管道应力师应知问题集锦

AUDIT FOR CHINESE STRESS ENGINEER
A) UNDERSTANDING CAESAR II
1. What kind of calculation and evaluation is not covered by C2 in piping system? 蠕变分析，管道或设备的局部应力分析，管道失稳等
How to check if piping system expose to buckling problem by using C2?
负压、偶然荷载、集中荷载、埋地管的土壤约束等荷载都会引起管道的失稳；
但CAESAR II 并不能评定管道的失稳（需要借助压力容器设计软件进行管道的失稳设计）；
CAESAR II addresses negative pressures as follows: the absolute value of the longitudinal pressure stress (PD/4t) term is added to the appropriate code equations; pressure thrust forces applied to expansion joint ends will be compressive; and buckling is not addressed in CAESAR II 临界失稳压力：C D EI P m
c 321124⨯⎪⎭⎫ ⎝⎛-=υ E —弹性模量（MPa ）；
I —截面惯性矩（mm4/mm ）；
v —泊松比，0.35—0.45；
Dm —管道平均直径；
C —椭圆修正系数，()3
10/r r ，r1—椭圆管道的弯曲半径，r0—圆形管道半径； 允许的管壁冲击荷载：5.03''0)]/(32[)/1(m w D EI E B R D FS N =
2. Global/local loads in C2 output, The reason why we need the local elements loads? 为了获得作用在设备管口上准确的外载，以进行局部应力分析；另外通过局部坐标推力的分析，可以仔细察看管道单元内部的相互作用关系，协助发现问题，并尽快找到答案。

3. On input sheet, what is different for Force, Uniform load, Rigid element with weight. -the
temperature base of Elastic modulus input?
集中力（力或弯矩作用于管道上一点，一般模拟外载力的作用效果，对于一些额外重
量，如支架根部，最好不用力来输入，因为如果计算地震，这些质量都不存在。

）、均布载荷（荷载均布于管道所有点上，我们一般用它来模拟雪载）、带重量的刚性件（横向刚度无穷大横向没有弯曲，刚性件只传导位移和力，我们一般用它来模拟阀门，管道设备等，但要注意，刚性件有直径和壁厚，他们对他的横向变形会有影响。

）。

软件缺省的弹性模量是冷态的。

但用户可以选择。

4. What is non-linear system? Area there any special cautions in input/output for
non-linear case?
非线性系统就是：依据胡克定律F=K*X ，我们认为k 是变化的。

管道在使用支架、吊
杆，支架加间隙，摩擦力的情况下，系统变成非线性的。

管系从冷态—>热态或热态—>偶然工况过程中由于非线性约束的作用导致管系刚度发生改变；
如果你输入过多的非线性支架，可能导致软件计算不收敛。

陷入死循环。

我们一般先
判断，根据直观感觉决定一些点，加入非线性约束。

其他处根据计算结果，在调整支架。

5. How to check the lift-off support point? What should Engineer check for lift-off problem?
What is hot sustained stress?
检查约束报告，垂直方向受力为0的点即支架托空点；
支架托空点应考虑采用弹性支吊；
Hot sustain stress—计算热态持续应力。

依据B31.3 Appendix P, 用户可以校核热态持续应力。

主要是考虑支架脱空情况下持续应力。

Generally Hot sustained stress is carried out by removing the support at the point of lift off ,& check for sustained stresses. My question is :- Is there any guide lines or any proper basis available for neglecting small lift off for hot sustained stress check. I assume that the meaning of small liftoff means Liftoff by small positive displacement..
Suppose u'r system has three cases
1 operating
2 design
3 Upset
And in the system u'r two support are going to liftoff ( may be by small displacement ) and due to the removal of these two support u'r system get failed in sustained case ... What u can do here is just check whether thesse two supports are lifting in the same case or different.. if they lift in different case check for removal of one support at one time... in my view u should not ignore small deflection because they will act as constant acting load.... which will cause failure
6. What is Liberal stress allowable?
一次应力的余量可以添加到二次应力的许用应力上来，我们将这个余量称为Liberal stress allowable。

