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Steel Construction Published the List of Highly Influential Articles of 2020
2022 Vol. 37, No. 6
Abstract
PDF (8215KB)Modern large-scale livestock and poultry breeding houses,slaughterhouses,agricultural products processing workshops and other buildings often adopt light-weight steel portal frame structure systems,steel column base often adopts simple exposed column base.This kind of buildings have high indoor humidity and a certain corrosive sometimes,in order to protect the steel column base and improve the durability of the structure,the practice of secondary pouring concrete is often used.Because the pouring concrete is usually plain concrete,the influence of the secondary pouring concrete on the bending capacity,rotational stiffness and ductility is often ignored in the structural analysis and design,which makes the analysis results differ from the actual working conditions to a certain extent,and may bring about waste in design or hidden safety hazards.Therefore,taking the light-weight steel structure of this kind of buildings as the engineering background,considering the three types of pouring concrete thickness of 100 mm,150 mm and 200 mm under the action of axial compression and bending moment,it is found that the pouring concrete can obviously improve the bending capacity and ductility of the column base,and the bigger the thickness is,the bigger the improvement is.At the same time,there is a certain law of increasing the rotational stiffness.Further in the package thickness under the condition of 150 mm,considering the pouring concrete without reinforcement net,add a layer of reinforcement net and add two layers of reinforcement net three scenarios,in pouring concrete section 4 mm and 6 mm outer clad steel of two situations,with the general commercial finite element software simulation,it compared the eight kinds of conditions on the properties of the steel column base mechanical performance,the emphasis was placed on the bending capacity,rotational stiffness and ductility.
The results show that the plastic stress concentration exists in the tensile side and the compression side of the pouring concrete,the lower part of the compression side is more concentrated than the upper part,and the upper part of the tensile side is more concentrated than the lower part.With the increase of the pouring concrete thickness,the bending capacity and ductility coefficient of column base increase more and more.The addition of two kinds of reinforcement net can improve the rotational stiffness to a certain extent,and the effect of laying two layers of reinforcement net is more obvious.Adding a layer of reinforcement net on the top makes the plastic strain area on the top of the pouring concrete smaller.The plastic strain areas of the upper and lower parts of the concrete are reduced by adding two layers of reinforcement net,which indicates that the reinforcement net provides effective constraints on the concrete and can delay the crack development of the pouring concrete.The upper and lower layers of reinforcement net bear a certain tensile stress,especially the upper layer of reinforcement net bear a greater tensile stress.With the addition of outer clad steel,the bending capacity of column base is not significantly improved,but the rotational constraint stiffness of column base is improved to a certain extent.
Therefore,it is suggested that the contribution of secondary pouring concrete to column base bending capacity,rotational stiffness and ductility should be taken into account in mechanical performance analysis of portal frame structure,which can make the design more accurate.If the pouring concrete is thicker,additional reinforcement net or outer clad steel,the rotation constraint of column base should be considered,and the hinged analysis should not be used any more,which can make the structural analysis of portal frame more reasonable.
In order to study the influence of material degradation on the fatigue performance of steel-concrete composite beam bridge welds,the weight loss rate of reinforcement and steel plate and the time-varying strength of concrete are calculated according to the law of reinforcement corrosion,the law of concrete strength and the law of steel corrosion.The finite element model of degraded bridge was established by using ANSYS software.Taking the weld joint at the junction of main beam mid span web and lower flange as the research object,firstly,under the action of AASHTO standard fatigue vehicle,the stress time history of the welded joints of the main beam under different degradation conditions was extracted,and the influence of material degradation on the joint stress was discussed;then,based on Miner's linear cumulative damage theory,the fatigue damage development curves under different degradation years were calculated,the influence of material degradation on the fatigue damage curve was analyzed,and the variation laws of the maximum stress amplitude and the number of equivalent stress cycles of the bridge were discussed;finally,the fatigue damage ratio was defined to study the effect of material degradation on the fatigue damage of welding details of composite beam bridge.
