Steel Frame Model Research Articles

EXPERIMENTAL STUDIES OF A STEEL FRAME MODEL WITH AND WITHOUT BUCKLING-RESTRAINED BRACES

This paper presents comparative experimental studies of a five-storey steel-frame model at a scale of 1/10 with, and without, buckling-restrained braces (BRBs). The building model was subjected to free vibration tests and shaking table tests. The latter were conducted using low-intensity white noise and seismic input. From the free vibration tests and shaking table tests with low-intensity white noise, it was found that the BRBs contributed a significant amount of damping. This happened to the model even at low levels of vibration. The shaking table tests with seismic input were conducted using seven earthquake records, taken in the lakebed zone of Mexico City with seismic intensities from pga=0.1g to 0.25g. At an intensity of pga=0.1g, the results show that the model fitted with BRBs had a significantly smaller response than the bare model, in terms of displacement, inter-storey drift, floor velocity and floor acceleration. The higher intensities were only applied to the model fitted with BRBs. The results indicate that the model with BRBs was able to withstand about 2.5 times the seismic intensity of the bare model, in terms of lateral displacement, inter-storey drift and Arias Intensity, as a measure of the energy contents of the movement. At the end of the tests, all BRBs were removed and the model remained in its original undamaged state.

Fundamental period of masonry infilled moment-resisting steel frame buildings

Summary It is known to be a necessary practice to study the effect of infill walls on fundamental period and revise the equations included in the current building codes. In this research, the fundamental period of vibration, by modeling an infill wall as a compression strut in three-dimensional numerical models of moment-resisting steel frames, was studied. Areas studied in the present research were structures of symmetric infill wall arrangements wherein the effects of various infill percentage, various moduli of elasticity of masonry wall materials, and different numbers of spans were investigated. The mean fundamental period obtained by the formula provided in FEMA450 was 1.3 times greater than the value resulted from the numerical modeling of infilled moment-resisting steel frames. Moreover, the corresponding coefficient of determination, R2, of the curve fitted to numerically obtained periods was found to be 0.65 when the fundamental period of the infilled frames was only estimated based on the height of buildings, indicating a great deal of variation within the results. A new formula was proposed to estimate the fundamental period based on the structure height, infill wall percentage, and modulus of elasticity, at an acceptable level of accuracy so that the R2 coefficient was determined to be 0.99 for the results of the proposed formula.

Decoupling algorithm for evaluating multiple beam damages in steel moment‐resisting frames

SummaryPost‐earthquake safety evaluation of steel moment‐resisting frames mainly relies on the inspection of seismic damage to beam–column connections. Recently, in order to evaluate seismic damage of steel connections in a prompt and precise manner, a local damage evaluation method based on dynamic strain responses has been proposed and receives attention. In the evaluation method where strain responses are measured by piezoelectric strain sensors, a strain‐based damage index has been developed for evaluating individual seismic beam damage in a steel frame. However, for a steel frame suffering multiple beam damages, the damage index deteriorates its performance in identifying small damages with the presence of neighboring severe damages because of the moment redistributions induced by larger damages. This paper presents a decoupling algorithm that removes the issue of damage interaction and improves the performance of the damage index. The decoupling algorithm was derived on the basis of damage‐induced moment release and redistribution mechanism. The effectiveness of the decoupling algorithm was numerically and experimentally investigated using a nine‐story steel frame model and a large scale five‐story steel frame testbed that can simulate multiple fractures at beam ends. Copyright © 2016 John Wiley & Sons, Ltd.

