پروپوزال، معرفی کار پژوهشی است که در مقطع بعدی تحصیلی تان قصد انجام تحقیق در آن موضوع خاص را دارید و در واقع برنامه ای کلی و مختصر از اهداف تحقیق، دلایل اهمیت موضوع تحقیق، پیشینه ای از تحقیقات مشابه انجام شده در این موضوع خاص و موضوعات مشابه و مجموعه ای از رفرنس های استفاده شده جهت ارجاع در مطالعات گسترده آینده می باشد و اغلب در مقطع فوق لیسانس و خصوصا دکتری لازم است ارائه شود.
سبک نگارش آن به شیوه ی یک پایان نامه کوچک با تعداد صفحاتی بین 10 تا 20 صفحه است که لزوما حاوی اطلاعات لازم و ضروریست و نه حواشی و اضافیات. فرمت آن مانند بخش های یک پایان نامه کارشناسی ارشد است و دارای فهرست و کلیه فصل هاست اما به طور کوتاه و خلاصه.
در زیر برای نمونه، پروپوزالی در زمینه رشته عمران قرار داده شده است. امید است که ضمن مفید بودن، از کپی برداری آن خودداری کنید.
Project Title: advantages of Concrete-filled steel tube (CFT) columns compared to conventional steel or concrete columns
A Dissertation Proposal Presented to
DEPARTMENT OF Civil Engineering
FACULTY OF Engineering
University Of ………, Malaysia
Table of Contents
- Problem definition
- Main objective
- Literature review
- he steel tube provides formwork for the concrete core.
- The concrete prolongs local buckling of the steel tube wall.
- The tube prohibits concrete spalling.
- Composite columns add significant stiffness compared to traditional steel frame construction.
- Steel provides confinement for core concrete.
Concrete-filled steel tube (CFT) columns offer many advantages compared to conventional steel or concrete columns. Some of these advantages include:
However, the use of CFT columns has been limited due, in part, to a lack of construction experience and the complexity of connections to such columns.
Connections are one of the most vital and important structural elements that prediction of their seismic response for the structural stability is very important. Connection ductility due to earthquake and its shear and flexural strength are important parameters for connections that have been noted in literature. For the case of steel, ductility of connection is more than reinforced concrete connections and this is a disadvantage for concrete connections. For this reason, various studies have been done on the investigating and improvement of the concrete connections that are confined by steel tubes. Almost all of these studies have been done on the concrete filled steel tubes (CFT) that are connected to steel beams but in limited cases, composite steel-concrete beams which are connected to CFT columns have been investigated. Therefore there is a scientific attraction for studying on this kind of connections.
Main objective of this research is investigating improvement of beam-column joints subjected to cyclic loading such as strength, stiffness and ductility considering nonlinear behavior of materials
There are many investigations done on behavior of this kind of connections. One of the prior experiments on these joints is experimental studies of Alostaz and Schneider. They tested 213 full scale samples in 6 main categories under cyclic loading (1).
Connection Type I represented the simplest of the connection details in which the girder was welded directly to the face of the steel tube. Connection Type IA was identical to connection Type I, however, the connection-stub web was extended through the pipe. The external diaphragm plates in connection Type II were fabricated using square plates with each comer of the plate cut to match the width of the girder flange. Connection Type III was identical to connection Type I except that weldable deformed bars were welded to each girder flange and embedded into the concrete core through holes drilled in the steel tube wall. Connection Type VI continued only the flanges through the concrete core. Finally connection type VII continued the entire girder cross-section through the concrete core. The results show that welding the girder to the steel tube skin should be avoided in moment-resisting frames constructed in active seismic regions. Severe tube wall distortions prohibited the development of the plastic bending strength of the girder, and fracture of the flange, the weld, or the tube wall is likely to occur for this connection detail. Extending the web through the tube improved the inelastic performance of the simple welded connection. However, significant rotational ductility demands were imposed on the web once the flanges fractured, which eventually tore the web over the full depth of the girder. Consequently, it is important to prevent flange fracture of the connection for moment resisting connections. This connection detail may be more suitable for braced frames. A minimum sized diaphragm was not efficient in alleviating the severe distortions of the tube wall. However, the performance of this detail was a significant improvement compared to the simple welded connection detail. External diaphragm connections might be used in regions with low seismic risk. Wieldable deformed bars that transfer some of the girder flange forces to the concrete core significantly enhanced the inelastic cyclic behavior of the simple welded connection. Transferring approximately 85% of the flange force produced a connection-stub flexural strength of 1.5 times the plastic bending strength of the connected girder. Stable strain hardening characteristics were observed up to an approximate 5% total rotation. This connection could be used at least in regions of moderate seismic risk. Continuing flange plates, as tested, should not be used in moment resisting frames. The inability of the weld to transfer flange forces to bearing stresses on the concrete core resulted in large deformations. This produced a very pinched inelastic cyclic behavior. Improvements to this connection are possible, provided the slip of the connection-stub flange plates is prevented. The cyclic behavior for the continuous girder connection-stub was limited by the connected girder. This connection exhibited stable strain hardening behavior, and developed a full plastic hinge in the connection-stub and the girder. Continuing the connected girder through the CFT column could be used in regions of high seismic risk.
