رسائل دكتوراة
English
2023
Structural Response of Composite Reinforced Concrete Deck-Cold Formed Steel Beam to Column Semi-Rigid Connections
مصطفى صلاح شاكر محمود, هيثم حسن متعب الدعمي
كلية الهندسة-جامعة بابل · العراق
Designers have recognized the benefits of designing semi-rigid connections. It decreases beam weight, reduces beam depth, overall building height, and increases energy absorption. In addition, cold-formed steel (CFS) is becoming more popular in several countries, indicating good potential for using lightweight materials as an alternative to conventional steel. However, there is still a scarcity of data on joint behavior, particularly for composite connections integrated with CFS, which gives more motivation to study this type of composite joint.
A composite beam-to-column semi-rigid joint formed by a composite concrete slab and two cold-formed steel C-sections as a beam and column is investigated experimentally in this study. Thirteen specimens with cruciform subassemblies of CFS beam-to-column joints are tested experimentally with a novel approach to different beam-to-column connection shapes and different types and degrees of the shear connector. In addition, nine push-out test specimens are prepared to investigate the shear strength, stiffness, and ductility of the bolted shear connector with a single embedded nut and CFS plate shear connectors, such as single plate, single angle, single corrugated, and double angle plate, that are used in composite joint specimens.
The experimental study is divided into three parts: the experimental test of push-out specimens; the experimental test of three trial composite joints with minimum reinforcement and 300 mm slab width; and the experimental test of ten main composite joints reinforced by Ø10 @ 100 mm in both directions and 750 mm slab width with different beam-to-column connection shapes, tested under monotonic and cyclic load and different types and degrees of the shear connector; and a numerical study.
The results show that tested specimens with beam-to-column joints connected by angles in the main composite joint group possessed high ductile properties, where the rotation capacity exceeded 30 mrad. Hence, all these specimens classify as semi-rigid joints according to Eurocode 4 (EC4) and are adequate for plastic analysis and seismic design. While a back-to-back web connection forming a box column section increased the ultimate load by 33% and decreased the rotation capacity by 76%. In contrast, the specimen with a back-to-back web connection forming a box beam section increased the ultimate load by 90% and decreased the rotation capacity by 78% compared to the specimen with an I-section shape for the beam and column connected by angles.
On the other hand, the cyclic load has little effect on the ultimate moment capacity of composite joints, but it greatly increases their rotation capacity. The suggested composite cold-formed steel beam-to-column connection shapes are effective in terms of stiffness and ultimate moment capacity. Also, using a novel approach to the CFS angle plate shear connector showed a significant improvement in the moment and initial stiffness of the joint. The partially bolted shear connector used in this study, up to 50% of which is fully shear connected, produced acceptable results and is within the recommended limits for semi-rigid joints according to the European Code.
The analytical study uses the finite element method, which investigates the nonlinear behavior of composite joints. The analytical models are carried out using ABAQUS Standard/Explicit 2017. The results of finite element models include the deformed shape at ultimate load and the moment-rotation curves. The finite element model results show good agreement with the experimental results. The program's ability to extend the study provides more insights into understanding the actual behavior of composite joints.
In this thesis, a parametric analysis is performed to investigate a wide range of the main variables (top and seat angle thickness, reinforcing ratio, use of stiffener in the column web, column shape, and the number of bolts). It is concluded from the parametric study that the used angle with a thickness-to-width ratio equal to 0.092 improves the moment capacity of a composite joint by 17.3%, and the use of a stiffener in the column web improves the moment capacity by 42.65% and prevents the buckling of the column web while maintaining a semi-rigid behavior of the joint.