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Steel Construction Published the List of Highly Influential Articles of 2020
2020 Vol. 35, No. 8
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2020, 35(8): 1-16.
doi: 10.13206/j.gjgSE20042701
Abstract
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Abstract:
A concept of moment resistant frame structure with beam-to-column connection by replaceable angles that link the flanges of steel beams has been proposed and experimentally studied. It is expected that structural damage shall be concentrated on the angles during expected earthquakes, and the damaged angles can be easily replaced in the rehabilitation process. Meanwhile, the concrete slab above the steel beam shall develop tolerable cracks only, considering the quick recovery of the building function after an earthquake. Experimental research has been carried out with three phases, including connections of bare steel beam in a sub-structural model, connections of steel-concrete beam in a sub-structural model, and dynamic tests on frame structure model.
In this paper, a brief review of the results for the first two phases is presented, a report of the third phase study is followed, i. e., the scaled frame model with the special connection tested on shaking table is reported. The following conclusions can be drawn from the experiment. The angle design about shape and size can guarantee the deformation requirement and avoid the fracture of section, thus the angle can efficiently absorb ground motion energy before the damage of other structural members. Severe cracking or crush of concrete slab can be avoided with properly designed connection details. Quick replacement work is possible when the main structural members keep elastic or experience minor plastic deformation. The structural stiffness and resistance of the repaired frame model may recover to its status as that before damaged.
A concept of moment resistant frame structure with beam-to-column connection by replaceable angles that link the flanges of steel beams has been proposed and experimentally studied. It is expected that structural damage shall be concentrated on the angles during expected earthquakes, and the damaged angles can be easily replaced in the rehabilitation process. Meanwhile, the concrete slab above the steel beam shall develop tolerable cracks only, considering the quick recovery of the building function after an earthquake. Experimental research has been carried out with three phases, including connections of bare steel beam in a sub-structural model, connections of steel-concrete beam in a sub-structural model, and dynamic tests on frame structure model.
In this paper, a brief review of the results for the first two phases is presented, a report of the third phase study is followed, i. e., the scaled frame model with the special connection tested on shaking table is reported. The following conclusions can be drawn from the experiment. The angle design about shape and size can guarantee the deformation requirement and avoid the fracture of section, thus the angle can efficiently absorb ground motion energy before the damage of other structural members. Severe cracking or crush of concrete slab can be avoided with properly designed connection details. Quick replacement work is possible when the main structural members keep elastic or experience minor plastic deformation. The structural stiffness and resistance of the repaired frame model may recover to its status as that before damaged.
2020, 35(8): 17-23.
doi: 10.13206/j.gjgS20040201
Abstract:
The honeycomb panel structure is composed of two upper and lower panels and a honeycomb core in the middle. It has the characteristics of light weight, high strength and high rigidity, and is widely used in the fields of aerospace, ships, automobiles and buildings. At present, the structure of honeycomb core is usually connected by cementing agent. The change of cementing agent has a great influence on its mechanical properties and its aging performance is not clear. The honeycomb panel is often used on the outer surface of the building, which is affected by the external environment for a long time, which puts a great test on its durability. The targeted index of structural durability evaluation usually needs to be set according to different use requirements. The honeycomb structure pays different attention to the objects according to different working conditions, among which the mechanical properties are an important evaluation index. This article focuses on the flat compressive strength of honeycomb panels.
This paper mainly conducts high temperature accelerated aging test on the structure of Titanium-Zinc honeycomb core, evaluate its durability by changing its flat compressive strength and predicts its service life. The life expectancy is set to 0, 25, 30 years, and the reaction rate change formula based on the Arrhenius equation to derive the temperature change is used to derive the high-temperature accelerated aging time. Select the standard test pieces of honeycomb core provided by four typical manufacturers, whose size is 60 mm×60 mm×20 mm, group them according to the expected life of 0, 25, and 30 years and perform accelerated aging at high temperature. One sample is reserved for each group, only accelerated aging without quasi-static compression, and the remaining groups are tested for quasi-static compression. Test the quasi-static compressive force of the sample piece by piece, record the load characteristic curve, read the crushing load, and record the crushing form. The flat compression strength and peak strength of the sample after aging are analyzed and compared with the corresponding values of the samples of the same batch before aging. Deviation is used for durability analysis, and the performance index of the sample before and after aging is set to not exceed ±15%.