Perhaps it would be of some benefit to review the meaning of the term ?liberal allowable stress range?. First of all, this is not a term that is used by the ASME B31 Pressure Piping Codes. Caesar II (C2) uses the term as a sort of ?short-hand? for referring to the increase in thermal (displacement) allowable stress range that is allowed in B31.1 (paragraph 102.3.2(D)) and B31.3 (paragraph 302.3.5(d). In these paragraphs, the B31 Codes allow the positive difference between the calculated combined longitudinal stresses (due to weight (bending) and longitudinal pressure) and the maximum allowable stress, Sh, to be added to the term ?0.25 Sh? (the second term) in the equation for calculating the maximum allowable stress range, SA. The B31 Codes say that it ?MAY? be added into the ?0.25Sh? term, thereby making it optional. If the analyst elects to ignore the additional allowable stress range the decision (all other things being equal) would be judged conservative. If the analyst elect to employ this additional allowable stress range, the resulting allowable stress range is sometimes termed ?liberal?. It is, of course, all semantics. The Code allows the additional allowable stress range for a very good reason.
The concept underlying this rule is very well described in the famous book by S.W. Spielvogle (Piping Stress Calculations Simplified, Fifth Edition, 1955). Spielvogle explains that the B31 rules intend for the analyst to be able to use the entire range of stress from the material yield point at the operating (hot) temperature to the material yield point at the ambient (cold) temperature (less a factor of safety). Since Sh (neglecting the possibility of creep) is set at 2/3 Sy for both the hot and cold conditions, we can calculate the hot yield stress as Sh*1.5 and we can calculate the cold yield
stress as Sc*1.5. Taken together the total allowable stress range for the combined loadings of weight (bending), longitudinal pressure (tension) and thermal expansion (displacement) would be (1.5*Sc) + (1.5*Sh), or 1.5(Sc + Sh). This range of allowable stress has been reduced slightly to allow for the vagaries of material and for other ?real world? inaccuracies. The Code philosophy would then permit the total allowable stress range (after the factor of safety is applied) for all the combined loading described above to be 1.25(Sc + Sh) (if ,in this discussion, we neglect the stress range reduction factor for simplicity). But the Code uses 1.0Sh for the sustained loadings of weight and longitudinal pressure and this leaves 1.25*Sc + 0.25*Sh for the allowable thermal expansion (displacement) stress range (bet you wondered where that came from). Because the Code intends for the entire strength of the material (from hot yield to cold yield) to be used (except for the ?adjustment? made for vagaries), it follows that the rule in the paragraphs cited above allows the analyst to put the unused (difference between calculated sustained longitudinal stresses and the allowable 1.0*Sh) portion to use in increasing the allowable thermal expansion (displacement) stress range. You will recognize that the ?excess? sustained case allowable stress will vary across the system being analyzed and that the variation will directly reflect how well supported the system is (bending stresses will have the greater effect). This variation in ?excess? sustained case allowable stress from node to node in the model will (when the ?liberal? option is used) result in the allowable stress range, Sa, being different at every node when the Code compliance report is viewed.
So, one might ask, why would an analyst opt to not use the ?liberal? allowable stress range for comparison to calculated expansion (displacement) stress range? This is an engineering judgement. For example, if the sustained stresses were calculated as 80 or 90 percent of Sh and the system were operated in the material?s creep range, the designer might want to take the conservative decision to not use the ?liberal? allowable stress range when evaluating thermal (displacement) stress ranges. Another example might be offered as a case when the system is in severe cyclic service (see B31.3 paragraph 300.2 for the definition) and the designer is looking for a longer fatigue life. Going the ?conservative? route might also appeal to the designer (or owner) if the system would be operating within the pressure/temperature variations described in paragraph 302.2.4 in B31.3 or paragraph 102.2.4 in B31.1. If we have some degree of uncertainty, we employ an additional measure of conservatism. As the saying goes, ?when in doubt, build it stout?. Thank you for bringing up the topic for discussion. Good luck with your projects.
Of course, all the above is just my opinion and does not reflect the opinion of ASME or any Code Committee. John.
A conservative formulation of the allowable expansion stress range for many codes in CAESAR II is calculated from: f ( 1.25 Sc + .25 Sh ) When the user requests that the "Liberal Allowable" be used, the difference between Sh and Sl, provided Sh > Sl, will be added to the term inside the parenthesis, i.e. SA(Liberal) = f[ 1.25 Sc + .25 Sh + ( Sh - Sl) ] The liberal expression will only be employed when there is at least one sustained stress case in the load set. If there is more than one sustained stress case in a single problem, then the largest of Sl, considering all of the sustained cases, for any single element end will be chosen to subtract from Sh. Because the sustained stress varies from one pipe to another, the allowable expansion stress will also vary.
7 How to incorporate the installation temperature in C2?
可在CII 环境变量中更改环境温度；环境温度在管道应力分析中是个很重要的设计条
件，我们一般会去年平均的温度来进行考虑。