Beutel and Thambiratnam have done experiments on 4 specimens with welded bars. Their samples were different at diameter of bars and concrete compressive stress used in joint core (2).
These specimens were subjected to monotonic loading to complete yielding and moment – rotation and force-displacement diagrams were obtained for them. Diagrams show that by increasing diameter of rebar, connection’s ability to transfer load between beam flange and concrete core has been increased and joint is strong enough to form plastic hinge in beam.
Kang et al investigated 10 samples with external stiffeners in addition to elements penetrated in concrete core (3).
These specimens were subjected to monotonic loading to complete yielding and moment – rotation and force-displacement diagrams were obtained for them. Diagrams show that by increasing diameter of rebar, connection’s ability to transfer load between beam flange and concrete core has been increased and joint is strong enough to form plastic hinge in beam. Connection type RB was reinforced with rebars and T shape stiffeners, type PL with penetrated plate in concrete core and T shape stiffeners and type ST with just T shape stiffeners and without penetrating elements.
The results show that without considering penetrating elements, existence of T shape stiffeners allow section to reach its plastic capacity. Penetrating elements cause to increase in stiffness of section instead of moment capacity of it. Also there was no difference between rebars and steel plates in behavior of these samples.
Elremaily and Azizinamini have done experiments of beams penetrating into CFT columns with 7 specimens of 2/3 scale (4). These experiments were designed to show 3 failure modes of joints like: beam failure, column failure and shear failure of joint.
These specimens were subjected to monotonic loading to complete yielding and moment – rotation and force-displacement diagrams were obtained for them. Diagrams show that by
The results show that connection can be an ideal model of a clamped joint with crossing column section.
Finally, Jiangou Nie et al, carried out 14 experiments in specimens consisted of CFT columns and composite beams (5; 6; 7) in which, strength, deformation and energy dissipation capacity of connections are investigated empirically and numerically. And the results show that in the case of connections with interior diaphragm, strength is good but ductility is poor. Also ductility of samples with stud is high but they have a lower strength. Specimens with exterior diaphragms show a higher strength, ductility and energy absorption capacity in comparison with others and these connections are recommended for use in active seismic regions.
In this study, the challenge is to propose a finite element model for behavior of CFT connections and verify the analyses results using experimental results carried out by other researchers and validate the numerical model after verifying it to use the assumptions in this model to extend proposed model to new models. The assumptions in modeling are as follow:
- Concrete confinement inside steel tube
- 3D modeling
- Nonlinear behavior of materials
- Cyclic loading
- Complete bond of rebar inside concrete
5-3. Software used
Using finite element analysis packages with nonlinear modeling capacities like ABAQUS
1. Experimental Behavior of Connections to Concrete-filled Steel Tubes. Alostaz, Stephen P. Schneider & Yousef M. 3, 1998, J. Construct. Steel Res, Vol. 45, pp. 321-352.
2. Monotonic behaviour of composite column to beam connections. Jason Beutel, Professor David Thambiratnam , Nimal Perera (Director). 2001, Engineering Structures, Vol. 23, pp. 1152-61.
3. Hysteresis behavior of CFT column to H-beam connections with external T-stiffeners and penetrated elements. Chang-Hoon Kang, Kyung-Jae Shin, Young-Suk Oh, Tae-Sup Moon. 2001, Engineering Structures, Vol. 23, pp. 1194-1201.
4. Seismic behavior of connections composed of CFSSTCs and steel–concrete composite beams—experimental study. Jianguo Nie, Kai Qin, C.S. Cai. 2008, Journal of Constructional Steel Research, Vol. 64, pp. 1178–1191.
5. Seismic behavior of connections composed of CFSSTCs and steel–concrete composite beams—finite element analysis. Jianguo Nie, Kai Qin, C.S. Cai. 2008, Journal of Constructional Steel Research, Vol. 64, pp. 680–688.
6. Experimental behavior of steel beam to CFT column connections. Ahmed Elremaily, Atorod Azizinamini. 2001, Journal of Constructional Steel Research, Vol. 57, pp. 1099-1119.
7. Behavior ofwelded CFT column to H-beam connections with external stiffeners. Kyung-Jae Shin, Young-Ju Kim, Young-Suk Oh, Tae-Sup Moon. 2004, Engineering Structures, Vol. 26, pp. 1877–1887.
8. Seismic behavior of composite connections – flexural capacity analysis. Jianguo Nie, Kai Qin , C.S. Cai. 2009, Journal of Constructional Steel Research, Vol. 65, pp. 111-1120.
9. Seismic performance of steel beams to concrete-filled steel tubular column connections. Chin-Tung Cheng, Lap-Loi Chung. 2003, Journal of Constructional Steel Research, Vol. 59, pp. 405–426.