Experimental studies on steel frame structures of traditional-style buildings

This paper experimentally investigated the behavior of steel frame structures of traditional-style buildings subjected to combined constant axial load and reversed lateral cyclic loading conditions. The low cyclic reversed loading test was carried out on a 1/2 model of a traditional-style steel frame. The failure process and failure mode of the structure were observed. The mechanical behaviors of the steel frame, including hysteretic behaviors, order of plastic hinges, load-displacement curve, characteristic loads and corresponding displacements, ductility, energy dissipation capacity, and stiffness degradation were analyzed. Test results showed that the Dou-Gong component (a special construct in traditional-style buildings) in steel frame structures acted as the first seismic line under the action of horizontal loads, the plastic hinges at the beam end developed sufficiently and satisfied the Chinese Seismic Design Principle of columns-weak beams, strong joints-weak members. The pinching phenomenon of hysteretic loops occurred and it changed into Z-shape, indicating shear-slip property. The stiffness degradation of the structure was significant at the early stage of the loading. When failure, the ultimate elastic-plastic interlayer displacement angle was 1/20, which indicated high collapse resistance capacity of the steel frame. Furthermore, the finite element analysis was conducted to simulate the behavior of traditional-style frame structure. Test results agreed well with the results of the finite element analysis.

Electromagnetic energy harvesting from structural vibrations during earthquakes

Energy harvesting is an emerging technique that extracts energy from surrounding environments to power low-power devices. For example, it can potentially provide sustainable energy for wireless sensing networks (WSNs) or structural control systems in civil engineering applications. This paper presents a comprehensive study on harvesting energy from earthquake-induced structural vibrations, which is typically of low frequency, to power WSNs. A macroscale pendulum-type electromagnetic harvester (MPEH) is proposed, analyzed and experimentally validated. The presented predictive model describes output power dependence with mass, efficiency and the power spectral density of base acceleration, providing a simple tool to estimate harvested energy. A series of shaking table tests in which a single-storey steel frame model equipped with a MPEH has been carried out under earthquake excitations. Three types of energy harvesting circuits, namely, a resistor circuit, a standard energy harvesting circuit (SEHC) and a voltage-mode controlled buck-boost converter were used for comparative study. In ideal cases, i.e., resistor circuit cases, the maximum electric energy of 8.72 J was harvested with the efficiency of 35.3%. In practical cases, the maximum electric energy of 4.67 J was extracted via the buck-boost converter under the same conditions. The predictive model on output power and harvested energy has been validated by the test data.

Structural damage detection using ARMAX time series models and cepstral distances

A novel damage detection algorithm for structural health monitoring using time series model is presented. The proposed algorithm uses output-only acceleration time series obtained from sensors on the structure which are fitted using Auto-regressive moving-average with exogenous inputs (ARMAX) model. The algorithm uses Cepstral distances between the ARMAX models of decorrelated data obtained from healthy and any other current condition of the structure as the damage indicator. A numerical model of a simply supported beam with variations due to temperature and operating conditions along with measurement noise is used to demonstrate the effectiveness of the proposed damage diagnostic technique using the ARMAX time series models and their Cepstral distances with novelty indices. The effectiveness of the proposed method is validated using the benchmark data of the 8-DOF system made available to public by the Engineering Institute of LANL and the simulated vibration data obtained from the FEM model of IASC-ASCE 12-DOF steel frame. The results of the studies indicate that the proposed algorithm is robust in identifying the damage from the acceleration data contaminated with noise under varied environmental and operational conditions.

Finite element modeling and capacity analysis of post-tensioned steel frames against progressive collapse

Post-tensioned (PT) steel frames, in which beams are connected to columns through high-strength PT strands, have been successfully developed in the past decade as a novel earthquake-resistant structural system. Compared to conventional steel moment frames, a PT steel frame demonstrates superior seismic performance, notably the minimum damages in main structural components and the self-centering capability under a design basis earthquake. Despite the abundant research on the seismic behavior of PT steel frames, there is an apparent lack of study on their load-redistribution behavior upon the notional removal of critical load-bearing columns, a commonly used threat-independent local structural damage scenario that potentially triggers the progressive collapse of the column-removed frame. This paper presents a first-of-its-kind numerical investigation on the unique structural behavior of PT steel connections and frames in redistributing the unbalanced gravity loads due to column removal. High-fidelity finite element structural models are constructed and validated using the available experimental data in the literature. The capacity of PT steel frames subjected to a gradually increasing vertical displacement along the removed column line is systematically studied. It is found that, besides the resistance of energy-dissipating elements, beam arching action and strand catenary action are the major sources of structural capacity of a PT steel frame against progressive collapse. The corresponding failure modes are identified and the design implications are suggested.