真正的环境温度是指管道安装最后焊缝施工时的环境温度，这样就可以决定安装的初态。

8. What is thermal bowing effect?
管道暴露在阳光下，管道上部的温度和下部的温度会不同，管道会在这个温度作用下出现热拱效果。

9. What kind of piping system should the Bourdon effect be considered to?
包尔登效应，盘管在压力作用下有伸直的效果。

一般是指弯头在压力作用下，有要伸直的效果。

There is a pressure-sensing device called a bourdon tube which is a coiled flexible tube with fluid pressure on the inside. As pressure increases, the coil tends to want to straighten out against spring pressure (since there is a bigger surface area around the outside curve of the coil than the inside curve of the coil... with same pressure applied on both).
I would assume that a piping elbow wants to straighten out for the same reason. The higher the pressure, the higher the force... also probably depends on the geometry of the elbow.
the bourdon effect is the difference between the pressure inside the tube or pipe in relation to the pressure outside the tube or pipe. If the inside presurer is greater than the outside presure the tube or pipe will expand. And if the tube or pipe is bent in a circular form, the expansion is noticable and can be converted to a calibrated reading as in a pressure gauge.
Electricpete is correct. Internal pressure can affect the pipe bend or elbow in 2 ways. The Bourdon effect describes the tendency for the pipe bend to "open" under internal pressure and "close" under external pressure. The reason is as described by Electricpete. The other effect is the "stiffening" of pipe bends and elbows as internal pressure is increased. The stiffening results from the internal pressure resisting the "ovalization" of the cross section that normally occurs when a bending moment is applied to the bend. One or both of these effects can occur in large diameter pipe with large D/t ratios. Reference B31.3, Appendix D, Table D300 and note (7). If you have piping systems of moderate diameter but are designing to B31.3, Chapter IX (high pressure - Class 2500 or higher) you will want to consider these effects. Good pipe stress computer programs (e.g., Caesar II) will give you the option of "toggling" these effects off or on.
Comments on Pressure Expansion
In CAEPIPE Version 5.1E (Mar 14, 2002) a change to the program states:
Presently pressure expansion (Bourdon effect) is treated as thermal expansion and applied to expansion (T) and operating (W+P+T) load cases. If an environment variable BOURDONP is set (i.e. set BOURDONP=y), pressure expansion is not treated as thermal expansion (i.e. pressure expansion is treated as pressure expansion and applied to sustained (W+P) and operating (W+P+T) load cases).
Treating a pressure caused stress as a thermal expansion-like stress may seem incorrect to some
analysts, but treating pressure expansion as a load similar to thermal expansion is the correct interpretation of the type of load and the failure mode related to that type of load. Pressure expansion causes displacement (secondary) stresses and leads to a fatigue failure. Hoop pressure (PD/2t) and longitudinal pressure (PD/4t) type stresses are sustained (primary) stresses, but pressure expansion, if the piping is unrestrained would not cause any displacement (secondary) stresses. Restraining the pipe, as in introducing more than one anchor or an intermediate support opposed to the direction of pressure expansion, causes stresses from the introduction of that restraint. A simple illustration is shown below:
Shown are two weightless piping layouts. Note the layout on the left has a single anchor and when pressurized will expand as shown to the dashed line configuration. Sustained load stresses due to hoop and longitudinal pressure exist, but no additional stresses due to pressure expansion exist. However, note what happens when an additional anchor is introduced, restraining the piping pressure expansion in the right hand layout. The deformed shape is indicative that stresses exist due to the "restraint of free end displacement" in addition to the hoop and longitudinal pressure stresses. These pressure expansion stresses are displacement (secondary) stresses and should be treated in a similar manner to thermal expansion stresses.
Note also, the Bourdon effect, which tries open elbows or curved members when such are pressurized, is a pressure expansion effect and should be treated the same way that simple pressure expansion as discussed above is, i.e., the Bourdon effect causes displacement (secondary) stresses.
Further note that Pressure expansion was usually ignored prior to the use of computer aided analysis techniques because most piping analyzed was metallic, typically steel, piping. It was ignored because the amount of pressure expansion was normally small compared to thermal expansion, i.e., typically less than 10 percent. However, with low modulus materials, such as nonmetallics (plastics), the amount of pressure expansion can be significant and may need to be considered in the analysis of piping systems made from such materials.