The results show that the stress in the weld joint area is easily affected by material degradation.The stress value of the weld joint increases with the increase of degradation years,and the closer the loading position is,the greater the stress value is.The fatigue damage development curve of bridge welding details shows a linear growth trend,and material degradation will lead to the acceleration of fatigue damage accumulation of fatigue details.When reaching the design basis,the maximum increase of fatigue damage value reaches 7.5 times;the maximum stress amplitude is more sensitive to material degradation,and the growth rate of the maximum stress amplitude generated by fatigue details shows an increasing trend.The growth rates of the stress amplitude of the four nodes in the 100-year degradation condition reach 10.4%,13.6%,8.5% and 14.7% respectively.However,the growth rate of the number of equivalent stress cycles does not show an obvious law.The fatigue damage ratio increases nonlinearly with the degradation time.When the degradation time is 100 years,the fatigue damage ratio of beam bridges is 7.0,7.4,6.4 and 7.52 respectively.In addition,the greater the degree of structural degradation is,the higher the nonlinear degree of fatigue damage ratio is.
Fatigue monitoring of steel structure is an important part of steel structure health monitoring system.In recent years,under the rapid development of image acquisition and data remote transmission technology,the application of non-contact digital image measurement technology in fatigue monitoring has attracted the attention.In order to achieve the goal of detecting the fatigue anomaly by means of the identification of certain parameter changes in the digital image before the appearance of identifiable cracks,Q345qD steel specimens were designed and processed for fatigue test.During the test,the ARAMIS optical measurement system was used to take pictures of the observation area dynamically and continuously to obtain the whole fatigue process image,and the image was converted into data inside the measurement system as the measured value.By comparing and analyzing the mechanical indexes and collection methods during the whole fatigue process,the shape and application feasibility of the strain and displacement parameters of the digital image were studied.Comparing the results of electrical strain gauge with image strain measurement in static load test to make sure that the accuracy of digital image measurement was satisfied or not.The strain and displacement changes of the specimen during fatigue process were studied.The sensitivity analysis of various parameter of the image with fatigue process was carried out.The optimal parameter index and the way to collect them were studied.Finally,the feasibility and implementation scheme of the application of digital image technology to fatigue monitoring are verified meanwhile both of objectivity and automation were in consideration.
It was shown that the ARAMIS optical measuring techniques can collect dynamically the image data of the measured surface without contact.The obtained 3D strain values meet the accuracy requirement.The nominal strain of cross-section can be obtained by average value method of cross section line.The fatigue abnormal information obtained from the displacement parameter is relatively late,which is unacceptable for fatigue monitoring.While it is acceptable to take the strain parameter as the monitoring object of digital image.It is proposed that the maximum strain eigenvalue on the equivalent cloud image can be intercepted as a numerical series for fatigue monitoring.The obtained data are objective,effective and practical,and are the optimal measurement parameters for the application of digital image to fatigue monitoring.
Container buildings are assembled with many standard containers,and they have a good application prospect with the advantages of fabricated and modular buildings.However,most of the researches on container buildings focus on the architectural design or the mechanical performance of single box structure.The simplified simulation methodologies of corrugated plate wall and structural design method of container buildings are lacking.
By summarizing the structural analysis methods of corrugated plate wall,a simplified simulation method of corrugated plate wall with considering both the vertical bearing and horizontal lateral resistance is presented.Firstly,a corrugated plate wall model is established by using finite element software,and concentrated force is applied to the top end of the wall.The force-displacement relationship curves of corrugated plate wall are obtained through finite element analysis,the initial horizontal lateral stiffness of the wall can be calculated.Then the structural models of upper and lower beams and corner columns of the corrugated plates are setup in the design software,and the functions of the corrugated plate wall is simulated by cross braces,and the cross-sectional area of cross brace is calculated according to the stiffness equivalent principle.Thus,the simulation of the horizontal lateral stiffness of the corrugated plate wall is realized in the design software.Besides,each corrugation is simplified into a column with hinged upper and lower ends according to the principle of area equivalence,which is connected with the upper and lower beams of the containers,thus realizing the simulation of the vertical bearing capacity of the corrugated plate wall.
