Large web openings in steel and composite beams
This paper presents the basis for the design of steel and composite beams with large web openings. The main design requirements are the transfer of shear by Vierendeel bending and the control of web buckling next to and between the openings. Cellular beams with regular circular openings are a common example of highly perforated beams and their flange areas are often highly asymmetric. For these beams, web-post moments may be generated to develop the full shear resistance of the cross-section. Tests on beams with circular, elongated circular and rectangular openings are presented which are used to verify the design methodology. In addition, the openings cause local displacements due to shear and bending, which add to the overall deflection of perforated beams. Simplified formulae are presented to determine the additional deflection relative to the equivalent solid-web beams.
Steel and composite beams are often designed with large web openings for routing services or for roofs or other long-span structures. Castellated beams with hexagonal openings and cellular beams with circular openings are formed by cutting and rewelding IPE or UB sections so that the resulting beams are deeper and therefore stronger than the parent section for the same section weight. Castellated beams are manufactured with lsquo;standardrsquo; hexagonal shapes in which the openings are two-thirds of the final section depth. Cellular beams are much more variable in terms of their component section shapes and the size and spacing of the openings. Circular openings amounting to 60 to 75 % of the beam depth are typical.
Often, IPE and HE sections are combined to create highly asymmetric sections, as shown in Fig. 1, which are efficient when used in composite construction. Elongated circular openings can be created by cutting away the webpost between circular openings, although these elongated openings are generally placed close to mid-span where shear forces are low.
Fabricated beams are made by welding together three plates, and these beams generally have large rectangular openings at isolated positions. Horizontal stiffeners are often welded above and below the openings to increase the resistance to transfer of shear forces by Vierendeel bending across the openings.
1.1 Design requirements for beams with large web openings
The following design verifications of the structural adequacy of steel and composite beams with isolated or closely spaced openings should be carried out:
图1由两个型钢制成的蜂窝梁（来源：Kloeckner Metals UK）
– Bending resistance of the reduced section based on the plastic or elastic section properties of the perforated sections, depending on the section class of the unsupported web.
– Shear resistance of the reduced section to existing Eurocode rules.
– Section class of the Tees in Vierendeel bending, which determines whether the plastic or elastic properties of the Tees may be used.
– Interaction of shear and axial forces on the bending resistance of the Tees.
– Contribution of local composite action in the Vierendeel bending resistance for composite beams. – Web buckling next to isolated openings.
– Web-post buckling between closely spaced openings.
– Effect of in-plane moments that may develop in the webposts for highly asymmetric sections.
– Additional flexural and shear deflections due to the web openings.
The potential modes of failure are shown in Fig. 3. The effect of the openings is mainly to reduce the shear resistance of the beam. Web buckling next to or between the openings is normally the critical design condition. These design verifications are reviewed in the following sections.
1.2 Proposed Eurocode rules for web openings
The design method for steel beams with web openings will be presented in a proposed Part 1.13 to EN 1993  and the supplementary rules for composite beams will be included in new clauses in EN 1994-1-1 . The scope of EN 1993 Part 1.13 will be based on design verifications already included in various national guidance documents , , and background information is based on research carried out in ECSC/RFCS projects, notably LWO (2002– 2005)  and DISCCo (2012–2015) .
带腹板开孔的钢梁的设计方法将在EN 1993的建议第1.13部分中介绍，复合梁的补充规则将包含在EN 1994-1-1的新条款中。EN 1993第1.13部分的范围将以各种国家指导文件、中已包含的设计验证为基础，背景信息以在ECSC/RFC项目中进行的研究为基础，特别是LWO（2002-2005）和Discco（2012-2015）。
The scope of the rules for large web openings is based on defining an equivalent rectangle for more regular opening shapes such as circular, elongated circular and hexagonal openings. The treatment of Vierendeel bending and web-pos