The test results show that the deformation of the honeycomb core layer during the flattening process passes through three stages of elastic deformation, plastic deformation and instability. Elastic deformation stage I: The load-displacement curve is an oblique straight line, and the honeycomb core shows elastic deformation. Plastic deformation stage Ⅱ: Degumming and brittle cracking occurs between the honeycomb core wall panels, plastic buckling deformation occurs, and the flat compression strength decreases rapidly. Instability phase Ⅲ: As the loading continues, the constraints between the wall panels fail, and the honeycomb core is gradually pressed. And the surrounding honeycomb structure is gradually destroyed. When the structure is pressed, the flat compressive strength is maintained on a relatively low platform. The analysis results show that the strength changes of the test specimen within 30 years of aging time did not exceed the deviation of the index of 15% of the quality standards. And as the aging time increases, the flat compressive strength decreases. When the honeycomb cores are arranged denser and in real time, the improvement of flat compression strength is more obvious, and the overall test piece performs better after flat compression, and can basically maintain a square shape. As the aging time increases, the flat compressive strength of the honeycomb panel generally shows a downward trend. Within 25 years of aging, the strength of each series decreased slightly, and some series even increased in strength. Therefore, the design life is limited to 25 years is more reasonable. However, due to the differences in the manufacturing methods, the mechanical properties of the products vary greatly which demonstrate the necessity and feasibility of the life prediction of the honeycomb core structure.
The honeycomb panel structure is composed of two upper and lower panels and a honeycomb core in the middle. It has the characteristics of light weight, high strength and high rigidity, and is widely used in the fields of aerospace, ships, automobiles and buildings. At present, the structure of honeycomb core is usually connected by cementing agent. The change of cementing agent has a great influence on its mechanical properties and its aging performance is not clear. The honeycomb panel is often used on the outer surface of the building, which is affected by the external environment for a long time, which puts a great test on its durability. The targeted index of structural durability evaluation usually needs to be set according to different use requirements. The honeycomb structure pays different attention to the objects according to different working conditions, among which the mechanical properties are an important evaluation index. This article focuses on the flat compressive strength of honeycomb panels.
This paper mainly conducts high temperature accelerated aging test on the structure of Titanium-Zinc honeycomb core, evaluate its durability by changing its flat compressive strength and predicts its service life. The life expectancy is set to 0, 25, 30 years, and the reaction rate change formula based on the Arrhenius equation to derive the temperature change is used to derive the high-temperature accelerated aging time. Select the standard test pieces of honeycomb core provided by four typical manufacturers, whose size is 60 mm×60 mm×20 mm, group them according to the expected life of 0, 25, and 30 years and perform accelerated aging at high temperature. One sample is reserved for each group, only accelerated aging without quasi-static compression, and the remaining groups are tested for quasi-static compression. Test the quasi-static compressive force of the sample piece by piece, record the load characteristic curve, read the crushing load, and record the crushing form. The flat compression strength and peak strength of the sample after aging are analyzed and compared with the corresponding values of the samples of the same batch before aging. Deviation is used for durability analysis, and the performance index of the sample before and after aging is set to not exceed ±15%.
The test results show that the deformation of the honeycomb core layer during the flattening process passes through three stages of elastic deformation, plastic deformation and instability. Elastic deformation stage I: The load-displacement curve is an oblique straight line, and the honeycomb core shows elastic deformation. Plastic deformation stage Ⅱ: Degumming and brittle cracking occurs between the honeycomb core wall panels, plastic buckling deformation occurs, and the flat compression strength decreases rapidly. Instability phase Ⅲ: As the loading continues, the constraints between the wall panels fail, and the honeycomb core is gradually pressed. And the surrounding honeycomb structure is gradually destroyed. When the structure is pressed, the flat compressive strength is maintained on a relatively low platform. The analysis results show that the strength changes of the test specimen within 30 years of aging time did not exceed the deviation of the index of 15% of the quality standards. And as the aging time increases, the flat compressive strength decreases. When the honeycomb cores are arranged denser and in real time, the improvement of flat compression strength is more obvious, and the overall test piece performs better after flat compression, and can basically maintain a square shape. As the aging time increases, the flat compressive strength of the honeycomb panel generally shows a downward trend. Within 25 years of aging, the strength of each series decreased slightly, and some series even increased in strength. Therefore, the design life is limited to 25 years is more reasonable. However, due to the differences in the manufacturing methods, the mechanical properties of the products vary greatly which demonstrate the necessity and feasibility of the life prediction of the honeycomb core structure.
