Question and answer of portal steel structure 3

Question and answer of portal steel structure 3

  • 24 Jul 2020
  • steel structure

Question and answer of portal steel structure 3

61. What is ground motion?

Answer: ground motion refers to the ground motion caused by the seismic wave released by the source. This kind of ground motion can be expressed by the time function of acceleration, velocity or displacement of ground particle. The remarkable characteristic of ground motion is the irregularity of its time history function.

62. Can the sliding door and the small door of the workshop meet the fire evacuation requirements?

Answer: according to the current code, the sliding door cannot be used for the evacuation door of the factory building, even if the small door is opened on the sliding door. Therefore, In order to to use the sliding door, we can only set another side door for evacuation.

63. What is the wind vibration coefficient? What is gust coefficient?

Answer: the wind-induced vibration coefficient mainly reflects the influence of wind on structural vibration, and is the dynamic response caused by wind load. The gust coefficient is only used to calculate the wind response augmentation factor of the envelope directly bearing the wind load.

64. Should the interlayer displacement be calculated according to the distance between two points in the plane projection, or should it be calculated separately according to the X and Y direction increments of the two points?

Answer: calculated by displacement increment.

65. Is full section welding of steel structure rigid connection?

Answer: the rigid connection is certain. The web and flange are welded, and the web shear force and flange transfer moment can be realized. Only the joint form should be improved: first, it is not convenient for construction; second, it is easy to cause weld stress concentration, which has an impact on structural safety. It can be changed to the form of full flange connection.

66. In the multi span portal frame structure, the internal force envelope diagram of the middle column is basically the same. Why is the thickness design of the foundation plate of the middle column different in the calculation results?

Answer: the design of the base plate thickness of the STS middle column is to calculate the internal force of the column under all working conditions, and take the most unfavorable calculation result. For the multi span structure, because STS program can consider the unfavorable arrangement of live load, the internal force of the intermediate column under various working conditions will have certain differences, resulting in the design size and thickness of each intermediate column floor.

67.In the design of steel structure or super high-rise building structure, the effective mass coefficient is more than 90%, but the shear weight ratio is not enough. How to deal with this situation?

Answer: this situation is often caused by structural stiffness and quality mismatch. It can be checked and handled according to the following aspects: a. Increase the structural stiffness or adjust the structural layout. b. Check whether there is any problem in the structural loading. Too small load is also one of the reasons for the low floor mass and the small shear weight ratio. c. Only after the structural scheme (structure layout and load action) is confirmed to be reasonable, the function of minimum seismic shear amplification factor in the program can be used. Otherwise, it should be considered that the structural scheme is unreasonable and needs to be readjusted.

68. What is single bias? What is double bias?

Answer: the calculation method of single bias and double bias is different. When calculating reinforcement in X direction under single bias, the effect of Y-direction reinforcement is not considered, and the calculation result is unique; on the contrary, double bias pressure should be considered to overlap with Y-direction steel bar when calculating X-direction reinforcement, and the calculation result is not unique.

69. What is eccentric support? What is central support?

Answer: the central support means that the support axis intersects with the beam column intersection point; the eccentric support means that the intersection point of the support axis and the beam axis has a certain distance from the intersection point of the beam column, and the beam section between the two intersection points is the so-called energy dissipation beam section.

70. What is a node domain?

Answer: the joint area generally refers to the frame joint area. The thickness of the flange plate and web plate of the steel frame column is relatively thin. There is shear deformation in the frame joint area that can not be ignored, which has an impact of 10 ~ 20% on the horizontal displacement of the frame. The shear deformation of the joint region also affects the internal force, which is generally less than 10%. If the frame is braced, the shear deformation in the joint region will decrease sharply with the increase of the lateral stiffness of the brace system.

71. What is the area moment of the centering axis?

Answer: the product of the area of a micro element on the section and the distance from a specified axis on the section is called the static moment of the area of the element to the specified axis.

