Steel Structure Model Research Articles

屋外環境における大気腐食モニタリング

A study on atmospheric corrosion monitoring by electrochemical impedance method has been reviewed. A new type of corrosion sensor, which consists of pin and ring electrodes embedded concentrically in epoxy resin, was successfully applied for the corrosion monitoring. The sensor response showed that the corrosion rate of steel in the sunny day was higher at night than in daytime. The corrosion loss calculated from the monitoring data agreed well with that estimated from the surface roughness by a laser microscope. In addition, the monitoring system has been applied to estimate corrosion resistance at each part of steel model structure exposed to outdoor environment. Low solution resistance and high corrosion rate were measured at all parts in rainfall time. From the corrosion monitoring for about a year, the corrosion loss was larger at horizontal part than at perpendicular part, and the under side of flange gave the largest corrosion loss.

Experimental study in the shaking table of the input motion characteristics in the dynamic SSI of a SDOF model

In conventional seismic design the capacity of the system is generally exploited only at the superstructure level. However, soil non-linearity as well as soil-foundation interface non-linearity can be crucial in the seismic response of structures. The results of tests performed on physical models allow the main aspects of these interaction mechanisms to be identified and also provide a benchmark for subsequent theoretical or numerical analyses. The present paper deals with two shaking table tests performed at the University of Bristol’s EERC laboratory. The tests were performed on a physical model consisting of a Leighton Buzzard sand deposit and a one-storey steel model structure. Some of the test results are presented and discussed in terms of acceleration and displacement responses. Both time- and frequency-domain representations were adopted to highlight the influence of the frequency and amplitude of the input motion on the coupled and/or uncoupled response of the tested soil-structure system, as well as the effect of soil non linear behaviour.

Performance-based fire modelling of intumescent painted steel structures and comparison to EC3

Following the present directives for building products, the manufacturers of intumescent paints for fire protection of structural steel typically offer tables for presentation of the product's insulating efficiency showing its dry film thicknesses (DFTs) required to sufficiently delay the defined steel critical temperature. From these tables only the final time of reaching this critical limit is obtained clearly, but the overall time evolution of steel temperature remains unknown. In connection to EC3, these data are only sufficient for the use of a simplified design procedure, mostly the method of critical temperature (MCT). Although of a questionable adequacy for cases of restrained thermal dilatations this method is, thus, often applied regardless of the specifics of the structural assembly. The severity of the error implemented by such a simplification is taken as the principal focus of the paper. In providing an answer, fire test results are presented for 13 different steel members protected by different DFTs of a selected intumescent coating. Then, the time-dependent thermal conductivity of the coating is derived and numerical procedure is composed for obtaining the real fire response of intumescent painted assemblies. The method is implemented into a parametric study. The calculated critical times are compared against the critical times suggested by the MCT revealing the MCT being severely on the unsafe side for some cases. The paper thereby confirms the initial hypothesis that the present way of presenting the fire-protective intumescent paints for structural steel is insufficient and will need to be upgraded in the future.

Elastic tubular joint element for modelling of multi-brace, uni-planar tubular connections

Traditionally, an analytical model of an offshore structure is composed of beam-column elements rigidly interconnected. However, considerable flexibility exists at the joints where chord outer wall deforms locally, and produces flexibility. In this paper, a new elastic joint element is introduced to consider the local flexibilities for TY- and K-type tubular joints. The element is developed on the basis of flexibility matrix and it is implemented in a finite-element programme to account for local joint flexibility effects in numerical models of steel structures made from tubular members. The element is suitable for modelling of multi-brace, uni-planar tubular joints. The results are validated by more sophisticated model using multi-purpose programmes and compared against conventional rigid-joint models. Based on the results of this study, it is concluded that incorporating the effects of joint flexibility results in more realistic response prediction of offshore structures.