Image-based structural dynamic displacement measurement using different multi-object tracking algorithms

With the help of advanced image acquisition and processing technology, the vision-based measurement methods have been broadly applied to implement the structural monitoring and condition identification of civil engineering structures. Many noncontact approaches enabled by different digital image processing algorithms are developed to overcome the problems in conventional structural dynamic displacement measurement. This paper presents three kinds of image processing algorithms for structural dynamic displacement measurement, i.e., the grayscale pattern matching (GPM) algorithm, the color pattern matching (CPM) algorithm, and the mean shift tracking (MST) algorithm. A vision-based system programmed with the three image processing algorithms is developed for multi-point structural dynamic displacement measurement. The dynamic displacement time histories of multiple vision points are simultaneously measured by the vision-based system and the magnetostrictive displacement sensor (MDS) during the laboratory shaking table tests of a three-story steel frame model. The comparative analysis results indicate that the developed vision-based system exhibits excellent performance in structural dynamic displacement measurement by use of the three different image processing algorithms. The field application experiments are also carried out on an arch bridge for the measurement of displacement influence lines during the loading tests to validate the effectiveness of the vision-based system.

Dynamic performance of axially and rotationally restrained steel columns under fire

Columns in real buildings are normally axially and rotationally restrained by adjacent members. This paper investigates the dynamic performance of axially and rotationally restrained steel columns under fire via parametric analysis. Investigated parameters include the axial restraint stiffness, rotational restraint stiffness, column slenderness and load ratio. An explicit dynamic solver is employed to analyse the considered columns up to total failure. The numerical model is validated through comparing the results against those of a plane steel frame model which has been verified by means of experimental and analytical work. The results of the column model match well with those of the whole model of steel frame. Results show that the behaviour of restrained steel columns under fire may be quasi-static up to total failure or be with severe dynamic effects during buckling, depending on the restraint condition, load ratio and column slenderness. It is found that static analysis may significantly underestimate the maximum displacement for the case of dynamic buckling of columns under fire, and the maximum displacement of that case may even be larger than the final displacement of gradually removing the heated column. Axial restraint stiffness, rotational restraint stiffness and load ratio have significant effects on both the critical temperature and the initiation of dynamic effects. In this regard, dynamic buckling tends to occur with small axial and rotational restraint stiffness and a large load ratio. However, the performance of columns is found to be relatively insensitive to rotational stiffness ratio beyond a specific threshold value.

Improved independent component analysis based modal identification of higher damping structures

Structural modal parameter identification under ambient excitation has strong engineering value and theoretical significance. As the most popular tool for solving Blind Source Separation (BSS) problems, Independent Component Analysis (ICA) is able to directly extract the time-domain modal parameters, including frequencies, damping ratios and modal shapes. ICA, however, has a fatal flaw of failing to identify structures with higher damping. To overcome the flaw above, the paper proposes a new method named “ICA+IDT”. Firstly, free vibration response of a structure is obtained from structural outputs under ambient excitation. Inverse damping transfer (IDT) is employed to turn a highly damped signal into a low damping response signal without changing of frequencies and mode shapes. Then, structural modal parameters are extracted from the low damping response signal by ICA. Finally, the identified damping ratios are adjusted to eliminate the impact of IDT. To verify the effectiveness and applicability of IDT+ICA proposed herein, two numerical simulations—mass-spring model and simply supported concrete beam—and an experiment model of three-story steel frame are built, and the analysis results reveal that presented method can identify structures with higher damping effectively.

Optimal arrangement for an efficient scaffold support system

Scaffold support system is primarily used as temporary support during construction. However, no clear guidelines exist for a direct means of predicting the load carrying capacity of scaffolding. To increase the efficiency of scaffolding system, the number of tubes to be moved should be addressed to reduce costs and improve speed of construction without jeopardising the load carrying capacity. This translates into fewer tubes to be lifted, transported, and shifted during assembly. The paper proposes a simple numerical space steel frame model to predict the load carrying capacity of scaffold support system and provide optimal arrangement for fast and safe construction. The numerical results reasonably predicted the load carrying capacity of initial scaffold system arrangements and provided corresponding optimal arrangements scaffold arrangements. The obtained optimal arrangements reduced the number of utilised tubes by at least 7.14% and up to 42.31% and resulted in 5.14% to 25% savings in direct cost.

