钢板梁（板梁）Plate Girders

钢板梁（板梁）Plate Girders(中文5000字,英文10000字)
•    介绍
在本章中，我们考虑由板元件组成的大型弯曲构件（梁） - 特别是那些腹板非紧凑的或细长的。 在第5章“梁”中，我们介绍了热轧型钢，以及手册中的所有有关的标准部分，这些构件都非常紧凑。 虽然一些有着不紧凑的翼缘，但没有一个有细长的翼缘。 然而，由板材构成的型钢，翼缘和腹板都可以紧凑，不紧凑或细长。 这些组合型钢通常在弯曲力矩大于标准热轧型钢构件可抵抗的情况下使用，通常是因为跨度较大。 这些大梁总是非常长，导致会有不紧凑或细长的腹板。
AISC规范涵盖了F5节“具有细长腹板的双轴对称和单轴对称I型绕主轴弯曲的弯曲构件”。这是通常被认为是板梁的类别。 第F4节“其他具有紧凑或非紧凑腹板状梁的其他绕主轴弯曲的I形构件”中介绍了非紧密腹板型钢的弯曲构件。本节涉及双重和单一对称的截面。 有趣的是，非紧密腹板比细长腹板更难处理。 在F4部分的用户注释中，规范允许F4所涵盖的部分按照F5部分的规定进行设计。 在本书中，我们做到这一点，并将F5用于非紧凑或细长腹板的桁材。 我们将这两种类型称为板梁。  AISC第G章“剪切构件的设计”中介绍了所有弯曲构件的剪切要求条款。其他要求在AISC F13“梁和梁的部分”中给出。
板梁的横截面可以有多种形式。 图10.1显示了一些可能性。 通常的配置是带有两个相同翼缘的单个腹板，所有部件都通过焊接连接。 带有两个腹板和两个凸缘的箱体部分具有优异的扭转性能，当需要较大的无支撑长度时可以使用。 有时使用混合梁，其中翼缘中的钢的强度比腹板或腹板中的钢高。
使用焊接，连接横截面的部件是板梁设计中的主要考虑因素。 所有连接都是通过铆接完成的，因此无法将翼缘直接连接到腹板上，并且为了将荷载从一个部件传输到另一个部件的特定目的引入了额外的横截面元件。 通常的技术是使用一对背对背放置的角钢将翼缘连接到腹板上。 一对牛腿连接在腹板上，另一对连接在翼缘上，如图10.1b所示。 如果需要腹板加强筋，那么也可以采用成对的角钢来达到这个目的。 为避免加强筋角钢和凸缘角钢之间产生冲突，将填充板加到腹板上，以便加强筋可以清除凸缘角钢，如图10.1c所示。 如果需要可变横截面，则将一个或多个不同长度的盖板铆接到翼缘上。  （尽管盖板也可用于焊接板梁，但更简单的方法是在沿梁长度的不同位置使用端到端焊接的不同厚度的翼缘板。）很明显，焊接板梁在简单性和效率方面远优于铆接或栓接梁。 本章仅考虑I形焊接板梁。
在考虑具体的AISC规范要求之前，我们需要以非常一般的方式检查板梁的特性，而不是普通的轧制梁。

Plate Girders
10.1    INTRODUCTION
In this chapter, we consider large flexural members (girders) that are composed of plate elements—in particular, those with noncompact or slender webs. In Chapter 5, “Beams,” we covered hot-rolled shapes, and for all the standard sections in the Manual, the webs are compact. Some have noncompact flanges, but none have slen- der flanges. With shapes built up from plates, however, both flanges and webs can be compact, noncompact, or slender. These built-up shapes usually are used when the bending moments are larger than standard hot-rolled shapes can resist, usually because of a large span. These girders are invariably very deep, resulting in non- compact or slender webs.
The AISC Specification covers flexural members with slender webs in Section F5, “Doubly Symmetric and Singly Symmetric I-Shaped Members with Slender Webs Bent About Their Major Axis.” This is the category usually thought of as plate girders. Flexural members with noncompact webs are covered in Section F4, “Other I-shaped Members with Compact or Noncompact Webs Bent About Their Major Axis.” This section deals with both doubly and singly symmetric sections. Interest- ingly, noncompact webs are more difficult to deal with than slender webs. In a User Note in Section F4, the Specification permits members covered by Section F4 to be designed by the provisions of Section F5. In this book, we do this and use Section F5 for girders with either noncompact or slender webs. We refer to both types as plate girders. Shear provisions for all flexural members are covered in AISC Chapter G, “Design of Members for Shear.” Other requirements are given in AISC F13, “Pro- portions of Beams and Girders.”
A plate girder cross section can take several forms. Figure 10.1 shows some of the possibilities. The usual configuration is a single web with two equal flanges, with all parts connected by welding. The box section, which has two webs as well as two flanges, is a torsionally superior shape and can be used when large unbraced lengths are necessary. Hybrid girders, in which the steel in the flanges is of a higher strength than that in the web or webs, are sometimes used.