Selection of length and width of steel structure workshop
time：2020-07-19 count： source：sunwaysteel
1. Selection of length and width of steel structure workshop
Generally speaking, when arranging column nets for steel structures, the principle that the length is greater than the width should be followed, which can reduce the steel consumption of the rigid frame, and also reduce the wind load of the support between the columns, thereby reducing the steel consumption of the support system.
Example 1: The engineering size of the steel structure factory building is 60×50m, when the factory building is arranged, 60m should be taken as the length direction and 50m as the span direction, that is: 60(L)×50(W) instead of 50(L)×60 (W).
The technical and economic comparison shows that the most economical column under the standard load is 8~9m. When it exceeds 9m, the steel consumption of the roof purlin and wall frame system increases too much, and the overall cost is not economical. The standard load here refers to: roof live load 0.3KN/m2, basic wind pressure 0.5KN/m2, when the load is greater, the economic column distance should be reduced accordingly. For factories with more than 10 tons of traffic, the economic distance should be 6~7m.
When arranging column spacing, if unequal column spacing is required, the end span should be arranged as small as possible than the middle span. This is because the wind load of the end span is larger than the middle span. In addition, when using a continuous purlin design, the end The deflection and span of the span are always greater than other spans. The use of a smaller end span can make roof purlin design more convenient and economical.
Example 1: Engineering length of steel structure workshop = 70m
Economic column spacing is desirable: 1@7 + 7@8 + 1@7 or 1@8 + 6@9 + 1@8
Example 2: Engineering length of steel structure workshop = 130m, driving 10 tons
Economic column distance is desirable: firstname.lastname@example.org + 17@7 +email@example.com or firstname.lastname@example.org
III. Determination of the reasonable span of steel structure workshop
Different production processes and use functions determine the span of the plant to a large extent, and some owners even require light steel manufacturers to determine a more economical span according to their use functions. In order to meet the production process and use function as much as possible, a reasonable span should be determined according to the height of the house. Under normal circumstances, when the column height and load are fixed, the span is appropriately increased, the steel consumption of the rigid frame is not obvious, but it saves space, the basic cost is low, and the comprehensive benefit is considerable. Through a large number of calculations, it has been found that when the eaves height is 6m and the column distance is 7.5m, and the load conditions are completely consistent, the steel amount per unit (Q345-B) of the rigid frame with a span between 18-30m is 10-15kg/m2, when the span The steel consumption per unit of the rigid frame between 21-48m is 12-24kg/m2. When the eave height is 12m and the span exceeds 48m, the multi-span rigid frame (swing column in the middle) should be used. The frame saves more than 40%, so when designing the portal rigid frame, choose a more economical span according to specific requirements, and it is not suitable to blindly pursue a large span.
Fourth, the choice of steel structure roof slope
The slope of the roof needs to be determined according to the comprehensive factors such as the structure of the roof slab, the length of the drainage slope and the height of the column structure, and generally takes 1/10~1/30. Studies have shown that different roof slopes have a greater impact on the steel consumption of the rigid frame.
The following are the results obtained by calculating and analyzing the steel consumption under different roof breakages with a single span of 42m and a cornice height of 6m:
When the roof breakage is 0.5:10, the weight of one frame is: 3682 Kg
When the roof breakage is 1.0:10, the weight of one frame is: 3466 Kg
When the roof breakage is 1.5:10, the weight of one frame is: 3328 Kg
When the roof breakage is 2.0:10, the weight of one frame is: 3240 Kg
It can be seen that for a single-span rigid frame, a better way to reduce the weight of the rigid frame is to increase the roof slope, the greater the slope, the more steel is saved.
However, the situation is different for multi-span frames. Large slope will increase the amount of steel used for the frame. This is because the large breakage will cause the inner column length to increase. When the span of the steel structure factory building is large, the increased breakage can reduce the deflection of the steel stain on the roof.
Calculated through research, the more economic slope is:
Multi-span building: 1:20
Single span, span less than 45m: 0.5:10
Single span, span less than 60m: 1.5:10
Single span, span greater than 60m: 2.0:10
In fact, the choice of roof slope is also related to whether the building has parapets. Increasing the slope will cause the cost of parapets to increase.
