Steel Structure Design common issues
1, a portal frame quiz to see bending moment diagram, you can see the moment, but the moment and I do not know what relationship the member section?
A: Bending member bending capacity of Mx / (γx * Wx) + My / (γy * Wy) ≤f wherein W is a sectional resistance moment sectional resistance moment can be manually counted roughly sectional
2, H-shaped steel is butt what provisions?
A: like how to pick how to pick, huh main consideration is the moment and / or shear transfer In addition, the dynamic loads more in the place, especially the careful design of welded joints to be flush.:
3, "tight flat top plane", no longer plane flattened tight after welding it?
A: Grinding is a top tight way power transmission, multi-position to withstand dynamic loads. To avoid fatigue cracks of the weld and take a power transmission mode. Not required polished top tight welding, welding is also required. See specific drawings. Contact surface finish requirement of not less than 12.5, check the contact area with a feeler. Planing flat top tight purpose is to increase the contact surface of the contact area, generally used in a certain horizontal displacement, simply supported node, and this node should have other connections (such as the top tight flange, it is possible to use the web bolted).
This node requires a general plane flattened tight welded parts do not need to be welded, then flattened tight plane in the welding melt is not conducive to the depth and weld quality will be poor, even if the welding site without groove We will not ask the top tight. Tight top and welding are mutually contradictory, so the above said top tight then welded parts are not accurate, but there is also a situation may arise top tight welding, node is the top tight constraints on the other degrees of freedom is not enough, and no other parts serving constraints, it is possible in the top tight welding parts to constrain the freedom of the other direction, which is a mounting weld seam, it is impossible to fully welded, but can not be used as the main force welds.
4, steel structure design, the deflection limit is exceeded, what will the consequences later?
A: The appearance affect the normal use or modification; or affect the normal use of the durability of the local damage (including crack); vibration affect the normal use; other specific status affect the normal use.
5. What is the role of extruded plate?
A: extruded polystyrene (XPS) insulation boards, polystyrene resin as the main raw material, through a special process of continuous extrusion molding of rigid foam sheet. Has a unique perfect closed cellular structure, anti-pressure, moisture-proof, airtight, non-absorbent, corrosion resistance, low thermal conductivity, light weight, long life, high-performance environment-friendly materials. Extruded polystyrene insulation board is widely used in wall insulation, cold storage facilities, parking platforms, building concrete roof pole roof structure and other areas of moisture-proof inexpensive decoration materials. Extruded plate has excellent long-lasting features: extruded plate stable performance, not aging. Available 30 - - 50 years, extremely excellent resistance to moisture, water vapor at high pressure environment, still able to maintain a low thermal conductivity. Insulation extruded plate with unparalleled performance: extruded plate having a closed-cell performance due to the structure, and the obturator rate of 99%, so its good insulation properties. While closed-cell urethane foam structure, but less than its closed-cell extruded sheet, only about 80%. Extrusion plate either insulation, compressive strength or water absorption characteristics and other aspects are better than other insulation materials, so the insulation performance but also in other insulation material can match. Compressive strength extruded plate having unexpected: compressive strength extruded plate can be achieved according to their different thickness models 150--500 kPa or more, while the compressive strength of other materials is only 150--300 kPa above it is apparent that the compressive strength of other materials, much lower than the compressive strength extruded plate. Extruded plate having a foolproof water absorption: for under the pavement and roadbed, effective water penetration. Especially in the north can reduce the occurrence of frost and frost affected by soil freezing, etc., the situation of ground frost heave control, effective moisture barrier to air from destruction.
6. What is the slenderness ratio of the radius of gyration:? Under the root (moment of inertia / area) slenderness ratio = Length / radius of gyration
A: The structure of the slenderness ratio λ = μl / i, i is the radius of gyration slenderness ratio. The concept can be seen from a simple formula out: slenderness ratio that is the ratio of the length of its corresponding component calculated radius of gyration. As can be seen from this formula concept slenderness ratio considering the end restraint conditions, the length of the section properties and member itself member member. Slenderness ratio concept for the affected strut member stability calculation is obvious, because the easier slenderness ratio greater destabilization. You can look at the formula on axial compression and bending member, which has the slenderness ratio related parameters. For tension member specification also gives the slenderness ratio limits, which is to ensure the rigidity in the member state of transportation and installation. Stability requirements for higher member, to regulate the stability limit is smaller.
