Numerical-Computational Model for Nonlinear Analysis of Frames with Semirigid Connection

A numerical-computational model for static analysis of plane frames with semirigid connections and geometric nonlinear behavior is presented. The set of nonlinear equations governing the structural system is solved by the Potra–Pták method in an incremental procedure, with order of cubic convergence, combined with the linear arc-length path-following technique. The algorithm pseudo-code is presented, and the finite element corotational method is used for the discretization of the structures. The equilibrium paths with load and displacement limit points are obtained. The semirigidity is simulated by a linear connection element of null length, which considers the axial, tangential, and rotational stiffness. Nonlinear analyses of 2D frame structures are carried out with the free Scilab program. The results show that the Potra–Pták procedure can decrease the number of iterations and the computing time in comparison with the standard and modified Newton–Raphson iterative schemes. Also, the simulations show that the connection flexibility has a strong influence on the nonlinear behavior and stability of the structural systems.

Seismic Behavior of the Removable Links in Eccentrically Braced Frames with Semirigid Connections

Eccentrically braced frames (EBFs) have good elastic stiffness, while semirigid joints can provide greater ductility and make all components easy to fabricate. With application of semirigid connections to EBFs, a seismic structure can be formed. After earthquake, damaged components can be easily replaced, and repair costs and maintenance time can be reduced. In order to study the seismic performance of this type of structure, four single-story plane specimens were tested under low-cycle cyclic loads. Also, a total of 7 EBF models were investigated through three-dimensional, nonlinear finite element analysis. Good agreement is achieved between the simulation and experimental results. The results show that the failure modes of the EBFs with semirigid connections are the fracture at link end plate connection, and no obvious buckling deformation and cracks occur in the other components. The EBFs with semirigid connections exhibit good inelastic rotation ability, and the inelastic rotation of all specimens and models exceeds the limit of 2016 AISC specification. Due to the slip between members, the hysteretic curves of those new structures show different degrees of pinching phenomenon and it becomes more obvious with the increase of the length of links. By analyzing the strain of the bolts, it is found that the bolt strains of the joints of link-to-beam are the highest, while the bolt strains of the joints of beam-to-column and column-to-brace are smaller. This structure system shows higher energy dissipation capacity and good economic benefits.

Experimental Research and Theoretical Analysis of the Seismic Behavior of Prefabricated Semirigid Steel Frame with X-Shaped Braces

Three semirigid connections which are convenient for prefabrication have been proposed in this paper. Based on them, the quasi-static test was conducted on three prefabricated semirigid steel frames with X-shaped braces in order to investigate their hysteresis behavior, bearing capacity, energy dissipation capacity, and failure mechanism. A comparative analysis of the semirigid connections was made to analyze their advantages and disadvantages. Then, a numerical simulation was carried out via using ABAQUS to verify the test results, and the causes of the errors were analyzed. The results showed that the prefabricated semirigid steel frames with X-shaped braces had good seismic behavior, the braces cooperated well with the steel frame in resisting lateral load, and the braces failed before the steel frame, which meant the structure had two seismic fortification lines. The results of the numerical simulation tallied with the test results, which means the finite element model could accurately simulate the structure’s mechanical behavior under cyclic loading. The structure had a better bearing capacity and ductility when using extended end-plate bolted connections.

Dynamic Instability in Shallow Arches under Transversal Forces and Plane Frames with Semirigid Connections

Structural engineering demands increasingly lighter systems, which can cause instability problems and compromise performance. A high slenderness index of a structural element makes it susceptible to instability. It is important to understand the problem, the limits of stability, and its postcritical behavior. An example that can occur in collapsed arches under a cross load is the dynamic snap-through behavior, where the structure in a given equilibrium condition jumps to a new remote equilibrium setting, causing usually sudden curvature. The semirigid connections are a source of physical nonlinearity and can influence the overall stability of the structural system, in addition to the distribution of stresses in the same system. Conventional approaches make use of static considerations. However, instability problems are inherently evolutionary processes, so a transient analysis is necessary for a complete description of structural behavior. The present work evaluates the geometrically nonlinear dynamic behavior of collapsed arches subjected to transverse force and plane frames with semirigid connections. The time domain responses, via Newmark's Method and positional formulation of the Finite Element Method, were obtained in terms of displacements, velocities, acceleration, and phase diagrams.

Accounting for the flexibility of nodes in the design of steel mesh dome

This paper presents the results of a study of the stress-strain state of a geodesic dome covering the planetarium designed in the city of Nizhny Novgorod. Four design schemes were created in the SCAD with different types of node modeling. A comparative analysis of the effect of the strain capacity of the “BrGTU” type unit on the stress-strain state of the dome cover has been carried out. The results are obtained on the change in the displacements of the structure nodes and internal forces in the dome bars, with rigid and hinged mates. The option of increasing the diameter of high-strength bolts to reduce the overall deformability of the system is considered. On the basis of the obtained results, it was concluded that it is necessary to take into account the strain capacity of the semirigid connections when designing mesh steel domes.