This article is written on the basis of the author's "Seven Ratios and Adjustment Methods that Need to Be Controlled in the Design of High-Rise Structure", and the necessary modifications and supplements are made to some errors and deficiencies in the original text, and some content is added on the basis of the original text.
The difficulty of high-rise structural design lies in the rational arrangement of vertical load-bearing components (columns, shear walls, etc.), and the design process mainly achieves this goal through the control of some target parameters.
First, the axial pressure ratio: mainly to limit the axial pressure ratio of the structure, to ensure the ductility requirements of the structure, the specification of the wall limbs and columns have corresponding limit requirements. See Anti-Regulation 6.3.7 and 6.4.6, High Regulation 6.4.2 and 7.2.14 and the corresponding provisions. The axial pressure ratio does not meet the requirements of the specification, and the ductility requirements of the structure cannot be guaranteed; if the axial pressure ratio is too small, it means that the economic and technical indicators of the structure are poor, and the cross-sectional area of the corresponding wall and column should be appropriately reduced.
Adjustment method when the axial pressure ratio does not meet the specification requirements:
1. Program adjustment: SATWE program cannot be implemented.
2. Structural adjustment: increase the wall, column section or increase the strength of the wall and column concrete on the floor.
Second, the shear-to-weight ratio: mainly to limit the minimum level of seismic shear force of each floor, to ensure the safety of the structure with a long period. See SR 5.2.5, SG 3.3.13 and the corresponding provisions. The shear-to-weight ratio does not meet the requirements of the specification, indicating that the stiffness of the structure is too small relative to the horizontal seismic shear force; but the shear-to-weight ratio is too large, which indicates that the economic and technical indicators of the structure are poor, and it is appropriate to reduce the cross-sectional area of vertical components such as walls and columns.
How to adjust when the weight reduction ratio does not meet the specification requirements:
1. Program adjustment: When the shear weight ratio is small but not much different from the specification limit (such as the shear weight ratio reaches more than 80% of the specification limit), it can be adjusted according to one of the following methods:
1) In SATWE's "Adjustment Information", check "Adjust the seismic internal force of each floor according to the seismic specification 5.2.5", SATWE automatically multiplies the floor minimum seismic shear coefficient directly by the sum of the representative values of the gravity load on the floor and above according to the resistance regulation 5.2.5, and adjusts the seismic shear force of the floor to meet the shear-to-weight ratio requirements.
2) Enter a coefficient greater than 1 in the "Seismic Amplification Coefficient of the Whole Building" in SATWE's "Adjustment Information" to increase the seismic effect to meet the shear-weight ratio requirements.
3) Appropriately reduce the coefficient in the "periodic reduction coefficient" in SATWE's "Earthquake Information" and increase the seismic effect to meet the requirements of shear-weight ratio.
2. Structural adjustment: When the shear weight ratio is small and the difference with the normative limit is large, it is advisable to adjust and strengthen the vertical components to strengthen the stiffness of vertical components such as walls and columns.
Third, the rigid-weight ratio: The upper limit of the specification is mainly used to determine whether the second-order effect caused by the displacement effect of gravity load in the horizontal action can be ignored. See SG 5.4.1 and 5.4.2 and the corresponding provisions. The rigid-to-weight ratio does not meet the upper limit of the specification, indicating that the impact of the second-order effect of gravity is large and should be considered. The lower limit of the specification is mainly to control the second-order effect caused by the displacement effect of gravity load in the horizontal action, so as not to be too large, so as to avoid the instability and collapse of the structure. See SG 5.4.4 and the corresponding provisions. The stiffness-to-weight ratio does not meet the lower limit of the specification, indicating that the stiffness of the structure is too small relative to the gravity load. However, if the rigid-weight ratio is too large, it means that the economic and technical indicators of the structure are poor, and it is appropriate to reduce the cross-sectional area of vertical components such as walls and columns.
How to adjust when the specification requirements are not met just now:
1. Program adjustment: The rigid-to-weight ratio does not meet the requirements of the upper limit of the specification, check "Consider P-Δ Effect" in SATWE's "Design Information", and the program is automatically counted into the impact of the gravity second-order effect.
