Refined Plastic Hinge Analysis of Steel Frame Structures Comprising Non-Compact Sections I: Formulation

Distributed plasticity analysis of steel frame structures comprising non-compact sections

Three‐dimensional (3D) base isolation can significantly improve the seismic performance of structures. However, significant 3D movement coupling and rocking behavior of the superstructure due to the high gravity center of the structure can be observed, which will lead to a complex design of the isolation system and the isolators. In addition, as the 3D isolators are installed beneath the structures, they need to support the heavy weight of the superstructure with low vertical stiffness. It is difficult to meet both the vertical load and stiffness design demands of the isolators using traditional isolation materials and mechanisms, especially for large‐size structures. A separated 3D isolation scheme is proposed by installing the horizontal isolation at the base of the superstructure and the vertical isolation under the floor slabs. Simulations are carried out to examine the dynamic responses including the acceleration, inter‐storey drift, and stress of structural members of a typical steel frame structure with the separated 3D isolation scheme. The isolation effect was also studied by shaking table tests of a two‐storey steel frame structure. The simulation and test results show that the proposed separated 3D isolation scheme has high performance in mitigating the structural accelerations in both horizontal and vertical directions, and the vertical load on isolators. The rocking behavior of the structure is effectively restrained for the separated 3D isolation scheme due to a low mass center configuration of the vertically isolated slabs. Although the isolation of the floor slabs from the beams in the structure with separated 3D isolation weakens the constraint of the floor slabs to the beam and column members as in a traditional frame structure, the horizontal isolation at the base of the superstructure reduces the adverse effect and the stress of structural members is similar to that in a horizontal base‐isolated structure and significantly lower than that in a base‐fixed structure. In addition, as the vertical isolation is installed under the slabs, the vertical load on the vertical isolators is small and it is easy to design the isolators.

A methodology of nonlinear analysis of timber frame structures with flexible connections has been developed in this paper. The methodology is based on the results of experimental investigation of connections behavior under static and cycling loading. The adopted numerical method is based on the concept of localized nonlinearity which facilitates the reproduction of the experimentally determined connections behavior in the analysis of frame structures. The methodology is also applicable to other types of timber structures.

According to the conditions of today's world, design of resistant structures against blast loading is an important subject that requires special attention. Thus, given the benefits of optimization in engineering, development and assessment of optimization methods for optimum design of structures against blast is of great importance. In this research, the optimum design of steel frame structures against blast loading is investigated. For this purpose first an optimization methodology is proposed. In the proposed method the structural analysis is performed using nonlinear explicit finite element analysis. Based on the proposed method a framework is developed and three numerical examples are investigated using different numerical optimization techniques. Results of this study show that by using nonlinear explicit FE analysis as the structural analysis method and NLPQLP optimization technique as the optimization method, the current optimization problem can be performed effectively, because the procedure is relatively accurate and computationally inexpensive.

Applications of simplified 3D FE model in seismic analysis for friction-damped posttensioned steel frame structures

Out-of-plane advanced analysis of steel structures

The analysis and design of skeletal structures is greatly influenced by the behaviour of beam-to-column connections, where patented designs have led to a wide range of types with differing structural quantities. The behaviour of beam-to-column connections plays an important role in the analysis and design of framed structures. This paper presents an overview of the influence of connection behaviour on structural stability, in the in-plane (bending) mode of sway. A computer-based method is presented for geometrically nonlinear plane frames with semi-rigid connections accounting for shear deformations. The analytical procedure employs transcendental modified stability functions to model the effect of axial force on the stiffness of members. The member stiffness matrix were found. The critical load has been searched as a suitable load parameter for the loss of stability of the system. Several examples are presented to demonstrate the validity of the analysis procedure. The method is readily implemented on a computer using matrix structural analysis techniques and is applicable for the efficient nonlinear analysis of frameworks. Combined with a parametric column effective length study, connection and frame stiffness are used to propose a method for the analysis of semi-rigid frames where column effective lengths are greatly reduced and second order (deflection induced) bending moments in the column may be distributed via the connectors to the beams, leading to significant economies.

Uniform story drift optimization seismic design of steel frame structures

Summary Based on the upper bound theorem, the fire resistance is studied using the combination of element collapse mechanisms of steel frames, where the element collapse mechanisms are automatically determined from independent mechanisms. The fire limit load is calculated by solving a nonlinear mathematical programming. The computing procedure is programmed by FORTRAN language. Results show that this method is useful to find the collapse mechanism with the lowest fire limit load, which can provide a theoretical and practical way for the fire design of steel frame structure.

