Investigation on Shear Capacity for Screw Connections of Cold-Formed Steel Framed Shear Walls with Steel Sheathing

Experimental and numerical investigations were carried out to learn the shear capacities for screw connections of cold-formed steel framed shear walls with steel sheets for the base layer combined with gypsum wallboards for the face layer. The design methods of test specimens, the loading equipment and the data processing method were introduced. According the phenomenon of tests for multiple self-drilled screw connections, the loading-deformation curves, shear capacity and failure modes were testified. The influence of end distance of screw, edge distance of screw, diameter of screw, spacing of screw, thickness of steel sheets, thickness of gypsum wallboards, thickness of studs on shear behavior for connections were investigated. The finite element software ABAQUS was used to simulate the shear behavior of screw connections. A comparison between the numerical simulations and the test results showed a good agreement. This study can be applied to numerical simulations of seismic behavior of steel sheathed cold-formed steel framed shear walls

Lateral performance of an innovative cold-formed steel shear wall system reinforced by frame

In this paper, cyclic test of a frame reinforced cold-formed steel(CFS) shear wall was carried out. The failure mode, hysteresis curve and envelope curve were obtained. Also, simplified model of the shear wall was established. The results show that: 1. With the help of steel frame, the failure of the shear wall change from brittle failure with buckling on the boundary studs to ductile failure with undamaged studs. 2. the constraint of the frame enables the specimen to maintain more than 70% shear strength under large deformation with a drift ratio of 1/20 rad. 3. The modelled result is in good agreement with the experimental result, and the simplified models can simulate seismic performance well.This research was supported by the National Natural Science Foundation of China (Grant No. 51978151), National Key Program Foundation of China (51538002), and the Scientific Research Foundation of Graduate School of Southeast University (YBPY1963)

Designing efficient grid structures considering structural imperfection sensitivity

At the initial design stage of a grid structure, shape optimisation is an effective way to find the optimal structural form. However, most of the shape optimisation methods do not take into consideration the imperfections, thus the actual buckling load capacity of the optimised structure is usually low. In this paper, an improved shape optimisation method is proposed, one that is considering the effect of structural imperfection sensitivity. In this method, the bending strain energy ratio is taken as a constraint, and when the total strain energy decreases, yet there is a certain proportion of bending strain energy in the structure. Consequently, the resulted shape is not sensitive to the initial geometry imperfection, and therefore, an efficient structure with higher buckling load capacity and low imperfection sensitivity is obtained. In order to evaluate the redundancy performance of the optimised structure, an index called structural overall redundancy, based on damage model is proposed herein. The damage model is simulated by removing a key rod of the structure. The results demonstrate that the overall redundancy of the structure obtained by the proposed method is higher than that obtained by the traditional method, thus an optimal design of a grid structure is obtained

Lateral performance of an innovative cold-formed steel shear wall system reinforced by frame

In this paper, cyclic test of a frame reinforced cold-formed steel(CFS) shear wall was carried out. The failure mode, hysteresis curve and envelope curve were obtained. Also, simplified model of the shear wall was established. The results show that: 1. With the help of steel frame, the failure of the shear wall change from brittle failure with buckling on the boundary studs to ductile failure with undamaged studs. 2. the constraint of the frame enables the specimen to maintain more than 70% shear strength under large deformation with a drift ratio of 1/20 rad. 3. The modelled result is in good agreement with the experimental result, and the simplified models can simulate seismic performance well.This research was supported by the National Natural Science Foundation of China (Grant No. 51978151), National Key Program Foundation of China (51538002), and the Scientific Research Foundation of Graduate School of Southeast University (YBPY1963)

Numerical Study on the Seismic Performance of Cold-Formed Steel Shear Walls with Steel Sheathing and Gypsum Board

The cold-formed steel shear wall with steel sheathing has gained increasing popularity due to its excellent shear capacity. To extend the applicability of this system to multi-story residences, aside from experimental investigations on the shear walls, it is essential to conduct a comprehensive study on the seismic performance of buildings. In this paper, numerical simulations were conducted on specimens subjected to monotonic and cyclic loading. Subsequently, seismic analysis of mid-rise building models was also carried out to investigate the influence of the proposed shear wall on building seismic performance. The research findings indicate that this study’s modeling method can effectively simulate the shear performance of the proposed shear wall under monotonic and cyclic loading. In addition, the proposed shear wall significantly enhances the structural stiffness and improves the seismic performance of the structure under seismic action

