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Steel Construction Published the List of Highly Influential Articles of 2020
2022 Vol. 37, No. 9
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2022, 37(9): 1-7.
doi: 10.13206/j.gjgS22071501
Abstract
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Abstract:
In the process of using, wearthing steel will be affected by temperature, collision, load and other effects, resulting in changes in its mechanical properties. It has been shown that corrosion has a significant effect on the mechanical properties of weathering steel, which can not be ignored. In order to obtain the tensile properties of corroded Q235NH, accelerated corrosion test was carried out on Q235NH specimen with neutral salt spray (salt solution with concentration of (50±5) g/L and pH value between 6.5 to 7.2) at 35 ℃,and the accelerated corrosion time was 6, 24, 48, 72, 96 h respectively. The tensile test was also carried out on the corroded Q235NH specimen. The corrosion surfaces, tensile fracture, stress-strain relationship curve and the change law of mechanical property parameters of Q235NH specimen were investigated. The change law of mechanical property parameters was fitted by formula, the constitutive model of stress-strain relationship was established and the degradation law of reduction coefficient was analyzed. The test results showed that: 1)at the initial stage of corrosion, there was only local corrosion. With the increase of corrosion time, the corrosion became more obvious, and the rust layer fell off. The stress-strain relationship curves of the specimen had an obvious yield plateau, and the stress-strain curve of Q235NH after corrosion was lower than that in the non corroded state, and the yield stage was shortened. With the increase of the corrosion time, the strength of the specimens decreased first, then increased, and then decreased. The reason for these phenomena was that after corrosion of weathering steel, a protective rust layer formed on its surface, which could protect the substrate. With the increase of corrosion time, the adsorption force of the rust layer increased, which slowed down the decline of the mechanical properties of the specimen. 2)The yield strength, tensile strength, yield-to-tensile strength ratio and its reduction factors showed a linear degradation trend with the increase of corrosion time, and then the linear regression relation was established. 3)The secondary plastic flow constitutive model was modified by the parameter of β on the strengthening stage. The modified quadratic plastic flow constitutive model could well simulate the stress-strain relationship of Q235NH before and after corrosion. At the same time, the shape parameters k1, k2 and k3 that affected the stress-strain relationship curve of Q235NH were analyzed, the recommended values of Q235NH shape control parameters k2 and k3 were proposed, and the linear degradation law of shape control parameter k1 with time was established. Through the tensile test of Q235NH under normal conditions, the reduction law of relevant parameters and bonding strength with corrosion time and the modified secondary plastic flow constitutive model could be obtained, and the reduction of mechanical properties of the material after corrosion could be calculated.
In the process of using, wearthing steel will be affected by temperature, collision, load and other effects, resulting in changes in its mechanical properties. It has been shown that corrosion has a significant effect on the mechanical properties of weathering steel, which can not be ignored. In order to obtain the tensile properties of corroded Q235NH, accelerated corrosion test was carried out on Q235NH specimen with neutral salt spray (salt solution with concentration of (50±5) g/L and pH value between 6.5 to 7.2) at 35 ℃,and the accelerated corrosion time was 6, 24, 48, 72, 96 h respectively. The tensile test was also carried out on the corroded Q235NH specimen. The corrosion surfaces, tensile fracture, stress-strain relationship curve and the change law of mechanical property parameters of Q235NH specimen were investigated. The change law of mechanical property parameters was fitted by formula, the constitutive model of stress-strain relationship was established and the degradation law of reduction coefficient was analyzed. The test results showed that: 1)at the initial stage of corrosion, there was only local corrosion. With the increase of corrosion time, the corrosion became more obvious, and the rust layer fell off. The stress-strain relationship curves of the specimen had an obvious yield plateau, and the stress-strain curve of Q235NH after corrosion was lower than that in the non corroded state, and the yield stage was shortened. With the increase of the corrosion time, the strength of the specimens decreased first, then increased, and then decreased. The reason for these phenomena was that after corrosion of weathering steel, a protective rust layer formed on its surface, which could protect the substrate. With the increase of corrosion time, the adsorption force of the rust layer increased, which slowed down the decline of the mechanical properties of the specimen. 2)The yield strength, tensile strength, yield-to-tensile strength ratio and its reduction factors showed a linear degradation trend with the increase of corrosion time, and then the linear regression relation was established. 3)The secondary plastic flow constitutive model was modified by the parameter of β on the strengthening stage. The modified quadratic plastic flow constitutive model could well simulate the stress-strain relationship of Q235NH before and after corrosion. At the same time, the shape parameters k1, k2 and k3 that affected the stress-strain relationship curve of Q235NH were analyzed, the recommended values of Q235NH shape control parameters k2 and k3 were proposed, and the linear degradation law of shape control parameter k1 with time was established. Through the tensile test of Q235NH under normal conditions, the reduction law of relevant parameters and bonding strength with corrosion time and the modified secondary plastic flow constitutive model could be obtained, and the reduction of mechanical properties of the material after corrosion could be calculated.