The principal aims of this research thesis were to assess the degree of improvement in performance achieved through the use of energy dissipative devices in the design of steel frame structures under seismic loading. The first part of the research reports on a series of monotonic and cyclic tests performed on the energy dissipative device mounted in a single-storey, planar K-braced frame. The device consists of a short length of square hollow section with a diaphragm plate of thickness either 2mm or 3mm welded inside it. It is installed between the bracing and the top member of the braced frame, with the diaphragm lying in the plane of the frame, so that it is loaded in pure shear as the frame undergoes lateral deformation. The devices can be easily fitted, remove and replace. In addition, the devices are cheap to manufacture. All the devices which were tested yielded at very low deformations and sustained very large ductility without failure. From the cyclic test results, it is shown that a device with 3mm is recommended as offering the best combination of dissipative capacity and robustness. For the second part of the research, an extensive analysis of 10-storey frames, both undamped moment-resisting frames and retrofitted with energy dissipative devices has been performed. This 10-storey building was modeled using the finite element program Strand 7 and was analyzed using linear time history analysis and non-linear static analysis. Upon comparison of the analysis, it was found that the dissipative system lead to a substantial improvement in frame performance, in terms of plastic hinge formation and deformations. Therefore it is concluded that these devices offer a simple, cheap and robust way of dissipating significant amounts of energy in seismically loaded frames.

To improve the seismic design of steel frame structures, the empirical formula for evaluation of fundamental periods of steel frame structures was investigated and a new formula was presented in the paper. A total number of 36 moment resisting steel frame structures were selected for the statistical analysis, and all the structures obtained seismic response records during past earthquakes. The fundamental periods of all structures before damaged were identified by using ARX method, and the new empirical formula for fundamental period of steel frame structure was obtained through nonlinear least square regression. The result shows that the fundamental period of steel frame structure can be expressed in terms of the height to the power of 0.6 and multiplied by the modified factor 0.12. The proposed empirical formula can be referenced for the seismic design code revision, steel frame structures seismic design and related researches.

Topology optimization of steel frame structures with constraints on overall and individual member instabilities

The efficiency of plasticity for the design of steel frame structures is analysed in the paper. Technical theory of plasticity and standard assumptions and requirements for numerical study are applied. Two types of simple frames (double-sided pinned supporting and fixing) with different loading, geometrical dimensions of the frames and cross-sections of their columns and beams are considered. Some results of the numerical study and conclusions are also presented.

Minimizing construction cost and reducing seismic damage are two conflicting objectives in the design of any new structure. In the present work, we try to develop a framework in order to solve the optimum performance-based design problem considering the construction cost and the seismic damage of steel moment-frame structures. The Park-Ang damage index is selected as the seismic damage measure because it is one of the most realistic measures of structural damage. The non-dominated sorting genetic algorithm (NSGA-II) is employed as the optimization algorithm to search the Pareto optimal solutions. To improve the time efficiency of the proposed framework, three simplifying strategies are adopted: first, simplified nonlinear modeling investigating minimum level of structural modeling sophistication; second, fitness approximation decreasing the number of fitness function evaluations; third, wavelet decomposition of earthquake record decreasing the number of acceleration points involved in time-history loading. The constraints of the optimization problem are considered in accordance with Federal Emergency Management Agency\'s (FEMA) recommended seismic design specifications. The results from numerical application of the proposed framework demonstrate the efficiency of the framework in solving the present multi-objective optimization problem.

In-filled frame structures are commonly used in buildings, even in those located in seismically active regions. Precent codes unfortunately, do not have adequate guidance for treating the modelling, analysis and design of in-filled frame structures. This paper addresses this need and first develops an appropriate technique for modelling the infill-frame interface and then uses it to study the seismic response of in-filled frame structures. Finite element time history analyses under different seismic records have been carried out and the influence of infill strength, openings and soft-storey phe- nomenon are investigated. Results in terms of tip deflection, fundamental period, inter-storey drift ratio and stresses are presented and they will be useful in the seismic design of in-filled frame structures. interface condition, friction coefficient, size of the mesh, relative stiffness of beam to column, relative size of infill wall have significant influence on the response of infilled frame, while the effect of orthotropy of infill material was insignificant. When the mesh density was made finer the stress pattern within the infill also improved, with maximum values of stresses at the compressive corners. The existence of friction coefficient at the interface was reported to in- crease the lateral stiffness of the system. However, friction coefficient is dependent on the quality of material and the workmanship CEB 1996 (6) which is difficult to define ac- curately, hence codes do not provide any guidance.