Editor's Note: Since version 3.32 (4/22/1992) CAEPIPE has been treating pressure expansion as a secondary load (similar to thermal expansion) and applying it to thermal and operating load cases. This is the default behavior of CAEPIPE (even now).
However, a few users want to treat pressure expansion as a primary load and apply it to the sustained and operating load cases because finite element programs and other piping programs do it this way. Starting v5.1E, these users (with some effort by setting an environment variable) can alter CAEPIPE's
behavior (i.e., treat pressure expansion as a primary load) to suit their needs. Please see the second para. above in this article for how to set the variable.
Author: Mr. Ron Haupt, P. E., of Pressure Piping Engineering () is a member of several piping code committees (B31, B31.1, B31.3, BPTCS, and others). He consults with us in the capacity of Nuclear QA Manager.
Note on Branch Connection Pressure Design
Recently there was some discussion regarding the branch connection pressure design rules in B31.3, Para. 304.3.3. Some differences were noted between the rules (also referred to as the area replacement rules) as manifested in the current equations in B31.3-2002 and Para. 104.3.1 of
B31.1-2001 including the 2002 Addenda. The discussion ended with the conclusion that there should be no difference between the B31.1 and B31.3 equations except in the unique nomenclature used by each.
B31.1 has recently spent a considerable effort to try to make its area replacement equations correct, and they can be assumed to be correct (unless the ASME editors have messed them up -- a situation possible to encounter).
A way to check branch connection pressure design rules is to review the equations so as to assure the designer that there is an adequate wall thickness at the end of plant life, i.e., from the run and branch piping remove the manufacturer's under thickness tolerance, remove the corrosion allowance (on the inside) and the remaining metal must satisfy the area replacement rules. That is, the amount of remaining metal removed that is required for pressure design must be at least replaced within the reinforcement zone. If one follows this concept the designer can always be assured of meeting the
B31.1 or B31.3 requirements.
In addition, there should be no difference between the rules or equations for branch connection pressure design in any B31 book (or for nozzles in any ASME boiler and pressure vessel code), with the exception that some B31 books consider either manufacturer's underthickness tolerances or corrosion allowances or both as negligible, e.g., B31.4 and B31.8.
Author: Mr. Ron Haupt, P. E., of Pressure Piping Engineering () is a member of several piping code committees (B31, B31.1, B31.3, BPTCS, and others). He consults with us in the capacity of Nuclear QA Manager.
Tip for the Month (Aug 2004)
To Include or Not to Include Hanger Stiffnesses?
In the 1970s, performing pipe stress analysis on mainframe computers was expensive (about $1000/run). So, pipe stress analysts would run a Thermal (T1) case alone first. Then, they would run a deadweight (DW) case with rigid supports at chosen hanger locations. Using the support loads and the hanger travel, analysts would select appropriate variable spring hangers from hanger manufacturer catalogs. To save on computing costs, they would not update the global stiffness matrix [K] with the hanger stiffnesses from the newly selected hangers because they would have to reanalyze the model which would cost
more money. Many industrial plants built 30 or 40 years ago in the USA and presumably in other countries have pipe stress analyses done in this manner. These plants have archived such analysis reports that do not include hanger stiffnesses (as part of the global stiffness matrix [K]).
In later years, as and when the analysts in these plants needed to reanalyze those piping systems, they had to use modern programs like CAEPIPE. But, before they accepted the new results, they sometimes liked to verify that the new results (from CAEPIPE ) matched the results from the old reports generated by the mainframe pipe stress analysis programs. This is the reason why CAEPIPE provides the option "Do not include (or include) hanger stiffnesses." It helps the engineers compare results from CAEPIPE with the old archived reports.
Today, with cheap PC computing power, there is no reason why hanger stiffnesses should be excluded from analysis. In fact, including hanger stiffnesses provides a more accurate picture of system behavior. As such, we recommend that you "include hanger stiffnesses" in every analysis. Due to the limited utility of this option, we plan to remove the "Do not include hanger stiffnesses" option from CAEPIPE in the near future, and include hanger stiffnesses for every analysis.
