相信许多留学生对数学代考都不陌生,国外许多大学都引进了网课的学习模式。网课学业有利有弊,学生不需要到固定的教室学习,只需要登录相应的网站研讨线上课程即可。但也正是其便利性,线上课程的数量往往比正常课程多得多。留学生课业深重,时刻名贵,既要学习知识,又要结束多种类型的课堂作业,physics作业代写,物理代写,论文写作等;网课考试很大程度增加了他们的负担。所以,您要是有这方面的困扰,不要犹疑,订购myassignments-help代考渠道的数学代考服务,价格合理,给你前所未有的学习体会。

我们的数学代考服务适用于那些对课程结束没有掌握,或许没有满足的时刻结束网课的同学。高度匹配专业科目,按需结束您的网课考试、数学代写需求。担保买卖支持,100%退款保证,免费赠送Turnitin检测报告。myassignments-help的Math作业代写服务,是你留学路上忠实可靠的小帮手!


物理代写|结构力学代写Structural Mechanics代考|Final Remarks

A good choice of redundant bars can reduce the level of calculation availed by Virtual Work. The middle lower bar in Fig. $5.2$ connects to symmetrical sub-structures on either side, which have the same statical properties from the overall loading – and only one side needs to be evaluated. Declaring the diagonal bar in Fig. $5.1$ to be redundant enabled the general set of equilibrium values to be recycled at various calculation stages.

However, the redundant bar in Fig. $5.2$ offers a more subtle point. A particular equilibrium solution arises in Table $5.4$ from $R$ taking any numerical value for the loads applied. If zero is set, the sub-structures are effectively disconnected from each other, and whatever the applied loading, their bar tensions are automatically easier to calculate. Thus, we seek out redundant members that connect simpler but isolated sub-structures.

Symmetry, as usual, complements this assessment. For example, the eight-bar truss in Fig. 5.4(a) has two redundancies, $b+r-D \cdot j=8+4 \times 2-2 \times 7=2=s$. The pair of horizontal bars are prime redundancy candidates, connected to three separate sub-structures – two being the same whatever the applied loading, Fig. 5.4(b).

But we cannot ‘extract’ any two redundant bars in this thought process; whatever partial structure is left behind should still be determinate without local mechanisms. The redundant declaration in Fig. 5.4(c) leaves the top bar ‘unsupported’, which is inadmissible.

Finally, the flip side of Virtual Work is equally important; of finding displacements or bar extensions. Indeterminate structures allow us to select the simplest virtual equilibrium set, ideally with as many zero bar tensions as possible, making $\Sigma T^* \cdot e$ easier to compute. This is the strength of the Virtual Work method, and can be verified by choosing more than one virtual equilibrium set for the same problem: the same real displacement or bar extension will emerge.

物理代写|结构力学代写Structural Mechanics代考|Why Does the Lower Bound Theorem Work

Rather, why should any equilibrium solution which does not violate permanent yielding of the material afford safe working of a structure? The answer is, of course, imbued by the mathematical formalism of the Lower Bound Theorem, which we now discuss informally.

Application of the Lower Bound Theorem relies upon ductility, where material yielding permits enough plastic straining for a pronounced structural manifestation. Metals are fortuitously, and mostly, ductile, but other Engineering materials, e.g. concrete, have to ‘contrive’ ductility in special cases, namely when there is insufficient metal reinforcement, which yields before catastrophic brittle failure of the concrete. Crucially, whatever the mechanism of yielding for our material, its ductility proceeds at constant stress.

A (metal) bar under tension will yield everywhere uniformly, giving a simple connection to structural ductility. Yielding in bending, however, is more complex, first occurring at the outermost fibres of the cross-section. Sustained bending causes plastic deformation to encroach from the top and bottom of the section towards the neutral axis, which strictly becomes the equal areas axis in the limit (see Chapter 15).