2, structural adjustment: the rigidity-to-weight ratio does not meet the requirements of the lower limit of the specification, and can only be strengthened by adjusting the vertical components, and the stiffness of vertical components such as walls and columns can be strengthened.
Fourth, the displacement angle between layers: mainly to limit the horizontal displacement of the structure under normal use conditions, to ensure the stiffness that the high-rise structure should have, to avoid excessive displacement and affect the bearing capacity, stability and use requirements of the structure. See SG 4.6.1, 4.6.2 and 4.6.3 and the corresponding provisions. The interlayer displacement angle does not meet the specification requirements, indicating that the above requirements of the structure cannot be met. However, the displacement angle between layers is too small, which indicates that the economic and technical indicators of the structure are poor, and it is appropriate to reduce the cross-sectional area of vertical components such as walls and columns.
Adjustment method when the interlayer displacement angle does not meet the specification requirements:
2, structural adjustment: can only be adjusted to enhance the vertical components, strengthen the stiffness of vertical components such as walls and columns.
1) Because the high-rise structure will inevitably be twisted under the action of the horizontal force, the maximum interlayer displacement of the high-rise structure that conforms to the rigid floor slab assumption often appears in the corner of the structure, so attention should be paid to strengthening the stiffness of the anti-lateral force member at the corresponding position of the structure periphery and reducing the lateral shift deformation of the structure. At the same time, in the design, the stiffness of the floor slab should be guaranteed on the structural measures.
2) Use the node search function of the program to quickly find the node between layers in the "Schematic Diagram of the Number of Reinforcement Components of Each Layer" in SATWE's "Analysis Results Graph and Text Display", and strengthen the stiffness of the corresponding walls, columns and other components of the node. The node number is looked up in the SATWE displacement output file.
Fifth, the displacement ratio (interlayer displacement ratio): mainly to limit the irregularity of the layout of the structural plan, so as to avoid excessive eccentricity and lead to a large torsional effect of the structure. See Anti-Regulation 3.4.2, High Regulation 4.3.5 and the corresponding provisions. The displacement ratio (including the displacement ratio between layers, the same below) does not meet the requirements of the specification, indicating that the distance between the rigid center of the structure deviates from the center of mass is large, the torsional effect is too large, and the arrangement of the structural resistance lateral force components is unreasonable.
Adjustment method when the displacement ratio does not meet the specification requirements:
2. Structural adjustment: only by adjusting the structural layout can the structural layout be changed to reduce the eccentric distance between the rigid center of the structure and the center of mass; the adjustment method is as follows:
1) Since the displacement ratio is calculated under the assumption of rigid floor slabs, the maximum horizontal displacement and interlayer displacement of the structure often appear in the corners of the structure; therefore, attention should be paid to adjusting the stiffness of the anti-lateral force components in the corresponding position of the structure periphery, and reducing the eccentric distance between the rigidity of the structure and the centroid. At the same time, in the design, the stiffness of the floor slab should be guaranteed on the structural measures.
2) For floors whose displacement does not meet the specification requirements, the node search function of the program can also be used to quickly find the node with the largest displacement in the "Schematic Diagram of the Number of Reinforcement Components of Each Layer" in SATWE's "Analysis Result Graph and Text Display" to strengthen the stiffness of the corresponding walls, columns and other components of the node. The node number is looked up in the SATWE displacement output file. It is also possible to find that the node with the smallest displacement weakens its stiffness until the displacement ratio meets the requirements.
Sixth, the cycle ratio: mainly to limit the torsional stiffness of the structure can not be too weak, so that the structure has the necessary torsional stiffness, reduce the adverse impact of torsion on the structure. See SG 4.3.5 and the corresponding provisions. The cycle ratio does not meet the specification requirements, indicating that the torsional stiffness of the structure is relatively small relative to the lateral shift stiffness, the torsional effect is too large, and the arrangement of the structural anti-lateral force components is unreasonable.