2022, 37(9): 8-16.
doi: 10.13206/j.gjgS22022202
Abstract:
Steel reinforced concrete structure has many advantages, such as high bearing capacity, good ductility in earthquake and controllable cracks. In recent years, it has been widely studied and applied in building structures. However, traditional steel reinforced concrete has the defects that reinforcement will weaken the bearing capacity of the steel during to penetrating the inner steel, and make the process of construction complex. As the tallest building in Ningxia Hui Autonomous Region, Yinchuan Greenland Center adopts steel reinforced concrete structure. A large number of stirrups need to penetrate the section steel at the beam column joints, which increases the processing capacity of the steel structure, and it is difficult to put the stirrups in place. A construction method of reinforcement without penetrating stirrup is proposed to solve the problem in construction according to the actural situation of the project. In view of this background, two kinds of steel reinforced concrete beam column joints model based on the completed tests was analyzed by using ABAQUS platform. The bearing capacity difference between the improved process and the prototypical process is studied after verification. On the basis of experimental verification of the numerical model, the feasibility of stirrup reinforced joint construction measures was analyzed, and the bearing capacity difference between the improved process and the prototypical process was investigated. In order to explore the influence of different design parameters on the bearing capacity of improved process, this paper analyzed the influence of parameters based on the numerical model of stirrup reinforced joint specimens, and investigated the influence of axial compression ratio, steel content of section steel, and reinforcement ratio of longitudinal reinforcement in column on the skeleton curve of stirrup reinforced joint.The results show that the numerical model can properly simulate the peak bearing capacity, skeleton curve and failure mode of specimens under constant axial pressure and horizontal displacement. The deformation capacity, failure mode and ultimate bearing capacity of the two processes are basically the same, which is consistent with the experimental phenomenon, indicating that the stirrup reinforced type can meet the requirements of structural bearing capacity and failure mode. The improved process therefore can be used to replace prototypical process where the process is complicated. The results of parameter analysis show that with the increase of axial compression ratio, the peak load of skeleton curve remains unchanged, and the ductility of joint test decreases gradually. With the increase of steel ratio of steel reinforced concrete, the bearing capacity of members has a certain range of improvement, and the steel ratio has little effect on the ductility of members with improved construction method. The ratio of main reinforcement has a great influence on the skeleton curve of stirrup reinforced joints, and the peak bearing capacity increases significantly with the increase of the ratio of main reinforcement.
