رسائل دكتوراة
English
2022
Shear and Flexural Behavior of Prefabricated Hybrid Steel Joist Girders Supporting FRC Slabs
جنان نعمة ياسر الموسوي, هيثم حسن متعب الدعمي
كلية الهندسة-جامعة بابل · العراق
The experimental program of the present study consisted of fabricating and testing two groups of specimens; all specimens were tested under monotonic load. The first group consisted of ten hybrid open web steel joists (HOWSJs) specimens; each pair of these specimens had the same cross-section and included three variables. The first variable was the shape of the cross-section of the joist, the second variable was the span-to-depth ratio of steel joists, and the third variable was the effect of the diameter of interior web members on the shear, flexural, and lateral-torsional buckling behavior of the HOWSJs.
The second group consisted of seven composite open web steel joists (COWSJs) specimens. Three specimens were tested with different cross-section shapes of HOWSJs to study the effect of the shape of the cross-section on the behavior of the composite open web steel joists. While four specimens had the same cross-section as the HOWSJs, many variables were investigated when testing these specimens. These variables were the effective width of the concrete slab deck, the span-to-depth ratio of HOWSJs, and the type of the concrete slab; two types of concrete were used in this study to cast the deck, which were steel fiber reinforced concrete (SFRC) and non-fibrous concrete (NC).
In this study, a new type of shear connector was used, so a push-out test was performed to determine the shear strength and stiffness of the shear connectors embedded in both NC and SFRC. The experimental results for the shear resistance of this type of shear stud were compared with some standard design codes, and the results showed that these equations could be used to calculate the shear resistance of shear studs for both NC and SFRC.
The experimental results of the HOWSJs showed that the length-to-depth ratio (L/D) affected the analysis behavior of the joists. Therefore, when the L/D decreased, the improvement of the ultimate capacity was very slight, about 1.81%; this slight increase was in the case of using the same bar diameter for the interior web used in prefabricated joists with L/D of 5.1 and joists with L/D of 3.6. However, when the interior web’s bar diameter was increased by about 24.48%, which led to a decrease in the slenderness ratio of the diagonal interior web members for HOWSJs, the increase in the ultimate capacity became about 25.7%, and the deflection decreased by about 11.3%.
Also, the shape of the cross-section of HOWSJs had a considerable effect on the behavior of the steel joists. For the HOWSJ, which was fabricated by welding the angles of the top and bottom chords back-to-back, the ultimate capacity increased almost 7.4% and 14.5% when compared with specimens fabricated by welding the angles of the chords either face-to-face without a gap or face-to-face with a gap. Meanwhile, the ductility index of the HOWSJ specimens with a face-to-face with gap cross-section was 1.52 and 1.35 times the ductility index of the HOWSJ specimens with back-to-back and face-to-face without gap cross-section, respectively.
The lateral-torsional buckling experimental and theoretical investigation showed that specimens with a face-to-face with gap cross-section were more stable against lateral deformations than the other two cross-sections. They had rotation and lateral deflection less than specimens with a back-to-back welded angle cross-section by about 25.1% and 30.7%, respectively. Also, they had rotation and lateral deflection less than specimens with a face-to-face without gap welded angle cross-section by about 7.3% and 11.2%, respectively.
Regarding the composite open web steel joists group, the experimental results showed that using SFRC to cast the slab slightly improved composite steel joists’ strength, stiffness, and ductility compared with using NC. On the other hand, increasing the span/depth ratio of HOWSJs for the two types of concrete slabs resulted in normalized deflections that were approximately 31% greater than COWSJs with a lower L/D ratio. While decreasing the span/depth ratio improved the ultimate load capacity by about 3.66% and 4.31% for the NC and SFRC slabs, respectively.
Using the SFRC deck slab in the COWSJ specimens for the three cross-section shapes of HOWSJs used in this study enhanced the ultimate load capacity, stiffness, toughness, and improved the stability of interior web members and chords, with reasonable ductility compared to the results of HOWSJ specimens.
Finally, a finite element analysis was performed using ABAQUS software to simulate the experimental program carried out in the present study. It was found that there was good convergence between the experimental and ABAQUS results, where the highest difference in ultimate flexural capacity was less than 8% and 9.5% for the HOWSJs and the COWSJs, respectively. While the largest difference in deflection at the ultimate load did not exceed 10.72% for both groups. The differences in rotation deformation and lateral deflection of the HOWSJs were less than 9% and 6%, respectively.