Both shear strength and non-deformability were notably enhanced by adopting reinforced end studs,and the specimens exhibited better energy-dissipating capacity after their yield limit.?When the web depth of end columns was enlarged from 89 mm to 140 mm,for a fully sheathed specimen,the elastic stiffness of the lower story was improved by nearly 41.5%,while there was no meaningful reduction in the non-deformability of the upper story if the opening area ratio was 20.8%at most.?Because of the second story,the shear capacity of each two-story specimen was less than that of the corresponding single-story shear wall;furthermore,the reduction degree of the shear capacity for specimens with small stud sections was lower.In addition,combined with the test results of single-story shear wall specimens,a comparative research on the influence of opening and its position was performed;it is indicated that,the shear resistance of mid-rise shear wall with openings in center can be accurately predicted by the simplified method for the shear capacity of single-story perforated shear walls;for walls with an opening on the side,the shear capacity of whether single-story or mid-rise shear wall can be determined based on the net wall length except opening.4.Based on the exrperimental study,Opensees was used to study the numerical simulation method on the shear performance of the wall.The main conclusions are as follows:?The modeling method based on screw connections can get the exact shear performance of single-story CFS shear wall with reinforced end studs,the maximum error for the shear performance indicators of the wall between test and calculated results is less than 13%.?Pinching4 constitutive model can accurately define the properties of screyxw connections,the pinching characteristic of load-displacement hysteretic curve can thereby be fully reflected.?During the analysis model establishment of the wall with an opening in center,the upper wall segment above the opening can be simplified into a linear elastic beam,and a horizontal force bending group should be set at both ends of the beam to simulate the bending moment transmission between the upper wall segment and the opening's end columns;while for the wall with an opening on the side,the upper wall segment of the opening can be neglected,the analysis model can be established only taking the net wall part outside the opening into account.?The modeling method based on screw connections can effectively predict the lateral performance of two-story CFS shear wall that subjected to inverted triangle lateral loads,and the result is safe and reliable;for mid-rise CFS shear wall with large aspect ratio and a lateral concentrated load being applied on the top,a simple analysis model,which considers those screw connections in the perimeter of the walls only,was established by reasonable simplification,by which the lateral performance of the wall can be obtained in accordance with the test results.5.In order to establish a theoretical hysteretic model which is easy to be mathematical described and can fully reflect the shear behavior of CFS shear wall with reinforced end studs,the hysteretic law of the walls was lucubrated based on the experimental research,and the hysteretic model was established in two steps:?Discrete coordinate method was proposed to establish the load-displacement skeleton curve of the wall,and then the governing deformations and their corresponding loads of those hysteretic loops under different loading cases were obtained.?Piecewise function was adopted to establish the hysteretic loop under each governing deformation,and the hysteretic model of the wall was further obtained;besides,the dominate parameters of the hysteretic model were given.Finally,the proposed hysteretic model was validated by the experimental results from others.It is shown that:?The fundamental factors that influence the development trend of the load-displacement skeleton curve of the wall are elastic lateral stiffness Ke and shear capacity Fp;?The hysteretic characteristics of CFS shear wall with reinforced end studs can be fully reflected by piecewise function hysteretic model,moreover,the model expression is intuitionistic and the physical significance of each parameter is clear.?Hysteretic models such as BWBN differential model,EPHM model,Pivot model as well as three-segment nonlinear pinching hysteretic model are suitable for traditional shear wall with coupled C section end studs,and limited to low-rise CFS structures;in contrast,the piecewise function hysteretic model is suitable for any form of CFS shear wall with reinforced end studs and more in line with the mid-rise CFS structure's requirements.6.During the seismic analysis of whole structures,simplification of CFS walls is necessary because fine wall model will lead to difficulties in calculation.In this thesis,Opensees was first used to study the nonlinear simplified calculation method of the wall.The results show that,the simplified calculation method that using equivalent bracing model with Pinching4 constitutive model can fully reflect the shear performance of the wall,and the maximum error of the shear performance indicators of the wall between test and calculated results is less than 17%.Based on the test results and existing specifications,lateral design objectives for mid-rise CFS structure under earthquake were proposed;besides,seismic analysis on a simplified calculation model of mid-rise CFS structure was carried out,which first considered the real mechanical performance of joints.The main conclusions are as follows:?It is safe and reliable that 1/300 and 1/100 being taken as the elastic and inelastic storey drift limits of mid-rise CFS structures under frequent and severe earthquake,respectively.?The arrangement of CFS shear walls has remarkable influence on the seismic performance of the structure;during the mid-rise CFS structure design,it is not suitable to adopt the shear wall combination with large difference in stiffness between two directions;besides,strengthening the shear strength of the walls along the direction with larger opening rate should be emphasized.?The mid-rise CFS structure that adopting shear walls with reinforced end studs will not collapse under severe earthquake with a degree of 9;for the design of mid-rise CFS structures in areas of particularly high seismicity,both the wall's shear strength and the vertical bearing capacity together with the reliability of end studs' bottom connection should be taken into account,to avoid overall failure of the structure caused by end studs' buckling. |
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