Tip for the Month (Sep 2004)
Bourdon Effect — Straight Pipe
In continuation to our tip on pressure expansion, we have included here a technical verification of this feature. As the previous article says,the expansion due to internal pressure was usually ignored in metallic pipes previously, but if you are using non-metallic pipes or have a high pressure system, the effect can be significant. So, it is recommended that you always include this option during model analysis.
Determinants of subjective contour: Bourdon illusions and "unbending" effects.
Wenderoth P, Criss G, van der Zwan R.
Department of Psychology, University of Sydney, New South Wales, Australia.
Wenderoth and O'Connor (1987b) reported that, although matches to the straight edge of two triangles placed apex to apex revealed an apparent bending in the direction of the chevron formed by the hypotenuse pair (the Bourdon effect), no perceptual unbending of the bent chevron occurred. Using subjective contour figures, Walker and Shank (1988b) found large and approximately equal bending and unbending effects, consistent with two theories that they proposed. In Experiment 1, using adjustable chevron matching and subjective contours, we found that Bourdon effects, equivalent in magnitude to those reported by Walker and Shank, were 4-5 times larger than unbending effects. In Experiment 2, we used a variation
of Walker and Shank's measurement technique, in which subjects selected a matching angle from a graded series. We obtained Bourdon effects similar to those in Experiment 1, but much larger unbending effects. Nevertheless, Bourdon effects were significantly larger than unbending effects in one set of data; and in another, Bourdon test means were larger than unbending test means. In both data sets, there was a large and significant pretest bending effect, which enhanced the magnitude of unbending test minus pretest scores. These results were consistent with our theory but not the theories of Walker and Shank. The variance of unbending test matches, 3-4 times that of Bourdon test matches, reflected the task difficulty. We propose that subjective obtuse angle contraction that exceeds real obtuse angle contraction explains the fact that unbending effects are larger in subjective than in real contours.
10. What are different for Hot load setting and Cold load setting?
答：热态荷载设置和冷态荷载设置的区别：
冷态荷载：W、P
热态荷载：W、T、P
SUS=W+P; OPE=W+P+T
11, Are there any special caution for load combination method to get valid stress and support load? If system include the non-linear case, how to prepare load combination for each stress (SUSOCC, EXP)?
答:
SELECT COMBINATION METHOD FOR COMBINATION CASES ONLY
Summary of most commonly used combination types:
ALG - signed algebraic combination disp./force level
Scalar - signed combination disp./force/stress level
ABS - unsigned combination disp./force/stress level
Detailed Description of all combination types:
ALG - Combine the displacement vectors and the force vectors
ALGebraically and calculate the stresses from the combined
forces.
Displacements are the algebraic combination of the
displacement vectors.
Forces are the algebraic combination of the force vectors.
Stresses are not combined; stresses are calculated from
the algebraically combined forces.
ALG would typically be used to calculate EXP code stresses.
Scalar - Combine the displacement vectors, the force vectors,
and the stress scalars.
Displacements are the algebraic combination of the
displacement vectors.
Forces are the algebraic combination of the force vectors.
Stresses are the scalar combination of the stress scalars.
The Displacements and Forces of an ALG case and Scalar case
are equivalent. There may be variation at the stress level,
since in an ALG combination the stresses are calculated and
in a Scalar combination the are combined. For example:
Load Case 1: Bending stress = 100 psi, due to X-moment
Load Case 2: Bending stress = 100 psi, due to Z-moment Algebraic (vectorial) sum = sqrt(100*100 + 100*100) = 144 psi
Scalar sum = 100 + 100 = 200 psi
Scalar would typically be used to sum (SUS + OCC) code
stresses.
SRSS - Combine square root of the sum of the squares (SRSS) of the displacements, square root of the sum of the squares (SRSS)
of the forces, and square root of the sum of the squares
(SRSS) of the stresses.
Displacements are the the square root of the sum of the
squares of the displacements of all cases included in the
combination.
Forces are the the square root of the sum of the squares
of the forces of all cases included in the combination.
Stresses are the the square root of the sum of the squares
of the stresses of all cases included in the combination.
SRSS would typically be used to combine seismic directional