2020, 35(8): 24-32.
doi: 10.13206/j.gjgS20051001
Abstract:
A steel-UHPC composite girder is a new girder type whose steel girder is connected to a UHPC slab by shear connectors. Compared to the steel-conventional composite girder, the slab thickness of steel-UHPC composite girder can be greatly reduced due to the ultrahigh strength mechanical properties of UHPC, which decreases significantly the structural weight and enhances the spanning ability. As a result of high tensile strength and strong self-healing ability of micro cracks of UHPC, the steel-UHPC composite girder improves the flaws of the bridge slab existing in steel-conventional composite girders to some extent, such as being prone to crack under external loads in the negative bending moment area and insufficient durability for concrete slab, which greatly improve the safety performance and reduce the maintenance cost for steel-concrete composite girders on the basis of ensuring the good durability of structure. At present, only few studies on the refined mechanical model and numerical analysis for steel-UHPC composite girders have been reported. Additionally, there is still no such an unified theoretical model that can describe compressively the constitutive relationship of UHPC because of the complexity of UHPC materials.
To conduct a refined numerical model and to investigate the flexural behavior of steel-UHPC composite girders, the damage factor was deduced based on the selected uniaxial tension and compression constitutive relation for UHPC. A numerical model of damage mechanics corresponding to a tested steel-UHPC composite girder failed by flexure was established by ABAQUS finite element program, whose applicability is analyzed by comparing the mechanical properties to the test girder. Taking the UHPC slab thickness, the web slenderness and the tension flange thickness as the main structural parameters, the mechanical properties in the whole process of bending failures for 36 numerical model steel-UHPC composite girders were analyzed.
The model validation analysis showed that the response trend of load-displacement curve from numerical calculation was in good agreement with that of the test curve before the failure stage. After the failure stage different from the rapid failure of the test girder, the model girder obtained a more complete load-displacement curve including failure stage and descending stage, showing a good ductility performance. The damage evolution characteristics of the UHPC slab from the numerical calculations were in good agreement with the test results. In General, the load-displacement curve and damage evolution characteristics of the UHPC slab from the numerical calculations were in good agreement with the test results, and therefore the established numerical model can simulate accurately the mechanical behavior of the whole failure process of steel-UHPC composite girders, and reveal truly the stress and strain field transfusions and the damage evolution characteristics of cracking and collapse of the UHPC slab. The flexural strength of steel-UHPC composite girders under unit steel consumption increases greater by increasing the web slenderness than that by increasing the tension flange thickness. However, increasing the UHPC slab thickness has a relatively small effect on the improvement of flexural strength for steel-UHPC composite girders. As the tension flange thickness increases, the ratio of elastic flexural strength to ultimate flexural strength for steel-UHPC composite girders increases significantly, but at the same time, the ductility ability of girders reduces to some extent. On the premise of meeting the ductility demand, the distribution of flexural strength in different working stages of composite girders can be effectively adjusted by changing the tension flange thickness to meet different flexural strength demands of structure.
A steel-UHPC composite girder is a new girder type whose steel girder is connected to a UHPC slab by shear connectors. Compared to the steel-conventional composite girder, the slab thickness of steel-UHPC composite girder can be greatly reduced due to the ultrahigh strength mechanical properties of UHPC, which decreases significantly the structural weight and enhances the spanning ability. As a result of high tensile strength and strong self-healing ability of micro cracks of UHPC, the steel-UHPC composite girder improves the flaws of the bridge slab existing in steel-conventional composite girders to some extent, such as being prone to crack under external loads in the negative bending moment area and insufficient durability for concrete slab, which greatly improve the safety performance and reduce the maintenance cost for steel-concrete composite girders on the basis of ensuring the good durability of structure. At present, only few studies on the refined mechanical model and numerical analysis for steel-UHPC composite girders have been reported. Additionally, there is still no such an unified theoretical model that can describe compressively the constitutive relationship of UHPC because of the complexity of UHPC materials.