Steel reinforced concrete structure has many advantages, such as high bearing capacity, good ductility in earthquake and controllable cracks. In recent years, it has been widely studied and applied in building structures. However, traditional steel reinforced concrete has the defects that reinforcement will weaken the bearing capacity of the steel during to penetrating the inner steel, and make the process of construction complex. As the tallest building in Ningxia Hui Autonomous Region, Yinchuan Greenland Center adopts steel reinforced concrete structure. A large number of stirrups need to penetrate the section steel at the beam column joints, which increases the processing capacity of the steel structure, and it is difficult to put the stirrups in place. A construction method of reinforcement without penetrating stirrup is proposed to solve the problem in construction according to the actural situation of the project. In view of this background, two kinds of steel reinforced concrete beam column joints model based on the completed tests was analyzed by using ABAQUS platform. The bearing capacity difference between the improved process and the prototypical process is studied after verification. On the basis of experimental verification of the numerical model, the feasibility of stirrup reinforced joint construction measures was analyzed, and the bearing capacity difference between the improved process and the prototypical process was investigated. In order to explore the influence of different design parameters on the bearing capacity of improved process, this paper analyzed the influence of parameters based on the numerical model of stirrup reinforced joint specimens, and investigated the influence of axial compression ratio, steel content of section steel, and reinforcement ratio of longitudinal reinforcement in column on the skeleton curve of stirrup reinforced joint.The results show that the numerical model can properly simulate the peak bearing capacity, skeleton curve and failure mode of specimens under constant axial pressure and horizontal displacement. The deformation capacity, failure mode and ultimate bearing capacity of the two processes are basically the same, which is consistent with the experimental phenomenon, indicating that the stirrup reinforced type can meet the requirements of structural bearing capacity and failure mode. The improved process therefore can be used to replace prototypical process where the process is complicated. The results of parameter analysis show that with the increase of axial compression ratio, the peak load of skeleton curve remains unchanged, and the ductility of joint test decreases gradually. With the increase of steel ratio of steel reinforced concrete, the bearing capacity of members has a certain range of improvement, and the steel ratio has little effect on the ductility of members with improved construction method. The ratio of main reinforcement has a great influence on the skeleton curve of stirrup reinforced joints, and the peak bearing capacity increases significantly with the increase of the ratio of main reinforcement.
2022, 37(9): 17-24.
doi: 10.13206/j.gjgS21011901
Abstract:
The String structure consists of a rigid body at the top chord, a flexible tie rod at the bottom chord and a rigid strut between them, steel cable or steel tie rod is usually used as flexible tie rod, in the structural system, it is a tension member. Special shaped truss string structure is arranged at skylight of Wenzhou Airport, the design institute has put forward a clear allowable range for the internal force in the construction of tension string structure steel tie rod. According to the overall construction scheme of steel structure, passive prestressing technology was adopted in the stage of floor assembly of string structure, after the initial tension was applied, the whole roof was lifted to the design elevation. The standard value of internal force of steel tie rod at the end of construction was defined in the design, it was called the standard value of forming internal force. Taking the standard value of forming internal force as the target value, combined with steel structure construction scheme and steel tie rod tension scheme, the whole process simulation analysis technology was adopted, the standard value of initial tension of steel tie rod was tried to calculate. In order to ensure that the forming internal force of steel tie rod meets the design requirements, master the change process of internal force of steel tie rod, ensure that the structure is in a safe state, it is necessary to monitor the internal force of steel tie rod during construction. The internal force of steel tie rod measured by frequency method is directly calculated by the correlation between frequency and internal force. By analyzing the characteristics of the string structure of the skylight, it can be found that, both ends of the steel tie rod are connected by pins,the boundary conditions are approximate to ideal hinge, this kind of boundary condition is suitable for the vibration of steel tie rod, the disturbance to vibration amplitude attenuation and vibration frequency is minimum. Therefore, the frequency method is suitable for the internal force monitoring of steel tie rod in this project. Lifting process is the process of structural stress system transformation, it's a dynamic process, and also the most frequent process of internal force fluctuation of steel tie rod, it is necessary to monitor the internal force of steel tie rod. According to the features of the strain method, such as mature technology, strong adaptability to environmental changes, it is easy to operate, and reliable results. In the process of upgrading, the method of installing strain sensor on steel tie rod is adopted to monitor internal force of steel tie rod. Through construction simulation, election of measuring points, construction preparation and equipment installation, field test, data acquisition and analysis, the results and conclusions are as follows: 1)the results measured by frequency method and strain method are within the allowable range, the phenomenon of insufficient tension or over tension is avoided, the feasibility of the construction technology of passive prestressing is verified; 2)the variation trend of measured internal force is consistent with that of theoretical calculation, the validity of the measured values is illustrated; 3)the relative value and absolute value of the difference between the two measurement methods meet the requirements of the Code for Construction of Steel Structures GB 50755—2020, which shows that both methods are suitable for the project.
