The use of stainless steel pipe and carbon steel tubes and their differences. The rules for the planning of carbon steel cannot be used for stainless steel because of the difference in the relationship between carbon steel and stainless steel:
1. Stainless steel has no yield point, and it is generally indicated by ó0.2 that the yield stress is considered to be an equivalent value.
2. The shape of the stress/strain curve is different. The elastic limit of stainless steel seamless pipe is about 50% of the yield stress. The value of the yield stress is lower than the yield stress of medium carbon steel in terms of the minimum value in the standard.
3. Stainless steel is hardened during cold working, for example, it has anisotropy when bent, that is, it has different lateral and longitudinal functions.
It is possible to use an increase in strength by cold working, but if the bending area is small compared to the total area and the increase is neglected, the increase in strength can advance the safety factor to a certain extent.
Fundamental planning processThe planning process for stainless steel is largely derived from the principles currently applicable to all aspects of structural engineering planning.
However, since the commonly used stainless steel is a thin standard steel, its planning process is much more messy than the carbon steel thin standard material. It is important to determine the final use of stainless steel, because in many applications stainless steel is not only used as a structural member and has a beautiful effect. In order to avoid partial bending and deformation of the stressed part of the component, the key element is the limit of the ratio of the width to the thickness of the material. It is also important to note that the material standard rules the maximum value of ó0.2. For austenitic stainless steel used in buildings, the value is about 240N/mm2, but the characteristic strength of the material is generally This factor is considered to be 15% higher than this value.
Planning basis
1. Comparison of stainless steel and carbon steel
First, look at the primary differences between general carbon steel and stainless steel.
2. Stress/strain curve
The linear portion of the stress/strain curve of carbon steel is actually a straight line straight to the yield point, while the linear region of stainless steel is about 50% of ó0.2.
When the stress level is in the inelastic zone, it is used in the bending planning theory and the Hooke rule in the structural planning, that is, the stress and the ratio should be proportional, which is not true for stainless steel.
Therefore, in the case of a low stress level, planning the structure of the stainless steel member is relatively simple, but in the case of a high stress level, it is required to look at the standard of deformation and partial bending.
3. tension
In modern structural regulations, the tensile stress plus the load factor is linked to the yield stress of the material of the gross section. The ratio of tensile ultimate strength to yield stress is used to verify the net section.
The ratio of tensile ultimate strength to yield stress of stainless steel is 2.4, while in carbon steel the plan is 1.6 to 2.1. Tensile members require two checks for their strength: Yield stress of 1 wool section 2 tensile ultimate strength of net useful section (maximum 1.2)
4. pressure
The pressure depends on the yield stress and the modulus, which is generally due to deflection due to damage to the compression member, which in turn is related to stiffness. Therefore, it is necessary to reduce the E value to increase the force that can be withstood. Since this indicates that the longitudinal bending force of the stainless steel member is lower than that of the same carbon steel structural member under the conditions of slenderness ratio.
When the slenderness is low, the two materials are the same.
When the slenderness is relatively high, the stress is low and the strength is similar, but the slenderness ratio is in the central value plan of 80 to 120, and the longitudinal bending force of the stainless steel is low.
5. bending
In the absence of longitudinal bending, the bending stress is generally related to the yield stress. Various rules, even those with flexible planning rules, know the importance of the shape factor. The shape factor increases the plastic moment value of the beam to a value that is much higher than the initial yield.
However, the strain hardening of the stainless steel is preliminary immediately after the initial yielding, so that the outer fiber is increased and the inner fiber is still deformed in the elastic region. Therefore, stainless steel can have a high bending ability due to strain hardening.
However, there is no provision for plastic analysis in Section 1.4 of EUROCODE3.
6. Shear and pressure
They are independent of stiffness and are directly related to yield stress and ultimate stress. Strain hardening can advance safety margins.
7. Vertical and horizontal functions
In the UK study, the results of the material inspections widely indicated that the vertical and horizontal functions did not exceed 7.5%. Structural analysis and planning in the United States. The new ANSI/ASCE standard replaces the allowable stress with a permissible load and force.Therefore, the safe load is calculated by adding a safety factor to the maximum strength, longitudinal bending force or yield strength calculated for the components and connections used.
Most of the terms also use dimensionless equations, which can then be easily applied to any unit for planning, which also simplifies the transformation of load and resistance planning patterns.Planning for structural stainless steel
1. “Technical Standards for Cold Formed Structural Parts”, see ANSI/ASCE 8-90, can be obtained from ASCE.
2. EUROINOX (European Stainless Steel) Association’s “Structural Stainless Steel Planning Manual”.
High temperature resistance of stainless steel
Stainless steel as a structural member, for example, a supporting angle of a brick wall, is likely to encounter high temperatures in the event of a fire.The function of stainless steel is superior to that of carbon steel. The test conducted by NiDI on the cable tray has now fully demonstrated this point and is described in the video “The most useful solution”.
Directly withstand heat
Direct heat test of the cable tray is the most telling problem. The cable trays have the same load bearing capacity. In order to mimic the typical working environment, the loading during the test is 50% of the load they may carry.
The 3-meter-long bridge is heated by 18 gas burners with a temperature of up to 1000 °C.The aluminum bridge was completely damaged in 26 seconds.The FRP bridge was damaged when the burner was not finished.The carbon steel bridge was tested for 5 minutes and arrived at the refinery’s request. The maximum temperature reached was 811 °C.
