1  When the portal frame looks at the bending moment diagram, the bending moment can be seen, but what is the relationship between the bending moment and the section of the component?

 

The flexural bearing capacity of the flexural member is Mx/(γx*Wx)+My/(γy*Wy)≤f, where W is the cross-section resistance moment and the approximate cross section can be manually calculated according to the cross-section resistance moment.

 

2  What is the definition of H-beam flat connection?

 

The main consideration is how to connect the bending moment and/or the shear force. In addition, where the dynamic load is high, the design of the welded joints should be particularly careful.

 

3 “Plane and flat top”, do you not need to weld again after the planer is tight?

 

Polishing is a kind of force transmission method, which is mostly used to bear the position of dynamic load. A force transfer method to avoid fatigue cracking of welds. There is a requirement to polish the top and not weld, and there is also a requirement for welding. Look at the specific drawing requirements. The contact surface requires a finish of not less than 12.5, and the contact area is checked with a feeler gauge. The purpose of planing the top is to increase the contact area of ​​the contact surface. It is generally used in nodes with a certain horizontal displacement and simple support, and such nodes should have other connection methods (such as the flange is tight, the web may be used). Bolted).

 

Generally, such a joint requires that the parts that are flattened and tightly pressed do not need to be welded. If welding is required, the planing top is not conducive to the deepening of the melt during welding, the quality of the weld will be poor, and the welded part will not be opened. It will not require a tight top. The top tightening and the welding are contradictory, so it is not accurate to re-weld the top tight parts. However, there is also a possibility that the top tight welding may occur, that is, the tightly packed nodes have insufficient constraints on other degrees of freedom, and there are no other parts. Providing constraints, it is possible to weld at the top tightness to constrain the freedom in other directions. This weld is a type of weld that is not fully welded and is less likely to be used as the main stressed weld.

 

4 When the steel structure is designed, the deflection exceeds the limit, what will happen?

 

Affecting the deformation of normal use or appearance;

 

Local damage (including cracks) that affect normal use or durability;

 

A vibration that affects normal use;

 

Affects other specific states of normal use.

 

5  What is the role of polyurethane composite panels?

 

Henan tens of thousands of polyurethane composite panels are generally used for the wall roofing outer panels of buildings. The panels have good insulation, heat insulation and sound insulation effects, and polyurethane does not support combustion and meets fire safety. The combination of the upper and lower plates and polyurethane has high strength and rigidity. The lower layer is smooth and flat, and the lines are clear, which increases the indoor appearance and flatness. It is easy to install, short in construction and beautiful in appearance. It is a new type of building material.

 

The visual effect of moving the scene. Combining a three-dimensional effect with an elegant decorative effect, the wall gloss, chromaticity, and brightness produce distinct bright and dark stripes depending on the angle and position of the light.

 

6 What is the slenderness ratio?

 

Radius of gyration: under the root number (inertia moment/area), slenderness ratio = calculated length / radius of gyration

 

The slenderness ratio of the structure is λ=μl/i, and i is the slender radius slenderness ratio.

 

The concept can be easily seen from the calculation formula: the slenderness ratio is the ratio of the calculated length of the component to its corresponding radius of gyration.

 

It can be seen from this formula that the concept of slenderness ratio takes into account the end constraint of the component, the length of the component itself and the cross-section characteristics of the component. The effect of the concept of slenderness ratio on the stability calculation of the compression member is obvious, because the larger the slenderness ratio, the more easily the member is unstable.

 

You can look at the calculation formula for the axial compression and bending members, which have parameters related to the slenderness ratio. The slenderness ratio specification is also given for the tension member specification, which is to ensure the rigidity of the member in the transportation and installation state. The higher the stability requirement, the smaller the stability limit given by the specification.

 

7 Is the buckling of the compression flange of the bent I-beam bent along the weak axis of the I-beam, or is it bent in the strong axis?

 

When the load is not large, the beam is basically bent in its maximum stiffness plane, but when the load is large enough, the beam will simultaneously produce large lateral bending and torsional deformation, and finally lose the ability to continue to bear. At this time, the overall instability of the beam must be lateral bending and bending.

 

There are roughly three solutions:

 

1. Increase the lateral support point of the beam or reduce the spacing of the lateral support points

 

2. Adjust the section of the beam, increase the lateral moment of inertia Iy of the beam or simply increase the width of the compression flange (such as the upper flange of the crane beam)

 

3. The constraint of the beam end support on the section, if the support can provide the rotation constraint, the overall stability of the beam will be greatly improved.