Improving Substructure Identification Using Structural Control with Limited Sensor Measurements

Substructure identification is a structural health monitoring technique that identifies a reduced-order model of structural behavior using local vibration measurements. The authors’ prior research on this inherently decentralized technique demonstrated that substructure identification can detect and localize stiffness changes in a shear building. However, identification performance varies from story to story, with parameters of a few stories not satisfactorily identified. To overcome this limitation, the authors and colleagues showed that a structural control device can be used to temporarily change the dynamics of the structure to improve identification performance; however, prior studies assumed full-state feedback, which is not achievable in full-scale implementations. This paper investigates structural control using limited sensor measurements to improve substructure identification. The substructure method is first summarized, followed by an error analysis that can predict a priori the level of error in story parameter estimates. Then, a novel controlled substructure identification procedure is introduced with constraints to ensure that the controlled responses improve substructure identification while reducing overall structural response. State feedback is utilized, with a Kalman filter to estimate states using various sets of acceleration sensor measurements to understand the performance trade-offs. The implementation methodology using an object-oriented programing paradigm is explained; a 3.66-m (12-ft) four-story single-bay steel structure model, subject to low levels of ground motion, is the test bed used for numerical simulations to demonstrate the proposed methodology. The control strategies that include a sensor measuring ground acceleration are shown to be nearly as effective in estimating stiffnesses as the full-state feedback control and all controlled strategies perform better than the uncontrolled case.

Polymeric Bearings – A New Base Isolation System to Reduce Structural Damage during Earthquakes

Base isolators, like lead rubber bearings, high damping rubber bearings or friction pendulum systems are extensively used in practice in many seismically active regions to protect structures against earthquake forces. The present paper reports the results obtained from the experimental study aimed to determine the effectiveness of the Polymeric Bearings in suppressing structural vibrations during dynamic excitations and therefore to minimize structural damage. The response of the analyzed two-storey structure model both fixed and supported by the Polymeric Bearings under different earthquake excitations was studied. The reduction in lateral response due to seismic events was measured by comparing the peak accelerations of the two-storey steel structure models – with and without base isolation system. The results of the study have shown that the use of the Polymeric Bearings leads to significant improvement in dynamic properties by suppressing structural vibrations. The results have indicated that the Polymeric Bearings can be successfully used to reduce damage of structures during seismic events.

On the Deduction and the Application of Dynamic Similarity Criteria of Steel Structure under Large Deformation Condition

Dynamic similarity criteria for large deformation of huge steel structure were derived according to Dimensional Matrix Analysis of the Buckingham Pi theorem and the similarity relations that must be satisfied by the physical quantities of model and prototype in huge steel structure model test are obtained. The 1/50 scale model of TC power is designed and made based on the similarity theory and the dynamic experiment is done. The calculation data with similarity theory are in agreement with that of experiment. So the model test can substitute for prototype test when they satisfy the similarity relations. A new way to solve dynamic analysis problem of huge steel structure is explored.

Experimental Study on Seismic Behaviors of Improved Composite Steel Staggered Truss Structures

According to the poorly seismic behaviors of composite staggered trusses system, an improved composite staggered trusses system was proposed. Based on the experimental study of a 1/3 scale improved composite staggered truss frame steel structure model under cyclic loading, the seismic behaviors and failure mechanism was studied, and the seismic behaviors was evaluated by the hysteretic behavior, ductility, energy dissipation and rigidity degeneration. The study showed that the improved composite staggered truss steel structures had the advantages in bearing capacity, ductility, deformability and energy dissipation, but the lateral rigidity was weak and non-uniform along its vertical layout. The stress measurement showed that the plastic hinge formed in the web members of the truss firstly, then, in the chord members of the truss, and finally the plastic hinges formed in the column, earthquake energy mostly dissipated by the truss members, the failure mechanism of the improved composite staggered truss steel structures was the beam hinges failure mechanism.

柱梁接合部の溶接費と施工性を考慮した鋼構造物の最適設計

Structural design is usually carried out with a number of repetitive processes in which trial and error between assumptions at each stage on the structural system is done toward the selection of final solutions with an enormous effort of engineers. The authors proposed a design supporting scheme which could center their ability on the essential design processes by saving time for the selection with the use of Multi-Objective Genetic Algorithm (MOGA). In addition, through the various analyses of the steel structure models such as rigid-frame, X-type braced frame and K-type braced frame, it has been clearly shown that we can obtain other alternative design solutions with lower cost and proper drift angle in the proposed structural system. In this paper, the proposed supporting design scheme will be extended and confirmed its validity with considering not only manufacture cost in the process for making steel members and the welding cost for connecting beams and columns as well as steel cost which is considered until now in the scheme but also the penalty function which is given to the optimization problem in order to ensure the constructability of the beam-column connection for more practical use of the supporting design scheme.

