الفهرس 
CHAPTER 1 INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 129 |  |  |
| | | from | 129 | | |
Abstract
1.1. General
Steel plate girders with typical I-sections are known to have high rigidity and moment resistance in their loaded plane and a lower rigidity in the other plane. When such sections are laterally unrestrained against motion or rotations, lateral torsional buckling (LTB) could be the dominant buckling mode. It is also considered a dominant buckling mode for intermediate to small slenderness values. For high local slenderness values, local buckling (LB) could be a participating buckling mode affecting section capacity. Lateral distortional buckling (LDB) could be the dominant buckling mode for unrestrained sections when web stiffness is very weak compared to the flange. When considering beam span, large span beams have higher LTB, while local buckling could be the dominating mode for short spans. The LDB could be a dominating mode for intermediate unrestrained beams. Different buckling modes are shown in (Figure 1-1).
Hollow tubular flanges (HTF) as shown in (Figure 1-2), could increase section torsional stiffness and twisting resistance. HTFs are considered an innovative solution to increase critical moment value for beams affected by LTB. LTB is the lateral moment occurring in compression flange and a section lateral rotation along beam length without web distortion. Hollow tubular flanges could also be cost-effective for their lower weight-to-depth ratio. Also, HTF increases local buckling resistance since there are no free edges in such sections.
Further to the previous structural performance, the aesthetics of the architectural appearance of any structure as well as the mechanical and electrical requirements to pass their ducts is also important. The conventional steel plate girders with solid web in outdoor pedestrian bridges may need web decoration or openings to achieve the architectural perspective. Also, web openings in buildings are required to provide ease of passing services through the opening and avoiding reduction of the floor height. Perforated beams with web openings are produced using different methods. One of those methods, as shown in (Figure 1-3) for castellated and cellular girders, is widely used by cutting an I-section in a pattern along the web length and rewelding of the resulting two tee parts forming the required openings. Such approach provides new section with larger depth, leading to an increase in the moment of inertia and section modulus which participates in the deflection and section moment resistance. A similar method is cutting a plate in the same way then welding flanges to the produced perforated web. This method offers a variety of dimensions and web depths instead of the limited depths of the hot-rolled I-profiles. Also, this method enables replacing the plate flange with a tubular one. In general, the perforated beams have a lower weight-to-depth ratio, which positively affects the cost. Such beams were found to be majorly affected by lateral buckling modes like LTB or LDB. Local buckling modes should also be considered as they affect section moment capacity, like web-post buckling or Vierendeel mechanism around the opening corners.
1.2. Research problems and objectives
Despite the previous studies on the flexural strength of hollow tubular flange beams, also on the flexural behavior of perforated girders, the flexural strength of both cases together has not been investigated before as per the author’s knowledge. Furthermore, rules to predict the flexural capacity of beams with hollow tubular flange, even if the web is solid, is not available in different design codes. Accordingly, the target of the present study is to combine the usage of hollow tubular flanges with the perforated web in a girder having long spans and evaluate flexural capacity of this newly introduced section.
The present research focuses on the flexural behavior and its failure modes such as lateral-torsional buckling and local buckling. The parameters that affect the capacity of these flexural members will be web slenderness and flange slenderness either compact (C), non-compact (N), or slender (S) classification as per the American code. In addition, the parameters cover the geometry and dimensions of web openings, also different shapes of openings, and location along web depth. The study uses a constant parameter as four-points loading criteria and laterally unsupported flange along the whole length. The results are verified with the American specification, AISC, as well as the European standards, EN. The research is developed by applying finite element analysis using the commercial software package ABAQUS.
The research objectives could be summarized in points as follows:
• Study the flexural behavior of steel girders having hollow tubular flange at the compression side.
• Study the flexural behavior of the same girders after adding web openings at the pure moment zone.
• Examine the effect of different configurations and location of the web openings.
1.3. Thesis contents
This thesis include five chapters as follows:
• Chapter 1: This chapter briefly introduces the research topic, primary goals, and existing research problems.
• Chapter 2: This chapter provides a review of various research works concerning three major points, lateral torsional buckling failure mode, beams with tubular flanges, and beams with perforated web.
• Chapter 3: This chapter describes the process of numerical analysis using ABAQUS software, also verifying the produced models against previous experimental works.
• Chapter 4: This chapter the parametric study considered in the research and discussed the results of each parameter either on hollow tubular flange girders with solid web, or with perforated web.
• Chapter 5: This chapter summarizes the work presented in the thesis, and recommendations for future studies in this field are also presented.