7, compression flange buckling of curved beams, is buckling along the weak axis I-beam, or the strong axis buckling?
A: When the load is not big, basically the beam in its largest plane bending rigidity, but when the load reaches a certain value, the beam will also have a greater lateral bending and torsional deformation, and soon the final loss to continue carrying ability. At this point the overall instability of the beam must be curved lateral bending and torsion.
Guangzhou Steel Solution roughly three ways:
1, increase the lateral support points of the beam or narrow lateral spacing of the anchor
2, adjust the cross-section of the beam, the beam increases lateral moment of inertia Iy or simply increasing the compression flange width (such as crane beam flange)
3, beam end bearing constraints section, the carrier if they can provide rotational restraint, the overall stability of the beam can greatly improve
8, Guangzhou, why not design of steel structures steel beam torsion calculation?
A: Under normal circumstances, the opening cross-section steel beams are (except box section), its torsional section modulus of about one order of magnitude smaller than the bending section modulus, that is, its ability to torsion about Bending 1 / 10, so that if the use of steel beams to withstand the torque uneconomical. So, usually constructed to ensure that it is not twisted, so the design of steel structures is not twisted steel beams by calculation.
9, without the use of cranes capitals displacement limit when masonry walls is h / 100 or h / 240?
A: Strut procedure has indeed been errata this limit, mainly capitals displacement of 1/100 can not guarantee that the wall is not pulled crack. If the puzzle in the same time frame inside the wall (eg inner wall), when we calculate capitals displacement is not considered the role of embedded solid wall of the frame (frame structure likened to a little exaggeration).
10, what is the maximum rigidity of the plane?
A: The biggest is the rigidity of the plane about the strong axis plane, there are two general cross-section axis, wherein the rotational moment of inertia around one of the large, called a strong axis, the other will go weak axis.
11, instead of a straight seam steel seamless pipe, do not know can not be used?
A: structural steel in theory, should be the same, the difference is not great, as good as seamless Longitudinal rules pipe centroid is likely not in the center, so when used as a compression member with particular attention to the presence weld pipe the probability of defects is relatively high, an important part of irreplaceable seamless pipe, seamless pipe wall thickness restricted process can not be made very thin (seamless pipe wall thickness than the average thickness of pipe the same diameter), many the case of seamless pipe material use efficiency is better, especially the large-diameter pipe.
The biggest difference is seamless and welded pipe used in gas or liquid pressure transmission (DN).
12, shear lag and shear lag What's the difference? What are their respective focus is?
A: shear lag is a common phenomenon in structural engineering mechanics, small as a member, to a large high-rise building, there will be shear lag phenomenon. Shear lag, sometimes called shear lag, say from mechanical in nature, is the Saint-Venant principle, specific performance is within a range of local, shear can play a limited role, the normal stress distribution is uneven, the this uneven distribution of normal stress phenomenon called shear lag.
Openings formed on the wall of the cylinder, also known as fasting frame tube, after the openings, so that deformation due beam shear transfer lag phenomenon, so that the column CKS stress distribution is parabolic, called shear lag phenomenon.
13, the force will lengthen the length of anchor bolts pillar of what impact?
A: The anchor axial tensile stress distribution is uneven, an inverted triangular distribution, the maximum upper axial tensile stress, lower axial tensile stress to zero. Anchoring depth increases, the stress gradually decreases, and finally to 25 to 30 times the diameter when reduced to zero. Therefore, additional anchorage length is no use. As long as the anchorage length to meet the above requirements and ends with a hook or anchor plates, concrete foundation is generally not pulled bad.
14, the similarities and differences guidelines stress amplitude and stress ratio guidelines and their respective characteristics?
A: For a long time fatigue design of steel structures has been carried out according to the guidelines stress ratio for a certain number of load cycles, fatigue strength and stress σmax member cycle characteristics to stress ratio R is represented by closely related to the introduction of a safety factor of σmax. design can be obtained fatigue stress allowable value [σmax] = f (R)
The stress is limited to [σmax], which is the stress ratio criterion.