Adjustment method when the cycle ratio does not meet the specification requirements:
2, structural adjustment: only through the adjustment of the structural layout to change the torsional stiffness of the structure. Since the anti-lateral force members on the periphery of the structure contribute the most to the torsional stiffness of the structure, the general adjustment principle is to strengthen the stiffness of the outer wall, column or beam of the structure, or appropriately weaken the stiffness of the middle wall and column of the structure. Using the inverse relationship between structural stiffness and period, the anti-lateral force components are reasonably arranged, the stiffness that needs to be reduced in the periodic direction (including the translation direction and the torsional direction) is strengthened, and the stiffness that needs to be increased in the periodic direction is weakened. When the first or second mode of the structure is torsional, it can be adjusted as follows:
1) The mode shapes in the SATWE program are sorted by the length of their periods.
2) The first and second mode shapes of the structure should be translational, and the torsional period should appear in the third mode and later. See Article 3.5.3 of the Resistance Gauge and the provision stating that "the dynamic characteristics (period and mode shape) of the structure in the direction of the two spindles should be similar".
3) When the first mode is torsional, it is stated that the torsional stiffness of the structure is relative to its two main axes (the angle direction of the second mode shape and the angle direction of the third mode shape, generally close to the X and Y axis) The anti-lateral shift is just too small, at this time it is appropriate to strengthen the stiffness of the outer part of the structure along the two main axes, and appropriately weaken the stiffness inside the structure.
4) When the second mode is torsional, it means that the anti-lateral shift stiffness of the structure along the two main axes is quite different, and the anti-lateral shift stiffness of the structure is reasonable relative to one of the main axes (the direction of the first mode angle); but the anti-lateral shift stiffness relative to the other spindle (the direction of the third mode shape angle) is too small, at this time, it is appropriate to weaken the stiffness of the structure along the "third mode shape angle direction", and appropriately strengthen the stiffness of the structure periphery (mainly along the first mode shape angle direction).
5) While making the above adjustments, care should be taken to make the cycle meet the requirements of the specification.
6) When the first mode is torsion, the cycle ratio certainly does not meet the requirements of the specification; when the second mode is torsion, the cycle is more difficult to meet the requirements of the specification.
Seventh, stiffness ratio: mainly to limit the vertical layout of the structure is irregular, to avoid structural stiffness along the vertical abrupt change, the formation of a weak layer. See SG 3.4.2, SG 4.4.2 and the corresponding provisions; for the weak layers formed, they are strengthened in accordance with SG 5.1.14.
How to adjust when the stiffness ratio does not meet the specification requirements:
1. Program adjustment: If the calculation result of the stiffness ratio of a certain floor does not meet the requirements, SATWE automatically defines the floor as a weak layer, and amplifies the seismic shear force of the floor by 1.15 times according to the height gauge 5.1.14.
2. Structural adjustment: If manual intervention is still required, it can be adjusted according to the following methods:
1) Appropriately reduce the height of the floor, or appropriately increase the height of the upper related floor.
2) Appropriately strengthen the stiffness of the walls, columns and beams of the floor, or appropriately weaken the stiffness of the walls, columns and beams of the upper related floors.
Eighth, the shear bearing capacity ratio between layers: mainly to limit the irregularity of the vertical arrangement of the structure, to avoid the shear bearing capacity of the floor anti-lateral force structure along the vertical abrupt change, the formation of a weak layer. See SR 3.4.2, SG 4.4.3 and the corresponding provisions; the weak layers formed should be strengthened in accordance with SG 5.1.14.
Adjustment method when the shear bearing capacity ratio between layers does not meet the requirements of the specification:
1. Program adjustment: Fill in the "number of designated weak layers" in SATWE's "Adjustment Information", and forcibly define the floor as a weak layer, and SATWE will enlarge the seismic shear force of the floor by 1.15 times according to the height gauge 5.1.14.
2. Structural adjustment: If manual intervention is still required, the strength of the components of the layer can be appropriately increased (such as increasing the reinforcement, improving the strength of the concrete or increasing the cross-section) to improve the shear bearing capacity of the anti-lateral force components such as the walls and columns of the layer, or appropriately reduce the shear bearing capacity of the anti-lateral force components such as the walls and columns of the upper relevant floors.
The adjustment of several parameters involves the change of the cross-section, stiffness and plane position of the component, which may be related to each other during the adjustment process, and care should be taken not to lose sight of the other.