Simplified Computation of Elastic-Plastic Displacement Response of High-Rise Steel Structure under Earthquake Considering Torsional Effect

Considering unavoidability of torsional vibration of high-rise buildings during earthquake, for a simpler and more accurate way to compute the maximum interstory drifts, through establishment of different structure calculation model. Structure analysis program CANNY 3D was used to conduct 3D and 2D time-history analyses on irregular steel structure models under frequently occurred small earthquakes and large earthquakes. Finally, by comparing maximum interstory drifts between each floor, a method was presented to simplify 3D computation of elastic-plastic interstory displacement of high-rise irregular steel structure into a computation plane 2D structure.

Seismic response of controlled structures with active multiple tuned mass dampers

Active multiple tuned mass dampers (referred to as AMTMD), which consist of several active tuned mass dampers (ATMDs) with identical stiffness and damping coefficients but varying mass and control force, have recently been proposed to suppress undesirable oscillations of structures under ground acceleration. It has been shown that the AMTMD can remarkably improve the performance of multiple tuned mass dampers (MTMDs) and is also more effective in reducing structure oscillation than single ATMDs. Notwithstanding this, good performance of AMTMD (including a single ATMD illustrated from frequency-domain analysis) may not necessarily translate into a good seismic reduction behavior in the time-domain. To investigate these phenomena, a three-story steel structure model controlled by AMTMD with three ATMDs was implemented in SIMULINK and subjected to several historical earthquakes. Likewise, the structure under consideration was assumed to have uncertainty of stiffness, such as ±15% of its initial stiffness, in the numerical simulations. The optimum design parameters of the AMTMD were obtained in the frequency-domain by implementing the minimization of the minimum values of the maximum dynamic magnification factors (DMF) of general structures with AMTMD. For comparison purposes, response analysis of the same structure with a single ATMD was also performed. The numerical analysis and comparison show that the AMTMD generally renders better effectiveness when compared with a single ATMD for structures subjected to historical earthquakes. In particular, the AMTMD can improve the effectiveness of a single ATMD for a structure with an uncertainty of stiffness of ±15% of its initial stiffness.

Analytical and Experimental Study of Toggle-Brace-Damper Systems

The toggle-brace mechanism has been recognized as an effective installation configuration of viscous dampers to a stiff structural system. In this paper, a toggle-brace-damper configuration with dampers directly installed to the beam–column joints is presented. To facilitate practical applications, a procedure for determining the relationship between the displacement magnification factor and the geometry of the toggle-brace mechanism is established. Shaking table tests are conducted to investigate the seismic responses of a three-story steel model structure with and without linear viscous dampers. The installation configurations of the dampers include the toggle-brace-damper and the diagonal-brace-damper systems. The test results show that the toggle-brace system is more efficient in enhancing the seismic response control on a stiff structure. However, due to the fact that the gaps existing in the hinge connections of the toggle-brace-damper system may affect the contribution of damping ratio to the structure, special care must be taken when installing toggle-brace-damper systems in practical applications.

Ultimate strength of cracked plate elements under axial compression or tension

In addition to corrosion, fatigue cracking is another important factor of age related structural degradation, which has been a primary source of costly repair work of aging steel structures. Cracking damage has been found in welded joints and local areas of stress concentrations such as at the weld intersections of longitudinals, frames and girders. Fatigue cracking has usually been dealt with as a matter under cyclic loading, but it is also important for residual strength assessment under monotonic extreme loading, because fatigue cracking reduces the ultimate strength significantly under certain circumstances. In this paper, an experimental and numerical study on the ultimate strength of cracked steel plate elements subjected to axial compressive or tensile loads is carried out. The ultimate strength reduction characteristics of plate elements due to cracking damage are investigated with varying size and location of the cracking damage, both experimentally and numerically. Ultimate strength tests on cracked steel plates under axial tension and cracked box type steel structure models under axial compression are undertaken. A series of ANSYS nonlinear finite element analyses for cracked plate elements are performed. Based on the experimental and numerical results obtained from the present study, theoretical models for predicting the ultimate strength of cracked plate elements under axial compression or tension are developed. The results of the experiments and numerical computations obtained are documented. The insights developed will be very useful for the ultimate limit state based risk or reliability assessment of aging steel plated structures with cracking damage.

