Experimental Pullout Capacity of Screw Piles in Dry Gypseous Soil

Screw piles are widely used in supporting structures subjected to pullout forces, such as power towers and offshore structures, and this research investigates their performance in gypseous soil of medium relative density. The bearing capacity and displacement of a single screw pile model inserted in gypseous soil with various diameters (D = 20, 30, and 40) mm are examined in this study. The soil used in the testing had a gypsum content of 40% and the bedding soil had a relative density of 40%. To simulate the pullout testing in the lab, a physical model was manufactured with specific dimensions. Three steel screw piles with helix diameters of 20, 30, and 40 mm are used, with a total length of 500 mm. The helix is continuous over the pile's embedded depth of 400 mm. The results of tests revealed that decreasing the length to diameter (H/D) ratio resulted in a higher pullout capacity of screw piles and a lower corresponding displacement.

Analysis of the Pullout Testing of Straight and Angled Abutments in Narrow Diameter Implants

Despite the success of osseointegrated implants, some biomechanical problems such as loosening or fracture of the abutment, crown fixation screw loosening and prosthetic instability, are common problems reported in the literature. Thus, the objective of the present study was to analyze the pullout resistance of straight and angled abutments in narrow diameter implants installed by means of friction. The specimen was composed of an implant of 3.3 mm x 11 mm fixed 2 mm above of a resin block. The abutments were fixed by friction receiving 3, 5 and 7 strikes of 0.05 J along the implant axis, and were positioned with 0 ̊, 10 ̊ and 20 ̊ of angulation. The abutments were subjected to pullout load, totalizing 10 repetitions for each test, i.e., the abutment was reinserted up to 10 times in the same implant. The results showed higher values of pullout load for the abutments with 7 strikes, and no statistical difference with 5 strikes suggesting better mechanical stability.

Stripping torques in human bone can be reliably predicted prior to screw insertion with optimum tightness being found between 70% and 80% of the maximum

Aims To devise a method to quantify and optimize tightness when inserting cortical screws, based on bone characterization and screw geometry. Methods Cortical human cadaveric diaphyseal tibiae screw holes (n = 20) underwent destructive testing to firstly establish the relationship between cortical thickness and experimental stripping torque (Tstr), and secondly to calibrate an equation to predict Tstr. Using the equation’s predictions, 3.5 mm screws were inserted (n = 66) to targeted torques representing 40% to 100% of Tstr, with recording of compression generated during tightening. Once the target torque had been achieved, immediate pullout testing was performed. Results Cortical thickness predicted Tstr (R2 = 0.862; p < 0.001) as did an equation based on tensile yield stress, bone-screw friction coefficient, and screw geometries (R2 = 0.894; p < 0.001). Compression increased with screw tightness up to 80% of the maximum (R2 = 0.495; p < 0.001). Beyond 80%, further tightening generated no increase in compression. Pullout force did not change with variations in submaximal tightness beyond 40% of Tstr (R2 = 0.014; p = 0.175). Conclusion Screw tightening between 70% and 80% of the predicted maximum generated optimum compression and pullout forces. Further tightening did not considerably increase compression, made no difference to pullout, and increased the risk of the screw holes being stripped. While further work is needed for development of intraoperative methods for accurate and reliable prediction of the maximum tightness for a screw, this work justifies insertion torque being considerably below the maximum. Cite this article: Bone Joint Res 2020;9(8):493–500.

BOND STRENGTH OF BAR USING GROUTING FOR PRECAST CONCRETE CONNECTION

In precast concrete, a connection is needed to unite the components so that they become a whole unified structure. This study aims to determine the reinforcement strength and length of reinforcement in precast concrete connections. To paste reinforcement into precast concrete, giving additional material in the form of grouting which is called sika grout 215 and functions as an adhesive is necessary. Pullout testing is carried out in the laboratory, and its simulation by modeling uses the finite element method based software. This research is divided into 2 phases. The first phase is making specimen to examine the bond strength between the concrete and reinforcement that has been given sika grout 215. So monolithic specimen is made as a comparison. The result of the bond strength of the monolithic test specimen is 6.24 MPa, and the sika grout 215 category is 6.52 MPa. From the experimental results in the laboratory with modeling, it is obtained the bond strength ratio of 0.94. The length of development (ld) based on the results of the testing phase I of 200 mm. The second phase is examining the damage pattern due to the stress that occurred. Specimens are made into 4 categories, namely modeling developments with the length of 120 mm (<40% ld), with the length of 160 mm (<20% ld), with length of 200 mm (= ld), and with the length of 260 mm(> 30% ld) both for monoliths and sika grout 215. The damage pattern, which is in the form of yielding and breaking reinforcement as the result of the pullout experiment in the laboratory shows not much different from the result of simulation using the software.