To conduct a refined numerical model and to investigate the flexural behavior of steel-UHPC composite girders, the damage factor was deduced based on the selected uniaxial tension and compression constitutive relation for UHPC. A numerical model of damage mechanics corresponding to a tested steel-UHPC composite girder failed by flexure was established by ABAQUS finite element program, whose applicability is analyzed by comparing the mechanical properties to the test girder. Taking the UHPC slab thickness, the web slenderness and the tension flange thickness as the main structural parameters, the mechanical properties in the whole process of bending failures for 36 numerical model steel-UHPC composite girders were analyzed.
The model validation analysis showed that the response trend of load-displacement curve from numerical calculation was in good agreement with that of the test curve before the failure stage. After the failure stage different from the rapid failure of the test girder, the model girder obtained a more complete load-displacement curve including failure stage and descending stage, showing a good ductility performance. The damage evolution characteristics of the UHPC slab from the numerical calculations were in good agreement with the test results. In General, the load-displacement curve and damage evolution characteristics of the UHPC slab from the numerical calculations were in good agreement with the test results, and therefore the established numerical model can simulate accurately the mechanical behavior of the whole failure process of steel-UHPC composite girders, and reveal truly the stress and strain field transfusions and the damage evolution characteristics of cracking and collapse of the UHPC slab. The flexural strength of steel-UHPC composite girders under unit steel consumption increases greater by increasing the web slenderness than that by increasing the tension flange thickness. However, increasing the UHPC slab thickness has a relatively small effect on the improvement of flexural strength for steel-UHPC composite girders. As the tension flange thickness increases, the ratio of elastic flexural strength to ultimate flexural strength for steel-UHPC composite girders increases significantly, but at the same time, the ductility ability of girders reduces to some extent. On the premise of meeting the ductility demand, the distribution of flexural strength in different working stages of composite girders can be effectively adjusted by changing the tension flange thickness to meet different flexural strength demands of structure.
2020, 35(8): 33-56.
doi: 10.13206/j.gjgS20052506
Abstract:
Bolt connections with the advantages of high reliability, fast fabrication and easy disassembly, have become the primary connection method in steel and composite construction. AISC 360-16 Specification for Structural Steel Buildings published by American Institute of Steel Construction, GB 50017—2017 Standard for Design of Steel Structures released by Chinese government have specified the bolt types, material property, bolt resistance and structural requirements of bolted connections. This paper analyzes and compares the differences and similarities between GB 50017—2017 and AISC 360-16, and provides a reference for structural engineers to understand and apply GB 50017—2017 and AISC 360-16 efficiently. Further improvements and revisions on GB 50017—2017 are also recommended. The main contents of this paper include:
1)There are two types of bolts recommended in AISC 360-16 and GB 50017—2017, ordinary bolts and highstrength bolts. The ordinary bolts used in China are Grade 4.6 and 4.8, also known as Grade C bolts. The bolts specified in ASTM A307 are equivalent to Grade 4.6 or 4.8 ordinary bolts. The high-strength bolts in China are Grade 8.8 and 10.9, which could be heavy hex bolts or twist-off bolts. AISC 360-16 also recommended highstrength bolts of heavy hex or twist-off type. Grade BC bolt specified in ASTM A354 is equivalent to Grade 8.8 bolt and Grade BD bolt is equivalent to Grade 10.9 bolt. ASTM F3125 / F3125M also specified high-strength bolts of Grade A325 and Grade A490, which are equivalent to Grade 8.8 and 10.9. ASTM F3111 and ASTM F3043 specified high-strength bolt with the tensile strength of 1 380 MPa, which is higher than that of Grade 12.9 bolt in China.
2) When applying ordinary bolts, the pretension is not required and bolts can be snug-tightened during installation. Whenever high-strength bolts are applied, the pretension should be specified as required by GB 500017—2017. AISC 360-16 allows structural designers to decide whether or not the pretension applied to the high-strength bolts. The pretension of high strength bolts specified in AISC 360-16 is about 15% higher than that specified in GB 50017—2017.