Research and Development of Measurement Method for Structural Fracturing Process in Shake Table Tests Using Image Processing Technique

The largest three-dimensional shake table is now being constructed in Hyogo prefecture, Japan for a solution of fracturing process of structures, buildings, and soils. However, it seems to be difficult to measure the fracturing processes of the structures during severe earthquake by using conventional methods and equipment, because the three-dimensional measurement of larger dynamic displacement in excess of elastic region of the structure will be the key to a solution and cannot be obtained by any of the vibration pick-ups such as displacement transducers and so on. In this study, R&D of the new measurement method to clarify the fracturing process of the structures by applying a so-called motion capture technique, which has been mainly studied for modeling of human actions and motions. This paper describes the concept of the system, the outline of the proto-type image processing system developed in the study and the results of the shake table test using five-story steel-structure model to investigate the measurable accuracy of the system.

Pseudo-Dynamic Tests on an Existing Steel Model Structure for Seismic Monitoring

Pseudo-Dynamic Tests on an Existing Steel Model Structure for Seismic Monitoring

Toggle-Brace-Damper Seismic Energy Dissipation Systems

Energy dissipation systems are being increasingly employed in the United States to provide enhanced seismic protection for new and retrofit building and bridge construction. The hardware utilized includes yielding steel devices, friction devices, viscoelastic solid devices, and mostly, so far, fluid viscous devices. This hardware has been used in either diagonal or chevron brace configurations. This paper presents three new configurations that utilize toggle-brace mechanisms to substantially magnify the effect of damping devices so that they can be utilized effectively in applications of small structural drift. Shake table testing of a large scale steel model structure and analysis are used to demonstrate the utility of these configurations. The experimental results demonstrate substantial increases in the damping ratio despite the use of small size damping devices, and, accordingly, significant attenuation of the seismic response of the tested stiff structure is observed. Moreover, the experimental results are found to be consistent with analytical predictions based on either simplified methods or response history analysis. Applications of the new configurations are briefly described.

Experimental and Numerical Evaluation of Surge Current Distribution in Buildings During a Direct Lightning Stroke

This paper reports an experimental and numerical Investigation into the surge current distribution in a reinforced concrete structure during a lightning stroke. An analytical method, which is based on a circuit approach, is described. The steel structure is modeled by a series of coupled φ-type circuits. The capacitance in the circuits is calculated by the means of average potential method, while the Inductance is evaluated by the Neumann’s formula. The effect of the earth (ground) is taken into consideration by the method of images. The analytical method was demonstrated and validated on three models of steel structures, and can be applied to estimate current distribution in the lightning protection system of a building.

Experimental study of seismic response of buildings with supplemental fluid dampers

AbstractThis paper presents the results of an experimental study of the seismic response of buildings with supplemental fluid damping devices. These devices operate on the principle of fluid flow through orifices specially shaped so as to produce damping forces proportional to the velocity, i.e. the devices operate as linear viscous dampers. The experimental results demonstrate that the addition of fluid dampers to the tested steel model structure resulted in reductions of interstory drifts, floor accelerations and story shear forces by factors of two to three in comparison with the response of the same structure without the dampers.

Seismic Design of Viscoelastic Dampers for Structural Applications

Some practical issues associated with the application of viscoelastic (VE) dampers to building structures for seismic performance enhancement are studied in this paper. A sequential procedure is developed for optimally placing VE dampers to structures, based on the concept of degree of controllability. This optimal placement procedure is then experimentally verified using a five‐story steel model structure. Economical use of the VE dampers is made possible by adding them to the optimal locations found by this procedure, as is clearly demonstrated by the numerical examples and experimental results presented in the paper. A design procedure is also presented by which damper dimensions, number, and locations needed to achieve desired level of additional damping can be determined in accordance with the structural parameters and structural‐response reduction requirement. Design of VE dampers for a 24‐story steel frame is presented as an example, showing the complete design procedure for applying VE dampers to ...