The String structure consists of a rigid body at the top chord, a flexible tie rod at the bottom chord and a rigid strut between them, steel cable or steel tie rod is usually used as flexible tie rod, in the structural system, it is a tension member. Special shaped truss string structure is arranged at skylight of Wenzhou Airport, the design institute has put forward a clear allowable range for the internal force in the construction of tension string structure steel tie rod. According to the overall construction scheme of steel structure, passive prestressing technology was adopted in the stage of floor assembly of string structure, after the initial tension was applied, the whole roof was lifted to the design elevation. The standard value of internal force of steel tie rod at the end of construction was defined in the design, it was called the standard value of forming internal force. Taking the standard value of forming internal force as the target value, combined with steel structure construction scheme and steel tie rod tension scheme, the whole process simulation analysis technology was adopted, the standard value of initial tension of steel tie rod was tried to calculate. In order to ensure that the forming internal force of steel tie rod meets the design requirements, master the change process of internal force of steel tie rod, ensure that the structure is in a safe state, it is necessary to monitor the internal force of steel tie rod during construction. The internal force of steel tie rod measured by frequency method is directly calculated by the correlation between frequency and internal force. By analyzing the characteristics of the string structure of the skylight, it can be found that, both ends of the steel tie rod are connected by pins,the boundary conditions are approximate to ideal hinge, this kind of boundary condition is suitable for the vibration of steel tie rod, the disturbance to vibration amplitude attenuation and vibration frequency is minimum. Therefore, the frequency method is suitable for the internal force monitoring of steel tie rod in this project. Lifting process is the process of structural stress system transformation, it's a dynamic process, and also the most frequent process of internal force fluctuation of steel tie rod, it is necessary to monitor the internal force of steel tie rod. According to the features of the strain method, such as mature technology, strong adaptability to environmental changes, it is easy to operate, and reliable results. In the process of upgrading, the method of installing strain sensor on steel tie rod is adopted to monitor internal force of steel tie rod. Through construction simulation, election of measuring points, construction preparation and equipment installation, field test, data acquisition and analysis, the results and conclusions are as follows: 1)the results measured by frequency method and strain method are within the allowable range, the phenomenon of insufficient tension or over tension is avoided, the feasibility of the construction technology of passive prestressing is verified; 2)the variation trend of measured internal force is consistent with that of theoretical calculation, the validity of the measured values is illustrated; 3)the relative value and absolute value of the difference between the two measurement methods meet the requirements of the Code for Construction of Steel Structures GB 50755—2020, which shows that both methods are suitable for the project.
2022, 37(9): 25-29.
doi: 10.13206/j.gjgS22061007
Abstract:
Steel structure buildings are favored by modern designers because of their advantages of high strength, good toughness, strong plasticity, short construction period, and green environmental protection. In the on-site installation of the steel structure, after the overall hoisting of the steel structure is completed and all loads are applied, unloading treatment is required. For the unloading of the long-span space tube truss structure, due to the large number of pipe fittings and different node forms, the overall internal force of the structure is complex and changeable, and the force between each member is difficult to determine, so blindly selecting the unloading sequence may it will cause the structure to be overstressed locally, resulting in plastic deformation or even structural damage of the structure, so it is particularly important to determine a reasonable unloading sequence. Taking the CSPC Health City project as the research object, an unloading method of the space tube truss structure was given, and the finite element simulation was carried out. Specifically, in the unloading process, primary unloading was performed first, that was, the non-main stress-bearing support was removed at one time, and then secondary unloading was performed, that was, the main stress-bearing support was unloaded step by step. In the whole process, MIDAS/Gen finite element analysis software was used to simulate and analyze the structure and main stress-bearing supports. Considering that the purpose of simulation was to determine the unloading sequence, the supports were replaced by ∅219×10 steel pipes, and were set as compression-only units, when unloading, the forced displacement was applied at both ends of the steel pipe. It was determined that the unloading sequence was mainly based on the simulated support reaction force of the support, and the support with large support reaction force was preferentially unloaded. Specifically, the two groups of supports with the largest support reaction force were the current unloading step, and the unloading amount was 10 mm each time, each unloading step was subjected to a force calculation, and the next unloading sequence was determined according to the size of the current support and reaction force, and the unloading was simulated reciprocally until the final unloading was completed, and the simulated specific unloading sequence was applied to the actual construction as a guide. In addition, in the whole simulation process, for the supports whose support and reaction force was 0 and did not change or change little, the support was directly removed, and the simulation calculation is no longer carried out. In the process of simulation analysis, the stress change of structural members was recorded, and the member with the maximum stress was marked. The feasibility of this unloading method was proved by the magnitude and change of the member stress. Stress monitoring of these members could be performed to ensure the stability of the overall structure during unloading. According to the simulation analysis, 19 unloading steps were required to complete the overall unloading. During the unloading process, there was no deformation and stress exceeding the limit. The extreme values of the results in the simulation process were: The maximun support reaction force of the bracket is 1 033 kN, the maximum deflection was 59.27 mm, and the maximum stress is 236.40 MPa.
