Seismic Response Analysis of Steel Structure Isolation System Under Long-Period Seismic Motion

To analyze the seismic response of steel structure isolation systems under long-period seismic motion,a 9-story steel frame building was selected as the subject.Five steel structure finite element models were established using SAP2000.Response spectrum analysis was conducted on the seismic motion to determine if it adhered to the characteristics of long-period seismic motion.Modal analysis of each structural model revealed that the isolation structure significantly prolonged the structural natural vibration period and enhanced seismic performance.Base reactions and floor displacements of various structures notably increased under long-period seismic motion compared to regular seismic activity.Placing isolation bearings in the lower part of the structure proved more effective under long-period seismic motion.In seismic design engineering,it is essential to consider the impact of long-period seismic motion on structures and the potential failure of isolation bearings.

Analysis of Soundproof Technology of Assembled Steel Structure Houses

The problem of noise has always been highlighted in assembled steel structure houses.Therefore,it is necessary to use effective soundproof measures where steel beams intersect with the reserved line pipe openings,doors,windows,elevator shafts,and other locations.In this paper,we will investigate the areas with subpar soundproof performance in an assembled steel structure residential project and propose suitable noise control measures to address this issue.

Discussion on Construction Technology and Welding Deformation of High-Rise Steel Frame Structure

Because of urbanization,land resources in China’s cities has become increasingly scarce.Therefore,modern buildings are becoming taller,making high-rise steel frame structures the new favorite of the construction industry.However,the construction of high-rise steel frame structures requires advanced technology.If the construction technology is effectively implemented and the welding techniques of the construction personnel align with the requirements for high-rise steel frame structures,it can help mitigate deformations in the steel structure,thus preserving the overall construction quality of high-rise steel frame structures.To enhance the applicability of steel frame structures in high-rise buildings,this paper focuses on analyzing the optimization path for the construction process of high-rise steel frame structures.It introduces a tailored approach to control welding-induced deformations in steel frame structures,aiming to make a valuable contribution to the advancement of China’s construction industry.

Fault Identification for Shear-Type Structures Using Low-Frequency Vibration Modes

Shear-type structures are common structural forms in industrial and civil buildings,such as concrete and steel frame structures.Fault diagnosis of shear-type structures is an important topic to ensure the normal use of structures.The main drawback of existing damage assessment methods is that they require accurate structural finite element models for damage assessment.However,for many shear-type structures,it is difficult to obtain accurate FEM.In order to avoid finite elementmodeling,amodel-freemethod for diagnosing shear structure defects is developed in this paper.This method only needs to measure a few low-order vibration modes of the structure.The proposed defect diagnosis method is divided into two stages.In the first stage,the location of defects in the structure is determined based on the difference between the virtual displacements derived from the dynamic flexibility matrices before and after damage.In the second stage,damage severity is evaluated based on an improved frequency sensitivity equation.Themain innovations of this method lie in two aspects.The first innovation is the development of a virtual displacement difference method for determining the location of damage in the shear structure.The second is to improve the existing frequency sensitivity equation to calculate the damage degree without constructing the finite elementmodel.Thismethod has been verified on a numerical example of a 22-story shear frame structure and an experimental example of a three-story steel shear structure.Based on numerical analysis and experimental data validation,it is shown that this method only needs to use the low-order modes of structural vibration to diagnose the defect location and damage degree,and does not require finite element modeling.The proposed method should be a very simple and practical defect diagnosis technique in engineering practice.

Comprehensive Molten Salt Storage Shell and Support Design and Analysis Ⅲ: A Complete 700 ℃ Thermal-Structural Interaction Design Using Theoretical Analysis of an 80 Foot Diameter and 46 Foot High MS Storage Shell Including Structural, Conductive and Convective Thermal Stress Analysis

The paper discusses the structural design of a futuristic 700℃ MS(Molten salt)Storage Shell,which considers many elements in providing an adequate and comprehensive design.In designing the structural carbon steel for the tank,temperature is an important consideration because steel has a yield strength at 700℃,that is 33%of its nominal yield,while the Young’s Modulus at 700℃ is 50%of its nominal Young’s Modulus.At this temperature,thermal stresses can yield or tear the structural steel unless free expansion of the structure is allowed.This is accomplished with sand layers below each layer of steel and by including a small gap behind the side carbon steel layer.A roof shell design for the tank is also presented in this paper,comparing various roof shell types and their designs.All designs include thermal insulation and an inner stainless steel corrosion layer to protect the structural and thermal insulation elements of the tank from the MS.