Wind Flow Characteristics of Multivortex Tornadoes

A multivortex tornado refers to a tornado that contains two or more small subvortices in the wind field. Due to the presence of multiple vortices, this type of tornado is likely to be more dangerous and destructive than single-vortex tornadoes. To understand the action of the multivortex tornado on civil structures, the wind flow characteristics are investigated and compared with those of single-vortex tornadoes, by using computational fluid dynamics (CFD) simulations. The results show that the inner flow structure of a multivortex tornado is completely different from that of a single-vortex tornado. First, a multivortex tornado possesses more than one subvortex in the domain around the core radius of the main vortex, and each subvortex flows together with the main vortex while rotating around its own center. Second, the wind flow of a multivortex tornado is more turbulent than a single-vortex tornado, which may lead to significant dynamic responses in some types of civil structures. Third, the maximum negative pressure occurs at the center of each subvortex instead of the center of the main vortex, which means that the largest negative pressure and highest wind speed occur at the same location. This unique feature in the multivortex tornado leads to different worst loading scenarios from single-vortex tornadoes and the worst-case scenario might be the combination of high tangential velocity and high negative pressure around the core radius. Fourth, for a multivortex tornado, the difference between instantaneous values and space-Averaged values of parameters is remarkable. Thus, the space-Averaged values should be carefully used for determining design tornadic wind loads for civil structures

Improvement of Tornado Simulation by Adjusting Boundary Conditions

Tornadoes have resulted in significant fatalities and property damage each year. To mitigate this natural hazard, the research on numerically simulating tornadic wind field and investigating the wind effects on civil structures has been conducted. Considering that the setup of the boundary conditions has a significant influence on the generated wind flow when conducting CFD simulations, this study is to investigate how the sizes of the pressure outlet and velocity inlet affect the characteristics of the generated tornadic wind flow by taking the CFD simulation of a real-world tornado (Tornado Spencer) as an example. Based on the observations in this study, the way to improve the tornado simulation by adjusting physical boundary condition is proposed

Identification of Nodal Snap-Through Instability in Civil Space Structures

In the community of structural health monitoring (SHM) and damage detection, the majority of previous research efforts has been focused on the detection of the reduction in cross-sectional areas of structural components or connections. However, the detection of the loss of stability, which can easily result in a structural failure, has been lacking. The objective of this study is to identify the occurrence of instability in civil space structures, such as domes, shells and reticulated shell structures. For this type of structure, nodal snap-Through instability occurs, where a node and connected members jump to a new equilibrium position, leading the geometric shape/pattern in a local area to change significantly. In this study, we propose to use tilting angles of members to identify the nodal snap-Through instability of civil space structures. Tilting angles of members actually reflect the change in geometric shape caused by instability. The effectiveness of this approach will be validated on numerical simulations of a reticulated shell structure. This research will bridge the gap between SHM and structural stability research and will make important contributions to the science of both SHM and structural instability

Detection of Pretension Loss of Cable-Net Structures

Due to aesthetic shapes, light weight and flexibility, cable-net structures have been widely used as roofs for venues where many people assemble, such as sports stadiums/arenas and gymnasiums. Failure of this type of structure may endanger the safety of many people. This type of structure consists of a separate grid of structural cables supporting a nonstructural weather shield. It is well known that the stiffness of this type of structure is established by pretension in the cables. Part of the pretension in the cables will be lost as time evolves. The detection of the pretension loss in cables of cable-stayed bridges has been widely studied. However, the detection of pretension loss in cables of cable-net structures has been lacking. In this study, the dynamic and static properties of cable-net structures will be investigated and the effectiveness of two damage detection approaches in detecting the pretension loss in cable-net structures will be investigated

Experimental and Simulation Study on the Hysteretic Behavior of Double-Ring Joints for a Single-Layer Grid Shell under Cyclic Eccentric Loading

Based on the mechanical characteristics of assembled joints in a single-layer grid shell, a cyclic eccentric loading method was designed to study the hysteretic behavior of double-ring joints under the action of axial force and moment through experiment and finite element analysis. The effects of structural parameters and axial force eccentric distance on the failure mode, hysteretic behavior and energy-dissipating capacity of double-ring joints were explored, which laid a foundation for the research on dynamic collapse properties and shape optimization of grid shell. The following conclusions were obtained: 1) Two main failure modes occurred for double-ring joints: the fracture of the bolt and the fracture of the central ring at the bolt hole. The failure mode was affected by the axial force. 2) All the hysteretic loops included five stages, and the plastic deformation of the central ring improved the energy-dissipating capacity of the joint. 3) Under the action of eccentric compression with eccentric distance δ ≤ 80 mm and eccentric tension, with increasing eccentric distance, the rotational stiffness and ultimate bending moment increases. Under the action of eccentric compression with eccentric distance δ \u3e 80 mm, the eccentric distance has little effect on the rotational stiffness and ultimate bending moment