72. How to calculate the effective length of columns in strong braced frames?

Answer: K1 and K2 can be calculated. K1 and K2 are the ratios of the sum of the linear stiffness of the cross beam and the sum of the linear stiffness of the column. Calculation length coefficient μ = [3 + 1.4 (K1 + K2) + 0.64k1k2] / [3 + 2 (K1 + K2) + 1.28k1k2]

73. What is the function of suspender?

Answer: the junction of primary and secondary beams should be preferred with 3 on each side If the stirrup shear resistance is not satisfied, the hanging reinforcement should be configured according to the calculation. The role of the hanging reinforcement is not only the shear resistance, because the concentrated force has been taken into account in the calculation of the stirrup of the main beam section. The additional hanging bar or stirrup is to prevent the concrete under the concentrated force from pulling off, and transfer the concentrated force to the top of the beam, or similar to the punching failure( When the limit load is close to the limit load, the top area of the secondary beam has cracks or the end bearing is hinged.

74. Why is the tensile strength of anchor bolt lower than the design value of tensile strength of steel members with the same strength? For example, the design value of tensile strength of Q235 anchor bolt is only 140, not 215. Why?

Answer: Although the bottom plate of column foot is generally thick, its out of plane stiffness is limited after all. Under the tensile force of anchor bolt, it will warp and deform. Meanwhile, the anchor bolt is subject to tension deformation, which weakens the anchoring effect of anchor bolt. In order to consider this situation without making the bottom plate too thick, the tensile bearing capacity of the anchor bolt is reduced in the specification, and the method of reducing the deformation of the anchor bolt is used to ensure that the bottom plate will not warp too much.

75. What is a construction joint?

Answer: because of the need of construction organization, the joints should be set between construction units. The construction joint is not a real "joint", it is only because the later pouring concrete exceeds the initial setting time, there is a joint surface between the later poured concrete and the first poured concrete, which is called the construction joint. Because the joint surface formed by concrete pouring is prone to various hidden dangers and quality problems, therefore, the treatment of construction joints in different structural projects needs to be cautious. Limited by the construction technology, the joint formed by the planned interruption of construction is called construction joint. Due to the layered pouring of concrete structure, the most common construction joint is the gap formed between this layer of concrete and the upper layer of concrete. So it's not a real seam, but a face.

76. What is settlement joint?

Answer: Due to the large difference in the number of floors or the load used, or the great difference in the compressibility of the foundation, in a word, when the foundation may be subject to uneven settlement, joints should be set to divide the structure into several parts to make the settlement ratio of each part more uniform, so as to avoid extra stress in the structure. The joint is called "settlement joint". In order to overcome the uneven settlement of the structure, the joints must be completely separated from the foundation to the superstructure.

77. What is an expansion joint?

Answer: if the plane size of the building is too long, it may cause excessive temperature stress in the structure due to thermal expansion and cold contraction. It is necessary to set a joint at a certain length of the structure to divide the building into several parts, which is called temperature joint.

78. What is a seismic joint?

Answer: In order to make the building more regular to help the structure aseismic and set the joint, the foundation can be opened continuously. In seismic fortification area, settlement joint and expansion joint must meet the requirements of seismic joint.

79. What is Poisson's ratio of materials?

Answer: the absolute value of the ratio of the transverse strain caused by the uniformly distributed longitudinal stress to the corresponding longitudinal strain within the proportional limit of the material. For example, when a rod is stretched, its axial elongation is accompanied by transverse contraction (and vice versa), and the ratio of transverse strain e 'to axial strain e is called Poisson's ratio.

80. What is elastic modulus?

Answer: It is also known as young's modulus. Elastic material is one of the most important and characteristic mechanical properties. It is a characterization of the difficulty of elastic t deformation of an object. Denoted by E. It is defined as the ratio of the stress to the corresponding strain (the ability to recover its original shape and structure when subjected to deformation stress). E is expressed as the force per unit area in N / m ^ 2. The properties of modulus depend on the properties of deformation. The modulus of shear deformation is called shear modulus, expressed by G; the modulus of compression deformation is called compression modulus, expressed by K. The reciprocal of the modulus is called compliance, expressed by J.