Since welded structures to withstand fatigue loads since, from engineering practice and come to realize that such structures are not closely related to the fatigue strength of the stress ratio R, but the stress amplitude Δσ. The formula is Δσ≤ guidelines stress amplitude Δσ [] [Δσ] is the allowable stress amplitude, which ships with construction details differ, but also with the destruction of pre-change cycles. welded structure fatigue calculation wish to stress amplitude as a criterion, because the internal structure of the residual stress non-welded components. for R> = 0 of stress cycles, stress amplitude criterion is fully applicable, because there is no residual stress and residual stress on fatigue strength or less. for R <0 stress cycles, using the guidelines stress amplitude is somewhat more secure.
15, what is the hot-rolled, cold-rolled what is, what is the difference?
A: hot rolled steel at 1000 degrees with a roller extrusion, thermal deformation usually small 2MM thick plate steel, high-speed machining has arrived in less than steel cooling area is increased, that is no guarantee that a temperature above 1000 degrees to process but to sacrifice the hot rolling process cheap and efficient method, rolling at room temperature, that hot-rolled and cold rolled to a thinner thickness to meet the market requirements. Of course, cold-rolled and bring new benefits, such as hardening, the steel strength increases, but not welding, soldering at least eliminated hardening, high strength and no the back of the strength of its hot-rolled, cold-formed steel available hot rolling material, such as steel, can also be used cold rolled sheet, cold rolled sheet or hot-rolled sheet, it is a criterion 2MM thick, the thinnest 2MM thick hot-rolled, cold rolled sheet thickest 3MM.
16. Why should the beam bending member stability calculation in a plane out of the plane, but can be calculated only when the gradient of the plane of stability can be?
A: The only external beam plane instability form. He never says that instability within the beam plane. The column is, when there is axial force, plane and calculate the length of the plane is different only in-plane and out of plane buckling checking. Of frame beams, despite the call for the beam, the number of total internal force is part of the axial force, so strictly speaking it should be checking column model, ie outside the plane of plane bending member had considered stable . But when the roof slope is small, the axial force is small and can be ignored, it can be used beam model, that is, without calculation stable plane. Door gauge the meaning (P33, Section 6.1.6-1 article) refers to when the roof slope less inclined beam member in a plane just to calculate strength, but out of the plane still considered stable.
17, why the secondary beams are typically designed with the main beam articulated?
A: If the secondary beam and the main beam rigid connection on both sides of the main beam in the same location has the same load of girders Fortunately, no words secondary beam end moment for the main beam is twisted out of the plane, but also to calculate torsion, involve torsional stiffness, moment of inertia of the fan and the like. Further rigid connection to increase the workload of the construction, greatly increased the workload of field welding. More harm than good, generally do not need secondary beam is not made rigid connection.
18, high-strength bolts of how to calculate the length?
A: The high-strength bolts screw length = 2 adapter plate thickness + thickness of a nut gasket thickness +2 +3 wire port length.
19. What is the physical concept of carrying capacity after buckling is?
A: Carrying Capacity postbuckled mainly refers to the ability of local buckling could continue after the member hosted, mainly in thin-walled structures, such as a cold-formed steel, using the effective width method in the calculation considering the bearing capacity after buckling. The size of the post-buckling bearing capacity depends on the constraints to-thickness ratio of the plate and the plate edge, generous ratio, the better the constraints, the higher the bearing capacity after buckling. On analysis, the current domestic and international norms primarily using the effective width method. But the factors in the calculation of national codes effective width considered different.
20, what is the plasticity algorithm? What is considered post-buckling strength
A: Plastic algorithm means statically indeterminate structure envisioned by the site reaches the yield strength of the emergence of plastic hinge, and thus achieve the purpose of the plastic internal force redistribution, and must ensure that the structure does not form a variable or transient system. After considering buckling strength means that the web still has a flexural members after the loss of local stability of a certain capacity, and using a full member after buckling strength of its calculation.
21, soft and hard hook crane hook What is the difference?
A: soft hook Crane: refers rope, hook lifting heavy objects. Hard crane hook: is lifting heavy objects, such as clamps, feed rake through the rigid body. Crane hook hard work frequently. High speed, the car attached to the cantilever structure so rigid hoist can not swing freely.
22, what is rigid tie rod, what is the flexible Tied?
A: That is a rigid tie bar tension can be compressed and can generally use double angle and pipe, but only tensile flexible bars, generally use single-angle or tube.
23, slenderness ratio and deflection is what to do with it?