Steel structure buildings are favored by modern designers because of their advantages of high strength, good toughness, strong plasticity, short construction period, and green environmental protection. In the on-site installation of the steel structure, after the overall hoisting of the steel structure is completed and all loads are applied, unloading treatment is required. For the unloading of the long-span space tube truss structure, due to the large number of pipe fittings and different node forms, the overall internal force of the structure is complex and changeable, and the force between each member is difficult to determine, so blindly selecting the unloading sequence may it will cause the structure to be overstressed locally, resulting in plastic deformation or even structural damage of the structure, so it is particularly important to determine a reasonable unloading sequence. Taking the CSPC Health City project as the research object, an unloading method of the space tube truss structure was given, and the finite element simulation was carried out. Specifically, in the unloading process, primary unloading was performed first, that was, the non-main stress-bearing support was removed at one time, and then secondary unloading was performed, that was, the main stress-bearing support was unloaded step by step. In the whole process, MIDAS/Gen finite element analysis software was used to simulate and analyze the structure and main stress-bearing supports. Considering that the purpose of simulation was to determine the unloading sequence, the supports were replaced by ∅219×10 steel pipes, and were set as compression-only units, when unloading, the forced displacement was applied at both ends of the steel pipe. It was determined that the unloading sequence was mainly based on the simulated support reaction force of the support, and the support with large support reaction force was preferentially unloaded. Specifically, the two groups of supports with the largest support reaction force were the current unloading step, and the unloading amount was 10 mm each time, each unloading step was subjected to a force calculation, and the next unloading sequence was determined according to the size of the current support and reaction force, and the unloading was simulated reciprocally until the final unloading was completed, and the simulated specific unloading sequence was applied to the actual construction as a guide. In addition, in the whole simulation process, for the supports whose support and reaction force was 0 and did not change or change little, the support was directly removed, and the simulation calculation is no longer carried out. In the process of simulation analysis, the stress change of structural members was recorded, and the member with the maximum stress was marked. The feasibility of this unloading method was proved by the magnitude and change of the member stress. Stress monitoring of these members could be performed to ensure the stability of the overall structure during unloading. According to the simulation analysis, 19 unloading steps were required to complete the overall unloading. During the unloading process, there was no deformation and stress exceeding the limit. The extreme values of the results in the simulation process were: The maximun support reaction force of the bracket is 1 033 kN, the maximum deflection was 59.27 mm, and the maximum stress is 236.40 MPa.
2022, 37(9): 30-55.
doi: 10.13206/j.gjgS22032603
Abstract:
A theoretical study is carried out for the flexural-torsional buckling capacity of beam-columns with box-section. The main works and developments are as follows: 1) Comparisons are carried out between the formulae used in the codes of GB50017-2017, AISC LRFD 2016, Eurocode 3 part 1-1 and the formulae derived in the flexural-torsional theory, possible improvements are pointed out. 2) As the first step of the development, plastic interactive relations are obtained for the axial force and bending moments about the strong axis and about the weak axis respectively. Fitting curves with good accuracy are provided for interaction equations of axial force-bending moments about the strong axis and about the weak axis. For the general cases of axial force and biaxial bending moments, exact analysis is carried out for the state of spatial plastic hinges and an approximate interactive equation for biaxial bending under a given axial force is also proposed. The effect of bi-moment is incorporated into the proposed equation. 3) Second-order analysis is carried out for the beam-columns with initial deflection and initial twisting, after introducing a specific relation between the initial deflection and initial twisting, simple expressions are obtained for the lateral displacement, twisting angle, lateral bending moments and bi-moments. 4) Based on the well-accepted and codified column strength reduction factor, the equivalent initial out-of-plane deflections are obtained by taking the buckling strength of the column about the weak axis as a plastic hinge state under the axial force and the amplified bending moment due to the second order effect and initial deflection, this equivalent initial deflection includes the effect of residual stress, initial deflection and the additional deflection increment due to plasticity development. 5) Introducing this equivalent initial deflection into the second-order bending moment about the weak axis and into the bi-moment, together with the second-order in-plane bending moment, they are substituted into the spatial interactive equation of the axial force and biaxial bending moments, the interactive equation of beam-column is derived for flexural-torsional buckling. But this is an upper bound solution of the interactive equation because the process of elastic-plastic development has not been included. After amplifying the second order in-plane bending moment, and further amplifying the out-of-plane bending moments and bi-moment to consider the elastic-plastic development, the obtained equation is applicable. A series of curves are provided to show the interaction curves, the curves are close to the interactive relation of strength when the slenderness is small, and the curves are close to the interactive relation for elastic flexural-torsional buckling when the slenderness is increased, and over it when the slenderness is further increased. The paper proposes also a new formula based on the observation of the derived curves. 6) Comparison shows that the in-plane and out-of-plane stability formluae in the current national code GB 50017—2107 govern safety of the beam-columns together, in the case that the out-of-plane formula is on the unsafe side, the in-plane formula will provide the safety.