Application of steel equivalent constitutive model for predicting seismic behavior of steel frame

In order to investigate the accuracy and applicability of steel equivalent constitutive model, the calculated results were compared with typical tests of steel frames under static and dynamic loading patterns firstly. Secondly, four widely used models for time history analysis of steel frames were compared to discuss the applicability and efficiency of different methods, including shell element model, multi-scale model, equivalent constitutive model (ECM) and traditional beam element model (especially bilinear model). Four-story steel frame models of above-mentioned finite element methods were established. The structural deformation, failure modes and the computational efficiency of different models were compared. Finally, the equivalent constitutive model was applied in seismic incremental dynamic analysis of a ten-floor steel frame and compared with the cyclic hardening model without considering damage and degradation. Meanwhile, the effects of damage and degradation on the seismic performance of steel frame were discussed in depth. The analysis results showed that: damages would lead to larger deformations. Therefore, when the calculated results of steel structures subjected to rare earthquake without considering damage were close to the collapse limit, the actual story drift of structure might already exceed the limit, leading to a certain security risk. ECM could simulate the damage and degradation behaviors of steel structures more accurately, and improve the calculation accuracy of traditional beam element model with acceptable computational efficiency.

Weak coupling of shell and beam computational models for failure analysis of steel frames

A hierarchical modeling of planar steel frames that is based on a weak coupling of shell and beam computational models is studied in detail. A shell finite element is used to compute failure response of a representative part of each column and each beam of a frame under consideration; elasto-plasticity, geometrical nonlinearity and material softening (along with a localization limiter) are taken into account. The computed results, which naturally include local buckling and/or localized material failure effects, are further incorporated into a beam inelastic stress-resultant constitutive model; the embedded-discontinuity-in-rotation Euler–Bernoulli finite element is considered in this work. The designed beam finite element formulation can be effectively used for the failure analysis of the steel frame. Important issues of such weak coupling concept are presented and results of several numerical simulations are discussed.

The application of the geometric offset method to the rigid joint modeling in the differential quadrature element model updating of frame structures

The following paper deals with the differential quadrature element (DQE) model updating of frame structures when the linear vibration behavior is of interest. To model the rigid L and T joints of the frame, a geometric offset method is employed to define a rigid region around each joint. The kinematic constraints due to the rigid joints, the equilibrium of axial and transverse forces, and the bending moments acting on the joint are utilized to model the joints in the DQE model of the frame. Then, to update the DQE model using the experimental natural frequencies, a minimization problem is defined to reduce an objective function based on the residuals between a measurement set obtained from modal testing on the frame and the corresponding DQE model predictions. Using the proposed approach, the DQE model of a three-story steel frame for in-plane vibrations is updated. To do so, several parameters of the model including the Young’s modulus, the density, the geometric offsets and mass parameters of the joints, and the stiffness of the rotational spring used to model the foundation are considered as the design parameters. The optimum values of the design parameters are then found by employing the particle swarm inspired multi-elitist artificial bee colony algorithm. The results of the model updating indicate a good coincidence of the modal parameters of the updated DQE and the experimental models. The sensitivity analysis also reveals that the highest eigenvalue sensitivities are to the joints’ parameters.

Mechanical Analysis of Tunnel Steel Frame with Steel Frame and Sprayed Concrete Combination Model

To research the mechanical regularity of steel frame in tunnel, Steel frame and Sprayed concrete Combination Model is applied and the large-section loess tunnel of highway is taken as an example. The hoop stress of flange and the radial stress of web were analyzed, the research results show that:The most areas of hoop stress of flange is in press, the compress value which most areas of flank edge is larger than the outer flank flange in the same area of steel frame. The hoop and radial stress of web is in press. The hoop stress value which most areas of flank edge are larger than the radial stress in the same area of steel frame.