81. Why is the gap between the middle stiffening plate and the lower flange of the traveling crane beam 50 mm ~ 100 mm?

Answer: the lower end of the middle transverse stiffener should be disconnected 50 ~ 100 mm away from the tension flange, The fatigue failure of crane beam generally starts from the crack in the tension zone. The welding seam of web plate can be reduced by using fillet welding or girdling or back welding at the lower end of rib. The lower end of the middle transverse stiffener should be disconnected at a distance of 50 ~ 100 mm from the tension flange, mainly considering the fatigue failure of the crane beam.

82. Function of foundation cushion?

Answer: plain concrete cushion has the function of protecting the foundation soil from disturbance, facilitating the setting out of construction and binding reinforcement, and reducing the corrosion of groundwater on the reinforced concrete foundation. In some cases, sand gravel cushion is used to replace soil to improve the application of local soft foundation in bearing stratum.

83. How is the reinforcement distributed in the foundation slab?

Answer: the transverse direction of the foundation is the stressed reinforcement (along the strong axis direction), and the longitudinal direction of the foundation is the distributed reinforcement, which is placed on the stressed reinforcement.

84. What is a rigid foundation? What is flexible foundation?

Answer: Rigid foundation refers to the use of brick, stone, lime soil, concrete and other materials with high compressive strength but low bending and shear strength (limited by rigid angle). It is used for small and medium-sized civil buildings with good foundation bearing capacity and low compressibility. Rigid angle: the angle between the leading line of relaxed foundation and the vertical line of wall.

Flexible foundation refers to the reinforced concrete material with good tensile, compressive, flexural and shear resistance as the foundation (not limited by the rigid angle). It is used for buildings with poor foundation bearing capacity, large upper load, basement and deep foundation. Large angle: the gradual grading form of brick foundation is called large angle. Function: increase the width of the bottom of the foundation, so that the upper load can be evenly transmitted to the foundation.

85. Design requirements for beam column connections?

Answer: there are two design methods for the connection of beam and column: one is common design method, the other is accurate design method. The stiffness of beam column joint area should be calculated in the joint calculation, and it should be strengthened when it is not enough. According to the code, the ultimate seismic bearing capacity of the joint is 1.3 times of the ultimate bearing capacity of the member. That is to say, when the joint is designed according to the equal strength, it must reach 1.3 times of the bearing capacity of the member.

85. Is the support between columns necessary?

Answer: Where there is horizontal support, column support should be set accordingly to maintain the stability of its spatial geometry. If there is no wind resistant column or inter column support, it is very unfavorable for the transmission of longitudinal horizontal force. The longitudinal horizontal force includes wind load, earthquake force and temperature stress. Generally, wind load is the main factor, because the house is light, the seismic force will be very small. The side column should be supported, and the middle column should also be added to the position, which is stipulated in the specification. However, the middle column can not be added in theory, because the horizontal force of the middle column can be transferred to the side column through the roof support, and then to the support, just as in the concrete structure, part of the lateral force resistance shear wall can not fall to the ground (the horizontal force is transferred to the wall through the floor),However, the support of side column and roof should be strengthened to ensure the transmission of horizontal force. The setting of support is a problem of structural system and concept, which can't be said as optional.

86. What is the function of the backing plate between the lower flange of the crane beam and the spring plate?

Answer: When the lower flange of the crane is screwed, the lower flange of the crane can be directly welded with the lower flange of the crane.

87. Can the mounting bolts be reused?

Answer: of course, the installation bolts can be reused. What we should understand here is that the bolts here are not the connection function of the bolts we understand, but the installation functions. The installation of bolts is temporary fixation. If there are no bolts on site, the reinforcement head can be used for temporary fixation, and the bolts can be removed after the components are welded.

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