3)The bolted connections can be designed to resist shear force, tensile force, combined shear and tensile force. When the bolted connection is subject to shear force, the connections can be designed as bearing type or slip-critical type. The pretension should be applied when high-strength bolt is designed as slip-critical type, and the slip factor of faying surface should be designated. The slip factors recommended in GB 50017—2017 is relevant to the surface treatment and steel grade of connected steel plate, while the slip factors specified in AISC 360-16 is only relevant to the surface treatment. The values of slip factors given in AISC 360-16 and GB 50017—2017 are more or less similar, and in the range of 0.3~0.5.
4) AISC 360-16 and GB 50017—2017 have specified the bolt spacing limits and bolt hole sizes. The maximum and minimum end distance and edge distance of bolt holes, and the maximum and minimum spacing of bolt holes should be limited. AISC 360-16 and GB 50017—2017 require that the standard bolt hole size should be larger than the bolt diameter about 2~3 mm, and oversize hole or slot hole is permitted for the high-strength bolt in slip-critical connections.
5) AISC 360-16 and GB 50017—2017 require that the resistance of bolts and connecting plates should be determined respectively when designing the bolted connections under different loading conditions. For the long joints subject to shear force, the reduction factor is introduced to consider the uneven distributions of bolt shear forces.
Bolt connections with the advantages of high reliability, fast fabrication and easy disassembly, have become the primary connection method in steel and composite construction. AISC 360-16 Specification for Structural Steel Buildings published by American Institute of Steel Construction, GB 50017—2017 Standard for Design of Steel Structures released by Chinese government have specified the bolt types, material property, bolt resistance and structural requirements of bolted connections. This paper analyzes and compares the differences and similarities between GB 50017—2017 and AISC 360-16, and provides a reference for structural engineers to understand and apply GB 50017—2017 and AISC 360-16 efficiently. Further improvements and revisions on GB 50017—2017 are also recommended. The main contents of this paper include:
1)There are two types of bolts recommended in AISC 360-16 and GB 50017—2017, ordinary bolts and highstrength bolts. The ordinary bolts used in China are Grade 4.6 and 4.8, also known as Grade C bolts. The bolts specified in ASTM A307 are equivalent to Grade 4.6 or 4.8 ordinary bolts. The high-strength bolts in China are Grade 8.8 and 10.9, which could be heavy hex bolts or twist-off bolts. AISC 360-16 also recommended highstrength bolts of heavy hex or twist-off type. Grade BC bolt specified in ASTM A354 is equivalent to Grade 8.8 bolt and Grade BD bolt is equivalent to Grade 10.9 bolt. ASTM F3125 / F3125M also specified high-strength bolts of Grade A325 and Grade A490, which are equivalent to Grade 8.8 and 10.9. ASTM F3111 and ASTM F3043 specified high-strength bolt with the tensile strength of 1 380 MPa, which is higher than that of Grade 12.9 bolt in China.
2) When applying ordinary bolts, the pretension is not required and bolts can be snug-tightened during installation. Whenever high-strength bolts are applied, the pretension should be specified as required by GB 500017—2017. AISC 360-16 allows structural designers to decide whether or not the pretension applied to the high-strength bolts. The pretension of high strength bolts specified in AISC 360-16 is about 15% higher than that specified in GB 50017—2017.
3)The bolted connections can be designed to resist shear force, tensile force, combined shear and tensile force. When the bolted connection is subject to shear force, the connections can be designed as bearing type or slip-critical type. The pretension should be applied when high-strength bolt is designed as slip-critical type, and the slip factor of faying surface should be designated. The slip factors recommended in GB 50017—2017 is relevant to the surface treatment and steel grade of connected steel plate, while the slip factors specified in AISC 360-16 is only relevant to the surface treatment. The values of slip factors given in AISC 360-16 and GB 50017—2017 are more or less similar, and in the range of 0.3~0.5.
4) AISC 360-16 and GB 50017—2017 have specified the bolt spacing limits and bolt hole sizes. The maximum and minimum end distance and edge distance of bolt holes, and the maximum and minimum spacing of bolt holes should be limited. AISC 360-16 and GB 50017—2017 require that the standard bolt hole size should be larger than the bolt diameter about 2~3 mm, and oversize hole or slot hole is permitted for the high-strength bolt in slip-critical connections.
5) AISC 360-16 and GB 50017—2017 require that the resistance of bolts and connecting plates should be determined respectively when designing the bolted connections under different loading conditions. For the long joints subject to shear force, the reduction factor is introduced to consider the uneven distributions of bolt shear forces.