Computational finite element model updating tool for modal testing of structures

In this paper, the development of a new optimization software for finite element model updating of engineering structures titled as FemUP is described. The program is used for computational FEM model updating of structures depending on modal testing results. This paper deals with the FE model updating procedure carried out in FemUP. The theoretical exposition on FE model updating and optimization techniques is presented. The related issues including the objective function, constraint function, different residuals and possible parameters for FE model updating are investigated. The issues of updating process adopted in FemUP are discussed. The ideas of optimization to be used in FE model updating application are explained. The algorithm of Sequential Quadratic Programming (SQP) is explored which will be used to solve the optimization problem. The possibilities of the program are demonstrated with a three dimensional steel frame model. As a result of this study, it can be said that SQP algorithm is very effective in model updating procedure.

Research on Shaking Table Test of Base and Story Isolation Structures

The shaking table tests are conducted on a 5-floor steel frame model with a scale down of 1:6. The traditional anti-seismic structure and isolation structures with isolation layer in different position are adopted. The results indicate that the natural vibration periods of isolation structure are longer than anti-seismic structure, and when the isolation layer is located in a lower position, the period becomes longer and the damping effect is better.

Seismic Performance Analysis of Steel Frame with Wedge Devices Based on the Energy Dissipation

The steel frame with wedge devices is a kind of shock structure based on the node energy consumption. The seismic performances of steel frame with wedge and ordinary steel frame model under low cycle reciprocating load simulation analysis and time history analysis under earthquake loads are analyzed by using finite element software, compared the respective energy dissipation performance and seismic performance, the results show that the wedge spring damping device can effectively control story drifts of structure, reduce the seismic response of structure, and well consume the seismic energy, so the structure of the new column bases with wedge spring devices show better seismic performance.

Passive base isolation with superelastic nitinol SMA helical springs

Seismic isolation of structures such as multi-story buildings, nuclear reactors, bridges, and liquid storage tanks should be designed to preserve structural integrity. By implementing seismic isolation technology, the deformation of superstructures can be dramatically reduced, consequently helping to protect their safety as well. In this paper, an innovative type of passive base isolation system, which is mainly composed of superelastic nitinol SMA helical springs, is developed. In order to verify the effectiveness of the proposed system, a two-story experimental steel frame model is constructed, and two superelastic SMA helical springs are thermo-mechanically built in the laboratory. To describe the nonlinear mechanical properties of the superelastic SMA helical springs under reciprocating load, a phenomenological model is presented in terms of a series of tensile tests. Afterwards, a numerical model of the two-story frame with the suggested isolation system is set up to simulate the response of the isolated frame subjected to an earthquake. Both the experimental and the numerical simulation results indicate that the proposed base isolation system can remarkably suppress structural vibrations and has improved isolation effects when compared with a steel spring isolation system. Due to the capabilities of energy dissipation as well as fully re-centering, it is very applicable to utilize the suggested isolation system in base isolated structures to resist earthquakes.

Finite element model calibration of steel frame buildings with and without brace

This paper focuses on both the monitoring of the dynamic response of steel buildings with and without brace elements and the importance of model calibration on the steel buildings. The study involves the application of modal testing techniques to collect data from a three-story steel frame building model tested at the Civil Engineering Department of Karadeniz Technical University. The experimental measurements are performed under randomly generated loads. Dynamic characteristics (natural frequencies, mode shapes and modal damping ratios) obtained from bare and braced steel frame models are compared with each other. The initial analytical models of the steel model for bare and braced cases are developed and calibrated according to the experimental measurement results. The calibration process aims to minimize the differences between experimental and analytical natural frequencies. The connection rigidities of the beam-to-column are selected as a calibrating parameter in the model calibration process. It is observed that the brace elements cause an increase in the natural frequencies due to the increasing stiffness as well as the changes in the modal behavior. Static analyses of the steel frame model for bare and braced cases are carried out to emphasize the importance of the model calibration by comparing maximum lateral displacements. The calibrated analytical models produce larger lateral displacements than the initial models. The results reveal that the dynamic behavior of steel structures should be evaluated considering the calibrated models for safety of these structures.