Laser cleaning of steel structure surface for paint removal and repaint adhesion

Paint removal from steel structure is executed for shipyards of marine and offshore engineering.Due to environmental unfriendliness and unhealthy drawbacks of sand blasting technique, laser ablation technique is proposed as a substituting method.By absorbing high energy of the 1064 nm pulsed laser, the paint is vaporized quickly.The ablated debris is then collected by using a suction pump.Initial metal surface of the steel is exposed when laser beam irradiates perpendicularly and scans over it.The cleaned surface fulfills the requirements of surface preparation standards ISO 8501 of SA2.The adhesion is further characterized with pull-off test after carrying out painting with Jotamastic 87 aluminum paint.The repainting can be embedded onto the laser cleaned surface to bond much more tightly.The excellent adhesion strength of 20 MPa between repainted coating and the substrate is achieved, which is higher than what is required by shipyards applications.

Methodology to Estimate Remaining Service Life of Steel Structure by Possibilistic Reliability Theory

Steel structure system of crane deteriorates over time due to environmental effects, material fatigue, and overloading. System structural reliability and remaining service life assessment methods are developed during the few decades. But until now estimating remaining service life methods of crane steel system by reliability theory begin to develop. Safety assessment of existing steel structure system requires the development of a methodology that allows for an accurate evaluation of reliability and prediction of the remaining life. Steel structures are the supporting elements in the special equipment such as hoisting machinery. Structure reliability and remaining service life safe assessment are important for steel structures. For finding the reason which caused the failure modes （such as fatigue strength failure, stiffness failure and stability failure）, incremental loading method based on possibilistic reliability is applied into dynamic structure failure path research. Through reliability analyzing and calculating for crane, it is demonstrated that fatigue damage is the most common failure mode. Fuzzy fatigue damage accumulation theory is used for basis theory and Paris-Eadogan equations are used for mathematical modeling. All fatigue parameter values of the welding box girder of bridge cranes are determined and fatigue remaining life formulas are deduced. After field test and collecting working parameters of numerous cranes, typical fatigue load spectrum was compiled for the dangerous point of box girders used in the area. Fatigue remaining life is assessed for different types and lifting capacities. Safety for steel structure system of bridge crane is assessed by two quantitative indexs： reliability and remaining life. Therefore, the evaluation means is more comprehensive and reasonable. The example shows that the two quantitative indexs are mutually correlated. Through analyzing the 120 t-22.5 m bridge crane of a certain enterprise, a new methodology to estimate remaining service life of steel structure by possibilistic reliability theory is introduced for safety evaluation of structure system.

Preliminary investigation of seismic damage to two steel space structures during the 2013 Lushan earthquake

Severe damage to steel space structures is rarely reported when compared to other structural systems damaged during past major earthquakes around the world. Two gymnasiums of steel space structures in downtown Lushan County that were damaged during the 2013 M7.0 Lushan earthquake in China were investigated and the observations are summarized in this paper. Typical damage to these two steel space structures ranges from moderate to severe. Moderate damage includes global buckling and dislocation of bolted connections of truss members, and inelastic elongation of anchor bolts and sliding of pedestal plates of supports. Severe damage includes member fracture caused by local buckling, and fracture failure of anchor bolts and welds. The distribution of structural damage to these two structures is described in detail and future research opportunities are suggested.

INVESTIGATION OF LOW CYCLE FATIGUE BEHAVIOROF BUILDING STRUCTURAL STEELS UNDEREARTHQUAKE LOADING

Based on the failure model of building structural steels under earthquake loading, the low cycle fatigue test at constant strain, the stochastical fatigue test under real earthquake load spectrum and the structural fatigue test are carried out. The experimental results show that microalloying of V Ti and Nb can improve the anti-seismic propersties of steel bars. In the high strain and shori life range, both the static strength and ductility of steels are very important to increasing the low cycle fatigue resistance of steels.

Effects of low temperature on properties of structural steels

The experiments were carried out to measure the mechanical properties ofthree grades of structural steels (Q235A, 16Mn and Q390E steel) at low temperature. It was shownthat the strength of the steels increases while the plasticity and toughness decrease as temperaturedrops. In the transitional area the toughness drops rapidly with temperature. Among the threestructural steels, Q390E steel has the best toughness and the lowest sensitivity.