A theoretical study is carried out for the flexural-torsional buckling capacity of beam-columns with box-section. The main works and developments are as follows: 1) Comparisons are carried out between the formulae used in the codes of GB50017-2017, AISC LRFD 2016, Eurocode 3 part 1-1 and the formulae derived in the flexural-torsional theory, possible improvements are pointed out. 2) As the first step of the development, plastic interactive relations are obtained for the axial force and bending moments about the strong axis and about the weak axis respectively. Fitting curves with good accuracy are provided for interaction equations of axial force-bending moments about the strong axis and about the weak axis. For the general cases of axial force and biaxial bending moments, exact analysis is carried out for the state of spatial plastic hinges and an approximate interactive equation for biaxial bending under a given axial force is also proposed. The effect of bi-moment is incorporated into the proposed equation. 3) Second-order analysis is carried out for the beam-columns with initial deflection and initial twisting, after introducing a specific relation between the initial deflection and initial twisting, simple expressions are obtained for the lateral displacement, twisting angle, lateral bending moments and bi-moments. 4) Based on the well-accepted and codified column strength reduction factor, the equivalent initial out-of-plane deflections are obtained by taking the buckling strength of the column about the weak axis as a plastic hinge state under the axial force and the amplified bending moment due to the second order effect and initial deflection, this equivalent initial deflection includes the effect of residual stress, initial deflection and the additional deflection increment due to plasticity development. 5) Introducing this equivalent initial deflection into the second-order bending moment about the weak axis and into the bi-moment, together with the second-order in-plane bending moment, they are substituted into the spatial interactive equation of the axial force and biaxial bending moments, the interactive equation of beam-column is derived for flexural-torsional buckling. But this is an upper bound solution of the interactive equation because the process of elastic-plastic development has not been included. After amplifying the second order in-plane bending moment, and further amplifying the out-of-plane bending moments and bi-moment to consider the elastic-plastic development, the obtained equation is applicable. A series of curves are provided to show the interaction curves, the curves are close to the interactive relation of strength when the slenderness is small, and the curves are close to the interactive relation for elastic flexural-torsional buckling when the slenderness is increased, and over it when the slenderness is further increased. The paper proposes also a new formula based on the observation of the derived curves. 6) Comparison shows that the in-plane and out-of-plane stability formluae in the current national code GB 50017—2107 govern safety of the beam-columns together, in the case that the out-of-plane formula is on the unsafe side, the in-plane formula will provide the safety.
2022, 37(9): 56-58.
doi: 10.13206/j.gjgS22082205
Abstract:
Free body analysis of concrete-encased steel column base was carried out to reveal whether the exterior reinforced concrete wall was the support or a part of the steel-reinforced column(SRC). In case of enough studs, the minimum encasing height was proposed. Equations to determine the stud number were presented.
Free body analysis of concrete-encased steel column base was carried out to reveal whether the exterior reinforced concrete wall was the support or a part of the steel-reinforced column(SRC). In case of enough studs, the minimum encasing height was proposed. Equations to determine the stud number were presented.