components.
ABS - Combine the ABSolute value of the displacements, the
ABSolute value of the forces, and the ABSolute value
of the stresses.
Displacements are the sum of the absolute value of the
displacements of all cases included in the combination.
Forces are the sum of the absolute value of the
forces of all cases included in the combination.
Stresses are the sum of the absolute value of the
stresses of all cases included in the combination.
MAX - Compare the ABSOLUTE values of the displacements, forces, and stresses and report the MAXimum displacement, the MAXimum
force, and the MAXimum stress value of the cases combined
(retaining the original sign).
Displacements are the displacements having the maximum
ABSOLUTE values of all the load cases included in the
combination.
Forces are the forces having the maximum ABSOLUTE
values of all the load cases included in the combination.
Stresses are the stresses having the maximum ABSOLUTE
values of all the load cases included in the combination.
MAX would typically be used to report the greatest restraint
loads from among a selected set of load cases.
MIN - Compare the ABSOLUTE values of the displacements, forces, and
stresses and report the MINimum displacement, the MINimum
force, and the MINimum stress value of the cases combined
(retaining the original sign).
Displacements are the displacements having the minimum
ABSOLUTE values of all the load cases included in the
combination.
Forces are the forces having the minimum ABSOLUTE
values of all the load cases included in the combination.
Stresses are the stresses having the minimum ABSOLUTE
values of all the load cases included in the combination.
SIGNMAX - Compare the displacements, forces, and stresses and use the the MAXimum displacement, the MAXimum force, and the
MAXimum stress value of the cases combined (i.e., sign is
considered in the comparison).
Displacements are the maximum SIGNED values of all the
displacements from each case included in the combination.
Forces are the maximum SIGNED values of all the forces
from each case included in the combination.
Stresses are the maximum SIGNED values of all the stresses
from each case included in the combination.
SIGNMAX would typically be used in conjunction with SIGNMIN to
report the envelope of restraint loads from among a selected
set of load cases.
SIGNMIN - Compare the displacements, forces, and stresses and use the the MINimum displacement, the MINimum force, and the
MINimum stress value of the cases combined (i.e., sign is
considered in the comparison).
Displacements are the minimum SIGNED values of all the
displacements from each case included in the combination.
Forces are the minimum SIGNED values of all the forces
from each case included in the combination.
Stresses are the minimum SIGNED values of all the stresses
from each case included in the combination.
SIGNMIN would typically be used in conjunction with SIGNMAX to
report the envelope of restraint loads from among a selected
set of load cases.
NOTE: Load case results are multiplied by any associated scale factors
prior to performing the combination/comparison.
SUS=W+P; OPE=W+P+T
如果出现非线性工况：则二次应力和偶然应力的评定准则为：
EXP=Dope-Dsus；OCC=(OCC+OPE)-OPE+SUS
12 How to model the closely spaced miter and widely spaced miter bend. What are they? 答：
13. Output review 输出结果查看
-Code stress, Bending stress, Torsion stress, axial stress, 3D-max intensity
-规范合成应力，弯曲应力，扭转应力，轴向应力，空间最大应力强度；
- The reason why C2 does not show the allowable value for operating load
因为B31.1和B31.3规范不计算热态应力。

- APPENDIX P
ALTERNATIVE RULES FOR EV ALUA TING STRESS RANGE
(a) This Appendix provides alternative rules for evaluating the stress range in piping systems. It considers stresses at operating conditions, including both displacement and sustained loads, rather than displacement stress range only. The method is more comprehensive than that provided in Chapter II and is more suitable for computer analysis of piping systems, including nonlinear effects such as pipes lifting off of supports. (b) The paragraph numbers of this Appendix, except for para. P300, correspond to those of Chapters I and II of the base Code. The prefix P is used. (c) In the application of these alternative rules, all of the provisions of Chapters I and II of the base Code apply, except those that are specifically modified by this Appendix.
P300.2 Definitions
Replace the definition of severe cyclic conditions with the following: severe cyclic conditions: conditions applying to specific piping components or joints in which SE, computed in accordance with para. P319.4.4, exceeds 0.8SoA [as defined in para. P302.3.5(d)] and the equivalent number of cycles [N in para. P302.3.5(d)] exceeds 7000; or other conditions which the designer determines will produce an equivalent effect.
P302.3.5 Limits of Calculated Stresses Due to Sustained。