 

8 Why is there no calculation of the torsion of the steel beam in the steel structure design specification?

 

Normally, the steel beams are all open sections (except the box section), and the torsional section modulus is about an order of magnitude smaller than the flexural section modulus, which means that the torsion ability is about 1/10 of the bending. This is uneconomical if the steel beam is used to withstand the torque. Therefore, the structure is usually used to ensure that it is not twisted, so there is no calculation of the torsion of the steel beam in the steel structure design specification.

 

9 Does the ceiling displacement limit when using a masonry wall without a crane is h / 100 or h / 240?

 

The light steel regulations have indeed been calibrated to this limit, mainly because the top displacement of 1/100 does not guarantee that the wall will not be cracked. At the same time, if the wall is built inside the rigid frame (such as the inner partition wall), we calculate the displacement of the top of the column without considering the effect of the wall on the rigid frame (exaggeration is a metaphor for the frame shear structure).

 

10 What is the maximum stiffness plane?

 

The largest plane of stiffness is the plane of rotation about the strong axis. The general section has two axes. The moment of rotation around one of them is called the strong axis, and the other is the weak axis.

 

11 Using straight seam steel pipe instead of seamless pipe, I wonder if it can be used?

 

The structural steel pipe should be the same in theory, the difference is not very large, the straight seam welded pipe is not as good as the seamless pipe rule, and the shape of the welded pipe may not be in the center, so it is especially necessary to pay attention to the welded pipe when the welded pipe is defective. The probability is relatively high, the important part can not replace the seamless pipe, the seamless pipe is limited by the processing technology, the pipe wall thickness can not be made very thin (the average pipe thickness of the same pipe diameter is thicker than the welded pipe), in many cases Seamless pipe materials are not as efficient as welded pipes, especially large diameter pipes.

 

The biggest difference between seamless and welded pipes is the use of pressurized gas or liquid transport (DN).

 

12 What is the difference between shear lag and shear lag? What are their respective focuses?

 

The shear lag effect is a ubiquitous mechanical phenomenon in structural engineering. As small as a component, as large as a super high-rise building, there will be shear lag.

 

Shear lag, sometimes called shear lag, is essentially the Saint-Venant principle. The specific performance is that within a certain local range, the shear force can have a limited effect, so the normal stress distribution is uneven. This phenomenon of uneven distribution of normal stress is called shear lag.

 

13 What effect does the lengthening of anchor bolts have on the force of the column?

 

The axial tensile stress distribution in the anchor bolt is not uniform, and the inverted triangular shape is distributed, the upper axial tensile stress is the largest, and the lower axial tensile stress is zero. As the anchoring depth increases, the stress gradually decreases, and when it reaches 25 to 30 times the diameter, it decreases to zero. Therefore, it is useless to increase the anchor length. As long as the anchoring length meets the above requirements and the end is provided with hooks or anchor plates, the foundation concrete is generally not pulled.

 

14 The similarities and differences between the stress amplitude criterion and the stress ratio criterion and their respective characteristics?

 

For a long time, the fatigue design of steel structures has been carried out according to the stress ratio criterion. For a certain number of load cycles, the fatigue strength σmax of the members is closely related to the stress cycle characteristics represented by the stress ratio R. The safety factor is introduced for σmax. The allowable fatigue stress tolerance value [σmax] = f(R) is obtained, and the stress is limited to [σmax], which is the stress ratio criterion.

 

Since the welded structure is used to withstand the fatigue load, the engineering community has gradually realized from practice that it is not the stress ratio R, but the stress amplitude Δσ. The calculation formula of the stress amplitude criterion is Δσ ≤ [Δσ]. [Δσ] is the allowable stress amplitude, which varies with the construction details and also varies with the number of cycles before failure. The fatigue calculation of the welded structure should be based on the stress amplitude, due to the residual stress inside the structure. Non-welded members. For R > The stress cycle of =0, the stress amplitude criterion is completely applicable, because the fatigue strength of the components with residual stress and no residual stress is not much different. For the stress cycle with R<0, the stress amplitude criterion is more safe.

 

15 What is hot rolling, what is cold rolling, what is the difference?

 

Hot-rolling is the steel is pressed out at 1000 degrees or more with a roll. Usually, the plate is as small as 2 mm thick. The deformation heat of the steel during high-speed machining can not meet the heat dissipation of the steel area, that is, it is difficult to maintain the temperature above 1000 degrees. Sacrificing hot rolling, an efficient and cheap processing method, rolling steel at normal temperature, that is, re-cold rolling the hot rolled material to meet the market demand for thinner thickness.