For multi-storey container buildings,the performance-based seismic design principle of high bearing capacity and low ductility is used according to China standard for design of steel structures(GB50017-2017).The members are strength checked according to the seismic forces under frequent and intermediate earthquakes,the plates in member section have lower ductility and the allowable width-thickness ratio of plates can be taken a larger value.
The method described above is used to analyze a two-storey container building functioning as a fire station with two parking spaces.The lateral stiffness of corrugated plate wall is figured out by using ANSYS software,and the stiffness reduction effect of wall openings is considered.In design software PKPM,the corrugated plate wall is simulated by equivalent cross braces and a certain number of columns with pinned connections at both ends,and the structural analysis model is established.According to the structure height and fortification intensity,the performance level is set as performance 3,the ductility level is set as grade V,and the width-thickness ratio of all plates is set as type S5.The bearing capacity of beams,columns and supporting members under frequent and intermediate earthquakes are checked.The results show that the maximum inter-story drift angle of the structure is equal to 1/527,the maximum stress ratios of the beam and the corner column on the second floor are equal to 0.92 and 0.35,respectively.All parameters meet the requirements of performance-based design.
The north block of the Belt and Road Cultural Exchange Center series public construction project is a 400 m long asymmetric twin tower connected structure,among which the 150 m aerial bridge is the single steel connected bridge with the largest span in China.The steel bridge weighs about 42 000 kN and is welded to the towers at both ends.The main body of the bridge is composed of sheet trusses,arc-shaped triangular trusses and the horizontal beam supports between them.At one end of the bridge is provided with a 36 m long and 4 500 kN weightunder theaxillary structure is installed at the bottom of one end of the connecting bridge.Under the projection of the bridge is the multi-elevation roof of the single and double basement,and the construction conditions are complex.At the present stage,the research on lifting construction mainly focuses on the theoretical and practical analysis of the overall lifting of connected structures with small span and light weight.However,there is no complete set of key technique research and application results for the construction of ultra-long and overweight connecting bridges with the above unconventional structural characteristics and various external complex environments.After a comprehensive analysis of the key and difficult points of steel bridge construction,combined with the existing case studies of upgrading construction in the industry,It had innovated and developed a set of key techniques for dynamic forming construction of large-span special-shaped steel connecting bridges,including linear control technology for dynamic forming of large-span special-shaped steel connecting bridges,internal force control and stress monitoring technology for large-span special-shaped steel connecting bridges,and hazard source control technique for assembly construction of large-span special-shaped steel connecting bridges under complex working conditions.
In the process of dynamic forming of special-shaped steel bridges,the axillary structure is installed step by step,which makes the center of gravity of the structure change continuously,which poses a greater challenge to the linear control of the structure forming.The 150 m long span bridge is assembled into a whole by multiple sections of thick plate steel components,and is dynamically formed by stage lifting.In the process of forming,the internal force is constantly redistributed,so the internal force control and real-time monitoring in the construction process are very important.In addition,the bridge volume is large,most of the components of the single weight of 300 kN,its assembly construction for large lifting equipment demand and projection of the basement roof below the relatively weak bearing capacity of the contradiction between the construction safety hazard source control technique put forward higher requirements.In this technique,asymmetric prearch technique was proposed,welding sequence optimization was optimized,cycle preassembly and virtual preassembly were applied,and the alignment control problem of asymmetric super long bridge was solved.With the application of full-cycle simulation,the lifting system of "multiple lifting points distribution and the combination of main and passive forces" was developed,and the stress discrimination standard of "difference value method" was developed,which solved the problems of structural internal force and stress monitoring in the construction process.The floor reinforcement of "steel support+post-pouring cap" was put forward,and the multi-elevation assembled platform system was developed to ensure the construction safety.
