One of the strategies for decarbonizing the construction industry is to enhance the efficiency of engineering design in order to minimize the demand for building materials.Recent advancements in the production of high-strength steel have enabled this possibility.The effective utilization of high strength steel in engineering structures can decrease the dimensions of components and the usage amount of steel,consequently leading to reduced manufacturing,transportation,and construction expenses,which aids in resource conservation and contributes to the reduction of carbon emissions.Compared to the ordinary carbon steel Q355,the Q690 high strength steel exhibits excellent strength to self-weight ratios despite its high yield-to-tensile strength ratio and low elongations at fracture.The properties of high strength steel Q690 can greatly influence structural performance.Therefore,it is crucial to quantify the impact of these properties on structural performance in order to determine their suitability for use in building structures.The calculation method for the overall buckling bearing capacity of axial compression members in the current main structural steel design codes is primarily based on research data for ordinary carbon steels Q235 and Q355,and their applicability to Q690 high strength steel needs to be further verified.So it is very necessary to check the applicability of these design methods for axial compression members made of Q690 high strength steel using various fabrication processes. To investigate the overall buckling of cold-formed square columns made of Q690 high strength steel under axial compression,a total of eight specimens were designed.These specimens included four different cross-sectional sizes and eight slenderness ratios.The plate thicknesses used were 6 mm and 10 mm.The overall buckling of these specimens was examined through axial compression tests.Prior to the tests,measurements were taken to determine the geometrical initial bending,load initial eccentricity,and longitudinal residual stress distribution of the sections.Residual stress measurements revealed large residual tensile strain on both the inner and outer surfaces at the welded seams of the cold-formed square section.Additionally,significant residual tensile and compressive strains were found at the outer and the inner surfaces respectively of the round corners of section.It was found that all specimens exhibited overall buckling as the primary mode of failure under axial compression.The test results were compared with the calculation results of Chinese code GB 50017-2017 and European code Eurocode 3.The results indicate that the calculation results based on the design curves suggested by the Chinese code and Eurocode are conservative,and the Chinese code being more conservative compared to the European code.Based on the comparison of test results and design curves in the design code,it is recommended to use the column curve a in GB 50017-2017 and Eurocode 3 for the design of Q690 high strength steel cold-formed square tube columns.
The grid structure is a spatial grid structure with various forms.Because of its advantages of good force performance,light weight,large rigidity,good seismic performance,low cost and easy forming,it is widely used in the roof of terminals,hangars,gymnasiums,theaters,exhibition halls,stations and other buildings.The roof of the main building of Terminal 2 of Zhuhai Airport adopts a large-span continuous ultra-long variable curvature hyperboloid local evacuation steel grid structure system.The modeling characteristics and structural system composition of the roof are introduced,and the construction process is carried out by partition and blocking cumulative lifting process according to its complexity,and the construction sequence is proposed and the lifting scheme is given.The construction steps of the steel structure of the main building roof are expounded,the construction steps of each step are simulated and analyzed,and the design load is applied to the grid structure after the unloading of the supporting frame,and the displacement and stress indicators of the whole process of the steel structure roof construction of the main building are obtained,and the performance of the steel structure of the main building based on construction simulation under the design and use load is evaluated.The construction technology that combines the whole process monitoring of the grid frame with the construction simulation is adopted,and the lifting status and block size of the grid are adjusted in real time through the comparison and analysis of the stress and strain values in the actual monitoring data and the simulation,so as to realize the accurate control of the force state of the grid lifting process. The results show that the construction scheme of the steel structure roof of the main building is feasible,and the structural deformation and internal force meet the requirements during the lifting process.After considering the influence of the construction process,the vertical deflection of mid span of the steel grid increases,and reliable measures should be taken to reduce the adverse effects caused by the increase of deflection;in the process from the beginning of construction to the final forming of the steel grid frame,the force mode of the local member changes from length to slenderness ratio control to force control,and the cross-section needs to be enlarged;it is necessary for the large-span grid frame to be reviewed by using the load input construction simulation analysis model according to the design after the construction simulation unloads the tire frame.The monitoring results show that the measured stress displacement of the grid frame is basically consistent with the construction simulation,which indicates the accuracy of the construction simulation analysis.
Fire is one of the critical safety threats to steel structures.The main conventional fire-resistant measures include painting fire-resistant coating,forming composite structures by combining steel with concrete and setting fire-resistant plates,among which the fire-resistant coating is the most widely used.However,the fire-resistant coating painted outdoors performs poor durability,owning the hidden danger that the coating may fall and hurt people.In addition,the extremely thick coating is required for steel structures with strict demand on fire resistance,which will especially affect the architectural rending of landmark buildings.In recent years,fire-resistant steel has been paid more attention for its ability to effectively avoid the above drawbacks,as a novel fire-resistant approach.However,the cost usually becomes higher due to the massively added high-price alloy Mo.As a result,the novel fire-resistant steel proposed by the Institute of Nanjing Iron&Steel Co.Ltd gained widespread attention owing to the much lower cost by reducing the additive quantity of alloy Mo while maintaining excellent fire-resistant properties. This paper investigates the feasibility of applying low-Mo fire-resistant steel in the fire-resistant design,based on the carrying capacity method and relying on a large steel canopy with a tall space.The large canopy should meet the 3 h fire-resistant requirement as a landmarking building.First of all,the material properties of domestic fire-resistant steel are investigated under high temperatures.It is found that the novel fire-resistant steel meets the requirements of general fire-resistant steel by comparing with the current specification and the reduction of material properties can be accurately predicted according to corresponding equations in the specification.Subsequently,a total of 11 fire scenes located at the side-span and the middle-span are identified according to the structural design criterion,which is thought to include all the possible fire scenes of the large canopy during service.Furthermore,it is analyzed that the heating laws of the large canopy under various fire scenes.The results show that the highest temperatures of air and steel beam are close to 750℃and 730℃,respectively,when the canopy is in the side-span fire scene,and those for the canopy in the mid-span fire scene are 600℃and 570℃,respectively.All of them are much lower than the temperature in a standard fire specified in ISO 834,which demonstrates that the tall space structure could be the main application scene of fire-resistant steel.Finally,the bearing capacity and stability of the structural members are analyzed and validated using the general structural steel Q355 and the domestic fire-resistant steel Q345FR. It is indicated that the steel beams GL3,GL3a and GL4 fail to meet the load-carrying requirements when using the general structural steel Q355,while the strength and overall stability requirements can be achieved when applying the fire-resistant steel Q345FR.
This paper investigated the stability coefficient of columns which provide lateral support to leaning columns.The present paper revealed that,the stability coefficient of framed columns should not only be determined by an amplified effective length,but also the column curve used should be lower,in the case of the leaning column carrying the same axial load as the framed column,the column curve should be changed from the curve b to the curve c in Eurocode 3.Using the well-known Jezek model,the above conclusions were verified.
Seismic design has the characteristic of self-fulfillment.Seismic behavior of members depends on three aspects:capacity,ductility and plumpness of hysteretic curves.Method for seismic design to standard GB 50017-2017 is introduced.For system performance factors the required modifications incorporating effects of short period,MDOF,second order effect and damping are introduced.The control of ductility development mechanism and its control method are introduced.A new explanation is provided for the enlargement of seismic effect in the bottom stories,finally the design technique of second-order analysis used for seismic design is discussed.