Finite element model updating for large span spatial steel structure considering uncertainties

In order to establish the baseline finite element model for structural health monitoring,a new method of model updating was proposed after analyzing the uncertainties of measured data and the error of finite element model.In the new method,the finite element model was replaced by the multi-output support vector regression machine(MSVR).The interval variables of the measured frequency were sampled by Latin hypercube sampling method.The samples of frequency were regarded as the inputs of the trained MSVR.The outputs of MSVR were the target values of design parameters.The steel structure of National Aquatic Center for Beijing Olympic Games was introduced as a case for finite element model updating.The results show that the proposed method can avoid solving the problem of complicated calculation.Both the estimated values and associated uncertainties of the structure parameters can be obtained by the method.The static and dynamic characteristics of the updated finite element model are in good agreement with the measured data.

Evaluation Indicators and Extraction Method for Pitting Corrosion of Structural Steel

A set of evaluation indicators based on corrosion ratio in theory for assessing the extent of pitting corrosion and performance reduction are proposed. In order to quantify the morphology of pitting corrosion and extract the evaluation indicators,the 3D profile data obtained by pitting morphology measurement are imported into a special written program to automatically determine the location of each corrosion pit and distill any desired data pertinent to the pitting morphology. The results show that this method seems to be effective to analyze the corroded surface and characterize the pitting morphology.

Numerical Simulation of Dynamic Response and Collapse for Steel Frame Structures Subjected to Blast Load

The progressive collapse of steel frame structures under the blast load was investigated using LS-DYNA. The multi-material Eulerian and Lagrangian coupling algorithm was adopted. A flu-id-structure coupling finite element model was established which consists of Lagrange element for simulating steel frame structures and concrete ground, multiple ALE element for simulating air and TNT explosive material. Numerical simulations of the blast pressure wave propagation, struc-tural dynamic responses and deformation, and progressive collapse of a five-story steel frame structure in the event of an explosion near above ground were performed. The numerical analysis showed that the Lagrangian and Eulerian coupling algorithm gave good simulations of the shock wave propagation in the mediums and blast load effects on the structure. The columns subjected to blast load may collapse by shear yielding rather than by flexural deformation. The columns and joints of steel beam to column in the front steel frame structure generated enormous plastic defor-mation subjected to intensive blast waves, and columns lost carrying capacity, subsequently lead-ing to the collapse of the whole structure. The approach coupling influence between struc-tural deformation and fluid load well simulated the progressive collapse process of structures, and provided an effective tool for analyzing the collapse mechanism of the steel frame structure under blast load.

Wind Vibration Study of Long-span Steel Arch Structure of Beijing Capital International Airport

The wind-induced dynamic response of long-span light-weight steel arch structure of the global transportation center (GTC) of Beijing Capital International Airport was studied. A composite technique with combination of WAWS(Weighted Amplitude Wavelet Superposition) and FFT(Fast Fourier Transformation) was introduced to simulate wind velocity time series of hundreds of spatial points simultaneously. The structural shape factors of wind load was obtained from wind tunnel model test. The wind vibration factor based on structural displacement response was investigated. After comparing the computational results with wind tunnel model test data, it was found out that the two results accord with each other if wind comes from 0° direction angle, but are quite different if wind comes from 180° direction angle in the area blocked off by airport terminals. The possible reasons of this difference were analyzed. Haar wavelet was used to transform and analyze wind velocity time series and structural wind-induced dynamic responses. The relationship between exciting wind loads and structural responses was studied in time and frequency domains.

DUCTILE CRACK INITIATION AND STEADY-STATE PROPAGATION OF HIGH STRENGTH STRUCTURAL STEEL

The resistance to crack propagation at earlier stage for a high strength structural steel with certain ductility and its correlation to microstructures,stress states,deformation history and strain characteristics have been investigated.The resistance to crack propagation is mainly de- termined by the plastic constrain ahead of the crack tip,the elastic energy and plastic work absorbed in the stress-strain field.These are connected with the state function of triaxial stress.The deformation history and strain characteristic during deformation of material are described by the flow line in which the deformation history and strain characteristic restrain the crack initiation at stage Ⅱ and the crack propagation at stage Ⅲ.The strain hardening rate may sensitively reflect the stress distribution and micro-fracture mechanism in the interi- or of material.