Fifth, the selection of the height of the cornice of the steel structure workshop
The height of cornice has a great influence on the cost, which is mainly manifested in the following aspects
1. Increasing the height of the cornice will increase the area of the wall panel, increase the purlin of the wall, and increase the amount of steel used for the column;
2. If the steel column has no lateral support (such as the center column or the side column cannot be equipped with corner bracing), the influence of the cornice height on the weight of the frame will be more prominent;
3. Increasing the height of the cornice will cause an increase in the wind load acting on the frame. If the cornice height/building width is >0.8, in order to control the lateral displacement, sometimes it is even necessary to change the column foot from hinge to rigid connection.
The height of the cornice is determined by the following factors:
1. The net height requirement at the cornice;
2. When there is an interlayer, the net height requirement of the interlayer and the height of the interlayer beam;
3. When there is a crane, the height of the crane beam and crane hook.
Six, temperature section
According to the light steel regulations, the maximum longitudinal length is not more than 300m, and the horizontal direction should not be more than 150m. The expansion joints in the longitudinal temperature section can be arranged in a double-column arrangement, or a single-column expansion joint with elliptical holes can be connected to the purlin.
What needs to be explained here is that the maximum length specified in the regulations is not the length allowed by all buildings. For different buildings, according to the use conditions of the steel structure plant project itself, the natural conditions of the location, and the largest temperature zone that can be calculated according to the calculation.
Seven. Steel structure factory support arrangement
(1) The role of support
Between each temperature section of the portal frame grid, a complete supporting system should be arranged to form a complete spatial structure system. The lateral stability of the light portal frame in the width direction is guaranteed by the rigidity of the frame to resist the lateral load. Because the longitudinal structural rigidity in the longitudinal direction is weak, it is necessary to provide support along the longitudinal direction to ensure its longitudinal stability. The forces on the support are mainly longitudinal wind load, crane braking force, earthquake action and temperature effect. When calculating the internal force of the support, it is generally assumed that the node is hinged, and the effect of eccentricity is ignored, and the general support is considered according to the tie rod. Therefore, it is generally suitable for two-way arrangement.
(2) Common types of support
The figure shows the general arrangement of the layer supports and the transmission path of the force of the wind load acting on the gable. The type of inter-column support commonly used for light portal frame is shown in the figure. Due to building function and appearance requirements, or the arrangement of process equipment, when the above supports are not allowed to be used, consider using a vertical frame. At this time, it is necessary to use the bending stiffness of the weak axis of the column
(3) Basic principles of support structure for steel structure workshop
1. Although some roofing panels have a certain skin effect, this effect is currently difficult to quantify, so this skin effect cannot be considered when designing the support;
2. The inter-column support should be set at the same span as the roof support as much as possible. When the wall cannot be installed due to the door opening, the inter-column support can be set at the pro-span;
3. Generally speaking, the spacing of supports should not exceed 5 spans; when there is no crane, it should be 30~45m; when there is a crane, the spacing should not be more than 60m;
4. The roof support needs to be disconnected at the ridge.
5. The following situations need to consider setting up a vertical horizontal roof support
(1) When there is a pumping column, such as a partial pumping column, only a partial longitudinal support is required;
(2) When the column distance is large and the side column adopts the scheme of false wall frame column;
(3) The crane has a tonnage greater than 15 tons and has a cab.
6. When the width of the steel structure plant is greater than 60m, it is appropriate to increase the inter-column support in the inner column. When the cross support cannot be arranged, the support form of Figures 3-4b and 3-4c can be used. It is also possible to increase the specifications of roof support or inter-column support without adding internal inter-pillar support. In this case, internal force calculations must be strictly performed to ensure the safety of the support.
7. In the same column, different types of supports should not be mixed, otherwise the support with small stiffness will have less stress and will not play its due role, and the support with high stiffness will be damaged due to overload work. Inter-column supports should preferably use cross supports.
8. In the following cases, the support between the columns of the steel structure factory building needs to be set in layers.
(1) When there is a high and low span (or with a long long canopy), the upper and lower supports between the columns need to be layered at the high and low span (or the big canopy);
(2) When the cornice height is greater than 9m, double-layer column support can be set according to the angle of the support. The angle between the cross support and the horizontal plane is preferably 45°, and should not be greater than 55°;
(3) When there is a crane, the upper support and the lower support between the columns need to be layered at the crane beam. No lower support is required in the end bay to reduce the temperature stress of the crane beam.