 

Of course, cold rolling brings new benefits, such as work hardening, which increases the strength of the steel, but it is not suitable for welding. At least the work hardening of the weld is eliminated, and the high strength is gone. Returning to the strength of the hot rolled material, the cold-formed steel Hot-rolled materials, such as steel pipes, can also be used for cold-rolled materials, cold-rolled materials or hot-rolled materials. 2MM thick is a criterion. The hot-rolled material is the thinnest 2MM thick, and the cold-rolled material is the thickest 3MM.

 

16 Why does the beam bending member perform the calculation of the in-plane in-plane stability, but when the slope is small, can only calculate the in-plane stability?

 

The beam is only in the form of an out-of-plane instability. There has never been a theory of instability in the plane of the beam. For the column, when there is axial force, the calculated lengths in the out-of-plane and in-plane are different, and the in-plane and out-of-plane instability check is performed.

 

For the rigid frame beam, although it is called a beam, some of its internal force is always a part of the axial force, so its calculation should strictly use the model of the column, that is, the plane in and out of the curved member is stable. . However, when the slope of the roof is small, the axial force is small and negligible, so the model of the beam can be used, that is, the in-plane stability is not calculated. The meaning of the door gauge (P33, Article 6.1.6-1) means that when the slope of the roof is small, the inclined beam member only needs to calculate the strength in the plane, but it still needs to be stable outside the plane.

 

17 Why is the secondary beam generally designed to articulate with the main beam?

 

If the secondary beam is just connected to the main beam, the secondary beam with the same load on both sides of the main beam is good. If not, the secondary beam bending moment is out of plane for the main beam, and the torsion is calculated. Torsional stiffness, fan moment of inertia, etc. In addition, just increase the construction workload, the amount of on-site welding work is greatly increased. It is not worth the loss. Generally, it is not necessary to make the secondary beam not just connected.

 

18 How is the length of the high-strength bolt calculated?

 

High-strength bolt screw length = 2 joint end plate thickness + one nut thickness + 2 washer thickness + 3 wire mouth length.

 

19 What is the physical concept of bearing capacity after buckling?

 

The bearing capacity after buckling mainly refers to the ability of the member to continue to bear after local buckling, mainly in thin-walled members, such as cold-formed thin-walled steel. In the calculation, the effective width method is used to consider the bearing capacity after buckling.

 

The bearing capacity after buckling mainly depends on the width-thickness ratio of the plate and the constraint of the edge of the plate. The larger the aspect ratio, the better the constraint and the higher the bearing capacity after buckling.

 

In terms of analytical methods, the current domestic and international specifications mainly use the effective width method. However, national factors have different factors influencing the calculation of effective width.

 

20 What is a plastic algorithm? What is the post-buckling strength?

 

The plasticity algorithm refers to the plastic hinge in the statically indeterminate structure to the yield strength according to the expected position, thereby achieving the purpose of plastic internal force redistribution, and it must be ensured that the structure does not form a variable or transient system.

 

Considering the post-buckling strength refers to a component calculation method that still has a certain bearing capacity after the web of the bent member loses local stability, and fully utilizes the post-buckling strength.

 

21 What is the difference between a soft hook crane and a hard hook?

 

Soft hook crane: refers to the lifting of heavy objects through steel ropes and hooks. Hard hook crane: refers to the lifting of heavy objects such as clamps and magazines through rigid bodies. Hard hook cranes work frequently. The running speed is high, and the rigid cantilever structure attached to the trolley makes the hoisting weight unable to swing freely.

 

22 What is a rigid tie rod, what is a flexible tie rod?

 

The rigid tie rod can be pressed and pulled. Generally, double angle steel and round tube are used, and the flexible tie rod can only be pulled. Generally, single angle steel or round tube is used.

 

23 What is the relationship between slenderness ratio and deflection?

 

1. Deflection is the amount of deformation of a component after loading, that is, its displacement value.

 

2. "The slenderness ratio is used to indicate the stiffness of the axially loaded member." The slenderness ratio should be the material property. The properties of any component, the stiffness of the axially loaded component, can be measured by the slenderness ratio.

 

3. Deflection and slenderness ratio are completely different concepts. The slenderness ratio is the ratio of the calculated length of the rod to the radius of gyration of the section. Deflection is the displacement value of a point after the component is stressed.