It should be noted that for a combination system similar to the frame-shear structure, there is a problem of appropriate stiffness with each other. Analyzing the shear deformation curve of the frame and the curved deformation curve of the shear wall, it can be found that in the lower floor, the displacement of the shear wall is small, the displacement of the frame is larger, and the shear wall pulls the frame to limit its interlayer displacement angle; the upper layers are the opposite, the interlayer displacement angle of the shear wall gradually increases, the interlayer displacement angle of the frame gradually decreases, and the frame in turn pulls the shear wall to limit its interlayer displacement angle. Changing the stiffness and arrangement of the shear wall is the main means to control the displacement and cycle of the frame shear structure, so when the interlayer displacement angle of several layers in the upper layer of the frame shear structure is larger, it should be more effective to appropriately weaken the stiffness of the shear wall of these layers.
If the vertical orientation of the structure is more regular, only one standard layer of the structure can be built during the first trial, and other standard layers can be added after the cycle ratio, displacement ratio, shear weight ratio, rigid weight ratio, etc. of the structure are satisfied; this can reduce the repeated modifications in the modeling process and speed up the modeling speed.
to be continued
Correlation and stiffness control of the overall control parameters of the high-rise structure
The overall control of the structure is an important part of the seismic design of the high-rise structure, and the stiffness of each control parameter and the structural lateral force member have a direct or indirect relationship, so it is inevitably related to each other. Understanding the correlation between various control parameters can help improve the efficiency of overall structural control and help make structural design more economical and reasonable. This article will lead to this article and discuss this topic with you.
The process of overall control of the structure, that is, the process of controlling and adjusting the stiffness of the structure. In the control parameters, the displacement ratio and period ratio are not only related to the stiffness of the structure, but also to the distribution of the stiffness of the structure. These two parameters reflect the torsional effect of the structure, which is the difficulty of the overall control of the structure, and also the starting point of the overall control of the structure.
Displacement Ratio & Period Ratio: Since the displacement ratio is calculated under the assumption of "full floor rigid floor slabs", each floor slab is assumed to have infinite stiffness within the floor plan. Because the calculation of the displacement ratio takes into account accidental eccentricity, so that under the action of horizontal seismic forces, even a regularly symmetrical structure cannot be purely translational, and its maximum horizontal displacement and interlayer displacement must occur somewhere in the corner of the floor. Therefore, in general, the displacement ratio is determined by the horizontal displacement and interlayer displacement in the corners of the structure. Therefore, adjusting the stiffness of the peripheral resistance member of the structure is the most effective way to control the displacement ratio. The control of the cycle ratio is that the structure has sufficient torsional stiffness, and the peripheral resistance components of the structure contribute the greatest to the torsional stiffness of the structure. Therefore, when adjusting the stiffness of the peripheral resistance member of the structure to control the displacement ratio, it will inevitably have a greater impact on the cycle ratio. Considering the impact on the cycle ratio, when adjusting the displacement ratio, especially when the cycle ratio is close to the specification limit, care should be taken not to weaken the stiffness of the peripheral resistance member of the structure. Similarly, adjustments to the cycle ratio may also affect the displacement ratio. Especially when the displacement ratio in a spindle direction is close to the normative limit, the adjustment of the stiffness of the opposing lateral force member should be as symmetrical as possible with the center of mass of the structure as the center.
Cycle ratio & Shear weight ratio: Analyzing the reaction spectral curve (seismic coefficient curve) can be found that when the self-resonance period of the structure exceeds the characteristic period, the seismic influence coefficient shows a decreasing trend, and in the case of a small self-resonance period, the decrease is faster. That is to say, the larger the period of the structure, the smaller the role of the earthquake; the smaller the period of the structure, the greater the role of the earthquake. Using this law, when the shear weight ratio of a certain spindle direction of the structure does not meet the requirements of the specification, the self-vibration period of the structure can be reduced by strengthening the stiffness of the spindle direction, so as to increase the seismic effect of the structure and then increase the shear weight ratio. The self-resonance period of the structure can also be controlled within the appropriate range according to the reaction spectral curve to obtain greater seismic action or reduce seismic action. Similarly, when adjusting the cycle ratio, it should also be treated differently according to the size of the shear weight ratio, when the shear weight ratio of a spindle direction is less than or close to the specification limit, it is advisable to strengthen the stiffness of the peripheral anti-lateral force member of the spindle direction structure; when the shear weight ratio in the direction of a spindle is greater than the normative limit, it is advisable to weaken the stiffness of the internal anti-lateral force component of the spindle direction structure to obtain better economic and technical indicators.