Determining the precise extent of plastic deformation must consider all three structural imperatives, but eventually full plasticity is achieved from being ductile. In practice though, excessive deformation tends to localise rather than to pervade. In tensile bars, we see familiar necking at a given cross-section, and in bending, most of the beam off-loads away from concentrated deformation into a so-called plastic hinge.
But therein lies the paradox: why is ductility, which implies significant yield strains, a prerequisite for applying the Lower Bound Theorem, in order to return a safe loading limit where the structure has not collapsed, i.e. not yielded critically (or entirely)?
First, we note that a safe load does not necessarily invoke a purely elastic response; part or parts of the structure can have yielded already without substantive deformation and no local collapse. As the loading rises, elastic stresses elsewhere build up even though the yielded regions have saturated in terms of stress levels – but not strain levels from being ductile. This process of redistribution, as it is known, maintains the capacity for the load increasing up to its ultimate value, just before collapse occurs.
A statically determinate structure is governed, however, by a single equilibrium solution. Its internal stresses are known exactly when material yielding begins, which defines a single limit of safe loading without any redistribution. Geometrical compatibility is automatically and separately satisfied.

物理代写|结构力学代写Structural Mechanics代考|CE310

物理代写|结构力学代写结构力学代考|最后备注

.


一个好的冗余条的选择可以减少虚拟工作所使用的计算级别。图$5.2$中下端的横条连接到两侧对称的子结构,它们在整体荷载作用下具有相同的静力特性——只需要评估一侧。将图$5.1$中的对角线声明为冗余,可以在各个计算阶段循环使用一般的平衡值集


然而,图$5.2$中的冗余条提供了一个更微妙的观点。表$5.4$中的$R$给出了一个特殊的平衡解,取所施加载荷的任意数值。如果设置为零,则子结构有效地相互断开,并且无论施加的加载是什么,它们的杆张力自动更容易计算。因此,我们寻找连接更简单但孤立的子结构的冗余成员。


像往常一样,对称是对这种评价的补充。例如,图5.4(a)中的八杆桁架有两个冗余,$b+r-D \cdot j=8+4 \times 2-2 \times 7=2=s$。这对水平杆是主要的冗余候选结构,连接到三个独立的子结构——无论施加的荷载是什么,其中两个都是相同的,如图5.4(b)


但是我们不能在这个思维过程中“提取”任何两个多余的条;不管留下什么局部结构,都应该由局部机制决定。图5.4(c)中的冗余声明使顶部栏“不受支持”,这是不可接受的


最后,虚拟工作的另一面也同样重要;求位移或杆的延伸。不确定结构允许我们选择最简单的虚拟平衡集,理想情况下有尽可能多的零杆张力,使$\Sigma T^* \cdot e$更容易计算。这就是虚功法的强度,可以通过为同一问题选择多个虚平衡集来验证:将出现相同的实位移或杆的延伸

物理代写|结构力学代写结构力学代考|为什么下界定理有效


相反,为什么任何不违背材料永久屈服的平衡解都能提供结构的安全工作?答案当然是由我们现在非正式讨论的下界定理的数学形式主义所赋予的


下界定理的应用依赖于延性,其中材料屈服允许足够的塑性应变,以明显的结构表现。金属是偶然的,而且大多是延性的,但其他工程材料,如混凝土,必须在特殊情况下“设计”延性,即当金属钢筋不足时,在混凝土发生灾难性脆性破坏之前屈服。至关重要的是,无论我们材料的屈服机制是什么,它的延展性在恒定的应力下得到提高


A(金属)棒在拉力下会均匀屈服,这与结构延展性有简单的联系。然而,弯曲屈服更复杂,首先发生在截面的最外层纤维。持续弯曲导致塑性变形从截面的顶部和底部向中性轴侵蚀,在极限处严格成为等面积轴(见第15章)


确定塑性变形的精确程度必须考虑所有三个结构要求,但最终完全塑性是通过延性实现的。但实际上,过度的变形倾向于局部而不是扩散。在拉伸杆中,我们可以在给定的截面上看到熟悉的颈缩,在弯曲中,大部分梁从集中变形中卸载到所谓的塑性铰链中。但这其中存在一个悖论:为什么延性,这意味着显著的屈服应变,是应用下界定理的先决条件,以返回一个安全的加载极限,当结构没有倒塌,即没有临界屈服(或完全屈服)?首先,我们注意到,安全负载不一定调用纯粹的弹性响应;部分或部分结构可能已经屈服,而没有实质性的变形和局部倒塌。随着载荷的增加,其他地方的弹性应力会增加,即使屈服区域的应力水平已经饱和——但韧性的应变水平没有饱和。这个再分配的过程,正如它所知,维持了负荷增加到其最终值的能力,就在崩溃发生之前。然而,静定结构受单一平衡解支配。当材料开始屈服时,它的内应力是准确知道的,这定义了一个安全加载的单一极限,没有任何再分配。几何兼容性自动单独满足。