A: 1. Deflection is the amount of deformation after loading member, that is, the displacement value. 2. "slenderness ratio used to indicate the axial stiffness of force by members of the" slenderness ratio should be material in nature. Any member can have properties that axial stiffness force member, you can use the slenderness ratio to measure. 3. deflection and slenderness ratio are completely different concepts. Slenderness ratio is the ratio of the length and cross section of the rod calculate the radius of gyration. Deflection displacement value of a point after the member force.
24, what grade earthquake that four grades specifically how the division?
A: The seismic level: one, two, three, four. Seismic intensity: 6,7,8,9 degrees. Seismic categories: A, B, C, D four categories. Earthquake level: regular earthquake, occasional earthquake, less earthquake, rare earthquake.
25, as bracing can support it? And other support is the difference?
A: 1, bracing and support structure are the two concepts. Bracing steel beam cross-section to ensure stability, and is used to support the steel structure together to form a stable system and ensure its deformation and bearing capacity to meet the requirements. 2, bracing as a steel beam compression flange plane fulcrum. It is used to ensure the overall stability of the steel beams.
26, what is to be considered by the steel axial tension member design?
A: 1, without fatigue static loads, residual stress has no effect on the bearing capacity of the trolley. 2, the rod cross-section if there is a sudden change, the change of the stress distribution is no longer uniform. 3, the design should yield as a lever bearing capacity limit state. 4, the bearing capacity limit state to consider both gross and net section from the cross-section. 5, to consider the efficiency of the net section.
27, how to calculate the stiffness of spring steel columns? What formula is? Spring stiffness concrete columns and concrete columns are how to calculate the stiffness of the spring ring beam when? What formula is?
A: The spring stiffness is considered by column cantilever member, in the role of a unit force capitals to calculate the lateral displacement caused by this displacement is the spring stiffness, the unit is generally KN / mm ring beam if there is a case, no circle. beam direction constraint, spring rate calculated with the boom member in the other direction, because there are capitals ring beam, so the sum of the calculation formula of EI for the direction of all columns.
28. What is the skin effect?
A: In the vertical loads, movement trend crest portal frame roof is down, the roof outward deformation. The roof in the form of deep beams together to resist this trend and modification support purlins. In this case, the roof to withstand shear, act deep beam web. The edge of the purlin to withstand axial forces from deep beam flange effect. Obviously, the roof shear resistance is much greater than the resistance to bending. Therefore, the skin effect refers skin panels because of their shear stiffness for the inner plane of the plate resistant to deformation effect of load [26] [28] [29]. For the top of the hill portal frame to resist vertical loads skin effect depends on the roof slope, the greater the slope of the skin effect is more significant; and resist lateral loads of the skin effect increases with decreasing slope.
Constitute the entire structure of the skin effect is skin cells. Skin cells from the skin plate frame between two specimens, the edge member and the connecting member and the intermediate member, as shown in Figure 2-6. Edge member refers to two adjacent frame side beams and purlins (roof and eaves purlin), the intermediate member refers to the middle of the purlins. Key performance indicators skin effect is strength and stiffness.
29, in terms of specification 8.5.6, the transverse stiffeners crane beam, which should end in the ribs landing arc, what is the meaning?
A: refers to the stiffener end to continuous welding, such as welding take around the corner, around the welding and other methods. Prevent fatigue caused cracks in the web.
30, the inner box column separator last welding seam is how to do this?
A: electroslag welding, quality assurance is easy!
31, cantilever and cantilever column length factor is different, how to explain?
A: cantilever length factor 1.0, the cantilever column length factor 2.0. Column is bending member, or simply under pressure to consider the stability factor, so take two. Curved beams, it should be the distinction.
32, the deflection in the design does not meet specifications, to ensure that by bagging Can do this?
A: 1, the deflection control structure is normal limit state design. For steel, the deflection is too large easily affect roof drainage, inflict fear, for a concrete structure deflection is too large, it will cause local damage durability (including concrete cracks). I think, because of structural deflection caused by too much more damage can be solved by bagging. 2, bagging some structure is as easy as double slope portal frame beams, if absolutely overrun deflection can be adjusted by increasing the slope of the roof in the production. Some bagging structure is not easy, such as for large-span beams, if the relative deflection overrun, then each beam should bagging, bagging the beam due after stitching as polylines and curves for the deflection of the two lines is difficult to coincide, It will cause uneven roof. For flat beam frame is harder camber, you can not make the flat beam arc line. 3, if you are prepared to bagging a way to reduce the amount of steel by the deflection control structure to reduce the deflection control provisions, when necessary to control the deflection under live load, dead load deflection by bagging to ensure .