Displacement ratio & shear weight ratio: As mentioned earlier, the adjustment of the displacement ratio will affect the self-vibration period of the structure, which in turn will affect the seismic effect of the structure, so that the shear weight ratio of the structure will change. Therefore, when adjusting the displacement ratio, it should be treated differently according to the size of the shear weight ratio, when the shear weight ratio of a spindle direction is less than or close to the normative limit, it is advisable to strengthen the stiffness of the anti-lateral force member on the side of the structural rigidity relative to the eccentricity of the centroid; when the shear-weight ratio in the direction of a spindle is greater than the normative limit, it is advisable to weaken the stiffness of the anti-lateral force member relative to the other side of the centroid eccentricity of the structure. Similarly, adjustments to the shear-to-weight ratio may also affect the displacement ratio. In particular, when the displacement ratio of a spindle direction is close to the specification limit, the adjustment of the stiffness of the anti-lateral force member in the direction of the spindle at this time should be as symmetrical as possible with the center of mass of the structure as the center.
Displacement Ratio & Rigid Weight Ratio: Analyzing the definition of the rigid-to-weight ratio, it can be found that the rigid-to-weight ratio is proportional to the lateral shift stiffness of the structure. That is, in the case that the quality of the structure remains basically unchanged, the greater the lateral shift stiffness of the structure, the greater the stiffness of the lateral shift of the structure, and the smaller the stiffness of the stiffness-to-weight ratio. As mentioned earlier, the adjustment of the displacement ratio will cause a change in the stiffness of the lateral shift of the structure, which will affect the stiffness-to-weight ratio. Therefore, when adjusting the displacement ratio, it should be treated differently according to the size of the rigid-to-weight ratio, when the stiff-to-weight ratio of a spindle direction is less than or close to the normative limit, it is advisable to strengthen the stiffness of the anti-lateral force member on the side of the structural rigidity relative to the eccentric center of the mass; when the stiff-to-weight ratio of a spindle direction is greater than the normative limit, it is advisable to weaken the stiffness of the anti-lateral force member in the rigid center of the structure relative to the other side of the centroid eccentricity. Similarly, adjustments to the stiff-to-weight ratio may also affect the displacement ratio. In particular, when the displacement ratio of a spindle direction is close to the specification limit, the adjustment of the stiffness of the anti-lateral force member in the direction of the spindle at this time should be as symmetrical as possible with the center of mass of the structure as the center.
Cycle Ratio & Rigid Weight Ratio: As mentioned earlier, the rigid weight ratio is directly proportional to the lateral shift stiffness of the structure; the adjustment of the periodic ratio will lead to a change in the lateral shift stiffness of the structure, which will affect the stiffness of the stiffness of the stiffness of the structure. Therefore, when adjusting the cycle ratio, it should be treated differently according to the size of the rigid-to-weight ratio, when the stiff-to-weight ratio of a spindle direction is less than or close to the normative limit, it is advisable to strengthen the stiffness of the external anti-lateral force component of the spindle direction structure; when the stiffness-to-weight ratio of the spindle direction is greater than the normative limit, it is advisable to weaken the stiffness of the internal anti-lateral force component of the spindle direction structure to obtain better economic and technical indicators. Similarly, adjustments to the rigid-to-weight ratio may also affect the cycle ratio. Especially when the cycle ratio of the structure is close to the specification limit, it is advisable to strengthen the stiffness of the peripheral resistance lateral force member of the structure.
Shear Weight Ratio & Rigid Weight Ratio: As mentioned earlier, both parameters are closely related to and proportional to the stiffness of the structure. When the stiffness of the structure changes, the trend of change of these two parameters is basically the same. When the shear weight is relatively small, such as less than 0.02, the stiffness of the structure can meet the requirements of the horizontal displacement limit, but often cannot meet the requirements of the stiff weight ratio. Both of these parameters reflect the absolute demand for stiffness of the structure and must be met at design time.