物理代写|结构力学代写Structural Mechanics代考

myassignments-help数学代考价格说明

1、客户需提供物理代考的网址,相关账户,以及课程名称,Textbook等相关资料~客服会根据作业数量和持续时间给您定价~使收费透明,让您清楚的知道您的钱花在什么地方。

2、数学代写一般每篇报价约为600—1000rmb,费用根据持续时间、周作业量、成绩要求有所浮动(持续时间越长约便宜、周作业量越多约贵、成绩要求越高越贵),报价后价格觉得合适,可以先付一周的款,我们帮你试做,满意后再继续,遇到Fail全额退款。

3、myassignments-help公司所有MATH作业代写服务支持付半款,全款,周付款,周付款一方面方便大家查阅自己的分数,一方面也方便大家资金周转,注意:每周固定周一时先预付下周的定金,不付定金不予继续做。物理代写一次性付清打9.5折。

Math作业代写、数学代写常见问题

留学生代写覆盖学科?

代写学科覆盖Math数学,经济代写,金融,计算机,生物信息,统计Statistics,Financial Engineering,Mathematical Finance,Quantitative Finance,Management Information Systems,Business Analytics,Data Science等。代写编程语言包括Python代写、Physics作业代写、物理代写、R语言代写、R代写、Matlab代写、C++代做、Java代做等。

数学作业代写会暴露客户的私密信息吗?

我们myassignments-help为了客户的信息泄露,采用的软件都是专业的防追踪的软件,保证安全隐私,绝对保密。您在我们平台订购的任何网课服务以及相关收费标准,都是公开透明,不存在任何针对性收费及差异化服务,我们随时欢迎选购的留学生朋友监督我们的服务,提出Math作业代写、数学代写修改建议。我们保障每一位客户的隐私安全。

留学生代写提供什么服务?

我们提供英语国家如美国、加拿大、英国、澳洲、新西兰、新加坡等华人留学生论文作业代写、物理代写、essay润色精修、课业辅导及网课代修代写、Quiz,Exam协助、期刊论文发表等学术服务,myassignments-help拥有的专业Math作业代写写手皆是精英学识修为精湛;实战经验丰富的学哥学姐!为你解决一切学术烦恼!

物理代考靠谱吗?

靠谱的数学代考听起来简单,但实际上不好甄别。我们能做到的靠谱,是把客户的网课当成自己的网课;把客户的作业当成自己的作业;并将这样的理念传达到全职写手和freelancer的日常培养中,坚决辞退糊弄、不守时、抄袭的写手!这就是我们要做的靠谱!

数学代考下单流程

提早与客服交流,处理你心中的顾虑。操作下单,上传你的数学代考/论文代写要求。专家结束论文,准时交给,在此过程中可与专家随时交流。后续互动批改

付款操作:我们数学代考服务正常多种支付方法,包含paypal,visa,mastercard,支付宝,union pay。下单后与专家直接互动。

售后服务:论文结束后保证完美经过turnitin查看,在线客服全天候在线为您服务。如果你觉得有需求批改的当地能够免费批改,直至您对论文满意为止。如果上交给教师后有需求批改的当地,只需求告诉您的批改要求或教师的comments,专家会据此批改。

保密服务:不需求提供真实的数学代考名字和电话号码,请提供其他牢靠的联系方法。我们有自己的工作准则,不会泄露您的个人信息。

myassignments-help擅长领域包含但不是全部:

myassignments-help服务请添加我们官网的客服或者微信/QQ,我们的服务覆盖:Assignment代写、Business商科代写、CS代考、Economics经济学代写、Essay代写、Finance金融代写、Math数学代写、report代写、R语言代考、Statistics统计学代写、物理代考、作业代写、加拿大代考、加拿大统计代写、北美代写、北美作业代写、北美统计代考、商科Essay代写、商科代考、数学代考、数学代写、数学作业代写、physics作业代写、物理代写、数据分析代写、新西兰代写、澳洲Essay代写、澳洲代写、澳洲作业代写、澳洲统计代写、澳洲金融代写、留学生课业指导、经济代写、统计代写、统计作业代写、美国Essay代写、美国代考、美国数学代写、美国统计代写、英国Essay代写、英国代考、英国作业代写、英国数学代写、英国统计代写、英国金融代写、论文代写、金融代考、金融作业代写。