33, what is the center of the seat pad paste method of steel column?
A: Install the central steel column base plate slurry method, while saving time and labor, construction accuracy can be controlled within 2mm, can improve the overall efficiency of more than 20%. Construction steps are as follows: (1) according to the construction diagram steel column foundation construction (construction methods as usual), the basis of the above than the bottom surface of the steel columns installed standard level 30 ~ 50mm, to prepare slurry placed center seat pad, (2) based on steel column weight Q, bolt preload F, foundation concrete compressive strength P, calculate the minimum pressure area Amin. (3) steel sheet with a thickness of 10,12mm made into square or round plate plasma center seat, the area should not be less than twice the minimum bearing area of Amin. (4) has been completed on the basis of attendance pulp slurry and placed center seat pad. Required foot level, a level, and other tools for the construction of precise measurements to ensure that the center plate levelness, to ensure consistency with the center plate mounting axis, elevation and ensure steel columns installed above the bottom surface of the pad elevation consistent. (5) to be seat in coated concrete strength of more than 75% of the design strength of steel columns were lifting. Lifting steel columns can be directly, simply by adjusting the bolt to be leveling alignment. (6) secondary grouting, shrink-free concrete or micro - expansion concrete. Secondary grouting.
34, axial compression members with small deflection and bending buckling large deflection theory, I would like to know that a small deflection and small deformation theory What is the difference?
A: The small deformation theory is to say structural changes in the deformed geometry can not be considered, based upon the size before deformation when the internal force calculation! Here Transformations include all variants: tensile, compression, bending, shear, torsion, and combinations thereof. Small deflection theory that displacement is very small, are linear geometry problems, you can go with a deflection curve equation approximation in order to establish energy derived = 1 / ρ instead of a stability factor, deformation curvature can be approximated by y "! With Y`` instead of the curvature, is used to analyze the elastic rod small deflection theory. in the rigid rod with a spring inside, is not the case. also, the analysis with a large deflection theory, does not mean that after buckling load can increase, for example, cylindrical shell pressure, only buckling after holding steady at lower loads. simply put, small deflection theory can only get critical load, can not be judged stable or critical buckling load after big deflection after buckling theory can be solved performance.
35. What is a second order moment, second elastoplastic analysis?
A: For many structures, often undeformed structure as computation graph for analysis, the results accurate enough. In this case, the resulting deformation between load and linear relationship, this analysis method known as linear geometric analysis, also known as the First Order (First Order) analysis. And for some structure, the structure must be deformed as the calculation basis for analysis of internal force, otherwise the results on a large error. In this case, the relationship between deformation and load the resulting non-linear analysis. This analysis method is called geometric nonlinear analysis, also known as the Second Order (Second Order) analysis. Structural deformation as the calculation basis, and consider the elastic-plastic material (material nonlinearity) for structural analysis, is the second order elastoplastic analysis.
36, what is "Bauschinger effect" big impact on the steel structure design it?
A: The package is in effect after the new grid material plastically deformed, the deformation can not be restored after the break load left, this deformation is plastic deformation, this deformation of the structure would affect the course and can only think of!
37, what is like layers of steel tear?
Lamellar tearing occurrence steel sheet in the thickness direction is generally greater tensile stress in welded joints, the weld cooling, will produce shrinkage: A. If thin or no constraints on the deformation, deformation of the steel sheet to release stress. However, if the plate is very thick or stiffeners constraint plate adjacent plates are constrained from free deformation, will have a lot of stress in the direction perpendicular to the plate surface. Constrained strong regional, local stress caused by shrinkage of the weld may be many times greater than the yield limit of the material, causing the steel to produce lamellar tearing.
38, brittle fracture of steel or steel refers to steel tensile stress below the yield or failure occurs suddenly rupture strength of the case.
A: Guangzhou Steel particular welded structure, due to steel manufacturing, welding quality and construction on, there is often similar to that of crack defects. Mostly due to brittle fracture resulting in the development of these defects unstable crack growth occurs when the slow crack growth to a certain extent, that is a very high rate of fracture extension, without any warning before the sudden brittle fracture, damage.
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