 

24 I would like to ask how the four levels of the earthquake level are specifically divided?

 

Earthquake resistance level: one, two, three, four. Seismic fortification intensity: 6, 7, 8, 9 degrees.

 

Seismic fortification categories: A, B, C, D.

 

Earthquake level: frequent earthquakes, accidental earthquakes, rare earthquakes, rare earthquakes.

 

25 Can you support it as a support? What is the difference with other support?

 

1. Support and support are two structural concepts. The truss is used to ensure the stability of the steel beam section, while the support is used to form a structural system stability with the steel frame, and to ensure that its deformation and bearing capacity meet the requirements.

 

2. The truss can be used as a fulcrum outside the plane of the steel flange. It is used to ensure the overall stability of the steel beam.

 

26 What should be considered when designing the steel structure axial tension member?

 

1. Under the static load without fatigue, the residual stress has no effect on the bearing capacity of the tie rod.

 

2. If there is a sudden change in the cross-section of the tie rod, the distribution of the stress at the change is no longer uniform.

 

27 How to calculate the spring stiffness of the steel column? What is the calculation formula? How to calculate the spring stiffness of the concrete column and the spring stiffness when there is a ring beam on the concrete column? What is the calculation formula?

 

The spring stiffness is considered to be based on the cantilever member, and a unit force is applied at the top of the column to calculate the induced lateral displacement. This displacement is the spring stiffness, and the unit is generally KN/mm. If there is a ring beam, the ringless beam is constrained. In the direction, the spring stiffness is calculated in the same direction as the cantilever member. In the other direction, because the top of the column has a ring beam, the EI in the formula is the sum of all the columns in that direction.

 

28 What is the skin effect?

 

Under the vertical load, the movement trend of the sloping door frame is that the ridge is downward and the eaves are deformed outward. The roof panel will resist the deformation trend in the form of deep beams together with the support beams. At this time, the roof panel is subjected to shearing force and functions as a web of deep beams. The edge purlins receive the axial force to function as a deep beam flange. Obviously, the shear resistance of the roof slab is much greater than its resistance to bending.

 

Therefore, the skinning effect refers to the resistance effect of the skinboard due to its shear stiffness to the load that causes deformation in the plane of the plate [26][28][29]. For the sloping portal frame, the skin effect against the vertical load depends on the slope of the roof. The greater the slope, the more significant the skin effect; while the skin effect against the horizontal load increases with the slope.

 

It is the skinning unit that constitutes the skinning effect of the entire structure. The skin unit consists of a skin panel, an edge member and a connecting piece and an intermediate member between the two rigid frames. The edge member refers to two adjacent rigid frame beams and side girders (ridge and eaves), and the intermediate member refers to The middle part is purlined. The main performance indicators of the skinning effect are strength and stiffness.

 

29 Specification 8.5.6, for the lateral stiffeners of the crane beam, this should be the arc at the lower end of the rib. What does it mean?

 

Refers to the continuous welding of the end of the stiffener, such as rounding, welding and other methods. Prevent fatigue cracks on the web.

 

30 How is the welding of the last weld of the box-type column partition?

 

With electroslag welding, the quality is easy to guarantee!

 

31 Cantilever beam and cantilever column calculated length coefficient is different, how to explain?

 

The cantilever beam has a length coefficient of 1.0 and a cantilever column has a length factor of 2.0. The column is a bent member, or it is simply pressed. Consider the stability factor, so take 2 . The beam is bent, it should be the difference.

 

32 deflection is not in accordance with the specifications at the time of design, use arching to ensure that it can be done?

 

1. The structure controls the deflection and is designed according to the normal use limit state. For steel structures, excessive deflection can easily affect roof drainage and cause fear. For concrete structures, excessive deflection can cause local damage to durability (including concrete cracks). I believe that the above damage caused by excessive deflection of the building structure can be solved by arching.

 

2. Some structures are easy to arch, such as double-slope door frame beams. If the absolute deflection exceeds the limit, it can be adjusted by increasing the slope of the roof. Some structures are not easy to arch. For example, for large-span beams, if the relative deflection exceeds the limit, each segment of the beam should be arched. Since the arched beams are spliced ​​into fold lines and the deflection is curved, the two lines are difficult to overlap. Will cause uneven roofing. For the flat beam of the frame, it is more difficult to arch, and the flat beam cannot be made into an arc.

 

3. If you are going to use arching to reduce the amount of steel used in the structure controlled by deflection, the deflection control regulations should be reduced. At this time, the deflection under live load must be controlled. The deflection generated by the dead load is guaranteed by arching. .