Flexural Capacity Formula of Diaphragm-Through Joints of Concrete-Filled Square Steel Tubular Columns

Finite element analysis and parametric studies were performed to investigate the flexural capacity of the panel zone of diaphragm-through joints between concrete-filled square steel tubular columns and H-shaped steel beams. Through the comparisons of failure modes, load–displacement curves, and bearing capacity, it was found that the flexural capacity of the panel zone of diaphragm-through joints was determined by the tensile action and influence of the web of H-shaped steel beams, and the axial load should be taken into account. The steel tube and the diaphragm were the major parts of the joint that resisted the bending moment. The contribution of in-filled concrete had little influence on the flexural capacity of the panel zone of the joint and could be neglected. According to the results of these numerical studies, a formula that considered the influence of the web of H-shaped steel beams and the axial load was developed based on the yield lines in the diaphragm and the steel tube. The results of the proposed formula were in good agreement with the numerical data of this investigation. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

Analysis on seismic performance of a new type of joint in steel structures

To examine the seismic performance of a newly fabricated weakened joint at the beam end position,four groups of energy-consuming steel plates with different weakening depths and thicknesses were subjected to horizontal cyclic reciprocating loading tests on beam ends.The tests were designed to evaluate the beams'hysteresis curve,skeleton curve,bearing capacity degradation curve,stiffness degradation curve,and ductility and the nodes'energy dissipation capacity.The test results show that a newly fabricated joint will not undergo brittle damage when the beam-column joint is welded at a displacement of 105 mm.Thus,the hysteresis curve will show an inverse S shape,and an obvious slip phenomenon will occur,which is mainly due to splicing.The diameter of the bolt connecting the slab to the beam flange is slightly smaller than the aperture.Due to the existence of slippage,the skeleton curve has no evident yield point.The joint ductility coefficient is less than 3.0,and the initial rotational stiffness of the joint is also small.The buckling of the splicing panel causes a rapid decrease in the joint bearing capacity.The main approaches,appropriately reducing the weakening depth and increasing the thickness of the splicing plate,can delay the occurrence of buckling and improve the ductility of the joint.

Experimental Study on Flexural Behavior of Corroded Channel Steel Beams

In order to study the mechanical behavior of corroded channel steel beam,experiment on five corroded channel steel beams is carried out. Test results show that the bending failures may occur under the ultimate load carrying capacity of members,compared with the calculating results of non-corrosion channel steel beam,and the bearing capacity of corroded channel steel beam is reduced,while the deflection is increased. With the increase of shear-span ratio,the bearing capacity of corroded channel steel beam reduces and the deflection increases gradually; with the increment of heightspan ratio, the bearing capacity increases and the deflection decreases gradually; with the enhancement of width-height ratio,the bearing capacity reduces and the deflection-span ratio increases gradually. The measured results indicate that the load-deflection relationship curves of corroded channel steel beam may be divided into four sections: the exfoliated rust layer stage,the elastic stage,the yielding stage and the descending stage. The load-strain relationship curves include two sections: the elastic stage and the yielding stage. The strain measurement of web proves that the average strains agree well with the assumption of plane section. This paper could provide some scientific bases for the maintenance and reinforcement of the corroded steel structure.

Simplified Thermodynamic Model for Pro-Eutectoid Ferrite Formation in Multicomponent Structural Steel

By introducing aparameter of difference in ferrite formation temperature between binary Fe-C and multicomponent system,and referring to the thermodynamic model for Fe-C binary system,a simplified thermodynamic model for pro-eutectoid ferrite formation in Fe-ΣXiC multicomponent structural steels(Xi=Mn,Si,Mo,Cr,Ni or Ti,etc)was suggested.The comparison of the calculated Ae3 temperatures with the measured data of steels 42 shows that the relative standard deviation and root-mean-square(RMS)error between them are only 0.71% and 8.92 K,respectively.However,the deviations between the same measured data and the values calculated from the superelement model are as high as 1.86% and 23.83 K,respectively.It can be concluded that the simplified thermodynamic model for pro-eutectoid ferrite formation in multicomponent structural steels is acceptable and the calculated Ae3 temperatures are in good agreement with the experimental data.

MICROSTRUCTURE TRANSFORMATION IN THE WELDING HEAT AFFECTED ZONE OF 800MPa GRADE ULTRA FINE STRUCTURED STEEL

The transformation behavior and microstructure development in the heat affected zone(HAZ)of 800MPa grade ultra fine structured steel was investigated.It was found that the HAZ has intermediate temperature transformation characteristics in a wide range of cooling rates,with the bainite sheaves consisting of bainite ferrite plates without carbide precipitation and retained austenite in the fast cooling regime.At relatively high cooling rates,which corresponded to low heat inputs,the hardness of the simulated HAZ was above that of the base metal.When the cooling rate was below 9C/s,the welding HAZ would have an obvious softening.The analysis of transformation rates in continuous cooling processes was completed by numerical differential method.The result indicated that the microstructure transformation rate of the HAZ in 800MPa grade ultra fine structured steel changed sharply to slow speeds when the cooling time t8/5 is longer than 7s.