 

33 What is the central block pad method for steel structural columns?

 

The central block pad method installed on the steel structure column saves labor and time, the construction precision can be controlled within 2mm, and the comprehensive benefit can be increased by more than 20%.

 

The construction steps are as follows:

 

(1) According to the construction drawing, the steel column foundation construction (same as the usual construction method), the foundation upper surface is 30~50mm lower than the installation height of the steel column bottom surface, in order to place the central seat pad.

 

(2) Calculate the minimum bearing area Amin according to the steel column self-weight Q, the bolt pre-tightening force F, and the foundation concrete bearing strength P.

 

(3) A square or circular central seat pad is made of steel plates with a thickness of 10 or 12 mm, and the area thereof is not less than twice the minimum bearing area Amin.

 

(4) The slurry is placed on the finished foundation and the center slurry pad is placed. During construction, it is necessary to use tools such as level and level to make accurate measurement to ensure the level of the center plate and ensure that the center of the plate is consistent with the installation axis, and ensure that the elevation above the plate is consistent with the installation height of the bottom of the steel column.

 

(5) When the concrete strength of the grouting layer reaches 75% of the design strength, the lifting of the steel column is carried out. The lifting of the steel column can be carried out directly, and the leveling can be performed by adjusting the anchor bolts.

 

(6) Secondary grouting is carried out, and secondary grouting is carried out using non-shrinkage concrete or micro-expansion concrete.

 

34 The bending and buckling of axial compression members adopts the theory of small deflection and large deflection. I want to know the difference between small deflection and small deformation theory.

 

The small deformation theory means that the change of the geometric dimension after the deformation of the structure can be ignored, and the internal force is still calculated according to the size before the deformation! The deformation here includes all deformations: pull, press, bend, shear, twist and combinations thereof.

 

The small deflection theory holds that the displacement is very small and belongs to the geometric linear problem. It can be approximated by a deflection curve equation to establish energy and derive the stability coefficient. The deformation curvature can be approximated by y=1/ρ! The use of Y instead of curvature is a small deflection theory used to analyze elastic rods.

 

This is not the case with rigid rods with springs. Also, analysis with large deflection theory does not mean that the load can be increased after buckling. For example, the cylindrical shell is compressed and can only be stabilized under lower load after buckling.

 

To put it simply, the small deflection theory can only obtain the critical load, and it cannot judge the critical load or the stability after buckling. The large deflection theory can solve the post-buckling performance.

 

35 What is the second-order bending moment, second-order elastoplastic analysis?

 

For many structures, the undeformed structure is often used as a calculation graph for analysis, and the results are sufficiently accurate. At this point, the resulting deformation is linear with the load. This method of analysis is called geometric linear analysis, also known as First Order analysis. For some structures, the internal force analysis must be carried out with the deformed structure as the basis for calculation. Otherwise, the error of the obtained result is large.

 

At this time, the relationship between the obtained deformation and the load is nonlinear. This method of analysis is called geometric nonlinear analysis, also known as second order (Second Order) analysis. The structural analysis is based on the deformed structure and considering the elastoplasticity (material nonlinearity) of the material, which is the second-order elastoplastic analysis.

 

36 What is the "Baoxinge effect", does it have a great influence on the design of steel structure?

 

The Bauschinger effect is the unrecoverable deformation left after unloading after the material has reached plastic deformation. This deformation is plastic deformation. Whether this deformation has an effect on the structure is of course conceivable!

 

37 What is the layered tear of steel?

 

The lamellar tear of the steel sheet generally occurs when there is a large tensile stress in the thickness direction. In the welded joint, when the weld is cooled, shrinkage deformation occurs. If it is thin or does not have a constraint on deformation, the steel sheet will deform and release the stress. However, if the steel plate is thick or has stiffeners, the constraints of the adjacent plates, the steel plate is constrained and cannot be freely deformed, and a large stress is generated in the direction perpendicular to the plate surface. In areas with strong confinement, local stresses due to weld shrinkage may be several times greater than the yield limit of the material, causing lamellar tearing of the steel sheet.

 

38 Brittle fracture of steel or steel structure refers to the failure of sudden fracture under the condition that the stress is lower than the tensile strength or yield strength of the steel.

 

Steel structures, especially welded structures, often have crack-like defects due to quality and structural reasons such as steel, machining, and welding. Most brittle fractures occur due to the development of these defects and the instability of cracks. When the cracks slowly expand to a certain extent, the fractures expand at a very high speed, and suddenly occur without any warning before brittle fracture.